Heterostructured CoP/MoO2 on Mo Foil as High-Efficiency Electrocatalysts for Hydrogen Evolution Reaction in both Acidic and Alkaline Media

Heterostructured CoP nanoarrays/MoO2 films on Mo foil (CoP-MoO2/MF) were synthesized through low-temperature phosphorization process using pre-oxidized MF supported cobalt hydroxide-carbonate nanoneedles as precursor. Such CoP-MoO2/MF heterostructure exhibits the superior HER performance with low overpotentials of 42 mV (alkaline) and 65 mV (acid) to achieve the current density of 10 mA cm-2, robust stability, large exchange current density and high turnover frequency. The experimental characterizations and DFT calculations unveil that the presence of MoO2 possess the inherent ability to adsorb water and cleave H-O bonds, and favoring hydrogen transfer to accelerate Volmer step. The heterointerfacial charge redistribution endows the optimal hydrogen adsorption ability on adjacent P sites to boost the Heyrovsky step, and as a result, the hydrogen adsorption free energy (∆GH*) can be reduced from 0.08 eV on CoP (011) and -0.78 eV on MoO2 (011) to 0.02 eV on the heterointerface of CoP-MoO2, which significantly improves HER activity and accelerates catalytic kinetics. This work highlights the roles of the heterointerface in electrocatalysis, and provides an avenue to design electrocatalysts.