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2024 Volume 40 Issue 3
2024, 40(3): 230404
doi: 10.3866/PKU.WHXB202304040
Abstract:
The theoretical and experimental technologies used for electrochemical characterization methods, which are essential for determining surface structures and elucidating electrochemical reaction mechanisms, have been significantly improved after more than two centuries of development. Traditional chemical methods like cyclic voltammetry (CV) can provide the exact electrochemical reaction rate in different potential ranges, which is beneficial for identifying the electrochemical performance of electrocatalytic materials. However, traditional chemical methods alone are often inadequate when it comes to achieving a deep understanding of reaction mechanisms. In this regard, spectroscopic methods, which are powerful tools to identify the active sites and intermediate species during electrochemical reactions, are widely applied to elucidate the electrochemical mechanism at a molecular or even atomic level. In this review, three molecular-vibration-spectroscopy-based electrochemical characterization technologies, viz., infrared (IR) spectroscopy, surface-enhanced Raman spectroscopy (SERS), and sum frequency generation (SFG) spectroscopy, are comprehensively reviewed and discussed. IR, SERS, and SFG are all non-destructive spectroscopic techniques with ultra-high surface sensitivity and are indispensable when detecting surface species during electrochemical reactions. Consequently, researchers have strived to combine these spectroscopic techniques with basic electrochemical instruments. In fundamental electrochemical research, detecting electrochemical reactions in model single-crystal systems and determining the structure of interfacial water molecules have been two major research topics in recent years. Single-crystal surfaces are important in fundamental electrochemical research because of their defined atom arrays and energy states, serving as model systems to help bridge experimental results and theoretical calculations. Meanwhile, the structure of interfacial water influences most electrochemical reaction processes, and as such, probing interfacial water structures is a challenging but valuable target in fundamental electrochemical research. Additionally, the application of electrochemical spectroscopic methods to analyze fuel cells has become important, and this review covers recent SERS studies of oxygen reduction reactions (ORR) and hydrogen oxidation reactions (HOR) in hydrogen fuel cells. Concurrently, electrochemical IR and SFG studies on the electrooxidation of small organic molecules are discussed. Finally, owing to the significance of lithium-ion batteries, studies of electrochemical spectroscopic methods on solid electrolyte interphase (SEI) and cathode-electrolyte interface (CEI) are becoming increasingly important and are introduced here. In conclusion, recent advances and the future developments of electrochemical spectroscopy methods are summarized in this review article.
The theoretical and experimental technologies used for electrochemical characterization methods, which are essential for determining surface structures and elucidating electrochemical reaction mechanisms, have been significantly improved after more than two centuries of development. Traditional chemical methods like cyclic voltammetry (CV) can provide the exact electrochemical reaction rate in different potential ranges, which is beneficial for identifying the electrochemical performance of electrocatalytic materials. However, traditional chemical methods alone are often inadequate when it comes to achieving a deep understanding of reaction mechanisms. In this regard, spectroscopic methods, which are powerful tools to identify the active sites and intermediate species during electrochemical reactions, are widely applied to elucidate the electrochemical mechanism at a molecular or even atomic level. In this review, three molecular-vibration-spectroscopy-based electrochemical characterization technologies, viz., infrared (IR) spectroscopy, surface-enhanced Raman spectroscopy (SERS), and sum frequency generation (SFG) spectroscopy, are comprehensively reviewed and discussed. IR, SERS, and SFG are all non-destructive spectroscopic techniques with ultra-high surface sensitivity and are indispensable when detecting surface species during electrochemical reactions. Consequently, researchers have strived to combine these spectroscopic techniques with basic electrochemical instruments. In fundamental electrochemical research, detecting electrochemical reactions in model single-crystal systems and determining the structure of interfacial water molecules have been two major research topics in recent years. Single-crystal surfaces are important in fundamental electrochemical research because of their defined atom arrays and energy states, serving as model systems to help bridge experimental results and theoretical calculations. Meanwhile, the structure of interfacial water influences most electrochemical reaction processes, and as such, probing interfacial water structures is a challenging but valuable target in fundamental electrochemical research. Additionally, the application of electrochemical spectroscopic methods to analyze fuel cells has become important, and this review covers recent SERS studies of oxygen reduction reactions (ORR) and hydrogen oxidation reactions (HOR) in hydrogen fuel cells. Concurrently, electrochemical IR and SFG studies on the electrooxidation of small organic molecules are discussed. Finally, owing to the significance of lithium-ion batteries, studies of electrochemical spectroscopic methods on solid electrolyte interphase (SEI) and cathode-electrolyte interface (CEI) are becoming increasingly important and are introduced here. In conclusion, recent advances and the future developments of electrochemical spectroscopy methods are summarized in this review article.
2024, 40(3): 230403
doi: 10.3866/PKU.WHXB202304036
Abstract:
Near-neutral zinc-air batteries show great promise for long-cycle applications in ambient air owing to their impressive deposition/stripping compatibility with zinc anodes and greater chemical stability towards CO2 in ambient air compared to batteries with traditional alkaline electrolytes. However, the inherent water volatilization of liquid electrolytes and the flexibility of electrolytes required for wearable devices severely limit the practical application of this system. In this study, a fumed SiO2-based composite hydrogel polymer electrolyte (SiO2-HPE) was prepared for application in near-neutral zinc-air batteries. The design of the SiO2-HPE was carried out considering the following three aspects. Firstly, it is widely acknowledged that the polyacrylamide polymer skeleton is beneficial to excellent ionic conductivity and the mechanical strength of the SiO2-HPE. Secondly, fumed SiO2 bearing multiple silicon hydroxyl groups is a suitable option as a water-retaining additive. Thirdly, the near-neutral liquid electrolyte (1 mol·kg-1 Zn(OTf)2) absorbed in the SiO2-HPE is stable towards CO2 in ambient air. In conclusion, these three aspects of the electrolyte design contribute to the practical application of the SiO2-HPE. Raman spectroscopy and scanning electron microscopy revealed that the synthesized SiO2-HPE exhibited a high degree of polymerization, plentiful surface pores, and a uniform distribution of elements. According to the infrared and Raman spectra, the abundant hydroxyl groups located on the surface of the SiO2 particles enhanced water molecule binding by altering the hydrogen bond network within the SiO2-HPE. This conclusion was further confirmed by thermogravimetry and differential scanning calorimetry. After exposure to ambient air (30% relative humidity) for 96 h, the SiO2-HPE exhibited a water retention capacity of 49.52%, which is 6.23% and 1.73% higher than those for 1 mol·kg-1 Zn(OTf)2 and the HPE (hydrogel polymer electrolyte without SiO2). Moreover, owing to the dynamic recombination of the hydrogen bonds between the silicon hydroxyl groups and the gel skeleton, SiO2-HPE exhibited a higher mechanical strength and modulus than HPE under tensile and compressive conditions, respectively. This further rendered it an ideal electrolyte for flexible zinc-air batteries. The near-neutral zinc-air battery assembled with the SiO2-HPE exhibited a cycle life of up to 200 h under 30% relative humidity, far exceeding those of 1 mol·kg-1 Zn(OTf)2 and the HPE. Based on such remarkable performance, the flexible near-neutral zinc-air battery device assembled by the SiO2-HPE has shown a satisfactory performance under special conditions, such as bending and cutting, and can be used as a power supply for different electronic devices, making it a promising next-generation electrochemical energy storage device. Overall, this work provides new insight into the development of flexible zinc-air battery devices with long-term stability in ambient air.
Near-neutral zinc-air batteries show great promise for long-cycle applications in ambient air owing to their impressive deposition/stripping compatibility with zinc anodes and greater chemical stability towards CO2 in ambient air compared to batteries with traditional alkaline electrolytes. However, the inherent water volatilization of liquid electrolytes and the flexibility of electrolytes required for wearable devices severely limit the practical application of this system. In this study, a fumed SiO2-based composite hydrogel polymer electrolyte (SiO2-HPE) was prepared for application in near-neutral zinc-air batteries. The design of the SiO2-HPE was carried out considering the following three aspects. Firstly, it is widely acknowledged that the polyacrylamide polymer skeleton is beneficial to excellent ionic conductivity and the mechanical strength of the SiO2-HPE. Secondly, fumed SiO2 bearing multiple silicon hydroxyl groups is a suitable option as a water-retaining additive. Thirdly, the near-neutral liquid electrolyte (1 mol·kg-1 Zn(OTf)2) absorbed in the SiO2-HPE is stable towards CO2 in ambient air. In conclusion, these three aspects of the electrolyte design contribute to the practical application of the SiO2-HPE. Raman spectroscopy and scanning electron microscopy revealed that the synthesized SiO2-HPE exhibited a high degree of polymerization, plentiful surface pores, and a uniform distribution of elements. According to the infrared and Raman spectra, the abundant hydroxyl groups located on the surface of the SiO2 particles enhanced water molecule binding by altering the hydrogen bond network within the SiO2-HPE. This conclusion was further confirmed by thermogravimetry and differential scanning calorimetry. After exposure to ambient air (30% relative humidity) for 96 h, the SiO2-HPE exhibited a water retention capacity of 49.52%, which is 6.23% and 1.73% higher than those for 1 mol·kg-1 Zn(OTf)2 and the HPE (hydrogel polymer electrolyte without SiO2). Moreover, owing to the dynamic recombination of the hydrogen bonds between the silicon hydroxyl groups and the gel skeleton, SiO2-HPE exhibited a higher mechanical strength and modulus than HPE under tensile and compressive conditions, respectively. This further rendered it an ideal electrolyte for flexible zinc-air batteries. The near-neutral zinc-air battery assembled with the SiO2-HPE exhibited a cycle life of up to 200 h under 30% relative humidity, far exceeding those of 1 mol·kg-1 Zn(OTf)2 and the HPE. Based on such remarkable performance, the flexible near-neutral zinc-air battery device assembled by the SiO2-HPE has shown a satisfactory performance under special conditions, such as bending and cutting, and can be used as a power supply for different electronic devices, making it a promising next-generation electrochemical energy storage device. Overall, this work provides new insight into the development of flexible zinc-air battery devices with long-term stability in ambient air.
2024, 40(3): 230404
doi: 10.3866/PKU.WHXB202304044
Abstract:
The development of efficient synthetic routes for ammonia (NH3) production is the cornerstone of the modern industrial processes and human survival. Owing to the chemical inertness of nitrogen, the current ammonia industry suffers from high energy consumption and high CO2 emission. Electrochemical nitrogen reduction reaction (NRR) provides a promising alternative to the energy-intensive Haber-Bosch (HB) process, enabling green and sustainable NH3 production. However, a low NH3 yield and limited energy conversion efficiency due to the chemical inertness of N2 and competitive hydrogen evolution reaction (HER) are still critical challenges in artificial nitrogen fixation using the electrochemical NRR. Herein, we report a hole-enriched P-doped carbon (PC)-supported Zn3(PO4)2/Zn2P2O7 nanocomposite (h-PC/Zn3(PO4)2/Zn2P2O7) for efficient electrocatalytic conversion of N2 to NH3 in both acidic and neutral media. Remarkably, the unique hierarchical porous structure of the h-PC/Zn3(PO4)2/Zn2P2O7 catalyst improves the surface roughness and facilitates the diffusion of N2 within the catalyst layer, thereby prolonging the residence time of N2 and improving the utilization of active sites. The uniform distribution of multiple components modulates the electronic structure of the active sites and optimizes the adsorption behavior of various reaction intermediates, enhancing the intrinsic activity of the catalyst. Benefiting from the porous structure and multicomponent active sites, including the Zn species and PC, the h-PC/Zn3(PO4)2/Zn2P2O7 achieves an excellent NRR performance with an NH3 yield rate of 38.7 ± 1.2 μg·h-1·mgcat-1 and Faradaic efficiency (FE) of 19.8% ± 0.9% at -0.2 V vs. reversible hydrogen electrode (RHE) in 0.1 mol·L-1 HCl electrolyte. Moreover, it delivers a high NH3 yield rate of 17.1 ± 0.8 μg·h-1·mgcat-1 with an FE of 15.9% ± 0.6% at -0.2 V vs. RHE in 0.1 mol·L-1 Na2SO4 solution, which is superior to those of PC/Zn3P2, C/ZnO, and many other non-noble-metal-based electrocatalysts. Ex situ X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and X-ray diffraction (XRD) studies were conducted to monitor the changes in the composition and structure of h-PC/Zn3(PO4)2/Zn2P2O7 after being used in NRR. In particular, a new signal of N appeared in the XPS profile after NRR, confirming the occurrence of NRR. This work provides a new strategy for synchronously constructing mass transfer channels and coupling different active sites to synergistically enhance the NRR activity and selectivity of a catalyst, which is of great significance in progressing the industrialization of green ammonia production.
The development of efficient synthetic routes for ammonia (NH3) production is the cornerstone of the modern industrial processes and human survival. Owing to the chemical inertness of nitrogen, the current ammonia industry suffers from high energy consumption and high CO2 emission. Electrochemical nitrogen reduction reaction (NRR) provides a promising alternative to the energy-intensive Haber-Bosch (HB) process, enabling green and sustainable NH3 production. However, a low NH3 yield and limited energy conversion efficiency due to the chemical inertness of N2 and competitive hydrogen evolution reaction (HER) are still critical challenges in artificial nitrogen fixation using the electrochemical NRR. Herein, we report a hole-enriched P-doped carbon (PC)-supported Zn3(PO4)2/Zn2P2O7 nanocomposite (h-PC/Zn3(PO4)2/Zn2P2O7) for efficient electrocatalytic conversion of N2 to NH3 in both acidic and neutral media. Remarkably, the unique hierarchical porous structure of the h-PC/Zn3(PO4)2/Zn2P2O7 catalyst improves the surface roughness and facilitates the diffusion of N2 within the catalyst layer, thereby prolonging the residence time of N2 and improving the utilization of active sites. The uniform distribution of multiple components modulates the electronic structure of the active sites and optimizes the adsorption behavior of various reaction intermediates, enhancing the intrinsic activity of the catalyst. Benefiting from the porous structure and multicomponent active sites, including the Zn species and PC, the h-PC/Zn3(PO4)2/Zn2P2O7 achieves an excellent NRR performance with an NH3 yield rate of 38.7 ± 1.2 μg·h-1·mgcat-1 and Faradaic efficiency (FE) of 19.8% ± 0.9% at -0.2 V vs. reversible hydrogen electrode (RHE) in 0.1 mol·L-1 HCl electrolyte. Moreover, it delivers a high NH3 yield rate of 17.1 ± 0.8 μg·h-1·mgcat-1 with an FE of 15.9% ± 0.6% at -0.2 V vs. RHE in 0.1 mol·L-1 Na2SO4 solution, which is superior to those of PC/Zn3P2, C/ZnO, and many other non-noble-metal-based electrocatalysts. Ex situ X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and X-ray diffraction (XRD) studies were conducted to monitor the changes in the composition and structure of h-PC/Zn3(PO4)2/Zn2P2O7 after being used in NRR. In particular, a new signal of N appeared in the XPS profile after NRR, confirming the occurrence of NRR. This work provides a new strategy for synchronously constructing mass transfer channels and coupling different active sites to synergistically enhance the NRR activity and selectivity of a catalyst, which is of great significance in progressing the industrialization of green ammonia production.
2024, 40(3): 230404
doi: 10.3866/PKU.WHXB202304046
Abstract:
Owing to the increasingly serious environmental problems, there is an urgent need for clean energy with a high energy density and low carbon emissions. As such, electrocatalytic water decomposition has attracted significant interest as an efficient hydrogen production method. The electrolysis of water has two important half-reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Among these two reactions, OER is considered to be the crucial and rate-determining step due to its slower kinetic process and higher overpotential compared to HER. Although noble metal oxides such as IrO2 and RuO2 have excellent OER properties under alkaline conditions, their high cost and scarcity limit their commercial application. Therefore, it is of significant interest to develop alternative OER electrodes with excellent catalytic activity, extremely low overpotential, high durability, and low cost. Ni2P has attracted interest as an electrocatalyst and has improved activity after combination with a cocatalyst. The improved activity is due to heterojunction formation changing the electronic structure and charge transport at the active site. To this end, a novel highly efficient Cu3P/Ni2P heterojunction catalyst has been successfully constructed, in which Cu3P functions solely as a cocatalyst to enhance the electrocatalytic activity by regulating the electron transfer and surface reconstruction of Ni2P. Consequently, Cu3P/Ni2P exhibits superior OER activity and has an ultra-low overpotential of 213 mV at a current density of 10 mA·cm-2 and a small Tafel slope of 62 mV·dec-1 in 1 mol·L-1 KOH. Additionally, this peculiar self-supporting electrode possesses excellent electrochemical stability and long-term durability at a current density of 10 mA·cm-2 in an alkaline medium. Through a combination of experimental results and theoretical calculations, it has been shown that the Cu3P cocatalyst effectively tailors the electronic structure of the Ni center. This results in charge redistribution and a lower reaction energy barrier, thereby significantly improving the OER catalytic activity. In addition, the abundant grain boundaries and lattice distortions induced by the Cu3P cocatalyst promote surface reconstruction to form Ni5O(OH)9, providing an efficient active site for OER. This work constructed a novel heterojunction electrocatalyst by introducing a cocatalyst, offering an avenue for the optimization of the electrocatalytic performance of transition metal phosphide.
Owing to the increasingly serious environmental problems, there is an urgent need for clean energy with a high energy density and low carbon emissions. As such, electrocatalytic water decomposition has attracted significant interest as an efficient hydrogen production method. The electrolysis of water has two important half-reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Among these two reactions, OER is considered to be the crucial and rate-determining step due to its slower kinetic process and higher overpotential compared to HER. Although noble metal oxides such as IrO2 and RuO2 have excellent OER properties under alkaline conditions, their high cost and scarcity limit their commercial application. Therefore, it is of significant interest to develop alternative OER electrodes with excellent catalytic activity, extremely low overpotential, high durability, and low cost. Ni2P has attracted interest as an electrocatalyst and has improved activity after combination with a cocatalyst. The improved activity is due to heterojunction formation changing the electronic structure and charge transport at the active site. To this end, a novel highly efficient Cu3P/Ni2P heterojunction catalyst has been successfully constructed, in which Cu3P functions solely as a cocatalyst to enhance the electrocatalytic activity by regulating the electron transfer and surface reconstruction of Ni2P. Consequently, Cu3P/Ni2P exhibits superior OER activity and has an ultra-low overpotential of 213 mV at a current density of 10 mA·cm-2 and a small Tafel slope of 62 mV·dec-1 in 1 mol·L-1 KOH. Additionally, this peculiar self-supporting electrode possesses excellent electrochemical stability and long-term durability at a current density of 10 mA·cm-2 in an alkaline medium. Through a combination of experimental results and theoretical calculations, it has been shown that the Cu3P cocatalyst effectively tailors the electronic structure of the Ni center. This results in charge redistribution and a lower reaction energy barrier, thereby significantly improving the OER catalytic activity. In addition, the abundant grain boundaries and lattice distortions induced by the Cu3P cocatalyst promote surface reconstruction to form Ni5O(OH)9, providing an efficient active site for OER. This work constructed a novel heterojunction electrocatalyst by introducing a cocatalyst, offering an avenue for the optimization of the electrocatalytic performance of transition metal phosphide.
2024, 40(3): 230500
doi: 10.3866/PKU.WHXB202305007
Abstract:
Li-ion batteries (LIBs) have been considered as one of the most promising power sources for electric vehicles, portable electronics and electrical equipment because of their long cycle life and high energy density. The free-standing electrodes without binder, current collector and conductive agent can effectively obtain lager energy density as compared to the traditional electrodes where the addition of inactive components is required. In addition, the free-standing electrode plays an important role in developing flexible electronic devices. Currently, conventional graphite is still the main commercial anode material, but its theoretical specific capacity is limited, and the rate performance is poor. In recent years, the high temperature pyrolytic hard carbon has attracted wide attention due to its higher theoretical specific capacity and more defects than graphite carbon. Moreover, polymer polyacrylonitrile (PAN) can be used as the raw material for preparation of free-standing anodes without any conductive additives or binders by electrospinning technique. Meanwhile, it is beneficial to reduce the production cost and simplify the manufacturing procedures of electrode. However, PAN-based hard carbon anode materials also have certain problems, such as low conductivity, poor rate performance, unsatisfactory cycling stability, and inferior initial Coulombic efficiency (CE). In addition, soft carbon has advantages of high carbon yield, good conductivity, superior cycling stability, high initial CE and relatively low price, but its specific capacity is generally lower than that of hard carbon materials. Based on above analysis, carbon anode materials with good electrochemical performance can be obtained by combining hard carbon and soft carbon, but the specific capacity of carbon materials is still low. Tin (Sn), as an anode material for LIBs, has a high theoretical specific capacity (994 mAh·g-1) and a low lithium alloying voltage. Nonetheless, the practical use of Sn anode has been limited by its huge volume change (theoretically ∼260%) during the repeated alloying-dealloying process, resulting in large pulverization and cracking, which triggers the rapid capacity fading. Hence, in order to increase the specific capacity of carbon anode materials of LIBs, the C-Sn composite film with uniform Sn nanoparticles embedded in N-doped carbon nanofibers was prepared by electrospinning method following by a low-temperature carbonization process. The film was directly used as a free-standing electrode for LIBs and exhibited good electrochemical performance, and the introduction of Sn significantly improved the electrochemical properties of the carbon nanofiber film. The formed fibrous structure after Sn was uniformly coated with carbon can promote the conduction of ions and electrons, and effectively buffers the volume change of Sn nanoparticles during cycling, thus effectively preventing pulverization and agglomeration. The C-Sn-2 electrode with a Sn content of about 25.6% has the highest specific capacity and best rate performance among all samples. The electrochemical test results show that, the charge (discharge) capacity reaches 412.7 (413.5) mAh·g-1 at a current density of 2 A·g-1 even after 1000 cycles. Density functional theory (DFT) calculations show that N-doped amorphous carbon has good affinity with lithium, which is conducive to anchoring the SnxLiy alloy formed after alloying reaction on the carbon surface, thereby relieving the volume change of Sn during charge-discharge. This article provides a feasible strategy for the design of high-performance lithium storage materials.
Li-ion batteries (LIBs) have been considered as one of the most promising power sources for electric vehicles, portable electronics and electrical equipment because of their long cycle life and high energy density. The free-standing electrodes without binder, current collector and conductive agent can effectively obtain lager energy density as compared to the traditional electrodes where the addition of inactive components is required. In addition, the free-standing electrode plays an important role in developing flexible electronic devices. Currently, conventional graphite is still the main commercial anode material, but its theoretical specific capacity is limited, and the rate performance is poor. In recent years, the high temperature pyrolytic hard carbon has attracted wide attention due to its higher theoretical specific capacity and more defects than graphite carbon. Moreover, polymer polyacrylonitrile (PAN) can be used as the raw material for preparation of free-standing anodes without any conductive additives or binders by electrospinning technique. Meanwhile, it is beneficial to reduce the production cost and simplify the manufacturing procedures of electrode. However, PAN-based hard carbon anode materials also have certain problems, such as low conductivity, poor rate performance, unsatisfactory cycling stability, and inferior initial Coulombic efficiency (CE). In addition, soft carbon has advantages of high carbon yield, good conductivity, superior cycling stability, high initial CE and relatively low price, but its specific capacity is generally lower than that of hard carbon materials. Based on above analysis, carbon anode materials with good electrochemical performance can be obtained by combining hard carbon and soft carbon, but the specific capacity of carbon materials is still low. Tin (Sn), as an anode material for LIBs, has a high theoretical specific capacity (994 mAh·g-1) and a low lithium alloying voltage. Nonetheless, the practical use of Sn anode has been limited by its huge volume change (theoretically ∼260%) during the repeated alloying-dealloying process, resulting in large pulverization and cracking, which triggers the rapid capacity fading. Hence, in order to increase the specific capacity of carbon anode materials of LIBs, the C-Sn composite film with uniform Sn nanoparticles embedded in N-doped carbon nanofibers was prepared by electrospinning method following by a low-temperature carbonization process. The film was directly used as a free-standing electrode for LIBs and exhibited good electrochemical performance, and the introduction of Sn significantly improved the electrochemical properties of the carbon nanofiber film. The formed fibrous structure after Sn was uniformly coated with carbon can promote the conduction of ions and electrons, and effectively buffers the volume change of Sn nanoparticles during cycling, thus effectively preventing pulverization and agglomeration. The C-Sn-2 electrode with a Sn content of about 25.6% has the highest specific capacity and best rate performance among all samples. The electrochemical test results show that, the charge (discharge) capacity reaches 412.7 (413.5) mAh·g-1 at a current density of 2 A·g-1 even after 1000 cycles. Density functional theory (DFT) calculations show that N-doped amorphous carbon has good affinity with lithium, which is conducive to anchoring the SnxLiy alloy formed after alloying reaction on the carbon surface, thereby relieving the volume change of Sn during charge-discharge. This article provides a feasible strategy for the design of high-performance lithium storage materials.
2024, 40(3): 230501
doi: 10.3866/PKU.WHXB202305012
Abstract:
Conventional oxidation methods of sterol intermediates using the heavy metal chromium as an oxidant has critical drawbacks, such as high toxicity and environmental pollution. Electrocatalytic oxidation (ECO), on the other hand, is considered a promising alternative to conventional processes owing to its high efficiency, eco-friendliness, and controllability. However, ECO currently faces two major challenges: low current densities and reduced space-time yields. In this study, a single-step solvothermal method was employed to synthesize self-supported nickel-iron metal-organic framework (NiFe-MOF) nanosheet electrocatalysts on graphite felt. Various analytical techniques were employed to comprehensively characterize the synthesized NiFe-MOF, including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and Brunauer-Emmett-Teller (BET) analysis Furthermore, we implemented a synergistic electrocatalytic strategy by combining the NiFe-MOF catalyst with aminoxyl radicals, i.e., 4-acetamido-2,2,6,6-tetramethyl-1-piperidine-N-oxyl (ACT), to enhance the performance of the ECO reaction. According to the results of structural characterization, the synthesized NiFe-MOF exhibited an amorphous nanosheet structure with a high specific surface area and microporosity. Moreover, we successfully achieved continuous flow with enhanced mass transfer during the electrocatalytic oxidation of 19-hydroxy-4-androstene-3,17-dione (1a) at a current density of 100 mA·cm-2. The optimal reaction conditions for the ECO reaction were as follows: 100 mmol·L-1 concentration of 1a, 10% (molar fraction) of ACT, a 1 mol·L-1 Na2CO3/acetonitrile electrolyte (6: 4), room temperature, pH 12.5, and a flow rate of 225 mL·min-1. Under these conditions, the conversion and selectivity of the reaction reached outstanding levels of 99 and 98%, respectively. Moreover, the space-time yield was calculated to be as high as 15.88 kg·m-3·h-1, with a remarkable 35-fold increase compared to that achieved in a batch reactor. The NiFe-MOF/ACT synergistic system demonstrated a high conversion rate for ECO even after 10 reaction cycles. To assess the system’s efficacy in converting other sterols, we conducted an analysis of substrate expansion, which yielded conversion rates exceeding 95%. The SEM, TEM, and XPS results of the catalyst obtained before and after the reaction indicated that the alkaline electrolyte could effectively reconstitute the NiFe-MOF structure, leading to a significant improvement in its performance. By leveraging a ten-fold increased surface area of the NiFe-MOF and constructing a continuous flow electroreactor for ECO with a constant current, we achieved a remarkable space-time yield of 12.99 kg·m-3·h-1. Thus, we developed a synergistic electrocatalytic oxidation strategy based on NiFe-MOF/ACT, and this study not only provides valuable insights for realizing the selective oxidation of sterols but also contributes to the advancement of sustainable and efficient chemical processes.
Conventional oxidation methods of sterol intermediates using the heavy metal chromium as an oxidant has critical drawbacks, such as high toxicity and environmental pollution. Electrocatalytic oxidation (ECO), on the other hand, is considered a promising alternative to conventional processes owing to its high efficiency, eco-friendliness, and controllability. However, ECO currently faces two major challenges: low current densities and reduced space-time yields. In this study, a single-step solvothermal method was employed to synthesize self-supported nickel-iron metal-organic framework (NiFe-MOF) nanosheet electrocatalysts on graphite felt. Various analytical techniques were employed to comprehensively characterize the synthesized NiFe-MOF, including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and Brunauer-Emmett-Teller (BET) analysis Furthermore, we implemented a synergistic electrocatalytic strategy by combining the NiFe-MOF catalyst with aminoxyl radicals, i.e., 4-acetamido-2,2,6,6-tetramethyl-1-piperidine-N-oxyl (ACT), to enhance the performance of the ECO reaction. According to the results of structural characterization, the synthesized NiFe-MOF exhibited an amorphous nanosheet structure with a high specific surface area and microporosity. Moreover, we successfully achieved continuous flow with enhanced mass transfer during the electrocatalytic oxidation of 19-hydroxy-4-androstene-3,17-dione (1a) at a current density of 100 mA·cm-2. The optimal reaction conditions for the ECO reaction were as follows: 100 mmol·L-1 concentration of 1a, 10% (molar fraction) of ACT, a 1 mol·L-1 Na2CO3/acetonitrile electrolyte (6: 4), room temperature, pH 12.5, and a flow rate of 225 mL·min-1. Under these conditions, the conversion and selectivity of the reaction reached outstanding levels of 99 and 98%, respectively. Moreover, the space-time yield was calculated to be as high as 15.88 kg·m-3·h-1, with a remarkable 35-fold increase compared to that achieved in a batch reactor. The NiFe-MOF/ACT synergistic system demonstrated a high conversion rate for ECO even after 10 reaction cycles. To assess the system’s efficacy in converting other sterols, we conducted an analysis of substrate expansion, which yielded conversion rates exceeding 95%. The SEM, TEM, and XPS results of the catalyst obtained before and after the reaction indicated that the alkaline electrolyte could effectively reconstitute the NiFe-MOF structure, leading to a significant improvement in its performance. By leveraging a ten-fold increased surface area of the NiFe-MOF and constructing a continuous flow electroreactor for ECO with a constant current, we achieved a remarkable space-time yield of 12.99 kg·m-3·h-1. Thus, we developed a synergistic electrocatalytic oxidation strategy based on NiFe-MOF/ACT, and this study not only provides valuable insights for realizing the selective oxidation of sterols but also contributes to the advancement of sustainable and efficient chemical processes.
2024, 40(3): 230501
doi: 10.3866/PKU.WHXB202305016
Abstract:
Solid-state lithium batteries (SSLBs) have the potential to further boost the energy density of Li-ion batteries and improve their safety by facilitating the use of Li-metal anodes and limiting flammability, respectively. Solid electrolytes, as key SSLB materials, significantly impact battery performance, among which composite polymer/garnet electrolytes are promising materials for manufacturing SSLBs on a large scale, owing to polymer electrolyte processing ease in combination with the thermal stabilities and high ionic conductivities of garnet electrolytes, both of which are beneficial. Uniformly dispersing garnet particles in the polymer matrix is important for ensuring a highly ionically conductive composite polymer electrolyte. However, high nanoparticle surface energies and incompatible organic–inorganic interfaces lead to garnet particle agglomeration in the polymer matrix and a poorly ionically conductive composite electrolyte. With the aim of promoting Li6.4La3Zr1.4Ta0.6O12 (LLZTO) particle dispersion in both solvents and polymer matrices, in this study, we introduced the 3-glycidyloxypropyl trimethoxy silane (GPTMS) coupling agent onto the LLZTO surface. A 5-nm-thick GPTMS shell was constructed on each LLZTO nanoparticle by covalently bonding GPTMS molecules on the surface of the nanoparticle. The lipophilic epoxy group in GPTMS enables the uniform dispersion of GPTMS-modified LLZTO nanoparticles (LLZTO@GPTMS) in organic solvents, such as acetonitrile, N-methylpyrrolidone, and N,N-dimethylformamide. Particle-size-distribution experiments reveal that LLZTO-nanoparticle dispersity is positively correlated with solvent polarity. Well-dispersed LLZTO suspensions led to superior polyethylene-oxide-based (PEO-based) composite polymer electrolyte ionic conductivities of 2.31 × 10-4 S·cm-1 at 30 °C. Both symmetric lithium batteries and SSLBs that use LiFePO4 (LFP) cathodes, lithium-metal anodes, and the optimal PEO: LLZTO@GPTMS electrolyte exhibited prolonged cycling lives. Moreover, the polyethylene separator was homogeneously coated with LLZTO nanoparticles following GPTMS modification. LFP|Li batteries with LLZTO@GPTMS-coated PE separators exhibited better cycling stabilities than those of batteries with unmodified LLZTO/PE. This study demonstrated that GPTMS effectively improves LLZTO-nanoparticle dispersibility in both organic solvents and polymer matrices, which is also instructive for other organic–inorganic composite systems.
Solid-state lithium batteries (SSLBs) have the potential to further boost the energy density of Li-ion batteries and improve their safety by facilitating the use of Li-metal anodes and limiting flammability, respectively. Solid electrolytes, as key SSLB materials, significantly impact battery performance, among which composite polymer/garnet electrolytes are promising materials for manufacturing SSLBs on a large scale, owing to polymer electrolyte processing ease in combination with the thermal stabilities and high ionic conductivities of garnet electrolytes, both of which are beneficial. Uniformly dispersing garnet particles in the polymer matrix is important for ensuring a highly ionically conductive composite polymer electrolyte. However, high nanoparticle surface energies and incompatible organic–inorganic interfaces lead to garnet particle agglomeration in the polymer matrix and a poorly ionically conductive composite electrolyte. With the aim of promoting Li6.4La3Zr1.4Ta0.6O12 (LLZTO) particle dispersion in both solvents and polymer matrices, in this study, we introduced the 3-glycidyloxypropyl trimethoxy silane (GPTMS) coupling agent onto the LLZTO surface. A 5-nm-thick GPTMS shell was constructed on each LLZTO nanoparticle by covalently bonding GPTMS molecules on the surface of the nanoparticle. The lipophilic epoxy group in GPTMS enables the uniform dispersion of GPTMS-modified LLZTO nanoparticles (LLZTO@GPTMS) in organic solvents, such as acetonitrile, N-methylpyrrolidone, and N,N-dimethylformamide. Particle-size-distribution experiments reveal that LLZTO-nanoparticle dispersity is positively correlated with solvent polarity. Well-dispersed LLZTO suspensions led to superior polyethylene-oxide-based (PEO-based) composite polymer electrolyte ionic conductivities of 2.31 × 10-4 S·cm-1 at 30 °C. Both symmetric lithium batteries and SSLBs that use LiFePO4 (LFP) cathodes, lithium-metal anodes, and the optimal PEO: LLZTO@GPTMS electrolyte exhibited prolonged cycling lives. Moreover, the polyethylene separator was homogeneously coated with LLZTO nanoparticles following GPTMS modification. LFP|Li batteries with LLZTO@GPTMS-coated PE separators exhibited better cycling stabilities than those of batteries with unmodified LLZTO/PE. This study demonstrated that GPTMS effectively improves LLZTO-nanoparticle dispersibility in both organic solvents and polymer matrices, which is also instructive for other organic–inorganic composite systems.
2024, 40(3): 230502
doi: 10.3866/PKU.WHXB202305021
Abstract:
Co-based oxides have shown promise as catalysts for the oxygen evolution reaction (OER), as evidenced by experimental and theoretical studies. However, these common Co-based catalysts suffer from poor stability in acidic environments, making them susceptible to corrosion in acid electrolytes. Consequently, developing OER catalysts that can maintain both activity and stability under strongly acidic conditions is a challenging task for large-scale industrial hydrogen production applications. To address this challenge, the incorporation of manganese (Mn) into the spinel lattice of Co3O4 (CoMn1O) has been proposed, resulting in a defect-rich catalyst with improved lifetime in acidic electrolytes. The crystalline phase structures and chemical valence states were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and energy-dispersive spectroscopy (EDS) elemental maps. The introduction of Mn led to the generation of a significant number of defects due to changes in the local crystal structure. Additionally, as the amount of Mn atoms increased, a red shift was observed in the Co 2p spectrum, indicating an increase in the overall valence of Co and the formation of more stable Co―O bonds. Moreover, when the Mn-to-Co ratio reached 1 (CoMn1O), the resulting catalyst exhibited promising OER activity, with overpotentials of 415 and 552 mV at 10 and 50 mA·cm-2, respectively. Detailed physical characterization and electrochemical tests demonstrated that CoMn1O exhibited over four times the stability of Mn-free Co3O4 (CoMn0O). This enhanced stability can be attributed to the introduction of Mn, which promotes electron density bias of Co towards O, resulting in the formation of more stable Co―O bonds. Mn also facilitates acidic oxygen evolution by delaying the oxidation rate of the Co active sites, thereby enhancing stability. Density functional theory (DFT) calculations were further employed to analyze the electronic structures of CoMn1O and CoMn0O. The d-band center of Co 3d (εd) in CoMn1O shifted closer to the Fermi level (EF) compared to that of CoMn0O, indicating a reduced reaction energy barrier for CoMn1O and enhanced bonding interaction with OER intermediates. Overall, this work presents a promising strategy for achieving highly efficient and stable acidic oxygen evolution using noble-metal-free electrocatalysts.
Co-based oxides have shown promise as catalysts for the oxygen evolution reaction (OER), as evidenced by experimental and theoretical studies. However, these common Co-based catalysts suffer from poor stability in acidic environments, making them susceptible to corrosion in acid electrolytes. Consequently, developing OER catalysts that can maintain both activity and stability under strongly acidic conditions is a challenging task for large-scale industrial hydrogen production applications. To address this challenge, the incorporation of manganese (Mn) into the spinel lattice of Co3O4 (CoMn1O) has been proposed, resulting in a defect-rich catalyst with improved lifetime in acidic electrolytes. The crystalline phase structures and chemical valence states were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and energy-dispersive spectroscopy (EDS) elemental maps. The introduction of Mn led to the generation of a significant number of defects due to changes in the local crystal structure. Additionally, as the amount of Mn atoms increased, a red shift was observed in the Co 2p spectrum, indicating an increase in the overall valence of Co and the formation of more stable Co―O bonds. Moreover, when the Mn-to-Co ratio reached 1 (CoMn1O), the resulting catalyst exhibited promising OER activity, with overpotentials of 415 and 552 mV at 10 and 50 mA·cm-2, respectively. Detailed physical characterization and electrochemical tests demonstrated that CoMn1O exhibited over four times the stability of Mn-free Co3O4 (CoMn0O). This enhanced stability can be attributed to the introduction of Mn, which promotes electron density bias of Co towards O, resulting in the formation of more stable Co―O bonds. Mn also facilitates acidic oxygen evolution by delaying the oxidation rate of the Co active sites, thereby enhancing stability. Density functional theory (DFT) calculations were further employed to analyze the electronic structures of CoMn1O and CoMn0O. The d-band center of Co 3d (εd) in CoMn1O shifted closer to the Fermi level (EF) compared to that of CoMn0O, indicating a reduced reaction energy barrier for CoMn1O and enhanced bonding interaction with OER intermediates. Overall, this work presents a promising strategy for achieving highly efficient and stable acidic oxygen evolution using noble-metal-free electrocatalysts.
2024, 40(3): 230503
doi: 10.3866/PKU.WHXB202305039
Abstract:
Solid electrolyte interphase (SEI) layers derived from the side reactions between Li metal anode and electrolyte, have great impacts on the electrochemical performance of lithium batteries. In solid-state batteries, SEI layers are also required as the electrical insulators but an ionic conductors, and the mechanical reinforcements for withstanding volume change and suppressing dendritic growth in Li metal anode. Introducing LiF substrates into SEI layers can significantly reduce the electron tunneling ability from Li anode to SEI layer, meanwhile providing the excellent interfacial mechanical strength. However, LiF has a very high energy barrier for ion diffusion, hindering the rapid lithium ion diffusion from SEI layer to lithium anode. Therefore, it is necessary to introduce lithium alloy phases with higher ionic conductivity into the LiF matrix to provide sufficient ion diffusion channels. By the data mining technology, high-throughput first-principle calculation and ab-initio molecular dynamics simulations, this work performed phase diagram and ion diffusion energy barrier calculations to evaluate the thermodynamic stabilities and lithium diffusion abilities of several lithium alloys. 27 lithium alloys that can be used as Li-ion conducting phases in the LiF-based artificial SEI layers are screened. Meanwhile, the structure-function relationship analysis of lithium alloys uncovers that the crystal structure type of lithium alloys has more significant impacts on lithium ion diffusion than alloy elements, that is, lithium alloy structures with the space group of I43d and Fm3m have very excellent lithium ion transport performance, while the diffusion channels of lithium alloy structures with the space group of Pm3m and F43m are narrow, leading to the poor lithium ion transport performance. In addition, this work uncovers a physical image of lithium ion transport in artificial SEI interface, that is, lithium ion diffusion in LiF crystal bulk is quite difficult, while the diffusion resistance at LiF grain boundaries and LiF/LiM alloy interfaces is small.
Solid electrolyte interphase (SEI) layers derived from the side reactions between Li metal anode and electrolyte, have great impacts on the electrochemical performance of lithium batteries. In solid-state batteries, SEI layers are also required as the electrical insulators but an ionic conductors, and the mechanical reinforcements for withstanding volume change and suppressing dendritic growth in Li metal anode. Introducing LiF substrates into SEI layers can significantly reduce the electron tunneling ability from Li anode to SEI layer, meanwhile providing the excellent interfacial mechanical strength. However, LiF has a very high energy barrier for ion diffusion, hindering the rapid lithium ion diffusion from SEI layer to lithium anode. Therefore, it is necessary to introduce lithium alloy phases with higher ionic conductivity into the LiF matrix to provide sufficient ion diffusion channels. By the data mining technology, high-throughput first-principle calculation and ab-initio molecular dynamics simulations, this work performed phase diagram and ion diffusion energy barrier calculations to evaluate the thermodynamic stabilities and lithium diffusion abilities of several lithium alloys. 27 lithium alloys that can be used as Li-ion conducting phases in the LiF-based artificial SEI layers are screened. Meanwhile, the structure-function relationship analysis of lithium alloys uncovers that the crystal structure type of lithium alloys has more significant impacts on lithium ion diffusion than alloy elements, that is, lithium alloy structures with the space group of I43d and Fm3m have very excellent lithium ion transport performance, while the diffusion channels of lithium alloy structures with the space group of Pm3m and F43m are narrow, leading to the poor lithium ion transport performance. In addition, this work uncovers a physical image of lithium ion transport in artificial SEI interface, that is, lithium ion diffusion in LiF crystal bulk is quite difficult, while the diffusion resistance at LiF grain boundaries and LiF/LiM alloy interfaces is small.
2024, 40(3): 230504
doi: 10.3866/PKU.WHXB202305040
Abstract:
The anode-free solid-state lithium battery (AFSSLB) is a type of lithium battery that utilizes an initial charging process to generate lithium metal as the anode. With a 1: 1 anode-to-cathode capacity ratio, it enables any lithiated cathode system to achieve a maximal energy density. Furthermore, the incorporation of inorganic solid electrolytes in the AFSSLB greatly enhances its intrinsic safety. However, the AFSSLB faces challenges related to interfacial issues between the electrolyte and collector. During the cycling process, uneven lithium-ion flux can result in contact loss and dendrite growth, ultimately leading to rapid battery failure. Addressing these interfacial problems is crucial for the successful implementation and performance of AFSSLBs. The absence of initial lithium metal material prevents the battery system from accommodating additional lithium through a modified anode. Instead, it relies on high Coulomb efficiency during cycling. Consequently, ensuring continuous and uniform contact at the anode interface is crucial for maintaining the reversibility of lithium deposition. Herein, a nanocomposite current collector is introduced to enhance the interface between the collector and electrolyte in AFSSLB. In this approach, silver nanoparticles are dispersed within the carbon materials to construct a composite current collector. The incorporation of the silver-carbon nanocomposite layer results in a low interfacial impedance of 10 Ω·cm-2, indicating that the electrolyte-collector interface maintains contact throughout the charging and discharging processes. The focused ion beam (FIB) technology and electron microscopy were employed to analyze the battery cross sections, revealing that lithium metal could be deposited in a thickness of more than 25 μm without short-circuiting using this silver-carbon nanocomposite current collector. The solid-state batteries equipped with nanocomposite current collectors exhibited an enhanced dissolution of silver in the lithium metal, leading to the formation of abundant lithiophilic sites. The nanocomposites facilitate the rapid transfer of Li atoms within the anodes, thus achieving uniform lithium metal deposition. Theoretical analysis using the nucleation equation demonstrates that using nano-silver as a current collector can reduce the nucleation work required for deposition by at least four orders of magnitude. The smaller nucleation force contributes to the uniform and stable deposition of lithium metal during continuous cycling. The solid-state batteries demonstrated improved interfacial contact, resulting in the uniform and stable lithium metal deposition of over 7.0 mAh·cm-2 for more than 200 cycles at 0.25 mA·cm-2. The cycling performances of all-solid-state batteries can be significantly improved through the design of nanocomposite collectors. This presents an effective strategy for advancing the practical implementation of all-solid-state lithium metal batteries, particularly those utilizing an anode-free configuration.
The anode-free solid-state lithium battery (AFSSLB) is a type of lithium battery that utilizes an initial charging process to generate lithium metal as the anode. With a 1: 1 anode-to-cathode capacity ratio, it enables any lithiated cathode system to achieve a maximal energy density. Furthermore, the incorporation of inorganic solid electrolytes in the AFSSLB greatly enhances its intrinsic safety. However, the AFSSLB faces challenges related to interfacial issues between the electrolyte and collector. During the cycling process, uneven lithium-ion flux can result in contact loss and dendrite growth, ultimately leading to rapid battery failure. Addressing these interfacial problems is crucial for the successful implementation and performance of AFSSLBs. The absence of initial lithium metal material prevents the battery system from accommodating additional lithium through a modified anode. Instead, it relies on high Coulomb efficiency during cycling. Consequently, ensuring continuous and uniform contact at the anode interface is crucial for maintaining the reversibility of lithium deposition. Herein, a nanocomposite current collector is introduced to enhance the interface between the collector and electrolyte in AFSSLB. In this approach, silver nanoparticles are dispersed within the carbon materials to construct a composite current collector. The incorporation of the silver-carbon nanocomposite layer results in a low interfacial impedance of 10 Ω·cm-2, indicating that the electrolyte-collector interface maintains contact throughout the charging and discharging processes. The focused ion beam (FIB) technology and electron microscopy were employed to analyze the battery cross sections, revealing that lithium metal could be deposited in a thickness of more than 25 μm without short-circuiting using this silver-carbon nanocomposite current collector. The solid-state batteries equipped with nanocomposite current collectors exhibited an enhanced dissolution of silver in the lithium metal, leading to the formation of abundant lithiophilic sites. The nanocomposites facilitate the rapid transfer of Li atoms within the anodes, thus achieving uniform lithium metal deposition. Theoretical analysis using the nucleation equation demonstrates that using nano-silver as a current collector can reduce the nucleation work required for deposition by at least four orders of magnitude. The smaller nucleation force contributes to the uniform and stable deposition of lithium metal during continuous cycling. The solid-state batteries demonstrated improved interfacial contact, resulting in the uniform and stable lithium metal deposition of over 7.0 mAh·cm-2 for more than 200 cycles at 0.25 mA·cm-2. The cycling performances of all-solid-state batteries can be significantly improved through the design of nanocomposite collectors. This presents an effective strategy for advancing the practical implementation of all-solid-state lithium metal batteries, particularly those utilizing an anode-free configuration.
2024, 40(3): 230504
doi: 10.3866/PKU.WHXB202305041
Abstract:
In recent years, hydrogen production has driving a growing focus in the researches of clean energy, particularly the significance of the oxygen evolution reaction (OER) in water splitting. However, the most fascinating OER catalysts of noble metals are hindered by high cost, limited resources, and poor stability. Therefore, the development of low-cost, efficient, stable, and replaceable electrocatalysts is of utmost importance to accelerate the rate of OER in water splitting and realizing renewable, clean, and large-scale energy conversion technologies. Bimetallic and polymetallic electrocatalysts have shown enormous potential, as each metal component can independently or synergistically enhance the electrocatalytic activity. However, during the catalytic process, some metal ions may leach, leading to changes in the catalyst surface morphology and a significant reduction in activity and stability. Extensive research efforts are being devoted to effectively address the challenges associated with metal dissolution. In this study, we have developed a simple method for preparing bimetallic CoNi zeolitic imidazolate framework (CoNi-ZIF) by removing guest molecules through low-temperature pyrolysis and firmly loading CoNi-ZIF nanosheets onto carbon cloth (CoNi-ZIF-CC-200). The resulting free-standing electrodes have several advantages, including independence from adhesives and avoidance of ineffective surface area, thereby significantly improving the catalytic activity and mass transfer efficiency of the catalyst. The electrochemical test results indicate that the CoNi-ZIF-CC-200 free-standing electrode exhibits good electrochemical activity and stability during the OER process. Specifically, the CoNi-ZIF-CC-200 electrode demonstrates a low overpotential of 255 mV under a current density of 10 mA·cm-2 and maintains stable operation for over 10 h during potentiostatic measurements. Additionally, the water splitting system consisting of the CoNi-ZIF-CC-200 free-standing electrode as the anode and Pt/C as the cathode exhibits excellent stability. The research highlights the use of a low-temperature pyrolysis strategy for firmly loading bimetallic ZIF-L nanosheets onto carbon cloth. This approach results in well-arranged nanosheet arrays, which prevent ineffective surface area and improve mass transfer efficiency during the OER process. Moreover, the removal of guest molecules at low temperatures leads to the formation of Co/Ni oxides, which play a crucial role in catalyzing the OER. The prepared free-standing electrode based on bimetallic ZIF and oxide demonstrates excellent electrochemical activity and stability in both three-electrode and two-electrode water splitting systems using 1 mol·L-1 KOH as the electrolyte. It is strongly believed that CoNi-ZIF-CC-200 holds great promise for future applications in large-scale electrocatalytic hydrogen production systems.
In recent years, hydrogen production has driving a growing focus in the researches of clean energy, particularly the significance of the oxygen evolution reaction (OER) in water splitting. However, the most fascinating OER catalysts of noble metals are hindered by high cost, limited resources, and poor stability. Therefore, the development of low-cost, efficient, stable, and replaceable electrocatalysts is of utmost importance to accelerate the rate of OER in water splitting and realizing renewable, clean, and large-scale energy conversion technologies. Bimetallic and polymetallic electrocatalysts have shown enormous potential, as each metal component can independently or synergistically enhance the electrocatalytic activity. However, during the catalytic process, some metal ions may leach, leading to changes in the catalyst surface morphology and a significant reduction in activity and stability. Extensive research efforts are being devoted to effectively address the challenges associated with metal dissolution. In this study, we have developed a simple method for preparing bimetallic CoNi zeolitic imidazolate framework (CoNi-ZIF) by removing guest molecules through low-temperature pyrolysis and firmly loading CoNi-ZIF nanosheets onto carbon cloth (CoNi-ZIF-CC-200). The resulting free-standing electrodes have several advantages, including independence from adhesives and avoidance of ineffective surface area, thereby significantly improving the catalytic activity and mass transfer efficiency of the catalyst. The electrochemical test results indicate that the CoNi-ZIF-CC-200 free-standing electrode exhibits good electrochemical activity and stability during the OER process. Specifically, the CoNi-ZIF-CC-200 electrode demonstrates a low overpotential of 255 mV under a current density of 10 mA·cm-2 and maintains stable operation for over 10 h during potentiostatic measurements. Additionally, the water splitting system consisting of the CoNi-ZIF-CC-200 free-standing electrode as the anode and Pt/C as the cathode exhibits excellent stability. The research highlights the use of a low-temperature pyrolysis strategy for firmly loading bimetallic ZIF-L nanosheets onto carbon cloth. This approach results in well-arranged nanosheet arrays, which prevent ineffective surface area and improve mass transfer efficiency during the OER process. Moreover, the removal of guest molecules at low temperatures leads to the formation of Co/Ni oxides, which play a crucial role in catalyzing the OER. The prepared free-standing electrode based on bimetallic ZIF and oxide demonstrates excellent electrochemical activity and stability in both three-electrode and two-electrode water splitting systems using 1 mol·L-1 KOH as the electrolyte. It is strongly believed that CoNi-ZIF-CC-200 holds great promise for future applications in large-scale electrocatalytic hydrogen production systems.
2024, 40(3): 230505
doi: 10.3866/PKU.WHXB202305053
Abstract:
Lithium metal is a promising anode candidate for high-energy-density secondary batteries due to its high theoretical capacity and low electrochemical potential, while the uncontrolled dendrite growth causing poor cycling performance and safety concerns poses serious challenges for the practical application of lithium metal batteries. During the electrodeposition process, the lithium-ion (Li+) diffusion process is directly related to the electrode/electrolyte interfacial Li+ concentration gradient as well as the dendritic morphology. Regulating the anisotropic Li+ diffusion property is a convenient way to reshape its transfer behavior without introducing any external fields (e.g., temperature field, magnetic field, acoustic field, etc.) or increasing the weight of batteries. Despite the large amount of experimental and theoretical work on the effect of the anisotropic Li+ diffusion behavior on the dendritic morphology, some open questions remain to be deliberated, e.g., correlating the dynamic evolution of dendrite growth with the anisotropic Li+ diffusion induced by the electrolyte property, electric potential, and separator structure. In this paper, an electrochemical phase-field model is applied to explore the influences of electrolyte inherent anisotropic Li+ diffusion, electric potential-induced anisotropic Li+ diffusion, and separator-structure-induced anisotropic Li+ migration on dendrite growth via a homemade MATLAB code. Instead of a fixed numerical value, the modified Li+ diffusivity in the electrolyte (DL) is expressed as a second-order tensor by decomposing into two components along the x (Dxx) and y (Dyy) directions, which is not only able to explore the electrolyte inherent anisotropic Li+ diffusion but also easy to describe the electric potential-induced fluctuations of DL and the corresponding Li+ concentration distribution. Predicted results indicate that with the increase of Dyy: Dxx, the interfacial Li+concentration gradient is alleviated due to the accelerated longitudinal Li+ replenishment and decelerated transversal “entrainment” phenomenon, thus decreasing the driving force of dendrite growth. Besides, the electric potential-induced interfacial Li+ fast diffusion layer can also reduce the electric potential gradients surrounding the dendrite tips and then uniform the dendrite morphologies. Surprisingly, separators with higher matrix tilt angles are demonstrated to achieve effective anisotropic Li+ diffusion in electrolyte, which can not only reduce the dendrite-growth velocity, but also extend the dendrite-growth pathway and prolong the battery short circuit time. Following this, electrolyte with the Dyy: Dxx = 10: 1 and separator with the matrix tilt angle of arctan (0.5) are evaluated as promising materials for lithium metal batteries. This study provides a rational guidance for designing electrolytes or separators with dendrite-inhibiting capability.
Lithium metal is a promising anode candidate for high-energy-density secondary batteries due to its high theoretical capacity and low electrochemical potential, while the uncontrolled dendrite growth causing poor cycling performance and safety concerns poses serious challenges for the practical application of lithium metal batteries. During the electrodeposition process, the lithium-ion (Li+) diffusion process is directly related to the electrode/electrolyte interfacial Li+ concentration gradient as well as the dendritic morphology. Regulating the anisotropic Li+ diffusion property is a convenient way to reshape its transfer behavior without introducing any external fields (e.g., temperature field, magnetic field, acoustic field, etc.) or increasing the weight of batteries. Despite the large amount of experimental and theoretical work on the effect of the anisotropic Li+ diffusion behavior on the dendritic morphology, some open questions remain to be deliberated, e.g., correlating the dynamic evolution of dendrite growth with the anisotropic Li+ diffusion induced by the electrolyte property, electric potential, and separator structure. In this paper, an electrochemical phase-field model is applied to explore the influences of electrolyte inherent anisotropic Li+ diffusion, electric potential-induced anisotropic Li+ diffusion, and separator-structure-induced anisotropic Li+ migration on dendrite growth via a homemade MATLAB code. Instead of a fixed numerical value, the modified Li+ diffusivity in the electrolyte (DL) is expressed as a second-order tensor by decomposing into two components along the x (Dxx) and y (Dyy) directions, which is not only able to explore the electrolyte inherent anisotropic Li+ diffusion but also easy to describe the electric potential-induced fluctuations of DL and the corresponding Li+ concentration distribution. Predicted results indicate that with the increase of Dyy: Dxx, the interfacial Li+concentration gradient is alleviated due to the accelerated longitudinal Li+ replenishment and decelerated transversal “entrainment” phenomenon, thus decreasing the driving force of dendrite growth. Besides, the electric potential-induced interfacial Li+ fast diffusion layer can also reduce the electric potential gradients surrounding the dendrite tips and then uniform the dendrite morphologies. Surprisingly, separators with higher matrix tilt angles are demonstrated to achieve effective anisotropic Li+ diffusion in electrolyte, which can not only reduce the dendrite-growth velocity, but also extend the dendrite-growth pathway and prolong the battery short circuit time. Following this, electrolyte with the Dyy: Dxx = 10: 1 and separator with the matrix tilt angle of arctan (0.5) are evaluated as promising materials for lithium metal batteries. This study provides a rational guidance for designing electrolytes or separators with dendrite-inhibiting capability.
2024, 40(3): 230900
doi: 10.3866/PKU.WHXB202309009
Abstract:
This paper provides a comprehensive overview of the establishment and subsequent adjustment to the discipline codes of Physical Chemistry in China. In light of the research developments in Physical Chemistry over the past decade, the optimized reclassification into Catalysis & Surface Interface Chemistry and Chemical Theory & Mechanism, effective from 2018, plays an important role in advancing cutting-edge foundational researches and enhancing the grant effectiveness of science foundation. Constructive insights and recommendations are provided for further optimizing discipline allocation, serving as a valuable guide for shaping future development strategies within the field of Physical Chemistry.
This paper provides a comprehensive overview of the establishment and subsequent adjustment to the discipline codes of Physical Chemistry in China. In light of the research developments in Physical Chemistry over the past decade, the optimized reclassification into Catalysis & Surface Interface Chemistry and Chemical Theory & Mechanism, effective from 2018, plays an important role in advancing cutting-edge foundational researches and enhancing the grant effectiveness of science foundation. Constructive insights and recommendations are provided for further optimizing discipline allocation, serving as a valuable guide for shaping future development strategies within the field of Physical Chemistry.
