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 (j). During alkaline seawater oxidation (ASO) at high j, 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 SO₄²⁻ 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 SO₄²⁻ 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 j. This work presents a viable strategy for achieving efficient and stable ASO under high j, contributing to the development of large-scale direct seawater electrolysis driven by renewable energy.