Constructing an OH⁻-enriched microenvironment on the electrode surface for natural seawater electrolysis

Powered by clean energy, the hydrogen fuel production from seawater electrolysis is a sustainable green hydrogen technology, however, chlorine corrosion and correlative oxidation reactions severely erode the catalysts. Our previous work demonstrates that direct seawater electrolysis without a desalination process and strong alkali addition can be realized by introducing a hard Lewis acid oxide on the catalyst surface to capture OH⁻. However, the criteria for selecting Lewis acid oxides and the origin of OH⁻ enrichment in chlorine chemistry inhibition on the catalyst surface remain unexplored. Here, we compare the ability of a series of Lewis acid oxides with different acidity constants (pKa), including MnO₂, Fe₂O₃, and Cr₂O₃, to enrich OH⁻ on the Co₃O₄ anode catalyst surface. Comprehensive analyses suggest that the lower pKa value of the Lewis acid oxide, the higher concentration of OH⁻ enriched on Co₃O₄ surface, and the lower Cl⁻ concentration. As established correlation among pKa of Lewis acid oxide, OH⁻ enrichment and Cl⁻ repulsion provide direct guidance for future design of highly active, selective and durable catalysts for natural seawater electrolysis.