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2024 Volume 40 Issue 6
2024, 40(6): 230600
doi: 10.3866/PKU.WHXB202306006
Abstract:
Silicon (Si) has a high theoretical gravimetric capacity (3579 mAh∙g−1 for Li15Si4), which is almost ten times higher than that of graphite (372 mAh∙g−1) anode. Besides, it has low electrochemical potentials (0.4 V vs. Li+/Li), and abundant reserves. Thus, Si becomes a key anode material for the development of high-energy lithium-ion batteries. Nano-Si, typically compounded with graphite, has opened its commercialization. But the specific capacity of commercial Si/graphite composites is generally below 600 mAh∙g−1, which is far below the theoretical specific capacity of Si. In the meanwhile, the high cost, high specific surface area and low tap density of nano-Si limit its volumetric energy density and large-scale production further. Compared to the above materials, micro-Si (1–10 μm) is gaining industry attention for its low cost, as it does not require high-energy ball milling to reduce the particle size. Also, low specific surface area and high tap density conduce to reducing interfacial side reactions and increasing volumetric energy density. Therefore, micro-Si has a particular advantage over application in high volumetric energy density storage devices. However, due to the huge stress caused by significant volume change (300%), there are more severe problems such as particle pulverization, electrode disintegration, conductive network failure and uncontrolled growth of solid electrolyte interphases, which greatly hinder its commercialization. Binders are essential in adapting to Si volume changes to ensure the integrity of the electrode and keeping the tight contact among the active material, conductive additive and current collector to provide a stable conductive network. The development of high-capacity and high-stability micro-Si-based anodes poses greater challenges to the design of binders. In this review, we first clarify the binding mechanism of binders, factors that influence the bonding forces, and design strategies of binders for relieving the volume change of Si electrodes. As a major part, we systematically discuss the strategies and corresponding mechanisms of functional binders for silicon-based anodes from aspects of self-healing binders, conductive binders, ion-conductive binders, and the facilitating effect of functional binders on the stable SEI (Solid Electrolyte Interphase) formation. Finally, the existing problems and challenges are pointed out in terms of long-cycle stability, initial Coulombic efficiency (ICE) and binder ratio under commercial loading. We put forward the promising directions for developing functional binders towards the practical use of micro-Si anode: an ideal binder should be multifunctional and helpful to robust electron/ion conductive networks and stable SEI throughout the long cycling life of micro-Si, where the polymer molecular structure of functional binders can be systematically designed by artificial intelligence and machine learning technologies. ![]()
Silicon (Si) has a high theoretical gravimetric capacity (3579 mAh∙g−1 for Li15Si4), which is almost ten times higher than that of graphite (372 mAh∙g−1) anode. Besides, it has low electrochemical potentials (0.4 V vs. Li+/Li), and abundant reserves. Thus, Si becomes a key anode material for the development of high-energy lithium-ion batteries. Nano-Si, typically compounded with graphite, has opened its commercialization. But the specific capacity of commercial Si/graphite composites is generally below 600 mAh∙g−1, which is far below the theoretical specific capacity of Si. In the meanwhile, the high cost, high specific surface area and low tap density of nano-Si limit its volumetric energy density and large-scale production further. Compared to the above materials, micro-Si (1–10 μm) is gaining industry attention for its low cost, as it does not require high-energy ball milling to reduce the particle size. Also, low specific surface area and high tap density conduce to reducing interfacial side reactions and increasing volumetric energy density. Therefore, micro-Si has a particular advantage over application in high volumetric energy density storage devices. However, due to the huge stress caused by significant volume change (300%), there are more severe problems such as particle pulverization, electrode disintegration, conductive network failure and uncontrolled growth of solid electrolyte interphases, which greatly hinder its commercialization. Binders are essential in adapting to Si volume changes to ensure the integrity of the electrode and keeping the tight contact among the active material, conductive additive and current collector to provide a stable conductive network. The development of high-capacity and high-stability micro-Si-based anodes poses greater challenges to the design of binders. In this review, we first clarify the binding mechanism of binders, factors that influence the bonding forces, and design strategies of binders for relieving the volume change of Si electrodes. As a major part, we systematically discuss the strategies and corresponding mechanisms of functional binders for silicon-based anodes from aspects of self-healing binders, conductive binders, ion-conductive binders, and the facilitating effect of functional binders on the stable SEI (Solid Electrolyte Interphase) formation. Finally, the existing problems and challenges are pointed out in terms of long-cycle stability, initial Coulombic efficiency (ICE) and binder ratio under commercial loading. We put forward the promising directions for developing functional binders towards the practical use of micro-Si anode: an ideal binder should be multifunctional and helpful to robust electron/ion conductive networks and stable SEI throughout the long cycling life of micro-Si, where the polymer molecular structure of functional binders can be systematically designed by artificial intelligence and machine learning technologies.
2024, 40(6): 230605
doi: 10.3866/PKU.WHXB202306050
Abstract:
Bulk-heterojunctions (BHJ) Organic solar cells (OSCs) have garnered considerable attention in the past two decades due to their advantages, including mechanical flexibility, lightweight, low-cost solution-processability, and semitransparency. The recent years have witnessed rapid progress in the realm of OSCs centered around non-fullerene acceptors (NFAs) thanks to the distinct merits of NFAs's stronger and broader absorption, highly adjustable energy levels, and easily modification of molecular structures. The power conversion efficiency (PCE) of single-junction OSCs has now reached high values of over 19%, which brings them closer to the threshold for commercial viability. This increase in PCE is attributed to advancements in active layer materials, device engineering, and a deeper comprehension of device physics. Nevertheless, achieving high PCE is not the only requirement for commercialization, while the stability of the devices is equally pivotal. The photovoltaic performance degradation of BHJ OSCs devices has been widely observed, however, the research on the stability of NFA-based OSCs has received less attention than efforts directed towards improving PCE through novel material development. The instability of NFA-OSCs has been one of the key obstacles limiting their transition to commercial applications. Various factors, encompassing both external and intrinsic variables, influence their stability. External factors, such as light, heat, water, and stress, exert significant impact on the stability of OSCs. Effective encapsulation can protect the devices from contact with oxygen and water, curtailing degradation. Encapsulated OSCs have demonstrated encouraging operational lifetimes of several years under certain degradation environments, in stark contrast to unencapsulated OSCs which often succumb to rapid degradation, losing their performance within a matter of minutes to days. Intrinsic degradation processes within NFA-OSCs involve material stability, morphology stability of BHJ and interface stability. The degradation of NFA based cells was not fully investigated as has been done on the fullerene based OSCs. There remains a lack of concrete molecular design rules to enhance the stability of NFA based OSCs. Therefore, it is still highly needed to further understand the intrinsic degradation processes of NFA-OSCs and to find proper ways to suppress these degradation processes. Herein, in this context, we present a comprehensive review encompassing the intrinsic fundamentals of instability including photo-oxidation of NFAs, interlayer-induced degradation of NFAs and the blend film morphology. Furthermore, we summarize recent advancements in strategies aimed at enhancing the stability of NFA-OSCs. These include stable NFA molecular design, mitigation of interfacial chemical reactions, and implementation of ternary strategies. It is our aspiration that this concise review will serve as a valuable resource for researchers interested in stability considerations, providing a guiding framework for future endeavors in achieving both efficient and stable NFA-OSCs. ![]()
Bulk-heterojunctions (BHJ) Organic solar cells (OSCs) have garnered considerable attention in the past two decades due to their advantages, including mechanical flexibility, lightweight, low-cost solution-processability, and semitransparency. The recent years have witnessed rapid progress in the realm of OSCs centered around non-fullerene acceptors (NFAs) thanks to the distinct merits of NFAs's stronger and broader absorption, highly adjustable energy levels, and easily modification of molecular structures. The power conversion efficiency (PCE) of single-junction OSCs has now reached high values of over 19%, which brings them closer to the threshold for commercial viability. This increase in PCE is attributed to advancements in active layer materials, device engineering, and a deeper comprehension of device physics. Nevertheless, achieving high PCE is not the only requirement for commercialization, while the stability of the devices is equally pivotal. The photovoltaic performance degradation of BHJ OSCs devices has been widely observed, however, the research on the stability of NFA-based OSCs has received less attention than efforts directed towards improving PCE through novel material development. The instability of NFA-OSCs has been one of the key obstacles limiting their transition to commercial applications. Various factors, encompassing both external and intrinsic variables, influence their stability. External factors, such as light, heat, water, and stress, exert significant impact on the stability of OSCs. Effective encapsulation can protect the devices from contact with oxygen and water, curtailing degradation. Encapsulated OSCs have demonstrated encouraging operational lifetimes of several years under certain degradation environments, in stark contrast to unencapsulated OSCs which often succumb to rapid degradation, losing their performance within a matter of minutes to days. Intrinsic degradation processes within NFA-OSCs involve material stability, morphology stability of BHJ and interface stability. The degradation of NFA based cells was not fully investigated as has been done on the fullerene based OSCs. There remains a lack of concrete molecular design rules to enhance the stability of NFA based OSCs. Therefore, it is still highly needed to further understand the intrinsic degradation processes of NFA-OSCs and to find proper ways to suppress these degradation processes. Herein, in this context, we present a comprehensive review encompassing the intrinsic fundamentals of instability including photo-oxidation of NFAs, interlayer-induced degradation of NFAs and the blend film morphology. Furthermore, we summarize recent advancements in strategies aimed at enhancing the stability of NFA-OSCs. These include stable NFA molecular design, mitigation of interfacial chemical reactions, and implementation of ternary strategies. It is our aspiration that this concise review will serve as a valuable resource for researchers interested in stability considerations, providing a guiding framework for future endeavors in achieving both efficient and stable NFA-OSCs.
2024, 40(6): 230701
doi: 10.3866/PKU.WHXB202307017
Abstract:
Amidst widespread consumption and the scarcity of non-renewable fossil fuels, the advancement of clean energy sources like solar and wind energy holds immense significance. Nevertheless, these clean energy sources grapple with unstable power supply, underscoring the pressing need for the enhancement of large-scale energy conversion and storage devices. Zinc-air batteries, boasting high energy density, safety, affordability, ease of assembly, eco-friendliness, and abundant zinc metal resources, exhibit promising potential as energy storage and conversion solutions. Nevertheless, various challenges persist in their application, including a limited cycle life and inadequate power density. Throughout the charge and discharge cycles, factors such as the dendritic growth of the zinc negative electrode, the formation of ZnO passivation layers, electrolyte evaporation, and side reactions involving the diffusion of zincate ions to the positive electrode collectively exert influence on the performance of zinc-air batteries. The separator plays a crucial role in zinc-air batteries by isolating the positive and negative electrodes to prevent short circuits, and these aforementioned issues can be resolved through optimization of the design. Until now, the commonly employed separators in zinc-air batteries can be categorized into various types: standard porous separators, anion exchange membranes, polymer gel electrolyte membranes, and composite membranes comprising diverse polymer compositions. Among these, within the context of separator research, porous separators of the polyolefin type are generally utilized in aqueous alkaline zinc-air batteries. Nevertheless, their pronounced hydrophobic nature results in markedly diminished ion conductivity. Conversely, gel-based solid-state or semi-solid-state electrolyte membranes are tailored for flexible electronic device applications. This adaptation ensures that zinc-air batteries uphold favorable electrochemical performance even under deformation conditions, simultaneously addressing the challenge of electrolyte volatilization to a certain degree. Fundamental attributes of the separator, such as pore size, hydrophilicity, and other properties, significantly impact the battery's lifespan and charge/discharge performance. Nevertheless, research on separators and their modifications to enhance zinc-air battery performance, along with the underlying principles, lags behind other aspects of zinc-air battery research, presenting ample room for advancement. This review offers a concise overview of zinc-air battery development, using aqueous alkaline zinc-air batteries as an example to elucidate their operational principles. The objective is to grasp the challenges leading to battery failure in different components and to particularly analyze how separator performance influences overall battery efficiency. This includes aspects such as ion selectivity, ion conductivity, stability, and water retention of the separator. The overview is divided into two main sections: (1) elucidating the fundamental structure and operational principles of the zinc-air battery, and (2) comprehensively exploring the fundamental attributes of the separator and its pivotal function within the zinc-air battery. The research progress and perspective for the development of zinc-air battery separators are also discussed and anticipated. ![]()
Amidst widespread consumption and the scarcity of non-renewable fossil fuels, the advancement of clean energy sources like solar and wind energy holds immense significance. Nevertheless, these clean energy sources grapple with unstable power supply, underscoring the pressing need for the enhancement of large-scale energy conversion and storage devices. Zinc-air batteries, boasting high energy density, safety, affordability, ease of assembly, eco-friendliness, and abundant zinc metal resources, exhibit promising potential as energy storage and conversion solutions. Nevertheless, various challenges persist in their application, including a limited cycle life and inadequate power density. Throughout the charge and discharge cycles, factors such as the dendritic growth of the zinc negative electrode, the formation of ZnO passivation layers, electrolyte evaporation, and side reactions involving the diffusion of zincate ions to the positive electrode collectively exert influence on the performance of zinc-air batteries. The separator plays a crucial role in zinc-air batteries by isolating the positive and negative electrodes to prevent short circuits, and these aforementioned issues can be resolved through optimization of the design. Until now, the commonly employed separators in zinc-air batteries can be categorized into various types: standard porous separators, anion exchange membranes, polymer gel electrolyte membranes, and composite membranes comprising diverse polymer compositions. Among these, within the context of separator research, porous separators of the polyolefin type are generally utilized in aqueous alkaline zinc-air batteries. Nevertheless, their pronounced hydrophobic nature results in markedly diminished ion conductivity. Conversely, gel-based solid-state or semi-solid-state electrolyte membranes are tailored for flexible electronic device applications. This adaptation ensures that zinc-air batteries uphold favorable electrochemical performance even under deformation conditions, simultaneously addressing the challenge of electrolyte volatilization to a certain degree. Fundamental attributes of the separator, such as pore size, hydrophilicity, and other properties, significantly impact the battery's lifespan and charge/discharge performance. Nevertheless, research on separators and their modifications to enhance zinc-air battery performance, along with the underlying principles, lags behind other aspects of zinc-air battery research, presenting ample room for advancement. This review offers a concise overview of zinc-air battery development, using aqueous alkaline zinc-air batteries as an example to elucidate their operational principles. The objective is to grasp the challenges leading to battery failure in different components and to particularly analyze how separator performance influences overall battery efficiency. This includes aspects such as ion selectivity, ion conductivity, stability, and water retention of the separator. The overview is divided into two main sections: (1) elucidating the fundamental structure and operational principles of the zinc-air battery, and (2) comprehensively exploring the fundamental attributes of the separator and its pivotal function within the zinc-air battery. The research progress and perspective for the development of zinc-air battery separators are also discussed and anticipated.
2024, 40(6): 230305
doi: 10.3866/PKU.WHXB202303057
Abstract:
Formamidinium lead iodide (FAPbI3) perovskite solar cells (PSCs) have attracted significant attention owing to their outstanding optoelectronic properties, but long-term device stability is still a crucial issue related to FAPbI3 PSCs. FAPbI3 undergoes phase transition from black perovskite phase to yellow non-perovskite phase at room temperature, and moisture triggers this phase transition. One of the most widely used methods to improve the stability of PSCs is interface engineering. Being green functional solvents, ionic liquids (ILs) have been regarded as potential alternatives to toxic interface modifiers, thereby increasing their commercial viability and accelerating their adoption in the renewable energy market. In this study, an IL, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM[BF4]) was used to modify the interface between the electron transport layer and perovskite layer due to its low volatility, low toxicity, high conductivity, and high thermal stability. The introduction of IL not only reduces interface defects but also improves perovskite film quality. Density functional theory (DFT) calculations show that there is a strong interface interaction between the IL and perovskite surface that is beneficial to decrease the density of defect states of the perovskite surface and stabilize the perovskite lattice. Apart from the defects in the perovskite film, solution-processed SnO2 also suffers from surface imperfections. Defects on the SnO2 surface generate defect states, which cause band alignment issues and stability issues. DFT calculations show that the surface gap states with IL are smaller than those without IL. Such weakened surface gap states indicate reduced carrier recombination at the surface region, which improves the device performance. Consequently, we achieved a power conversion efficiency exceeding 22% for the IL-modified FAPbI3 PSCs (control ~21%). After storing for over 1800 h in a dry box (relative humidity (RH) ~20%), the champion device retained ~90% of its initial efficiency, while the control devices degraded into non-perovskite yellow hexagonal phase (δ-FAPbI3). ![]()
Formamidinium lead iodide (FAPbI3) perovskite solar cells (PSCs) have attracted significant attention owing to their outstanding optoelectronic properties, but long-term device stability is still a crucial issue related to FAPbI3 PSCs. FAPbI3 undergoes phase transition from black perovskite phase to yellow non-perovskite phase at room temperature, and moisture triggers this phase transition. One of the most widely used methods to improve the stability of PSCs is interface engineering. Being green functional solvents, ionic liquids (ILs) have been regarded as potential alternatives to toxic interface modifiers, thereby increasing their commercial viability and accelerating their adoption in the renewable energy market. In this study, an IL, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM[BF4]) was used to modify the interface between the electron transport layer and perovskite layer due to its low volatility, low toxicity, high conductivity, and high thermal stability. The introduction of IL not only reduces interface defects but also improves perovskite film quality. Density functional theory (DFT) calculations show that there is a strong interface interaction between the IL and perovskite surface that is beneficial to decrease the density of defect states of the perovskite surface and stabilize the perovskite lattice. Apart from the defects in the perovskite film, solution-processed SnO2 also suffers from surface imperfections. Defects on the SnO2 surface generate defect states, which cause band alignment issues and stability issues. DFT calculations show that the surface gap states with IL are smaller than those without IL. Such weakened surface gap states indicate reduced carrier recombination at the surface region, which improves the device performance. Consequently, we achieved a power conversion efficiency exceeding 22% for the IL-modified FAPbI3 PSCs (control ~21%). After storing for over 1800 h in a dry box (relative humidity (RH) ~20%), the champion device retained ~90% of its initial efficiency, while the control devices degraded into non-perovskite yellow hexagonal phase (δ-FAPbI3).
2024, 40(6): 230500
doi: 10.3866/PKU.WHXB202305004
Abstract:
With the depletion of fossil fuel resources and the increasing severity of environmental pollution, it has become imperative to seek energy conversion devices with low cost, high efficiency and excellent environmental compatibility. Considering their high theoretical energy density, affordability and environmentally friendly nature, Zn-air batteries (ZABs) are regarded as promising energy storage and conversion devices. The utilization of seawater in ZABs (S-ZABs) holds great potential, given the abundance of seawater reserves, offering economic and social benefits such as reducing electrolyte costs and alleviating competition for freshwater consumption in human activities. However, the application of S-ZABs remains challenging, particularly in constructing high-performance cathode oxygen reduction reaction (ORR) catalysts that are highly resistant to Cl− corrosion in seawater-based electrolytes. In this study, we have engineered an ultrathin carbon-chainmail-shell encapsulated Co9Se8 nanoparticles on N-doped mesoporous carbon (named as NMC-Co9Se8) electrocatalysts using the high-temperature selenization strategy. The ultrathin carbon-chainmail-shell on the outside improves electron transfer during the electrocatalysis and suppresses nanoparticles agglomeration. Additionally, it could act as armor for protecting the inner active site from the adsorption of corrosive Cl−. Benefit from this unique structure, the NMC-Co9Se8 catalyst exhibits excellent ORR performance, with an onset potential of 0.904 V and a half-wave potential of 0.860 V in seawater-based electrolytes. The catalyst also affords the lowest Tafel slope (35.5 mV∙dec−1) and the highest kinetics current density of 9.816 mA∙cm−2 at 0.85 V among all investigated samples. Owing to the protective effect of the ultrathin carbon-chainmail-shell on the inner active sites, the NMC-Co9Se8 catalyst retains 91.6% of its initial activity after continuous operation for 50000 s, surpassing the commercial Pt/C catalyst (with a current retention rate of 62.8%). More importantly, the S-ZABs based on the NMC-Co9Se8 catalyst deliver a high maximum power density of 172.4 mW∙cm−2 and a high specific capacity of 643.9 mAh∙g−1, exceeding those of S-ZABs powered by the commercial Pt/C catalyst (151.2 mW∙cm−2 and 548.3 mAh∙g−1). Furthermore, the S-ZABs driven by the NMC-Co9Se8 catalyst demonstrate a discharge stability for up to 150 h and maintain a stable charge-discharge cycle stability over 200 h, demonstrating the practical application performance of the NMC-Co9Se8 catalyst. In practical applications, the S-ZABs driven by the NMC-Co9Se8 catalyst can illuminate a light-emitting diode (LED) with a driving voltage of 2 V for several hours. This work provides new ideas for developing efficient and durable catalysts with high Cl− corrosion resistance for applications in seawater-based Zn-air batteries and other energy conversion technologies. ![]()
With the depletion of fossil fuel resources and the increasing severity of environmental pollution, it has become imperative to seek energy conversion devices with low cost, high efficiency and excellent environmental compatibility. Considering their high theoretical energy density, affordability and environmentally friendly nature, Zn-air batteries (ZABs) are regarded as promising energy storage and conversion devices. The utilization of seawater in ZABs (S-ZABs) holds great potential, given the abundance of seawater reserves, offering economic and social benefits such as reducing electrolyte costs and alleviating competition for freshwater consumption in human activities. However, the application of S-ZABs remains challenging, particularly in constructing high-performance cathode oxygen reduction reaction (ORR) catalysts that are highly resistant to Cl− corrosion in seawater-based electrolytes. In this study, we have engineered an ultrathin carbon-chainmail-shell encapsulated Co9Se8 nanoparticles on N-doped mesoporous carbon (named as NMC-Co9Se8) electrocatalysts using the high-temperature selenization strategy. The ultrathin carbon-chainmail-shell on the outside improves electron transfer during the electrocatalysis and suppresses nanoparticles agglomeration. Additionally, it could act as armor for protecting the inner active site from the adsorption of corrosive Cl−. Benefit from this unique structure, the NMC-Co9Se8 catalyst exhibits excellent ORR performance, with an onset potential of 0.904 V and a half-wave potential of 0.860 V in seawater-based electrolytes. The catalyst also affords the lowest Tafel slope (35.5 mV∙dec−1) and the highest kinetics current density of 9.816 mA∙cm−2 at 0.85 V among all investigated samples. Owing to the protective effect of the ultrathin carbon-chainmail-shell on the inner active sites, the NMC-Co9Se8 catalyst retains 91.6% of its initial activity after continuous operation for 50000 s, surpassing the commercial Pt/C catalyst (with a current retention rate of 62.8%). More importantly, the S-ZABs based on the NMC-Co9Se8 catalyst deliver a high maximum power density of 172.4 mW∙cm−2 and a high specific capacity of 643.9 mAh∙g−1, exceeding those of S-ZABs powered by the commercial Pt/C catalyst (151.2 mW∙cm−2 and 548.3 mAh∙g−1). Furthermore, the S-ZABs driven by the NMC-Co9Se8 catalyst demonstrate a discharge stability for up to 150 h and maintain a stable charge-discharge cycle stability over 200 h, demonstrating the practical application performance of the NMC-Co9Se8 catalyst. In practical applications, the S-ZABs driven by the NMC-Co9Se8 catalyst can illuminate a light-emitting diode (LED) with a driving voltage of 2 V for several hours. This work provides new ideas for developing efficient and durable catalysts with high Cl− corrosion resistance for applications in seawater-based Zn-air batteries and other energy conversion technologies.
2024, 40(6): 230601
doi: 10.3866/PKU.WHXB202306013
Abstract:
Solid oxide electrolysis cells (SOECs) could convert CO2 to CO powered by clean electricity with low overpotential, high Faradaic efficiency, and high current density. Since the performance of SOEC is affected by sluggish oxygen evolution reaction (OER) kinetics at the anodes, the modification of anode materials is crucial for the further application of SOEC. Perovskites with high configurational entropy exhibit high catalytic activity in many reactions, but are rarely reported in SOECs. Herein, two kinds of high entropy perovskites (HEPs), with formulas of (Pr0.2La0.2Sm0.2Nd0.2Gd0.2)BaCo2O6−δ (A-HEP) and Pr(Ba0.2Sr0.2Ca0.2Na0.2K0.2) Co2O6−δ (A′-HEP), are synthesized by doping different rare earth metal, and alkaline metal or alkaline earth metal ions into A-site and A′-site of the double perovskites. Rietveld refinement of X-ray diffraction patterns and elemental maps of scanning electron microscope images confirm the successful synthesis of the two samples. The tetragonal double perovskite structure of A-HEP and the transformation to orthorhombic structure of A′-HEP due to the difference in average atomic radii and oxidation states of the doped ions are also detected. Co 2p X-ray photoelectron spectroscopy (XPS) and O K-edge X-ray absorption spectroscopy reveal that the average oxidation state of Co is lifted from +3.23 in Aʹ-HEP to +3.39 in A-HEP, and the hybridization of Co 2p and O 1s orbitals is also enhanced in A-HEP, which increase the electron transfer pathway and reduce the transfer barrier. Therefore, the electrical conductivity of A-HEP at 800 ℃ is higher than that of Aʹ-HEP. Moreover, the increased absorption oxygen species concentration of A-HEP in O 1s XPS and O2-temperature programmed desorption results indicates more surface oxygen vacancies, thus increasing active sites for the anodic OER. Consequently, the anodic polarization resistances related to oxygen transportation, electron transfer and surface reaction processes are decreased remarkably in A-HEP, resulting in a high current density of 1.76 A∙cm−2 at 800 ℃ and a stability of 200 h. This work presents a new method for designing high-performance HEPs as SOEC anode materials. ![]()
Solid oxide electrolysis cells (SOECs) could convert CO2 to CO powered by clean electricity with low overpotential, high Faradaic efficiency, and high current density. Since the performance of SOEC is affected by sluggish oxygen evolution reaction (OER) kinetics at the anodes, the modification of anode materials is crucial for the further application of SOEC. Perovskites with high configurational entropy exhibit high catalytic activity in many reactions, but are rarely reported in SOECs. Herein, two kinds of high entropy perovskites (HEPs), with formulas of (Pr0.2La0.2Sm0.2Nd0.2Gd0.2)BaCo2O6−δ (A-HEP) and Pr(Ba0.2Sr0.2Ca0.2Na0.2K0.2) Co2O6−δ (A′-HEP), are synthesized by doping different rare earth metal, and alkaline metal or alkaline earth metal ions into A-site and A′-site of the double perovskites. Rietveld refinement of X-ray diffraction patterns and elemental maps of scanning electron microscope images confirm the successful synthesis of the two samples. The tetragonal double perovskite structure of A-HEP and the transformation to orthorhombic structure of A′-HEP due to the difference in average atomic radii and oxidation states of the doped ions are also detected. Co 2p X-ray photoelectron spectroscopy (XPS) and O K-edge X-ray absorption spectroscopy reveal that the average oxidation state of Co is lifted from +3.23 in Aʹ-HEP to +3.39 in A-HEP, and the hybridization of Co 2p and O 1s orbitals is also enhanced in A-HEP, which increase the electron transfer pathway and reduce the transfer barrier. Therefore, the electrical conductivity of A-HEP at 800 ℃ is higher than that of Aʹ-HEP. Moreover, the increased absorption oxygen species concentration of A-HEP in O 1s XPS and O2-temperature programmed desorption results indicates more surface oxygen vacancies, thus increasing active sites for the anodic OER. Consequently, the anodic polarization resistances related to oxygen transportation, electron transfer and surface reaction processes are decreased remarkably in A-HEP, resulting in a high current density of 1.76 A∙cm−2 at 800 ℃ and a stability of 200 h. This work presents a new method for designing high-performance HEPs as SOEC anode materials.
2024, 40(6): 230700
doi: 10.3866/PKU.WHXB202307006
Abstract:
Sodium-ion batteries (SIBs), featuring with adequate sodium resources, relatively high safety, and similar chemical properties between sodium and lithium, have been considered one of the most potential candidates to lithium-ion batteries (LIBs). However, the larger radii of sodium ions (vs. lithium ions) lead to sluggish diffusion kinetics of sodium ions, low storage capacity, and adverse volume variation during sodiation and desodiation. In particular, anode materials work well in LIBs have been proved ineffective in SIBs. Therefore, the development of cheap anode materials with remarkable performance is critical to the commercialization of SIBs. Despite the good conductivity and robust stability of carbon materials, they usually showcase moderate discharge capacity and poor rate performance in SIBs. Iron sulfides are considered promising anode materials for SIBs due to their high theoretical capacity. Nevertheless, iron sulfides exhibit severe volumetric expansion during charge and discharge, resulting in low rate performance and poor stability. In this regard, hybridizing carbon materials with iron sulfides to configure composite materials is an important way to improve the electrochemical performance of SIBs. Here, three-dimensional cluster-structured sulfur-doped carbon-coated Fe0.95S1.05 nanospheres (Fe0.95S1.05@SC) are crafted by one-step annealing of ferrocene and sulfur powder, of which the implementation as anode of sodium ion batteries is reported. Scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results confirm the successful synthesis of the Fe0.95S1.05@SC composite. The coated sulfur-doped carbon layer can improve the conductivity of the Fe0.95S1.05 material and alleviate corresponding volume expansion during the reaction process, thus delivering a robust electrochemical stability. The interconnected cluster structures of Fe0.95S1.05@SC provide channels for the transport of electrons and ions, enabling the material excellent rate performance. Thanks to the unique structures of as-made Fe0.95S1.0@SC, when acting as anodes of SIBs, it demonstrates stable cycling performance and high rate performance. The electrochemical reaction process on Fe0.95S1.05@SC electrode is studied by cyclic voltammetry, validating that this electrode has good electrochemical reversibility. During the first few cycles of charging and discharging process, stable solid electrolyte interphase (SEI) layer forms on the surface of the carbon layer, which helps to avoid the direct exposure of Fe0.95S1.05 to the electrolyte and prevent the material from inactivation by the dissolution or escape of the sulfur element within Fe0.95S1.0. In the half-battery system, after 100 cycles at 0.1 A∙g−1, the high specific capacity of 614.7 mAh∙g−1 for Fe0.95S1.05@SC is retained, and the specific capacity at 10 A∙g−1 can still reach 235.7 mAh∙g−1. In the full battery system, the reversible capacity at 0.1 and 10 A∙g−1 is 482.8 and 288.3 mAh∙g−1, respectively. The as-made Fe0.95S1.05@SC with excellent electrochemical properties holds promise as anodes for sodium-ion batteries.![]()
Sodium-ion batteries (SIBs), featuring with adequate sodium resources, relatively high safety, and similar chemical properties between sodium and lithium, have been considered one of the most potential candidates to lithium-ion batteries (LIBs). However, the larger radii of sodium ions (vs. lithium ions) lead to sluggish diffusion kinetics of sodium ions, low storage capacity, and adverse volume variation during sodiation and desodiation. In particular, anode materials work well in LIBs have been proved ineffective in SIBs. Therefore, the development of cheap anode materials with remarkable performance is critical to the commercialization of SIBs. Despite the good conductivity and robust stability of carbon materials, they usually showcase moderate discharge capacity and poor rate performance in SIBs. Iron sulfides are considered promising anode materials for SIBs due to their high theoretical capacity. Nevertheless, iron sulfides exhibit severe volumetric expansion during charge and discharge, resulting in low rate performance and poor stability. In this regard, hybridizing carbon materials with iron sulfides to configure composite materials is an important way to improve the electrochemical performance of SIBs. Here, three-dimensional cluster-structured sulfur-doped carbon-coated Fe0.95S1.05 nanospheres (Fe0.95S1.05@SC) are crafted by one-step annealing of ferrocene and sulfur powder, of which the implementation as anode of sodium ion batteries is reported. Scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results confirm the successful synthesis of the Fe0.95S1.05@SC composite. The coated sulfur-doped carbon layer can improve the conductivity of the Fe0.95S1.05 material and alleviate corresponding volume expansion during the reaction process, thus delivering a robust electrochemical stability. The interconnected cluster structures of Fe0.95S1.05@SC provide channels for the transport of electrons and ions, enabling the material excellent rate performance. Thanks to the unique structures of as-made Fe0.95S1.0@SC, when acting as anodes of SIBs, it demonstrates stable cycling performance and high rate performance. The electrochemical reaction process on Fe0.95S1.05@SC electrode is studied by cyclic voltammetry, validating that this electrode has good electrochemical reversibility. During the first few cycles of charging and discharging process, stable solid electrolyte interphase (SEI) layer forms on the surface of the carbon layer, which helps to avoid the direct exposure of Fe0.95S1.05 to the electrolyte and prevent the material from inactivation by the dissolution or escape of the sulfur element within Fe0.95S1.0. In the half-battery system, after 100 cycles at 0.1 A∙g−1, the high specific capacity of 614.7 mAh∙g−1 for Fe0.95S1.05@SC is retained, and the specific capacity at 10 A∙g−1 can still reach 235.7 mAh∙g−1. In the full battery system, the reversible capacity at 0.1 and 10 A∙g−1 is 482.8 and 288.3 mAh∙g−1, respectively. The as-made Fe0.95S1.05@SC with excellent electrochemical properties holds promise as anodes for sodium-ion batteries.
2024, 40(6): 230600
doi: 10.3866/PKU.WHXB202306005
Abstract:
The storage of intermittent wind and solar electricity requires grid-level energy storage devices, and due to the abundance and wide distribution of Na resources, Na-ion batteries (NIBs) are much more cost-effective and have shown greater potential for large-scale energy storage than Li-ion batteries (LIBs). However, the lack of suitable cathode hinders the practical use of NIBs, so exploring suitable cathode materials that can maintain a balance between high energy density and cost-effectiveness is essential for NIBs. Ni-Mn based layered oxides are important cathode materials for NIBs, offering relatively high potential through the multi-electron redox reaction of Ni4+/Ni3+/Ni2+ as well as the low-cost and non-toxic nature of Mn4+. P2-Na0.67[Ni0.33Mn0.67]O2 was the first reported Ni-Mn based Na-ion battery cathode with a high capacity of ~160 mAh∙g−1 in the voltage range of 2.0–4.5 V, while irreversible P2-O2 phase transition above 4.1 V makes poor capacity retention and limits their applications. Moreover, a dilemma has emerged in that a costly element (Ni) is used for sodium-ion batteries, which is supposed to be low-cost. With the intensive research in recent years, introducing an appropriate amount of anionic redox can effectively improve energy density while simultaneously reducing the amount of high-cost transition metals, such as V, Co, and Ni. However, because of irreversible oxygen loss and Mn4+/Mn3+ redox activation, voltage decay is difficult to avoid for most of these anion-redox materials. In this research, we report a Li-substituted Nax[Ni, Mn]O2 cathode, the designed formula being Na0.85[Li0.2Ni0.15Mn0.65]O2. This material shows a unique combination of both cationic redox (Ni4+/Ni3+/Ni2+) and anionic redox (O2−/O2n−) during charge and discharge, showing a high capacity of ~150 mAh∙g−1 (10 mA∙g−1, 1.5–4.5 V) with only 0.15 Ni. With an optimized voltage range, the material shows a capacity of ~100 mAh∙g−1 and stable cycling performance (80% of initial capacity after 100 cycles at 10 mA∙g−1 within 2.5–4.25 V) and high-rate capability (the capacity of 500 mA∙g−1 is 80% of 10 mA∙g−1, 2.5–4.25 V). Moreover, we demonstrate an effective way to suppress the voltage decay and Mn reduction through Ni3+ as a redox barrier. Specifically, during the discharge process, the Mn4+/Mn3+ reduction process was replaced by the Ni3+/Ni2+ reduction process with higher redox potential in the layered oxides. In addition, the full Ni2+/Ni4+ redox can compensate for the partial oxygen redox loss in the subsequent cycles. We believe that introducing the anion redox through Li substitution and the use of Ni3+ as a redox barrier to suppress the voltage decay will provide a new way in the design of NIBs’ cathode materials, with potential benefits such as higher energy density, lower cost, and longer cycle life.![]()
The storage of intermittent wind and solar electricity requires grid-level energy storage devices, and due to the abundance and wide distribution of Na resources, Na-ion batteries (NIBs) are much more cost-effective and have shown greater potential for large-scale energy storage than Li-ion batteries (LIBs). However, the lack of suitable cathode hinders the practical use of NIBs, so exploring suitable cathode materials that can maintain a balance between high energy density and cost-effectiveness is essential for NIBs. Ni-Mn based layered oxides are important cathode materials for NIBs, offering relatively high potential through the multi-electron redox reaction of Ni4+/Ni3+/Ni2+ as well as the low-cost and non-toxic nature of Mn4+. P2-Na0.67[Ni0.33Mn0.67]O2 was the first reported Ni-Mn based Na-ion battery cathode with a high capacity of ~160 mAh∙g−1 in the voltage range of 2.0–4.5 V, while irreversible P2-O2 phase transition above 4.1 V makes poor capacity retention and limits their applications. Moreover, a dilemma has emerged in that a costly element (Ni) is used for sodium-ion batteries, which is supposed to be low-cost. With the intensive research in recent years, introducing an appropriate amount of anionic redox can effectively improve energy density while simultaneously reducing the amount of high-cost transition metals, such as V, Co, and Ni. However, because of irreversible oxygen loss and Mn4+/Mn3+ redox activation, voltage decay is difficult to avoid for most of these anion-redox materials. In this research, we report a Li-substituted Nax[Ni, Mn]O2 cathode, the designed formula being Na0.85[Li0.2Ni0.15Mn0.65]O2. This material shows a unique combination of both cationic redox (Ni4+/Ni3+/Ni2+) and anionic redox (O2−/O2n−) during charge and discharge, showing a high capacity of ~150 mAh∙g−1 (10 mA∙g−1, 1.5–4.5 V) with only 0.15 Ni. With an optimized voltage range, the material shows a capacity of ~100 mAh∙g−1 and stable cycling performance (80% of initial capacity after 100 cycles at 10 mA∙g−1 within 2.5–4.25 V) and high-rate capability (the capacity of 500 mA∙g−1 is 80% of 10 mA∙g−1, 2.5–4.25 V). Moreover, we demonstrate an effective way to suppress the voltage decay and Mn reduction through Ni3+ as a redox barrier. Specifically, during the discharge process, the Mn4+/Mn3+ reduction process was replaced by the Ni3+/Ni2+ reduction process with higher redox potential in the layered oxides. In addition, the full Ni2+/Ni4+ redox can compensate for the partial oxygen redox loss in the subsequent cycles. We believe that introducing the anion redox through Li substitution and the use of Ni3+ as a redox barrier to suppress the voltage decay will provide a new way in the design of NIBs’ cathode materials, with potential benefits such as higher energy density, lower cost, and longer cycle life.
2024, 40(6): 230603
doi: 10.3866/PKU.WHXB202306039
Abstract:
Metallic lithium (Li) offers Li metal batteries (LMBs) with an opportunity to meet the high-energy demand in many fields. At present, the main cathode materials used for high-energy-density batteries are nickel-rich layered oxides, including nickel cobalt lithium manganese oxides (NCM) with intercalation chemistry. According to this plan, NMC811 demonstrates great merits in this aspect. However, there are still many problems with Li metal anode. The failure of Li anode is mainly caused by the high reactivity of Li metal, which can cause irreversible continuous reactions between Li and electrolyte to shorten cycling life. Due to multiple electroplating and stripping processes, Li anode undergoes significant volume and morphology change, increasing side reactions and the growth of Li dendrites caused by the first two factors. Electrolyte engineering, as a simple and effective modification method, can effectively solve the above problems. Among them, using electrolyte additives is a simple, efficient, and economical electrolyte engineering strategy. Herein, we proposed an anion acceptor electrolyte additive strategy for optimizing the component/structural characteristics of solid/cathode electrolyte interphases to inhibit the growth of Li dendrites and Li+ transition on cathode surface for enhancing cycling and rate performance of Li|| NCM811 battery, which is also ascribed to the regulation of Li+ solvation structure by hexafluorobenzene (HFBen) to realizing the stability of PF6− and the conductivity enhancement of electrolyte. As expected, Li||Li cells with 1% (wt) HFBen-contained electrolyte could achieve a stable cycling above 400 h at 1 mA∙cm−2, and the capacity retention rate of Li||NCM811 battery could reach 75% after 100 cycles at 200 mA∙g−1. Finally, the cycling and rate performance of Li||NMC811 batteries were significantly enhanced at 4.5 V with the help of HFBen. This work demonstrates that HFBen as an additive can effectively improve the electrochemical performance of LMBs. Moreover, the interfacial reaction mechanism across the batterywas analyzed and studied. This study provides new insights for the interface reaction between electrolyte and Li anode.![]()
Metallic lithium (Li) offers Li metal batteries (LMBs) with an opportunity to meet the high-energy demand in many fields. At present, the main cathode materials used for high-energy-density batteries are nickel-rich layered oxides, including nickel cobalt lithium manganese oxides (NCM) with intercalation chemistry. According to this plan, NMC811 demonstrates great merits in this aspect. However, there are still many problems with Li metal anode. The failure of Li anode is mainly caused by the high reactivity of Li metal, which can cause irreversible continuous reactions between Li and electrolyte to shorten cycling life. Due to multiple electroplating and stripping processes, Li anode undergoes significant volume and morphology change, increasing side reactions and the growth of Li dendrites caused by the first two factors. Electrolyte engineering, as a simple and effective modification method, can effectively solve the above problems. Among them, using electrolyte additives is a simple, efficient, and economical electrolyte engineering strategy. Herein, we proposed an anion acceptor electrolyte additive strategy for optimizing the component/structural characteristics of solid/cathode electrolyte interphases to inhibit the growth of Li dendrites and Li+ transition on cathode surface for enhancing cycling and rate performance of Li|| NCM811 battery, which is also ascribed to the regulation of Li+ solvation structure by hexafluorobenzene (HFBen) to realizing the stability of PF6− and the conductivity enhancement of electrolyte. As expected, Li||Li cells with 1% (wt) HFBen-contained electrolyte could achieve a stable cycling above 400 h at 1 mA∙cm−2, and the capacity retention rate of Li||NCM811 battery could reach 75% after 100 cycles at 200 mA∙g−1. Finally, the cycling and rate performance of Li||NMC811 batteries were significantly enhanced at 4.5 V with the help of HFBen. This work demonstrates that HFBen as an additive can effectively improve the electrochemical performance of LMBs. Moreover, the interfacial reaction mechanism across the batterywas analyzed and studied. This study provides new insights for the interface reaction between electrolyte and Li anode.
2024, 40(6): 230701
doi: 10.3866/PKU.WHXB202307015
Abstract:
Designing efficient single-atom catalysts (SACs) with high selectivity for the electrocatalytic reduction of nitrate to ammonia formation is both crucial and challenging. This challenge arises due to the intricate and competitive electronic interactions among intermediates, metal active centers, and coordination environments. In this work, we present a comprehensive investigation detailing how to enhance the activity and selectivity of the electrocatalytic nitrate reduction reaction (NO3RR) by transitioning from single-layer SACs to bilayer SACs (BSACs). This enhancement is achieved through axial d–d orbital hybridization, as elucidated by a systematic study of 27 SACs and BSACs utilizing density functional theory (DFT) calculations. Considering potential pathways involving O-terminal, N-terminal, NO-terminal, and NO-dimer configurations, our calculations reveal that among monolayer SAC candidates, Ti-Pc and V-Pc exhibit low limiting potentials (UL) of −0.24 and −0.48 V, respectively. Furthermore, analyses of formation energy, dissolution potential, and ab initio molecular dynamics results demonstrate the robust stability of these catalysts under reaction conditions. In these single-layer transition metal (TM)-Pc complexes, the d-band energy levels and occupation numbers are influenced by dxz/dyz and pz orbital hybridizations. Notably, the presence of axial dz2 orbitals introduces a novel avenue for fine-tuning d-band characteristics and reactivity through dz2–dz2 interactions. Building on these insights, the formation of BSACs using Ti-Pc and V-Pc as substrates, facilitated by axial d–d orbital hybridization, offers a distinctive approach to modulating the catalytic performance of NO3RR. Significantly, we establish a two-dimensional volcano correlation encompassing the d-band center (εd), dxz + dyz orbital occupation numbers, and UL to describe NO3RR catalytic efficacy. Optimal BSACs should possess concurrent appropriate εd and dxz + dyz occupation numbers. Remarkably, Ti-Mo and Ti-Ta BSACs emerge as exceptional NO3RR catalyst candidates, both displaying a remarkably low UL of −0.13 V. The hybridization between dz2–dz2 orbitals heightens charge transfer and structural stability within double-layer metals. The scarcity of contiguous metal sites introduces a substantial energy barrier hindering NO2, NO, and N2 formation, effectively suppressing NO3RR by-products. In summation, this investigation imparts valuable insights into effectively enhancing nitrate reduction on SACs and BSACs, offering valuable guidance for advancing electrocatalyst development.![]()
Designing efficient single-atom catalysts (SACs) with high selectivity for the electrocatalytic reduction of nitrate to ammonia formation is both crucial and challenging. This challenge arises due to the intricate and competitive electronic interactions among intermediates, metal active centers, and coordination environments. In this work, we present a comprehensive investigation detailing how to enhance the activity and selectivity of the electrocatalytic nitrate reduction reaction (NO3RR) by transitioning from single-layer SACs to bilayer SACs (BSACs). This enhancement is achieved through axial d–d orbital hybridization, as elucidated by a systematic study of 27 SACs and BSACs utilizing density functional theory (DFT) calculations. Considering potential pathways involving O-terminal, N-terminal, NO-terminal, and NO-dimer configurations, our calculations reveal that among monolayer SAC candidates, Ti-Pc and V-Pc exhibit low limiting potentials (UL) of −0.24 and −0.48 V, respectively. Furthermore, analyses of formation energy, dissolution potential, and ab initio molecular dynamics results demonstrate the robust stability of these catalysts under reaction conditions. In these single-layer transition metal (TM)-Pc complexes, the d-band energy levels and occupation numbers are influenced by dxz/dyz and pz orbital hybridizations. Notably, the presence of axial dz2 orbitals introduces a novel avenue for fine-tuning d-band characteristics and reactivity through dz2–dz2 interactions. Building on these insights, the formation of BSACs using Ti-Pc and V-Pc as substrates, facilitated by axial d–d orbital hybridization, offers a distinctive approach to modulating the catalytic performance of NO3RR. Significantly, we establish a two-dimensional volcano correlation encompassing the d-band center (εd), dxz + dyz orbital occupation numbers, and UL to describe NO3RR catalytic efficacy. Optimal BSACs should possess concurrent appropriate εd and dxz + dyz occupation numbers. Remarkably, Ti-Mo and Ti-Ta BSACs emerge as exceptional NO3RR catalyst candidates, both displaying a remarkably low UL of −0.13 V. The hybridization between dz2–dz2 orbitals heightens charge transfer and structural stability within double-layer metals. The scarcity of contiguous metal sites introduces a substantial energy barrier hindering NO2, NO, and N2 formation, effectively suppressing NO3RR by-products. In summation, this investigation imparts valuable insights into effectively enhancing nitrate reduction on SACs and BSACs, offering valuable guidance for advancing electrocatalyst development.
2024, 40(6): 230605
doi: 10.3866/PKU.WHXB202306054
Abstract:
Handling hydrazine/urea wastewater through electrochemical oxidation technology (HzOR/UOR) holds significant importance for sewage disposal and nitrogen recycling, as the presence of hydrazine/urea leads to severe environmental issues. On the other hand, hydrazine/urea could potentially serve as a new type of fuel. However, at present, this remains a considerable challenge. The development of a low-cost, highly efficient, and stable electrocatalyst stands as a prerequisite for achieving this goal. In this study, a novel Ni2P/CoP3-Znvac bimetallic phosphide catalyst is designed and constructed using a hydrothermal-alkali etching-phosphating three-step method. This catalyst integrates P-rich CoP3, P-poor metallic Ni2P, and abundant Zn2+ cation vacancies into a single structure for HzOR/UOR. Copious P in CoP3 provides a wealth of negative electrons, which aids in the adsorption of positive reactive intermediates. Meanwhile, P-poor metallic Ni2P exhibits excellent electrical conductivity, ensuring rapid reaction dynamics. Both physical and electrochemical experiments confirm the successful creation of the Ni2P/CoP3-Znvac heterojunction, along with the distinctive electron structure of Ni2P and CoP3. Electron paramagnetic resonance (EPR) results validate the presence of cation vacancies, which significantly enhance the density of active sites. Consequently, this innovative Ni2P/CoP3-Znvac heterojunction catalyst displays remarkable electrocatalytic activity, achieving a potential of −47 mV/1.311 V to attain 10 mA∙cm−2 for HzOR and UOR, respectively. The Tafel slopes of 54.3 and 37.24 mV∙dec−1 for HzOR and UOR are significantly smaller than those of single-phased Ni2P and CoP3, as well as the two-phased phosphide without alkali etching. Building upon the excellent HzOR/UOR performance of the Ni2P/CoP3-Znvac heterojunction, a two-electrode cell for direct hydrazine fuel cells (DHzFC) and direct urea-hydrogen peroxide fuel cells (DUHPFC) is assembled with a Ni2P/CoP3-Znvac anode. This configuration demonstrates a maximum power density of 229.01 mW∙cm−2 for DHzFC and 16.22 mW∙cm−2 for DUHPFC. Moreover, both DHzFC and DUHPFC exhibit exceptional stability for up to 24 h. A homemade aqueous Zn-Hz battery, equipped with a Ni2P/CoP3-Znvac cathode, further demonstrates its practicality for energy conversion. This work underscores a promising avenue for developing cost-effective and highly stable solutions for UOR and HzOR.![]()
Handling hydrazine/urea wastewater through electrochemical oxidation technology (HzOR/UOR) holds significant importance for sewage disposal and nitrogen recycling, as the presence of hydrazine/urea leads to severe environmental issues. On the other hand, hydrazine/urea could potentially serve as a new type of fuel. However, at present, this remains a considerable challenge. The development of a low-cost, highly efficient, and stable electrocatalyst stands as a prerequisite for achieving this goal. In this study, a novel Ni2P/CoP3-Znvac bimetallic phosphide catalyst is designed and constructed using a hydrothermal-alkali etching-phosphating three-step method. This catalyst integrates P-rich CoP3, P-poor metallic Ni2P, and abundant Zn2+ cation vacancies into a single structure for HzOR/UOR. Copious P in CoP3 provides a wealth of negative electrons, which aids in the adsorption of positive reactive intermediates. Meanwhile, P-poor metallic Ni2P exhibits excellent electrical conductivity, ensuring rapid reaction dynamics. Both physical and electrochemical experiments confirm the successful creation of the Ni2P/CoP3-Znvac heterojunction, along with the distinctive electron structure of Ni2P and CoP3. Electron paramagnetic resonance (EPR) results validate the presence of cation vacancies, which significantly enhance the density of active sites. Consequently, this innovative Ni2P/CoP3-Znvac heterojunction catalyst displays remarkable electrocatalytic activity, achieving a potential of −47 mV/1.311 V to attain 10 mA∙cm−2 for HzOR and UOR, respectively. The Tafel slopes of 54.3 and 37.24 mV∙dec−1 for HzOR and UOR are significantly smaller than those of single-phased Ni2P and CoP3, as well as the two-phased phosphide without alkali etching. Building upon the excellent HzOR/UOR performance of the Ni2P/CoP3-Znvac heterojunction, a two-electrode cell for direct hydrazine fuel cells (DHzFC) and direct urea-hydrogen peroxide fuel cells (DUHPFC) is assembled with a Ni2P/CoP3-Znvac anode. This configuration demonstrates a maximum power density of 229.01 mW∙cm−2 for DHzFC and 16.22 mW∙cm−2 for DUHPFC. Moreover, both DHzFC and DUHPFC exhibit exceptional stability for up to 24 h. A homemade aqueous Zn-Hz battery, equipped with a Ni2P/CoP3-Znvac cathode, further demonstrates its practicality for energy conversion. This work underscores a promising avenue for developing cost-effective and highly stable solutions for UOR and HzOR.
2024, 40(6): 230700
doi: 10.3866/PKU.WHXB202307007
Abstract:
In recent years, Cu-based multi-metallic nanocrystals with controlled elemental distributions have been extensively studied for potential applications as electrocatalysts for CO2 reduction reaction (CO2RR). Modifying Cu electrocatalysts with secondary or additional metals offers a viable approach to manipulate the overall d-band structure which would cause the shift in the d-band center. Such manipulation can affect the surface affinity of Cu towards key intermediates and thus the following catalytic pathway. Apart from endeavors to adjust the electronic structure, morphological engineering provides effective avenues to enhance the electrocatalytic performance of CO2RR. In contrast to quasi-spherical particles with irregular shapes, a 3D-assembled porous structure utilizing 2D nanosheets as building blocks offers advantages such as maximizing surface atom exposure and creating numerous diffusion channels and reactive sites for intermediates formed during catalysis. Yet, it is technique challenging to construct such type of nano-architecture via a rationally-design synthetic routes and traditional stepwise self-assembling strategy is time-consuming and lack of versatile control over the structural parameters of resulting products. Therefore, it holds significant value to develop a synthesis method capable of yielding high-purity formations of unique nanostructures. These structures should possess accurately controlled elemental compositions and electronic configurations, and establish a potential correlation between structural benefits and enhanced electrochemical performance in CO2RR. Herein, we report the controlled synthesis of palladium-copper-silver (Pd-Cu-Ag) nanocrystals with rationally-designed two-dimensional (2D)-three-dimensional (3D) hybrid architectures and validated with the promising use for electrochemical CO2 reduction (CO2RR). The synthetic procedure includes the conversion of Au@CuxO nanospheres into CuAg hierarchical nanoflowers (HNFs), as directed by the capping agent octadecyltrimethyl ammonium chloride. Interestingly, the nanosheets are formed in situ as the building block. Following galvanic replacement reaction between CuAg HNFs and Na2PdCl4 removes Ag and Cu, introduces zero-valent Pd, and creates abundant pores on the nanosheets. These CuAg-based products are tested as CO2RR electrocatalysts, in which the Pd0.7Cu40.0Ag59.7 PHNFs displayed the optimized performance in terms of C2+ products selectivity (69.5%) and C2+ partial current density (−349.1 mA·cm−2). As revealed by density functional theory (DFT) simulations, PdAgCu surface has distinct electronic property, which lower the reaction barrier for C-C coupling, protruding the exceptional advantage of the Pd doping towards CuAg electrocatalysts for CO2 reduction. The present study offers a straightforward approach to fabricate hierarchical multi-metallic nanostructures with the porous nanosheet as building block, and validates its structural advantage in electrocatalysis, shedding light on the rational design of efficient CO2RR catalyst.![]()
In recent years, Cu-based multi-metallic nanocrystals with controlled elemental distributions have been extensively studied for potential applications as electrocatalysts for CO2 reduction reaction (CO2RR). Modifying Cu electrocatalysts with secondary or additional metals offers a viable approach to manipulate the overall d-band structure which would cause the shift in the d-band center. Such manipulation can affect the surface affinity of Cu towards key intermediates and thus the following catalytic pathway. Apart from endeavors to adjust the electronic structure, morphological engineering provides effective avenues to enhance the electrocatalytic performance of CO2RR. In contrast to quasi-spherical particles with irregular shapes, a 3D-assembled porous structure utilizing 2D nanosheets as building blocks offers advantages such as maximizing surface atom exposure and creating numerous diffusion channels and reactive sites for intermediates formed during catalysis. Yet, it is technique challenging to construct such type of nano-architecture via a rationally-design synthetic routes and traditional stepwise self-assembling strategy is time-consuming and lack of versatile control over the structural parameters of resulting products. Therefore, it holds significant value to develop a synthesis method capable of yielding high-purity formations of unique nanostructures. These structures should possess accurately controlled elemental compositions and electronic configurations, and establish a potential correlation between structural benefits and enhanced electrochemical performance in CO2RR. Herein, we report the controlled synthesis of palladium-copper-silver (Pd-Cu-Ag) nanocrystals with rationally-designed two-dimensional (2D)-three-dimensional (3D) hybrid architectures and validated with the promising use for electrochemical CO2 reduction (CO2RR). The synthetic procedure includes the conversion of Au@CuxO nanospheres into CuAg hierarchical nanoflowers (HNFs), as directed by the capping agent octadecyltrimethyl ammonium chloride. Interestingly, the nanosheets are formed in situ as the building block. Following galvanic replacement reaction between CuAg HNFs and Na2PdCl4 removes Ag and Cu, introduces zero-valent Pd, and creates abundant pores on the nanosheets. These CuAg-based products are tested as CO2RR electrocatalysts, in which the Pd0.7Cu40.0Ag59.7 PHNFs displayed the optimized performance in terms of C2+ products selectivity (69.5%) and C2+ partial current density (−349.1 mA·cm−2). As revealed by density functional theory (DFT) simulations, PdAgCu surface has distinct electronic property, which lower the reaction barrier for C-C coupling, protruding the exceptional advantage of the Pd doping towards CuAg electrocatalysts for CO2 reduction. The present study offers a straightforward approach to fabricate hierarchical multi-metallic nanostructures with the porous nanosheet as building block, and validates its structural advantage in electrocatalysis, shedding light on the rational design of efficient CO2RR catalyst.
