Preparation of carboxylic cellulose nanofibrils via FeCl3-catalyzed maleic acid hydrolysis and application for self-supporting electrode

The cellulose nanofibrils (CNFs)/MXene composite film has been widely studied in the field of energy storage, sensing, etc. The carboxyl group in CNFs can form hydrogen bond interaction with −F, −O and –OH in MXene to preventing the self-stacking of MXene. In addition, for energy storage, carboxyl groups also promote ion transport in the electrolyte, improving electrochemical performance. Therefore, the green preparation for carboxylic CNFs is important. Herein, CNFs with high carboxyl content were prepared by introducing ferric chloride (FeCl 3 ) catalyst to promote the hydrolysis efficiency of bleached softwood kraft pulp (BSKP) by maleic acid (MA). It was found that the optimized CNFs demonstrated a narrow diameter distribution, high yield (90 %), high carboxyl content (0.5 mmol/g), and good thermal stability (T max was about 343 °C). In addition, the obtained CNFs were further combined with MXene by filtration to obtain a composite film, and the composite film was used for self-supporting electrodes. XRD showed increased layer spacing of MXene in composite film, indicating that CNFs effectively inhibited MXene self-stacking. CNFs/MXene film as the self-supporting electrode showed good electrochemical performance (areal capacitance of 2051.4 mF cm −2 at 2 mA cm −2 ) in three-electrode system.