Effect Of Surface And Interface Structure Of BiVo4 Composite Photoanode On Photogenerated Carriers Behavior And Photoelectrochemical Properties

Photoelectrochemical（PEC）water splitting is to directly convert solar energy to hydrogen energy,which is a green and pollution-free clean energy.The PEC hydrogen production device has been broadly known as one of the most promising methods to convert solar energy into storable energy.Oxygen evolution reaction（OER）is the rate determining step of the PEC water splitting with the light-absorbing semiconductor as photoanode.At present,the improvement of photoanode materials has been developed.However,the mechanism of how the surface and interface structure of photoanode affect the photogenerated carriers behavior and the photoelectrochemical properties is still not clear.In this paper,BiVO₄ is used as the photoanode,the surface states are passivated by photoelectrochemical treatment,and the footprints of photogenerated holes are traced by transient photovoltage techniques,which prove the existence of surface trap states.The effect of surface structure on photocharge transfer behavior and PEC properties was investigated by studying the role of surface oxygen vacancies formation and recovery in surface passivation process.The transition metal cobalt compound was modified on the semiconductor surface as oxygen evolution catalyst,and the effect of different interface structure on charge transfer and reaction activity was discussed.The research content of this paper is mainly divided into the following two parts:1.Illuminating the charge transport at photoanode-electrolyte interface is pivotal for optimizing photoelectrochemical（PEC）water oxidation performance of BiVO₄.Our study demonstrates a preferentially photogenerated electrons trapping process at BiVO₄ surface,followed by the formation of surface-bound excitons.A facile LSV treatment method is described,which remarkably passivate the surface electron trapping states by the formation surface oxygen vacancies.The surface oxygen vacancies could“free”the photogenerated holes from the surface-bound excitons.As a result,more photogenerated holes are available on BiVO₄ surface and the PEC performance is enhanced.2.Cocatalysts-modified semiconductor photoanodes are one essential elements of PEC water splitting systems,but the effect of semiconductor/catalyst interface properties on the interface charge transfer behavior is still not well understood.In this work,the transition-metal oxyhydroxide（Co OOH）films with electrolyte-permeability were prepared on BiVO₄ semiconductor by electrodeposition,and then the dense oxide（Co₃O₄）catalysts were obtained by annealing.As a result of the high bulk activity and effective barrier height,the ion-permeable BiVO₄/Co OOH exhibit excellent oxygen evolution reaction kinetics process and generate a larger photovoltage to provide the primary driving force for charge separation at the sem/cat interface.Otherwise,for dense Co₃O₄,the dominant strategy to improve the separation efficiency is to reduce the trapping charge recombination between the semiconductor and the catalyst layer by passivating the surface state of the semiconductor.Our study demonstrates that the type of catalyst structure greatly affects the charge transfer at the semiconductor/catalyst interface,making a significant difference in the mechanism of improving OER reaction.The results show that BiVO₄/Co OOH photoanodes have more excellent PEC performance than BiVO₄/Co₃O₄,which proves that the permeability of electrolyte nature is a determining factor in promoting water oxidation.