Boosting the Electrocatalytic HER Performance of Co9S8@Mo2C@Co3O4 Heterostructure: Experimental and DFT Insights

Abstract MXenes are known for their remarkable properties, such as high conductivity, hydrophilic surfaces, high densities of active sites, mechanical properties, easy mass transport, unique tunable electronic properties, etc., which have established them as a rising star in the field of 2D materials. In the present study, a Co9S8@Mo2C@Co3O4 heterostructure was synthesized, and its electrocatalytic activity toward the hydrogen evolution reaction (HER) was evaluated. The Co9S8@Mo2C@Co3O4 electrocatalysts exhibited a low overpotential of 103 mV at 10 mA cm−2 and a Tafel slope of 79 mV dec−1, indicating faster HER kinetics in 0.5 M H2SO4. Furthermore, its stability was tested by performing 5000 LSV cycles and chronoamperometry for 24 h, where no significant deviation in its performance was noted. Moreover, this study was also corroborated by performing multistep chronopotentiometry, which proved the long-term operational stability of the electrode under repeated current cycling. The experimental evidence was substantiated by computational studies, which showed that the Co9S8@Mo2C@Co3O4 heterostructure exhibited a closer to optimal hydrogen adsorption free energy (ΔGH*) of −0.18 eV, indicating weaker H* binding that promotes rapid H2 evolution. The superior HER activity is ascribed to an upshifted d-band center (−0.46 eV) and strong interfacial charge transfer from Mo2C to Co9S8 and consequently to electron-enriched Co3O4 in Co9S8@Mo2C@Co3O4 heterostructure. This superior HER performance of the synthesized Co9S8@Mo2C@Co3O4 heterostructure was convincingly established through a synergistic combination of experimental and theoretical insights.