Evaluation of chitosan composites with functionalized carbon nano-onions for supercapacitor applications

The growing need for devices boasting substantial energy and power storage capabilities, like capacitors, is driving extensive research and development efforts toward novel materials endowed with superior electrochemical properties. An example of a promising material in this field is found in carbon nanoonions (CNOs). These carbon-based nanostructures boast remarkable properties such as high conductivity, surface area, and stability. Unfortunately, their low energy density and capacitance act as a hindrance to their potential electrochemical application. To bypass this issue, chemical treatment is often employed as a means to improve the sorption processes and, thus, optimize the charge/discharge dynamics. Herein, three types of materials were prepared using commercially available chitosan (Chit) and unfunctionalized carbon nano-onions (p-CNOs), as well as functionalized CNOs with carboxylic fragments (ox-CNOs) and benzoic groups (benz-CNOs). The capacitance of each material was evaluated through cyclic voltammetry using different electrolytes (1.0 M), obtaining values of 34.1, 23.7, 14.1, 43.0, 59.3, and 36.2 Fg-1 for p-CNOs, benz-CNOs, ox-CNOs, p-CNOs/Chit 2:1, benz-CNOs/Chit 2:1, and ox-CNOs 3:1, respectively in Na2SO4, and for the composite p-CNOs/Chit 2:1 in MgSO4, with a specific capacitance of 43.0 Fg-1. We also used electrochemical impedance spectroscopy (EIS) to study the charge/discharge process at the electrodes, concluding that the fragments of the electron-withdrawing groups in the materials improved their electrochemical properties without compromising other intrinsical properties.