Diminishing the Uncoordinated N Species in Co-N-C Catalysts toward Highly Efficient Electrochemical CO₂ Reduction

Abstract

Atomically dispersed metal and nitrogen codoped carbon (M-N-C) catalysts with N-coordinated metal (MN x ) sites have shown compelling performance in electrochemical CO 2 reduction (ECR). However, extra uncoordinated N species commonly coexist with MN x 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 (FE CO ) 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 FE CO 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 CoN 4 sites can reduce the energy barrier required for the formation of COOH* and suppress the occurrence of hydrogen evolution compared with CoN 4 sites with extra uncoordinated N species, thus resulting in enhanced activity and selectivity in CO production.

Defect chemistry of electrocatalysts for CO2 reduction

“…The authors revealed that the electronegativity offset of the bimetal atoms induced the strong electron interactions, thereby accelerating the *COOH adsorption and decreasing water dissociation kinetics ( Figure 1G ). Wang et al synthesized a Co-N-C catalyst dominated with isolated CoN 4 sites (CoN 4 -CNT) ( Wang et al, 2022 ). When employed in CO 2 RR, CoN 4 -CNT exhibited both excellent selectivity (FE CO = 99.4%) and activity ( j CO = −24.8 mA cm −2 ) at a low overpotential of 0.49 V in H-type cell, and the FE CO remained above 90% with increasing current density from 50 to 600 mA cm −2 in the flow cell.…”

A nanoclay-confined single atom catalyst: tuning uncoordinated N species for efficient water treatment

“…10 N species that are not coordinated with Mn (denoted as uncoordinated N species) remain in the form of pyridine N, pyrrolic N, graphitic N, and N oxides on the graphene basal plane. [10][11][12] Nevertheless, it is unclear whether uncoordinated N species in NG-SACs are related to their spatial coordination configuration; the catalytic properties have been overlooked and only slightly explored to date. 10 NG-SACs are promising peroxymonosulfate (PMS) activators in PMS-based advanced oxidation processes.…”

“…These are generally related to the coordination structure of NG-SACs. [12][13][14][15] Considering these features, we evaluated the role of uncoordinated N species in PMS activation, which is vital for the rational design of NG-SACs in environmental remediation. Developing a tunable and predictable approach for the synthesis of NG-SACs is critical to establishing the correlation between uncoordinated N species and catalytic properties of NG-SACs.…”

“…They can generate versatile reactive intermediates (sulfate radical , superoxide radicals , hydroxyl radicals (˙OH), and singlet oxygen ( 1 O 2 )) for pollutant removal. 12–15 These reactive processes can occur via a nonradical pathway to produce 1 O 2 or via a radical pathway to form ˙OH, , and . These are generally related to the coordination structure of NG-SACs.…”

“…These are generally related to the coordination structure of NG-SACs. 12–15 Considering these features, we evaluated the role of uncoordinated N species in PMS activation, which is vital for the rational design of NG-SACs in environmental remediation.…”