NiMo-based alloy and its sulfides for energy-saving hydrogen production via sulfion oxidation assisted alkaline seawater splitting

Establishing an energy-saving and affordable hydrogen production route from infinite seawater presents a promising strategy for achieving carbon neutrality and low-carbon development. Compared with the kinetically sluggish oxygen evolution reaction (OER), the thermodynamically advantageous sulfion oxidation reaction (SOR) enables the S^2- pollutants recovery while reducing the energy input of water electrolysis. Here, a nanoporous NiMo alloy ligament (np-NiMo) with AlNi₃/Al₅Mo heterostructure was prepared for hydrogen evolution reaction (HER, -0.134 V versus reversible hydrogen electrode (vs. RHE) at 50 mA/cm²), which needs an Al₈₉Ni₁₀Mo₁ as a precursor and dealloying operation. Further, the np-NiMo alloy was thermal-treated with S powder to generate Mo-doped NiS₂ (np-NiMo-S) for OER (1.544 V vs. RHE at 50 mA/cm²) and SOR (0.364 V vs. RHE at 50 mA/cm²), while still maintaining the nanostructuring advantages. Moreover, for a two-electrode electrolyzer system with np-NiMo cathode (1 M KOH + seawater) coupling np-NiMo-S anode (1 mol/L KOH + seawater + 1 mol/L Na₂S), a remarkably ultra-low cell potential of 0.532 V is acquired at 50 mA/cm², which is about 1.015 V below that of normal alkaline seawater splitting. The theory calculations confirmed that the AlNi₃/Al₅Mo heterostructure within np-NiMo promotes H₂O dissociation for excellent HER, while the Mo-dopant of np-NiMo-S lowers energy barriers for the rate-determining step from *S₄ to *S₈. This work develops two kinds of NiMo alloy with tremendous prominence for achieving energy-efficient hydrogen production from alkaline seawater and sulfur recycling from sulfion-rich sewage.