Novel Black BiVO4/TiO2-x Photoanode with Enhanced Photon Absorption and Charge Separation for Efficient and Stable Solar Water Splitting

Recent advances in solar water splitting by using BiVO4 as a photoanode have greatly optimized charge carrier and reaction dynamics, but relatively wide bandgap and poor photostability are still bottlenecks. Here, an excellent photoanode of black BiVO4@amorphous TiO2-x to tackle both problems is reported. Its applied bias photon-to-current efficiency for solar water splitting is up to 2.5%, which is a new record for a single oxide photon absorber. This unique core-shell structure is fabricated by coating amorphous TiO2 on nanoporous BiVO4 with the aid of atomic layer deposition and further hydrogen plasma treatment at room temperature. The black BiVO4 with moderate oxygen vacancies reveals a bandgap reduction of approximate to 0.3 eV and significantly enhances solar utilization, charge transport and separation simultaneously, compared with conventional BiVO4. The amorphous layer of TiO2-x acts as both oxygen-evolution catalyst and protection layer, which suppresses anodic photocorrosion to stabilize black BiVO4. This configuration of black BiVO4@amorphous TiO2-x may provide an effective strategy to prompt solar water splitting toward practical applications.