WO3/Ag2S type-II hierarchical heterojunction for improved charge carrier separation and photoelectrochemical water splitting performance

Abstract

In the present work, WO3/Ag2S heterojunction was fabricated to achieve an improved photoelectrochemical (PEC) water splitting performance. To prepare the working electrodes, a two-step method was adopted which includes, a thin film of WO3 deposited using DC sputtering and well-separated Ag2S nanorods fabricated by glancing angle deposition. The PEC response was studied for bare WO3, Ag2S, and WO3/Ag2S heterojunction. The as-prepared WO3/Ag2S heterojunction samples revealed higher absorption as well as a higher photocurrent density of 2.40 mA/cm2 (at 1 V Ag/AgCl) as compared to bare WO3 thin film (0.34 mA/cm2). The enhancement in the photocurrent density of WO3/Ag2S electrodes could be ascribed to the formation of the type-II heterojunction between WO3 and Ag2S which effectively separates and transfers the charge carriers at the interface. In addition, increased trapping of light due to vertically tilted Ag2S nanorods structures results in effective absorption of light. Furthermore, electrochemical impedance spectra measurements showed that WO3/Ag2S samples have lower charge transfer resistance at the semiconductor electrolyte interface with high flat band potential. This work provides a deeper insight into the role of the interface formed between WO3 and Ag2S for the photoelectrochemical water splitting response.