Cr-enhanced selective dealloying and sequential electrochemical reconstruction to tailor NiFe-based integrated catalysts for industrial-level water oxidation

In situ reconstruction of multi-element alloys into oxyhydroxides is a promising path to efficient, durable oxygen evolution reaction (OER) electrocatalysts. However, uncontrolled elemental dissolution during reconstruction disrupts target compositions, compromising long-term stability under industrial conditions. Here, we present a controllable multi-step electrochemical etching strategy for precise surface composition and structure regulation. Through sequential Cr-reinforced acid and basic etching under high current densities, we fabricate an integrated NiFe–OOH@Ni/Fe–Cr₂O₃@NiFeCr catalyst (NiFeCr–aee/bee). Acid electrochemical etching drives competitive dealloying and surface oxidation, generating a mixed Ni/Fe-doped Cr₂O₃ and NiFe–OOH nanostructure (Ni/Fe–Cr₂O₃). Subsequent basic electrochemical etching induces surface Cr leaching and enhances surface Ni/Fe hydroxylation, forming more refined NiFe–OOH@Ni/Fe–Cr₂O₃ core–shell nanoparticles with abundant active sites. This process rearranges energy levels, greatly enhancing charge transfer and OER kinetics. NiFeCr–aee/bee requires an overpotential of only 292 mV at 1000 mA cm⁻² and a Tafel slope of 27.3 mV dec⁻¹. After over 1000 h of continuous operation at 500 mA cm⁻², the overpotential decreases by 12 mV, indicating ongoing surface activation. Coupled with a Ni₄Mo/MoO₂/Ni cathode in full-cell electrolysis, only 1.63 V is needed for 500 mA cm⁻² with stability exceeding 1100 h. This work introduces a novel approach for customizing high-performance electrocatalysts by precisely controlling the selective dealloying and self-reconstruction of multi-element alloys through multi-step electrochemical etching.