Amorphous MoS2 nanosheets on MoO2 films/Mo foil as free-standing electrode for synergetic electrocatalytic hydrogen evolution reaction

A facile oxidation-sulfidation strategy is proposed to fabricate the vertically aligned amorphous MoS2 nanosheets on MoO2 films/Mo foil (MF) as free-standing electrode, which features as the integration of three merits (high conductivity, abundant exposures of active sites, and enhanced mass transfer) into one electrode for hydrogen evolution reaction (HER). Density functional theory (DFT) calculations reveal the strong interaction between MoS2 and MoO2, which can enhance the intrinsic conductivity with narrow bandgap, and decreases hydrogen adsorption free energy (ΔGH∗ = ~0.06 eV) to facilitate the HER process. Benefiting from the unique hierarchical structure with amorphous MoS2 nanosheets on conductive MoO2 films/MF to facilitate the electron/mass transfer by eliminate contact resistance, controllable number of stacking layers and size of MoS2 slabs to expose more edge sites, the optimal MoS2/MoO2/MF exhibits outstanding activity with overpotential of 154 mV at the current density of 10 mA cm−2, Tafel slope of 52.1 mV dec−1, and robust stability. Furthermore, the intrinsic HER activity (vs. ECSA) on MoS2/MoO2/MF is significantly enhanced, which shows 4.5 and 18.6 times higher than those of MoS2/MF and MoO2/MF at overpotential of 200 mV, respectively.