Boosting Electrochemical CO2 Reduction by Controlling Coordination Environment in Atomically Dispersed Ni@NxCy Catalysts

Atomically dispersed Ni-N-C is known as an efficiently active site for the CO2 reduction reaction (CO2RR). However, the effect of the coordination environment between the Ni-N and Ni-C sites on catalytic activity has still not been studied systematically. Herein, atomically dispersed Ni-based catalysts with various N/C coordination numbers (named Ni@NxCy) were fabricated with cost-effective carbon substrates. EXAFS fitting analysis confirmed that the N coordination number decreased from 4 to 1 in Ni@NxCy, catalysts when the pyrolysis temperature increased from 800 to 1100 degrees C, whereas the C coordination number showed an opposite trend. The Ni@NxCy-1000 catalyst with the optimum coordination numbers of two N and two C atoms pyrolyzed at 1000 degrees C achieved the highest FEco of 98.7% at a potential of -0.7 V vs RHE. The density functional theory (DFT) calculation clarified that Ni-N2C2 active sites were favorable to generate more unoccupied Ni 3d orbitals to decrease the free energy (to +0.80 eV) of the rate-determining step, so as to dramatically increase CO2RR catalytic activity.