Unraveling the Dynamic Reconstruction of Active Co(IV)‐O Sites on Ultrathin Amorphous Cobalt‐Iron Hydroxide Nanosheets for Efficient Oxygen‐Evolving

Highly-efficient and cost-effective electrocatalysts toward the oxygen evolution reaction (OER) are crucial for advancing sustainable energy technologies. Herein, a novel approach leveraging corrosion engineering is presented to facilitate the in situ growth of amorphous cobalt-iron hydroxides on nickel-iron foam (CoFe(OH)_x-m/NFF) within a NaCl-CoCl₂ aqueous solution. By adjusting the concentration of the solution, the compositions can tailored and morphologies of these hydroxides to optimize the OER electrocatalytic performance. Specifically, the CoFe(OH)_x-500/NFF electrode manifests as distinctive 3D flower-like clusters composed of remarkably thin nanosheets, measuring a mere 1 nm in thickness. By virtue of the amorphous and ultrathin nanosheet structure, the CoFe(OH)_x-500/NFF electrode exhibits superior OER activity, characterized by notably low overpotentials (η₁₀₀, 274 mV) and an exceptionally small Tafel slope of 40.54 mV dec^-1. Moreover, the electrode's performance remains robust, maintaining low overpotentials for 168 h at 100 mA cm^-2. In situ Raman spectroscopy indicates that the hydroxides experience surface structural reconstruction and transform into high-valent CoFeO₂ with active Co(IV)-O sites during the OER. Theoretical calculations underscore the critical role of the NiFe substrate in enhancing the electrode's OER activity by improving electrical conductivity and modifying the adsorption energy of reaction intermediates, thereby reducing the energy barrier for the reaction.