The Role of Transition Metal and Nitrogen in Metal-N-C Composites for Hydrogen Evolution Reaction at Universal pHs

For the first time, we demonstrated that transition metal and nitrogen codoped carbon nanocomposites synthesized by pyrolysis and heat treatment showed excellent catalytic activity toward hydrogen evolution reaction (HER) in both acidic and alkaline media. The overpotential at 10 mA cm(-2) was 235 mV in a 0.5 M H2SO4 solution at a catalyst loading of 0.765 mg cm(-2) for Co-N-C. In a 1 M KOH solution, the overpotential was only slightly increased by 35 mV. The high activity and excellent durability (negligible loss after 1000 cycles in both acidic and alkaline media) make this carbon-based catalyst a promising alternative to noble metals for HER. Electrochemical and density functional theory (DFT) calculation results suggested that transition metals and nitrogen played a critical role in activity enhancement. The active sites for HER might be associated with metal/N/C moieties, which have been also proposed as reaction centers for oxygen reduction reaction.