Nickel based oxide film formed in molten salts for efficient electrocatalytic oxygen evolution

Abstract

Implementation of non-precious, active and durable catalysts towards the oxygen evolution reaction (OER) is a promising protocol addressing challenges in energy and environmental sustainability. Herein, a binder-free film composed of nickel ferrite is prepared by the anodic oxidation of a nickel alloy in molten salts. Merits of the electrochemical oxidation in molten salts are highlighted by the generation of the spinel NiFe₂O₄ film over the Ni–Fe–Cu substrate with full exposure of OER-active Fe species, absence of OER-inert CuO species and good adhesion with the substrate. The prepared film electrode therefore exhibits higher electrocatalytic activity than the commercial IrO₂/Ta₂O₅–Ti electrode towards the OER in an alkaline electrolyte. The overpotential to drive a current density of 10 mA cm⁻² for the as-prepared electrode is only 326 mV, 27 mV less than that for the IrO₂/Ta₂O₅–Ti electrode. Besides, the prepared nickel ferrite film also exhibits a low Tafel slope of 35.9 mV dec⁻¹, an excellent turnover frequency (TOF) value of 0.85 s⁻¹ at an overpotential of 300 mV and high stability after electrolysis at 50 mA cm⁻² for 60 h in 1.0 M KOH. The present study highlights the potential for utilization of electrochemical oxidation of metallic substrates in molten salts for the fast preparation of high-quality oxide films with promising functionalities.