Facile extraction of Mo2Ti2C3Tx MXene via hydrothermal synthesis for electrochemical energy storage

The increasing interest in investigating the distinctive characteristics of two-dimensional (2D) nanomaterials has provided opportunities to achieve desired properties through structural tuning. The emergence of double transition metal carbides and nitrides, referred to as DTM MXenes, has gained significant attention in research owing to their adaptable structure, exceptional physicochemical properties, and adjustable electrochemical attributes for energy storage. However, extracting DTM MXenes from the quaternary MAX phase has remained challenging. In this work, we have reported the first-time successful etching of an out-of-plane ordered Mo2Ti2AlC3 MAX phase using ammonium fluoride (NH4F) and hydrochloric acid (HCl) using hydrothermal method. In particular, the effect of different etching durations (12, 24, 48 and 72 h) on the synthesis of Mo2Ti2C3Tx MXene has been investigated. XRD revealed successful aluminum etching from the Mo2Ti2AlC3, while FESEM provided visual evidence of stacked lamellar morphology. The EDS confirmed a significant reduction in aluminum contents from 8.55 wt% (Mo2Ti2AlC3) to 0.44 % (Mo2Ti2C3Tx), further substantiating the successful formation of Mo2Ti2C3Tx. XPS analysis corroborated the existence of the intended chemical bonds and surface termination on the Mo2Ti2C3Tx. The electrochemical energy storage performance of the synthesized Mo2Ti2C3Tx was evaluated via cyclic voltammetry (CV) and, galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy. The Mo2Ti2C3Tx MXene electrode (synthesized over 48 h) exhibited the highest specific capacitance of 108.5 F/g through CV curves. This study provides a novel approach for synthesizing DTM carbide MXenes using non-typical fluoride etchant. It also provides the initial insights to choose the facile hydrothermal method in which the etching time can influence the electrochemical performance of the Mo2Ti2C3Tx MXene. This study opened new avenues for synthesizing and controlling the surface terminations of DTM MXenes that can lead to improvements in their energy storage ability.