Diminishing the Uncoordinated N Species in Co-N-C Catalysts toward Highly Efficient Electrochemical CO<sub>2</sub> Reduction
Cai Wang, Yuping Liu, Houan Ren, Qingxin Guan, Shulei Chou, Wei Li
Abstract
Atomically dispersed metal and nitrogen codoped carbon (M-N-C) catalysts with N-coordinated metal (MNx) sites have shown compelling performance in electrochemical CO2 reduction (ECR). However, extra uncoordinated N species commonly coexist with MNx sites in M-N-C, which are impossible to ignore due to their inevitable interference in catalytic performance. Considering this, we developed high-performance Co-N-C for ECR by diminishing the uncoordinated N species. The resulting electrocatalyst displays a CO faradic efficiency (FECO) of 99.4% with a CO current density of −24.8 mA·cm–2 at a low overpotential of 0.49 V in an H-type cell, and a high FECO over 90% is obtained in a flow cell within a wide current density window (50–600 mA·cm–2), exceeding all reported Co-N-C catalysts. Density functional theory calculations reveal that isolated CoN4 sites can reduce the energy barrier required for the formation of COOH* and suppress the occurrence of hydrogen evolution compared with CoN4 sites with extra uncoordinated N species, thus resulting in enhanced activity and selectivity in CO production.