Spatially resolved X-ray absorption spectroscopy investigation of individual cation-intercalated multi-layered Ti3C2Tx MXene particles

Abstract

Ti3C2Tx MXene is a two dimensional (2D) material possessing highly active hydrophilic surfaces coupled with high metallic conductivity. Cation intercalation between the Ti3C2Tx nanosheets has a significant role in many applications such as water purification, desalination, and electrochemical energy storage. The pseudocapacitive charging mechanism involving surface redox reactions at the Ti3C2Tx surface enables higher energy densities than electrical double-layer capacitors, and higher power densities than batteries. In this context, the oxidation state of surface Ti atoms involved in redox reactions has a high impact on the capacitance of Ti3C2Tx MXene and this can be impacted by cation intercalation. The electronic structure of multi-layered Ti3C2Tx particles can be investigated by X-ray absorption (XA) spectroscopy, while also benefitting from a high spatial resolution of 30 nm from X-ray photoemission electron microscopy. In this work, the XA spectra from multi-layered intercalated Ti3C2Tx particles of different thicknesses were recorded at the Ti L- and O K-edges. The Ti oxidation state in pristine, Li-, and Mg-intercalated Ti3C2Tx was found to be thickness-dependent, while Na- and K-intercalated Ti3C2Tx particles did not reveal differences upon changing thickness. This work demonstrates thickness-dependent modification of the MXene surface chemistry upon cation intercalation in different individual Ti3C2Tx particles.