Prussian blue analog-derived 2D ultrathin CoFe₂O₄ nanosheets as high-activity electrocatalysts for the oxygen evolution reaction in alkaline and neutral media

Developing highly efficient and stable oxygen evolution reaction (OER) catalysts is of vital importance for large-scale energy storage and conversion technologies. Herein, we report a simple and facile strategy to synthesize 2D ultrathin CoFe₂O₄ nanosheets (NSs) with abundant oxygen vacancies by the reduction of Prussian blue analogs (PBAs) at room temperature using NaBH₄. With large surface area, high density of surface-active sites, high electron transfer capability and durability, CoFe₂O₄ NSs show a low overpotential of 275 mV at 10 mA cm⁻² with a Tafel slope of 42.1 mV dec⁻¹ for the OER in alkaline medium, which is superior to that of the benchmark RuO₂. What's more, CoFe₂O₄ NSs also exhibit a high catalytic activity for the OER with a low onset potential of 1.505 V and a high current density of 4.8 mA cm⁻² at 1.8 V in neutral medium. Both the oxygen vacancies and the synergistic effect between oxygen vacancies and Co³⁺ contribute to the excellent OER activity of CoFe₂O₄ NSs. Our finding opens up a new general route for developing highly efficient electrocatalysts for the OER.