Rapid Molten-Salt Synthesis of Phase-Controlled Mo-Doped Sulfides for Water Splitting

Transition metal sulfides are promising electrocatalysts for water electrolysis. This work develops an innovative rapid low-temperature molten-salt template approach that enables one-step fabrication of free-standing Mo-doped sulfide nanowire arrays (Mo-Ni₃S₂@Ni₉S₈/NF) on nickel foam (NF) within merely 30 min, substantially reducing synthesis time compared to conventional methods. XRD and Raman analyses show that the doping of Mo makes the original NiS convert into Ni₉S₈ with higher catalytic activity. Electrochemical measurements reveal low overpotentials of 320 mV for the OER (at 100 mA cm^-2) and 248 mV for the HER (at 50 mA cm^-2), with excellent stability over a 50 h operation. When employed as a bifunctional catalyst in an alkaline electrolyzer, the Mo-Ni₃S₂@Ni₉S₈/NF-based system achieves 10 mA cm^-2 at just 1.51 V. Furthermore, DFT calculations reveal that the Mo-Ni₃S₂@Ni₉S₈/NF heterostructure shows enhanced activity due to optimized ΔG_H* and reduced OER overpotential. Besides, comparative analysis reveals that surface reconstruction of pristine NiS@Ni₃S₂/NF solely generates Ni(OH)₂, whereas Mo-doped Mo-Ni₃S₂@Ni₉S₈/NF additionally forms the NiOOH phase with better catalytic performance. This study employs an innovative strategy to achieve the rapid synthesis of high-performance electrocatalysts with significantly reduced reaction time.