Insight into atomically dispersed porous M-N-C single-site catalysts for electrochemical CO2 reduction

Transitional metal single site catalysts have unique activities for electrochemical CO2 reductions. However, the exact active center and reaction mechanism remains unclear due to the high challenge in controllable synthesis of single atom catalysts (SACs) and defects in metal supports. Here we combine both experimental and theoretical calculation to systematically explore the mechanistic reaction path of selected transition metals single sites on nitrogen doped porous carbon. Facile pyrolysis was employed to prepare a fullerene type carbon with 0.35 nm interlayer distances to support family of M-N-C (M= Ni, Fe, Co and Cu). Experimentally, Ni and Fe outperform the other metals with high faradic efficiency up to >97% and 86.8% respectively. The theoretical calculations reveal that Ni-N-C exhibits the optimum activity for CO2 reduction to CO at higher overpotential because of the moderate *CO binding energy at the Ni site, which accommodates the *COOH formation and the*CO desorption. Further the strong binding energy of *CO on Fe site enables the catalyst to reduce CO2 beyond CO. A remarkable current density of 17.6mA cm-2 has been achieved with Ni-N-C catalyst and a record of 5.74 s-1 TOF has been realized at -0.8V vs RHE for Ni-N-C catalyst