Enhancing the Energy Storage Capabilities of Ti₃C₂T_x MXene Electrodes by Atomic Surface Reduction

MXenes are a large class of 2D materials that consist of few-atoms-thick layers of transition metal carbides, nitrides, or carbonitrides. The surface functionalization of MXenes has immense implications for their physical, chemical, and electronic properties. However, solution-phase surface functionalization often leads to structural degradation of the MXene electrodes. Here, a non-conventional, single-step atomic surface reduction (ASR) technique is adopted for the surface functionalization of MXene (Ti₃C₂T_x) in an atomic layer deposition reactor using trimethyl aluminum as a volatile reducing precursor. The chemical nature of the modified surface is characterized by X-ray photoelectron spectroscopy and nuclear magnetic resonance techniques. The electrochemical properties of the surface-modified MXene are evaluated in acidic and neutral aqueous electrolyte solutions, as well as in conventional Li-ion and Na-ion organic electrolytes. A considerable improvement in electrochemical performance is obtained for the treated electrodes in all the examined electrolyte solutions, expressed in superior rate capability and cycling stability compared to those of the non-treated MXene films. This improved electrochemical performance is attributed to the increased interlayer spacing and modified surface terminations after the ASR process.