A critical analysis of the X-ray photoelectron spectra of Ti3C2Tz MXenes

Since their discovery in 2011, MXenes have garnered worldwide interest. Given their 2D structure, surface, or termination, chemistries play a vital role in most applications. X-ray photoelectron spectroscopy (XPS) is one of the most common characterization tools for quantifying surface terminations and overall chemistry. Herein, we critically review the XPS fitting models proposed for Ti 3 C 2 T z MXene in the literature and make the case that they are at best incomplete and at worst contradictory. We propose a new fitting algorithm based on all the data obtained from previously published studies and propose a new method for quantifying the surface terminations in Ti 3 C 2 T z. In our approach, we assign the Ti 2p peak at 455. 1 eV to the C–Ti–O, and the peaks at 456. 0, 457. 0, 457. 9, and 459. 6 eV are assigned to C–Ti–O, C–Ti–O, C–Ti–F, and TiO 2-x F 2x, respectively. The first four represent possible Ti atom terminations; the last is an oxyfluoride. The C 1s peak at 282 eV, ascribed to C atoms surrounded by 6 Ti atoms, is so universal that it can almost be used as a reference.