Understanding the photoelectrochemical properties of a reduced graphene oxide-WO₃ heterojunction photoanode for efficient solar-light-driven overall water splitting

WO₃-reduced graphene oxide (WO₃-RGO) heterojunction electrodes were prepared for photoelectrochemical (PEC) overall water splitting. The WO₃ photoanode incorporated with RGO showed significantly enhanced PEC properties and, hence, photocatalytic water splitting, compared to the bare WO₃ at a bias larger than 0.7 V vs. Ag/AgCl, while a decrease in the PEC properties of WO₃-RGO compared to the WO ₃ electrode was observed at a bias smaller than 0.7 V vs. Ag/AgCl. RGO could play a favorable role in enhancing the electron-hole separation due to the presence of interface states according to the Bardeen model, but it could also provide active sites for the electron-hole recombination. A more positive applied bias is in favor of effective electron-hole separation, by means of quick collection and transport of electrons by RGO. As a result, a higher PEC performance of WO₃-RGO can only be realised at a relatively more positive bias. This study gives insights into the complex nature of a RGO-semiconductor heterojunction, and its implications on the overall photoconversion efficiency.