Metal Sulfide Composite Photoanode:Fabrication And Photoelectrochemical Water Oxidation Performance

As the fossil energy shortage problem and environmental pollution become increasingly serious in recent years,the exploitation and utilization of renewable energy is the key to solving these problems.Photoelectrochemical(PEC)water splitting offers a feasible approach for solar-to-hydrogen conversion to achieve the effective utilization of solar energy,which is also one of the most promising strategies to solve the energy crisis PEC water splitting contains three main processes:generation of photogenerated charges,separation and transmission of photogenerated charges,and water redox reaction.The rational design and fabrication of suitable photoanode materials are crucial for achieving efficient PEC water splitting system.Most metal sulfides have been widely studied as typical PEC photoanodes,owing to their strong visible-light absorption and appropriate band position for water redox reaction.However,the severe recombination of photogenerated charges in semiconductors material during transmission limits its PEC performance.To solve these problems,we improved the PEC performance by the means of morphology control,construction of heterojunctions and doping.Finally,we design and facbricate 3D trilayer Bi2WO6/TiO2/CdS and oxygen gradient doped In2S3/WO3.The main research contents are as follows(1)In order to solve the problems of serious carrier recombination in CdS materials and insuff-icient contact between CdS particles and electrolyte,a 3D trilayer Bi2WO6/TiO2/CdS nanoflake array on fluorine-doped tin oxide substrates has been successfully synthesized by combining template method,atomic layer deposition technique and microwave-hydrothermal process,in which Bi2WO6 porous nanosheet nanoarray acts as skeleton to support more CdS particles,anatase TiO2 serves as a band-matching layer to improve the interfacial charge separation efficiency,CdS works as visible light absorber By optimizing the thickness of TiO2(8 nm best),the photocurrent density of the composite photoanode reaches 4.91 mA cm-2 at 1.23 V vs.reversible hydrogen electrode(RHE),which is 3.1 and 2.1 times that of CdS particle films and Bi2WO6/CdS films,respectively The enhancement of PEC performance is attributed to the enlarged surface area,increased light harvesting ability,and improved charge transport efficiency(2)To address the serious charge recombination of In2S3 bulk phase,the gradient oxygen doped WO3/In2S3 heterostructure photoanode has been successfully designed and synthesized by combining hydrothermal,water bath process and polyvinylpyrrolidone(PVP)solution treatment.By varying the water bath reaction time and PVP treatment time,2D In2S3 nanosheets are grown on the 3D WO3 nanowalls with the optimal morphology and gradient oxygen doping.Such design takes the advantage of both type Ⅱ and gradient band structure to facilitate the bulk carrier transport.Furthermore,the PVP treatment enhances carrier density,prolongs carrier lifetime,and increases surface active sites,thereby promoting the improvement of the PEC performance of photoanode.Finally,after 3 hours of PVP treatment,the photocurrent density of WO3/In2S3 photoanode reaches 1.61 mA cm-2 at 1.23 V vs.RHE,which is 2.3 times that of untreated sample.