Ti<inf>3</inf>C<inf>2</inf>T<inf>x</inf> MXene functionalization induced enhancement of photoelectrochemical performance of TiO<inf>2</inf> nanotube arrays

Due to a unique planar structure, hydrophilic functional groups, and excellent metallic conductivity, recently developed two-dimensional (2D) MXene offers great potential in applications such as energy storage, photothermal conversion, gas sensing, etc. Herein, we have fabricated 2D Ti3C2Tx MXene functionalized TiO2 nanotube arrays (TNTs) to achieve enhanced photoelectrochemical (PEC) water splitting. We have observed ∼30% increase in photocurrent density for MXene functionalized TNTs over that of bare TNTs. Impedance spectroscopy analysis suggests a decrease in charge transfer resistance from ∼11.38 kΩ to ∼2.94 kΩ at an optimal amount of MXene functionalization. Analysis of Mott-Schottky measurement shows that donor density increases in MXene functionalized TNT sample. Under light irradiation, Ti3C2Tx MXene shows a localized surface plasmon resonance (LSPR) effect and injects electrons to the conduction band of TNT thereby increasing the photogenerated charge carriers, which in turn, enhances the PEC performance of bare TNTs. The work provides a pathway to design new plasmonic heterostructure materials based on monolayers MXene flakes for overall water splitting application.