<p>The development of commercially available water-splitting system is essential to combining green hydrogen production with renewable energy. In this respect, the replacement of noble-metal electrocatalysts to lower the high cost of materials is needed. In this study, we introduce the Co single atom catalysts (SACs) supported on different transition metal-based MXenes (M₂CO₂, M = Cr, Hf, Mo, Nb, Ta, Ti, V, W, and Zr) for the efficient oxygen evolution reaction (OER) under alkaline condition. Using density functional theory (DFT) calculation, we investigated Co/M₂CO₂ electrochemical activity and stability. As a result, the Co/V₂CO₂ catalyst was predicted to possess the best OER activity (U_onset = 0.96&#xa0;V), and most of Co/M₂CO₂ catalysts showed significant electrochemical stability with highly positive dissolution potentials except for Co/Zr₂CO₂, Co/Nb₂CO₂ Co/Hf₂CO₂ and Co/Ta₂CO₂. In addition, we unveiled that charge loss in Co single atom weakens the oxygen adsorption energies, which can improve the OER activity, via Bader charge analysis. In addition, through the density of states analysis near the Fermi energy level, we found that higher DOS(density of states) values near the Fermi energy level correlate with enhanced catalytic activity. Based on the density of states analysis, d-band states of Co single atom were identified to be tunable with various MXene supports utilization. We believe that this study will provide significant insights for the future development of next-generation OER catalysts.</p>