Highly efficient and stable NiFe oxide-based electrocatalysts for oxygen evolution in alkaline and saline solutions

Developing cost-effective and stable oxygen evolution reaction (OER) catalysts is crucial for advancing hydrogen production via water electrolysis. Given the growing scarcity of freshwater resources, seawater electrolysis offers a promising alternative. However, maintaining both high catalytic activity and long-term durability in saline environments remains a significant challenge. In this study, four catalysts, nickel oxide (NiO), two nickel-iron oxides (Ni₀.₈₅Fe₀.₁₅O and Ni₀.₆₅Fe₀.₃₅O), and iron oxide (Fe₂O₃), were synthesized using a simple chemical bath deposition method and systematically characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–visible spectroscopy, and X-ray photoelectron spectroscopy (XPS). Among them, Ni₀.₈₅Fe₀.₁₅O exhibited the best OER performance, achieving a low overpotential of 348 mV at 10 mA cm⁻² and a Tafel slope of 52 mV dec⁻¹ after 24 h of operation in surrogate seawater (1 M KOH + 2.45 wt % NaCl). This superior activity is attributed to its compact nanosheet morphology and the synergistic interaction between Ni²⁺ and Fe³⁺, which induces lattice strain and increases the density of active sites, as confirmed by SEM and XPS. Electrochemical surface area (ECSA) analysis further revealed a high number of accessible and stable active sites under saline conditions, supporting the catalyst's intrinsic activity. Ni₀.₈₅Fe₀.₁₅O demonstrates OER performance and durability comparable to state-of-the-art seawater electrolysis catalysts, underscoring its potential for scalable and sustainable hydrogen production.