Local Alkaline Microenvironment Enables over 800 h Stable Photocatalytic Overall Seawater Splitting

Photocatalytic seawater splitting offers a promising route for cost-effective green hydrogen production, yet its long-term stability is restricted by chloride-related corrosive issues. Here, a surface modification strategy of introducing a Cr2O3 nanolayer is applied to the oxygen-evolution cocatalyst, which enables both high efficiency and long-term stability of seawater splitting. In situ Raman and local pH analyses reveal that the as-introduced Cr2O3 Lewis acid layer enriches interfacial OH– to construct a local alkaline microenvironment, promoting water oxidation while suppressing competitive chlorine oxidation and reactive-site corrosion. Theoretical calculations further identify facilitated water dissociation and surface hydroxylation on Cr2O3 as the origin of the interfacial alkalization. The resulting photocatalyst maintains stable seawater splitting performance over 800 h and high quantum efficiency (>90%) comparable to the record value in pure water, demonstrating a robust approach and offering guidance for designing highly stable photocatalysts for practical seawater splitting applications.