As seen from the presence of the Nb2AlC MAX signal in the 93 Nb, Al, and 13 C spectra, not all aluminum had been etched out during the HF treatment, consistent with prior work on other MXenes: V2AlC was observed in V2CTx samples and Ti3AlC2 in Ti3C2Tx samples in their respective C NMR spectra. The 27 Al NMR spectra of the MXene samples (Figure ) also show an AlO6-like aluminum oxide environment, while the Nb2CTx sample also shows a signal consistent with AlF3×nH2O, a common impurity in MXenes and one that can be readily identified with NMR spectroscopy.