Cu single atoms on Ti₂CO₂ as a highly efficient oxygen reduction catalyst in a proton exchange membrane fuel cell

Although carbon-based single-atom catalysts (SACs), especially Fe-N-C, have been demonstrated as highly promising electrocatalysts for the oxygen reduction reaction (ORR) in alkaline media, their application remains a great challenge in acidic proton exchange membrane fuel cells (PEMFCs). Here, by performing high throughput first-principles calculations for 3d, 4d and 5d transition-metal single atoms immobilized on two-dimensional (2D) titanium carbide (Ti₂CT and Ti₃C₂T) surfaces as active sites, we rationally design SACs towards a highly efficient ORR and further propose a composition descriptor to provide atomic-level insights into the structure-activity relationship. Significantly, the parameters involved in the present descriptor can be conveniently obtained from the periodic table of elements. More importantly, we found that the Ti₂CO₂-supported non-noble Cu SACs exhibit excellent ORR activity with much lower overpotential (0.25 V) than that of Pt/C (0.4 V), high selectivity for 4e oxygen reduction, excellent stability and acid-resistance and are quite promising ORR catalysts for PEMFCs. The present method can be extended to other 2D transition-metal carbides, i.e., MXenes.