Electrochemically activated binder-free carbon nanocomposite electrode for enhanced electrochemical capacitor

This study introduces a simple approach for designing and assembling a binder-free bioderived carbon nano composite electrode using a physical deposition technique, followed by electrochemical oxidation, offering a faster, more cost-effective, and energy-efficient alternative to traditional physical and chemical activation processes. The electrochemical performance of the binder-free electrodes was evaluated on both three-electrode cell systems and conventional coin cell devices, using cyclic voltammetry, galvanostatic charge discharge, and electrochemical impedance spectroscopy. Electrochemical activation of carbon surface electrodes in nitric acid enhanced the specific capacitance from 54 F/g to 190 F/g at 2 mV/s scan rate for the three-electrode cell system in 3 M H2SO4 electrolyte. To further assess the electrochemical performance of the prepared electrodes, two-electrode cell devices were assembled and tested in various electrolytes (H2SO4, Na2SO4, and NaOH). The highest registered specific capacitance was observed with the sulfuric acid electrolyte, reaching 224 F/g at a 1 mA GCD current. Additionally, the equivalent series resistance (ESR) and overall gravimetric capacitance of the cells were measured in each electrolyte. The stability of the two-electrode samples was evaluated over 10,000 charge-discharge cycles, showing a capacitance retention of 82 % for the device using H2SO4 electrolyte. Scanning Electron Microscope (SEM) images and Energy Dispersive X-ray Spectroscopy (EDX) results were presented and analyzed for the prepared electrodes. Electrochemical characterization, including cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy, were also performed, and thoroughly discussed. Alongside introducing a simple binder-free assembly method, this work underscores the potential of electrochemical activation to enhance the performance of carbon electrodes intended for electrochemical capacitor devices. The findings open avenues for further exploration of electrochemical activation of bio-derived carbon surfaces and the optimization of its parameters. •A simple method to fabricate binder-free carbon composite electrodes with enhanced performance.•Sustainable carbon from walnut shell waste deposited on a CNT @ CP substrate.•Electrochemical activation in an acidic environment enhanced electrode properties.•Electrochemical tests were performed in acidic, alkaline, and neutral electrolytes.•Comprehensive electro