Photovoltaic-Assisted Water Oxidation on MoCoOx-Coupled Multi-Element-Doped BiVO4 Photoanode Enabling 6.4% Unbiased Solar-to-Hydrogen Efficiency under Visible Light

Abstract

Herein, a synergistic strategy combining intrinsic multi-element doping and efficient oxygen evolution catalyst (OEC) integration is employed to overcome the fundamental limitations of bismuth vanadate (BiVO4) photoanodes. Multi-element doping with Ti, W, and P significantly enhances the intrinsic photovoltaic effect and electrical conductivity of BiVO4, promoting efficient photocarrier separation and transport, and delivering a high photocurrent density of 4.37 mA cm-2 at 1.23 V vs reversible hydrogen electrode (RHE) with a reduced water-oxidation onset potential of 0.45 VRHE under AM 1.5G (100 mW cm-2) visible-light (400-950 nm) illumination in neutral electrolyte. Further incorporation of a MoCoOx OEC suppresses surface-state-mediated recombination, de-pins the surface Fermi level, enhances interfacial band bending and surface photovoltage, and boosts hole-injection efficiency to over 80% at low applied bias (0.6–1.0 VRHE). As a result, the MoCoOx/TiWP–BiVO4 photoanode exhibits an enhanced intrinsic photovoltage with a high open-circuit voltage, achieving a fill factor of 31.2% and a photocurrent density of 4.75 mA cm-2 at 1.23 VRHE. When integrated with a commercial Si solar cell in a tandem configuration, the system delivers an unassisted solar-to-hydrogen efficiency of 6.4%. This work provides fundamental insights into intrinsic and surface photovoltaic effects, as well as the regulation of electronic structure for efficient unassisted solar energy conversion.