We report herein a new sulfur-functionalized MXene Ti2C (Ti2CS2)-supported osmium-metal single-atom catalyst (SAC) Os1/Ti2CS2 with high low-temperature catalytic activity for CO oxidation. Using periodic density functional theory calculations, the most stable SAC, Os1/Ti2CS2, has been screened from series of group 8–11 transition metal SACs M1/Ti2CS2 (M = Fe, Co, Ni, Cu; Ru, Rh, Pd, Ag; Os, Ir,...