Theoretical Design of Mo ₂ TiC ₂ O ₂ MXene as an Efficient Sulfur Immobilizer and Electrocatalyst for Lithium- and Sodium-Sulfur Batteries

The development of multifunctional host materials capable of simultaneously immobilizing and catalyzing polysulfides is essential for improving lithium–sulfur (Li–S) and sodium–sulfur (Na–S) batteries. In this work, density functional theory calculations were employed to investigate the adsorption behavior, electronic structure, and catalytic activity of S8 and Li(Na)2Sn (n = 1, 2, 4, 6, and 8) species on double-ordered O-terminated Mo2TiC2 MXene. Strong binding energies (−1.26 to −4.28 eV) indicate effective polysulfide immobilization, particularly for short-chain species dominated by chemisorption, whereas long-chain clusters show a greater contribution from van der Waals interactions. Charge density difference maps and Bader analysis reveal significant interfacial charge transfer, confirming strong electronic coupling between polysulfides and the MXene surface. Importantly, projected density of states (PDOS) results demonstrate that intrinsic metallic conductivity is preserved after adsorption. Gibbs free energy profiles reveal favorable discharge pathways, with potential-determining steps of 0.74 eV for Li–S and 1.26 eV for Na–S systems. The moderate decomposition barriers of Li2S (0.91 eV) and Na2S (0.97 eV), and diffusion coefficients indicate kinetically feasible ion migration. These findings establish Mo2TiC2O2 MXene as a promising dual-functional material for advanced metal–sulfur batteries.