Improvement of electrochemical double-layer capacitance by fast and clean oxygen plasma treatment on activated carbon as the electrode material from walnut shells

In this study, a simple, fast, and clean oxygen plasma method is presented to increase the surface area of activated carbon from walnut shells (WAC) and to connect functional groups containing oxygen to the carbon sample surface. X-ray photoelectron spectroscopy (XPS), nitrogen adsorption technique, Fourier-transform infrared spectroscopy (FTIR), X-Ray Diffraction (XRD), and scanning electron microscope (SEM) analyses to investigate the properties of the WAC and WACP are performed. Cyclic voltammetry(CV) and electrochemical impedance spectroscopy(EIS) measurements are used to investigate the capacitance properties of the supercapacitors. A significant increase in the surface area of the WAC was increased from 22 m2 g−1 to 78 m2 g−1 after oxygen plasma treatment. The specific capacitance was improved from 6.98 F g−1 to 76.89 F g−1 at 2.5 mV s−1. The devices with functionalized electrodes exhibited cyclic stability of 78% after 5000 cycles. •AC was prepared from walnut shells with H3PO4 as an activation agent.•Oxygen plasma treatment on the obtained AC was applied.•WAC modified with plasma treatment was used as supercapacitors.•Surface area of AC was increased by about 4-fold with plasma method.•Specific capacitance by plasma treatment showed a significant increase.