Controllable synthesis of nickel sulfides integrated with carbon fibers towards enhanced hydrogen evolution reaction...

Nickel sulfides are considered as one of the promising electrocatalysts for the hydrogen evolution reaction (HER). Herein, the monolith NiS _x @CNFs was constructed as a HER working electrode via in situ electrospinning, and the crystal phase of Ni₉S₈ and NiS could be controlled by adjusting the annealing temperature and S source. Specifically, NiS-800@CNFs exhibits excellent activity with the required overpotential of 119 mV at 10 mA cm^-2. This is attributed to the sulfur-deficient Ni₉S₈ crystal that provides sufficient hydrogen adsorption sites, with the coexistence of the NiO phase that is beneficial for water dissociation, which synergically promotes the alkaline HER process. Based on the electrochemical impedance spectroscopy (EIS) characterization, the HER mechanisms of the NiS _x @CNFs series were systematically explored. It is revealed that the sulfur-rich NiS crystal surface is not conducive to the desorption of adsorbed hydrogen to produce hydrogen. This work provides a valuable reference for the regulation of phase structure and the HER mechanism of nickel sulfides.