Unveiling the catalytic mechanism of defect graphene supported Sm single-atom catalyst on Li₂O₂ oxygen evolution reaction: First-principles study

Lithium-oxygen batteries (LOBs) are renowned for their ultrahigh theoretical energy density. 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 designed and optimized 17 configurations of Sm SACs for LOBs using first-principles calculations, denoted as SmNxCy (x + y = 4 or 6). Through comprehensive screening for stability and catalytic activity, we identified the SmN₃C₃-1 catalyst as the optimal candidate for LOBs. The catalytic mechanism of the SmN₃C₃-1 SAC on the oxygen evolution reaction of the Li₂O₂ molecule has been 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 SmN₃C₃-1 effectively mitigates the shielding effect on the Sm 4f orbitals, facilitates interfacial charge transfer, and significantly enhances the catalytic performance of the Li₂O₂ oxidation. This study provides novel insights into the potential of rare-earth-based SACs for improving the performance of LOBs.