Surface reconstruction and sulfur vacancies engineering in pentlandite for improving hydrogen evolution reaction

Transition metal sulfide pentlandite, (Fe, Ni)(9)S-8, emerges as a prominent catalyst for electrolytic hydrogen evolution reaction (HER) owing to high conductivity and stability. In order to investigate the effect of sulfur (S) vacancy content on the HER activity of (Fe, Ni)(9)S-8 for optimal HER activity, controlled levels of S vacancies need to be generated. Herein, Fe5Ni4S8_x electrocatalysts toward HER were developed through surface reconstruction and S vacancy engineering through a simple heat treatment method. The surface reconstruction could regulate the surface structure to be more stable and lead to a higher number of exposed active sites. S vacancies provided an Fe-Ni synergistic effect to facilitate the hydrogen adsorption, further improving catalytic activity. The optimal Fe5Ni4S8_x electrocatalyst exhibited the overpotential of 107 mV at 10 mA cm(-2) in acidic media. Tafel slope and electrochemical impedance spectroscopy further demonstrate that the proposed thermal treatment to modulate the S vacancy content is a feasible approach to further accelerate the HER kinetics. This study provides valuable insights for the rational formulation of high-efficiency pentlandite electrocatalysts.