Probing into the effect of heterojunctions between Cu/Mo2C/Mo2N on HER performance

Hydrogen is one of the cleanest forms of energy which can solve several issues, including environmental pollution and depletion of fossils fuels. Hydrogen evolution reaction (HER), being a carbon-neutral process can reduce the carbon footprint in the earth’s atmosphere. Molybdenum based solids are among the most popular electrocatalysts, which have been explored extensively for HER processes as an alternative to Platinum. Herein, we report a nanostructured electrocatalyst (CuMoCat) consist of molybdenum carbide, molybdenum nitride, and elemental copper, forming a heterojunction within the composite. Copper doping in molybdenum carbide/nitride composite not only facilitates the lowering of the overpotential but also improves the catalyst to perform at high current density. CuMoCat exhibits an overpotential of 82 mV for attaining a current density of 10 mA cm^-2 with a Tafel slope value of 33 mV/dec and shows excellent stability of 3000 cycles in acidic media. The theoretical study reveals that Cu doping brings a change in the electronic properties of the catalyst, which improves the overall adsorption and desorption of hydrogen on the catalyst surface during the hydrogen evolution reaction. The Free Energy diagram for ‘Mo’ and ‘N’ hydrogen adsorptions sites of CuMoCat displays, a shift of free energy making these more favourable for HER with respect to Mo/N sites of the un-doped catalyst.