Coupling Facet‐Selective Photodeposition with Oxygen Vacancy‐Mediated Size Control of Pd Cocatalyst Over BiVO ₄ for Solar‐Driven H ₂ O ₂ Production

ABSTRACT In this work, we demonstrate an effective surface modulation strategy via facet‐selective photodeposition coupled with oxygen vacancy‐mediated size control of palladium (Pd) cocatalysts on monoclinic BiVO ₄ for efficient visible‐light‐driven H ₂ O ₂ synthesis. By adjusting the pH during synthesis, a series of monoclinic BiVO ₄ with different degrees of oxygen vacancies is obtained; higher pH induces elevated vacancy levels, whereas only low to moderate pH preserves the decahedral structure with distinguished facets. Upon facet‐selective photodeposition of Pd metal onto the (010) surface, increased oxygen vacancy concentrations enhance the electrostatic interactions with PdCl ₄ ²⁻ precursors, leading to the formation of smaller Pd nanoparticles with higher active‐site density and accelerated surface reaction kinetics. However, the loss of well‐defined facet geometry of the BiVO ₄ prepared under high pH weakens intrinsic spatial charge separation and compromises facet‐selective Pd photodeposition, eventually diminishing photocatalytic activity. Thus, the optimized Pd/BiVO ₄ photocatalyst achieves an excellent H ₂ O ₂ production rate of 2.35 mм/h, with an apparent quantum efficiency (AQE) of 19.2% at 420 nm, representing a significant performance advancement among BiVO ₄ ‐based systems. This study not only sets a new benchmark but also offers valuable insights into the rational integration of defect and facet engineering for designing efficient metal/semiconductor composites for photocatalytic H ₂ O ₂ production.