Highly Stable Single‐Atom Modified MXenes as Cathode‐Active Bifunctional Catalysts in Li–CO₂ Battery

Abstract The exploration of cathode catalysts with low overpotentials for the carbon dioxide reduction reaction (CRR) and carbon dioxide evolution reaction (CER) is essential for Li–CO₂ batteries. MXenes have been suggested as potential candidates owing to their high electrical conductivity and effective CO₂ activation performance. Herein, the stability and bifunctional CRR/CER catalytic activities of bare MXene (M₂C), oxygen‐functionalized MXene (M₂CO₂), and single‐atom (SA) modified M₂CO₂ are systemically investigated. Among bare MXenes, Mo₂C exhibits the best catalytic activity, comparable to that of carbon nanotubes, whereas oxygen‐functionalized MXene has poor activity. Notably, introducing an SA on the surface of oxygen‐functionalized MXene decreases the overpotential by 12.2%–68.1%, which can even outperform graphene catalysts, suggesting their potential as bifunctional cathode catalysts in Li–CO₂ batteries. This high activity is appropriate reactivity in origin, as highlighted by the volcano‐type relationship between the Gibbs free energy and the overpotential for key steps. The descriptor ξ, which is related to adsorption behavior, is effective in determining bifunctional catalytic activity, which depends on the ability of SA electrons to fill antibonding orbitals and SA–oxygen/carbon bonding. This study not only identifies promising MXene‐based bifunctional CRR/CER catalysts but also provides a rational design rule for SA modified catalysts.