| With the depletion of fossil energy resources,decomposition of water assisted by solar energy may become an important way to solve the energy crisis.The most important problem of photoelectrochemical water splitting is to obtain the highly efficient and stable semiconductor photoelectrodes.Perovskite oxides are one of them.This paper focuses on Bi Fe O3(BFO)and Bi VO4(BVO)in Bi series oxides.The former is a typical ferroelectric material,and the internal electric field caused by spontaneous polarization in the film can help the photocarriers to be separated.In recent years,it has mostly been studied as a photocathode.The latter is an n-type semiconductor,and it is valued for excellent performance of its photoanodic properties.However,Bi related materials are generally unstable in acidic and alkaline electrolytes.In this paper,Ti O2 protective layer is used to obtain highly efficient and stable photoelectrodes,and we have mainly carried out the following two aspects:(1)Due to the good ferroelectric properties and relatively narrow band gap(~ 2.4 e V),BFO has been studied as a photoelectrode for water splitting in recent years,but the photocurrent under one-solar illumination is mostly within 100 ?A/cm2.Pt is the best catalyst for hydrogen production,however,the BFO photocathode can not benefit because their band structures do not match and an upward barrier will be formed between BFO and Pt which impedes the transfer of electrons,.On the other hand,the stability of BFO photoelectrode is generally around 1 hours,proving that its surface can not be directly exposed to electrolytes.In this paper,the amorphous Ti O2 buffer layer is used to insert between BFO film and Pt catalyst,which is found to increase the photoelectrochemical activity of the photoelectrode and increase its stability simultaneously.Under 0 V versus reversible hydrogen electrode(0 V vs.RHE),the current density of ITO/BFO/Ti O2/Pt photocathode reached 460 ?A/cm2,and the open circuit voltage reached 1.25 V vs.RHE.Here,Ti O2 functions as a buffer layer to remove the upward barrier between BFO and Pt,and makes the photogenerated carriers separate efficiently.In addition,the photocathode also shows high stability in acid solution after a 10-h PEC continuous testing,proving that Ti O2 is good to protect the surface of BFO.The work has been published in Applied Physics Letters.111,123901(2017).(2)Inspired by the above work,we also try to use amorphous Ti O2 layer to protect BVO photoanode.First,the FTO/WO3/BVO composite structure is found to have higher efficiency of water splitting than the single WO3 and BVO electrodes.The current density of the electrode reaches 1.70 m A/cm2 at 1.23 V vs.RHE,and the open circuit voltage is 0.21 V vs.RHE.However,the stability is not good.After 11 h continuous testing,the photocurrent density decreases by nearly 16%.On this basis,the Ti O2 protection layer is used.At 1.23 V vs.RHE,the current density of FTO/WO3/BVO/Ti O2 photoanode decreases slightly to 1.58 m A/cm2,however the stability improves a lot,and there is no trend of attenuation for photocurrent during the 11 h continuous test.A thin layer of Ti O2 can also protect the BVO surface. |
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