Thermally stabilized NiFeS nanowire electrodes for long-term alkaline oxygen evolution

The development of durable and highly active electrocatalysts is essential for advancing cost-effective hydrogen production through alkaline water electrolysis. In this work, we report template-assisted electrodeposition of composition-optimized NiFeS nanowires, followed by a low-temperature thermal treatment designed to stabilize sulphur species and improve durability. The resulting ternary alloy, containing 17 at% sulphur and 7 at% iron, exhibited remarkable oxygen evolution activity, which may be related to its partially amorphous nature and the sulphur-induced increase in active site density. However, medium- and long-term stability tests revealed progressive sulphur leaching and a consequent loss of the catalytic performance in the untreated samples. To mitigate this effect, post-deposition thermal treatment was introduced. After thermal treatment, the NiFeS nanowires required an overpotential of 206 mV at a current density of 10 mA cm⁻² and exhibited fast reaction kinetics with a Tafel slope of 30 mV dec⁻¹ in 30 wt% KOH. Long-term electrolysis experiments showed only a 30 mV increase in operating potential after 125 h of continuous operation at ambient temperature, indicating improved durability. Structural and compositional characterization confirmed that heat treatment effectively suppresses sulphur loss while preserving electrode integrity. Overall, these results demonstrate that thermally treated NiFeS nanostructured electrodes are highly promising oxygen evolution catalysts for alkaline electrolysis, offering a practical route to combine excellent catalytic performance with prolonged operational stability.