Integrated bulk-interface modulation of bismuth vanadate via gradient molybdenum doping and molybdenum trioxide...

Bismuth vanadate (BVO) photoanodes commonly require separate doping and surface passivation treatments, which limits the synergistic regulation of bulk and interfacial charge-transfer dynamics. Here, a one-step annealing-enabled integrated strategy is proposed to simultaneously achieve gradient Mo doping within the BVO bulk and the in-situ formation of a molybdenum trioxide MoO₃ passivation layer. This unified modulation enables complementary regulation of charge transport in the BVO bulk, the near-surface electronic environment, thereby improving the utilization of photogenerated carriers. Further deposition of a NiCoOOH cocatalyst, the optimized NiCoOOH/MoO₃/Mo:BVO photoanode delivers a photocurrent density of 6.52 mA cm^-2 at 1.23 V vs. RHE, and maintains stable PEC operation for 100 h. When coupled with a Cu(In,Ga)Se₂ photocathode, the photoanode enables bias-free overall water splitting with a matched photocurrent density of 4.05 mA cm^-2 and a solar-to‑hydrogen (STH) efficiency of 4.98%. The tandem device also maintains stable H₂ and O₂ evolution under simulated AM 1.5G illumination. These results demonstrate that spatially coordinated regulation from the BVO bulk to the catalytic interface is effective for overcoming the coupled charge-transport and surface-reaction limitations of BVO and provides a practical strategy for developing efficient and durable solar water-splitting photoelectrodes.