Iron-Facilitated Transformation of Mesoporous Spinel Nanosheets into Oxyhydroxide Active Species in the Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is critical for many clean energy conversion and storage technologies because it contributes the electrons required for converting renewable electricity into value-added chemicals. Electrocatalysts can promote the sluggish oxygen evolution process involving four-electron transfer. Herein, we prepare mesoporous spinel oxide nanosheets and develop an efficient strategy using Fe substitution to enable mesoporous NiCo₂O₄ nanosheets to generate superior active centers for the OER. Additionally, the iron substitution also promotes the preoxidation of Co/Ni and facilitates the formation of active species. Raman spectroscopy data reveal that the active species of mesoporous NiCo₂O₄ nanosheets for the OER is NiCo₂O₄ itself, and the active species of Fe substitution in NiCo₂O₄ nanosheets are Ni(Co) oxyhydroxides. Therefore, the iron substitution is beneficial to facilitate the transformation of spinel NiCo₂O₄ into active Ni(Co) oxyhydroxides under OER conditions. Owing to the mesoporous nanosheet structure and the formation of oxyhydroxide active species, the optimized mesoporous Fe_0.2Ni_0.8Co₂O₄ nanosheet catalyst exhibits a low overpotential of 270 mV to deliver a current density of 10 mA cm^-2 and a small Tafel slope of 39 mV dec^-1 for the oxygen evolution reaction in alkaline media.