Boosting Electrochemical CO₂ Reduction\nby Controlling Coordination Environment in Atomically Dispersed Ni@N_<i>x</i>C_<i>y</i> Catalysts

Abstract

Atomically dispersed Ni–N–C\nis known as an efficiently\nactive site for the CO₂ reduction reaction (CO₂RR). However, the effect of the coordination environment between\nthe Ni–N and Ni–C sites on catalytic activity has still\nnot been studied systematically. Herein, atomically dispersed Ni-based\ncatalysts with various N/C coordination numbers (named Ni@N_<i>x</i>C_<i>y</i>) were fabricated with\ncost-effective carbon substrates. EXAFS fitting analysis confirmed\nthat the N coordination number decreased from 4 to 1 in Ni@N_<i>x</i>C_<i>y</i> catalysts when the\npyrolysis temperature increased from 800 to 1100 °C, whereas\nthe C coordination number showed an opposite trend. The Ni@N_<i>x</i>C_<i>y</i>-1000 catalyst with\nthe optimum coordination numbers of two N and two C atoms pyrolyzed\nat 1000 °C achieved the highest FEco of 98.7% at a potential\nof −0.7 V vs RHE. The density functional theory (DFT) calculation\nclarified that Ni–N₂C₂ active sites were\nfavorable to generate more unoccupied Ni 3d orbitals to decrease the\nfree energy (to +0.80 eV) of the rate-determining step, so as to dramatically\nincrease CO₂RR catalytic activity.