Design Of Bismuth Vanadate/Amorphous Molybdate Oxide Composite Photoanode And Study On Photoelectric Performance

Extensive use of fossil fuels has caused energy shortages and environmental pollution,which seriously threatens human survival and social development.Using solar photoelectric catalysis（PEC）to split water into hydrogen production technology can convert solar energy into clean and easy-to-storage hydrogen energy,which is considered to be one of the effective ways to solve the above problems.Bismuth vanadate（BiVO₄）has the advantages of suitable band gap（2.4 e V）,theoretical photocurrent up to 7.5m A/cm²,favorable band edge position（the conduction band is close to the hydrogen evolution potential）,cheap and nontoxic.Therefore,BiVO₄ is considered as a photoanode material with practical application potential,which is expected to realize the efficient and low-cost conversion of solar energy to hydrogen energy.However,at present,BiVO₄ still suffers from problems such as easy recombination of photogenerated electron-hole pairs and sluggish kinetics of surface water oxidation,which limit its photoelectric catalytic performance.The surface loading of crystalline cocatalysts can effectively improve the photocatalytic performance of BiVO₄ photoanode,but the harsh preparation conditions are not conducive to the batch preparation of crystalline cocatalysts.Therefore,there is a need to develop an efficient,batch-synthesizable,and low-cost cocatalyst for BiVO₄.Due to the advantages of uniform chemical composition distribution and high active site density,the amorphous materials of transition metals can be used as cocatalysts of photoanode,thereby further improving the catalytic activity of photoanode.In addition,the relatively simple preparation of amorphous catalysts also provides the possibility to prepare cocatalysts in large quantities.In this dissertation,transition metal（nickel,iron,cobalt）-based amorphous molybdate oxides were used as cocatalysts for BiVO₄,and the photoelectric catalytic water splitting performance of the composite electrode was modified by adjusting the types and proportions of transition metals in the cocatalysts.The main research of this paper is as follows:1.Three transition metal-based molybdate oxide cocatalysts（Ni Mo,Fe Mo,Co Mo）were synthesized in batches by supersaturated co-precipitation method.The phase structure characterization results showed that Ni Mo and Fe Mo had amorphous structure,while Co Mo showed crystalline structure.Three cocatalyst-supported BiVO₄ composite photoanodes（BiVO₄/Ni Mo,BiVO₄/Fe Mo and BiVO₄/Co Mo）were prepared by drop coating method.Among them,BiVO₄/Ni Mo has the highest photocurrent（2.95 m A/cm²）under the applied bias voltage of 1.23 V_RHE,which is about 1.7 times higher than that of pure BiVO₄ photoanode.The photoelectrochemical characterization results of the samples showed that the interfacial charge injection efficiency of the BiVO₄ photoanode increased from 25.07%to 45.67%after the amorphous cocatalyst Ni Mo was loaded,which was the main reason for the increase in the photocurrent of the composite electrode.2.Amorphous nickel-iron blended molybdate oxide cocatalyst（a-Ni Fe Mo）was prepared by supersaturated co-precipitation method.BiVO₄/a-Ni Fe Mo composite electrode was obtained by loading a-Ni Fe Mo onto the surface of BiVO₄ photoanode by drop coating.The BiVO₄/a-Ni Fe Mo composite electrode achieves a photocurrent of 3.85m A/cm² and an interfacial charge injection efficiency of 63.7%at 1.23 V_RHE.Due to the amorphous nature of a-Ni Fe Mo,BiVO₄/a-Ni Fe Mo can achieve rapid surface reconstruction in potassium phosphate solution by in-situ CV treatment.After in-situ CV treatment of BiVO₄/a-Ni Fe Mo,its photocurrent at 1.23 V_RHE was further enhanced to5.01 m A/cm².The photoelectrochemical characterization results of the samples showed that the interfacial charge injection efficiency of BiVO₄ photoanode increased from 25.07%of BiVO₄ to 45.67%after loading the amorphous cocatalyst Ni Mo,which was the main reason for the increase of the photocurrent of the composite electrode.3.Amorphous nickel-cobalt-iron blended molybdate oxide cocatalyst（Ni Co Fe Mo）was prepared by supersaturated coprecipitation method.The BiVO₄/Ni Co Fe Mo composite electrode was obtained by loading it onto the surface of BiVO₄ photoanode by drop coating.The presence of appropriate amount of Co in Ni Co Fe Mo can further enhance the photocurrent of BiVO₄.Among them,the BiVO₄/Ni Co Fe Mo composite electrode with optimal Co content achieved a photocurrent of 4.57 m A/cm² at 1.23 V_RHE.After in situ CV treatment,the photocurrent was further improved to 5.47 m A/cm².The photoelectrochemical composite characterization results of the samples after CV treatment showed that the high interfacial charge injection efficiency（85.76%）of the composite electrode was the main reason for its high photocurrent.In addition,due to the presence of Co,the composite electrode exhibits a low onset potential of 0.28 V_RHE after CV treatment,which is negatively shifted by 180 m V and 300 m V compared to BiVO₄/a-Ni Fe Mo and BiVO₄,respectively.Therefore,the composite electrode can achieve an ABPE efficiency of 1.78%at 0.65 V_RHE.