Study On The Kinetics Of Photoelectrochemical Water Splitting By Bismuth Vanadate-based Photoanode

Recently,Bi VO₄ has received considerable attention as a photoanode material for PEC due to the maximum photocurrent density estimated to be 7.5 m A cm^-2,and9.2%of theoretical solar-to-hydrogen conversion efficiency.At the same time,it also has some problems such as insufficient optical utilization,serious carrier recombination,slow oxygen evolution kinetics.Here,we have implemented a series of strategies to overcome the drawbacks,including PEG-Bi VO₄,Al₂O₃/Bi VO₄photoanodes,which significantly improves the photoelectrochemical performance of Bi VO₄-based photoanode materials.The research including:1.The rate-determining step of the oxygen evolution reaction based on semiconductor photoanode is formation of O-O bond.Herein,the polyethylene glycol（PEG）modified Bi VO₄photoanodes is reported,in which the proton can be transferred quickly due to high proton conductivity of PEG,resulting in the acceleration of the O-O bond formation rate.These have been fully demonstrated by different kinetic isotope effect（KIE）values.Moreover,open circuit voltage（Uoc）has further illustrated that PEG passivates the surface states and surface charge recombination is reduced.The composite photoanode can achieve a maximum photocurrent density of3.64 m A cm^-2 at 1.23 V compared to 1.04 m A cm^-2 for pure Bi VO₄,and an onset potential of 170m V,which was 230 m V negative shift compared to pure Bi VO₄.This work provides a new strategy to accelerate water oxidation kinetics for photoanodes by speeding up the transfer of the proton and the O-O bond formation rate.2.The Al₂O₃ layer was loaded on Bi VO₄photoanodes,in which the surface states can be passivated,this result can be demonstrated by cyclic voltammogram（CV）.Moreover,the onset potential was reduced and the reaction kinetics was accelerated by adding hydrazine（N₂H₄）into the electrolyte solution,resuiting from the oxidation reaction of hydrazine is more thermodynamically favorable.A surface charge transfer efficiencyof 62%at 1.23V vs.RHE for Al₂O₃/Bi VO₄ photoanode,And after the addition of hydrazine,the system finally achieved a high photocurrent density of 4.10 m A cm^-2 and an ultralow onset potential of-0.04 V.These further illustrated that Al₂O₃ acts as a passivation layer to suppress the Fermi level pinning effect and reduce the recombination of electrons and holes in the trapped states on the surface.And the adjustment via hydrazine substantially boost the reaction kinetics.This work sheds light on combine the photoanode with electrolyte to improve the performance of PEC water splitting.