Effective Corrosion-Resistant Single-Atom Alloy Catalyst on HfO2-Passivated BiVO4 Photoanode for Durable (≈800 h) Solar Water Oxidation

Green hydrogen (H₂) production from solar water splitting necessitates photoelectrodes with superior photoelectrochemical (PEC) activity and durability. However, surface defects and photocorrosion instability—especially at high potentials—limit PEC performance and stability. Herein, the prototypical bismuth vanadate (BiVO₄) photoanode is used to demonstrate a holistic approach to improve photocurrent density and long-term stability. In this approach, high surface-area nanostructuring of BiVO₄ is combined with barium (Ba) doping with semi-crystalline hafnium oxide (HfO₂) surface passivation and single-atom nickel platinum (NiPt) catalysts. The introduction of Ba²⁺ ions into BiVO₄ increases the concentration of conductive V⁴⁺ ions or the ratio of V⁴⁺ ions to oxygen vacancies, avoiding V⁵⁺ dissolution during water oxidation. The semi-crystalline HfO₂, which serves as a passivation layer, prevents BiVO₄ photocorrosion by suppressing harmful chemical reactions when holes are transferred to the electrolyte. The synergistic use of isolated single-atom and Ni-Pt coordination improves charge transfer at the photoanode/electrolyte interface, leading to enhanced PEC kinetics and stability. As a result, a photoelectrode is demonstrated with ≈6.5 mA cm⁻² at 1.23 V versus a reversible hydrogen electrode (RHE) and continuous operation for 800 h with a negligible degradation rate. This work provides a promising approach to improve photoanodes for PEC H₂ production.