Dynamic role of dopant and graphene on BiVO4 photoanode for enhanced photoelectrochemical hydrogen production

The development of an efficient and stable electrode remains an attractive challenge for photoelectrochemical (PEC) water splitting to generate cheaper and green hydrogen (H-2). Herein, we have fabricated a novel multicomponent molybdenum (Mo) doped bismuth vanadate/graphene (Mo-doped BiVO4@graphene) photoanode by simple spin coating technique followed by an annealing process. Precise control over Mo and graphene doping concentration (GR3/BVO:Mo-0.5) was attained, enabling excellent photocurrent density (4-fold increase as compared to BVO) with an enhanced rate of H-2 production. This is attributed to the synergistic effect between molybdenum and graphene enhancing charge carrier density and suppressing the recombination rate of photo-generated electrons and holes. Our DFT studies indicate a reduction in the band gap value after doping pure BVO with Mo. In addition, we observed that the potential determining step of the oxygen evolution reaction (OER) is the electrochemical adsorption of hydroxyl radical (H2O(l) + * -> HO* + H-(aq)(+) + e(-)), which is reduced by similar to 0.8 eV after doping with Mo. This study reports on the unique design of a Mo-doped BiVO4@graphene hybrid electrode, which can be used as a superior electrode for green hydrogen generation under sunlight.