Aerophobic/Hydrophilic Nickel–Iron Sulfide Nanoarrays for Energy-Saving Hydrogen Production from Seawater Splitting Assisted by Sulfion Oxidation Reaction

Electrolysis of infinite seawater is a promising and sustainable approach for clean hydrogen production. However, it remains a big challenge to accomplish corrosion-resistant and chlorine-free seawater electrolysis at low power input. Herein, the bimetallic nickel-iron sulfide-based electrocatalytic nanoarrays are constructed by a facile hydrothermal sulfidation of redox-etched iron foam (IF), which manifests an effective and reliable strategy for the sulfion oxidation reaction (SOR) to assist alkaline seawater electrolysis for the achievement of energy-saving hydrogen production and value-added sulfion upcycling. The resulting NiFeS_<i>x</i>/FeNi₃/IF required 0.353 and 0.415 V vs RHE for SOR at current densities of 50 and 100 mA cm^-2, which are considerably lower than the theoretical potential of the oxygen evolution reaction (OER, 1.23 V vs RHE). <i>In situ</i> spectroscopy analysis demonstrated efficient sulfion oxidation on the surface of NiFeS_<i>x</i>/FeNi₃/IF. Furthermore, the NiFeS_<i>x</i>/FeNi₃/IF-assembled electrolyzer delivered a greatly reduced cell voltage of 0.92 V at 50 mA cm^-2 and maintains excellent durability for 30 h, achieving high Faradaic efficiency for both hydrogen production and sulfion degradation. In addition, under natural sunlight (660.4 W m^-2), only a 0.947 V voltage of the solar panel smoothly powers the SOR-coupled seawater electrolysis for green hydrogen production and economic sulfur recovery.