Effect of Fe/Ni ratio on electrodeposition of Ni-Fe alloys and their bifunctional catalytic performance in hydrogen and oxygen evolution reactions

Improving electrocatalysts for water splitting is crucial for advancing clean energy technologies. Nickel (Ni) and nickel–iron (Ni-Fe) alloys are among the most promising materials for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this study, Ni-Fe alloys were synthesized by electrodeposition using a fixed Ni 2+ concentration (0.4 M) and varying Fe 2+ concentrations (0.01–0.1 M). The effects of iron content on surface morphology, wettability, and catalytic performance were examined. The alloy made with 0.1 M Fe 2+ showed the best OER performance, with the lowest overpotential (350 mV) and Tafel slope (105 mV dec −1 ). However, it also had the highest HER overpotential (−318 mV) and Tafel slope (176 mV dec −1 ). In contrast, the sample with 0.01 M Fe 2+ had better HER activity, with an overpotential of −220 mV, but a much higher OER overpotential (550 mV). The 0.1 M Fe 2+ alloy lowered OER overpotential by 36 % compared to the 0.01 M sample, while HER overpotential increased by 30 %. Gas bubble size decreased with more iron during OER, but increased during HER. All films remained hydrophilic, with contact angles increasing with iron content. Characterization (SEM, XRD, XRF, EDX) confirmed structural and compositional differences. • Ni-Fe alloys were electrodeposited with varying Fe/Ni ratios. • High Fe content improved OER activity; low Fe favored HER efficiency. • Bubble size reduced with optimal alloy composition for HER and OER. • High Fe alloy content shows 350 mV lower OER overpotential than low Fe alloy 550 mV. • High Fe alloy content shows HER overpotential of −318 mV vs. −220 mV for low Fe.