Sulfur-Doped High-Entropy Spinel Oxide (FeCoNiCuCrAlZn)₃O₄ Electrocatalyst for Seawater Electrolysis

Natural seawater electrolysis represents a promising approach to green hydrogen production. However, it faces major challenges such as kinetically sluggish oxygen evolution reaction (OER) and competing chlorine evolution reaction. In this study, a sulfur(S)-doped high entropy spinel ((FeCoNiCuCrAlZn)₃O₄-S) electrocatalyst was synthesized on nickel foam (NF) via a hydrothermal method as the anode for seawater splitting. The obtained (FeCoNiCuCrAlZn)₃O₄-S/NF electrode exhibited a low OER overpotential of 266 mV at 10 mA·cm^-2 and maintained stable operation for over 200 h at a current density of 100 mA·cm^-2. When it was employed in an anion exchange membrane electrolyzer as the anode, a current density of 500 mA·cm^-2 at a voltage of 2.3 V was achieved with a stable operation for over 40 h in 1.0 M KOH natural seawater, showing a great potential for achieving high-efficiency and low-cost seawater splitting. It is considered that the superior OER performance of (FeCoNiCuCrAlZn)₃O₄S is attributed to sulfur-induced electronic structure reconfiguration, which boosts the intrinsic activity of active sites and accelerates reaction kinetics. This provides valuable insights for designing efficient and stable non-noble metal electrocatalysts for seawater splitting.