In Situ Microenvironment Engineering Enables Synergistic Suppression of Protons and Chloride for Durable Seawater Oxidation

Direct seawater electrolysis powered by coastal/offshore renewable energy offers a sustainable route for hydrogen production, but its industrial application is hindered by local acidification and chloride-induced anodic catalyst deactivation and corrosion under industrial-level current densities (<i>j</i>). During alkaline seawater oxidation (ASO) at high <i>j</i>, rapid generation and accumulation of H⁺ decreases the local pH, which, in conjunction with reactive chlorine species, synergistically suppresses catalytic activity and accelerates electrode corrosion. Herein, we report for the first time a NiS₂/Cr₂S₃/NF catalyst, leveraging the synergistic interaction between in situ SO₄^2- formation at S sites and hydroxide enrichment at Cr sites, enabling stable ASO for over 3000 h at 1 A cm^-2 and over 800 h at 2 A cm^-2. Furthermore, when integrated into the anode of a practical anion exchange membrane water electrolysis device, it demonstrates long-term durability exceeding 600 h at 1 A cm^-2. Mechanistic studies reveal that SO₄^2- generated at sulfur sites electrostatically repels Cl^-, while OH^- accumulation at chromium sites neutralizes H⁺, thus stabilizing a highly negative, alkaline anodic microenvironment. This microenvironment effectively suppresses chlorine evolution and local acidification, leading to robust ASO under high <i>j</i>. This work presents a viable strategy for achieving efficient and stable ASO under high <i>j</i>, contributing to the development of large-scale direct seawater electrolysis driven by renewable energy.