Investigation on the Structure–Performance Correlation of TiC MXenes as Cathode Catalysts for Li-O2 Batteries

Two-dimensional TiC MXenes have high stability and large specific surface area, as well as show great application prospect as cathode catalysts for Li-O2 batteries. There are at least three different structures of TiC MXenes labeled as Ti2C, Ti3C2, and Ti4C3 MXenes. Understanding the effect of structure on the catalytic activity of TiC MXenes is of great significance for the rational design of catalyst. In this study, the adsorption structures of H, O, F, and OH functional groups upon TiC MXenes under single atom and full coverage were first constructed. The results of first-principles calculation show that O has the highest adsorption energy, which means that O-terminated TiC MXenes are typical structures present. The overpotentials were used to assess the catalytic activity quantitatively for Ti2C, Ti3C2, and Ti4C3 with and without O group. The catalytic activity follows such a trend: Ti2C < Ti3C2 < Ti4C3 < Ti4C3O2 < Ti3C2O2 < Ti2CO2. The electronic properties of the Ti 3d orbital near Fermi level for Ti2CO2 MXene lead to its high catalytic activity. These findings provide theoretical guidance for the design of TiC MXenes as cathode catalysts in Li-O2 batteries.