Anion-Mediated Rapid and Direct Synthesis of FeNiOOH for Robust Water Oxidation

FeNiOOH is regarded as the most stable active species in the oxygen evolution reaction (OER), but the high oxidation energy of NiOOH poses a challenge to directly synthesize FeNiOOH as a real OER catalyst. Herein, an anion-mediated kinetically controlled strategy is proposed, coupled with cation-induced geometric topology modulation, to directly synthesis FeNiOOH with ultra-thin, densely packed nanosheet architectures. Specifically, the Cl⁻-mediated in situ generation of hypochlorous acid promotes the direct formation of NiFeOOH. Concurrently, high-valence competitive Ru³⁺ mitigate electrostatic repulsion, fostering a compact and densely packed assembly of Ru/FeNiOOH nanosheet branches. Furthermore, the intrinsic electron-capturing ability of FeOOH, in synergy with the stabilizing effect of doped Ru atoms, further promote the formation and stabilization high-valence NiOOH. Consequently, the hierarchical Ru/FeNiOOH@NiPO_x nanoarray catalyst displays exceptional OER performance, with an overpotential of 172 mV at 10 mA cm⁻² and outstanding stability. This study provides a novel strategy to directly construct a real catalyst.