The paper focuses on the conductivity of the fuel cell electrolyte in a membraneless glucose-fueled alkaline fuel cell. The electrolyte conductivity is interpreted using simple physical models, considering either the ...The paper focuses on the conductivity of the fuel cell electrolyte in a membraneless glucose-fueled alkaline fuel cell. The electrolyte conductivity is interpreted using simple physical models, considering either the empirical behavior of the solution’s viscosity, or the consideration of ions and molecules colliding in solutions. The conductivity is expressed as a function of KOH and glucose concentrations. The physical properties of the species (i.e. radii, thermal velocity) and the chemical equilibrium constant of the reaction that glucose undergoes in an alkaline solution can be estimate by comparing the experimental results with the theory.展开更多
Alkaline hydrazine liquid fuel cells(AHFC) have been highlighted in terms of high power performance with non-precious metal catalysts.Although Fe-N-C is a promising non-Pt electrocatalyst for oxygen reduction reaction...Alkaline hydrazine liquid fuel cells(AHFC) have been highlighted in terms of high power performance with non-precious metal catalysts.Although Fe-N-C is a promising non-Pt electrocatalyst for oxygen reduction reaction(ORR),the surface density of the active site is very low and the catalyst layer should be thick to acquire the necessary number of catalytic active sites.With this thick catalyst layer,it is important to have an optimum pore structure for effective reactant conveyance to active sites and an interface structure for faster charge transfer.Herein,we prepare a Fe-N-C catalyst with magnetite particles and hierarchical pore structure by steam activation.The steam activation process significantly improves the power performance of the AHFC as indicated by the lower IR and activation voltage losses.Based on a systematic characterization,we found that hierarchical pore structures improve the catalyst utilization efficiency of the AHFCs,and magnetite nanoparticles act as surface modifiers to reduce the interracial resistance between the electrode and the ion-exchange membrane.展开更多
We report modified nitrogen-doped graphene （CN） as electrocatalyst for ORR （oxygen reduction reaction） in alkaline medium. CN was synthesized by a novel procedure based on graphite oxide thermally treated with cya...We report modified nitrogen-doped graphene （CN） as electrocatalyst for ORR （oxygen reduction reaction） in alkaline medium. CN was synthesized by a novel procedure based on graphite oxide thermally treated with cyanamide suitable for facile N-doping and large-scale production, whereas cyanamide was used as N-precursor. The structure of the material was characterized by TEM （transmission electron microscopy）, SEM （scanning electron microscopy）, Raman spectroscopy and XPS （X-ray photoelectron spectroscopy）. Structural and electrochemical properties of CN were compared with those of non-modified graphene （TRGO （thermally reduced graphite oxide））. The electrochemical characterization of TRGO and CN in alkaline solution demonstrates enhanced electrocatalytic ORR activity and improved long-term stability for N-doped CN. Voltammetric studies confirmed that, oxygen reduction on CN rather follows four-electron pathway. Compared with commercial 20% PtC catalyst, CN is characterized by exceptional methanol crossover resistance and superb long-term operation stability. Owing to these factors, nitrogen-doped graphene has a great potential to be used as metal-free electrocatalyst in cathodes of alkaline fuel cells.展开更多
In this study, we first attempted to discover the optimal configuration of membrane-electrode assemblies(MEAs) used to achieve a high performance of direct hydrazine fuel cells(DHFCs). We have investigated the effect ...In this study, we first attempted to discover the optimal configuration of membrane-electrode assemblies(MEAs) used to achieve a high performance of direct hydrazine fuel cells(DHFCs). We have investigated the effect of water management and the electrode thickness on the performance of DHFCs, depending on the hydrophobicity of the gas diffusion layers in the cathode and the catalyst loading in the anode with the carbon-supported Ni, synthesized by a polyol process. With the optimal water management and electrode thickness, the MEA constructed using the as-prepared Ni/C anode catalyst containing the metallic and low oxidative state and ultra-low Pt loading cathode reduced the ohmic resistance and mass transfer limitation in the current-voltage curves observed for the alkaline DHFC, achieving an impressive power performance over 500 mW cm^(–2).展开更多
The development of the hydrogen electrode is vital for the application of alkaline polymer electrolyte fuel cells(APEFCs).In this study,a series of Ni(OH)_2 decorated Ni/C catalysts(Ni(OH)_2-Ni/C) were prepared by a t...The development of the hydrogen electrode is vital for the application of alkaline polymer electrolyte fuel cells(APEFCs).In this study,a series of Ni(OH)_2 decorated Ni/C catalysts(Ni(OH)_2-Ni/C) were prepared by a three-step electrochemical treatment of Ni/C.The existence of Ni(OH)_2 was demonstrated by X-ray photoelectron spectroscopy(XPS),and the surface molar ratio of Ni(OH)_2/Ni of the samples was estimated via an electrochemical method.The HOR catalytic activity of the catalysts was evaluated by a rotation disk electrode(RDE) method,and a "volcano plot" was established between the HOR exchange current(j0) and the surface molar ratio of Ni(OH)_2/Ni.On top of the "volcano",the surface molar ratio of Ni(OH)_2/Ni is1.1:1,the j0 of which was 6.8 times of that of Ni/C.The stability of the samples toward HOR was evaluated to be good.Our study added a systematic experimental evidence to the HOR research,showing that the HOR catalytic activity of Ni can be deliberately controlled via decoration of Ni(OH)_2,which may help understanding the HOR mechanism on Ni.展开更多
Platinum catalysts play a major role in the large scale commercialization of direct methanol fuel cells(DMFC).Here,we present a procedure to create a nanostructural graphene-platinum(Gr Pt)composite containing a small...Platinum catalysts play a major role in the large scale commercialization of direct methanol fuel cells(DMFC).Here,we present a procedure to create a nanostructural graphene-platinum(Gr Pt)composite containing a small amount(5.3 wt%)of platinum nanoparticles coated with at least four layers of graphene.The composite,as Gr Pt ink,was deposited on a glassy carbon electrode and its electrocatalytic activity in a methanol oxidation reaction(MOR)was evaluated in a 1 M CH3OH/1 M NaOH solution.The results indicated an enhanced catalytic performance of GrPt towards MOR in alkaline media compared with the Pt/C material.Electron energy-loss spectroscopy and X-ray photoelectron spectroscopy(recorded before and after the electrochemical assays)were employed to analyze the changes in the chemical composition of the nanomaterial and to explain the transformations that took place at the electrode surface.Our findings suggest that growing of graphene on platinum nanoparticles improve the catalytic performance of platinum-graphene composites towards MOR in alkaline media.展开更多
Anion exchange membrane(AEM)fuel cells have gained great attention partially due to the advantage of using non-precious metal as catalysts.However,the reaction kinetics of hydrogen oxidation reaction(HOR)is two orders...Anion exchange membrane(AEM)fuel cells have gained great attention partially due to the advantage of using non-precious metal as catalysts.However,the reaction kinetics of hydrogen oxidation reaction(HOR)is two orders of magnitude slower in alkaline systems than in acid.To understand the slower kinetics of HOR in base,two major theories have been proposed,such as(1)pH dependent hydrogen binding energy as a major descriptor for HOR;and(2)bifunctional theory based on the contributions of both hydrogen and hydroxide adsorption for HOR in alkaline electrolyte.Here,we discuss the possible HOR mechanisms in alkaline electrolytes with the corresponding change in their Tafel behavior.Apart from the traditional Tafel-Volmer and Heyrovsky-Volmer HOR mechanisms,the recently proposed hydroxide adsorption step is also discussed to illustrate the difference in HOR mechanisms in acid and base.We further summarize the representative works of alkaline HOR catalyst design(e.g.,precious metals,alloy,intermetallic materials,Ni-based alloys,carbides,nitrides,etc.),and briefly describe their fundamental HOR reaction mechanism to emphasize the difference in elementary reaction steps in alkaline medium.The strategy of strengthening local interaction that facilitates both H2 desorption and Hads+OHads recombination is finally proposed for future HOR catalyst design in alkaline environment.展开更多
Fuel cells are one of the most competitive alternative energy sources because their theoretical efficiency is~15%higher than that of internal combustion engines (ICEs) and they are considered cleaner and safer.When fu...Fuel cells are one of the most competitive alternative energy sources because their theoretical efficiency is~15%higher than that of internal combustion engines (ICEs) and they are considered cleaner and safer.When fuel cells are used to replace ICEs in cars and energy conversion systems,the system efficiency increases;furthermore,the process becomes more environmentally-friendly because fuel cells produce electricity by using only hydrogen and oxygen,obtained by purifying atmospheric air by filtering out dust and pollutants.Hence,their final product is only water,instead of pollutants like carboFuel cells are one of the most competitive alternative energy sources because their theoretical efficiency is~15%higher than that of internal combustion engines (ICEs) and they are considered cleaner and safer.When fuel cells are used to replace ICEs in cars and energy conversion systems,the system efficiency increases;furthermore,the process becomes more environmentally-friendly because fuel cells produce electricity by using only hydrogen and oxygen,obtained by purifying atmospheric air by filtering out dust and pollutants.Hence,their final product is only water,instead of pollutants like carbon dioxide.n dioxide.展开更多
A Pd-Cu catalyst, with primary B2-type phase, supported by VulcanXC-7R carbon was synthesized via a solvothermal method. The catalysts were physically and electrochemically characterized by X-ray diffraction （XRD）, ...A Pd-Cu catalyst, with primary B2-type phase, supported by VulcanXC-7R carbon was synthesized via a solvothermal method. The catalysts were physically and electrochemically characterized by X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, trans- mission electron microscopy （TEM） and both cyclic and linear sweep voltammetry using a rotating disk electrode （RDE）. During the RDE testing, the half-wave potential of the Pd-Cu/Vulcan catalyst was 50 mV higher compared to that of commercial Pt/C catalyst for the oxygen reduction reaction （ORR） in alkaline media. The Pd-Cu/Vulcan exhibited a specific activity of 1.27 mA/cm2 and a mass activity of 0.59 A/mgpd at 0.9 V, which were 4 and 3 times greater than that of the commercial Pt/C catalyst, respectively. The Pd-Cu/Vulcan catalyst also showed higher in-situ alkaline exchange membrane fuel cell （AEMFC） performance, with operating power densities of 1100 MW/cm2 operating on H2/O2 and 700 MW/cm2 operating on H2/Air （CO2-free）, which were markedly higher than those of the commercial Pt/C. The Pd-Cu/ Vulcan catalyst also exhibited high stability during a short-term, in-situ AEMFC durability test, with only around 11% performance loss after 30 hours of operation, an improve- ment over most AEMFCs reported in the literature to date.展开更多
Anion exchange membrane(AEM)stability has been a long-standing challenge that limited the widespread development and adoption of AEM fuel cells(AEMFCs).The past five years have been a period of exceptional progress in...Anion exchange membrane(AEM)stability has been a long-standing challenge that limited the widespread development and adoption of AEM fuel cells(AEMFCs).The past five years have been a period of exceptional progress in the development of several alkaline-stable AEMs with remarkable both ex situ and in situ AEMFC stability.Certain cycloaliphatic quaternary ammonium(cQA)(mainly five-and six-membered)based AEMs appear to be among those having the most promising overall performance.In this review,we categorize cQAs as cage-like(such as quaternized 1,4-diazabicyclo[2.2.2]octane,(QDABCO)and quinuclidinium),non-cage-like(such as pyrrolidinium and piperidinium)and N-spirocyclic(such as 6-azonia-spiro[5.5]undecane(ASU)).The degradation mechanisms of categorized cQAs are first elucidated.Through an understanding of how the cations are attacked by strongly nucleophilic OH–,improved structural design of incorporating alkaline-stable cations into AEMs is facilitated.Before a detailed description and comparison of the alkaline stability of cQAs and their respective AEMs,current protocols for the assessment of alkaline stability are discussed in detail.Furthermore,the initial AEMFC performance and fuel cell performance stability based on cQA AEMs are also examined.The main focus and highlight of this review are recent advances(2015–2020)of cQA-based AEMs,which exhibit both excellent cation and membrane alka-line stability.We aim to shed light on the development of alkaline-stable cQA-type AEMs,which are trending in the AEM community,and to provide insights into possible solutions for designing long-lived AEM materials.展开更多
The study focuses on the in flue nee of Ni and Bi on alkali me etha nol oxidati on reacti on (EOR) activities, stabilities and structure characteristics of carb on supported Pd-based nano catalysts (Pd/C, Pd6oNi4o/C, ...The study focuses on the in flue nee of Ni and Bi on alkali me etha nol oxidati on reacti on (EOR) activities, stabilities and structure characteristics of carb on supported Pd-based nano catalysts (Pd/C, Pd6oNi4o/C, Pd6oBi4o/C, Pd6oNi2oBi2o/C) by cyclic voltammetry/chr ono amperometry using rotating disk electrode and various physico-chemical methods such as X-ray powder diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy coupled with energy dispersive X-ray spectroscopy and inductively coupled plasma optical emission spectrometry. Nickel generates more adsorbed OH on the Pd catalyst surface than Bi and promotes the oxidation of adsorbed ethanol species. This results in a low onset potential toward ethanol oxidation with high current density. The presenee of Bi facilitates high toleranee toward various reaction in termediates resulting from the incomplete etha nol oxidation, but might also initiate the agglomerati on of Pd nano particles. The no vel Pd60Ni20Bi20/C nanocatalyst displays exceptional byproduct toleranee, but only satisfying catalytic activity toward ethanol oxidation in an alkaline medium. Therefore, the EOR performanee of the novel carbon supported ternary PdxNiyBiz anode catalyst with various atomic variations (Pd70Ni25Bi5/C, Pd70Ni20Bi10/C, Pd80Ni10Bi10/C and Pd40Ni20Bi40/C) using the common instant reduction synthesis method was further optimized for the alkaline direct ethanol fuel cell. The carbon supported Pd:Ni:Bi nano catalyst with atomic ratio of 70:20:10 displays outsta nding catalytic activity for the alkaline EOR compared to the other PdxNiyBiy/C nanocatalysts as well as to the benchmarks Pd/C, Pd60Ni40/C and Pd60Bi40/C. The synergy and the optimal content in consideration of the oxide species of Pd, Ni and Bi are crucial for the EOR kinetic enhancement in alkaline medium.展开更多
Hydroxyl anion conducting membrane composed of poly(vinyl alcohol)(PVA),poly(diallyldimethylammonium chloride)(PDDA),and hydroxylated multiwalled carbon nanotubes(MWCNTs-OH)have been synthesized via a facile blending-...Hydroxyl anion conducting membrane composed of poly(vinyl alcohol)(PVA),poly(diallyldimethylammonium chloride)(PDDA),and hydroxylated multiwalled carbon nanotubes(MWCNTs-OH)have been synthesized via a facile blending-casting method assisted by a hot-chemical cross-linking process.Fourier-transform infrared spectroscopy(FTIR)and scanning electron microscopy(SEM)showed that PDDA and MWCNTs-OH were successfully introduced into the PVA matrix and MWCNTs-OH could effectively improve the network structure of the membrane.With the addition of MWCNTs-OH,many properties of the membranes such as thermal,chemical,mechanical stability and swelling property were improved significantly.Most prominent is the improvement of mechanical property,where the PVA/PDDA/MWCNTs-OH(1:0.5/3 wt.%)membrane showed high tensile strength of 40.3 MPa,tensile elongation of 12.3%and high Young's modulus of 782.8 MPa.Moreover,MWCNTs-OH bound the polymer chains in the membranes more compactly,resulting in decreased water uptake.By tuning the mass fraction of PVA,PDDA,and MWCNTs-OH in the membrane,the maximum OH-conductivity(0.030 S cm^(-1)at room temperature)was achieved for the composition of 0.5 wt.%MWCNTs-OH doped with the PVA:PDDA(1:0.5 by mass)blend.The membranes showed excellent oxidative stability when treated with both a solution of H_(2)O_(2)(30 wt.%)at room temperature and in a hot KOH solution(8 M)at 80℃.Based on the full aliphatic structure membrane(PVA/PDDA-OH/1 wt.%MWCNTs-OH),membrane electrode assemblies(MEAs)fabricated with Pt/C cathode catalyst can achieve power densities of 41.3 mW cm^(-2)and 66.4 mW cm^(-2)in a H_(2)/O_(2)system at room temperature and 40℃,respectively.Using CoPc as the Pt-free cathode catalyst,power densities of 9.1 mW cm^(-2)and 14.0 mW cm^(-2)at room temperature and 40℃ were obtained,respectively.展开更多
文摘The paper focuses on the conductivity of the fuel cell electrolyte in a membraneless glucose-fueled alkaline fuel cell. The electrolyte conductivity is interpreted using simple physical models, considering either the empirical behavior of the solution’s viscosity, or the consideration of ions and molecules colliding in solutions. The conductivity is expressed as a function of KOH and glucose concentrations. The physical properties of the species (i.e. radii, thermal velocity) and the chemical equilibrium constant of the reaction that glucose undergoes in an alkaline solution can be estimate by comparing the experimental results with the theory.
基金supported by the GIST Research Institute(GRI)grant funded by GIST in 2021supported by the KBSI grants(C140140 and C140110)。
文摘Alkaline hydrazine liquid fuel cells(AHFC) have been highlighted in terms of high power performance with non-precious metal catalysts.Although Fe-N-C is a promising non-Pt electrocatalyst for oxygen reduction reaction(ORR),the surface density of the active site is very low and the catalyst layer should be thick to acquire the necessary number of catalytic active sites.With this thick catalyst layer,it is important to have an optimum pore structure for effective reactant conveyance to active sites and an interface structure for faster charge transfer.Herein,we prepare a Fe-N-C catalyst with magnetite particles and hierarchical pore structure by steam activation.The steam activation process significantly improves the power performance of the AHFC as indicated by the lower IR and activation voltage losses.Based on a systematic characterization,we found that hierarchical pore structures improve the catalyst utilization efficiency of the AHFCs,and magnetite nanoparticles act as surface modifiers to reduce the interracial resistance between the electrode and the ion-exchange membrane.
文摘We report modified nitrogen-doped graphene （CN） as electrocatalyst for ORR （oxygen reduction reaction） in alkaline medium. CN was synthesized by a novel procedure based on graphite oxide thermally treated with cyanamide suitable for facile N-doping and large-scale production, whereas cyanamide was used as N-precursor. The structure of the material was characterized by TEM （transmission electron microscopy）, SEM （scanning electron microscopy）, Raman spectroscopy and XPS （X-ray photoelectron spectroscopy）. Structural and electrochemical properties of CN were compared with those of non-modified graphene （TRGO （thermally reduced graphite oxide））. The electrochemical characterization of TRGO and CN in alkaline solution demonstrates enhanced electrocatalytic ORR activity and improved long-term stability for N-doped CN. Voltammetric studies confirmed that, oxygen reduction on CN rather follows four-electron pathway. Compared with commercial 20% PtC catalyst, CN is characterized by exceptional methanol crossover resistance and superb long-term operation stability. Owing to these factors, nitrogen-doped graphene has a great potential to be used as metal-free electrocatalyst in cathodes of alkaline fuel cells.
基金supported by Technology Development Program to Solve Climate Changes through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT (2018M1A2A2063861)。
文摘In this study, we first attempted to discover the optimal configuration of membrane-electrode assemblies(MEAs) used to achieve a high performance of direct hydrazine fuel cells(DHFCs). We have investigated the effect of water management and the electrode thickness on the performance of DHFCs, depending on the hydrophobicity of the gas diffusion layers in the cathode and the catalyst loading in the anode with the carbon-supported Ni, synthesized by a polyol process. With the optimal water management and electrode thickness, the MEA constructed using the as-prepared Ni/C anode catalyst containing the metallic and low oxidative state and ultra-low Pt loading cathode reduced the ohmic resistance and mass transfer limitation in the current-voltage curves observed for the alkaline DHFC, achieving an impressive power performance over 500 mW cm^(–2).
基金supported by the National Natural Science Foundation of China (21573167,21633008,91545205)the Innovative Research Team in Wuhan University (2042017kf0232)+1 种基金the National Key Research and Development Program (2016YFB0101203)the Fundamental Research Funds for the Central Universities (2014203020207)
文摘The development of the hydrogen electrode is vital for the application of alkaline polymer electrolyte fuel cells(APEFCs).In this study,a series of Ni(OH)_2 decorated Ni/C catalysts(Ni(OH)_2-Ni/C) were prepared by a three-step electrochemical treatment of Ni/C.The existence of Ni(OH)_2 was demonstrated by X-ray photoelectron spectroscopy(XPS),and the surface molar ratio of Ni(OH)_2/Ni of the samples was estimated via an electrochemical method.The HOR catalytic activity of the catalysts was evaluated by a rotation disk electrode(RDE) method,and a "volcano plot" was established between the HOR exchange current(j0) and the surface molar ratio of Ni(OH)_2/Ni.On top of the "volcano",the surface molar ratio of Ni(OH)_2/Ni is1.1:1,the j0 of which was 6.8 times of that of Ni/C.The stability of the samples toward HOR was evaluated to be good.Our study added a systematic experimental evidence to the HOR research,showing that the HOR catalytic activity of Ni can be deliberately controlled via decoration of Ni(OH)_2,which may help understanding the HOR mechanism on Ni.
基金financially supported by Romanian National Authority for Scientific Research and Innovation (ANCSI) by NUCLEU Program PN 18 03 02 02
文摘Platinum catalysts play a major role in the large scale commercialization of direct methanol fuel cells(DMFC).Here,we present a procedure to create a nanostructural graphene-platinum(Gr Pt)composite containing a small amount(5.3 wt%)of platinum nanoparticles coated with at least four layers of graphene.The composite,as Gr Pt ink,was deposited on a glassy carbon electrode and its electrocatalytic activity in a methanol oxidation reaction(MOR)was evaluated in a 1 M CH3OH/1 M NaOH solution.The results indicated an enhanced catalytic performance of GrPt towards MOR in alkaline media compared with the Pt/C material.Electron energy-loss spectroscopy and X-ray photoelectron spectroscopy(recorded before and after the electrochemical assays)were employed to analyze the changes in the chemical composition of the nanomaterial and to explain the transformations that took place at the electrode surface.Our findings suggest that growing of graphene on platinum nanoparticles improve the catalytic performance of platinum-graphene composites towards MOR in alkaline media.
文摘Anion exchange membrane(AEM)fuel cells have gained great attention partially due to the advantage of using non-precious metal as catalysts.However,the reaction kinetics of hydrogen oxidation reaction(HOR)is two orders of magnitude slower in alkaline systems than in acid.To understand the slower kinetics of HOR in base,two major theories have been proposed,such as(1)pH dependent hydrogen binding energy as a major descriptor for HOR;and(2)bifunctional theory based on the contributions of both hydrogen and hydroxide adsorption for HOR in alkaline electrolyte.Here,we discuss the possible HOR mechanisms in alkaline electrolytes with the corresponding change in their Tafel behavior.Apart from the traditional Tafel-Volmer and Heyrovsky-Volmer HOR mechanisms,the recently proposed hydroxide adsorption step is also discussed to illustrate the difference in HOR mechanisms in acid and base.We further summarize the representative works of alkaline HOR catalyst design(e.g.,precious metals,alloy,intermetallic materials,Ni-based alloys,carbides,nitrides,etc.),and briefly describe their fundamental HOR reaction mechanism to emphasize the difference in elementary reaction steps in alkaline medium.The strategy of strengthening local interaction that facilitates both H2 desorption and Hads+OHads recombination is finally proposed for future HOR catalyst design in alkaline environment.
基金supported by the National Research Foundation of Korea (NRF2018M1A2A2063174)。
文摘Fuel cells are one of the most competitive alternative energy sources because their theoretical efficiency is~15%higher than that of internal combustion engines (ICEs) and they are considered cleaner and safer.When fuel cells are used to replace ICEs in cars and energy conversion systems,the system efficiency increases;furthermore,the process becomes more environmentally-friendly because fuel cells produce electricity by using only hydrogen and oxygen,obtained by purifying atmospheric air by filtering out dust and pollutants.Hence,their final product is only water,instead of pollutants like carboFuel cells are one of the most competitive alternative energy sources because their theoretical efficiency is~15%higher than that of internal combustion engines (ICEs) and they are considered cleaner and safer.When fuel cells are used to replace ICEs in cars and energy conversion systems,the system efficiency increases;furthermore,the process becomes more environmentally-friendly because fuel cells produce electricity by using only hydrogen and oxygen,obtained by purifying atmospheric air by filtering out dust and pollutants.Hence,their final product is only water,instead of pollutants like carbon dioxide.n dioxide.
文摘A Pd-Cu catalyst, with primary B2-type phase, supported by VulcanXC-7R carbon was synthesized via a solvothermal method. The catalysts were physically and electrochemically characterized by X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, trans- mission electron microscopy （TEM） and both cyclic and linear sweep voltammetry using a rotating disk electrode （RDE）. During the RDE testing, the half-wave potential of the Pd-Cu/Vulcan catalyst was 50 mV higher compared to that of commercial Pt/C catalyst for the oxygen reduction reaction （ORR） in alkaline media. The Pd-Cu/Vulcan exhibited a specific activity of 1.27 mA/cm2 and a mass activity of 0.59 A/mgpd at 0.9 V, which were 4 and 3 times greater than that of the commercial Pt/C catalyst, respectively. The Pd-Cu/Vulcan catalyst also showed higher in-situ alkaline exchange membrane fuel cell （AEMFC） performance, with operating power densities of 1100 MW/cm2 operating on H2/O2 and 700 MW/cm2 operating on H2/Air （CO2-free）, which were markedly higher than those of the commercial Pt/C. The Pd-Cu/ Vulcan catalyst also exhibited high stability during a short-term, in-situ AEMFC durability test, with only around 11% performance loss after 30 hours of operation, an improve- ment over most AEMFCs reported in the literature to date.
基金the National Natural Science Foundation of China(21875161)。
文摘Anion exchange membrane(AEM)stability has been a long-standing challenge that limited the widespread development and adoption of AEM fuel cells(AEMFCs).The past five years have been a period of exceptional progress in the development of several alkaline-stable AEMs with remarkable both ex situ and in situ AEMFC stability.Certain cycloaliphatic quaternary ammonium(cQA)(mainly five-and six-membered)based AEMs appear to be among those having the most promising overall performance.In this review,we categorize cQAs as cage-like(such as quaternized 1,4-diazabicyclo[2.2.2]octane,(QDABCO)and quinuclidinium),non-cage-like(such as pyrrolidinium and piperidinium)and N-spirocyclic(such as 6-azonia-spiro[5.5]undecane(ASU)).The degradation mechanisms of categorized cQAs are first elucidated.Through an understanding of how the cations are attacked by strongly nucleophilic OH–,improved structural design of incorporating alkaline-stable cations into AEMs is facilitated.Before a detailed description and comparison of the alkaline stability of cQAs and their respective AEMs,current protocols for the assessment of alkaline stability are discussed in detail.Furthermore,the initial AEMFC performance and fuel cell performance stability based on cQA AEMs are also examined.The main focus and highlight of this review are recent advances(2015–2020)of cQA-based AEMs,which exhibit both excellent cation and membrane alka-line stability.We aim to shed light on the development of alkaline-stable cQA-type AEMs,which are trending in the AEM community,and to provide insights into possible solutions for designing long-lived AEM materials.
文摘The study focuses on the in flue nee of Ni and Bi on alkali me etha nol oxidati on reacti on (EOR) activities, stabilities and structure characteristics of carb on supported Pd-based nano catalysts (Pd/C, Pd6oNi4o/C, Pd6oBi4o/C, Pd6oNi2oBi2o/C) by cyclic voltammetry/chr ono amperometry using rotating disk electrode and various physico-chemical methods such as X-ray powder diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy coupled with energy dispersive X-ray spectroscopy and inductively coupled plasma optical emission spectrometry. Nickel generates more adsorbed OH on the Pd catalyst surface than Bi and promotes the oxidation of adsorbed ethanol species. This results in a low onset potential toward ethanol oxidation with high current density. The presenee of Bi facilitates high toleranee toward various reaction in termediates resulting from the incomplete etha nol oxidation, but might also initiate the agglomerati on of Pd nano particles. The no vel Pd60Ni20Bi20/C nanocatalyst displays exceptional byproduct toleranee, but only satisfying catalytic activity toward ethanol oxidation in an alkaline medium. Therefore, the EOR performanee of the novel carbon supported ternary PdxNiyBiz anode catalyst with various atomic variations (Pd70Ni25Bi5/C, Pd70Ni20Bi10/C, Pd80Ni10Bi10/C and Pd40Ni20Bi40/C) using the common instant reduction synthesis method was further optimized for the alkaline direct ethanol fuel cell. The carbon supported Pd:Ni:Bi nano catalyst with atomic ratio of 70:20:10 displays outsta nding catalytic activity for the alkaline EOR compared to the other PdxNiyBiy/C nanocatalysts as well as to the benchmarks Pd/C, Pd60Ni40/C and Pd60Bi40/C. The synergy and the optimal content in consideration of the oxide species of Pd, Ni and Bi are crucial for the EOR kinetic enhancement in alkaline medium.
基金This work was financially supported by Chinese National Natural Science Foundation(grant no.51803175)。
文摘Hydroxyl anion conducting membrane composed of poly(vinyl alcohol)(PVA),poly(diallyldimethylammonium chloride)(PDDA),and hydroxylated multiwalled carbon nanotubes(MWCNTs-OH)have been synthesized via a facile blending-casting method assisted by a hot-chemical cross-linking process.Fourier-transform infrared spectroscopy(FTIR)and scanning electron microscopy(SEM)showed that PDDA and MWCNTs-OH were successfully introduced into the PVA matrix and MWCNTs-OH could effectively improve the network structure of the membrane.With the addition of MWCNTs-OH,many properties of the membranes such as thermal,chemical,mechanical stability and swelling property were improved significantly.Most prominent is the improvement of mechanical property,where the PVA/PDDA/MWCNTs-OH(1:0.5/3 wt.%)membrane showed high tensile strength of 40.3 MPa,tensile elongation of 12.3%and high Young's modulus of 782.8 MPa.Moreover,MWCNTs-OH bound the polymer chains in the membranes more compactly,resulting in decreased water uptake.By tuning the mass fraction of PVA,PDDA,and MWCNTs-OH in the membrane,the maximum OH-conductivity(0.030 S cm^(-1)at room temperature)was achieved for the composition of 0.5 wt.%MWCNTs-OH doped with the PVA:PDDA(1:0.5 by mass)blend.The membranes showed excellent oxidative stability when treated with both a solution of H_(2)O_(2)(30 wt.%)at room temperature and in a hot KOH solution(8 M)at 80℃.Based on the full aliphatic structure membrane(PVA/PDDA-OH/1 wt.%MWCNTs-OH),membrane electrode assemblies(MEAs)fabricated with Pt/C cathode catalyst can achieve power densities of 41.3 mW cm^(-2)and 66.4 mW cm^(-2)in a H_(2)/O_(2)system at room temperature and 40℃,respectively.Using CoPc as the Pt-free cathode catalyst,power densities of 9.1 mW cm^(-2)and 14.0 mW cm^(-2)at room temperature and 40℃ were obtained,respectively.
