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 Cr 2 O 3 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 Cr 2 O 3 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 Cr 2 O 3 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.