Preparation of NiMnFeOx Electrocatalysts for Oxygen Evolution Reaction Using Galvanic Exchange

In this work, NiMnFe oxide catalyst materials were prepared by electrodeposition for the oxygen evolution reaction (OER) in an alkaline solution. Incorporation of Fe into these catalyst structures was carried out using galvanic replacement of Mn within the electrodeposited NiMn alloy to produce more surface Fe sites, which led to the leaching of Mn from the NiMn alloy, resulting in surface defects. The electrocatalysts were studied by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDX) and X-ray photoelectron spectroscopy (XPS). They were electrochemically characterized for OER by cyclic voltammetry and electrochemical impedance spectroscopy. SEM–EDX demonstrated an increase in Fe content in the catalyst due to the galvanic exchange and the incorporation of Fe from the KOH solution onto the Ni disc. XPS showed that after OER experiments, the surface is highly oxidized, dominated by Fe³⁺ and Ni³⁺ species. During the OER studies in 1 M KOH, the NiMnFe material demonstrated an overpotential of 321 mV at a current density of 10 mA cm⁻² and a Tafel slope of 41 mV dec⁻¹, showing a 15 mV overpotential improvement over the bare Ni disc. The difference of the overpotential grew to 24 mV when moving to an OER current density of 100 mA cm⁻².

Graphical Abstract

Textual Abstract

NiMn was electrodeposited on Ni discs. Employing galvanic exchange of Mn by Fe on electrodeposited NiMn film led to a 42 mV oxygen evolution reaction overpotential decrease at a current density of 100 mA cm⁻². An overpotential of 368 mV was observed for the best-performing material, achieved through the galvanic exchange.