Modulating Interband Energy Separation of Boron-Doped Fe7S8/FeS2 Electrocatalysts to Boost Alkaline Hydrogen Evolution Reaction

Cost-effective transition metal sulfides (TMSs) are potential electrocatalysts for alkaline hydrogen evolution reaction (HER). However, free energies of hydrogen intermediates adsorbed on the TMSs (e.g., iron sulfides) are too negative, hindering their hydrogenase-like catalytic activity. With an aim to improve the inherently catalytic activity of the TMSs, design of boron-doped Fe7S8/FeS2 (B-Fe7S8/FeS2) electrocatalysts on the base of the density functional theory (DFT) calculation results is first conducted in this work. Boron atoms doped into the Fe7S8/FeS2 electrocatalysts are found to optimize the electronic structures of d-electrons of Fe atoms and p-electrons of S atoms. The interband energy separation between the d-orbitals of Fe atoms and the p-orbitals of S atoms in the B-Fe7S8/FeS2 electrocatalysts is thus shorter than that of a Fe7S8 or FeS2 electrocatalyst. The optimal B-Fe7S8/FeS2 electrocatalyst induces a boosted charge transfer process and features a low energy barrier of water dissociation and a high desorption efficiency of adsorbed hydrogen intermediates. In alkaline media, this HER electrocatalyst exhibits the overpotential of 113 mV to harvest a current density of 10 mA cm(-2). The proposed heteroatom-doping is a feasible approach to modulate electronic structures of TMS electrocatalysts and further achieve their accelerated HER kinetics.