Synergistic effects of oxygen vacancy formation and interfacial electronic coupling in Bi2WO6/NiFe-LDH heterostructures toward photoelectrochemical enhancement

Abstract

Bismuth tungstate (Bi2WO6, BWO) nanosheets were synthesized using a hydrothermal method and subsequently etched with sodium hydroxide (NaOH) solutions of varying concentrations to precisely control the formation of oxygen vacancies. As the etching concentration increased, the defect density also rose, with the 0.5 M sample (BWO-E3) showing the optimal level of vacancies. Following this, nickel iron layered double hydroxide (NiFe LDH) was electrodeposited onto the etched samples at different loading ratios (NF1-NF4), resulting in BWO/ NiFe LDH heterostructures. This setup allowed us to investigate the synergistic effects of defect engineering and the coupling with the cocatalyst. The introduction of oxygen vacancies significantly enhanced charge separation efficiency, increased the number of active surface sites, and improved charge transport behavior. Furthermore, the incorporation of LDH established a type-II band alignment and created an interfacial built-in electric field, facilitating directional carrier migration under illumination. Among all prepared samples, the BWO-E3-NF2 photoanode exhibited the highest photocurrent density of 0.054 mA cm-2 . This reflects an approximate 13fold enhancement compared to the pristine BWO, accompanied by a notable reduction in charge-transfer resistance, from 14.2 k Omega to 1.21 k Omega. This illustrates that the combined approach of oxygen vacancy modulation and LDH heterostructure design is a compelling strategy for enhancing BWO-based photoelectrochemical photoanodes.