Theoretical investigations of transition metal atom-doped MoSi2N4 monolayers as catalysts for electrochemical CO2 reduction reactions

Following the principle of single-atom catalysts (SACs), the fourth-period transition metals (TM) were designed as active sites on a MoSi2N4 monolayer surface with N vacancy, and the catalytic mechanisms of these single atom active sites for the conversion of CO2 to CO were investigated by first-principles calculations. Our results show that the doped TM atoms on the MoSi2N4 surface greatly enhance the CO2 reduction reaction (CO2RR) activity, compared with the pristine MoSi2N4 monolayer. Of all the doped structures analyzed in our work, we found: (1) the Sc, Ti, and Mn doped structures exhibit very low limiting potentials; (2) out of Sc, Ti and Mn doping structures, the Mn@MoSi2N4-Nv structure shows the best catalytic performance with a limiting potential of only –0.16 V and also has an advantage over the hydrogen evolution reaction, which is the competitive reaction of CO2RR. However, the positive binding free energy at 298.15 K of intermediate reactant *COOH on Mn@MoSi2N4-Nv surface indicates its unstable state, which cause troubles for the CO product generation process. This is different from the results derived from adsorption/binding energy at 0 K, which indicates that temperature effect cannot be ignored when considering adsorption/binding energy. Our work provides insights on the temperature effects in the catalytic mechanisms for CO2RR through TM doped MoSi2N4 monolayers.