Novel black BiVO₄/TiO_2−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 TiO_2−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 ≈0.3 eV and significantly enhances solar utilization, charge transport and separation simultaneously, compared with conventional BiVO₄. The amorphous layer of TiO_2−x acts as both oxygen-evolution catalyst and protection layer, which suppresses anodic photocorrosion to stabilize black BiVO₄. This configuration of black BiVO₄@amorphous TiO_2−x may provide an effective strategy to prompt solar water splitting toward practical applications.