Tailoring the Electrocatalytic Activity and Corrosion Resistance of CoCrFeNi and MnCrFeNi Thin Films by Anodization

Abstract

Transition metal oxides like Co, Ni, and Mn are promising alternatives to noble metals such as Pt for oxygen electrocatalysis in green energy. Alloying these metals forms multicomponent catalysts with compelling properties. In this study, CoCrFeNi and MnCrFeNi thin films are synthesized using High-Power Impulse Magnetron Sputtering (HiPIMS) and their catalytic activity for the Oxygen Reduction Reaction (ORR), the Oxygen Evolution Reaction (OER), and corrosion resistance in 1 molar (1 M) potassium hydroxide (KOH) are evaluated. MnCrFeNi films exhibit a fine-grained single face-centered cubic (FCC) phase, while CoCrFeNi films have larger grains and multiple phases. ORR on CoCrFeNi follows a 2+1 electron transfer pathway, producing hydroxide radicals, while MnCrFeNi exhibits a 2-electron pathway, yielding hydrogen peroxide. Anodization reduces the CoCrFeNi overpotential from 0.9 to 0.5 V versus the reversible hydrogen electrode (RHE), comparable to platinum and iridium catalysts (Pt/C, Ir/C). Anodization also shifts CoCrFeNi ORR to a 2-electron pathway. In situ Raman spectroscopy detects no ORR intermediates, but nickel oxyhydroxide (NiOOH) appears during OER. Substituting Mn for Co increases corrosion resistance by raising the corrosion potential. All films show passive behavior during polarization, demonstrating their potential for corrosion protection and electrocatalysis in green energy applications.