MXene-nanocellulose composite development by hydrothermal method for supercapacitor application

Abstract

MXenes, as representative of two-dimensional (2D) materials, stand out unique in many applications. Among MXene family, Tin+1CnTx is the most mentioned and used one, which displayed large surface area and high electrical conductivity, even higher than well-known graphene. Owing to these merits, Tin+1CnTx is an excellent candidate as electrode material for energy storage application, such as supercapacitor. However, Tin+1CnTx easily undergoes re-stacking together with poor flexibility and low mechanical strength, which limit its performance and application. Herein, cellulose nanofibers (CNF) were introduced in order to address these issues, which are expected to prevent the re-stacking and increase the strength and flexibility of composite film. Composites were prepared with MXene and different types of CNF by hydrothermal method, supposedly bringing good dispersion. The as-prepared high-charge CNF/MXene composite exhibited relatively low areal capacitance of 12.6 mF/cm2 at applied current density of 1 mA/cm2 while it maintained capacitance retention of higher than 90% after 1000 cycles, displaying good cycling stability. Besides, composite films with different mass ratios of MXene and CNF (10M:90C, 50M:50C, 70M:30C) were fabricated to investigate the optimal amount of MXene used for self-standing film electrode. It turned out that all the films did not show desirable conductivity. Spectroscopic analyses and comparisons of films, prepared by hydrothermal treatment and sonication, implied that the oxidation of Ti atoms within MXene during hydrothermal process might be the reason for low conductivity, whereas sonication worked better for homogeneous dispersion of MXene and CNF, further leading to uniform conductivity of composite film.