Cr-leaching induced in-situ surface reconstruction of trimetallic CoFeCr-hydroxide on Ni foam for highly efficient water oxidation

Rationally regulating the inevitable dynamic evolution of the catalyst surface structure towards high efficiency for water electrolysis remains a significant challenge. Here, the ternary cobalt-iron-chromium double hydroxide (DH) was synthesized on nickel foam as a monolithic catalytic electrode (CoFeCr-DH/NF) for the oxygen evolution reaction (OER) via a simple electrodeposition technique. The optimized Co_0.7Fe_0.3Cr-DH/NF electrode exhibited remarkable catalytic activity and stability. The overpotential at the current density of 100 mA cm⁻² is only 281 mV, far exceeding those of other monolithic catalytic electrodes. Furthermore, we elucidated the variations in the valence states of metals during the OER process and found the electrochemical oxidation of Co²⁺ to Co³⁺ and leaching of Cr. Importantly, Cr-leaching can induce surface reconstruction, which not only optimizes the surface electronic structure to enhance the intrinsic activity but also increases the surface irregularity to enlarge the electrochemically active surface area, thereby significantly improving the OER performance. Theoretical calculations revealed that OER preferentially occurred at the adjacent Cr-leached Co sites and confirmed that the Cr-leached trimetallic CoFeCr-DH performs an outstanding OER performance.