Electrocatalytic CO2 Reduction on M,N4-Doped Graphene Quantum Dots. A DFT Study

A density functional theory (DFT) study was performed to investigate the mechanism of electrochemical carbon dioxide reduction reaction (CO2RR) on nitrogen-doped graphene quantum dots containing MN4 active sites (M = Ag, Cu, Fe, Sn, Zn). Three structural motifs representing different configurations of nitrogen atoms surrounding the metal center were evaluated: pyrrolic-type (NPyr), pyridinic-type (NPy), and mixed (NPyr/NPy) coordination environment. The computational results demonstrate that the nitrogen coordination environment plays a crucial role in the catalytic activity. The adsorption of CO2 is highly endergonic on the structures with pyridine-type and mixed nitrogen motifs. In contrast, the pyrrolic-type M(NPyr)4/GQD complexes exhibit high activity for CO2 binding, except for the silver-containing substrate. Among the investigated systems, the copper-doped structure, Cu(NPyr)4/GQD, stands out as the most promising candidate. It facilitates a favorable exergonic pathway for the formation of C2-products via a stable dimeric *(CO)2 intermediate, while efficiently suppressing the competing *CO reduction. The findings provide valuable theoretical insights for designing high-performance single-atom carbon catalysts for selective carbon dioxide conversion.