Sulfur vacancy modulated nickel-doped Co4S3 hollow nanocube/nitrogen-doped V2CTx MXene nanosheet composites for optimizing the hydrogen evolution reaction

Abstract

Vacancy engineering and heteroatom doping of transition metal-based electrocatalysts have attracted extensive attention. Herein, in this work, sulfur vacancy modulated nickel-doped Co₄S₃ hollow nanocube/nitrogen-doped V₂CT_x MXene nanosheet (abbreviated as Ni-Co₄S₃ (S_v)/N-V₂CT_x) electrocatalysts are achieved by a sulfuration process along with ultrasonic treatment. Besides, the electrocatalytic activity influenced by sulfur vacancies, hollow configurations, and nickel/nitrogen doping is systematically studied and explored. The sulfur vacancy within Ni-Co₄S₃ (S_v) HNs could boost electron injection from the electrode to the active site by decreasing the contact resistance. The unique hollow porous structure could furnish rich contact regions to boost electrolyte penetration and undertake efficient electron ion transport. The heteroatom doping could effectively settle the stacking problem of MXenes, exposing rich active sites and accelerating electron transfer. Consequently, the obtained Ni-Co₄S₃ (S_v)/N-V₂CT_x acquires an extraordinary hydrogen evolution reaction (HER) activity with an overpotential of 127 mV at a current density of 10 mA cm⁻², which is highly considerable compared to those of the recent transition metal-based catalysts. Overall, the sulfur vacancy, hollow porous structure and nickel/nitrogen doping offer the optimal HER electrocatalytic performance of MXene-based catalysts.