We investigated the catalytic mechanism of RuO2 (211) during discharge and charge processes by DFT calculations in order to better guide the cathode catalyst design for Mg-CO2 batteries. Proceeding with the studied substrate, the calculated lattice parameter for the five-layer stochiometric rutile RuO2 (211) was a = 9.684 Å and b = 13.696 Å. The atomic positions of the three bottom layers of the RuO2 slab are fixed, while the positions of the remaining atoms are relaxed to their minimum energy state. To determine the adsorption energy, we used the following formula: Eads = EMg/CO 2 + Esurf -EMg/CO 2 +surf wherein, EMg/CO 2 , Esurf and EMg/CO 2 +surf are the DFT energies of the reactants, the studied RuO2 (211) surface, and the reactant We found that both Mg and CO2 reactants can be bonded spontaneously with the RuO2 substrate with the calculated binding energies of -3.31 eV and -1.10 eV, respectively. Our findings reveal that the most stable adsorption site for Mg adsorption is the hollow site atop the Ru and O atoms, whereas for CO2 adsorption, the favorable site is on the top of the Ru atom (see Figure and). The shortest bond distance between Mg and CO2 adsorbed RuO2 substrate are 2.14 Å and 2.27 Å. After a detailed examination of CO2 adsorbed structure, we found that the O of CO2 (2.27 Å) is closer to the substrate compared to that of C of CO2 (3.35 Å). Strong adsorption of CO2 and subsequent activation is an important step because of CO2's strong thermodynamic stability. We found that after CO2 adsorption on the RuO2 substrate, the bond angle between two C=O bonds is 179 degrees, and the C=O bond distance is 1.168 Å, which are similar to a gaseous CO2 molecule. These observations indicate that the adsorbed CO2 is inactivated and hence the first reaction step of possible studied pathways is the Mg adsorption. A similar kind of behavior is found in Li-CO2 battery electrocatalysts as well. To further investigate the electronic structure of the RuO2 (211) catalyst, we perform projected density of states (DOS) calculations before and after the adsorption of reaction intermediates. The electrical conductivity of the studied RuO2 (211) catalyst is depicted in Figure , which shows that the material has a metallic character with significant electron states around the Fermi level. Notably, the Ru-4d states' contribution to the catalyst's metallic behavior is highlighted by the PDOS analysis (Figure ). In addition, the electrical conductivity is preserved after adsorption, as shown by a comparison of the PDOS before and after intermediate adsorption. Figure shows that after Mg adsorption, the Mg peak is significantly reduced, indicating a robust charge transfer with the substrate. In contrast, for CO2 adsorption, there is no significant change in the DOS near the Fermi level and could separate the peaks of C-2p of CO2, indicating no obvious charge transfer for CO2 intermediate adsorption. Moreover, MgCO3 adsorption is found to exhibit stronger hybridization compared to MgC2O4, expected to enhance adsorption phenomenon, charge transfer and minimize the overpotential for overall battery performance.