Preparation And Photoelectrochemical Properties Of Novel Heterojunction Photoelectrodes

With the continuous development of science and technology,the shortage of fossil energy has become an important problem hindering social development,and the development of sustainable new energy has become the primary way to solve the problem.Due to the advantages of high calorific value of combustion and pollution-free of combustion products,hydrogen energy has become one of the important energy sources to realize the sustainable development of energy.Among many hydrogen production schemes,photoelectrochemical（PEC）water decomposition based on photoelectric complementarity strategy directly converts huge solar energy into hydrogen energy,which has obvious advantages over other hydrogen production schemes.Photoelectric electrode material is a major components of PEC system.Selecting high-performance photoelectric electrode material is one of the important topics of PEC research.Photoelectrode materials not only need to have appropriate energy band structure,but also need to excite the photogenerated electron hole required for water decomposition reaction.In addition,it needs the conditions of high carrier transmission productivity,appropriate light absorption range and good stability,but there are few photoelectric electrode materials with the above conditions.Therefore,it is one of the important methods to improve the photoelectrochemical properties of the existing photoelectrode materials.In this paper,the properties of existing photoanode materials were improved by constructing heterostructures.Hematite（Fe₂O₃）and bismuth molybdate（Bi₂MoO₆）with visible light response were chose as the research object.The photoelectrochemical properties and mechanism of photoanode were researched by taking the sample structure morphology,surface chemical state and energy band structure as the analysis tools.Hematite and bismuth molybdate had become potential semiconductor materials because of appropriate band gap and energy band position,but there were still problems of low charge separation efficiency and poor carrier mobility.In view of the problems existing in the sample,the heterojunction was constructed according to the characteristics of the semiconductor,so that the Photoelectric conversion efficiency was significantly improved.The main research substances were as follows:1.Fe₂O₃/FePO₄/FeOOH nanorods photoanode with stepped energy band structure.Fe₂O₃/FePO₄/FeOOH nanorods photoanode with stepped energy band structure was successfully prepared by hydrothermal method and water bath method.The photocurrent density of Fe₂O₃/FePO₄/FeOOH photoanode was 2.02 m A·cm^-2,which was 2.5 time that of Fe₂O₃/FePO₄ photoanode,and 3.2 time that of Fe₂O₃/FeOOH photoanode.The charge separation efficiency of ternary heterojunction was higher than that of the traditional type II heterojunction,which might be due to the efficient cascade charge transfer and separation effect of the ternary stepped energy band heterojunction.As expect,the H₂ and O₂ evolution rates for photoelectrochemical water splitting of Fe₂O₃/FePO₄/FeOOH photoanode were 0.247 and 0.111μmol/min,which was 2.15 and1.95 times that of Fe₂O₃/FePO₄ photoanode,and 2.50 and 2.06 times that of Fe₂O₃/FeOOH photoanode,respectively.The incident photon-to-current conversion efficiency（IPCE）of Fe₂O₃/FePO₄/FeOOH photoanode was 18.17%under 365 nm light irradiation,which was 1.5 and 1.8 times that of Fe₂O₃/FePO₄ and Fe₂O₃/FeOOH photoanodes,respectively.Our work provides an attractive strategy for solar energy conversion to construct efficient photoelectrochemical photoanode materials.2.p-n Bi₂MoO₆/CuO heterojunction photoanode.Bi₂MoO₆/CuO heterojunction photoanodes with p-n structure were successfully prepared by electrophoretic deposition and dip-coating technique.By changing the impregnation times,the loading amount of CuO in Bi₂MoO₆/CuO films were controlled to explore the influence of different content of loaded films on the PEC properties.The results showed that the carrier transmission capacity of Bi₂MoO₆/CuO was significantly enhanced.The photocurrent density of Bi₂MoO₆/CuO-3 photoanode was 16 times higher than that of pure Bi₂MoO₆ photoanode.Under 365 nm light,the IPCE of Bi₂MoO₆/CuO-3 photoanode was 3.4 times that of pure Bi₂MoO₆ photoanode under365 nm light irradiation.