To explore the overall electrochemical performance, we investigated the cathode reaction using the four-electron reaction mechanism during the discharging (CO2RR)/charging (CO2ER) process of Mg-CO2 batteries. The performance assessment of the Mg-CO2 battery relies on the calculation of discharge overpotential (ηdis), charge overpotential (ηchg), and total overpotential (ΔEtotal) using the following equations: ηdis = Ueq -Udis, ηchg = Uchg -Ueq, and ΔEtotal = ηdis + ηchg. The equilibrium potential (Ueq) serves as the driving force for spontaneous charging and discharging reactions, with a lower overpotential indicating enhanced battery performance. The discharging potential (Udis) and charging potential (Uchg) are determined as the minimum and maximum electrode potentials, respectively, to ensure that all steps in the optimal pathway exhibit energetically downhill behavior. This approach provides a quantitative measure for evaluating the electrochemical performance on the RuO2 (211) surface. The results are illustrated in Figure and the detailed calculation methodology is given in SI.