To prepare Nb4AlC3, powders of niobium (99.9% metals basis, 325 mesh), aluminum (99.8% purity, 300 mesh), and carbon black (99% purity, 300 mesh) were mixed and the synthesis was performed as previously reported. To prepare Nb4C3Tx, 0.4 g Nb4AlC3 powder was added to 30 mL HF solution (aqueous, 49%, Millipore-Sigma) and stirred at room temperature (20-25 ℃) for 6 days. The produced acidic mixture was washed by DI water followed by centrifugation (3500 rpm, 2 min per cycle). After each centrifugation cycle, the supernatant was discarded and the sediment was dispersed in DI water until neutral pH (~7) was reached. In order to delaminate the Nb4C3Tx, 1 mL of TMAOH (25% in H2O, Millipore-Sigma) was mixed with 9 mL DI H2O, added to Nb4C3Tx, and shaken for 15 minutes at room temperature. The excess TMAOH was separated from the product by repeated centrifugation at 3500 rpm. . These variable-offset cumulative spectra (VOCS) measurements were recorded in steps of 170 kHz (~1000 ppm). Ti spectra were recorded with a CPMG pulse sequence using VOCS acquisition in steps of 80 kHz (~2000 ppm) with 115 echoes of 0.8 ms each and recycle delays of 0.1 s; the subspectra were combined by taking the skyline projection: for each point, the highest intensity value from the overlapping sub-spectra is taken, rather than adding their intensities together.