Dielectric relaxation and polaron hopping in biomass derived activated carbon

Abstract

Activated carbon samples were obtained by alkali (KOH) activation and subsequent carbonisation of an identified biomass precursor at 600 °C, 800 °C, 1000 °C, and 1200 °C temperatures, in nitrogen atmosphere. Dielectric property changes with respect to the change in microstructure in the activated carbon samples was studied. High dielectric constant values at low-frequency regions (<103 Hz) were observed in all samples, due to trapped K+ ions, polar groups (C = C, C = O, –NH2, –OH), and interfacial polarisation. The trapped K+ ions also contributed to high dielectric dispersion at low-frequency regions. Carbonisation at 600 °C resulted in amorphous carbon formation with some intact cellulose crystallites. Thermal de-trapping of K+ ions resulted in an increase in dielectric constant with frequency up to 103 Hz. Carbonisation at 800 °C and 1000 °C resulted in nanocrystalline graphene oxide (GO), with interfacial polarisations dominant in charge storing and in the relaxation processes. Carbonisation at 1200 °C resulted in a carbon nanotube (CNT) network and negative dielectric constant values at 70 °C was observed due to the Surface Plasmon Resonance effects of the formed CNT. With increase in carbonisation temperature, a change in Debye-type to non-Debye-type relaxation process was observed, supported by the Dielectric formalism studies and the Cole–Cole plot.