Microstructure Engineered BiVO₄ Photoanode For Photoelectrochemical Hydrogen Peroxide Synthesis

Hydrogen（H₂）energy is a cleanest energy source,H₂produced by photocatalytic water splitting is called"Dream of the technology in the 21st century".At present,in order to improve the efficiency of photocatalytic water splitting to produce H₂,hole sacrificial agents are generally used to accelerate the photocatalytic water reduction reaction.However,hole sacrificial agents are often high value-added organics,such as methanol,ethanol,triethanolamine,etc.,which are costly and easily oxidized by holes to generate CO₂that is harmful to the environment.The efficiency of photocatalytic overall water splitting is generally low,and the oxygen produced by water oxidation has no economic value.H₂O₂is an important raw material in inorganic chemical field,and is high value-added product,but it faces big synthesis challenges,such as low product selectivity and easy decomposition from photoelectrocatalytic water splitting.Therefore,this article focuses on the research direction of promoting the generation of water oxidative H₂O₂production.By adjusting the microstructure and surface structure of the bismuth vanadate（BiVO₄）photoanode,the Faraday efficiency and the accumulation of hydrogen peroxide are improved:（1）The grain size of the monoclinic BiVO₄photoanode synthesized by electrodeposition was controlled by pre-heating process,so as to improve the photoelectrochemical performance and the selective H₂O₂generation of BiVO₄photoanode.The experimental results show that the grain size of the pre-heated monoclinic H₂O₂photoanode decreases with the increase of the pre-heated temperatures.The photocurrent density of optimal BiVO₄photoanode prepared at 150℃reaches 3.95 m A/cm²under 1.76 V vs RHE（reversible hydrogen electrode）,compared with the photocurrent density of BiVO₄without preheating treatment increased by 1.56 m A/cm².The highest generation rate of H₂O₂is 0.265μmol/min/cm²at 1.48 V vs RHE.The increased in the photocurrent density and the generation rate of H₂O₂can be ascribed to smaller the grain size of BiVO₄,which more conducive to the separation of electron holes.（2）Based on the synthesis of BiVO₄photoanode,SnO₂passivation layer was loaded on the surface of BiVO₄photoanode by electrodeposition and annealed in different environmental atmosphere to obtain SnO₂passivation layer with oxygen vacancies.The results show that the stability of BiVO₄photoanode are improved significantly after being passivated by SnO₂layer.The photocurrent density of best SnO_2-x/BiVO₄photoanode achieves 5.0 m A/cm²at 1.76 V vs RHE.TS-SPV（Transient surface photovoltage spectrum）results indicate that SnO₂passivation layer can reduce the recombination of photogenerated electron/hole pairs and adjust the reaction kinetics of hole oxidation on the surface of photoanode.The average Faraday efficiency of BiVO₄photoanode loaded with SnO_2-xpassivation layer is about 86%in a wide bias range of 0.6～2.1 V vs RHE.The average H₂O₂generation rate of SnO_2-x/BiVO₄photoanode reaches 0.825μmol/min/cm²at 1.23 V vs RHE.Through further analysis of its mechanism,it is found that the existence of SnO₂passivation layer transforms the complete reaction of H₂O₂and O₂into the H₂O₂and OH radicals（OH·）evolution process,and the decomposition of H₂O₂is inhibited.The research results provide a feasible way to produce high value-added products,H₂and H₂O₂with high-efficiency and high-selectivity,which has important scientific significance and practical value for promoting the development of solar energy conversion and green chemical industry.