First-principles study on catalytic mechanism of Li<sub>2</sub>O<sub>2</sub> molecule oxidation reaction over defective graphene- supported Sm single-atom catalysts

Lithium-oxygen batteries (LOBs) are renowned for their ultrahigh theoretical energy densities. However, their practical applications are significantly limited by sluggish oxidation kinetics and elevated charge overpotentials. Most single-atom catalysts (SACs) utilized in LOBs are predominantly based on transition metals, which feature unsaturated d-orbital coordination. In contrast, the rare-earth element samarium (Sm) possesses a rich array of 4f-orbital electrons. Recent studies have demonstrated that Sm SACs can effectively enhance the conversion of polysulfides in lithium-sulfur batteries (LSBs) and achieve remarkable cycling stability in full-cell experiments. Inspired by the work, we systematically design and optimize 17 configurations of Sm SACs for LOBs by using first-principles calculations, which are denoted as SmN<i><sub>x</sub></i>C<sub><i>y</i></sub> (<i>x</i> + <i>y</i> = 4 or 6). Through comprehensive screening for stability and catalytic activity, we identify the SmN<sub>3</sub>C<sub>3</sub>-1 catalyst as an optimal candidate for LOBs. The catalytic mechanism of the SmN<sub>3</sub>C<sub>3</sub>-1 SAC over the oxygen evolution reaction of the Li<sub>2</sub>O<sub>2</sub> molecule is investigated. The Gibbs free energy of the two-electron dissociation process indicates that the second step of the reaction is the rate-determining step (RDS). At the equilibrium potential, the charge overpotential is 0.52 V. Furthermore, mechanistic analysis reveals that the d-f-p orbital hybridization in SmN<sub>3</sub>C<sub>3</sub>-1 effectivelyreduces the shielding effect on the Sm 4f orbitals, facilitates interfacial charge transfer, and significantly improves the catalytic performance of the Li<sub>2</sub>O<sub>2</sub> oxidation. This study provides novel insights into the potential of rare-earth-based SACs for improving the performance of LOBs.