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2023 Volume 39 Issue 3
2023, 39(3): 220900
doi: 10.3866/PKU.WHXB202209002
Abstract:
Sodium-ion battery is one of the most promising and feasible energy storage candidates. However, compared to the lithium ion, the larger ionic radius and higher molecular mass of the sodium ion lead to inferior electrochemical performance of sodium-ion batteries. Therefore, achieving the rational design and construction of high-performance electrode materials is a key point and remains a great challenge for sodium-ion batteries. In this work, we focus on the transport properties of sodium ions and electrons and discuss design strategies of sodium electrodes from the perspective of solid-state ionics. First, for the bulk sodium electrode materials, investigating their transport properties, such as ionic conductivity, electronic conductivity, and diffusion coefficient, is a prerequisite for electrode design. Although there are various methods of measuring the diffusion coefficient, separately achieving the intrinsic ionic and electronic conductivity of the pure materials is highly important. Doping and carbon-coating are the most useful approaches to improve the specific transport properties of the investigated materials. Building defect chemistry models based on measured transport properties and relevant defect chemistry theory is crucial but remains a great challenge for the design of sodium electrodes. Second, for the nano sodium electrodes, size effects can be applied to design and construct electrodes from a nanoionics perspective. Thermodynamically, the equilibrium shape and equilibrium voltage change with a reduction in the particle size and facilitate the discovery of new electroactive electrode materials. Kinetically, according to τ~L2/D (where τ is diffusion time, L is particle radius, and D is diffusion coefficient), a smaller particle size leads to better kinetic behavior (higher rate performance) and also improves the diffusion coefficient in some cases. In terms of sodium transport and storage mechanisms, size effects result in the transition from a two-phase to a single-phase mechanism, an increase in the interfacial storage and surface reaction, as well as a variation of the sodium storage mechanism in pores, further leading to variation of the discharge voltage plateau. Finally, whether for bulk or nano-electrode materials, constructing efficient electrochemical circuits by the optimization of the phases and dimensionalities based on the transport properties of electrode materials is significant in achieving the rational design of sodium electrode materials and optimizing the electrochemical performance of sodium-ion batteries. We believe that this study will serve as a useful guide for the development of sodium electrode materials and will certainly contribute to the commercialization of sodium-ion batteries. ![]()
Sodium-ion battery is one of the most promising and feasible energy storage candidates. However, compared to the lithium ion, the larger ionic radius and higher molecular mass of the sodium ion lead to inferior electrochemical performance of sodium-ion batteries. Therefore, achieving the rational design and construction of high-performance electrode materials is a key point and remains a great challenge for sodium-ion batteries. In this work, we focus on the transport properties of sodium ions and electrons and discuss design strategies of sodium electrodes from the perspective of solid-state ionics. First, for the bulk sodium electrode materials, investigating their transport properties, such as ionic conductivity, electronic conductivity, and diffusion coefficient, is a prerequisite for electrode design. Although there are various methods of measuring the diffusion coefficient, separately achieving the intrinsic ionic and electronic conductivity of the pure materials is highly important. Doping and carbon-coating are the most useful approaches to improve the specific transport properties of the investigated materials. Building defect chemistry models based on measured transport properties and relevant defect chemistry theory is crucial but remains a great challenge for the design of sodium electrodes. Second, for the nano sodium electrodes, size effects can be applied to design and construct electrodes from a nanoionics perspective. Thermodynamically, the equilibrium shape and equilibrium voltage change with a reduction in the particle size and facilitate the discovery of new electroactive electrode materials. Kinetically, according to τ~L2/D (where τ is diffusion time, L is particle radius, and D is diffusion coefficient), a smaller particle size leads to better kinetic behavior (higher rate performance) and also improves the diffusion coefficient in some cases. In terms of sodium transport and storage mechanisms, size effects result in the transition from a two-phase to a single-phase mechanism, an increase in the interfacial storage and surface reaction, as well as a variation of the sodium storage mechanism in pores, further leading to variation of the discharge voltage plateau. Finally, whether for bulk or nano-electrode materials, constructing efficient electrochemical circuits by the optimization of the phases and dimensionalities based on the transport properties of electrode materials is significant in achieving the rational design of sodium electrode materials and optimizing the electrochemical performance of sodium-ion batteries. We believe that this study will serve as a useful guide for the development of sodium electrode materials and will certainly contribute to the commercialization of sodium-ion batteries.
2023, 39(3): 221001
doi: 10.3866/PKU.WHXB202210017
Abstract:
The resolution limit of scanning transmission electron microscopy (STEM) has now reached atomic resolution. Further, owing to its flexible multi-channel imaging and powerful spectral characterization abilities, STEM has shown immense promise for microscale characterization in materials sciences, life sciences, and other fields. However, the traditional STEM detector is limited by its single-pixel integral detection mechanism, due to which it can only collect scattered electrons at a specific angle. This not only results in a loss of angle-resolved information of the scattered electrons, but also reduces the dose efficiency of the incident electrons. Therefore, it is imperative that new imaging techniques are developed to achieve high-throughput, high-electron-dose-efficiency imaging. Recent advances in electron direct detection techniques and detectors with partitioned or pixelated configurations, as well as the rapidly increasing computing power and disk storage, have contributed to the rapid development of four-dimensional STEM (4D-STEM) technology. Uniquely, 4D-STEM allows one to acquire structural information associated with scattered electrons. During the acquisition of 4D-STEM data, the convergent electron beam performs two-dimensional scanning on the sample plane, while a pixelated array detector with a high frame rate, wide dynamic range, and high signal-to-noise ratio collects two-dimensional diffraction data in the far field. Because these diffraction data are angle-resolved, they can be used for conventional STEM imaging as well as phase contrast imaging at the leading edge. For example, electron ptychography is used to reconstruct the sample object function from a series of diffraction patterns measured at different spatial locations. In addition, 4D-STEM technology can be explored to obtain more information about the internal structure of materials, providing opportunities for the multi-scale characterization of materials. This paper introduces the basic principles of 4D-STEM imaging and summarizes a series of 4D-STEM applications ranging from the microstructural characterization of materials to the analysis of their physicochemical properties. Typical applications include virtual detector imaging as well as measurements of micro-electromagnetic fields, micro-crystal orientations, micro-strain distributions, and the local specimen thickness. In addition, electron ptychography imaging technology realized using 4D-STEM data is highly promising for low-electron-dose applications owing to its high utilization efficiency of scattered electrons. The application of 4D-STEM technology in low-electron-dose applications is discussed. Overall, with the rapid development of electron detectors and post-processing analysis software for 4D-STEM data, it is believed that the novel 4D-STEM technology will eventually completely replace traditional STEM technology. ![]()
The resolution limit of scanning transmission electron microscopy (STEM) has now reached atomic resolution. Further, owing to its flexible multi-channel imaging and powerful spectral characterization abilities, STEM has shown immense promise for microscale characterization in materials sciences, life sciences, and other fields. However, the traditional STEM detector is limited by its single-pixel integral detection mechanism, due to which it can only collect scattered electrons at a specific angle. This not only results in a loss of angle-resolved information of the scattered electrons, but also reduces the dose efficiency of the incident electrons. Therefore, it is imperative that new imaging techniques are developed to achieve high-throughput, high-electron-dose-efficiency imaging. Recent advances in electron direct detection techniques and detectors with partitioned or pixelated configurations, as well as the rapidly increasing computing power and disk storage, have contributed to the rapid development of four-dimensional STEM (4D-STEM) technology. Uniquely, 4D-STEM allows one to acquire structural information associated with scattered electrons. During the acquisition of 4D-STEM data, the convergent electron beam performs two-dimensional scanning on the sample plane, while a pixelated array detector with a high frame rate, wide dynamic range, and high signal-to-noise ratio collects two-dimensional diffraction data in the far field. Because these diffraction data are angle-resolved, they can be used for conventional STEM imaging as well as phase contrast imaging at the leading edge. For example, electron ptychography is used to reconstruct the sample object function from a series of diffraction patterns measured at different spatial locations. In addition, 4D-STEM technology can be explored to obtain more information about the internal structure of materials, providing opportunities for the multi-scale characterization of materials. This paper introduces the basic principles of 4D-STEM imaging and summarizes a series of 4D-STEM applications ranging from the microstructural characterization of materials to the analysis of their physicochemical properties. Typical applications include virtual detector imaging as well as measurements of micro-electromagnetic fields, micro-crystal orientations, micro-strain distributions, and the local specimen thickness. In addition, electron ptychography imaging technology realized using 4D-STEM data is highly promising for low-electron-dose applications owing to its high utilization efficiency of scattered electrons. The application of 4D-STEM technology in low-electron-dose applications is discussed. Overall, with the rapid development of electron detectors and post-processing analysis software for 4D-STEM data, it is believed that the novel 4D-STEM technology will eventually completely replace traditional STEM technology.
2023, 39(3): 221004
doi: 10.3866/PKU.WHXB202210043
Abstract:
Lithium-ion batteries (LIBs) have attracted considerable attention owing to their high energy density and long cycle life. However, lithium resources have become scarcer with the rapid development of electric vehicles and smart grid technologies. Considering the inexpensive and abundant supply of sodium, sodium-ion batteries (SIBs) are expected to replace LIBs for large-scale energy storage systems. However, the development of high-energy SIBs is usually limited by the poor initial Coulombic efficiency (ICE) of the anode materials, although a series of advanced sodium storage electrode materials have been reported. This is because active sodium ions are all provided by the cathode material in a full cell. The low ICE of the anode indicates that numerous active sodium ions are irreversibly consumed during the first cycle, reducing the reversible capacity and shortening the cycle life of the full cell. The significant loss of active sodium ions is attributed to the formation of a solid electrolyte interface (SEI) on the anode side and irreversible sodium capture by defect sites and surface functional groups on the anode material. Consequently, excessive cathode material is required in the full cell, which significantly reduces the utilization rate of the cathode material and the energy density of the full cell. Furthermore, many reported cathode materials, such as Fe2S, are sodium-deficient and cannot be directly matched with anodes, limiting the selection of electrode materials. Presodiation technology is considered the most direct and effective method to solve the state-matching problem of cathode and anode materials by compensating for active sodium-ion loss and increasing the energy density, which are crucial for the commercial application of SIBs. The aim is to eliminate the irreversible capacity loss during the first cycle by incorporating additional active sodium ions to the electrode material in advance. This review comprehensively summarizes the latest research progress on various presodiation strategies, including short circuit with sodium metal, electrochemical presodiation, sodium metal addition, chemical presodiation, and cathode sacrificial additives. The advantages and challenges of existing methods are thoroughly analyzed and discussed from the perspective of their reaction mechanism, safety, compatibility, efficiency, and scalability. Emphasis is placed on the state-of-the-art advancements in chemical presodiation and cathode sacrificial additives, which are considered the two most promising methods for commercial applications. The unresolved scientific problems and technical difficulties are further discussed from a practical perspective. This review may provide guidance for the investigation of advanced presodiation technology and promote further development of high-energy SIBs. ![]()
Lithium-ion batteries (LIBs) have attracted considerable attention owing to their high energy density and long cycle life. However, lithium resources have become scarcer with the rapid development of electric vehicles and smart grid technologies. Considering the inexpensive and abundant supply of sodium, sodium-ion batteries (SIBs) are expected to replace LIBs for large-scale energy storage systems. However, the development of high-energy SIBs is usually limited by the poor initial Coulombic efficiency (ICE) of the anode materials, although a series of advanced sodium storage electrode materials have been reported. This is because active sodium ions are all provided by the cathode material in a full cell. The low ICE of the anode indicates that numerous active sodium ions are irreversibly consumed during the first cycle, reducing the reversible capacity and shortening the cycle life of the full cell. The significant loss of active sodium ions is attributed to the formation of a solid electrolyte interface (SEI) on the anode side and irreversible sodium capture by defect sites and surface functional groups on the anode material. Consequently, excessive cathode material is required in the full cell, which significantly reduces the utilization rate of the cathode material and the energy density of the full cell. Furthermore, many reported cathode materials, such as Fe2S, are sodium-deficient and cannot be directly matched with anodes, limiting the selection of electrode materials. Presodiation technology is considered the most direct and effective method to solve the state-matching problem of cathode and anode materials by compensating for active sodium-ion loss and increasing the energy density, which are crucial for the commercial application of SIBs. The aim is to eliminate the irreversible capacity loss during the first cycle by incorporating additional active sodium ions to the electrode material in advance. This review comprehensively summarizes the latest research progress on various presodiation strategies, including short circuit with sodium metal, electrochemical presodiation, sodium metal addition, chemical presodiation, and cathode sacrificial additives. The advantages and challenges of existing methods are thoroughly analyzed and discussed from the perspective of their reaction mechanism, safety, compatibility, efficiency, and scalability. Emphasis is placed on the state-of-the-art advancements in chemical presodiation and cathode sacrificial additives, which are considered the two most promising methods for commercial applications. The unresolved scientific problems and technical difficulties are further discussed from a practical perspective. This review may provide guidance for the investigation of advanced presodiation technology and promote further development of high-energy SIBs.
2023, 39(3): 220900
doi: 10.3866/PKU.WHXB202209004
Abstract:
Pt-based electrocatalysts have received extensive attention owing to their wide applications in various fields, including fuel cells, hydrogen production, degradation of organic pollutants, electrochemical sensors, and oxidation of small molecules. Therefore, the efficient synthesis and screening of high-performance Pt-based electrocatalysts is necessary for accelerating their further development and application in these fields. The conventional method for developing the advanced materials and optimizing their synthesis parameters is time-consuming, inefficient, and costly. Microfluidic high-throughput techniques have the great potential for optimizing the synthesis parameters of Pt-based electrocatalysts. However, microfluidic high-throughput synthesis without performance evaluation cannot maximize its advantages. Therefore, it is highly desirable to develop a platform that combines the high-throughput synthesis of materials and the evaluation of their properties in a high-throughput fashion to improve the overall screening efficiency of the novel materials. In this study, a versatile microfluidic high-throughput platform, combining the high-throughput synthesis and screening of materials, was constructed. The microfluidic chip generated 20-level concentration gradients of the three different precursors. Microreactor arrays with 100 microchannels were used for the material synthesis and electrochemical characterization. A wide range of concentration combinations of the three different precursor solutions was achieved using the microfluidic chip. Five groups of Pt-based ternary electrocatalysts (100 different components in total) were synthesized and electrochemically characterized using the designed platform. The obtained Pt-based electrocatalysts exhibited a loose particle morphology, and were composed of small nanoparticles. The efficient preparation of Pt-based electrocatalysts with controllable compositions was also achieved through the high-throughput synthesis platform. The catalytic performance of the Pt-based catalysts towards oxygen evolution reaction (OER) was characterized by chronoamperometry. The optimal composition of Pt-based ternary electrocatalysts for OER was directly determined using the designed platform. For NiPtCu, the samples with a relatively high atomic percentage (approximately 50%) of Pt (i.e., Ni0.30Pt0.56Cu0.14, Ni0.17Pt0.52Cu0.31 and Ni0.12Pt0.48Cu0.40) exhibited higher electrocatalytic activity and stability, whereas the samples with a relatively high atomic percentage (> 50%) of Cu possessed lower activity and stability. For AuPtNi and AuPtCu, the samples wherein Au and Pt accounted for a large proportion of the sample (i.e., Ni or Cu < 10%) and the atomic ratios of Au : Pt were (3–4) : 1, e.g., Au0.71Pt0.25Ni0.04 and Au0.77Pt0.18Cu0.05, displayed high electrocatalytic activity and stability. As the atomic fraction of Au decreased, the atomic ratio of Pt and Ni in AuPtNi approached 3 : 1 or that of Pt and Cu in AuPtCu reached to 1 : 1, the samples (Au0.54Pt0.35Ni0.11, Au0.35Pt0.42Cu0.23, Au0.27Pt0.41Cu0.32 and Au0.12Pt0.32Cu0.56) all demonstrated high electrocatalytic activity and stability. The samples (Pt0.06Cu0.94) wherein the atomic percentages of Au and Pt were all less than 10%, exhibited poor electrocatalytic activity and stability. For RhPtNi and RhPtCu, when the atomic percentage of Rh in RhPtNi and RhPtCu was high (50%–90%) and almost no Ni or Cu was present, the samples (Rh0.91Pt0.09 and Rh0.82Pt0.18 for RhPtNi, as well as Rh0.88Pt0.12 and Rh0.75Pt0.21Cu0.04 for RhPtCu) all had high electrocatalytic activity and stability. As the atomic percentage of Rh decreased and that of Pt increased, the atomic percentages of Rh and Pt were relatively close, Rh0.54Pt0.32Ni0.14 and Rh0.51Pt0.36Cu0.14 showing high electrocatalytic activity and stability. When the atomic percentages of Ni and Cu were high (> 50%), the RhPtNi and RhPtCu samples all showed the relatively poor electrocatalytic activity and stability. These results demonstrate the high efficiency and flexibility of the constructed microfluidic high-throughput platform, which significantly shortens the cycle for the development cycle of new materials and the optimization of their properties.![]()
Pt-based electrocatalysts have received extensive attention owing to their wide applications in various fields, including fuel cells, hydrogen production, degradation of organic pollutants, electrochemical sensors, and oxidation of small molecules. Therefore, the efficient synthesis and screening of high-performance Pt-based electrocatalysts is necessary for accelerating their further development and application in these fields. The conventional method for developing the advanced materials and optimizing their synthesis parameters is time-consuming, inefficient, and costly. Microfluidic high-throughput techniques have the great potential for optimizing the synthesis parameters of Pt-based electrocatalysts. However, microfluidic high-throughput synthesis without performance evaluation cannot maximize its advantages. Therefore, it is highly desirable to develop a platform that combines the high-throughput synthesis of materials and the evaluation of their properties in a high-throughput fashion to improve the overall screening efficiency of the novel materials. In this study, a versatile microfluidic high-throughput platform, combining the high-throughput synthesis and screening of materials, was constructed. The microfluidic chip generated 20-level concentration gradients of the three different precursors. Microreactor arrays with 100 microchannels were used for the material synthesis and electrochemical characterization. A wide range of concentration combinations of the three different precursor solutions was achieved using the microfluidic chip. Five groups of Pt-based ternary electrocatalysts (100 different components in total) were synthesized and electrochemically characterized using the designed platform. The obtained Pt-based electrocatalysts exhibited a loose particle morphology, and were composed of small nanoparticles. The efficient preparation of Pt-based electrocatalysts with controllable compositions was also achieved through the high-throughput synthesis platform. The catalytic performance of the Pt-based catalysts towards oxygen evolution reaction (OER) was characterized by chronoamperometry. The optimal composition of Pt-based ternary electrocatalysts for OER was directly determined using the designed platform. For NiPtCu, the samples with a relatively high atomic percentage (approximately 50%) of Pt (i.e., Ni0.30Pt0.56Cu0.14, Ni0.17Pt0.52Cu0.31 and Ni0.12Pt0.48Cu0.40) exhibited higher electrocatalytic activity and stability, whereas the samples with a relatively high atomic percentage (> 50%) of Cu possessed lower activity and stability. For AuPtNi and AuPtCu, the samples wherein Au and Pt accounted for a large proportion of the sample (i.e., Ni or Cu < 10%) and the atomic ratios of Au : Pt were (3–4) : 1, e.g., Au0.71Pt0.25Ni0.04 and Au0.77Pt0.18Cu0.05, displayed high electrocatalytic activity and stability. As the atomic fraction of Au decreased, the atomic ratio of Pt and Ni in AuPtNi approached 3 : 1 or that of Pt and Cu in AuPtCu reached to 1 : 1, the samples (Au0.54Pt0.35Ni0.11, Au0.35Pt0.42Cu0.23, Au0.27Pt0.41Cu0.32 and Au0.12Pt0.32Cu0.56) all demonstrated high electrocatalytic activity and stability. The samples (Pt0.06Cu0.94) wherein the atomic percentages of Au and Pt were all less than 10%, exhibited poor electrocatalytic activity and stability. For RhPtNi and RhPtCu, when the atomic percentage of Rh in RhPtNi and RhPtCu was high (50%–90%) and almost no Ni or Cu was present, the samples (Rh0.91Pt0.09 and Rh0.82Pt0.18 for RhPtNi, as well as Rh0.88Pt0.12 and Rh0.75Pt0.21Cu0.04 for RhPtCu) all had high electrocatalytic activity and stability. As the atomic percentage of Rh decreased and that of Pt increased, the atomic percentages of Rh and Pt were relatively close, Rh0.54Pt0.32Ni0.14 and Rh0.51Pt0.36Cu0.14 showing high electrocatalytic activity and stability. When the atomic percentages of Ni and Cu were high (> 50%), the RhPtNi and RhPtCu samples all showed the relatively poor electrocatalytic activity and stability. These results demonstrate the high efficiency and flexibility of the constructed microfluidic high-throughput platform, which significantly shortens the cycle for the development cycle of new materials and the optimization of their properties.
2023, 39(3): 220903
doi: 10.3866/PKU.WHXB202209033
Abstract:
Fenton-like activity of iron sulfides for the generation of reactive oxygen species and degradation of various organic pollutants has been extensively investigated due to its abundance in the natural environment. However, their Fenton-like activity is usually unsatisfactory due to the limited exposure of surface ferrous reactive sites. In this work, a new strategy to enhance the Fenton-like activity of iron sulfides, using pyrite (FeS2) as a model, was developed based on the heat treatment of FeS2 by water steam. It was found that the FeS2 heat-treated by water steam (Heat-FeS2) exhibited much higher heterogeneous Fenton activity in the degradation of alachlor (ACL) than its parent FeS2 prepared from hydrothermal reaction (Fresh-FeS2). At an initial pH of 6.3, the rate of degradation of ACL by Heat-FeS2 Fenton system was 0.48 min−1, which is ~23 times higher than that of Fresh-FeS2 Fenton system. Electron spin resonance analysis and benzoic acid probe experiments confirmed the production of more hydroxyl (•OH) and superoxide radicals (•O2−) in Heat-FeS2 Fenton system than Fresh-FeS2 Fenton system. The increased Fenton-like activity of Heat-FeS2 can be attributed to the increased content of highly reactive surface bonded Fe2+/Fe3+ species, higher amount of leached Fe2+, and optimal reaction pH due to stronger acidification of Heat-FeS2. Characterization studies by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy showed that heat treatment remarkably promoted the transformation of lattice Fe2+ to surface reactive Fe2+, allowing the exposure of more surface reactive Fe2+ and leaching of Fe2+; simultaneously, heat treatment enhanced the generation of surface SO42−, creating a highly acidic surface. The surface Fe2+ percentage in the surface total iron was raised from 13% in Fresh-FeS2 to 29% in Heat-FeS2. Fe2+ leaching from Heat-FeS2 was 0.23 mmol·L−1, much higher than that (< 0.02 mmol·L−1) for Fresh-FeS2. The change in the surface Fe and S species in the Heat-FeS2 system during the Fenton-like reaction was monitored by XPS to elucidate the enhanced Fenton oxidation mechanism. The characterization results showed that after Fenton reaction with H2O2, the surface contents of Fe2+ and Fe3+ species on Fresh-FeS2 and Heat-FeS2 were remarkably raised, while the surface content of S22− species was reduced, confirming the crucial role of S22− in the reductive cycle of Fe3+ to Fe2+. These findings increase understanding of the oxidative transformation and corrosion of iron sulfides and its relevant transformation and degradation of toxic organics in natural environments. The results of this work also provide an efficient Fenton-like oxidation method based on iron sulfides for highly efficient degradation of organic pollutants (e.g. ACL) in aqueous solution.![]()
Fenton-like activity of iron sulfides for the generation of reactive oxygen species and degradation of various organic pollutants has been extensively investigated due to its abundance in the natural environment. However, their Fenton-like activity is usually unsatisfactory due to the limited exposure of surface ferrous reactive sites. In this work, a new strategy to enhance the Fenton-like activity of iron sulfides, using pyrite (FeS2) as a model, was developed based on the heat treatment of FeS2 by water steam. It was found that the FeS2 heat-treated by water steam (Heat-FeS2) exhibited much higher heterogeneous Fenton activity in the degradation of alachlor (ACL) than its parent FeS2 prepared from hydrothermal reaction (Fresh-FeS2). At an initial pH of 6.3, the rate of degradation of ACL by Heat-FeS2 Fenton system was 0.48 min−1, which is ~23 times higher than that of Fresh-FeS2 Fenton system. Electron spin resonance analysis and benzoic acid probe experiments confirmed the production of more hydroxyl (•OH) and superoxide radicals (•O2−) in Heat-FeS2 Fenton system than Fresh-FeS2 Fenton system. The increased Fenton-like activity of Heat-FeS2 can be attributed to the increased content of highly reactive surface bonded Fe2+/Fe3+ species, higher amount of leached Fe2+, and optimal reaction pH due to stronger acidification of Heat-FeS2. Characterization studies by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy showed that heat treatment remarkably promoted the transformation of lattice Fe2+ to surface reactive Fe2+, allowing the exposure of more surface reactive Fe2+ and leaching of Fe2+; simultaneously, heat treatment enhanced the generation of surface SO42−, creating a highly acidic surface. The surface Fe2+ percentage in the surface total iron was raised from 13% in Fresh-FeS2 to 29% in Heat-FeS2. Fe2+ leaching from Heat-FeS2 was 0.23 mmol·L−1, much higher than that (< 0.02 mmol·L−1) for Fresh-FeS2. The change in the surface Fe and S species in the Heat-FeS2 system during the Fenton-like reaction was monitored by XPS to elucidate the enhanced Fenton oxidation mechanism. The characterization results showed that after Fenton reaction with H2O2, the surface contents of Fe2+ and Fe3+ species on Fresh-FeS2 and Heat-FeS2 were remarkably raised, while the surface content of S22− species was reduced, confirming the crucial role of S22− in the reductive cycle of Fe3+ to Fe2+. These findings increase understanding of the oxidative transformation and corrosion of iron sulfides and its relevant transformation and degradation of toxic organics in natural environments. The results of this work also provide an efficient Fenton-like oxidation method based on iron sulfides for highly efficient degradation of organic pollutants (e.g. ACL) in aqueous solution.
2023, 39(3): 221000
doi: 10.3866/PKU.WHXB202210002
Abstract:
Colloidal quantum dots (CQDs) are extremely promising infrared optoelectronic materials for efficient solar cells owing to their strong infrared absorption with tunable spectra. However, the liquid-state ligand exchange of CQDs using ammonium acetate (AA) as an additive generally resulted in intensive charge-transport barriers within the CQD solids. This is induced by the high-bandgap PbI2 matrix, which considerably affects the charge-carrier extraction of CQD solar cells (CQDSCs), and thus their photovoltaic performance. Herein, dimethylammonium iodide (DMAI) was used as an additive instead for the liquid-state ligand exchange, substantially eliminating the PbI2 matrix capping the CQDs and simultaneously restraining CQD fusion during the ligand exchange, thereby reducing the barriers for the charge-carrier transport within the CQD solids. Extensive experimental studies and theoretical calculations were performed to link the surface chemistry of the CQDs with the charge-carrier dynamics within the CQD solids and full solar cell devices. The theoretical calculation results reveal that DMAI which possess small dissociation energy could finely regulate the ligand exchange of CQDs, resulting in the suppressed energetic disorder and diminished charge-transport barriers in the CQD solids compared to those of the CQD solids prepared using AA. The DMAI-treated quantum dots were characterized and analyzed by transmission electron microscopy, X-ray photoelectron spectroscopy, and 2D grazing-incidence wide-and small-angle X-ray scattering spectrometry. The results show PbI2-related Bragg peaks in the AA-treated CQD solid films, indicating a thick layer of PbI2 crystal matrix being formed in the CQD solids, whereas there was no obvious PbI2 signal observed in DMAI-treated CQD solids. These results also demonstrate that DMAI provides additional I−, improving the surface passivation of the CQDs and reducing trap-assisted recombination. For the infrared photovoltaic applications, the CQDSC devices were fabricated, which shows that the photovoltaic performance of CQDSCs was significantly improved. The power conversion efficiency of DMAI-based CQDSCs was improved by 17.8% compared with that of the AA-based CQDSC. The charge-carrier dynamics in both CQD solids and full solar cell devices were analyzed in detail, revealing that the improved photovoltaic performance in DMAI-based CQDSCs was attributed to the facilitated charge-carrier transport within the CQD solids and suppressed trap-assisted recombination, resulting from eliminated charge-transport barriers and improved surface passivation of CQDs, respectively. This work provides a new avenue to controlling the surface chemistry of infrared CQDs and a feasible approach to substantially diminishing the charge transfer barriers of CQD solids for infrared solar cells.![]()
Colloidal quantum dots (CQDs) are extremely promising infrared optoelectronic materials for efficient solar cells owing to their strong infrared absorption with tunable spectra. However, the liquid-state ligand exchange of CQDs using ammonium acetate (AA) as an additive generally resulted in intensive charge-transport barriers within the CQD solids. This is induced by the high-bandgap PbI2 matrix, which considerably affects the charge-carrier extraction of CQD solar cells (CQDSCs), and thus their photovoltaic performance. Herein, dimethylammonium iodide (DMAI) was used as an additive instead for the liquid-state ligand exchange, substantially eliminating the PbI2 matrix capping the CQDs and simultaneously restraining CQD fusion during the ligand exchange, thereby reducing the barriers for the charge-carrier transport within the CQD solids. Extensive experimental studies and theoretical calculations were performed to link the surface chemistry of the CQDs with the charge-carrier dynamics within the CQD solids and full solar cell devices. The theoretical calculation results reveal that DMAI which possess small dissociation energy could finely regulate the ligand exchange of CQDs, resulting in the suppressed energetic disorder and diminished charge-transport barriers in the CQD solids compared to those of the CQD solids prepared using AA. The DMAI-treated quantum dots were characterized and analyzed by transmission electron microscopy, X-ray photoelectron spectroscopy, and 2D grazing-incidence wide-and small-angle X-ray scattering spectrometry. The results show PbI2-related Bragg peaks in the AA-treated CQD solid films, indicating a thick layer of PbI2 crystal matrix being formed in the CQD solids, whereas there was no obvious PbI2 signal observed in DMAI-treated CQD solids. These results also demonstrate that DMAI provides additional I−, improving the surface passivation of the CQDs and reducing trap-assisted recombination. For the infrared photovoltaic applications, the CQDSC devices were fabricated, which shows that the photovoltaic performance of CQDSCs was significantly improved. The power conversion efficiency of DMAI-based CQDSCs was improved by 17.8% compared with that of the AA-based CQDSC. The charge-carrier dynamics in both CQD solids and full solar cell devices were analyzed in detail, revealing that the improved photovoltaic performance in DMAI-based CQDSCs was attributed to the facilitated charge-carrier transport within the CQD solids and suppressed trap-assisted recombination, resulting from eliminated charge-transport barriers and improved surface passivation of CQDs, respectively. This work provides a new avenue to controlling the surface chemistry of infrared CQDs and a feasible approach to substantially diminishing the charge transfer barriers of CQD solids for infrared solar cells.
2023, 39(3): 221001
doi: 10.3866/PKU.WHXB202210014
Abstract:
MOF-derived metal selenides are promising candidates as effective anode materials in sodium-ion batteries (SIBs) owing to their ordered carbon skeleton structure and the high conductivity of selenides. They can be imparted with rapid electron/ion transport channels for the insertion/de-insertion of Na+. In this study, MOF-derived In2Se3 was prepared as an anode material for SIBs. However, the large volume expansion during cycling leads to structural collapse, which affects the charging and discharging circulation life of the battery. To address this, a two-dimensional rGO network was introduced on the MOF-derived In2Se3 surface by surface modification. Field-emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) results confirmed the successful synthesis of the In2Se3@C/rGO composite. The structures with two types of carbon enhanced the charge transfer kinetics and provided two stress-buffering layers. Thus, the volume change could be accommodated and simultaneously, electron transfer was accelerated. This technique was effective, as proved by the enhanced capacity retention of 95.2% at 1 A·g−1 after 500 cycles. In contrast, the capacity retention of the MOF-derived material without rGO was only 74.2%. Additionally, due to the synergistic effect of the rGO network and the MOF-derived In2Se3, the anode showed a superior capacity of 468 mAh·g−1 at 0.1 A·g−1. Conversely, at the same current density, the uncoated material delivered only a capacity of 393 mAh·g−1. To study the electrochemical process of the electrode, the In2Se3@C/rGO electrode was subjected to cyclic voltammetry (CV) measurements; the results showed that the In2Se3@C/rGO electrode had notable electrochemical reactivity. In addition, in situ X-ray diffraction (XRD) was performed to explore the sodium storage mechanism of In2Se3, demonstrating that In2Se3 had a dual Na+ storage mechanism involving conversion and alloying reactions, and revealing the origin of its high theoretical specific capacity. This study is expected to serve as a reference for preparing optimized rGO-based materials for use as SIB anodes.![]()
MOF-derived metal selenides are promising candidates as effective anode materials in sodium-ion batteries (SIBs) owing to their ordered carbon skeleton structure and the high conductivity of selenides. They can be imparted with rapid electron/ion transport channels for the insertion/de-insertion of Na+. In this study, MOF-derived In2Se3 was prepared as an anode material for SIBs. However, the large volume expansion during cycling leads to structural collapse, which affects the charging and discharging circulation life of the battery. To address this, a two-dimensional rGO network was introduced on the MOF-derived In2Se3 surface by surface modification. Field-emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) results confirmed the successful synthesis of the In2Se3@C/rGO composite. The structures with two types of carbon enhanced the charge transfer kinetics and provided two stress-buffering layers. Thus, the volume change could be accommodated and simultaneously, electron transfer was accelerated. This technique was effective, as proved by the enhanced capacity retention of 95.2% at 1 A·g−1 after 500 cycles. In contrast, the capacity retention of the MOF-derived material without rGO was only 74.2%. Additionally, due to the synergistic effect of the rGO network and the MOF-derived In2Se3, the anode showed a superior capacity of 468 mAh·g−1 at 0.1 A·g−1. Conversely, at the same current density, the uncoated material delivered only a capacity of 393 mAh·g−1. To study the electrochemical process of the electrode, the In2Se3@C/rGO electrode was subjected to cyclic voltammetry (CV) measurements; the results showed that the In2Se3@C/rGO electrode had notable electrochemical reactivity. In addition, in situ X-ray diffraction (XRD) was performed to explore the sodium storage mechanism of In2Se3, demonstrating that In2Se3 had a dual Na+ storage mechanism involving conversion and alloying reactions, and revealing the origin of its high theoretical specific capacity. This study is expected to serve as a reference for preparing optimized rGO-based materials for use as SIB anodes.
2023, 39(3): 221002
doi: 10.3866/PKU.WHXB202210026
Abstract:
Traditional industries, such as the production of cement, steel, refractory materials, and calcium carbide, involve the thermal decomposition of carbonates. Large amounts of carbon dioxide (CO2) emitted by these processes comprise more than 50% of the total industrial carbon emissions in China. Furthermore, to ensure the complete decomposition of carbonates, the input of excess heat is required, leading to the generation of residual heat. Notably, the reduction in CO2 emissions and complete utilization of the produced residual heat in the above processes are considerable challenges. However, co-thermal coupling of carbonate decomposition with H2, CH4, and other gases containing hydrogen molecules enables the production of high-value-added products such as syngas. Furthermore, this approach is environmentally friendly and economical, with potential for realization in the near future. This paper summarizes recent advances in the coupling of the thermal decomposition of carbonates with dry reforming of methane, dry reforming of alcohols, and CO2 capture. Combining CO2-emitting thermal decomposition of carbonates with the CO2-consuming methane reforming reaction allows the simultaneous reduction of CO2 emissions and syngas production. Although many experimental studies have been conducted on the coupling of the thermal decomposition of carbonates with dry reforming of methane, few reports have revealed the mechanism theoretically. At present, the theoretical research is limited to the adsorption of methane on carbonate surfaces without a clearly understood mechanism; this paper briefly introduces recent research progress in the thermal decomposition of carbonates coupled with H2 reduction and dry reforming of methane. Notably, alcohols are promising hydrogen donors for coupling with the thermal decomposition of carbonates because they can be produced by fermentation of biomass or renewable raw materials, including energy plants, waste materials from agro-industry or forestry residue materials, and organic municipal solid waste. In addition, CO2 can also be captured and converted using metal oxides (e.g., CaO, MgO); these are typical CO2 solid sorbents, which can capture CO2 by calcium looping and be regenerated in CH4. Our group has also recently made progress in the co-thermal coupling of the decomposition of carbonates with dry reforming of methane. By regulating the concentration of CH4, adding O2 to the CH4 atmosphere, and using catalysts, CO2 emissions can be decreased with the evolution of syngas. In this perspective, we summarize the latest results on the coupling of the thermal decomposition of carbonates with dry reforming of methane, including the results obtained by our research group, which allows efficient utilization of CO2 and emissions reduction. ![]()
Traditional industries, such as the production of cement, steel, refractory materials, and calcium carbide, involve the thermal decomposition of carbonates. Large amounts of carbon dioxide (CO2) emitted by these processes comprise more than 50% of the total industrial carbon emissions in China. Furthermore, to ensure the complete decomposition of carbonates, the input of excess heat is required, leading to the generation of residual heat. Notably, the reduction in CO2 emissions and complete utilization of the produced residual heat in the above processes are considerable challenges. However, co-thermal coupling of carbonate decomposition with H2, CH4, and other gases containing hydrogen molecules enables the production of high-value-added products such as syngas. Furthermore, this approach is environmentally friendly and economical, with potential for realization in the near future. This paper summarizes recent advances in the coupling of the thermal decomposition of carbonates with dry reforming of methane, dry reforming of alcohols, and CO2 capture. Combining CO2-emitting thermal decomposition of carbonates with the CO2-consuming methane reforming reaction allows the simultaneous reduction of CO2 emissions and syngas production. Although many experimental studies have been conducted on the coupling of the thermal decomposition of carbonates with dry reforming of methane, few reports have revealed the mechanism theoretically. At present, the theoretical research is limited to the adsorption of methane on carbonate surfaces without a clearly understood mechanism; this paper briefly introduces recent research progress in the thermal decomposition of carbonates coupled with H2 reduction and dry reforming of methane. Notably, alcohols are promising hydrogen donors for coupling with the thermal decomposition of carbonates because they can be produced by fermentation of biomass or renewable raw materials, including energy plants, waste materials from agro-industry or forestry residue materials, and organic municipal solid waste. In addition, CO2 can also be captured and converted using metal oxides (e.g., CaO, MgO); these are typical CO2 solid sorbents, which can capture CO2 by calcium looping and be regenerated in CH4. Our group has also recently made progress in the co-thermal coupling of the decomposition of carbonates with dry reforming of methane. By regulating the concentration of CH4, adding O2 to the CH4 atmosphere, and using catalysts, CO2 emissions can be decreased with the evolution of syngas. In this perspective, we summarize the latest results on the coupling of the thermal decomposition of carbonates with dry reforming of methane, including the results obtained by our research group, which allows efficient utilization of CO2 and emissions reduction.
2023, 39(3): 221002
doi: 10.3866/PKU.WHXB202210029
Abstract:
Peer review plays a crucial role in quality insurance of projects, especially for natural science projects, in evaluation or assessment activities. However, the results of assessment by reviewers for a proposal may scatter due to the intrinsic fuzzy attributes in the peer review process. Specifically, it may introduce a review bias with razor-thin margins in the conversion of descriptive opinions into quantified scores. The accumulation of the bias might cause overturning in the results of evaluation, leading proposals toward a twilight zone between approval and rejection. Here, a novel approach to handling scores in evaluation is presented to address the ambiguity of brink in a tight competition, whereby correlation information from multiple sources could be merged to improve the degree of consensus among reviewers for each proposal according to its essential value. This method may provide an alternate evaluation mechanism for proposal reviews and help tackle the challenges in decision intelligence.
Peer review plays a crucial role in quality insurance of projects, especially for natural science projects, in evaluation or assessment activities. However, the results of assessment by reviewers for a proposal may scatter due to the intrinsic fuzzy attributes in the peer review process. Specifically, it may introduce a review bias with razor-thin margins in the conversion of descriptive opinions into quantified scores. The accumulation of the bias might cause overturning in the results of evaluation, leading proposals toward a twilight zone between approval and rejection. Here, a novel approach to handling scores in evaluation is presented to address the ambiguity of brink in a tight competition, whereby correlation information from multiple sources could be merged to improve the degree of consensus among reviewers for each proposal according to its essential value. This method may provide an alternate evaluation mechanism for proposal reviews and help tackle the challenges in decision intelligence.
