Nitrogen-doped Fe₇S₈ as highly efficient electrocatalysts for the hydrogen evolution reaction

The high unoccupied d band energy of FeS₂ basically results in weak orbital coupling with water molecules, consequently leading to sluggish water dissociation kinetics. Herein, we demonstrate that the N-induced doping effect and phase transition engineering (FeS₂ to N-Fe₇S₈) can downshift the unoccupied d orbitals and strengthen the interfacial orbital coupling to boost the water dissociation kinetics. The fabricated N-Fe₇S₈/carbon cloth (CC) displays superb hydrogen evolution reaction performance with a low overpotential (89 mV at 10 mA cm^-2) and small Tafel slope (105 mV dec^-1) under alkaline conditions. It is revealed that the electronic structure of Fe is modulated by N doping and phase transition. The downshifted d band energy can strengthen water adsorption and reduce the energy barrier of water dissociation. Our work provides a new strategy to modify metal sulfide electrocatalysts for electrochemical energy conversion.