Interface and electronic structure regulation of Mo-doped NiSe2-CoSe2 heterostructure aerogel for efficient overall water splitting

Transition metal selenides (TMSes) with cubic pyrite-type crystal structure have been widely explored as electrocatalysts for oxygen evolution reaction (OER), but the insufficient hydrogen evolution reaction (HER) performance hinders the application of overall water splitting. Herein, we designed and prepared a Mo doped NiSe2-CoSe2 heterostructure aerogel as bifunctional electrocatalyst via facile spontaneous gelation and selenium vapor deposition. The active sites on the heterointerface possessed desirable Gibbs free energy of hydrogen adsorption, leading to better HER performance than single NiSe2 or CoSe2. Moreover, systematically experimental research and density functional theory (DFT) calculations revealed that fine regulated Mo doping improved the electropositivity of heterostructure, promoting the nucleophilic adsorption of water molecule. Benefit from those improvements, the optimal Mo doped NiSe2-CoSe2 aerogel exhibited an extremely low overpotential of 57 mV at the current density of 10 mA·cm-2 for HER with a small Tafel slope value of 38 mV·dec-1. Meanwhile, Mo doping provided higher electron transfer efficiency and better adsorptive property toward reaction intermediate in anodic reaction, resulting in low overpotential of 270 mV at the current density of 100 mA·cm-2 for OER with good electrocatalytic stability. This work provides an anticipated perspective of rational combination of metal doping and heterostructure for advanced electrocatalysts.