This study reports an original approach based on the CO2 plasma treatment on modification of the chemical or physical properties of activated carbon(AC) from the pistachio shells as a waste for application as electrochemical double-layer capacitors(EDLC). In the AC production experiments, impregnation ratio, impregnation pre-treatment temperature, activation temperature and activation time are investigated. In the AC modification experiments with plasma treatment, the effects of plasma gases, plasma power and plasma time are performed. The results of the different conditions indicated that the structural properties of the obtained AC were significantly dependent on the plasma and pyrolysis parameters. The surface properties of the raw AC and plasma-treated AC (PTAC) with X-ray photoelectron spectroscopy (XPS), nitrogen adsorption technique, and scanning electron microscope (SEM) are characterized. Surface area values for the raw AC and PTAC are 768 and 1250 m(2) g(-1), respectively. A change in the peak positions and an increase in the percentage of oxygen of the AC treated with CO2 plasma were obtained from XPS results. After 15 min of CO2 plasma activation, a significant increase in the capacitance of up to about 141% was obtained as a 118.4 F g(-1) compared to 49.98 F g(-1) for untreated AC. The results show that the plasma treatment on the specific surface area and surface functional groups of AC has a significant impact. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.