Temperature dependence of the electrical conductivity of activated carbons prepared from vine shoots by physical and chemical activation methods

A broadly varied series of activated carbons (ACs) was prepared from vine shoots (VS) by the method of physical activation in air, CO2 and steam, and by the method of chemical activation with H3PO4, ZnCl2 and KOH aqueous solutions. Here, the temperature dependence of the dc electrical conductivity for the ACs is studied from room temperature up to 200 degrees C. The bulk electrical conductivity of the carbon samples is found to be the result of a complex interplay between several factors, texture and surface chemistry likely being the most relevant ones. The best conductivity values are obtained for sample carbonized at 900 degrees C. The physical activation stage has been proved to decrease the conductivity of the carbonized products, the reduction being more pronounced for air than for CO2 and steam. Such a detrimental effect of physical activation on conductivity has been associated with the formation of oxygen groups and structures on carbon surface rather than with the porosity development. The conductivity of ACs prepared by chemical activation is even lower than for physically activated samples, likely due to the higher degree of porosity development. All carbon samples, irrespective of the activation method and activating agent, behave as semiconductor materials and therefore the electrical conduction is related to an energy gap (E-g). The Eg values widely vary from 0.084 eV for the sample carbonized at 900 degrees C up to 0.659 eV for the AC prepared by physical activation in air. (C) 2014 Elsevier Inc. All rights reserved.