Sonochemical regulation of oxygen vacancies for BiWO nanosheet-based photoanodes to promote photoelectrochemical performance.

Integration of oxygen vacancies (Vo) into nanostructured semiconductor-based photocatalysts has been recognized as a promising strategy for enhancing the performance of photoelectrochemical (PEC) water splitting. However, precisely controlling the Vo concentration in photocatalysts an effective and tunable approach remains challenging. Herein, a series of optimized bismuth tungstate (BiWO) nanosheet-based photoanodes with varying concentrations of Vo were prepared by a sonochemical method with cavitation detection, which enables accurate manipulation of the acoustic cavitation intensity applied to the surface of BiWO photoanodes in alkaline solution. Based on the analysis of the Vo concentration and sound field characteristics, the mechanism of sonochemical regulation of Vo in BiWO nanosheets was interpreted. Specifically, the increase in Vo concentration can be attributed to the enhancement of Bi-O bond dissociation. This enhancement is influenced not only by the intensified impact of shear force and the generation of active radicals by transient cavitation, but also by the accelerated diffusion of the reactant, a result of stable cavitation. By optimizing the transient and stable cavitation intensity, a Vo-rich BiWO photoanode was obtained without altering the microstructure of BiWO nanosheets. The presence of high concentration Vo facilitates the interfacial chemical reactivity and the transmission of photogenerated carriers, leading to the drastic promotion of the PEC water splitting performance. The transient photocurrent density of the Vo-rich BiWO photoanode reaches 69.2 μA cm (1.23 V RHE), 7.86 times that of the untreated BiWO photoanode. Additionally, the charge injection efficiency increases to 35.4%. This work provides a controllable and effective method for defect engineering of nanostructured semiconductor-based electrodes.