We use density functional theory (DFT) calculations to investigate the stability and activity of various terminated and non-terminated nitride and carbide MXenes of transition metals. We begin by exploring the MXenes of titanium and scandium such as Ti4N3, Ti4C3, Sc4N3, Sc4C3and their variants with the F, O and OH terminated groups. We observe that the nitrides are more stable than the carbides, and this trend holds also for the terminated compounds. Between the scandium and titanium MXenes, the titanium carbides are more stable than their scandium carbide equivalents; however, this observed trend is reversed for the nitride MXenes, with the scandium nitrides being more stable than titanium nitrides.
The nucleation overpotential for Li-O2 batteries is determined by the adsorption free energy of the intermediate LiO2 . We identify active MXene catalysts by computing the adsorption free energy through DFT calculations and we find that the non-terminated carbides and nitrides are stronger binding than the optimal binding strength. The transition metal and the termination group in the MXene are two tuning variables to weaken the binding in order achieve optimal binding strength. We will report on the activity and coverage effects of various transition metal carbide and nitride MXenes to identify promising cathodes for the Li-O2batteries.
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