Single-Step Synthesis of Fe-Doped Ni₃S₂/FeS₂ Nanocomposites for Highly Efficient Oxygen Evolution Reaction

Due to the sluggish kinetic reaction, the electrolytic oxygen evolution reaction (OER) is one of the obstacles in driving overall water splitting for green hydrogen production. In this study, we demonstrate a strategy to improve the OER performance of Ni₃S₂. The effect of addition of different FeCl₂ contents during the hydrothermal process on the OER activity is systematically evaluated. We found that all samples upon the addition of FeCl₂ produced Fe-doped Ni₃S₂ and FeS₂ to form a nanocomposite. Their OER performances strongly depend on the amount of FeCl₂, where the NSF-0.25 catalyst with 0.25 mmol FeCl₂ added during the hydrothermal synthesis shows the best OER performance. Its overpotential was 230 mV versus RHE and it achieves a high current density of 100 mA·cm^-2, which was much lower than that of pristine Ni₃S₂ (320 mV) or RuO₂ (370 mV) as the benchmark OER catalyst. The postcharacterizations reveal that NSF-0.25 has gone through an in situ phase transformation into an Fe-NiOOH phase during the OER test. This study presents a simple method and a low-cost material to improve the OER performance with in situ formation of oxyhydroxide.