Typical transition metal single-atom catalysts with a metal-pyridine N structure for efficient CO2 electroreduction

It is of great importance to establish a definite relationship between structure and catalytic properties for developing highly efficient single-atom catalysts (SACs); however, this remains a challenge. Herein, three single atoms anchored on a nitrogen-doped carbon matrix (M-N-C, M = Fe, Co, Ni) with a metal-pyridine N structure were prepared and investigated as catalysts for electrochemical CO2 reduction. M-N-C exhibit promising capability for CO2-to-CO conversion with the selectivity order of Ni > Co > Fe and the activity order of Co > Ni > Fe, in contrast to the previously reported performance order of Ni > Fe > Co. Among M-N-C catalysts, Ni-N-C shows superior selectivity (approximately 100% CO Faradaic efficiency from −0.66 V to −0.96 V), whereas Co-N-C exhibits high activity (CO current density = −24.24 mA cm−2 and CO turnover frequency = 7182 h−1 at −0.86 V) and capability of yielding syngas (CO/H2 = 0.5∼2.11). Density functional theory calculations support the experimental selectivity and activity orders. This study presents a new possibility for improving the catalytic performance of SACs by investigating the coordinated environments of metal atoms.