Preconfiguring a high−valent Ni state decouples lattice−oxygen activation from dynamic surface reconstruction for stable water oxidation at 2.0 A cm⁻²

Abstract

High−valent transition−metal (oxy)hydroxides commonly demonstrated high intrinsic activity for the oxygen evolution reaction (OER) via electrochemical self−reconstruction. However, this evolution inevitably compromises structural integrity and long−term durability at industrial current densities (>1 A cm⁻²). Here, we propose a sequential−engineering strategy that separates catalytic−site activation from surface reconstruction through the preconfiguring of a ligand−hole−rich (oxy)hydroxide. Combined structural and electrochemical analyses confirm that Fe³⁺ oxidizes L−cysteine into a moderated sulfur donor, enabling precise S incorporation (avoiding sulfides, e.g., Ni₃S₂), along with Fe−O−Ni inductive polarization, biasing Ni²⁺ toward Niˡˡˡ. In parallel, the preconfigured high Niˡˡˡ strengthens Ni─O covalency, while sulfur incorporation introduces ligand holes to O−2p band, thereby rendering lattice oxygen electrophilic. This pre−establishing framework allows lattice−oxygen to precede oxidation at Ni sites, affecting a kinetic decoupling that underpins durability. Consequently, the S−NiFeOOH delivers overpotentials of 182 mV and 214 mV at 10 mA cm⁻² in alkaline freshwater and seawater, respectively, while sustaining over 4000 hours of continuous operation at 2.0 A cm⁻². In an anion−exchange membrane water electrolyzer, it achieves 1 A cm⁻² at 1.67 V (freshwater) and 1.74 V (seawater) and maintains stable performance beyond 3,500 hours at 1.0 A cm⁻², underscoring its promise for large−scale green hydrogen production.