Preparation Of LDHs/BiVO₄ Composite Photoanodes And Study On Enhancement Of The Photoelectrochemical Performance

The demand for renewable and clean energy sources continuously rises due to the energy crisis and environmental pollution in society.Photoelectrochemical water splitting,which can convert solar energy into clean and sustainable hydrogen energy,is one of the most promising and economically viable strategies.Among many semiconductor candidate materials,Bi VO₄as an attractive photoanode candidate has been widely used in photocatalytic field due to its advantages such as suitable band gap（ca.2.4e V）,long carrier lifetime（～40 ns）and chemical stability.However,a series of problems such as low c arrier mobility,high electron-hole recombination efficiency,sluggish oxygen evolution reaction kinetics and severe photocorrosion have severely limited the industrial production and application of Bi VO₄,resulting in its actual photocurrent density being much lower than7.5 m A cm^-2（theoretical value）.In order to solve the above problems,based on Bi VO₄semiconductor materials,two kinds of efficient and stable composite photoanodes were designed and developed by loading layered double hydroxides（LDHs）as oxygen evolution cocatalysts,introducing oxygen vacancies,constructing heterojunctions and covering protective layer,and then they were applied in photoelectrochemical（PEC）water splitting to produce H₂and O₂.Specific research contents are as follows:（1）A series of Ni Fe-LDH/Bi VO₄photoanodes with well-controlled O_vacwere synthesized by a simple hydrothermal-controlled strategy via regulating p H and hydrothermal time of the precursor solution.At optimal experimental condition（p H=3.0,hydrothermal time=20 h）,the obtained photoanode i.e.O_vac-rich Ni Fe-LDH/Bi VO₄（v-Ni Fe-LDH/Bi VO₄）has excellent PEC water splitting performance.As a consequence,the optimized v-Ni Fe-LDH/Bi VO₄photoanode displays a high photocurrent density of 5.81 m A cm^-2(1.23 V_RHE),which is almost 3.6 times of that of pure Bi VO₄(1.62 m A cm^-2).In addition,v-Ni Fe-LDH/Bi VO₄photoanode has high bias photon-to-current efficiency（2.23%）,charge separation efficiency（83.00%）and transfer efficiency（91.66%）.Importantly,v-Ni Fe-LDH/Bi VO₄photoanode exhibits excellent photocorrosion resistance at 1.23 V_RHE,which remains stable in KBi+V electrolyte（p H=9.5）for over 80 h.（2）Highly efficient Ni Co Fe-LDH/VO₂/Bi VO₄photoanode was prepared by surface photoelectrochemical oxidation and electrochemical deposition.Ni Co Fe-LDH/VO₂/Bi VO₄photoanode shows a remarkable photocurrent density of 6.05 m A cm^-2at the applied bias of 1.23 V_RHE,which is superior to Bi VO₄(1.62 m A cm^-2)and VO₂/Bi VO₄(4.17 m A cm^-2)photoanodes.In addition,the surface charge separation and transfer efficiency of Ni Co Fe-LDH/VO₂/Bi VO₄photoanode can reach 86.03%and 95.12%,respectively,and the relative electrochemical surface area of Ni Co Fe-LDH/VO₂/Bi VO₄photoanode is much higher than that of pure Bi VO₄.Meanwhile,Ni Co Fe-LDH/VO₂/Bi VO₄photoanode shows excellent photocorrosion resistance with long-term photostability of over 110 h in KBi+V electrolyte（p H=9.5）at 1.23 V_RHE,indicating that the composite photoanode can significantly inhibit photocorrosion caused by the solution of V⁵⁺in the Bi VO₄lattice.