Electrochemical Reduction of Carbon Dioxide to Methanol on Defective Graphene Supported Cu Based Single-Atom Catalysts: A First Principles Approach

Abstract

Abstract Electrochemical CO2 reduction reaction to clean fuels is recently regarded as one of the most promising routes to meet the global demand for energy and environmental riskiness. In this work, we explored and compared the mechanism of electrochemical reduction of CO2 to methanol by graphene (G)-supported single-atom-copper (Cu) catalysts. The free energies of the CO2 reduction intermediates in electrochemical reaction pathways were calculated by using density functional theory coupled with a computational hydrogen electrode approach. Moreover, the physical and electronic characteristics of the two catalysts were examined via binding energy, atomic distance, bader charge, band structure, and density of states calculations. The computational results show that the three coordinated single-copper atom (Cu-G3) is slightly oxidized, whereas the four coordinated single-copper atom (Cu-G4) is heavily oxidized. In particular, the Cu-G3 is the more suitable catalytic for the conversion of CO2 to CH3OH. Moreover, two various pathways (*HCOO and *COOH) on the two proposed catalysts (Cu-G3 and Cu-G4) are explored based on the initially produced intermediates. The Cu-G3/G4 catalysts robustly promote the HCOO* pathway with an energy barrier of 0.41 eV (*HCOOH → *CHO) and 0.50 eV (*CO2 → *HCOO). However, the rate-limiting step for the *COOH pathway on Cu-G3/G4 catalysts is (*CO → *CHO), with limiting potentials of 1.1 eV and 1.13 eV, respectively. Hence, the reduction of CO2 to methanol on graphene supported single-atom-copper highly prefers to *HCOO pathway. Lastly, we focus on the mechanism of the rate-limiting step (*CO → *CHO). The linear relationship between *CO and *CHO binding energy is broken by the single Cu atom. And the s-p electrons of copper have filled the antibonding orbital of Cu-G4 and weakened the binding with CHO, resulting in a slightly higher energy barrier for the Cu-G4 than Cu-G3. Conclusively, the current study provides a reference for non-noble metal monatomic catalysis of carbon dioxide to methanol with optimal product selectivity.