Nanocellulose paper electrodes: Flexible, free-standing platforms for wearable electronic devices

Flexible supercapacitors are promising energy storage devices for wearable electronics; however, their practical application is limited by the low energy storage capacity of electrode materials. Nanocellulose, a naturally abundant and biodegradable material with high mechanical strength and low weight, offers potential as a sustainable platform for electrode design. In this study, flexible, free-standing electrode films were fabricated by vacuum filtration of cellulose nanofibers (CNF), carbon nanotubes (CNT), and cobalt oxide (Co₃O₄) at varying mass ratios. The composite films were characterized by Fourier transform infrared spectroscopy (FTIR) and electrochemically evaluated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). Among the tested compositions, the CNF/CNT/Co₃O₄ electrode with a 25/25/25 mass ratio demonstrated the best performance, achieving a specific capacitance of 23.24 F/g at 0.1 A/g, low internal resistance (∼20 Ω), and excellent capacitance retention. It also delivered an energy density of 0.517 Wh/kg and a power density of 21.28 W/kg within a 0.4 V voltage window. Mechanical tests confirmed the electrode's exceptional flexibility and durability, maintaining structural integrity under repeated folding and stretching. These results illustrate the potential of CNF/CNT/Co₃O₄ composite electrodes as environmentally friendly candidates for flexible energy storage in wearable electronics.