Synergistic Co ₃ O ₄ Surface Engineering of BiVO ₄ Photoanodes for Enhanced Photoelectrochemical Water Splitting

The global energy sector faces critical challenges that require the development of clean and sustainable alternatives. Hydrogen has emerged as a promising energy carrier, with photoelectrochemical (PEC) water splitting representing a viable route for solar-driven hydrogen production. However, the performance of PEC systems is largely limited by the efficiency of photoanodes. In this work, bismuth vanadate (BiVO4, BVO) photoanodes were fabricated via RF magnetron sputtering as a scalable approach, followed by the deposition of a Co3O4 cocatalyst through a hydrothermal method to enhance the water-oxidation reaction. PEC measurements revealed significant improvements after Co3O4 modification, including enhanced photocurrent density, a cathodic shift in onset potential, and increased charge separation and injection efficiencies. A maximum photocurrent density of 2.25 mA cm−2 at 1.23 VRHE was achieved, compared to 1.5 mA cm−2 for bare BVO. Mott–Schottky analysis indicates that the incorporation of Co3O4 modifies the interfacial energetics, promoting a cathodic shift and facilitating more efficient charge separation and surface charge injection. This effect is consistent with electrochemical impedance spectroscopy (EIS) results, which show a substantial reduction in charge transfer resistance under illumination, confirming improved interfacial charge transfer kinetics. Consequently, the Co3O4-modified BVO photoanode exhibits enhanced applied bias photoelectric conversion efficiency (ABPE) and incident photon-to-current efficiency (IPCE), reflecting more efficient photon-to-current conversion. This synergistic effect results in a marked improvement in the overall PEC water-splitting performance. These findings provide valuable mechanistic insights into cocatalyst-engineered BVO photoanodes and establish a rational strategy for the design of efficient and durable solar-driven water-splitting systems.