Electrocatalytic nitrogen reduction to ammonia at low overpotentials based on tungsten carbide doped by non-precious metal single cobalt atoms

The high overpotentials are substantial obstacles for electrocatalytic nitrogen reduction reaction (NRR). The development of non-precious metal electrocatalysts with low overpotentials and high Faradaic efficiencies is crucial for NRR. In this study, we synthesized a series of cobalt-doped WC electrocatalysts by incorporating Co single-atoms into WC lattices. The NRR performance was evaluated using linear sweep voltammetry, cyclic voltammetry, electrochemical impedance spectroscopy,and chronoamperometry in a 0.10 mol/L H2SO4 electrolyte.The results demonstrated that the potential onset for NRR on Co0.05W0.95C was −0.05 V vs RHE, and the ammonia yield of Co0.05W0.95C electrocatalyst reached 32.49 ± 0.06 µg·h−1·cm−2 with a Faradaic efficiency of 27.17 ± 0.5 % at a low overpotential of 192 mV under ambient conditions while the performance of the pure cobalt metal is very poor reported by the previous report for NRR. Furthermore,the addition of SCN- ions in the 0.10 mol/L H2SO4 electrolyte reduced the current for NRR.This observation suggests that the Co atoms doped in WC lattices serve as active sites for N2 reduction. Theory calculations further verified that N2 molecules were adsorbed on cobalt atoms in Co-doped WC lattices by N2-bridge bonds, called enzymatic mechanism, nitrogen molecules were reduced to ammonia following the enzymatic mechanism, which resulted in an extremely low overpotential for NRR.