Dual resistance ensures stable intermittent electrolysis of natural seawater

Renewable electricity-driven direct seawater electrolysis (DSE) offers a promising route for sustainable hydrogen production by utilizing abundant seawater resources. However, the intermittent nature of renewable energies leads to cathodic‒anodic potential fluctuations during operation‒shutdown cycles, triggering critical challenges such as calcium/magnesium precipitation, chlorine corrosion, and dynamic redox of active sites. Most current electrocatalysts for DSE suffer from irreversible consumption and deliver deceptive stability under these conditions. Here, we report ultrasmall oxidized Pt nanoparticles (Pt-oxo NPs) with virtually unchanged structural stability to deliver robust hydrogen evolution performance during intermittent DSE. The high-valent Pt species withstand oxidation corrosion during the shutdown period. The Pt-O-Na+ layer not only performs electrostatic repulsion against Ca2+ and Mg2+ ions, protecting the active sites from blockage but also enriches local OH– to limit the interaction between Cl– and Pt sites. Simultaneously, it broadens the operational voltage window to prevent both reduction and oxidation. The oxygen-rich surface forms hydrogen bonds with water, stabilizing the high surface energy and preserving the ultrasmall particle size under cathodic potentials. Our proposed electrocatalyst exhibits over 3100 h of stable operation at 2.5 A cm–2 in an intermittent DSE system with negligible voltage decay and without any dynamic structural changes.