Mo-doped BiVO₄ photoanodes with TiO₂ passivation and Co-Pi co-catalyst show enhanced performance under acidic conditions. Mo doping improves conductivity; TiO₂ prevents corrosion with stable photocurrent (≈0.3mAcm⁻²); Co-Pi enhances OER kinetics, achieving 1.9mAcm⁻² at 1.23V_RHE with improved durability, making this system promising for efficient solar-driven water oxidation.

In the quest for efficient photoelectrolysis devices for solar-driven water splitting, designing a high-performance photoanode compatible with the electrolyte buffer of the photocathode for tandem photoelectrochemical (PEC) cells remains a challenge. One promising solution is the development of an efficient and durable photoanode under acidic conditions. Despite the potential benefits, the limiting factors affecting performance under such conditions are not well understood yet. Two main strategies to enhance photocurrent density and durability are generally considered: applying a surface co-catalyst, or passivating using ultrathin titanium oxide layers as a barrier. In this study, we present a scalable alternative method that combines sol–gel chemistry and dip-coating, to create thinner TiO₂ layers on Mo doped-BiVO₄ photoanodes for surface passivation. We developed Mo-doped-BiVO₄/Co-Pi photoanodes with cobalt-phosphate (Co-Pi) as co-catalyst, which resulted in a major breakthrough by achieving a photocurrent density of 1.9 mA cm⁻² at 1.23V_RHE (pH 6) under standardized illumination conditions, along with a significant improvement in photoanode durability. Additionally, our investigation explores the evolution of the photoanode chemistry within the material after doping, and at the surface after Co-Pi deposition at different stages of the PEC process.