Preparation And Characterization Of CuBi₂O₄ Photoelectrodes For Photoelectrocatalytic Water Splitting

The spinel-structured CuBi₂O₄ photocathode material has attracted much attention due to its excellent photoelectrochemical properties,but the problems of impure phase structure,slow carrier transport and severe carrier surface complexation have limited the further development of this material.In this paper,Cu Bi₂O₄ photocathode thin films were prepared by spray pyrolysis method,and photocathode materials with pure phase structure were prepared by controlling the evaporation of atomized droplets,and the important factors affecting the photocatalytic performance of pure phase Cu Bi₂O₄ were revealed;photocathode materials with large grain size were prepared by using solvent pre-annealing+two-step annealing,and the effect of grain size on photogenerated carriers was analyzed,and the photochemical The effect of surface carrier migration on photocatalysis was investigated by photoelectrochemical tests;the relationship between applied bias and vacancy concentration was obtained by constructing vacancy defects with applied bias,revealing the mechanism of the effect of vacancy defects and preparing Cu Bi₂O₄ photoelectrode films with high catalytic performance.The above problems were improved by various improvement measures,and the specific findings are as follows:（1）The results of the physical phase characterization show that the impurity phase appears at low evaporation rates,and as the evaporation rate increases,the component structure of the deposited film is rapidly fixed and the time available for establishing the bias gradient is reduced,resulting in a pure-phase semiconductor film,which is a pure-phase structure when the deposition temperature is250°C.The photochemical tests revealed that the pure phase Cu Bi₂O₄ has a low photocurrent density and hole transport is an important factor affecting its photocatalytic performance,while Cu O can be used as a hole transport layer to promote the collection and transfer of holes and reduce the compounding of photogenerated carriers.（2）CuBi₂O₄ thin films with large grain size and improved photogenerated carrier transport efficiency were prepared by solvent preannealing and two-step annealing（STSA）.By optimizing the ethanol vapor concentration,we found that 40%ethanol vapor concentration has the best effect and obtained grain size up to 1μm,which is the largest grain size for producing Cu Bi₂O₄ thin films in recent years.Time-resolved photoluminescence spectroscopy（TRPL）revealed that the treatment of CuBi₂O₄ with STSA improved the carrier lifetime by more than one order of magnitude.This improvement was achieved due to the reduction of carrier complexation caused by lattice defects on the grain boundary surface during grain boundary transport.As a result,the photocurrent density of large grain Cu Bi₂O₄ reaches 0.27 m A/cm²,which is 27 times higher than that of the direct annealing treatment.The photogenerated carriers were found to compound on the electrode surface by chopped I-T curves,so we loaded the Zn O protective layer and Pt co-catalyst onto the Cu Bi₂O₄ surface and further increased the photocurrent density of Cu Bi₂O₄/Zn O/Pt to 0.46 m A/cm²（0.4 V vs.RHE）without the use of electron scavengers.（3）Oxygen vacancies were introduced in the CuBi₂O₄ photocathode film by applying a constant bias voltage.The Cu Bi₂O₄ photocathode with a duration of 600 s at 2.1 V vs.RHE bias was found to have the highest photocurrent density,which reached 0.55 m A/cm² at 0.4 V vs.RHE bias.The significant improvement in photocatalytic performance was attributed to the presence of Schottky or Frenkel-type dot defects in the Cu Bi₂O₄ lattice under the electric field that promoted ion migration,and ion migration causes the creation of oxygen vacancies...