Rational Design of Cobalt–Iron Selenides for Highly Efficient Electrochemical Water Oxidation

Exploring active, stable, earth-abundant, low-cost, and high-efficiency electrocatalysts is highly desired for large-scale industrial applications toward the low-carbon economy. In this study, we apply a versatile selenizing technology to synthesize Se-enriched Co_1–<i>x</i>Fe_<i>x</i>Se₂ catalysts on nickel foams for oxygen evolution reactions (OERs) and disclose the relationship between the electronic structures of Co_1–<i>x</i>Fe_<i>x</i>Se₂ (via regulating the atom ratio of Co/Fe) and their OER performance. Owing to the fact that the electron configuration of the Co_1–<i>x</i>Fe_<i>x</i>Se₂ compounds can be tuned by the incorporated Fe species (electron transfer and lattice distortion), the catalytic activity can be adjusted according to the Co/Fe ratios in the catalyst. Moreover, the morphology of Co_1–<i>x</i>Fe_<i>x</i>Se₂ is also verified to strongly depend on the Co/Fe ratios, and the thinner Co_0.4Fe_0.6Se₂ nanosheets are obtained upon selenization treatment, in which it allows more active sites to be exposed to the electrolyte, in turn promoting the OER performance. The Co_0.4Fe_0.6Se₂ nanosheets not only exhibit superior OER performance with a low overpotential of 217 mV at 10 mA cm^–2 and a small Tafel slope of 41 mV dec^–1 but also possess ultrahigh durability with a dinky degeneration of 4.4% even after 72 h fierce water oxidation test in alkaline solution, which outperforms the commercial RuO₂ catalyst. As expected, the Co_0.4Fe_0.6Se₂ nanosheets have shown great prospects for practical applications toward water oxidation