Studies On The Preparation And Properties Of Photoanode Film Toward Oxidation Evolution Reaction

With the development of economy and the improvement of life style,the demand for energy is increasing sharply,while environmental pollution is affecting our daily life seriously.In order to solve these problems,there is an urgent need for a transition from traditional fossil energy to renewable energy.Photoelectrochemical water splitting can convert inexhaustible solar energy into hydrogen energy.It has been proposed to be one of the most promising technologies in the future.Photoelectrochemical(PEC)water splitting system consists of two half reaction:the oxidation evolution reaction(OER)on the photoanode and the hydrogen evolution reduction(HER)on the photocathode.The oxidation evolution reaction in photoelectrochemical water splitting has a slow water oxidation kinetics,involving the migration of four protons and four electrons which takes a longer time scale,restricting the efficiency of photoelectrochemical water splitting system.In addition,photoanode materials still have many disadvantages in the practical application of photoelectrochemical water splitting,such as narrow light absorption range,low charge separation efficiency,severe recombination of electron-hole pairs and poor stability.In order to solve these problems,the photoanode material was modified by loading co-catalysts on the surface of photocatalysts and element doping for improving the performance of photoanode.The main research contents and results are presented as follows.(1)A composite photoanode was prepared by loading cobalt sulfide nanomaterial on the surface of BiVO₄ film through a simple two-step process.Cobalt sulfide as a novel oxygen evolution co-catalyst,can enrich photoproduction holes,accelerate water oxidation kinetics,increase the efficiency of electron-hole separation and injection,decrease the resistance of charge transfer and improve photocatalytic performance of BiVO₄ photoanode.The resulted electrode has achieved a significant enhanced photocurrent density of 3.2 m A cm^-2 under illumination at 1.23 V versus reversible hydrogen electrode,mainly contributed by a largely increased charge injection yield of 75.9%(36.7%for the pure BiVO₄film)and a charge separation efficiency of 79.8%(66.8%for the pristine BiVO₄film).This work expands the types of co-catalysts for oxidation evolution reaction and offers an alternative orientation to design efficient photoanodes by introducing co-catalyst for improving PEC water splitting performance.(2)Sulfur doping graphitic carbon nitride(g-C₃N₄)film was successfully prepared on the surface of conductive glass by cubic vapor deposition.The optimal growth temperature and sulfur doping concentration were determined by controlling the experimental conductions.The system analysis shows that S-doped g-C₃N₄ has a narrow band gap(2.67 e V).The doped-S plays a significant role in broadening the light absorption range,improving the light response ability of photoanode,and inhibiting charge recombination.At 1.23 V vs reversible hydrogen electrode,the optimized photoanode achieves a photocurrent density of 70.3?A·cm^-2.This method can be applied to the deposition of S-doped g-C₃N₄ film on other substrate for efficient photocatalyst.