Chemical bonding of termination species in 2D carbides investigated through valence band UPS/XPS of Ti3C2Tx MXene. (3rd September 2021)

• Record Type: Journal Article
• Authors: Näslund, Lars-Åke; Mikkelä, Mikko-Heikki; Kokkonen, Esko; Magnuson, Martin
• Is Part Of: 2D materials. Volume 8:Number 4(2021)
• Publication Date: 2021-09-03
• Subjects: 2D materials -- energy storage -- MXene -- molecular orbital -- UPS -- resonant PES -- photon energy dependence; Graphene -- Periodicals; Materials science -- Periodicals; Nanostructured materials -- Periodicals; 620.115
• DOI: 10.1088/2053-1583/ac1ea9
• Languages: English
• ISSNs: 2053-1583

Abstract

Abstract: MXenes are technologically interesting 2D materials that show potential in numerous applications. The properties of the MXenes depend at large extent on the selection of elements that build the 2D MX-layer. Another key parameter for tuning the attractive material properties is the species that terminate the surfaces of the MX-layers. Although being an important parameter, experimental studies on the bonding between the MX-layers and the termination species are few and thus an interesting subject of investigation. Here we show that the termination species fluorine (F) bonds to the Ti3 C2 -surface mainly through Ti 3 p —F 2 p hybridization and that oxygen (O) bonds through Ti 3 p —O 2 p hybridization with a significant contribution of Ti 3 d and Ti 4 p . The study further shows that the Ti3 C2 -surface is not only terminated by F and O on the threefold hollow face-centered-cubic site. A significant amount of O sits on a bridge site bonded to two Ti surface atoms on the Ti3 C2 -surface. In addition, the results provide no support for hydroxide (OH) termination on the Ti3 C2 -surface. On the contrary, the comparison of the valence band intensity distribution obtained through ultraviolet- and x-ray photoelectron spectroscopy with computed spectra by density of states, weighed by matrix elements and sensitivity factors, reveals that OH cannot be considered as an inherent termination species in Ti3 C2 T x . The results from this study have implications for correct modeling of the structure of MXenes and the corresponding materials properties. Especially in applications where surface composition and charge are important, such as supercapacitors, Li-ion batteries, electrocatalysis, and fuel- and solar cells, where intercalation processes are essential.