Interaction and kinetics of H2, CO2, and H2O on Ti3C2Tx MXene probed by X-ray photoelectron spectroscopy

• Intercalated H 2 O diffuses to the Ti 3 C 2 T x -surface during heat treatments. • H 2 O occupies the Ti-Ti bridge-sites as a termination species. • Hydrogen and carbon dioxide adsorb on the Ti on-top sites. • Adsorbates on the Ti on-top sites perturb molecular orbitals. • An O and H 2 O saturated Ti 3 C 2 T x -surface has the ability to split water. One of the most explored MXenes is Ti 3 C 2 T x , where T x is designated to inherently form termination species. Among many applications, Ti 3 C 2 T x is a promising material for energy storage, energy conversion, and CO 2 -capturing devices. However, active sites for adsorption and surface reactions on the Ti 3 C 2 T x -surface are still open questions to explore, which have implications for preparation methods when to obtain correct and optimized surface requirements. Here we use X-ray photoelectron spectroscopy (XPS) to study the adsorption of common gas molecules such as H 2 , CO 2 , and H 2 O, which all may be present in energy storage, energy converting, and CO 2 -capturing devices based on Ti 3 C 2 T x . The study shows that H 2 O, with a strong bonding to the Ti-Ti bridge-sites, can be considered as a termination species. An O and H 2 O terminated Ti 3 C 2 T x -surface restricts the CO 2 adsorption to the Ti on-top sites and may reduce the ability to store positive ions, such as Li + and Na + . On the other hand, an O and H 2 O terminated Ti 3 C 2 T x -surface shows the capability to split water. The results from this study have implications for the correct selection of MXene preparations and the environment around the MXene in different implementations, such as energy storage, CO 2 -capturing, energy conversion, gas sensing, and catalysts.