Direct chemical synthesis of ultrathin holey iron doped cobalt oxide nanosheets on nickel foam for oxygen evolution reaction

Highlights: • Fe-Co₃O₄ H-NSs/NF are obtained by a simple cyanogel−NaBH₄ route. • Co^III-Co^II cyanogel precursor plays a key role for Fe-Co₃O₄ H-NSs/NF formation. • The thickness of Fe-Co₃O₄ H-NSs is only ca. 1.5 nm. • Fe-Co₃O₄ H-NSs/NF with abundant pores own the high surface area and numerous defected atoms. • Fe-Co₃O₄ H-NSs/NF have a very small overpotential for the oxygen evolution reaction in the alkaline media. The oxygen evolution reaction (OER) on the anode is a vital electrocatalytic reaction in the field of energy conversion. Currently, transition metals-based nanomaterials are promising Ir/Ru-alternative OER electrocatalysts in alkaline media. In this work, we report that in-situ direct growth of atomically thick Fe doped Co₃O₄ holey nanosheets on nickel foam (Fe-Co₃O₄ H-NSs/NF) using a simple cyanogel−NaBH₄ route, which effectively avoids the tedious post-etch process of nanosheets using plasma, acid, alkali, and so on. Benefiting from ultrathin thickness (1.5 nm), numerous holes, and synergistic effect between Co and Fe atoms, Fe-Co₃O₄ H-NSs/NF provide a large specific surface area (199.12 m² g⁻¹) and highly active catalytic sites for the OER. Meanwhile, nickel foam substrate with three-dimensionally porous structure and high conductivity accelerates molecules/ions/gases transportation and electron transfer. Consequently, Fe-Co₃O₄ H-NSs/NF with optimal Co/Fe composition show super electrocatalytic performance for the OER, including an overpotential as small as ∼204 mV at 10 mA cm⁻² current density and a small Tafel slope of 38 mV dec⁻¹, which is much better than commercial RuO₂ nanoparticles.