Synergistic phase modulation of interstitial Mo and substitutional W single atom in Ni₃S₂ lattice-integrated CoSe heterostructure for industrial water electrolyzers

A rationally engineered non-noble metal catalyst is developed by introducing substitutional tungsten (W, 0.9 wt%) and interstitial molybdenum (Mo, 0.6 wt%) into crystalline nickel sulfide via a synergistic phase-modification strategy. This dual doping induces lattice expansion, structural distortion, and abundant defects in trigonal Ni₃S₂. The modified material is subsequently integrated with cobalt selenide nanowires grown on nickel foam, resulting in the formation of W_s/Mo_i-Ni₃S₂@CoSe/NF. Atomic-level structural changes are confirmed by scanning transmission electron microscopy and X-ray absorption fine structure analyses. The incorporated conductivity and Mo promotes electron delocalization, shifts the d-band center upward, enhances conductivity, and optimizes intermediate adsorption via Mo (dz²), W (dxz), Ni (dx²-y²), and Co (dx²-y²) orbitals, thereby accelerating hydrogen and oxygen evolution reaction kinetics. The catalyst achieves ultralow overpotentials for the hydrogen evolution reaction (15, 106, 216 mV) and oxygen evolution reaction (200, 295, 350 mV) at current densities of 10, 100, and 1000 mA cm⁻², respectively, in 1.0 M KOH. The assembled electrolyzer operates at just 1.48 V to reach 10 mA cm⁻² and stably delivers 1.0 A cm⁻² for over 1000 h with minimal degradation, surpassing benchmark RuO₂ and Pt/C catalysts. Furthermore, alkaline water electrolysis achieves cell voltages of 1.75 V and 1.88 V at 0.5 and 1.0 A cm⁻² in 6.0 M KOH, highlighting its promise for industrial-scale applications.