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 NiIII. In parallel, the preconfigured high NiIII 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.