Mixing polyanion cathode materials are promising candidates for the development of next-generation batteries, owing to their structural robustness and low-volume changes, yet low conductivity of polyanion hinders thei...Mixing polyanion cathode materials are promising candidates for the development of next-generation batteries, owing to their structural robustness and low-volume changes, yet low conductivity of polyanion hinders their practical capacity. Herein, the anion-site regulation is proposed to elevate the electrode kinetics and properties of polyanionic cathode. Multivalent anion P_(2)O_(7)^(4-) is selected to substitute the PO_(4)^(3-) in Na_(3)V_(2)(PO_(4))_(3) (NVP) lattice and regulate the ratio of polyanion groups to prepare Na_(3+x)V_(2)(PO_(4))_(3-x)(P_(2)O_(7))_(x)(NVPP_(x), 0 ≤ x ≤ 0.15) materials.The optimal Na_(3.1)V_(2)(PO_(4))_(2.9)(P_(2)O_(7))_(0.1) (NVPP_(0.1)) material can deliver remarkably elevated specific capacity(104 mAh g^(-1) at 0.1 C, 60 mAh g^(-1) at 20 C, respectively), which is higher than those of NVP. Moreover, NVPP_(0.1) exhibits outstanding cyclic stability(91% capacity retention after 300 cycles at 1 C). Experimental analyses reveal that the regulation of anions improves the structure stability, increases the active Na occupancy in the lattice and accelerates the Na+migration kinetics. The strategy of anion-site regulation provides the researchers a reference for the design of new high-performance polyanionic materials.展开更多
Electrochemical metallurgy at low temperature(<473 K)shows promise for the extraction and refinement of metals and alloys in a green and sustainable manner.However,the kinetics of the electrodeposition process is g...Electrochemical metallurgy at low temperature(<473 K)shows promise for the extraction and refinement of metals and alloys in a green and sustainable manner.However,the kinetics of the electrodeposition process is generally slow at low temperature,resulting in large overpotential and low current efficiency.Thus,the application of external physical fields has emerged as an effective strategy for improving the mass and charge transfer processes during electrochemical reactions.This review highlights the challenges associated with low-temperature electrochemical processes and briefly discusses recent achievements in optimizing electrodeposition processes through the use of external physical fields.The regulating effects on the optimization of the electrodeposition process and the strategies for select-ing various external physical fields,including magnetic,supergravity,and ultrasonic fields are summarized from the perspectives of equipment and mechanisms.Finally,advanced methods for in-situ characterization of external physical field-assisted electrodeposition processes are reviewed to gain a deeper understanding of metallic electrodeposition.An in-depth exploration of the mechanism by which external physical fields affect the electrode process is essential for enhancing the efficiency of metal extraction at low temperatures.展开更多
Microbial fuel cell(MFC) on the ocean floor is a kind of novel energy-harvesting device that can be developed to drive small instruments to work continuously.The shape of electrode has a great effect on the performanc...Microbial fuel cell(MFC) on the ocean floor is a kind of novel energy-harvesting device that can be developed to drive small instruments to work continuously.The shape of electrode has a great effect on the performance of the MFC.In this paper,several shapes of electrode and cell structure were designed,and their performance in MFC were compared in pairs:Mesh(cell-1) vs.flat plate(cell-2),branch(cell-3) vs.cylinder(cell-4),and forest(cell-5) vs.disk(cell-6) FC.Our results showed that the maximum power densities were 16.50,14.20,19.30,15.00,14.64,and 9.95 mWm-2 for cell-1,2,3,4,5 and 6 respectively.And the corre-sponding diffusion-limited currents were 7.16,2.80,18.86,10.50,18.00,and 6.900 mA.The mesh and branch anodes showed higher power densities and much higher diffusion-limited currents than the flat plate and the cylinder anodes respectively due to the low diffusion hindrance with the former anodes.The forest cathode improved by 47% of the power density and by 161% of diffusion-limited current than the disk cathode due to the former's extended solid/liquid/gas three-phase boundary.These results indicated that the shape of electrode is a major parameter that determining the diffusion-limited current of an MFC,and the differences in the elec-trode shape lead to the differences in cell performance.These results would be useful for MFC structure design in practical applica-tions.展开更多
Multilayer film was fabricated on an electrode surface by alternate layer-by-layer（LBL） adsorption of polycationic redox polymer（PEI-Fc） and dye-linked L-proline dehydrogenase（L-proDH）.The electrochemistry of th...Multilayer film was fabricated on an electrode surface by alternate layer-by-layer（LBL） adsorption of polycationic redox polymer（PEI-Fc） and dye-linked L-proline dehydrogenase（L-proDH）.The electrochemistry of the PEI-Fc/L-proDH multilayer modified electrode was investigated by cyclic voltammetry,and the enzyme catalysis mediated by the redox polymer was studied in a solution containing L-proline.It was observed that electron communication between L-proDH and the electrode was achieved with the help of PEI-Fc.A mathematical expression for the current response was evaluated based on the Michaelis-Menten kinetics mode,and the calculated currents fitted well with the experimental data.The kinetic analysis indicates that only a small fraction of the immobilized enzyme was efficiently electrically wired by the redox polymer.展开更多
Charge transfer at the liquid(electrolyte)-solid(metal)interfaces is of fundamental importance to metal electrochemical deposition that further determines the reversibility and kinetics of energy-dense rechargeable me...Charge transfer at the liquid(electrolyte)-solid(metal)interfaces is of fundamental importance to metal electrochemical deposition that further determines the reversibility and kinetics of energy-dense rechargeable metal batteries(RMBs).We demonstrate the fast charge transfer at the electrolyte-metal interfaces for lithium metal by designing and synthesizing electrolytes with chiral solvents:R(or S)-1,2-dimethoxy pro pane(R-DMP or S-DMP)and R(or S)-4-methyl-1,3-dioxolane(R-MDOL or S-MDOL).The chiral-induced spin selectivity is considered to produce spin-polarized metal surfaces,enabling the improvement in charge transfer rate and efficiency.The deposited Li metal in chiral electrolytes shows smooth and uniform morphologies,as well as high initial(>95%)and average(~99.2%)Coulombic efficiency for Li metal stripping/plating process,thus prolonging the life-span of batteries using thin lithium anode(50μm)to 400 cycles till 80%capacity retention.This work provides a distinct approach to regulate metal deposition beyond the limitation of ion de-solvation.展开更多
SnO_(2)-based anodes for lithium-ion batteries(LIBs)experience volume expansion,leading to rapid capacity decay and low conductivity.To address this problem,a composite consists of C/SnO_(2) with a core-shell structur...SnO_(2)-based anodes for lithium-ion batteries(LIBs)experience volume expansion,leading to rapid capacity decay and low conductivity.To address this problem,a composite consists of C/SnO_(2) with a core-shell structure and a carbonized nitrogen-doped Co-metal organic framework(Co-MOF)(NC)supported on carbon cloth(CC)was designed and prepared,which was denoted as C/SnO_(2)@NC@CC.C/SnO_(2)@NC@CC could be used directly as a flexible anode for LIBs.The combination of core-shell structure centered on carbon spheres,carbonized nitrogen-doped Co-MOF,and CC not only restricts the volume expansion but also functions as conductive networks to improve the electrical conductivity.C/SnO_(2)@NC@CC exhibits excellent electrochemical performance with charge and discharge specific capacities of 2066.0 and 2077.1 mAh/g,respectively,after 120 cycles at a current density of 0.5 A/g.展开更多
Currently the catalysis of hydrogen evolution reaction(HER)is mainly focused on the inherent electrocatalytic activity at relatively lower current densities while scarce at high current densities.Nevertheless,the latt...Currently the catalysis of hydrogen evolution reaction(HER)is mainly focused on the inherent electrocatalytic activity at relatively lower current densities while scarce at high current densities.Nevertheless,the latter is highly demanding in efficient mass-production of hydrogen.A SiO_(2) nanospheres template-synthesis is used to prepare mesoporous molybdenum carbide nanocrystals-embedded nitrogen-doped carbon foams(mp-Mo_(2)C/NC).The material shows much more excellent catalytic activity than the non-etched Mo_(2)C/NC toward hydrogen evolution reaction(HER)in acidic medium.More interestingly mp-Mo_(2)C/NC still has larger overpotential than Pt/C at lower current densities,but possess remarkably smaller overpotential than the latter at higher current densities for much better electrocatalytic performance.An approach is developed to investigate the electrode kinetics by Tafel plots,especially with eliminating the diffusion effect,indicating that Pt/C and mp-Mo_(2)C/NC display different reaction mechanisms.At low current densities the former presents reversible reaction,while the latter shows mixed electrochemical polarization/reversible electrode process.In the region of higher current densities,the former becomes totally gas-diffusion controlled with large overpotential,while the latter can still retain an electrode polarization process for much lower overpotential at the same current density.Result endorses that the meso-porously structured mp-Mo_(2)C/NC plays a critical role in avoiding gas diffusion control-resulting large overpotential at high current densities.This work holds great potential for an inexpensive catalyst better than Pt/C in practical applications of mass-production hydrogen at high current densities,while clearly shedding fundamental lights on designs of rational HER catalysts for the uses at high current densities.展开更多
The electrochemical oxidation of 1, 3-benzenedithiol was investigated in a 0. 100 mol/L tetrabutylammonium perchlorate/acetonitrile electrolyte. The electrochemical techniques used were potential sweep, bulk electroly...The electrochemical oxidation of 1, 3-benzenedithiol was investigated in a 0. 100 mol/L tetrabutylammonium perchlorate/acetonitrile electrolyte. The electrochemical techniques used were potential sweep, bulk electrolysis, rotating disc and the potential step method. The combination of the techniques yielded the number of electrons transferred per molecule, the reaction order, the transfer coefficient, the diffusion coefficient and concentration of dithiol anions, the standard heterogeneous rate constant as well as the formal potential and equilibrium constant of the preceeding dissociation reaction. This paper also illustrates the methods for studying the electrode kinetics of reactions which (a) involve a chemical reaction preceeding the electron-transfer process, (b) have insoluble polymer products, and (c) are totally irreversible.展开更多
The pH gradient caused by H^(+)/OH^(−)transport on an electrode surface is the key factor determining reaction performance,but its detailed impact on the electrode reaction kinetics has yet to be clarified.Here,the pH...The pH gradient caused by H^(+)/OH^(−)transport on an electrode surface is the key factor determining reaction performance,but its detailed impact on the electrode reaction kinetics has yet to be clarified.Here,the pH gradient effect was determined by developing electrode reaction equations,considering the overpotential assigned to the pH gradient called pH overpotential.The pH gradient effect was revealed to involve two aspects:(1)the Nernst pH overpotential,accounting for the common Nernst relationship with pH,and(2)the pH-dependent function of the electron-transfer coefficient(α_(pH)).Both parts were verified experimentally using oxygen reduction reaction and hydrogen evolution reaction,obviously,with differentα_(pH) functions.Detailedα_(pH) function effect was clarified based on numerical calculations of the electrode reaction equations.We found that the effect could be assessed suitably by an apparent constant(α_(app))and a nonlinear fitting method proposed forα_(app) value estimation.The results of this study provide the kinetic fundamentals of electrode reactions involving H^(+)/OH^(−)and contribute to the understanding and assessment of their performance with the H^(+)/OH^(−)transport effect.展开更多
Commercialization of Zn-metal anodes with low cost and high theoretical capacity is hindered by the poor reversibility caused by dendrites growth,side reactions,and the slow Zn^(2+)-transport and reaction kinetics.Her...Commercialization of Zn-metal anodes with low cost and high theoretical capacity is hindered by the poor reversibility caused by dendrites growth,side reactions,and the slow Zn^(2+)-transport and reaction kinetics.Herein,a reversible heterogeneous electrode of Zn-nanocrystallites/polyvinylphosphonic acrylamide(Zn/PPAm)with fast electrochemical kinetics is designed for the first time:phosphonic acid groups with strong polarity and chelation effect ensure structural reversibility and stability of the threedimensional Zn-storage-host PPAm network and the Zn/PPAm hybrid;hydrophobic carbon chains suppress side reactions such as hydrogen evolution and corrosion;weak electron-donating amide groups constitute Zn^(2+)-transport channels and promote“desolvation”and“solvation”effects of Zn^(2+)by dragging the PPAm network on the Zn-metal surface to compress/stretch during Zn plating/stripping,respectively;and the heterostructure and Zn nanocrystallites suppress dendrite growth and enhance electrochemical reactivity,respectively.Thus,the Zn/PPAm electrode shows cycle reversibility of over 6000 h with a hysteresis voltage as low as 31 mV in symmetrical cells and excellent durability and flexibility in fiber-shaped batteries.展开更多
The application of naive Koutecky-Levich analysis to micro- and nano-particle modified rotating disk electrodes of partially covered and non-planar geometry is critically analysed. Assuming strong overlap of the diffu...The application of naive Koutecky-Levich analysis to micro- and nano-particle modified rotating disk electrodes of partially covered and non-planar geometry is critically analysed. Assuming strong overlap of the diffusion fields of the particles such that transport to the entire surface is time-independent and one-dimensional, the observed voltammetric response reflects an apparent electrochemical rate o constant koapp, equal to the true rate constant ko describing the redox reaction of interest on the surface of the nanoparticles and the ratio,ψ, of the total electroactive surface area to the geometric area of the rotating disk surface. It is demonstrated that Koutecky-Levich analysis is applicable and yields the expected plots of I-1 versus ω-1 where I is the current and ω is the rotation speed but that the values of the electrochemical rate constants inferred are thereof koapp, not ko. Thus, for ψ 〉 1 apparent electrocatalysis might be naively but wrongly inferred whereas for ψ 〈 1 the deduced electrochemical rate constant will be less than ko. Moreover, the effect of ψ on the observed rotating disk electrode voltammograms is significant, signalling the need for care in the overly simplistic application of Koutecky-Levich analysis to modified rotating electrodes, as is commonly applied for example in the analysis of possible oxygen reduction catalysts.展开更多
Although hydrazine(N2 H4) oxidation in an electrochemical environment has been of great interest for years,its intrinsic electron transfer kinetics remain uncertain.We report that the phenomenological Butler-Volmer(BV...Although hydrazine(N2 H4) oxidation in an electrochemical environment has been of great interest for years,its intrinsic electron transfer kinetics remain uncertain.We report that the phenomenological Butler-Volmer(BV) theory is not appropriate for interpreting the process of hydrazine oxidation for which an astonishingly wide range of transfer coefficients,Tafel slopes and diffusion coefficient have been previously reported.Rather Tafel analysis for voltammetry recorded at Glassy Carbon(GC)electrodes reveals a strong potential dependence of the anodic transfer coefficient,consistent with the symmetric Marcus-Hush(sMH) theory.According to the relationship β=λ+FEf^0/2λ-F/2λ E,the reorganization energy(0.35±0.07 eV) and an approximate formal potential of the rate-determining first electron transfer were successfully extracted from the voltammetric responses.展开更多
Lithium-oxygen batteries(LOBs)have extensive applications because of their ultra-high energy densities.However,the practical application of LOBs is limited by several factors,such as a high overpotential,poor cycle st...Lithium-oxygen batteries(LOBs)have extensive applications because of their ultra-high energy densities.However,the practical application of LOBs is limited by several factors,such as a high overpotential,poor cycle stability,and limited rate capacity.In this paper,we describe the successful uniform loading of Mn_(3)O_(4) nanoparticles onto multi-walled carbon nanotubes(Mn_(3)O_(4)@CNT).CNTs form a conductive network and expose numerous catalytically active sites,and the one-dimensional porous structure provides a convenient channel for the transmission of Li+and O2 in LOBs.The electronic conductivity and electrocatalytic activity of Mn_(3)O_(4)@CNT are significantly better than those of MnO@CNT because of the inherent driving force facilitating charge transfer between different valence metal ions.Therefore,the Mn_(3)O_(4)@CNT cathode obtains a low overpotential(0.76 V at a limited capacity of 1000 mAh g^(-1)),high initial discharge capacity(16895 mAh g^(-1) at 200 mA g^(-1)),and long cycle life(97 cycles at 200 mA g^(-1)).This study provides evidence that transition metal oxides with mixed-valence states are suitable for application as efficient cathodes for LOBs.展开更多
基金financially supported by the National Natural Science Foundation of China (No. 91963118)Science Technology Program of Jilin Province (No. 20200201066JC)+1 种基金“13th Five-Year” Science and Technology Research from the Education Department of Jilin Province (No.JJKH20201179KJ)the 111 Project (No. B13013)。
文摘Mixing polyanion cathode materials are promising candidates for the development of next-generation batteries, owing to their structural robustness and low-volume changes, yet low conductivity of polyanion hinders their practical capacity. Herein, the anion-site regulation is proposed to elevate the electrode kinetics and properties of polyanionic cathode. Multivalent anion P_(2)O_(7)^(4-) is selected to substitute the PO_(4)^(3-) in Na_(3)V_(2)(PO_(4))_(3) (NVP) lattice and regulate the ratio of polyanion groups to prepare Na_(3+x)V_(2)(PO_(4))_(3-x)(P_(2)O_(7))_(x)(NVPP_(x), 0 ≤ x ≤ 0.15) materials.The optimal Na_(3.1)V_(2)(PO_(4))_(2.9)(P_(2)O_(7))_(0.1) (NVPP_(0.1)) material can deliver remarkably elevated specific capacity(104 mAh g^(-1) at 0.1 C, 60 mAh g^(-1) at 20 C, respectively), which is higher than those of NVP. Moreover, NVPP_(0.1) exhibits outstanding cyclic stability(91% capacity retention after 300 cycles at 1 C). Experimental analyses reveal that the regulation of anions improves the structure stability, increases the active Na occupancy in the lattice and accelerates the Na+migration kinetics. The strategy of anion-site regulation provides the researchers a reference for the design of new high-performance polyanionic materials.
基金supported by Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(No.SML2023SP243)the National Key Research and Development Program of China(No.2022YFC2906100)the National Natural Science Foundation of China(No.92475202)are acknowledged.
文摘Electrochemical metallurgy at low temperature(<473 K)shows promise for the extraction and refinement of metals and alloys in a green and sustainable manner.However,the kinetics of the electrodeposition process is generally slow at low temperature,resulting in large overpotential and low current efficiency.Thus,the application of external physical fields has emerged as an effective strategy for improving the mass and charge transfer processes during electrochemical reactions.This review highlights the challenges associated with low-temperature electrochemical processes and briefly discusses recent achievements in optimizing electrodeposition processes through the use of external physical fields.The regulating effects on the optimization of the electrodeposition process and the strategies for select-ing various external physical fields,including magnetic,supergravity,and ultrasonic fields are summarized from the perspectives of equipment and mechanisms.Finally,advanced methods for in-situ characterization of external physical field-assisted electrodeposition processes are reviewed to gain a deeper understanding of metallic electrodeposition.An in-depth exploration of the mechanism by which external physical fields affect the electrode process is essential for enhancing the efficiency of metal extraction at low temperatures.
基金supported by the Key Project of Natural Science Fund of Shandong Province (ZR2011BZ008)the Marine Renewable Energy Special Fund Project from the State Oceanic Administration PRC (GHME2011GD04)+2 种基金the Scientific and Technology Development Plan Project of Shandong Province,China (2008GG10007003)the Key Laboratory of Submarine Geoscience and Exploring Technology of the Ministry of Education,Ocean University of China (Grant No. 2008-01)the Key Laboratory of Marine Environment & Ecology,Ministry of Education (Grant No. 2008010)
文摘Microbial fuel cell(MFC) on the ocean floor is a kind of novel energy-harvesting device that can be developed to drive small instruments to work continuously.The shape of electrode has a great effect on the performance of the MFC.In this paper,several shapes of electrode and cell structure were designed,and their performance in MFC were compared in pairs:Mesh(cell-1) vs.flat plate(cell-2),branch(cell-3) vs.cylinder(cell-4),and forest(cell-5) vs.disk(cell-6) FC.Our results showed that the maximum power densities were 16.50,14.20,19.30,15.00,14.64,and 9.95 mWm-2 for cell-1,2,3,4,5 and 6 respectively.And the corre-sponding diffusion-limited currents were 7.16,2.80,18.86,10.50,18.00,and 6.900 mA.The mesh and branch anodes showed higher power densities and much higher diffusion-limited currents than the flat plate and the cylinder anodes respectively due to the low diffusion hindrance with the former anodes.The forest cathode improved by 47% of the power density and by 161% of diffusion-limited current than the disk cathode due to the former's extended solid/liquid/gas three-phase boundary.These results indicated that the shape of electrode is a major parameter that determining the diffusion-limited current of an MFC,and the differences in the elec-trode shape lead to the differences in cell performance.These results would be useful for MFC structure design in practical applica-tions.
基金Supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars of the Ministry of Education,Chinathe Natural Science Foundation of Tianjin City,China(No.06YFJMJC15000)
文摘Multilayer film was fabricated on an electrode surface by alternate layer-by-layer（LBL） adsorption of polycationic redox polymer（PEI-Fc） and dye-linked L-proline dehydrogenase（L-proDH）.The electrochemistry of the PEI-Fc/L-proDH multilayer modified electrode was investigated by cyclic voltammetry,and the enzyme catalysis mediated by the redox polymer was studied in a solution containing L-proline.It was observed that electron communication between L-proDH and the electrode was achieved with the help of PEI-Fc.A mathematical expression for the current response was evaluated based on the Michaelis-Menten kinetics mode,and the calculated currents fitted well with the experimental data.The kinetic analysis indicates that only a small fraction of the immobilized enzyme was efficiently electrically wired by the redox polymer.
基金supported by the National Key R&D Program of China(2021YFB2500300)the National Natural Science Foundation of China(22372083,52201259)+1 种基金the Natural Science Foundation of Tianjin(22JCZDJC00380)Young Elite Scientist Sponsorship Program by CAST。
文摘Charge transfer at the liquid(electrolyte)-solid(metal)interfaces is of fundamental importance to metal electrochemical deposition that further determines the reversibility and kinetics of energy-dense rechargeable metal batteries(RMBs).We demonstrate the fast charge transfer at the electrolyte-metal interfaces for lithium metal by designing and synthesizing electrolytes with chiral solvents:R(or S)-1,2-dimethoxy pro pane(R-DMP or S-DMP)and R(or S)-4-methyl-1,3-dioxolane(R-MDOL or S-MDOL).The chiral-induced spin selectivity is considered to produce spin-polarized metal surfaces,enabling the improvement in charge transfer rate and efficiency.The deposited Li metal in chiral electrolytes shows smooth and uniform morphologies,as well as high initial(>95%)and average(~99.2%)Coulombic efficiency for Li metal stripping/plating process,thus prolonging the life-span of batteries using thin lithium anode(50μm)to 400 cycles till 80%capacity retention.This work provides a distinct approach to regulate metal deposition beyond the limitation of ion de-solvation.
基金National Natural Science Foundation of China(No.61376017)。
文摘SnO_(2)-based anodes for lithium-ion batteries(LIBs)experience volume expansion,leading to rapid capacity decay and low conductivity.To address this problem,a composite consists of C/SnO_(2) with a core-shell structure and a carbonized nitrogen-doped Co-metal organic framework(Co-MOF)(NC)supported on carbon cloth(CC)was designed and prepared,which was denoted as C/SnO_(2)@NC@CC.C/SnO_(2)@NC@CC could be used directly as a flexible anode for LIBs.The combination of core-shell structure centered on carbon spheres,carbonized nitrogen-doped Co-MOF,and CC not only restricts the volume expansion but also functions as conductive networks to improve the electrical conductivity.C/SnO_(2)@NC@CC exhibits excellent electrochemical performance with charge and discharge specific capacities of 2066.0 and 2077.1 mAh/g,respectively,after 120 cycles at a current density of 0.5 A/g.
基金supported by the Start-up grant from Suzhou University of Science and Technology.
文摘Currently the catalysis of hydrogen evolution reaction(HER)is mainly focused on the inherent electrocatalytic activity at relatively lower current densities while scarce at high current densities.Nevertheless,the latter is highly demanding in efficient mass-production of hydrogen.A SiO_(2) nanospheres template-synthesis is used to prepare mesoporous molybdenum carbide nanocrystals-embedded nitrogen-doped carbon foams(mp-Mo_(2)C/NC).The material shows much more excellent catalytic activity than the non-etched Mo_(2)C/NC toward hydrogen evolution reaction(HER)in acidic medium.More interestingly mp-Mo_(2)C/NC still has larger overpotential than Pt/C at lower current densities,but possess remarkably smaller overpotential than the latter at higher current densities for much better electrocatalytic performance.An approach is developed to investigate the electrode kinetics by Tafel plots,especially with eliminating the diffusion effect,indicating that Pt/C and mp-Mo_(2)C/NC display different reaction mechanisms.At low current densities the former presents reversible reaction,while the latter shows mixed electrochemical polarization/reversible electrode process.In the region of higher current densities,the former becomes totally gas-diffusion controlled with large overpotential,while the latter can still retain an electrode polarization process for much lower overpotential at the same current density.Result endorses that the meso-porously structured mp-Mo_(2)C/NC plays a critical role in avoiding gas diffusion control-resulting large overpotential at high current densities.This work holds great potential for an inexpensive catalyst better than Pt/C in practical applications of mass-production hydrogen at high current densities,while clearly shedding fundamental lights on designs of rational HER catalysts for the uses at high current densities.
文摘The electrochemical oxidation of 1, 3-benzenedithiol was investigated in a 0. 100 mol/L tetrabutylammonium perchlorate/acetonitrile electrolyte. The electrochemical techniques used were potential sweep, bulk electrolysis, rotating disc and the potential step method. The combination of the techniques yielded the number of electrons transferred per molecule, the reaction order, the transfer coefficient, the diffusion coefficient and concentration of dithiol anions, the standard heterogeneous rate constant as well as the formal potential and equilibrium constant of the preceeding dissociation reaction. This paper also illustrates the methods for studying the electrode kinetics of reactions which (a) involve a chemical reaction preceeding the electron-transfer process, (b) have insoluble polymer products, and (c) are totally irreversible.
基金supported by the National Natural Science Foundation of China(grant nos.51525805,51727812,and 51808526).
文摘The pH gradient caused by H^(+)/OH^(−)transport on an electrode surface is the key factor determining reaction performance,but its detailed impact on the electrode reaction kinetics has yet to be clarified.Here,the pH gradient effect was determined by developing electrode reaction equations,considering the overpotential assigned to the pH gradient called pH overpotential.The pH gradient effect was revealed to involve two aspects:(1)the Nernst pH overpotential,accounting for the common Nernst relationship with pH,and(2)the pH-dependent function of the electron-transfer coefficient(α_(pH)).Both parts were verified experimentally using oxygen reduction reaction and hydrogen evolution reaction,obviously,with differentα_(pH) functions.Detailedα_(pH) function effect was clarified based on numerical calculations of the electrode reaction equations.We found that the effect could be assessed suitably by an apparent constant(α_(app))and a nonlinear fitting method proposed forα_(app) value estimation.The results of this study provide the kinetic fundamentals of electrode reactions involving H^(+)/OH^(−)and contribute to the understanding and assessment of their performance with the H^(+)/OH^(−)transport effect.
基金National Research Foundation of Korea,Grant/Award Numbers:2022R1F1A1074441,2022R1F1A1074707KIST Institutional Program,Grant/Award Numbers:2V09480,2E32582。
文摘Commercialization of Zn-metal anodes with low cost and high theoretical capacity is hindered by the poor reversibility caused by dendrites growth,side reactions,and the slow Zn^(2+)-transport and reaction kinetics.Herein,a reversible heterogeneous electrode of Zn-nanocrystallites/polyvinylphosphonic acrylamide(Zn/PPAm)with fast electrochemical kinetics is designed for the first time:phosphonic acid groups with strong polarity and chelation effect ensure structural reversibility and stability of the threedimensional Zn-storage-host PPAm network and the Zn/PPAm hybrid;hydrophobic carbon chains suppress side reactions such as hydrogen evolution and corrosion;weak electron-donating amide groups constitute Zn^(2+)-transport channels and promote“desolvation”and“solvation”effects of Zn^(2+)by dragging the PPAm network on the Zn-metal surface to compress/stretch during Zn plating/stripping,respectively;and the heterostructure and Zn nanocrystallites suppress dendrite growth and enhance electrochemical reactivity,respectively.Thus,the Zn/PPAm electrode shows cycle reversibility of over 6000 h with a hysteresis voltage as low as 31 mV in symmetrical cells and excellent durability and flexibility in fiber-shaped batteries.
文摘The application of naive Koutecky-Levich analysis to micro- and nano-particle modified rotating disk electrodes of partially covered and non-planar geometry is critically analysed. Assuming strong overlap of the diffusion fields of the particles such that transport to the entire surface is time-independent and one-dimensional, the observed voltammetric response reflects an apparent electrochemical rate o constant koapp, equal to the true rate constant ko describing the redox reaction of interest on the surface of the nanoparticles and the ratio,ψ, of the total electroactive surface area to the geometric area of the rotating disk surface. It is demonstrated that Koutecky-Levich analysis is applicable and yields the expected plots of I-1 versus ω-1 where I is the current and ω is the rotation speed but that the values of the electrochemical rate constants inferred are thereof koapp, not ko. Thus, for ψ 〉 1 apparent electrocatalysis might be naively but wrongly inferred whereas for ψ 〈 1 the deduced electrochemical rate constant will be less than ko. Moreover, the effect of ψ on the observed rotating disk electrode voltammograms is significant, signalling the need for care in the overly simplistic application of Koutecky-Levich analysis to modified rotating electrodes, as is commonly applied for example in the analysis of possible oxygen reduction catalysts.
文摘Although hydrazine(N2 H4) oxidation in an electrochemical environment has been of great interest for years,its intrinsic electron transfer kinetics remain uncertain.We report that the phenomenological Butler-Volmer(BV) theory is not appropriate for interpreting the process of hydrazine oxidation for which an astonishingly wide range of transfer coefficients,Tafel slopes and diffusion coefficient have been previously reported.Rather Tafel analysis for voltammetry recorded at Glassy Carbon(GC)electrodes reveals a strong potential dependence of the anodic transfer coefficient,consistent with the symmetric Marcus-Hush(sMH) theory.According to the relationship β=λ+FEf^0/2λ-F/2λ E,the reorganization energy(0.35±0.07 eV) and an approximate formal potential of the rate-determining first electron transfer were successfully extracted from the voltammetric responses.
基金the Nature Science Foun-dation of Shandong Province(Grant No:ZR2019BEM019)Future Plans of Young Scholars at Shandong University.
文摘Lithium-oxygen batteries(LOBs)have extensive applications because of their ultra-high energy densities.However,the practical application of LOBs is limited by several factors,such as a high overpotential,poor cycle stability,and limited rate capacity.In this paper,we describe the successful uniform loading of Mn_(3)O_(4) nanoparticles onto multi-walled carbon nanotubes(Mn_(3)O_(4)@CNT).CNTs form a conductive network and expose numerous catalytically active sites,and the one-dimensional porous structure provides a convenient channel for the transmission of Li+and O2 in LOBs.The electronic conductivity and electrocatalytic activity of Mn_(3)O_(4)@CNT are significantly better than those of MnO@CNT because of the inherent driving force facilitating charge transfer between different valence metal ions.Therefore,the Mn_(3)O_(4)@CNT cathode obtains a low overpotential(0.76 V at a limited capacity of 1000 mAh g^(-1)),high initial discharge capacity(16895 mAh g^(-1) at 200 mA g^(-1)),and long cycle life(97 cycles at 200 mA g^(-1)).This study provides evidence that transition metal oxides with mixed-valence states are suitable for application as efficient cathodes for LOBs.
