Since their discovery in 2011, the 2D transition metal carbide, nitrides, and carbonitridesdubbed MXenes -have garnered a lot of 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. In our approach, we assign the Ti 2p peak at 455.0 eV, to the C-Ti-O\O\O and C-Ti-C octahedra. The peaks at 456.0, 457.0, 457.9, and 459.6 eV are assigned to C-Ti-O\O\F, C-Ti-O\F\F, C-Ti-F\F\F, and TiO 2-x F 2x , respectively. The first four represent possible Ti atom terminations; the last is an oxyfluoride. In our proposed model we do not distinguish between O and OH terminations in the Ti 2p spectra; we only do so in the O spectra. Lastly, we propose and recommend a method for quantifying the surface terminations in Ti 3 C 2 T z .

MXenes are a new, and growing, family of 2D materials with very promising properties for a wide variety of applications. Obtained from the etching of MAX phases, numerous properties can be targeted thanks to the chemical richness of the precursors. Herein, we highlight how etching agents govern surface chemistries of Ti 3 C 2 T x , the most widely studied MXene to date. By combining characterization tools such as X-ray diffraction, X-ray photoelectron, Raman and electron energy loss spectroscopies, scanning and transmission electron microscopies and a surface sensitive electrochemical reactionthe hydrogen evolution reaction, HERwe clearly demonstrate that the etching agent (HF, LiF/HCl or FeF 3 /HCl) strongly modifies the nature of surface terminal groups (F, OH and/or O), oxidation sensitivity, delamination ability, nature of the inserted species, interstratification, concentration of defects and size of flakes. Beyond showing how using these different characterization tools to analyze MXenes, this work highlights that the MXene synthesis routes can influence targeted applications.

The MXenes, among which Ti 3 C 2 T x is the most studied, are a large family of 2D materials with proven potential in a variety of application fields (e.g., energy storage and conversion, water purification, electromagnetic interference shielding, humidity sensor, etc). For most of these applications, MXenes properties depend, at least partly, on their water sorption ability and on the induced structural swelling, which is commonly considered a stepwise process, like in clay-like materials. In the present study, we rather evidence the systematic coexistence of different hydrates in MXene interstratified crystals. Hydration heterogeneity and related structure disorder are described from the quantitative analysis of X-ray diffraction data. This specific methodological approach allows disentangling the complex interstratification and rationalizing the prediction of MXene electrical properties. The widespread use of this approach paves the way for a systematic and thorough determination of MXene structure, including order-disorder, and thus for grasping the influence of structural disorder (hydration heterogeneity) on a large number of MXene physical properties (e. g. optical transparency, capacitance). Deciphering this complex structural disorder is also essential in the design of new MXene-based materials for a variety of applications (supercapacitors, batteries, water treatment…).

Funding bodies included and grant numbers accurate Title of article OK All figures included Equations correct (symbols and sub/superscripts) Corrections should be made directly in the PDF file using the PDF annotation tools. If you have questions about this, please contact the editorial office. The corrected PDF and any accompanying files should be uploaded to the journal's Editorial Manager site.

Herein we topotactically reacted sulphur, S, with Mo 2 CT x MXene powders to synthesize Mo 2 CT x sheets covered by MoS 2 nanosheets and tested the resulting material as a hydrogen evolution reaction, HER, electrocatalyst. As a result, a high electrochemical active surface area catalyst was obtained. It allows driving a current density of 10 mA cm-2 at a low overpotential of only 150 mV. Stabilization of the water activated complex as well as interfacial charge transfer accompanied by changes in the adsorption energy hydrogen are most likely responsible for the high electrochemical activity. Moreover, no efficiency loss was observed under working conditions during 30 h in a 1 mol L-1 KOH electrolyte, confirming the remarkable electrochemical stability of this composite catalyst.

MXenes are a young family of two-dimensional transition metals carbides, nitrides, and carbonitrides with highly controllable structure, composition, and surface chemistry to adjust for target applications. Here, we demonstrate the modifications of two-dimensional MXenes by low-energy ion implantation, leading to the incorporation of Mn ions in Ti3C2Tx thin films.Damages and structural defects caused by the implantation process are characterized at different depths by XPS on Ti2p core-level spectra, ToF-SIMS and with electron energy loss spectroscopy analyses. Results show that the ion-induced alteration of the damage tolerant Ti3C2Tx layer is due to defects formation in both Ti and C sites, thereby promoting the functionalization of these sites with oxygen groups. This work contributes to the inspiring approach of tailoring 2D MXenes structure and properties through doping and defects formation by low-energy ion implantation to expand their practical applications.

No abstract

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.