Nitric acid functionalization of carbon monoliths for supercapacitors: Effect on the electrochemical properties

Activated carbon monoliths and oxidized carbon monoliths are prepared from Eucalyptus grandis wood by pyrolysis and subsequent activation under CO2 (aCMs) and further functionalization using nitric acid (ox-aCMs). Their textural and chemical properties are compared and the electrochemical characteristics as supercapacitor electrodes are tested. The nitric acid treatment does not produce substantial changes in the textural properties of the monolith obtained. Elemental analysis and X-ray photoelectron spectroscopy (XPS) reveal that the oxidized monolith presents a high content of oxygenated functional groups that can participate in pseudocapacitive reactions. This determines that the oxidized monoliths have higher electrical capacitance (80 F cm(-3)) at low current densities and higher energy density (up to W-v = 2.7 W h L-1) than the non-oxidized ones. The super capacitor cell containing the oxidized monoliths presents higher total resistance values and response time compared to the non-oxidized monolith. The non-oxidized monolith showed the highest power density (up to P-v = 94.5 W L-2). (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.