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

Abstract

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 °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 °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.