Hole transfer at the semiconductor-electrolyte interface is a key elementary process in(photo)electrochemical(PEC)water oxidation.However,up to now,a detailed understanding of the hole transfer and the influence of su...Hole transfer at the semiconductor-electrolyte interface is a key elementary process in(photo)electrochemical(PEC)water oxidation.However,up to now,a detailed understanding of the hole transfer and the influence of surface hole density on PEC water oxidation kinetics is lacking.In this work,we propose a model for the first time in which the surface accumulated hole density in BiVO_(4)and Mo-doped BiVO_(4)samples during water oxidation can be acquired via employing illumination-dependent Mott-Schottky measurements.Based on this model,some results are demonstrated as below:(1)Although the surface hole density increases when increasing light intensity and applied potential,the hole transfer rate remains linearly proportional to surface hole density on a log-log scale.(2)Both water oxidation on BiVO_(4)and Mo-doped BiVO_(4)follow first-order reaction kinetics at low surface hole densities,which is in good agreement with literature.(3)We find that water oxidation active sites in both BiVO_(4)and Mo-doped BiVO_(4)are very likely to be Bi^(5+),which are produced by photoexcited or/and electroinduced surface holes,rather than VO_(x)species or Mo^(6+)due to their insufficient redox potential for water oxidation.(4)Introduction of Mo doping brings about higher OER activity of BiVO_(4),as it suppresses the recombination rate of surface holes and increases formation of Bi^(5+).This surface hole model offers a general approach for the quantification of surface hole density in the field of semiconductor photoelectrocatalysis.展开更多
Perovskite LaCoO_(3) is being increasingly explored as an effective low-cost electrocatalyst for the oxygen evolution reaction(OER).Sr doping in LaCoO_(3)(La1-xSrxCoO_(3))has been found to substantially increase its c...Perovskite LaCoO_(3) is being increasingly explored as an effective low-cost electrocatalyst for the oxygen evolution reaction(OER).Sr doping in LaCoO_(3)(La1-xSrxCoO_(3))has been found to substantially increase its catalytic activity.In this work,we report a detailed study on the evolution of the electronic structure of La1-xSrxCoO_(3) with 0≤x≤1 and its correlation with electrocatalytic activity for the OER.A combination of X-ray photoemission spectroscopy(XPS)and X-ray absorption spectroscopy(XAS)was used to unravel the electronic density of states(DOS)near the Fermi level(EF),which provide insights into the key electronic structure features for the enhanced OER catalytic activity.Detailed analysis on the Co L-edge XAS suggest that LaCoO_(3) has a low spin state with t_(2g)^(6) e_(g)^(0) configuration at room temperature.This implies that the high OER catalytic activity of LaCoO_(3) should not be rationalized by the occupancy of eg=1 descriptor.Substituting Sr^(2+) for La^(3+) in LaCoO_(3) induces Co4+oxidation states and effectively dopes hole states into the top of valence band.A semiconductor-to-metal transition is observed for x>0.2,due to the holeinduced electronic DOS at the EF and increased hybridization between Co 3 d and O 2 p.Such an electronic modulation enhances the surface adsorption of the*OH intermediate and reduces the energy barrier for interfacial charge transfer,thus improving the OER catalytic activity in La_(1-x)Sr_(x)CoO_(3).In addition,we found that the La_(1-x)Sr_(x)CoO_(3) surface undergoes amorphization after certain period of OER measurement,leading to a partial deactivation of the electrocatalyst.High Sr doping levels accelerated the amorphization process.展开更多
V-pits have been intensively studied for their role in light-emitting diodes(LEDs).The coverage of V-pits in InGaN/GaN multiquantum wells(MQWs)is critical for suppressing leakage path through electron blocking layer(E...V-pits have been intensively studied for their role in light-emitting diodes(LEDs).The coverage of V-pits in InGaN/GaN multiquantum wells(MQWs)is critical for suppressing leakage path through electron blocking layer(EBL).In this study,we have investigated the coverage of V-pits in green mini-LEDs modulated via growth parameters optimization and systematically analyzed the characteristics of the photoelectric properties associated with V-pits coverage on device.Elevated temperatures and pressures result in enhanced adatoms migration,which can achieve a coverage up to 98.8% of V-pits,improving the crystal quality due to stable surface.Electrical characterization reveals that although high-coverage devices exhibit suppressed leakage current,their peak external quantum efficiency(EQE)decreases,more seriously spectral blue shift and operating voltage increase due to compromised hole transport uniformity.Intriguingly,intermediate-coverage samples demonstrate superior breakdown voltage characteristics.Current-voltage curve analysis shows the ideality factor increases from 1.8 to 2.5 with improved coverage,indicating aggravated Shockley-Read-Hall(SRH)recombination with covered V-pits.展开更多
The precise control on the combination of multiple metal atoms in the structure of metal-organic frameworks(MOFs)endowed by reticular chemistry,allows the obtaining of materials with compositions that are programmed f...The precise control on the combination of multiple metal atoms in the structure of metal-organic frameworks(MOFs)endowed by reticular chemistry,allows the obtaining of materials with compositions that are programmed for achieving enhanced reactivity.The present work illustrates how through the transformation of MOFs with desired arrangements of metal cations,multi-metal spinel oxides with precise compositions can be obtained,and used as catalyst precursor for the reverse water-gas shift reaction.The differences in the spinel initial composition and structure,determined by neutron powder diffraction,influence the overall catalytic activity with changes in the process of in s itu formation of active,metal-oxide supported metal nanoparticles,which have been monitored and characterized with in situ X-ray diffraction and photoelectron spectroscopy studies.展开更多
The design of heterostructured transition metal-based electrocatalysts with controlled composition and interfaces is key to increasing the efficiency of the water electrolysis and the elucidation of reaction mechanism...The design of heterostructured transition metal-based electrocatalysts with controlled composition and interfaces is key to increasing the efficiency of the water electrolysis and the elucidation of reaction mechanisms.In this work,we report the synthesis of well-controlled vertically aligned Ni/NiO nanocomposites consisting of Ni nanoclusters embedded in NiO,which result in highly efficient electrocatalysts for overall water splitting.We show that such a high catalytic efficiency toward both the hydrogen evolution reaction(HER)and the oxygen evolution reaction(OER)originates from a synergetic effect at Ni/NiO interfaces that significantly reduces the energy barrier for water dissociation,and favours the formation of reactive H*intermediates on the Ni side of the interface,and OH_(ads) on the NiO side of the interface.A study of water chemisorption based on near-ambient pressure photoelectron spectroscopy indicates that the abundant hetero-interfaces in Ni/NiO nanocomposite promote the dissociation of water with a three-fold increase in the surface concentration of OH_(ads) compared with pure NiO.Density functional theory calculations indicate that Ni/NiO interface leads to the reduction of the water dissociation energy barrier due to a high concentration of oxygen vacancies at NiO side of the interface,whereas the formation of highly active metallic Ni sites with an optimal value of Gibbs free energy of H*(ΔG_(H*)=−0.16 eV)owes to a favourable adjustment of the electron energetics at the interface,thus accelerating the overall electrochemical water splitting.展开更多
Hematite(α-Fe_(2)O_(3))is an ideal oxide semiconductor candidate for photoelectrochemical(PEC)water splitting.Doping of Fe_(2)O_(3)is known to benefit the PEC water oxidation efficiency,but despite extensive research...Hematite(α-Fe_(2)O_(3))is an ideal oxide semiconductor candidate for photoelectrochemical(PEC)water splitting.Doping of Fe_(2)O_(3)is known to benefit the PEC water oxidation efficiency,but despite extensive research efforts,the underlying mechanism still remains elusive.In this work,we report a comprehensive study on the relationship between the electronic structure,interfacial reaction kinetics and PEC activity of Ti-doped Fe_(2)O_(3)photoanodes.The results show that the interfacial charge transfer efficiency at the Fe_(2)O_(3)/electrolyte interface is the main factor in the significant increase of the PEC activity of doped Fe_(2)O_(3).Electrochemical impedance spectroscopy reveals that the interfacial charge transfer efficiency is determined by energy overlap between the water oxidation potential and energy distribution of an intermediate surface state that has been identified as Fe^(IV)=O groups on Fe_(2)O_(3)surface generated during PEC process.Interestingly,the potential energy distribution of this intermediate surface state can be modulated by Ti doping,and a shift towards a more positive potential of the intermediate surface state increases the overlap with the water oxidation potential and thus enhances the kinetics of charge transfer for PEC water splitting.The origin of such potential energy modulation is traced to the inductive effect from Ti-doping on the Fe^(3+)/Fe^(4+)redox transition and the Fe-O bond covalency.Our results provide new insight into the mechanism for the doping effect on the PEC water splitting,introducing new strategies to optimize the PEC activity by tuning the redox properties of active metal oxides.展开更多
基金support of the China Scholarship Council,affiliated to the Ministry of Education of the P.R.of China(Scholarships no.201708420159,202208320036 and 202008420222)JG and JPH acknowledge financial support from the German Ministry of Education and Research BMBF under project 03HY105HDr.Marcus Einert and Dr.Clément Maheu acknowledge funding from the German Research Foundation(DFG)under projects 469377211 and 423746744,respectively。
文摘Hole transfer at the semiconductor-electrolyte interface is a key elementary process in(photo)electrochemical(PEC)water oxidation.However,up to now,a detailed understanding of the hole transfer and the influence of surface hole density on PEC water oxidation kinetics is lacking.In this work,we propose a model for the first time in which the surface accumulated hole density in BiVO_(4)and Mo-doped BiVO_(4)samples during water oxidation can be acquired via employing illumination-dependent Mott-Schottky measurements.Based on this model,some results are demonstrated as below:(1)Although the surface hole density increases when increasing light intensity and applied potential,the hole transfer rate remains linearly proportional to surface hole density on a log-log scale.(2)Both water oxidation on BiVO_(4)and Mo-doped BiVO_(4)follow first-order reaction kinetics at low surface hole densities,which is in good agreement with literature.(3)We find that water oxidation active sites in both BiVO_(4)and Mo-doped BiVO_(4)are very likely to be Bi^(5+),which are produced by photoexcited or/and electroinduced surface holes,rather than VO_(x)species or Mo^(6+)due to their insufficient redox potential for water oxidation.(4)Introduction of Mo doping brings about higher OER activity of BiVO_(4),as it suppresses the recombination rate of surface holes and increases formation of Bi^(5+).This surface hole model offers a general approach for the quantification of surface hole density in the field of semiconductor photoelectrocatalysis.
基金funding support by the National Natural Science Foundation of China (Grant No. 21872116)financial support by the National Natural Science Foundation of China (Grant No. 21621091 and 21373166)+5 种基金funding supported by the EU (ERC CoG HyMAP 648319)Spanish AEI (NyMPhA PID2019-106315RB-I00)“Comunidad de Madrid” and European Structural Funds for their financial support to FotoArt-CM project (S2018/NMT-4367)the Fundación Ramón Arecesfinancial support by the China Scholarship Council (CSC)the Sino-German Mobility Program (Grant No. M-0377)。
文摘Perovskite LaCoO_(3) is being increasingly explored as an effective low-cost electrocatalyst for the oxygen evolution reaction(OER).Sr doping in LaCoO_(3)(La1-xSrxCoO_(3))has been found to substantially increase its catalytic activity.In this work,we report a detailed study on the evolution of the electronic structure of La1-xSrxCoO_(3) with 0≤x≤1 and its correlation with electrocatalytic activity for the OER.A combination of X-ray photoemission spectroscopy(XPS)and X-ray absorption spectroscopy(XAS)was used to unravel the electronic density of states(DOS)near the Fermi level(EF),which provide insights into the key electronic structure features for the enhanced OER catalytic activity.Detailed analysis on the Co L-edge XAS suggest that LaCoO_(3) has a low spin state with t_(2g)^(6) e_(g)^(0) configuration at room temperature.This implies that the high OER catalytic activity of LaCoO_(3) should not be rationalized by the occupancy of eg=1 descriptor.Substituting Sr^(2+) for La^(3+) in LaCoO_(3) induces Co4+oxidation states and effectively dopes hole states into the top of valence band.A semiconductor-to-metal transition is observed for x>0.2,due to the holeinduced electronic DOS at the EF and increased hybridization between Co 3 d and O 2 p.Such an electronic modulation enhances the surface adsorption of the*OH intermediate and reduces the energy barrier for interfacial charge transfer,thus improving the OER catalytic activity in La_(1-x)Sr_(x)CoO_(3).In addition,we found that the La_(1-x)Sr_(x)CoO_(3) surface undergoes amorphization after certain period of OER measurement,leading to a partial deactivation of the electrocatalyst.High Sr doping levels accelerated the amorphization process.
基金supported by the Special Key Project of Technological Innovation and Application Development in Chongqing(CSTB2023TIADKPX0017)the National Natural Science Foundation of China(Grant 22275154).
文摘V-pits have been intensively studied for their role in light-emitting diodes(LEDs).The coverage of V-pits in InGaN/GaN multiquantum wells(MQWs)is critical for suppressing leakage path through electron blocking layer(EBL).In this study,we have investigated the coverage of V-pits in green mini-LEDs modulated via growth parameters optimization and systematically analyzed the characteristics of the photoelectric properties associated with V-pits coverage on device.Elevated temperatures and pressures result in enhanced adatoms migration,which can achieve a coverage up to 98.8% of V-pits,improving the crystal quality due to stable surface.Electrical characterization reveals that although high-coverage devices exhibit suppressed leakage current,their peak external quantum efficiency(EQE)decreases,more seriously spectral blue shift and operating voltage increase due to compromised hole transport uniformity.Intriguingly,intermediate-coverage samples demonstrate superior breakdown voltage characteristics.Current-voltage curve analysis shows the ideality factor increases from 1.8 to 2.5 with improved coverage,indicating aggravated Shockley-Read-Hall(SRH)recombination with covered V-pits.
基金We acknowledge Institut Laue-Langevin and Spanish initiatives on Neutron Scattering(ILL-SpINS)for beamtime at instrum ent D2B and G.Cuellofor assistance during data acquisition(10.5291/ILL-DATA.5-21-1114).We thank M.C.Capel for the TEM images and TEM-EDS analysis acquisition at Instituto de Catalisis y Petroleoquimica(CSIC).Funding:Work at Instituto de Ciencia de Materiales de Madrid-Consejo Superior de Instigaciones Cientfficas(CSIC)has been supported by the Spanish Research Agency(Agenda Estatal de Investigacion,AEI),Projects MAT2016-78465-R,CTQ2017-87262-R.This work was supported by the EU(ERC CoG HyMAP 648319)and Spanish MINECO(ENE2016-79608-C2-1-R).Authors also wish to thank to“Com unidad de Madrid”and European Structural Funds for their financial support to FotoArt-CM project(S2018/NMT-4367).F.G.acknowledges financial support from MINECO Ramon y Cajal program(RyC-2015-18384).
文摘The precise control on the combination of multiple metal atoms in the structure of metal-organic frameworks(MOFs)endowed by reticular chemistry,allows the obtaining of materials with compositions that are programmed for achieving enhanced reactivity.The present work illustrates how through the transformation of MOFs with desired arrangements of metal cations,multi-metal spinel oxides with precise compositions can be obtained,and used as catalyst precursor for the reverse water-gas shift reaction.The differences in the spinel initial composition and structure,determined by neutron powder diffraction,influence the overall catalytic activity with changes in the process of in s itu formation of active,metal-oxide supported metal nanoparticles,which have been monitored and characterized with in situ X-ray diffraction and photoelectron spectroscopy studies.
基金the National Natural Science Foundation of China(21872116)F.E.Oropeza and V.A.de la Peña O’Shea are grateful for the funding supported by the EU(ERC CoG HyMAP 648319)and Spanish AEI(NyMPhA PID2019-106315RB-I00)+3 种基金Also,this work has been funded by the regional government of Comunidad de Madrid and European Structural Funds through their financial support to FotoArt-CM project(S2018/NMT-4367)Besides,Fundación Ramon Areces funded this work though ArtLeaf project.Kelvin H.L.Zhang also acknowledge the Sino-German Mobility Program(M-0377)SuperSTEM is the National Research Facility for Advanced Electron Microscopy,funded from the Engineering and Physics Research Council(EPSRC)M.Bugnet is grateful to the SuperSTEM Laboratory for microscope access,and to the School of Chemical and Process Engineering at the University of Leeds for a visiting associate professorship and financial support.
文摘The design of heterostructured transition metal-based electrocatalysts with controlled composition and interfaces is key to increasing the efficiency of the water electrolysis and the elucidation of reaction mechanisms.In this work,we report the synthesis of well-controlled vertically aligned Ni/NiO nanocomposites consisting of Ni nanoclusters embedded in NiO,which result in highly efficient electrocatalysts for overall water splitting.We show that such a high catalytic efficiency toward both the hydrogen evolution reaction(HER)and the oxygen evolution reaction(OER)originates from a synergetic effect at Ni/NiO interfaces that significantly reduces the energy barrier for water dissociation,and favours the formation of reactive H*intermediates on the Ni side of the interface,and OH_(ads) on the NiO side of the interface.A study of water chemisorption based on near-ambient pressure photoelectron spectroscopy indicates that the abundant hetero-interfaces in Ni/NiO nanocomposite promote the dissociation of water with a three-fold increase in the surface concentration of OH_(ads) compared with pure NiO.Density functional theory calculations indicate that Ni/NiO interface leads to the reduction of the water dissociation energy barrier due to a high concentration of oxygen vacancies at NiO side of the interface,whereas the formation of highly active metallic Ni sites with an optimal value of Gibbs free energy of H*(ΔG_(H*)=−0.16 eV)owes to a favourable adjustment of the electron energetics at the interface,thus accelerating the overall electrochemical water splitting.
基金financially supported by the funding support by the National Natural Science Foundation of China(22021001)funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 101030782+1 种基金the RYC2021-034254-I grant funded by MCIN/AEI/10.13039/501100011033 and European Union“Next Generation EU/PRTR”financial support from FJC2020-044866-I/MCIN/AEI/10.13039/501100011033 and European Union“Next Generation EU”/PRTR
文摘Hematite(α-Fe_(2)O_(3))is an ideal oxide semiconductor candidate for photoelectrochemical(PEC)water splitting.Doping of Fe_(2)O_(3)is known to benefit the PEC water oxidation efficiency,but despite extensive research efforts,the underlying mechanism still remains elusive.In this work,we report a comprehensive study on the relationship between the electronic structure,interfacial reaction kinetics and PEC activity of Ti-doped Fe_(2)O_(3)photoanodes.The results show that the interfacial charge transfer efficiency at the Fe_(2)O_(3)/electrolyte interface is the main factor in the significant increase of the PEC activity of doped Fe_(2)O_(3).Electrochemical impedance spectroscopy reveals that the interfacial charge transfer efficiency is determined by energy overlap between the water oxidation potential and energy distribution of an intermediate surface state that has been identified as Fe^(IV)=O groups on Fe_(2)O_(3)surface generated during PEC process.Interestingly,the potential energy distribution of this intermediate surface state can be modulated by Ti doping,and a shift towards a more positive potential of the intermediate surface state increases the overlap with the water oxidation potential and thus enhances the kinetics of charge transfer for PEC water splitting.The origin of such potential energy modulation is traced to the inductive effect from Ti-doping on the Fe^(3+)/Fe^(4+)redox transition and the Fe-O bond covalency.Our results provide new insight into the mechanism for the doping effect on the PEC water splitting,introducing new strategies to optimize the PEC activity by tuning the redox properties of active metal oxides.
