In Situ Synthesis of Co₃O₄/CoFe₂O₄ Derived from a Metal–Organic Framework on Nickel Foam: High-Performance Electrocatalyst for Water Oxidation

Co3O4/CoFe2O4 decorated on nickel foam (NF/Co3O4/CoFe2O4) was synthesized from a metal–organic framework by a solvothermal approach using nicotinic acid as an organic linker followed by annealing at 500 °C. The electrochemical activity of NF/Co3O4/CoFe2O4 for the oxygen evolution reaction (OER) was assessed in alkaline medium. Under basic conditions (pH > 10), the composite electrode revealed enhanced electrocatalytic OER activity requiring an overpotential of 215 mV versus RHE to reach 10 mA cm–2 with a Tafel slope of 90 mV dec–1. The enhanced OER activity was ascribed to the presence of Co3+ and Fe3+ in the octahedral sites of Co3O4 and CoFe2O4, respectively, and their synergic effect in Co3O4/CoFe2O4. This anode showed a stable current density of about 160 mA cm–2 for 20 h; the same Co3O4/CoFe2O4/NF anode was applied for several OER experiments without loss of activity.