English

• 1. Introduction

  Since the Industrial Revolution, the rapid consumption of fossil fuels such as coal, oil, and natural gas, which have been the main sources of energy for human development, has led to large amounts of CO₂ emissions [1-5]. Excess CO₂ emissions have led to a disruption of the natural balanced carbon cycle, resulting in increasing CO₂ concentrations in the atmosphere [6]. In addition, the atmospheric CO₂ concentration is expected to reach a peak of 850 ppm by the end of this century [7,8]. As a greenhouse gas, the rising concentration of CO₂ will lead to a range of global environmental problems, such as the greenhouse effect, ocean acidification, and extreme weather [9,10]. As a result, there is a growing awareness that the removal of excess carbon dioxide has become an urgent issue for environmental protection and sustainable development.

  To mitigate these negative effects of excess CO₂ emissions, various types of capture, storage, and conversion strategies have been developed in recent years [11-13]. The common ways to capture CO₂ include gas separation [14], chemical adsorption [15], and physical adsorption [16]. However, the capture of CO₂ not only consumes a lot of energy and costs but also easily reaches the capacity limit [17]. From another perspective, CO₂ is the cheapest and most abundant non-toxic C1 source and has been regarded as a potential raw material for industrial production of high-value organic compounds or petroleum substitutes [18-20]. Therefore, chemical conversion is an ideal strategy for both reducing atmospheric CO₂ concentrations and producing many valuable chemicals such as carbon monoxide, methane, formate, ethane, and ethylene [21-24]. There are many methods for the chemical conversion of CO₂, and extensive studies have been conducted in the past few decades, including biochemical catalysis [25], chemical reforming [26], photocatalysis [27], and electrocatalysis [28], all of which exhibit promising potential in this field [29]. However, the efficiency, selectivity, and stability of the reaction are still difficult to ignore on the avenue to practical applications [30-39].

  Among the above conversion methods, electrochemical CO₂ reduction reaction (CO₂RR) has become a valuable research topic all over the world due to its unique advantages such as mild conditions, simple device, and variety of products [40,41]. Especially with the increasing availability of renewable electricity, the economic viability of CO₂RR is growing by the day [42]. The CO₂RR system consists of a reaction device, electrolyte, and catalyst, of which the catalyst is the focus of the research [43,44]. To date, a variety of catalysts including metal alloys [45], metal oxides [46], metal sulfides [47], single atoms [48], metal complexes [49], metal-organic frameworks (MOFs) [50], and non-metallic materials [17] have been explored for their potential in the field of CO₂RR. Among them, MOF catalysts are one of the most prospective heterogeneous catalysts due to their unique characteristics. MOF is a kind of porous material composed of metal ions or clusters coordinated with organic ligands [51-53]. It has multiple adjustable structural characteristics, such as porous structure, high specific surface area, diverse catalytic active sites, and adjustable structures [54-59]. The designability of MOFs provides a platform to modify their physical and chemical properties by tuning the composition, metal nodes, and organic ligands at the molecular level. MOFs with specific structures can be prepared using methods including pre-assembly and post-modification to create the desired functional materials [60]. In addition, the higher structural stability and recyclability of MOFs allow them to be used as heterogeneous catalysts, which is beneficial for separation and recycling after reaction [61]. More importantly, the well-defined crystal structure and active sites of MOFs contribute to the in-depth investigation of the reaction mechanism. Since 2012, MOFs have been used to catalyze CO₂RR for the first time, and related research has grown exponentially in recent years [62,63].

  Recently, p-block metal-based MOF materials have been shown to possess unique advantages in MOF catalysts [40]. The p-block metals, including Al, Bi, Sn, In, and so on, have unique electronic configurations from ns²np¹ to ns²np⁶, endowing them with high electronegativity and low ionization energies. In the field of CO₂RR, MOF materials based on p-block metals have high selectivity for C1 products, especially formate, which is usually much higher than reported non-metallic carbon-based catalysts [64-66]. The potential of p-block metal-based MOF materials in converting CO₂ to formate makes them widely applicable [67]. Among the products of CO₂RR, formate has a high economic value with a broad market demand, as well as the highest energy utilization per unit [68]. In addition, formate also has the characteristic spatial structure of aldehydes, indicating that formate also has a certain degree of reducibility, making it a highly valuable organic acid in industrial applications [69]. Therefore, it is crucial to explore the potential reaction mechanism and structure-activity relationship of p-block metal-based MOF materials in CO₂RR, which will effectively guide the design of efficient catalysts for industrial applications (Scheme 1).

  Scheme 1

  

  Scheme 1.  p-block metal-based MOFs and MOF-derived materials as CO₂RR electrocatalysts.

  DownLoad: Full-Size Img PowerPoint

  In this article, we will summarize the latest research progress and development status of p-block metal-based MOF electrocatalysts for CO₂RR. Although there have been some reviews that comprehensively summarize the application of p-block metal-based electrocatalysts in CO₂RR, our focus is to exemplify p-block metal-based MOF materials used as electrocatalysts, especially for electrocatalysts with high selectivity for formate. This review will offer a comprehensive overview of the recent advances in the field of p-block metal-based MOF catalysts for CO₂RR. Furthermore, we will focus on catalyst modification methods and the relationships between structure performance. Finally, we will briefly discuss the challenges faced by this type of MOF-based materials and explore strategies to enhance catalytic performance in CO₂RR, including structural changes, defect engineering, and doping strategies. We hope this review will contribute valuable theoretical guidance for the development of efficient catalysts to facilitate the practical application of CO₂RR.

  2. Foundation of CO₂RR

  2.1 Mechanism of CO₂RR

  According to the molecular orbital theory, all electrons of CO₂ are distributed in bonding orbitals with a fully charged state [70]. According to the hybridization theory, in the CO₂ molecule, the two sp hybrid orbitals of the C atom form two σ bonds with each O atom respectively. Two p-orbitals and sp hybridized orbitals that do not participate in hybridization form a right angle and overlap side by side with the p orbitals of the O atom, resulting in two π delocalized bonds with three centers and four electrons. This feature shortens the distance between C=O, giving carbon-oxygen bonds in CO₂ a certain degree of triple bond characteristic, with a bond energy of 805 kJ/mol for C=O bonds. In this way, CO₂ appears as a stable chemical substance, making the reduction process require overcoming a high energy barrier [71,72].

  CO₂RR can generally be divided into the following steps: (1) CO₂ is dissolved in the electrolyte and then contacts or adsorbs on the surface of the catalyst; (2) The breaking of C=O bonds and the formation of intermediates are accompanied by the transfer of electrons and/or protons; (3) Product is desorbed from catalyst surface [73]. Due to the fact that the CO₂RR is a multi-electron and proton reduction reaction involving various reaction intermediates, CO₂ can be converted into diverse products via different reduction pathways. Typically, a wide range of C1~C3 carbon-oxygen and carbon-hydrogen products can be obtained depending on the differences in the transferred charges, proton numbers, and reduction potentials during the reaction (Table 1) [72]. Due to the focus of this paper being on p-block metal-based catalysts, the primary attention is paid to the mechanistic pathways of C1 products (CO and formate) (Fig. 1).

  Table 1

  

  Table 1.  Reduction potentials of electrochemical CO₂RR.

  DownLoad: CSV

  No.	Reaction	Potentials/V vs. RHE
  1	CO2 + e−→*CO2−	−1.49
  2	CO2 + 2H+ + 2e−→CO + H2O	−0.10
  3	CO2 + 2H+ + 2e−→HCOOH	−0.12
  4	CO2 + 4H+ + 4e−→HCHO + H2O	−0.10
  5	CO2 + 6H+ + 6e−→CH3OH + H2O	0.03
  6	CO2 + 8H+ + 8e−→CH4 + 2H2O	0.17
  7	2CO2 + 8H+ + 8e−→CH3COOH + 2H2O	0.11
  8	2CO2 + 12H+ + 12e−→C2H4 + 4H2O	−0.34
  9	2CO2 + 12H+ + 12e−→C2H5OH + 4H2O	0.09
  10	2CO2 + 14H+ + 14e−→C2H6 + 4H2O	0.14
  11	3CO2 + 18H+ + 18e−→C3H7OH + 5H2O	0.10

  Figure 1

  

  Figure 1.  Mechanism of CO₂RR to HCOOH and CO.

  DownLoad: Full-Size Img PowerPoint

  CO as the reduction product: Based on the current summary of possible reaction paths for the conversion of CO₂ into CO, the following process can be summarized. Firstly, CO₂ is dissolved in the electrolyte and then contacts with the catalyst to yield ^*CO₂⁻ intermediate through electron transfer to the adsorbed ^*CO₂. The C atom in ^*CO₂⁻ is first combined with the electrode surface through the proton-coupled electron-transfer (PCET) process. Alternatively, the C atom and O atom in ^*CO₂⁻ can be parallel to the electrode surface. In this case, the ^*COOH intermediate is yielded by the combination of protons. Subsequently, the ^*CO intermediate is generated and desorbed from the catalyst surface as CO [74-76].

  HCOOH as the reduction product: Unlike the CO pathway, the intermediates for the generation of HCOOH are not the same. The proposed pathways based on previous studies can be summarized as the following three pathways. The first is the formation of ^*CO₂⁻ followed by the PCET process, in which one or two O atoms in ^*CO₂⁻ combine with the electrode surface to yield ^*OCHO, followed by the acquisition of protons to yield HCOOH [77-80]. The second type is that the first proton in the aqueous solution is reduced to an H atom and adsorbed on the electrode. CO₂ electrophilic attacks the H atom on the electrode to produce HCOO^*, which is then transferred by protons to yield HCOOH [81]. The third pathway is similar to the CO generation pathway, in which a proton is obtained after the formation of ^*COOH to form HCOOH directly [82].

  2.2 The challenge of CO₂RR

  Since the pioneering work of Hori et al. in the 1980s and 1990s, tremendous efforts have been made in the research of electrocatalysts for CO₂RR [83-85]. The CO₂RR performance of the electrocatalysts was evaluated mainly from four aspects: current density, faraday efficiency (FE), stability, and energy efficiency (EE). Although electrocatalysts for CO₂RR have shown increasingly excellent performance in recent years, they are often limited by high costs for practical industrial production of hydrocarbon products or carbon-oxygen products. At present, the research on this technology is still mainly limited to the laboratory scale, and there are still great difficulties in industrial production [86,87]. Therefore, there are still insurmountable obstacles in the avenues of electrocatalytic CO₂ reduction to practical applications.

  Large overpotential: CO₂ possesses a very stable molecular structure with C=O bond energies as high as 805 kJ/mol, so a large amount of energy is required to activate the CO₂ molecule, leading to a large overpotential for driving the reaction. The step of converting CO₂ into the ^*CO₂⁻ intermediate requires a large potential of −1.49 V, which is the rate-determining step (RDS) of CO₂RR [88,89]. In addition, ^*CO₂⁻ continues to form different reaction intermediates on the catalyst surface and desorbs via complicated proton coupling and electron transfer, which also requires a large overpotential to overcome the slow reaction kinetics [90]. Therefore, it is urgent to reduce the overpotential to improve the economy of the reaction.

  Low selectivity: After CO₂ is activated to form ^*CO₂⁻, diverse products can be produced according to different electron transfers, including CO, formate, methane, ethylene, ethane, etc. [91]. The overpotential required to form the final product is usually greater than that required for CO₂ reduction to ^*CO₂⁻. Therefore, when CO₂ occurs reduction, subsequent reduction reactions will occur spontaneously, making it difficult to terminate the reaction at specific steps to achieve high selectivity. More importantly, the potential of −1.49 V is much more negative than the potential of hydrogen evolution, the hydrogen evolution reaction (HER) will become a powerful competitive reaction to further reduce product selectivity [92].

  Stability: The stability of electrocatalysts is an important indicator of catalyst performance. Furthermore, the stability of electrocatalysts determines their ability to maintain activity and selectivity under long-term constant current or constant potential [93]. Most of the CO₂RR electrocatalysts reported in recent years were stable up to a few hundred hours before structural collapse and active site deactivation. However, the stability of catalysts for industrial applications requires at least thousands of hours, which is still far from the stability of electrocatalysts studied so far [86,94].

  Energy efficiency (EE): The previous performance indicators of CO₂RR mostly focused on current density, selectivity, and FE. However, as a guiding standard for the industrial implementation and economic feasibility of CO₂RR, EE should also be fully considered [95]. EE is the percentage of the energy of target products divided by the total power input of the electrolysis system, closely related to battery voltage and FE [96,97]. From the perspective of technical and economic analysis, it is necessary to maximize the EE of the CO₂RR system at commercially relevant current densities to reduce total power input as electricity accounts for a significant portion of production costs [98]. On the other hand, due to the thermodynamic and kinetic consumption of the oxygen evolution reaction (OER) process occurring in the anode, the anode reaction in the CO₂RR system consumes a significant part of the supplied electrical power [99,100].

  Low CO₂ utilization: Due to the fact that HER is more advantageous in kinetics than CO₂RR under acidic conditions, most current research on CO₂RR favors alkaline conditions [101,102]. However, most of the input CO₂ reacts with OH⁻ in the electrolyte to produce CO₃²⁻ due to strong local alkaline conditions. The formation of carbonates poses significant limitations on carbon utilization efficiency [103]. Specifically, for each pair of electrons transferred in the CO₂RR process, the cathode produces a hydroxide that reacts with half of the CO₂ to generate a carbonate. Therefore, the maximum carbon utilization is 50% for two electron transfer processes such as CO₂ to CO. Carbon utilization is lower for multiple electron transfer processes [104]. The inefficient utilization of CO₂ in CO₂RR severely limits its prospects.

  2.3 Peculiar features of p-block metal-based MOFs

  The CO₂RR product is dependent on the reaction intermediate, which is related to the active site of the catalyst. As a group of metal resources with abundant reserves, p-block metals are cheaper than precious metals or other metals that produce formic acid, resulting in significant economic advantages as electrocatalysts for CO₂RR. In addition, p-block metals exhibit high electronegativity and low ionization energy due to their unique electronic structure (ns²np¹ to ns²np⁶) (Fig. 2). The p-block metals have a wide range of variable valence states, giving them the ability to form p-block metal-based catalysts with different valence states [68]. More importantly, due to their characteristic oxyphilic, the p-block metals facilitate the adsorption and formation of oxygen-bonded intermediates, such as ^*OOCH and ^*OCHO, which are major intermediates for the production of formate [105,106]. In addition, the low adsorption of the p-block metal for ^*H allows them to inhibit HER. Based on the above reasons, p-block metal-based MOFs are effective in reducing CO₂ to formate or CO. Rossmeisl and co-workers [107] compared the groups in terms of multiple binding energies of intermediates calculated by density functional theory. The results showed that the p-block metals have a unique selectivity for HCOOH (Figs. 2b and c).

  Figure 2

  

  Figure 2.  (a) Electronic structure of p-block elements. (b) The combined plot of the three proposed descriptors for converting CO₂ into H₂, CO, and HCOOH. (c) Calculation of catalytic products for different metals by ΔE_H⁺-ΔE_COOH⁻. Copied with permission [107]. Copyright 2017, Wiley Publishing Group.

  DownLoad: Full-Size Img PowerPoint

  3. Pristine MOFs as catalysts

  Due to the controllable structure and abundant active sites, various pristine MOF materials have been developed as effective catalysts for CO₂RR [108]. MOF catalysts are conducive to exposing active sites and enriching reaction substrates during CO₂RR due to their unique porous structure. More importantly, the well-defined crystal structure provides a promising opportunity for mechanistic investigations. Here we summarize and discuss the progress of p-block metal-based MOFs in the CO₂RR. The ligands involved in MOFs and MOF-derived catalysts mentioned in this review are shown in Fig. 3.

  Figure 3

  

  Figure 3.  The structure of selected organic ligands that was involved in this review. H₂BDC, terephthalic acid; H₂IPA, isophthalic acid; H₂BDC—NH₂, 2-aminoterephthalic acid; HIN, isonicotinic acid; HAIN, 3-aminoisonicotinic acid; H₃BTC, benzene-1,3,5-tricarboxylic acid; HCA, 5-chloronicotinic acid; HTA, 1H-1,2,3-triazole; HMD, 2-methylimidazole; PTA, p-phthalic acid; aPTA, 2-aminoterephthalic acid; DaTPA, 2,5-diaminoterephthalic acid; HAB, benzene-1,2,3,4,5,6-hexaamine; H₂PDC, pyrazole-3,5-dicarboxylic acid; H₂IDC, 4,5-Imidazoledicarboxylic acid; H₄PMA, pyromellitic acid; HTCD, trisodium citrate dihydrate; H₂ABDBC, (E)−4,4′-(diazene-1,2-diyl)dibenzoic acid; H₄BPTC, biphenyl-3,3′,5,5′-tetracarboxylic acid; H₂NDC, naphthalene-1,4-dicarboxylic acid; H₄BDP, 5,5′-(1,3,6,8-tetraoxo-1,3,6,8-tetrahydrobenzo[lmn][3,8]phenanthroline-2,7-diyl)diisophthalic acid; H₃BTB, 1,3,5-tris(4-carboxyphenyl)benzene; HHTP, 2,3,6,7,10,11-Triphenylenehexol; H₄BCP, 5-(2,6-bis(4-carboxyphenyl)pyridin-4-yl)isophthalic acid; H₄EA, 2,3,7,8-tetrahydroxychromeno[5,4,3-cde]chromene-5,10‑dione; H₄TA, [Ni(C₂S₂(C₆H₄COOH)₂)₂]; H₄TTFTB, tetrathiafulvalene-3,4,5,6-tetrakis(4-benzoic acid); TCPP, tetrakis (4-carboxyphenyl) porphyrin.

  DownLoad: Full-Size Img PowerPoint

  3.1 In-based MOFs

  Among numerous catalysts, In-based catalysts exhibit outstanding performance in converting CO₂ into formate. They are considered ideal catalysts due to their abundant reserves and environmental friendliness [109-111]. However, many In-based catalysts, including In oxide [112], In sulfide [113], and In complexes [114] hinder their further application due to their low atomic utilization and poor stability. Encouragingly, metal-organic frameworks (MOFs) with adjustable structures, tailorable channels, and highly dispersed active sites are considered potential electrocatalytic materials [115].

  In 2020, Gu's group [116] used an In-based MOF named In-BDC for the electro-reduction of CO₂ to formate, which can catalyze with a FE_HCOO⁻ exceeded 80% within the potential window of −0.419 V to −0.769 V (Fig. 4a). The maximum FE_HCOO⁻ of In-BDC was 88% with a maximum turnover frequency (TOF) of 4798 h⁻¹. Moreover, In-BDC maintained stable FE and current density within 21 h, indicating its stability in CO₂RR. Compared with commercial In catalysts, In-BDC presented better catalytic performance, indicating the promising application of In-MOFs in CO₂RR.

  Figure 4

  

  Figure 4.  (a) FE of HCOOH and CO for In-BDC, In, and BDC. Copied with permission [116]. Copyright 2020, American Chemical Society. (b) Scheme for the synthesis of MFM-300(In)-e. (c, d) The stability of electrolysis over 2 h. Copied with permission [120]. Copyright 2020, American Chemical Society. (e) Scheme for the synthesis MIL-68(In) and MIL-68(In)-NH₂. (f) FE of HCOOH for MIL-68(In) and MIL-68(In)-NH₂. (g) Uncorrected LSV curves of MIL-68(In)-NH₂ in the flow cell. Copied with permission [121]. Copyright 2021, Wiley Publishing Group.

  DownLoad: Full-Size Img PowerPoint

  In order to further improve the catalytic activity of In-MOF catalysts, strategies including defect engineering [117], post-functionalization modification [118], and metal doping [119] have been attempted. In 2020, Martin, Yang, and Han et al. [120] developed an ionic liquid electrolyte-assisted electrodeposition method to realize the direct growth of MOFs on substrates (Fig. 4b). Compared with the MFM-300(In)-t prepared by thermo-synthesis, electro-synthesized MFM-300(In)-e possesses more defects due to the competitive coordination of OAc⁻ in high concentrations of EmimOAc electrolytes, which was supported by BET, FTIR, and XPS. In addition, although the samples had the same crystal structure, the conductivity of the obtained MFM-300(In)-e was improved by one order of magnitude due to the closer contact between MOF and substrate. As a result, MFM-300(In)-e exhibited a FE_HCOOH of 99.1% with a j_HCOOH of −46.1 mA/cm², which exceeded all other MOFs at that time. According to DFT calculations, the formation of the ^*COOH on MFM-300(In)-e was spontaneously compared with that on MFM-300(In)-t, indicating that the absorption of the ^*COOH intermediate is facilitated by the defective In(Ⅲ) sites present in MFM-300(In)-e (Figs. 4c and d). It was also found that the ^*COOH intermediate is easier to form than ^*CO, resulting in a high selectivity for formate. This work pioneers an efficient method for the electrosynthesis of MOF catalysts while demonstrating the great potential of defect engineering for CO₂RR.

  Regulating the performance of MOF catalysts through the functionalization of ligands has also proven to be a promising strategy for constructing excellent catalysts. In 2021, Xia et al. [121] reported an In-MOF (MIL-68(In)-NH₂) with amino groups for the reduction of CO₂ into formate. The author introduced amino groups based on the existing ligands, which serve as free radicals to participate in the framework construction, rather than coordinating with In sites (Fig. 4e). Specifically, the strong electron donating ability of amino groups can significantly increase the electron density of In atoms. The change in electron density around the In atom is beneficial for the activation of CO₂ and the binding of reaction intermediates, thus improving the catalytic performance effectively [122]. As a result, MIL-68(In)-NH₂ had a higher current density and FE. FE_HCOO⁻ of MIL-68(In)-NH₂ reached the maximum value of 94.4% at −1.1 V and remained stable within 24 h (Figs. 4f and g). The author suggested that amino groups can enrich CO₂ adsorption via acid-base interactions and stabilize ^*CO₂⁻ intermediates via hydrogen bonds [123,124]. It is worth noting that MIL-68(In)-NH₂ inevitably undergoes during the electrocatalytic process, but the retained presence of amino groups still leads to a high FE of formate. This work reveals the influence of amino functionalization on active sites and proposes potential strategies for modifying MOF electrocatalysts with functional groups on ligands.

  In addition to immobilized amino groups, modification of the enzyme-mimicking redox-active units can also be effective in improving catalytic activity. Ding et al. [125] reported an In-MOF ((Me₂NH₂⁺)[In^Ⅲ-(TA)]·3DMF·1.5H₂O) based on a redox-active tetrathiafulvalene (TTF) ligand H₄TA, which is an inorganic analog with a metal site (Ni) replacing the central C=C bond (Fig. 5a). Compared to manufacturing structural defects that expose more catalytic sites, these unsaturated metal active sites are not dependent on the generation of structural defects. The unsaturated Ni sites in the ligand can emulate the activity of formate dehydrogenase and CO dehydrogenase [NiS₄] sites, thereby effectively converting CO₂ into formic acid in CO₂RR. Compared with isomorphic (Me₂NH₂⁺)[In^Ⅲ(TTFTB)]·0.7C₂H₅OH·DMF, (Me₂NH₂⁺)[In^Ⅲ(TA)]·3DMF·1.5H₂O exhibited significantly enhanced the catalytic performance in CO₂RR. At the applied potential of −1.3 V, the FE_HCOOH of (Me₂NH₂⁺)[In^Ⅲ(TA)]·3DMF·1.5H₂O reached 89.6% with a j_HCOO⁻ of −36.0 mA/cm² (Fig. 5b). There was no significant decrease in FE and current density over 12 h, demonstrating the good stability of the catalyst. Adsorption isotherms confirmed that [NiS₄] can serve as a binding site for CO₂. The author proposed that unsaturated redox activity [NiS₄] can serve as both CO₂ binding and catalytic sites, simulating the active [NiS₄] centers in formate dehydrogenase and CO dehydrogenase. DFT calculations suggested that the free energy of (Me₂NH₂⁺)[In^Ⅲ(TA)]·3DMF·1.5H₂O is lower than that of (Me₂NH₂⁺)[In^Ⅲ(TTFTB)]·0.7C₂H₅OH·DMF, confirming that the [NiS₄] sites indeed make an important role in the catalytic process (Figs. 5c and d).

  Figure 5

  

  Figure 5.  (a) Simplified diagram of CO₂RR for Me₂NH₂⁺)[In^Ⅲ(TA)]·3DMF·1.5H₂O and (Me₂NH₂⁺)[In^Ⅲ(TTFTB)]·0.7C₂H₅OH·DMF. (b) FE of HCOOH for Me₂NH₂⁺)[In^Ⅲ(TA)]·3DMF·1.5H₂O and (Me₂NH₂⁺)[In^Ⅲ(TTFTB)]·0.7C₂H₅OH·DMF. (c, d) Proposed reaction paths and free energy for [NiS₄] sites. Copied with permission [125]. Copyright 2021, American Chemical Society. (e) FE of In-ABDBC—HIN, InCo-ABDBC—HIN and In-ABDBC—HAIN. (f, g) The distribution of unpaired electrons in In-ABDBC—HIN and InCo-ABDBC—HIN. Copied with permission [119]. Copyright 2022, Royal Society of Chemistry.

  DownLoad: Full-Size Img PowerPoint

  In addition to regulating ligands, adjusting metal centers can also have a positive effect on CO₂RR. The addition of secondary metals to construct bimetallic compounds has been supposed to be an effective strategy for improving activity. In 2023, Zhai et al. [119] reported a series of In-based trinuclear MOFs (In-ABDBC—HIN, In-ABDBC—HAIN, and InCo-ABDBC—HIN) and investigated the effect of ligand functional groups in CO₂RR. The presence of Co and functional groups significantly increased the specific surface area and CO₂ adsorption capacity of the materials as revealed by N₂ and CO₂ adsorption-desorption isotherms. As a result, InCo-ABDBDC—HIN had the highest current density, followed by In-ABDBC—HIN and In-ABDBC—HAIN. The experimental results suggested that the substitution of Co atoms for In atoms is beneficial for improving catalytic performance, while the introduction of amino groups in the ligand decreased the catalytic performance. So InCo-ABDBC—HIN exhibited a maximum current density of −21.2 mA/cm² and a maximum FE of 81.5% for the C1 product at −2.2 V (Fig. 5e). According to DFT calculations, unpaired electron distributions were not observed on the metal atoms in In-ABDBC—HIN and In-ABDBC—HAIN, indicating that amino modification hardly affects the electron density in the In atoms. After doping Co into an In cluster, InCo-ABDC—HIN exhibited significant unpaired electron distribution on the Co atom. Amino group modifications both increase steric hindrance to prevent CO₂ adsorption at the active sites and lead to extremely poor DOS intensity to reduce conductivity, which ultimately negatively affects the catalytic performance (Figs. 5f and g).

  As the research continues, the poor conductivity of most In-MOF materials hinders the further improvement of the catalytic performance. How to enhance the conductivity becomes a crucial issue. Zhao's group [126] proposed an in situ pyrolytic construction of carbon nanoparticle-modified In-MOF materials by introducing a small-molecule carbon source to improve the catalytic properties of the materials (Fig. 6a). A three-dimensional In-MOFs {(Me₂NH₂)[In(BCP)]·2DMF}_n (V11) with two types of channels was first constructed as a model based on the H₄BCP ligand. Nanoscale pores and good stability facilitate the introduction of carbon sources. Considering the molecular size with respect to the carbonization temperature, methylene blue was screened as a carbon source to be introduced into the framework. After carbonization, methylene blue was converted into uniformly sized carbon nanoparticles while causing V11 to produce a large number of mesopores. As a result, the modified catalysts exhibited a significant enhancement in selectivity and current density, which was attributed to faster charge transfer with fully exposed metal active sites (Fig. 6b). More importantly, this strategy was also applicable to classic In-MOFs materials such as MIL-68, PF-110, and CPM-5 (Figs. 6c and d).

  Figure 6

  

  Figure 6.  (a) Scheme for the synthesis of CPs@V11. (b) FE of CPs@V11. (c, d) FE of the original In-MOFs and the CPs@MOFs. Copied with permission [126]. Copyright 2021, Wiley Publishing Group. (e) FE of formate and the total current density of In-TCPP. (f, g) The proposed mechanisms and corresponding energy profiles for In-TCPP. Copied with permission [82]. Copyright 2023, Tsinghua University Press.

  DownLoad: Full-Size Img PowerPoint

  Hu et al. [82] instead chose conductive MOFs with the ability to provide electrons as catalysts. They prepared a classic conductive large π conjugated In-based MOF (In-TCPP) nanosheets with different sizes for CO₂RR. In the flow cell under alkaline conditions, FE_HCOO⁻ of In-TCPP nanosheets reached the maximum FE of 90% at −0.8 V, and the CEE was 63.8% (Fig. 6e). It is worth noting that the selectivity and current density of In-TCPP remained almost unchanged within 50 h, indicating its excellent stability. In addition, in situ ATR-FTIR and DFT calculations confirmed that the In sites as the active sites could stabilize the ^*COOH intermediates, which facilitates the formation of formate (Figs. 6f and g). This work encourages further exploration of the potential of conductive MOF materials for CO₂RR applications.

  3.2 Bi-based MOFs

  Bi-based materials have been shown to be effective electrocatalysts for the electrochemical conversion of CO₂ into HCOOH [127]. Bi-based catalysts have received widespread attention due to the following advantages: (1) Low toxicity and environmental friendliness [128]; (2) Effective inhibition of the competitive reaction HER [129,130]; (3) High selectivity due to strong affinity for ^*OCHO intermediates and weak adsorption capacity for ^*CO intermediates [131]; (4) Lower cost and better stability compared to precious metal catalysts. Recently, Bi-MOFs have become potential Bi-based catalysts due to their clear coordination environment, exposed active sites, and controllable structure.

  In 2020, Sun et al. [132] prepared a highly stable 2D Bi-based MOF (Bi-MOF) with permanently accessible porosity for CO₂RR. Bi-MOF was constructed from helical BiO rods and H₂BTC ligands to form a 2D open framework, leading to a FE of 92.2% at −0.9 V within 30 h (Fig. 7a). The authors concluded that the larger pores and highly exposed two-dimensional structure of the framework facilitated mass transfer during the reaction. The abundant micropores are favorable for CO₂ enrichment and increase the local substrate concentration. More importantly, the open framework enables the Bi sites to be fully exposed, resulting in a mass-specific partial current density much higher than those of commercial Bi₂O₃ and Bi nanosheets. X-ray absorption fine structure spectroscopy (XAFS) showed that Bi^Ⅲ sites in the channels can be stabilized during the reaction, which plays an important role in enhancing CO₂ adsorption and HCOOH production.

  Figure 7

  

  Figure 7.  (a) FE of Bi-MOF. Copied with permission [132]. Copyright 2020, Elsevier. (b) FE of SU-101 NRs. (c) The energy profiles for the four pathways proposed on SU-101. Copied with permission [128]. Copyright 2022, Royal Society of Chemistry. (d) Schematic illustration of the metal-organic cube, linkage, and ACO topology from inorganic zeolites to ZMOFs, and Bi-ZMOFs. (e) FE of PZH-1. (f) Free energy for converting CO₂ into HCOOH of PZH-1 (red) and PZH-2 (blue), respectively. Copied with permission [133]. Copyright 2023, Wiley Publishing Group.

  DownLoad: Full-Size Img PowerPoint

  Zhang et al. [128] constructed a highly stable Bi-based MOF Bi₂O(H₂O)₂(C₁₄H₂O₈)·nH₂O·nH₂O (SU-101) with nanorod morphology based on H₄EA ligand. Impressively, SU-101 could maintain a stable crystal structure in a wide pH range of 2–14. SU-101 exhibited a maximum FE_HCOO⁻ of 93.66% at −1.06 V with j_HCOO⁻ of −14.57 mA/cm² (Fig. 7b). PXRD patterns suggested that SU-101 still maintained its original crystalline structure with rod-shaped after the electrocatalytic process. DFT calculations compared four possible reaction pathways, indicating that ^*OCHO is a critical reaction intermediate (Fig. 7c). The author believed the adsorption strength of Bi(Ⅲ) in SU-101 is moderate, not weak enough for HER to occur, and at the same time weakens the adsorption of C=O bonds to inhibit the generation of CO.

  In 2023, Zhou and Li et al. [133] constructed two Bi-MOFs (PZH-1 and PZH-2) to explore the effect of the interaction between metal centers and the coordinating environment on CO₂RR. One of them has a Bi-N coordination structure and the other has all Bi coordinated to oxygen atoms. The author was inspired by zeolitic metal-organic frameworks (ZMOFs) and successfully synthesized a 3D PZH-1 with an unreported zeolitic ACO topological structure by using a ligand-directing strategy. Compared with the hydrogen-bonded ZMOFs, Bi-ZMOF constructed by metal-oxygen coordination bond can improve the stability of the zeolite frameworks. And the [Bi₂(H₂O)N₄O₈] binuclear units were observed for the first time in Bi-MOFs. Interestingly, each [Bi₂(H₂O)N₄O₈] unit can bridge 8 identical [Bi₂(H₂O)N₄O₈] units, to form an interesting Bi₂₄ cubic cage with a pore size of approximately 12 × 12 Ų, which is the first Bi cube cage in MOFs (Fig. 7d). The FE_HCOOH for PZH-1was up to 91% at −1.1 V (Fig. 7e). After 12 h of electro-reduction reaction, XPS suggested that the main oxidation state after the reaction is Bi(Ⅲ), and no other Bi species were produced, confirmed the PZH-1 has good stability. In addition, the author prepared PZH-2 based on the H₄PMA ligand with a two-dimensional layered structure for comparison. The results indicated that the CO₂RR performance of PZH-2 was worse than PZH-1, confirming that Bi-N coordination promoted the conversion of CO₂ to HCOOH. DFT calculations indicated that porous structures are beneficial for exposing the active sites and further absorption of CO₂, while the Bi-N coordination facilitates the transfer of electrons from ligands to active sites, thereby activating the absorbed CO₂ and stabilizing intermediates (Fig. 7f).

  Although Bi-based MOF electrocatalysts have exciting performance in CO₂RR, low conductivity likewise hinders their further application. Conductive Bi-based MOFs attract the attention of researchers. Hu's group [134] reported a conductive Bi-MOF (Bi-HTPP) with unsaturated Bi(Ⅲ) active sites and rare zigzagging corrugated topology (Fig. 8a). Bi-HTPP possessed an excellent conductivity of 1.65 S/m above that of most Bi-MOFs. Electron paramagnetic resonance (EPR) spectroscopy revealed the presence of unpaired electrons, confirming the presence of unsaturated Bi(Ⅲ) sites. The Bi-HHTP exhibited a maximum FE_HCOOH of 95% at −0.7 V with 68.8% CEE (Fig. 8b). It is worth noting that there was no significant performance decay after 30 h of electro-reduction reaction, which is attributed to the far more stable structure than other reported Bi-MOFs confirmed by in situ Raman spectra. DFT calculations indicated that the high selectivity of Bi-HTPP for HCOOH is due to the strong ^*COOH intermediate at the Bi(Ⅲ) site, which weakens the C=O bond (Fig. 8c).

  Figure 8

  

  Figure 8.  (a) The scheme for the preparation of Bi-HHTP. (b) FE_HCOOH and j_HCOOH of Bi-HHTP. (c) The energy profiles for the four pathways proposed on Bi-HHTP. Copied with permission [134]. Copyright 2023, Royal Society of Chemistry. (d) Schematic illustration of CO₂RR for V12. (e) FE of Bi foil, V12@CC, V12@BF, and V12e. (f) The FE for HCOOH and MDDQ of V12e‖CAT-1@NF. Copied with permission [135]. Copyright 2021, Elsevier. (g) Crystal structure of Bi-FDCA MOF. (h) Schematic illustration of the ions transfers in the paired electrolysis with BPM. (i) FE of HCOOH and current density of Bi-FDCA MOF. Copied with permission [136]. Copyright 2022, Wiley Publishing Group.

  DownLoad: Full-Size Img PowerPoint

  Zhao's group [135] constructed a novel Bi-MOF {(Me₂NH₂)[Bi(BDP)]·4DMF·2H₂O}_n (V12) based on a naphthalenediimide-based ligand with redox properties, which had nanoscale one-dimensional pores and a total free volume of up to 69.8%. The author further prepared V12e using the classical ionic liquid-assisted electrochemical deposition method, which created more ligand-missing defects while obtaining a unique flower-like structure. The presence of defects effectively enhances the activity of Bi sites, and the unique nanostructure promotes the exposure of active sites (Fig. 8d). As a result, V12e prepared by electrodeposition had a higher FE_HCOO⁻ of 93.2% and 2-fold current density enhancement compared to V12 (Fig. 8e). In addition, in order to further reduce energy consumption and obtain a variety of high value-added products, the author utilized the oxidation reaction of tetrahydroisoquinoline instead of OER to form a new system. This strategy not only promoted sluggish kinetics but also realized the simultaneous generation of high value-added dihydroisoquinolines and formate, which provides inspiration for the construction of an efficient electrolytic system (Fig. 8f). He et al. [136] constructed a Bi-MOF based on 2,5-furandicarboxylic acid to catalyze the CO₂ reduction reaction paired with 5-hydroxymethylfurfural oxidation (Fig. 8g). Interestingly, the 5-hydroxymethylfurfural generated by 5-hydroxymethylfurfural oxidation will serve as a self-generated ligand to construct MOF materials for CO₂RR (Fig. 8h). The FE_HCOO⁻ of constructed Bi-MOFs exceeds 95% at −1.2 V with −19.6 mA/cm². Accompanied by the catalyze of Ni(OH)₂/CP prepared by electrodeposition in anodic, the new electrolysis system realized the production of FE_HCOOH with 95.6% and FE_FDCA with 75% (Fig. 8i).

  Unlike In-MOFs, many studies revealed that Bi-MOFs undergo structural evolution during the CO₂RR process, typically manifested as structural destruction with Bi(Ⅲ) being reduced to Bi(0) particles [137,138]. Lock et al. [139] reported a Bi(btb) with face-sharing BiO₉ chains as a precatalyst for CO₂RR. The authors have carried out an in-depth study of the structural evolution of Bi(btb). Grazing-incidence X-ray diffraction indicated that the pristine crystalline state of Bi(btb) disappears after 15 min of immersion in a KHCO₃ electrolyte solution to produce crystalline Bi under CO₂RR conditions. Pair distribution function analysis suggested that the carbonate and bicarbonate anions partly replace the linkers. As a result, the crystalline Bi(btb) was transformed into highly dispersed Bi nanoparticles embedded in a carbon matrix, which can produce formate with a FE of up to 95% (Figs. 9a and b).

  Figure 9

  

  Figure 9.  (a) Electrolysis results of Bi(btb) in CO₂ saturated electrolyte. (b) High-resolution TEM images of Bi nanoparticles. Copied with permission [139]. Copyright 2020, Wiley Publishing Group. (c) The electrochemical cell and reaction mechanism of MOF-derived Bi₂O₂CO₃. (d) FE and j of Bi-BTB. (e) XRD patterns of Bi-BTB with different treatments. (f) Measured CVs of MOF-derived at 10 mV/s. Copied with permission [140]. Copyright 2020, Royal Society of Chemistry.

  DownLoad: Full-Size Img PowerPoint

  Similarly, Gu and his co-workers [140] prepared two examples of Bi-based MOFs for CO₂RR, namely Bi-BTB and Bi-TATB, and proposed that Bi-based MOFs can be converted into carbonates in the presence of subcarbonate (Bi₂O₂CO₃), proving the significance of the HCO₃⁻ salt effect (Fig. 9c). The FE_HCOO⁻ of Bi-BTB reached 96.1% with a j_HCOO⁻ of −12.7 mA/cm² at −0.669 V (Fig. 9d). In addition, after the continuous electrolysis process at −0.669 V for 48 h, the electrocatalyst exhibited excellent electro-reduction stability. Through the PXRD patterns, it was found that Bi-BTB underwent structural changes induced by HCO₃⁻ during CO₂RR. Bi₂O₂CO₃ was the dominant phase with good stability in the CO₂RR process (Fig. 9e). The author believed that based on the Hard Soft Acid Base theory, Bi-BTB is theoretically unstable due to Bi(Ⅲ) ions and carboxylates belong to intermediate acids and hard bases, respectively. Therefore, the Bi-O bond of Bi-BTB may be disrupted by HCO₃⁻ in the electrolyte, achieving in situ conversion to Bi₂O₂CO₃ (MOF-derived Bi₂O₂CO₃). When NaSO₄ was used as the electrolyte instead of KHCO₃, the corresponding transformation did not take place but was reduced to Bi nanoparticles under the action of the potential, further demonstrating the induced effect of HCO₃⁻. From these results, it can be concluded that the Bi-O bond of Bi-MOF could be destroyed by HCO₃⁻. Furthermore, Bi₂O₂CO₃ derived from MOF has a layered structure composed of [Bi₂O₂]²⁺ and CO₃²⁻, which is analogous to layered Bi oxide halides. Compared with BiOCl and BiOBr, MOF-derived Bi₂O₂CO₃ had better stability and selectivity, which is more resistant to reduction to metal Bi(0) during the CO₂RR process (Fig. 9f).

  Qiao et al. [138] used CAU-17 as a model to further monitor the transformation process based on in situ characterization techniques. In the KHCO₃ solution, the nanorod-like CAU-17 transformed into a nanosheet-like Bi₂O₂CO₃ (Fig. 10a). Through in situ Raman spectra, it was visualized that the bands at 820 and 1002 cm⁻¹ attributed to C—H in the BTC³⁻ gradually weakened, while a new band assigned to the stretching vibration of C—O in Bi₂O₂CO₃ appeared at 1069 cm⁻¹. This result confirmed that the Bi coordination environment is altered and that the process is electrolyte concentration dependent. Subsequently, in situ Raman spectra further confirmed that with a gradual increase in overpotential, Bi₂O₂CO₃ in turn transformed into Bi nanosheets with the abundant unsaturated site, resulting in a high FE_HCOO⁻ of 92% (Fig. 10b). This work details that the reconstruction of CAU-17 consists of two steps: electrolyte-mediated and potential-mediated.

  Figure 10

  

  Figure 10.  (a) Scheme of the two-step reconstruction process of Bi NS. (b) FE_HCOO⁻ for the Bi NS. Copied with permission [138]. Copyright 2021, Wiley Publishing Group. (c) Scheme for the synthesis of Ni-NF-Af and Bi-enes. (d) FE of Bi-enes. (e) Voltage-dependent FE_HCOOH and corresponding i-t curves of anodic MOR and cathodic CO₂RR. Copied with permission [141]. Copyright 2021, Wiley Publishing Group.

  DownLoad: Full-Size Img PowerPoint

  Likewise, Zhu and Xu et al. [141] explored the structural evolution of Bi-MOFs constructed with different ligands including H₃BTC, H₂BDC, and H₂IDC during CO₂RR. Although Bi-BTC, Bi-BDC, and Bi-IDC have different morphologies such as cubic, rod, and flower clusters, all of them were converted to ultrathin Bi-nanosheets during the CO₂RR process (Fig. 10c). At a potential of −1.178 V, Bi-ene provides a FE_HCOO⁻ of 95% as well as a j_HCOO⁻ of −70 mA/cm², which far outperforms commercial Bi powders (Fig. 10d). Subsequently, by pairing the reaction with methanol oxidation, the authors further achieved the simultaneous generation of formate at both the cathode and anode with close to 100% selectivity (Fig. 10e).

  Liang et al. [142] prepared a Bi-based MOF (Bi-MOF) with BiO₉ nodes for CO₂RR, which could be transferred into a mixture of Bi and Bi₂O_2.5 in CO₂RR (Fig. 11a). For Bi-MOF, the FE_HCOOH of 92% and j_HCOO⁻ of −150 mA/cm² were achieved at −0.64 V, which could be maintained for 30 h (Fig. 11b). The Bi-MOFs transformed into Bi/Bi₂O_2.5 with perpendicular sheet morphology during the reaction. The Bi/BiO interface is beneficial for reducing the free energy of formation by the ^*OCHO intermediate [130], leading to high HCOOH selectivity (Fig. 11c).

  Figure 11

  

  Figure 11.  (a) Scheme for the formation of Bi/Bi-O interface for the CO₂RR. (b) FE of Bi-MOF. (c) In situ Raman spectra of Bi-MOF for the CO₂RR. Copied with permission [142]. Copyright 2021, Wiley Publishing Group. (d) The coordination environment and pore structures of MFM-220, MFM-221, and MFM-222. (e) FE of Bi-MOFs. (f) FT-IR spectra of Bi-MOFs. Copied with permission [143]. Copyright 2022, Royal Society of Chemistry.

  DownLoad: Full-Size Img PowerPoint

  Although the reconstruction process of Bi-MOFs has been well elucidated, the effect of the initial structure of Bi-MOFs on the reconstructed products has rarely been investigated. Therefore, Floriana Tuna et al. [143] reported a series of Bi-based MOFs (MFM-220, MFM-221, and MFM-222) based on the H₄BPTC ligand with different porosity to explore the effect of porosity in the structural evolution of MOFs during the CO₂RR process (Fig. 11d). Bi-MOFs were named MFM-200/−221/−222-e and 200/−221/−222-p when reacting with electrolytes and applying external potentials, respectively. Among them, MFM-220-p originates from the highest porosity MFM-220 had the best catalytic performance for CO₂RR. The FE of HCOOH was 90.4% at −1.1 V (Fig. 11e). In addition, MFM-220-p maintained activity against CO₂RR for at least 5 h. After adding the electrolyte for 30 min, PXRD patterns and FT-IR spectra confirmed the presence of Bi₂O₂CO₃ in MFM-220-e, MFM-221-e, and MFM-222-e (Fig. 11f). And MFM-220-e undergone the fastest transformation, while MFM-222-e undergoes an incomplete transformation. After applying an external potential, α-Bi₂O₃ and Bi appeared in MFM-220-p, MFM-221-p, and MFM-222-p. Similarly, MFM-220-p has the fastest conversion process, while the conversion of MFM-222-p was the slowest. The fast and complete conversion of porous MFM-220 improves the conductivity of MFM-220-p/CP, thereby enhancing the catalytic activity for CO₂RR. Therefore, the effect of porosity on the reconfiguration catalysts of Bi-MOFs should not be neglected, and high porosity contributes to the rapid reconfiguration into a highly porous structure, which improves the catalytic activity.

  3.3 Sn-based MOFs

  Sn-based materials can still be used as the potential catalysts for the electrocatalyst for CO₂ to formate because of their low cost and non-toxic [144-146]. Including Sn alloys [45], Sn nanoparticles [147], Sn oxides [148], and nonmetal doped Sn compounds [149] have been reported successively. For Sn-based MOFs, due to their clear Sn metal active sites and porous structure, they are expected to become potential electrocatalysts for achieving CO₂RR.

  In 2022, Zhang et al. [150] synthesized a Sn-MOF using a more environmentally friendly atmospheric stirring method in an aqueous solution, and further prepared Pb infiltrated Sn-MOF catalysts (Fig. 12a). It is worth noting that the presence of Pb in the form of Pb(0) or PbO rather than coordination with ligands, therefore the basic structure of Sn-MOF did not change substantially. Sn-MOF exhibited the FE_HCOO⁻ as high as 91.8% at −1.2 V. However, Sn-MOF_Pb5 exhibited a higher FE_HCOO⁻ compared with pure Sn-MOF, with FE_HCOO⁻ reaching 94.6% at −1.1 V (Fig. 12b). DFT calculations indicated that Sn centers have strong interactions with^*OCHO intermediates, which is a common reaction pathway intermediate for generating HCOOH, resulting in high formate selectivity for Sn-MOF (Fig. 12c).

  Figure 12

  

  Figure 12.  (a) Scheme for the CO₂RR of Sn-MOF. (b) FE of Sn-MOFs. (c) Free energy for H₂ and HCOOH on Sn-MOF. Copied with permission [150]. Copyright 2022, Elsevier. (d) Schematic illustration for synthesizing Sn-N6-MOF. (e) FE of Sn-N6-MOFs. Copied with permission [151]. Copyright 2022, Elsevier.

  DownLoad: Full-Size Img PowerPoint

  In the same year, Li et al. [151] synthesized a series of six N-coordinated Sn-MOFs (Sn-N6-MOFs) through solvent assisted linker exchange (SALE) strategy (Fig. 12d). Firstly ZIF-8 was used as a template to construct Sn-ZIF through metal doping. Subsequently, HTA was introduced to form Sn-N6-MOFs with Sn six-coordinated configuration via the SALE process. In the CO₂RR processes, the synthesized 2% Sn-N6-MOF exhibited high FE_HCOO⁻ with 85% at −1.23 V (Fig. 12e). Moreover, Sn-N6-MOF maintained a FE_HCOO⁻ of over 80% within 6 h, but the increase in current density within the first hour indicated that the Sn-N6-MOF may be restructured during the CO₂RR. The in situ Raman measurement indicated that the catalyst undergoes in situ dynamic recombination during the electro-reduction CO₂RR process, leading to a phase transition from 2% Sn-N6-MOF to Sn nanoclusters. Specifically, due to the destruction of organic ligands in the Sn-N6-MOF framework, the original framework structure of the catalyst was destroyed and reconstructed. The reconstruction of Sn-N6-MOF generated Sn nanoclusters as active sites for CO₂RR during the electro-reduction CO₂RR process.

  Due to the controllable structure of MOF materials, the functionalization of Sn-based MOFs can also effectively improve the activity of CO₂RR. In 2022, Sun et al. [152] synthesized a series of controllable functionalized Sn-CPs. The author achieved the amino functionalization of Sn-CPs by introducing one or two amino groups into the ligand PTA, named Sn-PTA, Sn-aPTA, and Sn-DaPTA, respectively (Fig. 13a). The FE_HCOOH of Sn-DaPTA up to 85% with a j_HCOOH of −11 mA/cm² at −0.8 V (Fig. 13b). Moreover, Sn-DaPTA exhibited high stability during the 18 reuse cycles (Fig. 13c). Compared with Sn-PTA, the introduction of -NH₂ effectively enhanced the CO₂ adsorption capacity of Sn-aPTA and Sn-DaPTA, resulting in a higher concentration of CO₂ around the electrode surface. This can effectively improve the activity of CO₂RR and inhibit the precipitation of hydrogen. Moreover, by exploring the electron transfer process of Sn-CPs in the CO₂RR process, it was found that the -NH₂ on the Sn-CPs can effectively enrich CO₂, promoting the transfer of the electron to form ^*CO₂⁻. In addition, the coordinated environment of Sn was changed by amino groups, leading to more Sn(Ⅱ) active sites on the surface for CO₂RR, facilitating the conversion of CO₂ to formate.

  Figure 13

  

  Figure 13.  (a) Schematic illustration for synthetic Sn-CPs. (b) FE of Sn-CPs. (c) The stability test of Sn-DaPTA. Copied with permission [152]. Copyright 2022, Elsevier. (d) FE of Sn-THO. (e) The free-energy diagrams of CO₂RR pathways for the Sn-THO. (f) Optimized structures of intermediates in the proposed CO₂RR pathways on Sn-THO. Copied with permission [153]. Copyright 2023, Wiley Publishing Group.

  DownLoad: Full-Size Img PowerPoint

  The selectivity of MOF catalyst is not only related to the type of metal element but also to the coordination environment, such as the coordination structure and its microenvironment [149]. Most studies have shown that Sn-based MOFs have excellent selectivity for the electrochemical conversion of CO₂ into formate. However, Chen's group [153] found a Sn-based MOF (Sn-THO) has excellent performance for the conversion of CO₂ into CH₄, which is the first example of a Sn-based MOF with high selectivity for hydrocarbon. It is worth noting that Sn-THO was easily activated in 1 mol/L KOH aqueous solution and remained stable at room temperature during 24 h. The oxidation state, structure, and morphology of Sn-THO were still maintained without generating any Sn or SnO_x clusters after undergoing CO₂RR. The authors believed that Sn-THO maintains high stability due to its interpenetrating structure and rigid ligand. Importantly, compared with other Sn-based catalysts, Sn-THO exhibited special FE_CH4 of 46.5% with a j_CH4 of −34.5 mA/cm² at −1.6 V (Fig. 13d). DFT calculations indicated that Sn^Ⅳ sites of Sn-THO are isolated, resulting in the inability to form V-shaped ^*OCHO intermediates at neighbouring metal sites via bridging modes. The special coordination geometry and environment of Sn^Ⅳ ions in Sn-THO are conducive to the generation of CH₄ by key ^*OCOH species, which can greatly inhibit the generation of HCOOH and CO by ^*OCHO and ^*COOH species, respectively, leading to high FE_CH4 (Figs. 13e and f). This work highlights the coordination environment of the active site in the catalytic selectivity for CO₂RR.

  Enhancing the electrocatalytic performance of MOFs through the synergistic effect of bimetallic materials is also a promising strategy. In 2023, Wu et al. [154] synthesized a series of Sn-In bimetallic MOFs (Sn-MOF/In_x) by PTA. By adjusting the amount of In added, the composition and structure of the MOF could be adjusted to prove the catalytic activity. PXRD patterns confirmed the successful introduction of the In metal and the incorporation of In had no effect on the structure of Sn-MOF. Sn-MOF/In₆ had a rougher surface, evenly dispersed particles, and a loose structure, resulting in less susceptibility to agglomeration. Among all the Sn-MOF/In_x, Sn-MOF/In₆ had the highest selectivity for formate with a selectivity of about 97.5% at −0.96 V, which was higher than that of 85% for Sn-MOF (Fig. 14a). The results displayed that the incorporation of In can improve the specific surface area of Sn-MOF/In₆ to promote gas adsorption, and significantly enhances the contact between the active site and CO₂, thereby improving the selectivity of formate.

  Figure 14

  

  Figure 14.  (a) FE of Sn-MOF/In. Copied with permission [154]. Copyright 2023, Royal Society of Chemistry. (b) Schematic illustration for synthetic CuSn-HAB. (c) FE and current density of CuSn-HAB. (d) Proposed reaction paths for yielding C₂H₄ and EtOH of Cu-Cu sites and Sn-Cu sites. (e) Catalytic mechanism of CuSn-HAB for CO₂RR. Copied with permission [155]. Copyright 2023, American Chemical Society.

  DownLoad: Full-Size Img PowerPoint

  Similarly, Chen and Liao et al. [155] designed a new MOF (CuSn-HAB) based on HAB. Due to the special -NH₂ sites of the HAB, Cu-HAB still has protons that can be removed. Taking advantage of this characteristic, the author designed an unprecedented heterogeneous metal Sn-Cu double sites, i.e., a pair of SnN₂O₂ and CuN₄ sites bridged through μ-N atoms (Fig. 14b). Surprisingly, the CuSn-HAB exhibited a high FE_ethanol of 56% with a j_ethanol of −68 mA/cm² at −0.57 V (Fig. 14c). Compared with Cu-HAB, CuSn-HAB avoids the production of ethylene and has specific selectivity for ethanol. Mechanistic studies have shown that the Sn sites have a stronger affinity for oxygen atoms compared to Cu. This enhanced oxygen atom affinity can effectively promote the formation of the crucial intermediate ^*OCH₂ rather than ^*CO at the Cu sites. ^*OCH₂ provided better protection of the C—O bonds, thus preparing for ethanol production. Specifically, compared with the common Cu-Cu sites, the Cu-Sn sites were more conducive to the asymmetric C—C coupling reaction between ^*CO and ^*OCH₂ to form the ^*CO-^*OCH₂, which is conducive to the generation of ethanol products (Figs. 14d and e).

  3.4 Other metal-based MOFs

  Compared to the MOF materials constructed based on In, Bi, and Sn, relatively few other p-block metal-based MOF materials have been reported. There is currently limited research on other metal-based MOFs in the p-block. This section mainly introduces the application of Al-based and Pb-based MOFs in CO₂RR.

  In 2015, Yang and Yaghi et al. [156] prepared an Al₂(OH)₂TCPP-Co MOFs thin film based on porphyrin ligands with nanoscale by selecting MOFs with catalytic connection units (Fig. 15a). Specifically, 50 times Atomic Layer Deposition (ALD) cycles were performed on the Al film deposited on a conductive carbon electrode and the Al film was transformed into a porphyrin containing [Al₂(OH)₂TCPP-M] (M=Zn, Cu, and Co). Electrochemical testing showed that the selectivity of Al₂(OH)₂TCPP-Co for CO exceeded 76% with a high TON of 1400 in 7 h (Fig. 15b). Importantly, most of the active sites in Al₂(OH)₂TCPP-Co were reduced to Co(Ⅰ) during the catalytic process. This research suggests the potential of ALD technology in the precise synthesis of MOF catalysts.

  Figure 15

  

  Figure 15.  (a) Controllable metal sites, organic linkers, and functional groups at Al₂(OH)₂TCPP-Co. (b) FE of Al₂(OH)₂TCPP-Co. Copied with permission [156]. Copyright 2015, American Chemical Society. (c) FE of HCOOH, CO, and H₂ for MIL-53(Al). Copied with permission [157]. Copyright 2020, American Chemical Society. (d) FE of Al-PMOFs. Copied with permission [160]. Copyright 2022, Elsevier. (e) FE of ER-HC. Copied with permission [161]. Copyright 2021, Elsevier.

  DownLoad: Full-Size Img PowerPoint

  In 2020, F. M. Toma et al. [157] prepared an example of Al-MOF (MIL-53(Al)) for CO₂RR. Compared with Al foil, the total FE of CO and formate was as high as 40% at −1.1 V (Fig. 15c). It is worth noting that Al(Ⅲ) in MIL-53(Al) underwent a reduction in CO₂RR to form Al(0) active sites. However, the spatial confinement originating from MIL-53(Al) can stabilize the catalytic sites. The author suggested that limiting the Al centers within the MIL-53(Al) framework can inhibit HER activity and significantly enhance the electro of CO₂. By changing the microenvironment around the metal active sites and providing a confined space similar to the enzyme chamber, unique catalytic performance can be endowed. Light irradiation may affect the electronic properties of certain electrocatalysts, such as accelerating electron transfer and reducing the binding energy between molecular catalysts and CO₂ [158]. Therefore, photocoupled electrocatalytic CO₂ reduction is an emerging method to improve the EE of electrocatalytic CO₂ reduction [159]. In 2023, Li et al. [160] proposed for the first time a photo-coupled electrocatalyst with Al-O chains as metal nodes and transition metal sites as metal centers. The ability of Al-PMOF(Co) to electro-reduce CO₂ to CO was satisfactory with a FE_CO of ~90% in 35 h (Fig. 15d). The results indicated that incorporating Co into Al-PMOF can activate the CO₂ and subsequent electro-reduction. DFT calculations suggested that the introduction of Co in Al-PMOF regulates the electronic properties of the d state and optimizes the adsorption of CO₂, intermediates ^*COOH, and ^*CO. From the perspective of the charge transfer mechanism, the addition of Co accelerates the charge transfer rate, and visible light accelerates the charge transfer, thereby improving the charge transfer efficiency.

  In 2022, Song et al. [161] used Pb-based MOF as a precursor and synthesized in situ hydrogenerusite [Pb₃(CO₃)₂(OH)₂] (ER-HC) thin films with defects on a Pb substrate via an electro-reduction method. The FE_HCOOH of ER-HC reached a maximum of 96.8% at −0.98 V (Fig. 15e). After five CO₂RR cycles, the catalytic performance of ER-HC remained basically unchanged, as did the catalyst structure and valence state of Pb. Mechanistic studies indicated that the defects of the ER-HC surface facilitate the generation of HCOOH and suppress HER. This work provides a metal Pb oxide electrode with excellent CO₂RR performance and extends the in situ electrochemical derivatization strategy of metal oxides.

  3.5 Summary of p-block metal-based MOFs

  P-block MOF materials exhibit surprising CO₂RR performance and advantages such as controllable structure and clear active sites [162]. However, MOF materials greatly restrict their application due to their poor conductivity and stability [163]. The p-block meatal-based MOF catalysts for CO₂RR have been listed in Table 2.

  Table 2

  

  Table 2.  CO₂RR on p-block metal-based MOFs.

  DownLoad: CSV

  Electrocatalyst	Electrolysis device	Electrolyte	Main product	FEmax (%)	jmain product at FEmax (mA/cm2)	Potential (V vs. RHE)	Ref.
  In-BDC	H-type cell	0.5 mol/L KHCO3	HCOOH	88	6.49	−0.669	[116]
  MFM-300(In)-e	H-type cell	0.5 mol/L EmimBF4/MeCN	HCOOH	99.1	46.1	−2.15 vs. Ag/Ag+	[120]
  MIL-68(In)-NH2	Flow cell	1.0 mol/L KHCO3	HCOOH	94.4	108	−1.1	[121]
  	MEA	1 mol/L KOH		/	800	−3.4
  ((Me2NH2+){InⅢ-[Ni(C2S2-(C6H4COO)2)2]}·3DMF·1.5H2O)	H-type cell	0.5 mol/L KHCO3	HCOOH	89.6	36	−1.3	[125]
  InCo-ABDBDC—HIN	H-type cell	0.5 mol/L EmimBF4/MeCN	C1	81.5	21.2	−2.2 vs. Ag/Ag+	[119]
  CPs@V11	H-type cell	0.5 mol/L KHCO3	HCOOH	90.1	6.87	−0.84	[126]
  In-TCPP	Flow cell	1 mol/L KOH	HCOOH	90	30	−1.0	[82]
  aNH2−MIL-68	H-type cell	0.5 mol/L EmimBF4/MeCN	HCOOH	93.3	34.2	−2.05 vs. Ag/Ag+	[162]
  SU-101	H-type cell	0.5 mol /L KHCO3	HCOOH	93.66	14.57	−1.1	[128]
  Bi-MOF	H-type cell	0.1 mol/L KHCO3	HCOOH	92.2	/	−0.9	[132]
  PZH-1	H-type cell	0.5 mol/L KOH	HCOOH	91	/	−1.1	[133]
  Bi—HHTP	Flow cell	1 mol/L KOH	HCOOH	95	/	−0.7	[134]
  V12e	H-type cell	0.5 mol/L KHCO3	HCOOH	93.2	11.78	−0.9	[135]
  Bi-FDCA	H-type cell	0.1 mol/L KHCO3	HCOOH	95.1	19.6	−1.2	[136]
  Bi-btb	H-type cell	0.5 mol/L KHCO3	HCOOH	95	5.4	−0.97	[139]
  Bi-BTB	H-type cell	0.5 mol/L KHCO3	HCOOH	96.1	12.7	−0.669	[140]
  CAU-17	H-type cell	0.1 mol/L KHCO3	HCOOH	92	/	−1.1	[138]
  Bi-enes	H-type cell	0.5 mol/L KHCO3	HCOOH	≈100	/	−0.978	[141]
  MFM-220-p	H-type cell	0.1 mol/L KHCO3	HCOOH	90.4	20.8	−1.1	[143]
  Bi-BTC	H-type cell	0.5 mol/L KOH	HCOOH	95	25	−0.9	[163]
  Sn-MOF	H-type cell	0.5 mol/L KHCO3	HCOOH	92	23.2	−1.2	[150]
  Sn—N6-MOF	H-type cell	0.5 mol/L KHCO3	HCOOH	85	23	−1.23	[151]
  Sn-DaPTA	H-type cell	0.5 mol/L KHCO3	HCOOH	85	11	−0.8	[152]
  Sn-THO	Flow cell	0.1 mol/L KHCO3	CH4	46.5	34.5	−1.6	[153]
  Sn-MOF/In6	H-type cell	0.5 mol/L KHCO3	HCOOH	97.5	16	−0.96	[154]
  CuSn—HAB	Flow cell	1 mol/L KOH	C2H5OH	56	68	−0.57	[155]
  Al2(OH)2TCPP-Co	H-type cell	0.5 mol/L K2CO3	CO	76	/	−0.7	[156]
  MIL-53(Al)	Flow cell	0.05 mol/L K2CO3	CO	21	/	−1.1	[157]
  			HCOOH	19
  Al-PMOF(Co)	H-type cell	0.1 mol/L KHCO3	CO	90	/	−0.8	[160]
  ER—HC	H-type cell	0.1 mol/L KHCO3	HCOOH	96.8	1.9	−0.88	[161]

  4. MOF-derived catalysts

  Crystalline p-block MOF materials exhibit great potential in the field of CO₂RR, in especially their well-defined crystal structures are advantageous in mechanism investigation [164]. However, the lower electrical conductivity and insufficient structure stability of most MOF materials limit their catalytic activity and stability. Many catalysts inevitably result in the aggregation of electrons due to their poor conductivity, leading to a decrease in the number of oxidized metal sites [165]. This will cause the structure of the catalysts to be restructured and reduce catalytic performance. As a result, MOF-derived materials have gradually attracted the attention of researchers. MOF materials are desirable precursors due to their diverse elemental compositions, designable structures, and controllable nanomorphology. Methods including pyrolysis [166,167], acid/base etching [168], laser metallurgy [169], sulfidation, and phosphitylation [170] have been developed for the synthesis of diverse MOF-derived materials in the form of single-atom materials, metal oxides, metal sulfides, metal hydroxides, etc. More importantly, MOF-derived catalysts typically have a high specific surface area, porous structure, and abundant unsaturated metal sites, which are advantages inherited from the original MOFs [148].

  4.1 Metals and metal/metal oxides

  In CO₂RR, the influence of the affinity of the catalyst to the reaction intermediates on the catalytic performance should not be neglected. Recent research has shown that combining multiple elements or multi-component catalysts is an effective way to improve the affinity between the metal sites and oxygenated intermediates [129]. In particular, bimetallic catalysts can adjust the binding energy between active sites and intermediates by adjusting their electronic structure and atomic arrangement, and enhance the performance of CO₂RR by stabilizing intermediates and inhibiting HER through synergistic effects [171,172].

  In 2021, Fan's group [173] reported a new method for preparing Cu-In bimetallic electrocatalysts through in situ growth of In-ZMOF by using Cu oxide foil as a precursor for the first time (Fig. 16a). Importantly, compared with oxide derived Cu (OD Cu) and Cu-based carbon material derivatives (Cu-CMD) grown in situ on Cu oxide foil, the periodic arrangement of metal sites and ligands in In-ZMOF resulting in a uniform distribution of In on the Cu foil surface. Moreover, the CO₂RR activity of the catalyst was efficiently boosted due to the synergistic effect between Cu and In. The Cu/In catalyst exhibited a higher FE_CO of 95% at −0.6 V with better stability than OD Cu and Cu-CMD (Fig. 16b). The excellent CO₂RR performance of Cu/In catalysts is attributed to their abundant lattice defects and high roughness factors. The DFT calculations indicated that the enhanced CO selectivity of the Cu/In catalyst is mainly due to the significant decrease in energy required for the generation of ^*COOH and the desorption of ^*CO at the In/Cu interface. In addition, In atoms stabilized by the vacancy defects in the surface Cu inhibited the HER and promoted the formation of ^*COOH. (Fig. 16c). In 2022, Liang et al. [174] reported a BiIn alloy NPs derived from bimetallic MOFs (Fig. 16d). The BiIn alloy NPs exhibited a surprising CO₂RR performance with a maximum FE_HCOOH of 97.8% at −0.92 V, superior to that with Bi NPs and In NPs (Fig. 16e). At the same time, the BiIn alloy NPs exhibited a FE_HCOOH exceeding 90% after the stability test for 20 h without a significant decrease in current density, indicating the long-term stability of BiIn alloy NPs. In addition, the charge transfer resistance of BiIn alloy NPs was lower and there were more abundant active sites. DFT calculations revealed that BiIn alloy NPs can efficiently promote CO₂ adsorption and lower the energy barrier for the conversion of ^*OCHO to ^*HCOOH. Therefore, the synergistic effect of Bi-In bimetallic sites can significantly promote the generation of HCOOH (Fig. 16f).

  Figure 16

  

  Figure 16.  (a) Schematic illustration for synthetic of In/Cu. (b) FE of In/Cu. (c) The free-energy diagrams of CO₂RR pathways for the In/Cu. Copied with permission [173]. Copyright 2021, Elsevier. (d) Schematic illustration for synthetic of Bi-In alloy NPs. (e) FE of Bi-In alloy NPs. (f) The free-energy diagrams of CO₂RR pathways for the Bi-In alloy NPs. Copied with permission [174]. Copyright 2022, Elsevier. (g) FE of Bi-In/C. (h) The free-energy diagrams of CO₂ to HCOOH for the Bi-In/C. (i). Schematic illustration of the CO₂RR device driven by a solar cell. Copied with permission [175]. Copyright 2023, Elsevier.

  DownLoad: Full-Size Img PowerPoint

  Similarly, Zhang et al. [175] designed an In nanocube Bi-In/C anchored with atomic Bi. HAADF-STEM demonstrated that Bi atoms are uniformly dispersed on the In surface through lattice gap anchoring. Compared with In/C and MIL-68, the maximum FE of Bi-In/C reached 94.2% at −1.0 V with the j_HCOOH of −33.6 mA/cm², and it remained stable during continuous electrolysis for 9 days, far higher than In/C and MIL-68 (Fig. 16g). DFT calculations confirmed that the construction of Bi-In/C materials would adjust the electron distribution on the catalyst surface to reduce the free energy of the reaction intermediates, ultimately facilitating the conversion of ^*OCHO intermediates to formate (Fig. 16h). In addition, the author utilized solar cells to provide power for the oxidation reactions of CO₂RR and 5-hydroxymethylfurfural, achieving the spontaneous generation of formate and FDCA (Fig. 16i). The selectivity of 88.2% for FDCA and the conversion rate of 99.9% for HMF were achieved. Importantly, the FE of HCOOH remained as high as 85.1% after approximately 4 h of electrolysis, demonstrating a highly promising solar fuel conversion.

  Heterogeneous structures integrating different functional components can produce synergistic effects to optimize electrocatalytic activity and selectivity [176,177]. In 2020, Zhao et al. [178] obtained In₂O₃ through pyrolysis of In-MOF, and then partially reduced the original In₂O₃ electrode to metal In through electro-reduction, forming a nanostructured In/In(Ⅲ) heterostructure with defects (Fig. 17a). Within the entire potential range, the FE value of C1 products, including CO and formate, was close to 100%. This indicated that the In/In(Ⅲ) electrode has excellent selectivity for CO₂RR and could significantly inhibit HER under applied potential. FE_HCOOH could reach a high value of over 80% at the wide potential range of −0.7 V to −1.2 V, and achieved the maximum FE_HCOOH of 93% at −0.8 V (Fig. 17b). The current density remained stable around −15 mA/cm² at −0.9 V for 25 h. Moreover, the structural analysis indicated that the heterogeneous structure composed of In and In₂O₃ was well preserved. The author suggested that the synergistic effect between In(0) and In(Ⅲ) is the reason for the excellent electrocatalytic performance (Fig. 17c). Metal In mainly catalyzed the electro-reduction of CO₂, while In oxide components further inhibited competition HER, thereby improving CO₂RR. Although the construction of In(Ⅲ)/In(0) heterostructures is promising to improve the intrinsic activity of In-based catalysts, the regulation mechanism still needs further clarification.

  Figure 17

  

  Figure 17.  (a) Scheme for synthetic In/In oxide. (b) FE of In/In oxide. (c) Schematic for the CO₂RR of In/In oxide. Copied with permission [178]. Copyright 2020, American Chemical Society. (d) Schematic illustration for synthetic In/In₂O₃ Ho-nt. (e) FE of In/In₂O₃ Ho-nt. (f) The free-energy diagrams of CO₂RR pathways for the In/In₂O₃ Ho-nt. Copied with permission [179]. Copyright 2023, Elsevier. (g) Schematic illustration for synthetic Sn(101)/SnO₂/C-500. (h) FE of Sn(101)/SnO₂/C-500. (i) The free-energy diagrams of CO₂RR pathways for the Sn(101)/SnO₂/C-500. Copied with permission [181]. Copyright 2021, American Chemical Society.

  DownLoad: Full-Size Img PowerPoint

  In 2023, He et al. [179] prepared In₂O₃ hollow nanotubes (In₂O₃ Ho-nt) by pyrolysis MIL-68(In)-NH₂, and then reduced them to In/In₂O₃ Ho-nt at constant potential (Fig. 17d). The synergistic effect between In(Ⅲ) and In(0) sites was researched. This catalyst can maintain a stable In(0)/In(Ⅲ) heterostructure over a wide potential range during CO₂RR. Compared with In/Ho-nt and In₂O₃ Ho-nt, In/In₂O₃ Ho-nt exhibited the highest catalytic activity. The maximum FE_HCOOH of In/In₂O₃ Ho-nt was 93% at −0.9 V with the current density of −650 mA/cm² at −1.2 V (Fig. 17e). It is worth noting that improving the hydrophobicity of GDE by adding PTFE, the MEA device could stably electrolyze for more than 70 h with the current density of −200 mA/cm² and FE_HCOOH over 80%. The author believed that the charge interaction between the In(Ⅲ) and In(0) sites resulted in the concentration of charge density at the In(0) sites and enhanced the intrinsic activity. Results indicated that the electron-deficient environment at the In(0) sites originates from charge redistribution between the In(Ⅲ) and In(0) sites, which promotes the adsorption of ^*CO₂⁻ intermediates and electron transfer kinetics (Fig. 17f). The electronic effect of adjacent two metal atoms provide additional accommodation sites, accelerating the PCET and the desorption of ^*CO, efficiently improving the performance of CO₂RR [180].

  In 2021, Gu et al. [181] first conducted DFT calculations to prove that the (101) crystal plane of Sn is more energetically favourable for CO₂RR. Subsequently, a variety of Sn/SnO₂/C composite with exposed (101) planes was successfully prepared by carbonization and etching of the Sn-MOF precursor at different temperatures (Fig. 17g). The electrochemical results indicated that the Sn(101) crystal surface can promote the catalytic activity. Sn(101)/SnO₂/C-500 exhibited a high FE_HCOOH of 93.3% at −0.8 V (Fig. 17h), which maintained stability for 20 h. In addition, the author confirmed that the etching conditions can significantly regulate the exposure of Sn(101) crystal planes, thereby affecting the catalytic activity of the material (Fig. 17i).

  4.2 Metal oxides and sulfides

  Xia et al. [182] reported a carbon-confined In₂O₃@C catalyst derived from MIL-68, which can efficiently produce formate in a solid-state electrolyte (SSE) mediated flow cell directly (Fig. 18a). Pyrolysis of MIL-68(In) was carried out in an Ar environment, and the organic ligand was destroyed and carbonized. On the contrary, ligands will be completely decomposed when heated in air, resulting in the formation of In₂O₃. Compared to In₂O₃ derived from pyrolysis of MIL-68 in air, In₂O₃@C had a higher specific surface area and stronger CO₂ adsorption capacity. In₂O₃@C exhibited the best CO₂RR performance with the FE_HCOOH over 90% at the wide potential range of −0.8~1.3 V and reached a maximum of 94% at −1.1 V (Fig. 18b). It is worth noting that In₂O₃@C possessed a higher ECSA, mainly due to the porous structure of carbon coated In oxide inhibiting particle aggregation and enhancing the exposure of active sites. Moreover, the carbon encapsulation and oxygen vacancies alter the d-band center and electronic properties of In₂O₃, enhancing its affinity for ^*CO₂⁻ intermediates. The author suggested that the carbon layer can protect the In oxide while improving its electrical conductivity, ensuring the timely transfer of electrons to avoid structural changes caused by excessive accumulation of electrons. Afterward, the author utilized porous cation exchange resins as SSE to form the MEA-SSE device for direct production of liquid pure formate solution. A liquid formate solution of approximately 0.12 mol/L could be directly and continuously generated in the MEA-SSE device with a current density of −30 mA/cm².

  Figure 18

  

  Figure 18.  (a) Schematic illustration for CO₂RR of In₂O₃@C in SEE. (b) FE of In₂O₃@C. Copied with permission [182]. Copyright 2022, Wiley Publishing Group. (c) FE of In₂O_3-C. (d) The free-energy diagrams of CO₂RR pathways for the In₂O_3-C. Copied with permission [185]. Copyright 2022, American Chemical Society. (e) Schematic illustration for in situ generation In₂O₃@In-Co PBA. (f) FE of In₂O₃@In-Co PBA. Copied with permission [186]. Copyright 2021, Elsevier.

  DownLoad: Full-Size Img PowerPoint

  Compared with a carbon coating, direct doping of carbon atoms into the In₂O₃ lattice is also effective in improving the catalyst performance [183,184]. Wu et al. [185] also synthesized In₂O₃—C nanorods by pyrolysis of MOF precursor MIL-68(In), exhibiting very high current density and FE. The FE of HCOOH reached 97.2% at −1.0 V, and maintained above 90% within a wide potential range of 500 mV (Fig. 18c). Importantly, the FE_HCOOH was maintained at 80.5% with the current density of −1 A/cm², which corresponds to a j_HCOOH of −805 mA/cm². At the industrial-related current density of −200 mA/cm², In₂O₃—C maintained a high FE_HCOOH of over 85% for more than 15 h. The author believed that the In₂O_3-C exhibits such excellent performance because the addition of carbon atoms increased the electronic density of In sites, rebalancing the conductivity and activity of In₂O₃ for CO₂RR. Moreover, the insertion of C atoms into the In₂O₃ lattice rather than encapsulating the outside with carbon can more effectively regulate the electron density of In atoms, thereby achieving simultaneous regulation of electronic structure and active sites, thus enabling In₂O_3-C catalysts to have high selectivity and excellent activity (Fig. 18d).

  Gao et al. [186] reported a new type of MOF In[Co(CN)₆] (In-Co PBA) nanocube, which was transformed through a controlled low-temperature conversion process. The nanocube retained the three-dimensional porous structure of PBA, and contained in situ generated In₂O₃ nanoparticles in the MOF channel (Fig. 18e). This new structure not only retained the appearance and structure of the original MOF but also had a higher specific surface area and porosity, which is conducive to CO₂RR. In₂O₃@In-Co PBA exhibited better CO₂RR performance than In-Co PBA, reaching a FE_HCOOH of 85% at −1.9 V (Fig. 18f). The current density of In₂O₃@In-Co PBA remained stable in 5 h of CO₂RR without significant attenuation. No significant reduction of In₂O₃ was observed, indicating that the In₂O₃@In-Co PBA quasi-MOF catalyst has good stability. The author suggested that the improved activity of quasi-MOF is mainly attributed to the retained original porous structure, which increases the specific surface area and promotes the dispersion of the In active sites in the pore structure. Atomically dispersed catalytic sites are conducive to the transfer of electrons at the gas-liquid-solid three-phase boundary [131]. In addition, the interaction between the cyanide groups in PBA and In₂O₃ nanoparticles in the pores facilitates the regulation of the electronic environment of surrounding nanoparticles, thereby stabilizing the HCOO^* intermediate obtained through proton-coupled electron transfer and ultimately improving catalytic performance. Generally speaking, the excellent CO₂RR performance of In-based catalyst is due to the oxidation state of metal active sites, which can effectively inhibit HER and promote the activation of CO₂ [187].

  Han et al. [188] synthesized a series of porous In-Cu bimetallic oxide catalysts with different Cu/In ratios (Fig. 19a). By adjusting the ratio of In/Cu in the MOF precursor, selective conversion of CO/H₂ could be easily achieved. When the Cu content increased to a Cu/In ratio of 0.92, the maximum FE_CO of InCuO-0.92 at −0.8 V potential was 92.1% (Figs. 19b and c). The CO₂ reduction activity was significantly enhanced, indicating a synergistic effect between In oxide and Cu oxide in the CO generation process. The author proposed that the surprising CO₂RR activity of porous In-Cu bimetallic oxides is due to their efficient adsorption of CO₂ and faster mass diffusion. In addition, Cu doped into In₂O₃ creates heterojunction interfaces, enhances CO₂ adsorption capacity, and reduces charge transfer resistance.

  Figure 19

  

  Figure 19.  (a) Schematic illustration for synthetic InCuO. (b) FE of InCuO. (c) Current density of InCuO. Copied with permission [188]. Copyright 2019, Royal Society of Chemistry. (d) Schematic illustration for synthetic Cu_x-Bi/Bi₂O₃@C. (e) FE of Cu_x-Bi/Bi₂O₃@C. Copied with permission [189]. Copyright 2022, Wiley Publishing Group. (f) FE of Ce-Bi@CeBiO_x/C. Copied with permission [190]. Copyright 2021, Royal Society of Chemistry.

  DownLoad: Full-Size Img PowerPoint

  Similarly, Chen's group [189] reported a series of Cu/Bi bimetallic catalysts Cu_x-Bi/Bi₂O₃ derived from MOF (Fig. 19d). Cu₁-Bi/Bi₂O₃@C displayed an excellent CO₂RR performance after optimized Cu content compared with Bi/Bi₂O₃@C. Under the condition of external potential −0.94 V, the FE of HCOOH was as high as 93% with a current density of −10.1 mA/cm² (Fig. 19e). As a result, Cu₁-Bi/Bi₂O₃@C has more active sites and the synergistic effect of Bi/Cu bimetallic can reduce the activation energy barrier of CO₂. Meanwhile, the electron transfer between Cu and Bi also regulates the binding strength of the catalyst surface intermediate ^*CO₂⁻.

  Interestingly, in addition to introducing transition metals, doping with rare earth metals may alter the electronic structure of the catalyst, thereby improving its electrocatalytic performance. In 2021, Guo et al. [190] synthesized Ce-doped Bi-MOFs using a modified method, resulting in a carbon-supported bimetallic nanocomposite material with a core-shell structure (Ce-Bi@CeBiO_x/C). XPS spectra showed that some electrons in Bi(Ⅲ) transfer from Bi to Ce, indicating that the electronic structure of Bi is adjusted by the strong interaction of Ce, leading to more O vacancies in the material after Ce doping. The FE_HCOOH of Ce-Bi@CeBiO_x/C was maintained above 80% within the wide potential range of −1.4 V to −1.9 V, with a maximum FE_HCOOH of 96% (Fig. 19f). During the 10 h electrolysis process, the total current density and the FE_HCOOH did not significantly decrease. The author believed that the surprising activity of Ce-Bi@CeBiO_x/C contributed to Ce doped core-shell structure. On the one hand, surface defects of O vacancies can create an electron rich environment, promoting the adsorption of CO₂ by O vacancies. On the other hand, the changes in electronic structure may benefit the electron transfer from the more electronegative O atom to the Bi atom, enhancing the adsorption of HCOO^* intermediates, thereby improving the activity of CO₂RR to generate formate.

  In 2020, Xia et al. [191] prepared a carbon nanotube encapsulated Bi oxide (Bi₂O₃@C) derived from a Bi-MOF (Fig. 20a). A series of derivatives were obtained by controlling the carbonization conditions, of which Bi₂O₃@C-800 exhibited the best CO₂RR performance with FE_HCOOH of 93% at −0.28 V (Fig. 20b). Bi₂O₃@C-800 had higher formate selectivity, lower resistance, and higher current density compared with Bi₂O₃@C-600, Bi@C-600, and Bi@C-800. The author believed that the excellent performance contributed to the synergistic effect originating from the special structure of Bi₂O₃ encapsulated in a carbon matrix, Bi₂O₃ contributes to the improvement of selectivity and reaction kinetics while the carbon substrate facilitates the increase of current density.

  Figure 20

  

  Figure 20.  (a) Schematic illustration for synthetic Bi₂O₃@C. (b) FE and current density of formate for Bi₂O₃@C. Copied with permission [191]. Copyright 2020, Wiley Publishing Group. (c) FE of SOR Bi@C NPs. (d) The free-energy diagrams of the CO₂RR process for the Bi (110) plane and Bi-O/Bi (110) plane. Copied with permission [194]. Copyright 2022, American Chemical Society. (e) Schematic illustration for synthetic BiS@Cx. (f) FE of BiS@Cx. Copied with permission [195]. Copyright 2022, Elsevier.

  DownLoad: Full-Size Img PowerPoint

  In addition, the oxygen-rich Bi surface can also significantly promote reaction kinetics and increase the activity of CO₂RR. Because Bi-O species promote the adsorption of CO₂ and the formation of ^*OCHO intermediates [192,193]. In 2022, Chen's group [194] prepared an oxygen-rich Bi@C nanoparticles (SOR Bi@C NPs) derived from SU-101 MOF. SOR Bi@C NPs achieved a high FE_HCOOH of over 91% within the potential range of 440 mV, achieving a high j_HCOOH of −140.5 mA/cm² (Fig. 20c). The average FE of SOR Bi@C NPs during continuous electrolysis for 18 h exceeded 92%. After CO₂RR, Bi-O species were partially reduced to form coexisting substances consisting of Bi and Bi-O in SOR Bi@CNPs. However, the Bi-O species still remained dominant and persistent, indicating the stability of the catalysts. DFT calculations suggested that the Bi-O/Bi(110) structure is beneficial for adsorbing CO₂ and generating ^*OCHO intermediates, which is the origin of promising CO₂RR activity of SOR Bi@CNPs (Fig. 20d).

  Except for improving the catalytic performance of CO₂RR with bimetallic catalysts, doping non-metallic elements into metal catalysts also has an encouraging effect. In 2022, Gao et al. [195] prepared a catalyst BS@Cx (x represents temperature) with uniformly dispersed stable active sites by sulfurizing Bi-BTC with thioacetamide (Fig. 20e). The Bi-S motif unit underwent modification with the increase of calcination temperature and gradually stabilized at high temperature. It is worth noting that unlike other Bi-based catalysts, BS@Cx exhibited excellent selectivity of methanol CO₂RR. Under the condition of −0.9 V, the maximum FE of BS@C800 for methanol and the selectivity of methanol reached 78.6% and 78.8%, respectively (Fig. 20f). After 12 h of continuous electrolysis, the FE and current density had not significantly decreased, proving the good stability of BS@Cx. The author proposed that the main product of CO₂RR changes from HCOOH to methanol is due to the special Bi-S motif. Doping S atoms to create the Bi-S motif changes the adsorption capacity of the original intermediate, resulting in the easier dehydroxylation of the formate intermediate (COOH^*) and stronger stability of CO on the surface of the Bi-S motif. As a result, the key intermediate CH₂O^* was generated and further reduced to methanol.

  4.3 Single-atom catalysts

  Single-atom catalysts have been proven to be potential catalysts for CO₂RR [196-199]. When the catalyst is dispersed into a single atom form, the electron distribution and atomic structures of the active components will undergo significant changes, which may lead to some performance advantages for catalytic applications [109]. In addition, studies have shown that single-atom catalysts with metal nitrogen (M-N_x) modified carbon-based structures can serve as ideal CO₂RR electrocatalysts [200,201]. Especially, the four coordinated structures (M-N₄) may be a favorable catalytic site for M-N_x catalysts [202,203].

  In 2020, Li et al. [109] designed a new In-MOF derivative for CO₂RR, there were exclusive In^δ+-N₄ interface groups on the N-doped carbon matrix (In-SAs/NC) derived from MOFs (Fig. 21a). The FE_HCOO⁻ of In-SAs/NC over than 85% in the wide potential range (−0.65~0.95 V) with the maximum value of 96% at −0.65 V (Fig. 21b). DFT results suggested that In has the lowest free energy for generating HCOO^* due to the presence of the In^δ+-N₄ interface compared to In-NPs/NC and NC. In addition, other M-N_x structures also exhibit unique catalytic activity (Fig. 21c). In 2021, Yin et al. [204] reported a catalyst with atomically dispersed In sites using an In/Zn zeolite imidazole framework as a template, which exhibited surprising catalytic performance in the conversion of CO₂ to HCOOH (Fig. 21d). The In-N-C prepared at high temperatures retained the porous structure of the original ZIF-8. During the CO₂RR process, the oxidation state of In in In-N-C can remain unchanged instead of being electrochemically reduced to metal In as in In₂O₃ as evidenced by XPS. This confirmed that the coordination of In to N shows better stability compared to the coordination to O. In-N-C achieved a maximum FE_HCOOH of 80% at −0.79 V (Fig. 21e). DFT calculations suggested that dispersed In atoms have strong electronic interactions with adjacent N atoms, which could effectively convert CO₂ to formate. The low energy barrier of the formation of ^*OCHO intermediates promotes the reduction of CO₂ to formate (Fig. 21f).

  Figure 21

  

  Figure 21.  (a) Schematic illustration for synthetic In SAs/NC. (b) FE of In SAs/NC. (c) The difference in limiting potentials for CO₂ reduction and H₂ evolution on In-SAs/NC. Copied with permission [109]. Copyright 2020, Wiley Publishing Group. (d) Schematic illustration for synthetic In-N-C. (e) FE of In-N-C. (f) The free-energy diagrams of CO₂RR pathways for the In-N-C. Copied with permission [204]. Copyright 2021, American Chemical Society. (g) Schematic illustration for synthetic In SACs. (h) FE of In SACs. (i) The free-energy diagrams of CO₂RR pathways for the In SACs. Copied with permission [205]. Copyright 2022, American Chemical Society.

  DownLoad: Full-Size Img PowerPoint

  In 2022, K. Daasbjerg and Liu et al. [205] reported two In-MOF derivatives, In@NC-900 and In@NC-1000, with a typical In-N₄ coordination structure and a low coordination In-N₃-V structure containing vacancies, respectively (Fig. 21g). Compared to In@NC-900, the In@NC-1000 generated more CO at −0.57 V with a maximum FE_CO of 95% (Fig. 21h). And during the 14 h CO₂RR process, the In-N₃-V coordination environment and active site distribution in In@NC-1000 were not changed, resulting in stable FE and current density. DFT calculations found that the orbitals energy of In atoms in In-N₃-V is higher than that of In-N₄, therefore closer to Fermi energy. This phenomenon is more pronounced in the hybrid s orbitals and p_z orbitals of In atoms, which is the main reason for the improvement of CO₂RR performance by catalysts of In@NC-1000. At the same time, In-N₃-V can reduce the energy barrier of COOH^* adsorbed on In sites, resulting in excellent selectivity for CO (Fig. 21i).

  Huang et al. [206] prepared a series of In SACs with MIL-68 as a precursor assisted by dicyandiamide, and customized the coordination environment of In centers by changing the annealing temperature (Fig. 22a). Specifically, In SACs with In-N_xC_4-x local coordination structures were successfully synthesized. Importantly, the selectivity of formate and CO can be adjusted by changing the proportion of C and N. CO is the only product for In SACs-1000 with FE_CO up to 97% at −0.6 V. For the In SACs-800, both HCOOH (38% at −0.9 V) and CO (52% at −0.5 V) were detected simultaneously (Fig. 22b). And the main product of In₂O₃ NPs was HCOOH with the FE_HCOOH of 67.8% at −0.8 V. These experimental data suggested that In SACs have significant product selectivity and the coordination structure has an important impact on the CO₂RR reaction pathway. And under a current of −0.4 A in MEA, it worked continuously for 60 h with a FE_CO over 90%, indicating excellent stability. DFT calculations suggested that the In sites in In SACs are active for the electro-reduction of CO₂ into formate, while the carbon atoms adjacent to In tend to follow the conversion pathway from CO₂ to CO (Fig. 22c). Due to the increase in annealing temperature, the proportion of carbon atoms increased. Therefore, the satisfactory CO₂RR performance of In SACs-1000 is achieved by switching the active site from the In site to the neighboring C atom. This work provides new insights into the practical catalytic active sites in SAC materials.

  Figure 22

  

  Figure 22.  (a) Schematic illustration for synthetic In SACs. (b) FE of In SACs. (c) The CO₂RR reaction pathway for pr-In-N₄-(In) and pr-In-N₃-(C2). Copied with permission [206]. Copyright 2022, Tsinghua University Press. (d) Schematic illustration for synthetic InNi DS/NC. (e) FE of InNi DS/NC. (f) The free-energy diagrams of CO₂RR pathways for the InNi DS/NC. Copied with permission [207]. Copyright 2022, Wiley Publishing Group. (g) FE of Bi SAs/NC. (h) The free-energy diagrams of CO₂RR pathways for the BiN₄/C surface. Copied with permission [48]. Copyright 2019, American Chemical Society.

  DownLoad: Full-Size Img PowerPoint

  In addition to single-atom catalysts, constructing heteronuclear double single-atom catalysts is also a promising CO₂RR strategy. In 2023, Hou et al. [207] designed an atomically dispersed InNi dual-site catalyst (InNi DS/NC) anchored on nitrogen carbon derived from zeolite imidazole frameworks. Bridged by an axial oxygen atom, In and Ni atoms build a unique O-In-N₆Ni unit (Fig. 22d). InNi DS/NC exhibited the best catalytic performance with the highest FE_CO of 96.7% at −0.7 V which was significantly better than In DS/NC and Ni DS/NC (Fig. 22e). The catalytic performance of InNi DS/NC could be maintained over 9 h at a high current density of −317.2 mA/cm² in 1 mol/L KOH. DFT calculations suggested that the CO selectivity of In active sites was improved by the incorporation of adjacent Ni atoms. Moreover, Ni and In can synergistically contribute to CO production via bridging O atoms (Fig. 22f).

  In 2019, Li et al. [48] designed an N- doped carbon network catalyst (Bi SAs/NC) composed of single Bi atoms, with a Bi-N₄ structure as the active sites to promote the CO₂RR. The author obtained the Bi-N₄ sites on porous carbon networks through the pyrolysis of Bi-MOF with DCD. DCD played a crucial role in redispersing Bi atoms and immobilizing Bi atoms in defects. Interestingly, unlike most Bi-based catalysts, Bi SAs/NC exhibited excellent selectivity for CO with FE_CO up to 97% at −0.5 V (Fig. 22g). Bi SAs/NC remained stable after a long-term electrolysis process of 4 h, further confirming its good stability. DFT calculations suggested that Bi-N₄/C active sites have a lower energy barrier for the generation of ^*COOH intermediate, resulting in unique selectivity and better CO₂RR performance (Fig. 22h).

  4.4 Summary of p-block metal-based MOF-derived catalysts

  MOF derivative catalysts can improve the stability and conductivity of the catalysts while retaining the structure of the original MOF precursor, thereby significantly enhancing the CO₂RR performance. However, how to obtain MOF derivatives with expected structures through design and synthesis methods is still the focus of current research. The p-block meatal-based MOF-derived catalysts for CO₂RR have been listed in Table 3.

  Table 3

  

  Table 3.  CO₂RR on p-block metal-based MOF-derived catalysts.

  DownLoad: CSV

  Electrocatalyst	Electrolysis device	Electrolyte	Main product	FEmax (%)	jmain product at FEmax (mA/cm2)	Potential (V vs. RHE)	Ref.
  In/In oxide	H-type cell	0.5 mol/L KHCO3	HCOOH	93	/	−1.1	[178]
  In/In2O3 Ho-nt	Flow cell	1 mol/L KOH	HCOOH	93	/	−0.9	[179]
  	MEA	0.1 mol/L KOH (MEA)	HCOOH	90.6	150	/
  Sn(101)/SnO2/C-500	H-type cell	0.5 mol/L KHCO3	HCOOH	93.3	8.2	−0.8	[181]
  InCuO-0.92	H-type cell	0.5 mol/L KHCO3	CO	92.1	/	−0.8	[188]
  In-Bi alloy NPs	Flow cell	1 mol/L KOH	HCOOH	97.8	250	/	[174]
  Cu1-Bi/Bi2O3@C	H-type cell	0.5 mol/L KHCO3	HCOOH	93	10.1	−0.94	[189]
  Ce-Bi@CeBiOx/C	H-type cell	0.5 mol/L KHCO3	HCOOH	96	/	−1.7	[190]
  In2O3@C	Flow cell	1 mol/L KOH	HCOOH	94	/	−1.1	[182]
  In2O3—C	Flow cell	1 mol/L KOH	HCOOH	80.5	1000	/	[185]
  In-Co PBA	H-type cell	0.1 mol/L KHCO3	HCOOH	85	/	−0.96	[186]
  Bi2O3@C-800	Flow cell	1 mol/L KOH	HCOOH	93	/	−0.28	[191]
  SOR Bi@CNPs	Flow cell	1 mol/L KOH	HCOOH	90	100	−1.12	[194]
  BiS@C800	H-type cell	0.1 mol/L KHCO3	CH3OH	78.6	/	−0.9	[195]
  In-SAs/NC	H-type cell	0.5 mol/L KHCO3	HCOOH	96	8.87	−0.65	[109]
  In—N—C	H-type cell	0.5 mol/L KHCO3	HCOOH	80	6.8	−0.79	[204]
  In@NC-1000	H-type cell	0.5 mol/L KHCO3	CO	95	/	−0.57	[205]
  In SACs-1000	H-type cell	0.5 mol/L KHCO3	CO	97	/	−0.6	[206]
  InNi DS/NC	H-type cell	0.5 mol/L KHCO3	CO	96.7	/	−0.7	[207]
  Bi SAs/NC	H-type cell	0.1 mol/L NaHCO3	CO	97	5.1	−0.5	[48]
  Cu/In	H-type cell	0.1 mol/L KHCO3	CO	95	/	−0.6	[173]
  Bi-In/C	H-type cell	0.5 mol/L KHCO3	HCOOH	94.2	33.6	−1.0	[175]

  5. Conclusion and outlook

  Electro-reduction of carbon dioxide into valuable chemicals has become a prospective strategy to meet environmental and energy challenges. P-block metals have been proven to have a high affinity for ^*OCHO due to their unique electronic orbitals and oxygen affinity, making them an environmentally friendly and economically feasible efficient CO₂RR electrocatalyst. Therefore, MOF materials constructed based on p-block metals have been emphasized in the field of electrocatalytic CO₂ reduction to formic acid. In this review, we summarized the latest progress in the electrocatalytic CO₂ field of p-block metal-based MOFs (In, Bi, Sn, Al, Pb, Ga) and MOF-derived catalysts. The catalyst structures, modification strategies, catalytic mechanisms, and structure-activity relationships were discussed. However, although p-block metal-based MOFs and MOF-derived catalysts have exhibited good potential in the CO₂RR field, most of them are still difficult to meet the demands of practical applications. Thus, further development of high-performance p-block metal-based MOFs and MOF-derived catalysts remains crucial, challenges and promising research directions can be considered in future research:

  (1) At present, lower conductivity and stability are still the main problems that limit the catalytic performance of most p-block metal-based MOFs. The low conductivity restricts the charge transfer of the reaction process while increasing the energy consumption of the reaction. Although the introduction of conductive species and the use of 2D-conducting MOFs have been reported to improve electrical conductivity, the related issues still need further investigation. The construction of complex catalysts is a convenient route. By introducing conducting supports such as graphene, MXene, MBene, the charge transfer during the reaction can be promoted on the one hand, and the hierarchical structure can be constructed on the other hand to promote the enrichment of the substrate. In addition, ligands with redox units have also exhibited promising performance in facilitating charge transfer during the reaction. More p-block metal-based MOFs constructed based on naphthalenediimide-based ligands, tetrathiafulvalene-based ligands, diphenylenedicarboxamido, etc. should be constructed and explored for their application in the field of CO₂RR.

  (2) Meanwhile, the stability of MOFs themselves also greatly affects the mechanism exploration and practical application of catalysts. Due to the oxyphilic nature of the p-block metal, most of these MOF materials are constructed based on carboxylic acid ligands, whose coordination bonds are difficult to adapt to the CO₂RR environment. The introduction of N coordination sites involved in coordination to form metal-N structure can effectively improve the stability of MOFs, especially in the usually basic conditions of CO₂RR. However, a rational design of ligand conformation is necessary to overcome the difficulties in synthesizing this class of MOFs. In addition, the stability of the frameworks can also be enhanced by introducing π-π or d-π interactions through rational structural design. Finally, enhancing the hydrophobicity of MOFs likewise prevents the coordination bonds from being attacked to improve the stability of the catalyst. The change of wettability can also modulate the gas and liquid mass transport during the reaction to improve the catalytic performance. Therefore, the potential of hydrophobic MOF materials in the field of CO₂RR should be further explored.

  (3) Furthermore, MOF-derived catalysts can significantly improve conductivity and stability based on inheriting the original structure of MOFs, which seems to be expected to be promising CO₂RR catalysts. However, due to the small variety of p-block metal-based MOF materials themselves compared to transition metal-based MOFs, only a limited number of classical structures have been used as precursors to prepare MOF-derived catalysts. Therefore, the variety of precursors should be further expanded to prepare more efficient catalysts. Moreover, current transformation methods include pyrolysis, acid/base etching, laser metallurgy, sulfidation, phosphitylation, etc., which are not mild enough to preserve the inherent structural features of MOFs. Therefore, milder conversion strategies should be developed to allow the derivative catalysts to preserve the structural advantages of MOFs as much as possible.

  (4) Moreover, in addition to the catalyst itself, factors such as the electrolyte, and electrolysis device in the reaction system likewise determine the prospects for CO₂RR applications. Currently, alkaline electrolytes have been widely used as electrolytes to obtain better catalytic selectivity. However, since CO₂ dissolves in the alkaline electrolyte, leading to higher energy consumption with lower CO₂ utilization. Acid electrolytes became an effective solution to the problem. However, very few p-block metal-based MOF catalysts have been reported for their catalytic activity under acidic conditions, and more efforts should be devoted to exploring their potential under such conditions. For the electrolysis device, the MEA-SSE device becomes desirable as the reduction product of the p-block metal-based catalyst is dominated by formic acid [182]. Pure formic acid solutions can be obtained by rinsing the layer of solid-state electrolyte with pure water or N₂ gas streams, which significantly reduces the separation cost of the product. However relevant reports are equally lacking and the variety of solid-state electrolytes should be expanded to improve the transfer efficiency.

  (5) Finally, exploring the CO₂RR reaction process is also one of the current major challenges. At present, the role of catalyst molecules on the electrode surface and the reaction pathway during the CO₂RR process is based on the binding energy between intermediates and the electrode surface and active sites, which rely on theoretical simulation calculations. Although the morphology, structure, and valence state changes of catalyst molecules after electro-reactions can be obtained through common surface characterization techniques, real-time monitoring during the CO₂RR process relies on in situ/operational characterization techniques. There is a lack of relevant knowledge and monitoring methods regarding the surface coverage and electrochemical active area of catalyst molecules, as well as the chemical state and true structure of MOFs and MOF-derived catalysts during the CO₂RR process. According to current mechanism research, the entire CO₂RR process involves a series of electron transfer proton coupling processes and complex mass transfer processes. More in-depth in situ/operando characterization techniques are needed to monitor the reaction microenvironment in real time, which can serve as an experimental basis to combine with DFT calculations for further unraveling the reaction mechanism.

  Declaration of competing interest

  The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

  CRediT authorship contribution statement

  Xinyu Wu: Writing – original draft, Resources, Investigation. Jianfeng Lu: Writing – original draft. Zihao Zhu: Writing – review & editing, Resources, Project administration, Funding acquisition. Suijun Liu: Writing – review & editing, Project administration. Herui Wen: Project administration.

  Acknowledgments

  This work was supported by the National Natural Science Foundation of China (Nos. 22061019 and 22261021), the Jiangxi Provincial Natural Science Foundation (Nos. 20224BAB203002, 20232ACB203018, 20232BAB203005, and 20224BAB213001), the Jiangxi Province Key Laboratory of Functional Crystalline Materials Chemistry (No. 2024SSY05161), the Ganzhou Key Research and Development Program (No. 2023PNS26963), the Youth Jinggang Scholars Program in Jiangxi Province (No. QNJG2019053), the Two Thousand Talents Program in Jiangxi Province (No. jxsq2019201068), the Doctor's Starting Research Foundation of Jiangxi University of Science and Technology (No. 205200100597), and the Science and Technology Research Project of Jiangxi Provincial Department of Education (No. GJJ2200860).

  
  
• 1. [1]

     T. Zheng, K. Jiang, H. Wang, Adv. Mater. 30 (2018) 1802066.

  2. [2]

     H. Zhao, D. Benetti, X. Tong, et al., Nano Energy 50 (2018) 756–765.

  3. [3]

     H. Zhao, G. Liu, S. You, et al., Energy Environ. Sci. 14 (2021) 396–406. doi: 10.1039/d0ee02235g

  4. [4]

     S. Chu, A. Majumdar, Nature 488 (2012) 294–303. doi: 10.1038/nature11475

  5. [5]

     Q. Hu, W. Zhou, S. Qi, et al., Nat. Sustain. 7 (2024) 442–451. doi: 10.1038/s41893-024-01302-0

  6. [6]

     X.L. Jiang, F.Y. Ren, Y. Shi, et al., CCS Chem. 6 (2024) 2333–2345. doi: 10.31635/ccschem.024.202303476

  7. [7]

     L. Li, Y. Huang, Y. Li, Energy Chem. 2 (2020) 100024.

  8. [8]

     D. Li, M. Kassymova, X. Cai, et al., Coord. Chem. Rev. 412 (2020) 213262.

  9. [9]

     M. Reichstein, M. Bahn, P. Ciais, et al., Nature 500 (2013) 287–295. doi: 10.1038/nature12350

  10. [10]

      D. Notz, J. Stroeve, Science 354 (2016) 747–750. doi: 10.1126/science.aag2345

  11. [11]

      C. Hepburn, E. Adlen, J. Beddington, et al., Nature 575 (2019) 87–97. doi: 10.1038/s41586-019-1681-6

  12. [12]

      C. Vogt, M. Monai, G.J. Kramer, et al., Nat. Catal. 2 (2019) 188–197. doi: 10.1038/s41929-019-0244-4

  13. [13]

      H. Xu, D. Rebollar, H. He, et al., Nat. Energy 5 (2020) 623–632.

  14. [14]

      R.L. Siegelman, E.J. Kim, J.R. Long, Nat. Mater. 20 (2021) 1060–1072. doi: 10.1038/s41563-021-01054-8

  15. [15]

      P.V. Kortunov, M. Siskin, L.S. Baugh, et al., Energy Fuels 29 (2015) 5940–5966. doi: 10.1021/acs.energyfuels.5b00985

  16. [16]

      J. Palomar, M. Larriba, J. Lemus, et al., Sep. Purif. Technol. 213 (2019) 578–586.

  17. [17]

      X. Duan, J. Xu, Z. Wei, et al., Adv. Mater. 29 (2017) 1701784.

  18. [18]

      K.T. Ngo, M. McKinnon, B. Mahanti, et al., J. Am. Chem. Soc. 139 (2017) 2604–2618. doi: 10.1021/jacs.6b08776

  19. [19]

      D. Xiang, D. Magana, R.B. Dyer, J. Am. Chem. Soc. 136 (2014) 14007–14010. doi: 10.1021/ja5081103

  20. [20]

      A. Otto, T. Grube, S. Schiebahn, et al., Energy Environ. Sci. 8 (2015) 3283–3297.

  21. [21]

      H. Rao, J. Bonin, M. Robert, J. Phys. Chem. C 122 (2018) 13834–13839. doi: 10.1021/acs.jpcc.8b00950

  22. [22]

      S. Dou, L. Tao, R. Wang, et al., Adv. Mater. 30 (2018) 1705850.

  23. [23]

      Y. Lum, J.W. Ager, Nat. Catal. 2 (2019) 86–93.

  24. [24]

      Z. Miao, P. Hu, C. Nie, et al., J. Energy Chem. 38 (2019) 114–118.

  25. [25]

      A.M. Appel, J.E. Bercaw, A.B. Bocarsly, et al., Chem. Rev. 113 (2013) 6621–6658. doi: 10.1021/cr300463y

  26. [26]

      Y.Y. Zhang, G.W. Yang, R. Xie, et al., Angew. Chem. Int. Ed. 59 (2020) 23291–23298. doi: 10.1002/anie.202010651

  27. [27]

      Y. Zhang, H. Liu, F. Gao, et al., Energy Chem. 4 (2022) 100078.

  28. [28]

      Q. Gong, P. Ding, M. Xu, et al., Nat. Commun. 10 (2019) 2807.

  29. [29]

      D.U. Nielsen, X.M. Hu, K. Daasbjerg, et al., Nat. Catal. 1 (2018) 244–254. doi: 10.1038/s41929-018-0051-3

  30. [30]

      W. Li, H. Wang, X. Jiang, et al., RSC Adv. 8 (2018) 7651–7669. doi: 10.1039/c7ra13546g

  31. [31]

      J. Xiong, J. Di, J. Xia, et al., Adv. Funct. Mater. 28 (2018) 1801983.

  32. [32]

      Q. Han, X. Bai, Z. Man, et al., J. Am. Chem. Soc. 141 (2019) 4209–4213. doi: 10.1021/jacs.8b13673

  33. [33]

      S. Xu, E.A. Carter, Chem. Rev. 119 (2019) 6631–6669. doi: 10.1021/acs.chemrev.8b00481

  34. [34]

      L. Zhang, Z.J. Zhao, J. Gong, Angew. Chem. Int. Ed. 56 (2017) 11326–11353. doi: 10.1002/anie.201612214

  35. [35]

      S.L. Xie, J. Liu, L.Z. Dong, et al., Chem. Sci. 10 (2019) 185–190. doi: 10.1039/c8sc03471k

  36. [36]

      K.L. Bae, J. Kim, C.K. Lim, et al., Nat. Commun. 8 (2017) 1156.

  37. [37]

      X. Li, C. Deng, Y. Kong, et al., Angew. Chem. Int. Ed. 62 (2023) e202309732.

  38. [38]

      C.J. Yang, L. Liu, Q.S. Gu, et al., CCS Chem. 6 (2024) 1612–1627. doi: 10.31635/ccschem.024.202403839

  39. [39]

      Q. Hu, S. Qi, Q. Huo, et al., J. Am. Chem. Soc. 146 (2024) 2967–2976. doi: 10.1021/jacs.3c06904

  40. [40]

      Z. Yang, F.E. Oropeza, K.H.L. Zhang, APL Mater 8 (2020) 060901.

  41. [41]

      A.S. Varela, W. Ju, P. Strasser, Adv. Energy Mater. 8 (2018) 1703614.

  42. [42]

      C. Chen, J.F. Khosrowabadi Kotyk, S.W. Sheehan, Chem. 4 (2018) 2571–2586.

  43. [43]

      C. Wei, S. Sun, D. Mandler, et al., Chem. Soc. Rev. 48 (2019) 2518–2534. doi: 10.1039/c8cs00848e

  44. [44]

      P. Shao, L. Yi, S. Chen, et al., J. Energy Chem. 40 (2020) 156–170.

  45. [45]

      D. Li, L. Huang, Y. Tian, et al., Appl. Catal. B 292 (2021) 120119.

  46. [46]

      S. Liu, J. Xiao, X.F. Lu, et al., Angew. Chem. Int. Ed. 58 (2019) 8499–8503. doi: 10.1002/anie.201903613

  47. [47]

      L. Ji, L. Chang, Y. Zhang, et al., ACS Catal. 9 (2019) 9721–9725. doi: 10.1021/acscatal.9b03180

  48. [48]

      E. Zhang, T. Wang, K. Yu, et al., J. Am. Chem. Soc. 141 (2019) 16569–16573. doi: 10.1021/jacs.9b08259

  49. [49]

      S. Roy, B. Sharma, J. Pécaut, et al., J. Am. Chem. Soc. 139 (2017) 3685–3696. doi: 10.1021/jacs.6b11474

  50. [50]

      X. Yang, Q.X. Li, S.Y. Chi, et al., SmartMat 3 (2022) 163–172.

  51. [51]

      M.R. Liu, Q.L. Hong, Q.H. Li, et al., Adv. Funct. Mater. 28 (2018) 1801136.

  52. [52]

      Y.X. Tan, F. Wang, J. Zhang, Chem. Soc. Rev. 47 (2018) 2130–2144. doi: 10.1039/c7cs00782e

  53. [53]

      H. Furukawa, K.E. Cordova, M. O'Keeffe, et al., Science 341 (2013) 1230444.

  54. [54]

      C.S. Diercks, Y. Liu, K.E. Cordova, et al., Nat. Mater. 17 (2018) 301–307. doi: 10.1038/s41563-018-0033-5

  55. [55]

      T. Qiu, S. Gao, Z. Liang, et al., Angew. Chem. Int. Ed. 60 (2021) 17314–17336. doi: 10.1002/anie.202012699

  56. [56]

      Z. Meng, Z. Qiu, Y. Shi, et al., eScience 3 (2023) 100092.

  57. [57]

      Z. Jiao, X. Zhao, J. Zhao, et al., Acta Phys. Chim. Sin. 39 (2023) 2301018. doi: 10.3866/pku.whxb202301018

  58. [58]

      G.L. Yang, Y. Xie, Z.H. Jiao, et al., J. Mater. Chem. A 11 (2023) 16255–16262. doi: 10.1039/d3ta02520a

  59. [59]

      Y. Lv, S.W. Ke, Y. Gu, et al., Angew. Chem. Int. Ed. 62 (2023) e202305246.

  60. [60]

      Z. Lei, Y. Xue, W. Chen, et al., Adv. Energy Mater. 8 (2018) 1801587.

  61. [61]

      Z.G. Gu, J. Zhang, Coord. Chem. Rev. 378 (2019) 513–532.

  62. [62]

      R.S. Kumar, S.S. Kumar, M.A. Kulandainathan, Electrochem. Commun. 25 (2012) 70–73.

  63. [63]

      R. Hinogami, S. Yotsuhashi, M. Deguchi, et al., ECS Electrochem. 1 (2012) H17–H19. doi: 10.1149/2.001204eel

  64. [64]

      T. Ma, Q. Fan, H. Tao, et al., Nanotechnology 28 (2017) 472001. doi: 10.1088/1361-6528/aa8f6f

  65. [65]

      S. Zhang, P. Kang, S. Ubnoske, et al., J. Am. Chem. Soc. 136 (2014) 7845–7848. doi: 10.1021/ja5031529

  66. [66]

      Z. Chen, K. Mou, S. Yao, et al., J. Mater. Chem. A 6 (2018) 11236–11243. doi: 10.1039/c8ta03328e

  67. [67]

      Z.H. Zhao, J.R. Huang, D.S. Huang, et al., J. Am. Chem. Soc. 146 (2024) 14349–14356. doi: 10.1021/jacs.4c04841

  68. [68]

      P. Li, F. Yang, J. Li, et al., Adv. Energy Mater. 13 (2023) 2301597.

  69. [69]

      N.V. Rees, R.G. Compton, J. Solid State Electrochem. 15 (2011) 2095–2100. doi: 10.1007/s10008-011-1398-4

  70. [70]

      A. Liu, M. Gao, X. Ren, et al., J. Mater. Chem. A 8 (2020) 3541–3562. doi: 10.1039/c9ta11966c

  71. [71]

      R. Francke, B. Schille, M. Roemelt, Chem. Rev. 118 (2018) 4631–4701. doi: 10.1021/acs.chemrev.7b00459

  72. [72]

      D.D. Zhu, J.L. Liu, S.Z. Qiao, Adv. Mater. 28 (2016) 3423–3452. doi: 10.1002/adma.201504766

  73. [73]

      A. Vasileff, Y. Zheng, S.Z. Qiao, Adv. Energy Mater. 7 (2017) 1700759.

  74. [74]

      J. Zhang, W. Cai, F.X. Hu, et al., Chem. Sci. 12 (2021) 6800–6819. doi: 10.1039/d1sc01375k

  75. [75]

      T. Cheng, H. Xiao, W.A. Goddard, J. Ⅲ, Am. Chem. Soc. 138 (2016) 13802–13805. doi: 10.1021/jacs.6b08534

  76. [76]

      S. Jin, Z. Hao, K. Zhang, et al., Angew. Chem. Int. Ed. 60 (2021) 20627–20648. doi: 10.1002/anie.202101818

  77. [77]

      S. Guo, T. Asset, P. Atanassov, ACS Catal. 11 (2021) 5172–5188. doi: 10.1021/acscatal.0c04862

  78. [78]

      T. Tang, Z. Wang, J. Guan, Adv. Funct. Mater. 32 (2022) 2111504.

  79. [79]

      J. Yu, J. Wang, Y. Ma, et al., Adv. Funct. Mater. 31 (2021) 2102151.

  80. [80]

      H.H. Cramer, B. Chatterjee, T. Weyhermüller, et al., Angew. Chem. Int. Ed. 132 (2020) 15804–15811. doi: 10.1002/ange.202004463

  81. [81]

      Y. Fang, J.C. Flake, J. Am. Chem. Soc. 139 (2017) 3399–3405. doi: 10.1021/jacs.6b11023

  82. [82]

      Z. Gao, Y. Gong, Y. Zhu, et al., Nano Res. 16 (2023) 8743–8750. doi: 10.1007/s12274-023-5685-z

  83. [83]

      Y. Hori, K. Kikuchi, S. Suzuki, Chem. Lett. 14 (1985) 1695–1698. doi: 10.1246/cl.1985.1695

  84. [84]

      Y. Hori, A. Murata, Electrochim. Acta 35 (1990) 1777–1780.

  85. [85]

      Y. Hori, H. Wakebe, T. Tsukamoto, et al., Electrochim. Acta 39 (1994) 1833–1839.

  86. [86]

      M. Jouny, W. Luc, F. Jiao, Ind. Eng. Chem. Res. 57 (2018) 2165–2177. doi: 10.1021/acs.iecr.7b03514

  87. [87]

      L. Yuan, S. Zeng, X. Zhang, et al., Mater. Rep. Energy 3 (2023) 100177.

  88. [88]

      Z.W. Seh, J. Kibsgaard, C.F. Dickens, et al., Science 355 (2017) eaad4998.

  89. [89]

      A.J. Welch, J.S. DuChene, G. Tagliabue, et al., ACS Appl. Energy Mater. 2 (2019) 164–170. doi: 10.1021/acsaem.8b01570

  90. [90]

      E.E. Benson, C.P. Kubiak, A.J. Sathrum, et al., Chem. Soc. Rev. 38 (2009) 89–99.

  91. [91]

      P. Kang, Z. Chen, M. Brookhart, et al., Top. Catal. 58 (2015) 30–45. doi: 10.1007/s11244-014-0344-y

  92. [92]

      R.Z. Zhang, B.Y. Wu, Q. Li, et al., Coord. Chem. Rev. 422 (2020) 213436.

  93. [93]

      N. Han, P. Ding, L. He, et al., Adv. Energy Mater. 10 (2020) 1902338.

  94. [94]

      S. Verma, B. Kim, H.R.M. Jhong, et al., ChemSusChem 9 (2016) 1972–1979. doi: 10.1002/cssc.201600394

  95. [95]

      W. Lai, Y. Qiao, J. Zhang, et al., Energy Environ. Sci. 15 (2022) 3603–3629. doi: 10.1039/d2ee00472k

  96. [96]

      J. Zhao, S. Xue, J. Barber, et al., J. Mater. Chem. A 8 (2020) 4700–4734. doi: 10.1039/c9ta11778d

  97. [97]

      X. Tan, C. Yu, Y. Ren, et al., Energy Environ. Sci. 14 (2021) 765–780. doi: 10.1039/d0ee02981e

  98. [98]

      R. Peters, M. Baltruweit, T. Grube, et al., J. CO2 Util. 34 (2019) 616–634.

  99. [99]

      Y. Wang, T. He, J. Mater. Chem. A 9 (2021) 87–110.

  100. [100]

       L. Gao, X. Cui, C.D. Sewell, et al., Chem. Soc. Rev. 50 (2021) 8428–8469. doi: 10.1039/d0cs00962h

  101. [101]

       Z. Wang, P. Hou, Y. Wang, et al., ACS Sustain. Chem. Eng. 7 (2019) 6106–6112. doi: 10.1021/acssuschemeng.8b06278

  102. [102]

       Y. Liu, C.C.L. McCrory, Nat. Commun. 10 (2019) 1683.

  103. [103]

       J.A. Rabinowitz, M.W. Kanan, Nat. Commun. 11 (2020) 5231.

  104. [104]

       J.E. Huang, F. Li, A. Ozden, et al., Science 372 (2021) 1074–1078. doi: 10.1126/science.abg6582

  105. [105]

       S. Chatterjee, I. Dutta, Y. Lum, et al., Energy Environ. Sci. 14 (2021) 1194–1246. doi: 10.1039/d0ee03011b

  106. [106]

       Y. Pei, H. Zhong, F. Jin, Energy Sci. Eng. 9 (2021) 1012–1032. doi: 10.1002/ese3.935

  107. [107]

       A. Bagger, W. Ju, A.S. Varela, et al., ChemPhysChem 18 (2017) 3266–3273. doi: 10.1002/cphc.201700736

  108. [108]

       Y.X. Du, Y.T. Zhou, M.Z. Zhu, Tungsten 5 (2023) 201–216. doi: 10.1007/s42864-022-00197-8

  109. [109]

       H. Shang, T. Wang, J. Pei, et al., Angew. Chem. Int. Ed. 132 (2020) 22651–22655. doi: 10.1002/ange.202010903

  110. [110]

       W. Luo, W. Xie, M. Li, et al., J. Mater. Chem. A 7 (2019) 4505–4515. doi: 10.1039/c8ta11645h

  111. [111]

       B. Jia, Z. Chen, C. Li, et al., J. Am. Chem. Soc. 145 (2023) 14101–14111. doi: 10.1021/jacs.3c04288

  112. [112]

       J. Zhang, R. Yin, Q. Shao, et al., Angew. Chem. Int. Ed. 58 (2019) 5609–5613. doi: 10.1002/anie.201900167

  113. [113]

       W. Ma, S. Xie, X.G. Zhang, et al., Nat. Commun. 10 (2019) 892.

  114. [114]

       Y.Y. Birdja, R.E. Vos, T.A. Wezendonk, et al., ACS Catal. 8 (2018) 4420–4428. doi: 10.1021/acscatal.7b03386

  115. [115]

       Z.H. Zhu, Z.L. Liang, Z.H. Jiao, et al., Angew. Chem. Int. Ed. 61 (2022) e202214243.

  116. [116]

       S.Z. Hou, X.D. Zhang, W.W. Yuan, et al., Inorg. Chem. 59 (2020) 11298–11304. doi: 10.1021/acs.inorgchem.0c00769

  117. [117]

       X. Kang, L. Li, A. Sheveleva, et al., Nat. Commun. 11 (2020) 5464.

  118. [118]

       L.L. Zhuo, P. Chen, K. Zheng, et al., Angew. Chem. Int. Ed. 61 (2022) e202204967.

  119. [119]

       S. Wang, Y. Wang, J.M. Huo, et al., Inorg. Chem. Front. 10 (2023) 158–167.

  120. [120]

       X. Kang, B. Wang, K. Hu, et al., J. Am. Chem. Soc. 142 (2020) 17384–17392. doi: 10.1021/jacs.0c05913

  121. [121]

       Z. Wang, Y. Zhou, C. Xia, et al., Angew. Chem. Int. Ed. 60 (2021) 19107–19112. doi: 10.1002/anie.202107523

  122. [122]

       R. Liang, R. Huang, X. Wang, et al., Appl. Surf. Sci. 464 (2019) 396–403.

  123. [123]

       R. He, A. Zhang, Y. Ding, et al., Adv. Mater. 30 (2018) 1705872.

  124. [124]

       X. Sun, L. Lu, Q. Zhu, et al., Angew. Chem. Int. Ed. 57 (2018) 2427–2431. doi: 10.1002/anie.201712221

  125. [125]

       Y. Zhou, S. Liu, Y. Gu, et al., J. Am. Chem. Soc. 143 (2021) 14071–14076. doi: 10.1021/jacs.1c06797

  126. [126]

       Z.H. Zhu, B.H. Zhao, S.L. Hou, et al., Angew. Chem. Int. Ed. 60 (2021) 23394–23402. doi: 10.1002/anie.202110387

  127. [127]

       Y. Zhang, F. Li, X. Zhang, et al., J. Mater. Chem. A 6 (2018) 4714–4720. doi: 10.1039/c8ta00023a

  128. [128]

       J. Li, C. Wang, D. Wang, et al., J. Mater. Chem. A 10 (2022) 20018–20023. doi: 10.1039/d2ta01727j

  129. [129]

       Y. Xing, X. Kong, X. Guo, et al., Adv. Sci. 7 (2020) 1902989.

  130. [130]

       T. Tran-Phu, R. Daiyan, Z. Fusco, et al., Adv. Funct. Mater. 30 (2020) 1906478.

  131. [131]

       J. Yang, X. Wang, Y. Qu, et al., Adv. Energy Mater. 10 (2020) 2001709.

  132. [132]

       F. Li, G.H. Gu, C. Choi, et al., Appl. Catal. B 277 (2020) 119241.

  133. [133]

       Z. Jiang, M. Zhang, X. Chen, et al., Angew. Chem. Int. Ed. 62 (2023) e202311223.

  134. [134]

       Z. Gao, M. Hou, Y. Shi, et al., Chem. Sci. 14 (2023) 6860–6866. doi: 10.1039/d3sc01876h

  135. [135]

       Z.H. Zhu, Z.L. Liang, S.L. Hou, et al., J. Energy Chem. 63 (2021) 328–335.

  136. [136]

       Z.W. Yang, J.M. Chen, Z.L. Liang, et al., ChemCatChem 15 (2023) e202201321.

  137. [137]

       N. Li, P. Yan, Y. Tang, et al., Appl. Catal. B 297 (2021) 120481.

  138. [138]

       D. Yao, C. Tang, A. Vasileff, et al., Angew. Chem. Int. Ed. 60 (2021) 18178–18184. doi: 10.1002/anie.202104747

  139. [139]

       P. Lamagni, M. Miola, J. Catalano, et al., Adv. Funct. Mater. 30 (2020) 1910408.

  140. [140]

       W.W. Yuan, J.X. Wu, X.D. Zhang, et al., J. Mater. Chem. A 8 (2020) 24486–24492. doi: 10.1039/d0ta08092f

  141. [141]

       C. Cao, D.D. Ma, J. Jia, et al., Adv. Mater. 33 (2021) 2008631.

  142. [142]

       L. Liu, K. Yao, J. Fu, et al., Colloids Surf. A 633 (2022) 127840.

  143. [143]

       L. Li, X. Kang, M. He, et al., J. Mater. Chem. A 10 (2022) 17801–17807. doi: 10.1039/d2ta04485d

  144. [144]

       G. Wen, D.U. Lee, B. Ren, et al., Adv. Energy Mater. 8 (2018) 1802427.

  145. [145]

       J. Wang, S. Ning, M. Luo, et al., Appl. Catal. B 288 (2021) 119979.

  146. [146]

       H. Xue, Z.H. Zhao, P.Q. Liao, et al., J. Am. Chem. Soc. 145 (2023) 16978–16982. doi: 10.1021/jacs.3c05023

  147. [147]

       Q. Wang, Y. Wu, C. Zhu, et al., Electrochim. Acta 369 (2021) 137662.

  148. [148]

       B. Kumar, V. Atla, J.P. Brian, et al., Angew. Chem. Int. Ed. 56 (2017) 3645–3649. doi: 10.1002/anie.201612194

  149. [149]

       Y. Fu, T. Wang, W. Zheng, et al., ACS Appl. Mater. Interfaces 12 (2020) 16178–16185. doi: 10.1021/acsami.9b18091

  150. [150]

       X. Wang, Y. Zou, Y. Zhang, et al., J. Colloid Interface Sci. 626 (2022) 836–847. doi: 10.3390/brainsci12070836

  151. [151]

       Y. Deng, S. Wang, Y. Huang, et al., Chin. J. Chem. Eng. 43 (2022) 353–359.

  152. [152]

       W. Geng, Q. Wang, C. Zhu, et al., J. Power Sources 529 (2022) 231252.

  153. [153]

       Z.H. Zhao, J.R. Huang, P.Q. Liao, et al., Angew. Chem. Int. Ed. 62 (2023) e202301767.

  154. [154]

       J. Yan, X. Wang, F. Ning, et al., Dalton Trans. 52 (2023) 11904–11912. doi: 10.1039/d3dt01610b

  155. [155]

       Z.H. Zhao, J.R. Huang, P.Q. Liao, et al., J. Am. Chem. Soc. 145 (2023) 26783–26790. doi: 10.1021/jacs.3c08974

  156. [156]

       N. Kornienko, Y. Zhao, C.S. Kley, et al., J. Am. Chem. Soc. 137 (2015) 14129–14135. doi: 10.1021/jacs.5b08212

  157. [157]

       M. Lee, A. De Riccardis, R.V. Kazantsev, et al., ACS Appl. Energy Mater. 3 (2020) 1286–1291. doi: 10.1021/acsaem.9b02210

  158. [158]

       X. Xiong, Y. Zhao, R. Shi, et al., Sci. Bull. 65 (2020) 987–994.

  159. [159]

       J.H. Cho, J. Ma, S.Y. Kim, Exploration 3 (2023) 20230001.

  160. [160]

       K. Wang, Y. Liu, J. Kang, et al., Appl. Catal. B 325 (2023) 122315.

  161. [161]

       D. Wang, S. Dong, L. Wen, et al., Chemosphere 291 (2022) 132889.

  162. [162]

       L. Liu, J. Zhang, X. Cheng, et al., Nano Res. 16 (2023) 181–188.

  163. [163]

       Q. Huang, X. Sha, R. Yang, et al., ACS Appl. Mater. Interfaces 16 (2024) 13882–13892. doi: 10.1021/acsami.4c01120

  164. [164]

       D.D. Ma, Q.L. Zhu, Coord. Chem. Rev. 422 (2020) 213483.

  165. [165]

       Y. Chen, C.W. Li, M.W. Kanan, J. Am. Chem. Soc. 134 (2012) 19969–19972. doi: 10.1021/ja309317u

  166. [166]

       F. Yu, X. Bai, M. Liang, et al., Chem. Eng. J. 405 (2021) 126960.

  167. [167]

       H. Dai, W. Zhou, W. Wang, Chem. Eng. J. 417 (2021) 127921.

  168. [168]

       D.H. Nam, O. Shekhah, G. Lee, et al., J. Am. Chem. Soc. 142 (2020) 21513–21521. doi: 10.1021/jacs.0c10774

  169. [169]

       W. Zhang, W. Yan, H. Jiang, et al., ACS Sustain. Chem. Eng. 8 (2020) 335–342. doi: 10.1021/acssuschemeng.9b05474

  170. [170]

       Y. Shi, B. Zhu, X. Guo, et al., Energy Stor. Mater. 51 (2022) 840–872.

  171. [171]

       J.D. Yi, D.H. Si, R. Xie, et al., Angew. Chem. Int. Ed. 60 (2021) 17108–17114. doi: 10.1002/anie.202104564

  172. [172]

       X. Guan, W. Gao, Q. Jiang, J. Mater. Chem. A 9 (2021) 4770–4780. doi: 10.1039/d0ta11012d

  173. [173]

       L. Yan, W. Su, X. Cao, et al., Chem. Eng. J. 412 (2021) 128718.

  174. [174]

       K. Yao, H. Wang, X. Yang, et al., Appl. Catal. B 311 (2022) 121377.

  175. [175]

       X. Cao, B. Wulan, Y. Wang, et al., Sci. Bull. 68 (2023) 1008–1016.

  176. [176]

       C.G. Morales-Guio, E.R. Cave, S.A. Nitopi, et al., Nat. Catal. 1 (2018) 764–771. doi: 10.1038/s41929-018-0139-9

  177. [177]

       Y. Zhao, C. Wang, Y. Liu, et al., Adv. Energy Mater. 8 (2018) 1801400.

  178. [178]

       W. Yang, Y. Zhao, S. Chen, et al., Inorg. Chem. 59 (2020) 12437–12444. doi: 10.1021/acs.inorgchem.0c01544

  179. [179]

       Z. Chen, D. Zhang, Y. Zhao, et al., Chem. Eng. J. 464 (2023) 142573.

  180. [180]

       W. Ren, X. Tan, W. Yang, et al., Angew. Chem. Int. Ed. 58 (2019) 6972–6976. doi: 10.1002/anie.201901575

  181. [181]

       J.X. Wu, X.R. Zhu, T. Liang, et al., Inorg. Chem. 60 (2021) 9653–9659. doi: 10.1021/acs.inorgchem.1c00946

  182. [182]

       Z. Wang, Y. Zhou, D. Liu, et al., Angew. Chem. Int. Ed. 61 (2022) e202200552.

  183. [183]

       Z. Chen, G. Yu, B. Li, et al., ACS Catal. 11 (2021) 14596–14604. doi: 10.1021/acscatal.1c04182

  184. [184]

       Y. Qi, J. Jiang, X. Liang, et al., Adv. Funct. Mater. 31 (2021) 2100908.

  185. [185]

       W. Wang, X. Wang, Z. Ma, et al., ACS Catal. 13 (2023) 796–802. doi: 10.1021/acscatal.2c05006

  186. [186]

       J. Zhai, Q. Kang, Q. Liu, et al., J. Colloid Interface Sci. 608 (2022) 1942–1950.

  187. [187]

       P. Deng, H. Wang, R. Qi, et al., ACS Catal. 10 (2020) 743–750. doi: 10.1021/acscatal.9b04043

  188. [188]

       W. Guo, X. Sun, C. Chen, et al., Green Chem. 21 (2019) 503–508. doi: 10.1039/c8gc03261k

  189. [189]

       Y. Xue, C. Li, X. Zhou, et al., ChemElectroChem 9 (2022) e202101648.

  190. [190]

       D.H. Zhuo, Q.S. Chen, X.H. Zhao, et al., J. Mater. Chem. C 9 (2021) 7900–7904. doi: 10.1039/d1tc01766g

  191. [191]

       P. Deng, F. Yang, Z. Wang, et al., Angew. Chem. Int. Ed. 59 (2020) 10807–10813. doi: 10.1002/anie.202000657

  192. [192]

       Y. Wang, Y. Li, J. Liu, et al., Angew. Chem. Int. Ed. 60 (2021) 7681–7685. doi: 10.1002/anie.202014341

  193. [193]

       Y. Li, J. Chen, S. Chen, et al., ACS Energy Lett. 7 (2022) 1454–1461. doi: 10.1021/acsenergylett.2c00326

  194. [194]

       S. Liu, Y. Fan, Y. Wang, et al., Nano Lett. 22 (2022) 9107–9114. doi: 10.1021/acs.nanolett.2c03573

  195. [195]

       Y. Jia, M. Lin, Z. Tian, et al., J. Catal. 413 (2022) 1077–1088.

  196. [196]

       J. Yang, W. Li, D. Wang, et al., Adv. Mater. 32 (2020) 2003300.

  197. [197]

       S. Ji, Y. Qu, T. Wang, et al., Angew. Chem. Int. Ed. 59 (2020) 10651–10657. doi: 10.1002/anie.202003623

  198. [198]

       N. Zhang, C. Ye, H. Yan, et al., Nano Res. 13 (2020) 3165–3182. doi: 10.1007/s12274-020-2994-3

  199. [199]

       R. Yun, R. Xu, C. Shi, et al., Nano Res. 16 (2023) 8970–8976. doi: 10.1007/s12274-023-5626-x

  200. [200]

       Y. Zhang, L. Jiao, W. Yang, et al., Angew. Chem. Int. Ed. 60 (2021) 7607–7611. doi: 10.1002/anie.202016219

  201. [201]

       Z. Chen, X. Zhang, W. Liu, et al., Energy Environ. Sci. 14 (2021) 2349–2356. doi: 10.1039/d0ee04052e

  202. [202]

       Q. Yang, C.C. Yang, C.H. Lin, et al., Angew. Chem. Int. Ed. 58 (2019) 3511–3515. doi: 10.1002/anie.201813494

  203. [203]

       Y. Cheng, S. Zhao, B. Johannessen, et al., Adv. Mater. 30 (2018) 1706287.

  204. [204]

       P. Lu, X. Tan, H. Zhao, et al., ACS Nano 15 (2021) 5671–5678. doi: 10.1021/acsnano.1c00858

  205. [205]

       S. Li, X. Lu, S. Zhao, et al., ACS Catal. 12 (2022) 7386–7395. doi: 10.1021/acscatal.2c01805

  206. [206]

       J. Zhang, G. Zeng, L. Chen, et al., Nano Res. 15 (2022) 4014–4022. doi: 10.1007/s12274-022-4177-x

  207. [207]

       Z. Fan, R. Luo, Y. Zhang, et al., Angew. Chem. Int. Ed. 62 (2023) e202216326.

• 

  Scheme 1  p-block metal-based MOFs and MOF-derived materials as CO₂RR electrocatalysts.

  下载: 全尺寸图片 幻灯片
  

  Figure 1  Mechanism of CO₂RR to HCOOH and CO.

  下载: 全尺寸图片 幻灯片
  

  Figure 2  (a) Electronic structure of p-block elements. (b) The combined plot of the three proposed descriptors for converting CO₂ into H₂, CO, and HCOOH. (c) Calculation of catalytic products for different metals by ΔE_H⁺-ΔE_COOH⁻. Copied with permission [107]. Copyright 2017, Wiley Publishing Group.

  下载: 全尺寸图片 幻灯片
  

  Figure 3  The structure of selected organic ligands that was involved in this review. H₂BDC, terephthalic acid; H₂IPA, isophthalic acid; H₂BDC—NH₂, 2-aminoterephthalic acid; HIN, isonicotinic acid; HAIN, 3-aminoisonicotinic acid; H₃BTC, benzene-1,3,5-tricarboxylic acid; HCA, 5-chloronicotinic acid; HTA, 1H-1,2,3-triazole; HMD, 2-methylimidazole; PTA, p-phthalic acid; aPTA, 2-aminoterephthalic acid; DaTPA, 2,5-diaminoterephthalic acid; HAB, benzene-1,2,3,4,5,6-hexaamine; H₂PDC, pyrazole-3,5-dicarboxylic acid; H₂IDC, 4,5-Imidazoledicarboxylic acid; H₄PMA, pyromellitic acid; HTCD, trisodium citrate dihydrate; H₂ABDBC, (E)−4,4′-(diazene-1,2-diyl)dibenzoic acid; H₄BPTC, biphenyl-3,3′,5,5′-tetracarboxylic acid; H₂NDC, naphthalene-1,4-dicarboxylic acid; H₄BDP, 5,5′-(1,3,6,8-tetraoxo-1,3,6,8-tetrahydrobenzo[lmn][3,8]phenanthroline-2,7-diyl)diisophthalic acid; H₃BTB, 1,3,5-tris(4-carboxyphenyl)benzene; HHTP, 2,3,6,7,10,11-Triphenylenehexol; H₄BCP, 5-(2,6-bis(4-carboxyphenyl)pyridin-4-yl)isophthalic acid; H₄EA, 2,3,7,8-tetrahydroxychromeno[5,4,3-cde]chromene-5,10‑dione; H₄TA, [Ni(C₂S₂(C₆H₄COOH)₂)₂]; H₄TTFTB, tetrathiafulvalene-3,4,5,6-tetrakis(4-benzoic acid); TCPP, tetrakis (4-carboxyphenyl) porphyrin.

  下载: 全尺寸图片 幻灯片
  

  Figure 4  (a) FE of HCOOH and CO for In-BDC, In, and BDC. Copied with permission [116]. Copyright 2020, American Chemical Society. (b) Scheme for the synthesis of MFM-300(In)-e. (c, d) The stability of electrolysis over 2 h. Copied with permission [120]. Copyright 2020, American Chemical Society. (e) Scheme for the synthesis MIL-68(In) and MIL-68(In)-NH₂. (f) FE of HCOOH for MIL-68(In) and MIL-68(In)-NH₂. (g) Uncorrected LSV curves of MIL-68(In)-NH₂ in the flow cell. Copied with permission [121]. Copyright 2021, Wiley Publishing Group.

  下载: 全尺寸图片 幻灯片
  

  Figure 5  (a) Simplified diagram of CO₂RR for Me₂NH₂⁺)[In^Ⅲ(TA)]·3DMF·1.5H₂O and (Me₂NH₂⁺)[In^Ⅲ(TTFTB)]·0.7C₂H₅OH·DMF. (b) FE of HCOOH for Me₂NH₂⁺)[In^Ⅲ(TA)]·3DMF·1.5H₂O and (Me₂NH₂⁺)[In^Ⅲ(TTFTB)]·0.7C₂H₅OH·DMF. (c, d) Proposed reaction paths and free energy for [NiS₄] sites. Copied with permission [125]. Copyright 2021, American Chemical Society. (e) FE of In-ABDBC—HIN, InCo-ABDBC—HIN and In-ABDBC—HAIN. (f, g) The distribution of unpaired electrons in In-ABDBC—HIN and InCo-ABDBC—HIN. Copied with permission [119]. Copyright 2022, Royal Society of Chemistry.

  下载: 全尺寸图片 幻灯片
  

  Figure 6  (a) Scheme for the synthesis of CPs@V11. (b) FE of CPs@V11. (c, d) FE of the original In-MOFs and the CPs@MOFs. Copied with permission [126]. Copyright 2021, Wiley Publishing Group. (e) FE of formate and the total current density of In-TCPP. (f, g) The proposed mechanisms and corresponding energy profiles for In-TCPP. Copied with permission [82]. Copyright 2023, Tsinghua University Press.

  下载: 全尺寸图片 幻灯片
  

  Figure 7  (a) FE of Bi-MOF. Copied with permission [132]. Copyright 2020, Elsevier. (b) FE of SU-101 NRs. (c) The energy profiles for the four pathways proposed on SU-101. Copied with permission [128]. Copyright 2022, Royal Society of Chemistry. (d) Schematic illustration of the metal-organic cube, linkage, and ACO topology from inorganic zeolites to ZMOFs, and Bi-ZMOFs. (e) FE of PZH-1. (f) Free energy for converting CO₂ into HCOOH of PZH-1 (red) and PZH-2 (blue), respectively. Copied with permission [133]. Copyright 2023, Wiley Publishing Group.

  下载: 全尺寸图片 幻灯片
  

  Figure 8  (a) The scheme for the preparation of Bi-HHTP. (b) FE_HCOOH and j_HCOOH of Bi-HHTP. (c) The energy profiles for the four pathways proposed on Bi-HHTP. Copied with permission [134]. Copyright 2023, Royal Society of Chemistry. (d) Schematic illustration of CO₂RR for V12. (e) FE of Bi foil, V12@CC, V12@BF, and V12e. (f) The FE for HCOOH and MDDQ of V12e‖CAT-1@NF. Copied with permission [135]. Copyright 2021, Elsevier. (g) Crystal structure of Bi-FDCA MOF. (h) Schematic illustration of the ions transfers in the paired electrolysis with BPM. (i) FE of HCOOH and current density of Bi-FDCA MOF. Copied with permission [136]. Copyright 2022, Wiley Publishing Group.

  下载: 全尺寸图片 幻灯片
  

  Figure 9  (a) Electrolysis results of Bi(btb) in CO₂ saturated electrolyte. (b) High-resolution TEM images of Bi nanoparticles. Copied with permission [139]. Copyright 2020, Wiley Publishing Group. (c) The electrochemical cell and reaction mechanism of MOF-derived Bi₂O₂CO₃. (d) FE and j of Bi-BTB. (e) XRD patterns of Bi-BTB with different treatments. (f) Measured CVs of MOF-derived at 10 mV/s. Copied with permission [140]. Copyright 2020, Royal Society of Chemistry.

  下载: 全尺寸图片 幻灯片
  

  Figure 10  (a) Scheme of the two-step reconstruction process of Bi NS. (b) FE_HCOO⁻ for the Bi NS. Copied with permission [138]. Copyright 2021, Wiley Publishing Group. (c) Scheme for the synthesis of Ni-NF-Af and Bi-enes. (d) FE of Bi-enes. (e) Voltage-dependent FE_HCOOH and corresponding i-t curves of anodic MOR and cathodic CO₂RR. Copied with permission [141]. Copyright 2021, Wiley Publishing Group.

  下载: 全尺寸图片 幻灯片
  

  Figure 11  (a) Scheme for the formation of Bi/Bi-O interface for the CO₂RR. (b) FE of Bi-MOF. (c) In situ Raman spectra of Bi-MOF for the CO₂RR. Copied with permission [142]. Copyright 2021, Wiley Publishing Group. (d) The coordination environment and pore structures of MFM-220, MFM-221, and MFM-222. (e) FE of Bi-MOFs. (f) FT-IR spectra of Bi-MOFs. Copied with permission [143]. Copyright 2022, Royal Society of Chemistry.

  下载: 全尺寸图片 幻灯片
  

  Figure 12  (a) Scheme for the CO₂RR of Sn-MOF. (b) FE of Sn-MOFs. (c) Free energy for H₂ and HCOOH on Sn-MOF. Copied with permission [150]. Copyright 2022, Elsevier. (d) Schematic illustration for synthesizing Sn-N6-MOF. (e) FE of Sn-N6-MOFs. Copied with permission [151]. Copyright 2022, Elsevier.

  下载: 全尺寸图片 幻灯片
  

  Figure 13  (a) Schematic illustration for synthetic Sn-CPs. (b) FE of Sn-CPs. (c) The stability test of Sn-DaPTA. Copied with permission [152]. Copyright 2022, Elsevier. (d) FE of Sn-THO. (e) The free-energy diagrams of CO₂RR pathways for the Sn-THO. (f) Optimized structures of intermediates in the proposed CO₂RR pathways on Sn-THO. Copied with permission [153]. Copyright 2023, Wiley Publishing Group.

  下载: 全尺寸图片 幻灯片
  

  Figure 14  (a) FE of Sn-MOF/In. Copied with permission [154]. Copyright 2023, Royal Society of Chemistry. (b) Schematic illustration for synthetic CuSn-HAB. (c) FE and current density of CuSn-HAB. (d) Proposed reaction paths for yielding C₂H₄ and EtOH of Cu-Cu sites and Sn-Cu sites. (e) Catalytic mechanism of CuSn-HAB for CO₂RR. Copied with permission [155]. Copyright 2023, American Chemical Society.

  下载: 全尺寸图片 幻灯片
  

  Figure 15  (a) Controllable metal sites, organic linkers, and functional groups at Al₂(OH)₂TCPP-Co. (b) FE of Al₂(OH)₂TCPP-Co. Copied with permission [156]. Copyright 2015, American Chemical Society. (c) FE of HCOOH, CO, and H₂ for MIL-53(Al). Copied with permission [157]. Copyright 2020, American Chemical Society. (d) FE of Al-PMOFs. Copied with permission [160]. Copyright 2022, Elsevier. (e) FE of ER-HC. Copied with permission [161]. Copyright 2021, Elsevier.

  下载: 全尺寸图片 幻灯片
  

  Figure 16  (a) Schematic illustration for synthetic of In/Cu. (b) FE of In/Cu. (c) The free-energy diagrams of CO₂RR pathways for the In/Cu. Copied with permission [173]. Copyright 2021, Elsevier. (d) Schematic illustration for synthetic of Bi-In alloy NPs. (e) FE of Bi-In alloy NPs. (f) The free-energy diagrams of CO₂RR pathways for the Bi-In alloy NPs. Copied with permission [174]. Copyright 2022, Elsevier. (g) FE of Bi-In/C. (h) The free-energy diagrams of CO₂ to HCOOH for the Bi-In/C. (i). Schematic illustration of the CO₂RR device driven by a solar cell. Copied with permission [175]. Copyright 2023, Elsevier.

  下载: 全尺寸图片 幻灯片
  

  Figure 17  (a) Scheme for synthetic In/In oxide. (b) FE of In/In oxide. (c) Schematic for the CO₂RR of In/In oxide. Copied with permission [178]. Copyright 2020, American Chemical Society. (d) Schematic illustration for synthetic In/In₂O₃ Ho-nt. (e) FE of In/In₂O₃ Ho-nt. (f) The free-energy diagrams of CO₂RR pathways for the In/In₂O₃ Ho-nt. Copied with permission [179]. Copyright 2023, Elsevier. (g) Schematic illustration for synthetic Sn(101)/SnO₂/C-500. (h) FE of Sn(101)/SnO₂/C-500. (i) The free-energy diagrams of CO₂RR pathways for the Sn(101)/SnO₂/C-500. Copied with permission [181]. Copyright 2021, American Chemical Society.

  下载: 全尺寸图片 幻灯片
  

  Figure 18  (a) Schematic illustration for CO₂RR of In₂O₃@C in SEE. (b) FE of In₂O₃@C. Copied with permission [182]. Copyright 2022, Wiley Publishing Group. (c) FE of In₂O_3-C. (d) The free-energy diagrams of CO₂RR pathways for the In₂O_3-C. Copied with permission [185]. Copyright 2022, American Chemical Society. (e) Schematic illustration for in situ generation In₂O₃@In-Co PBA. (f) FE of In₂O₃@In-Co PBA. Copied with permission [186]. Copyright 2021, Elsevier.

  下载: 全尺寸图片 幻灯片
  

  Figure 19  (a) Schematic illustration for synthetic InCuO. (b) FE of InCuO. (c) Current density of InCuO. Copied with permission [188]. Copyright 2019, Royal Society of Chemistry. (d) Schematic illustration for synthetic Cu_x-Bi/Bi₂O₃@C. (e) FE of Cu_x-Bi/Bi₂O₃@C. Copied with permission [189]. Copyright 2022, Wiley Publishing Group. (f) FE of Ce-Bi@CeBiO_x/C. Copied with permission [190]. Copyright 2021, Royal Society of Chemistry.

  下载: 全尺寸图片 幻灯片
  

  Figure 20  (a) Schematic illustration for synthetic Bi₂O₃@C. (b) FE and current density of formate for Bi₂O₃@C. Copied with permission [191]. Copyright 2020, Wiley Publishing Group. (c) FE of SOR Bi@C NPs. (d) The free-energy diagrams of the CO₂RR process for the Bi (110) plane and Bi-O/Bi (110) plane. Copied with permission [194]. Copyright 2022, American Chemical Society. (e) Schematic illustration for synthetic BiS@Cx. (f) FE of BiS@Cx. Copied with permission [195]. Copyright 2022, Elsevier.

  下载: 全尺寸图片 幻灯片
  

  Figure 21  (a) Schematic illustration for synthetic In SAs/NC. (b) FE of In SAs/NC. (c) The difference in limiting potentials for CO₂ reduction and H₂ evolution on In-SAs/NC. Copied with permission [109]. Copyright 2020, Wiley Publishing Group. (d) Schematic illustration for synthetic In-N-C. (e) FE of In-N-C. (f) The free-energy diagrams of CO₂RR pathways for the In-N-C. Copied with permission [204]. Copyright 2021, American Chemical Society. (g) Schematic illustration for synthetic In SACs. (h) FE of In SACs. (i) The free-energy diagrams of CO₂RR pathways for the In SACs. Copied with permission [205]. Copyright 2022, American Chemical Society.

  下载: 全尺寸图片 幻灯片
  

  Figure 22  (a) Schematic illustration for synthetic In SACs. (b) FE of In SACs. (c) The CO₂RR reaction pathway for pr-In-N₄-(In) and pr-In-N₃-(C2). Copied with permission [206]. Copyright 2022, Tsinghua University Press. (d) Schematic illustration for synthetic InNi DS/NC. (e) FE of InNi DS/NC. (f) The free-energy diagrams of CO₂RR pathways for the InNi DS/NC. Copied with permission [207]. Copyright 2022, Wiley Publishing Group. (g) FE of Bi SAs/NC. (h) The free-energy diagrams of CO₂RR pathways for the BiN₄/C surface. Copied with permission [48]. Copyright 2019, American Chemical Society.

  下载: 全尺寸图片 幻灯片

  Table 1.  Reduction potentials of electrochemical CO₂RR.

  No.	Reaction	Potentials/V vs. RHE
  1	CO2 + e−→*CO2−	−1.49
  2	CO2 + 2H+ + 2e−→CO + H2O	−0.10
  3	CO2 + 2H+ + 2e−→HCOOH	−0.12
  4	CO2 + 4H+ + 4e−→HCHO + H2O	−0.10
  5	CO2 + 6H+ + 6e−→CH3OH + H2O	0.03
  6	CO2 + 8H+ + 8e−→CH4 + 2H2O	0.17
  7	2CO2 + 8H+ + 8e−→CH3COOH + 2H2O	0.11
  8	2CO2 + 12H+ + 12e−→C2H4 + 4H2O	−0.34
  9	2CO2 + 12H+ + 12e−→C2H5OH + 4H2O	0.09
  10	2CO2 + 14H+ + 14e−→C2H6 + 4H2O	0.14
  11	3CO2 + 18H+ + 18e−→C3H7OH + 5H2O	0.10

  下载: 导出CSV

  Table 2.  CO₂RR on p-block metal-based MOFs.

  Electrocatalyst	Electrolysis device	Electrolyte	Main product	FEmax (%)	jmain product at FEmax (mA/cm2)	Potential (V vs. RHE)	Ref.
  In-BDC	H-type cell	0.5 mol/L KHCO3	HCOOH	88	6.49	−0.669	[116]
  MFM-300(In)-e	H-type cell	0.5 mol/L EmimBF4/MeCN	HCOOH	99.1	46.1	−2.15 vs. Ag/Ag+	[120]
  MIL-68(In)-NH2	Flow cell	1.0 mol/L KHCO3	HCOOH	94.4	108	−1.1	[121]
  	MEA	1 mol/L KOH		/	800	−3.4
  ((Me2NH2+){InⅢ-[Ni(C2S2-(C6H4COO)2)2]}·3DMF·1.5H2O)	H-type cell	0.5 mol/L KHCO3	HCOOH	89.6	36	−1.3	[125]
  InCo-ABDBDC—HIN	H-type cell	0.5 mol/L EmimBF4/MeCN	C1	81.5	21.2	−2.2 vs. Ag/Ag+	[119]
  CPs@V11	H-type cell	0.5 mol/L KHCO3	HCOOH	90.1	6.87	−0.84	[126]
  In-TCPP	Flow cell	1 mol/L KOH	HCOOH	90	30	−1.0	[82]
  aNH2−MIL-68	H-type cell	0.5 mol/L EmimBF4/MeCN	HCOOH	93.3	34.2	−2.05 vs. Ag/Ag+	[162]
  SU-101	H-type cell	0.5 mol /L KHCO3	HCOOH	93.66	14.57	−1.1	[128]
  Bi-MOF	H-type cell	0.1 mol/L KHCO3	HCOOH	92.2	/	−0.9	[132]
  PZH-1	H-type cell	0.5 mol/L KOH	HCOOH	91	/	−1.1	[133]
  Bi—HHTP	Flow cell	1 mol/L KOH	HCOOH	95	/	−0.7	[134]
  V12e	H-type cell	0.5 mol/L KHCO3	HCOOH	93.2	11.78	−0.9	[135]
  Bi-FDCA	H-type cell	0.1 mol/L KHCO3	HCOOH	95.1	19.6	−1.2	[136]
  Bi-btb	H-type cell	0.5 mol/L KHCO3	HCOOH	95	5.4	−0.97	[139]
  Bi-BTB	H-type cell	0.5 mol/L KHCO3	HCOOH	96.1	12.7	−0.669	[140]
  CAU-17	H-type cell	0.1 mol/L KHCO3	HCOOH	92	/	−1.1	[138]
  Bi-enes	H-type cell	0.5 mol/L KHCO3	HCOOH	≈100	/	−0.978	[141]
  MFM-220-p	H-type cell	0.1 mol/L KHCO3	HCOOH	90.4	20.8	−1.1	[143]
  Bi-BTC	H-type cell	0.5 mol/L KOH	HCOOH	95	25	−0.9	[163]
  Sn-MOF	H-type cell	0.5 mol/L KHCO3	HCOOH	92	23.2	−1.2	[150]
  Sn—N6-MOF	H-type cell	0.5 mol/L KHCO3	HCOOH	85	23	−1.23	[151]
  Sn-DaPTA	H-type cell	0.5 mol/L KHCO3	HCOOH	85	11	−0.8	[152]
  Sn-THO	Flow cell	0.1 mol/L KHCO3	CH4	46.5	34.5	−1.6	[153]
  Sn-MOF/In6	H-type cell	0.5 mol/L KHCO3	HCOOH	97.5	16	−0.96	[154]
  CuSn—HAB	Flow cell	1 mol/L KOH	C2H5OH	56	68	−0.57	[155]
  Al2(OH)2TCPP-Co	H-type cell	0.5 mol/L K2CO3	CO	76	/	−0.7	[156]
  MIL-53(Al)	Flow cell	0.05 mol/L K2CO3	CO	21	/	−1.1	[157]
  			HCOOH	19
  Al-PMOF(Co)	H-type cell	0.1 mol/L KHCO3	CO	90	/	−0.8	[160]
  ER—HC	H-type cell	0.1 mol/L KHCO3	HCOOH	96.8	1.9	−0.88	[161]

  下载: 导出CSV

  Table 3.  CO₂RR on p-block metal-based MOF-derived catalysts.

  Electrocatalyst	Electrolysis device	Electrolyte	Main product	FEmax (%)	jmain product at FEmax (mA/cm2)	Potential (V vs. RHE)	Ref.
  In/In oxide	H-type cell	0.5 mol/L KHCO3	HCOOH	93	/	−1.1	[178]
  In/In2O3 Ho-nt	Flow cell	1 mol/L KOH	HCOOH	93	/	−0.9	[179]
  	MEA	0.1 mol/L KOH (MEA)	HCOOH	90.6	150	/
  Sn(101)/SnO2/C-500	H-type cell	0.5 mol/L KHCO3	HCOOH	93.3	8.2	−0.8	[181]
  InCuO-0.92	H-type cell	0.5 mol/L KHCO3	CO	92.1	/	−0.8	[188]
  In-Bi alloy NPs	Flow cell	1 mol/L KOH	HCOOH	97.8	250	/	[174]
  Cu1-Bi/Bi2O3@C	H-type cell	0.5 mol/L KHCO3	HCOOH	93	10.1	−0.94	[189]
  Ce-Bi@CeBiOx/C	H-type cell	0.5 mol/L KHCO3	HCOOH	96	/	−1.7	[190]
  In2O3@C	Flow cell	1 mol/L KOH	HCOOH	94	/	−1.1	[182]
  In2O3—C	Flow cell	1 mol/L KOH	HCOOH	80.5	1000	/	[185]
  In-Co PBA	H-type cell	0.1 mol/L KHCO3	HCOOH	85	/	−0.96	[186]
  Bi2O3@C-800	Flow cell	1 mol/L KOH	HCOOH	93	/	−0.28	[191]
  SOR Bi@CNPs	Flow cell	1 mol/L KOH	HCOOH	90	100	−1.12	[194]
  BiS@C800	H-type cell	0.1 mol/L KHCO3	CH3OH	78.6	/	−0.9	[195]
  In-SAs/NC	H-type cell	0.5 mol/L KHCO3	HCOOH	96	8.87	−0.65	[109]
  In—N—C	H-type cell	0.5 mol/L KHCO3	HCOOH	80	6.8	−0.79	[204]
  In@NC-1000	H-type cell	0.5 mol/L KHCO3	CO	95	/	−0.57	[205]
  In SACs-1000	H-type cell	0.5 mol/L KHCO3	CO	97	/	−0.6	[206]
  InNi DS/NC	H-type cell	0.5 mol/L KHCO3	CO	96.7	/	−0.7	[207]
  Bi SAs/NC	H-type cell	0.1 mol/L NaHCO3	CO	97	5.1	−0.5	[48]
  Cu/In	H-type cell	0.1 mol/L KHCO3	CO	95	/	−0.6	[173]
  Bi-In/C	H-type cell	0.5 mol/L KHCO3	HCOOH	94.2	33.6	−1.0	[175]

  下载: 导出CSV
•