DC Magnetron Sputtering for Synthesizing Bimetallic NiFe Thin Films as Efficient OER-Catalyzing Electrodes

Industrial water electrolysis systems for hydrogen production use noble metal-based RuO₂/IrO₂ to catalyze the oxygen evolution reaction (OER). Replacing noble metal compounds with earth-abundant NiFe compounds requires a scalable synthesis technique with structural and morphological control. In this study, DC magnetron sputtering was systematically investigated as a scalable approach for synthesizing NiFe bimetallic thin-film electrocatalysts as alternatives to noble metal-based materials. NiFe thin films (~200 nm) with varying Fe contents were deposited on SS-316L substrates and characterized using compositional, morphological, structural, and electrochemical techniques. Scanning electron microscopy revealed a columnar morphology, while X-ray diffraction confirmed the formation of a NiFe random solid solution. The Fe ratio was found to strongly influence OER performance, with the Fe₂₄Ni₇₆ composition exhibiting the best activity, requiring an overpotential of 361 mV vs. RHE to achieve 10 mA · cm^-2 and delivering a current density of 363 mA · cm^-2 at 1.7 V vs. RHE. X-ray photoelectron spectroscopy indicated that the enhanced activity of Fe₂₄Ni₇₆ originated from increased oxidation of metallic Ni and a higher density of catalytically active oxide species. These results demonstrate that sputtered NiFe thin films, particularly at optimized compositions, are promising scalable and low-cost OER electrodes for next-generation water electrolysis systems.