Tuning Phase Composition and Electrocatalytic Activity via Nickel Doping in Magnetron-Sputtered Iron Oxide Coatings

This paper reports a study of Nickel-doped iron oxide coatings deposited on AISI 304 stainless steel via reactive magnetron sputtering using hematite and metallic nickel targets in an Ar/O2 atmosphere (70/30). The Ni target power varies between 25 and 60 W to control Ni incorporation and investigate its effect on phase transformations within the iron oxide matrix. Structural analysis demonstrates that Ni addition strongly influences both the degree of amorphization and the phase composition of the deposited coatings. Electrocatalytic evaluation toward the oxygen evolution reaction (OER) reveals no direct correlation between Ni concentration and catalytic performance. Instead, the results indicate that the phase composition and the interplay between different iron oxide phases play a decisive role in determining electrocatalytic activity. The highest performance is observed for the coating containing a combination of hematite, magnetite, and maghemite phases, which exhibited the lowest overpotential of 349.7 mV at a current density of 10 mA·cm–2.