Optimal sulfur-vacancy engineered Ni3S2 for enhanced alkaline hydrogen evolution via parameter controlled NaBH4 etching

A systematic understanding of how the sulfur vacancy concentration affects the hydrogen adsorption and charge transfer remains incomplete, thus making defect engineering in alkaline hydrogen evolution reaction (HER) difficult. Herein, sulfur vacancies are systematically introduced in Ni 3 S 2 @NF by varying the etching parameters (time, concentration, and temperature) of a mild chemical etching process, which is guided by the theoretical calculation from DFT. The optimized catalyst, Vs-Ni 3 S 2 @NF-30 demonstrates promising HER performance: 45, 75, and 88 mV at 10, 50, and 100 mA cm −2 , respectively, a Tafel slope of 43 mV dec −1 , and notable stability for over 54 h of continuous operation, 30,000 CV cycles and 50 days of air exposure. S-vacancy concentration of ∼12% optimizes Ni electronic structure, enhances water dissociation and hydrogen desorption, with minimal charge transfer resistance; under-etching and over-etching hinder performance. This parameter-controlled DFT etching offers guidelines for designing defects in transition-metal chalcogenides for enhanced HER.