Efficient promotion of charge separation with reduced graphene oxide (rGO) in BiVO4/rGO photoanode for greatly enhanced photoelectrochemical water splitting

Although BiVO4 (BVO) continues to attract strong attention as an ideal reactive semiconductor, its photoelectrochemical (PEC) water splitting performance remains low because most of the charge carriers are easily recombined in the bulk or on the surface of the photoanode before reaching the fluorine-doped tin dioxide (FTO). This study presents a facile and simple, visible-light-assisted, photocatalytic reduction of graphene oxide (GO) by using BVO for the preparation of highly stable BVO/reduced GO (rGO) nanocomposites with two different rGO weight ratios (5% and 10%). These as-prepared BVO/rGO nanocomposites were then drop-cast on an FTO substrate to demonstrate the key role played by the rGO in greatly improving the electron transport in the BVO/rGO films. In PEC water splitting experiments, the BVO/rGO-10% photoelectrode showed the highest photocurrent density (554.4 µA cm−2 at 1.2 V vs. Ag/AgCl), compared to BVO (111.7 µA cm−2) and BVO/rGO-5% (377.9 µA cm−2). The stable BVO/rGO also showed the highest charge carrier density, with an extended lifetime and improved the electrical conductivity, as compared to BVO. These results contributed to the excellent PEC performance of the BVO/rGO photoanode. Under simulated solar light illumination, the open-circuit potential (OCP) of the BVO/rGO films was shifted to a more negative value due to the enhanced electron-hole separation in the films. The photocurrent yields of the BVO and BVO/rGO electrodes were dependent on the solution pH. The photocurrent densities were higher over the full range of measured potential (0 to + 1.2 V vs. Ag/AgCl) in the NaOH electrolyte (1 M, pH = 13.5) than in the Na2SO4 electrolyte (0.1 M, pH = 6.5). This work demonstrates the essential role of the rGO coverage in the great enhancement of electron transport through the rGO in the BVO/rGO film.