DC AND AC CONDUCTIVITIES OF BIOCHAR-POLYMER COMPOSITES

Author

Muhammad Abdullah Iqbal, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2024

Degree Name

Master of Science

Department

Physics

First Advisor

Talapatra, Saikat

Abstract

The scope of this thesis was to study the electrical conduction properties of biochar-polymer composites in order to understand the fundamental mechanisms of charge transfer in them. Biochar is a type of porous carbon, which is a by-product, obtained by pyrolysis of organic waste. These materials can aid as components of multiple applications in a variety of fields, which includes biochar based conductive polymer electrodes for charge storage applications. Here we have investigated biochar polymer composites with four different compositional ratios of Biochar to Polymer (B:P). Specifically, samples with B:P ratio of 0.16:1; 0.375:1; B:P 1:1; and B:P 2:1 were fabricated by mechanically mixing commercially available Biochar and Poly Vinylidene Fluoride-Co-Hexafluoropropylene (PVD-HFP) by weight. These were characterized using Scanning Electron Microscopy and Electron Dispersive X-ray Spectroscopy (EDAX). DC and AC transport properties of two terminal devices fabricated from small strips of these samples were studied with in a temperature range of 290K < T < 430K. The DC conductivity values (σdc) were extracted from DC measurements as well as low frequency (5Hz) AC conductivity data obtained from Impedance Spectroscopy (IS) measured in the frequency (ω) range of 1 Hz < ω < 1 MHz. We found that in general σdc of the B:P composites studied increases with the content of biochar. Typical room temperature conductivity values of ~ 10-3 S/cm, were obtained for composites with B:P as 0.16:1; 0.375:1; and B:P 1:1. However, an order of magnitude increase (~ 10-3 S/cm) in conductivity was obtained for B:P composite with a ratio of 2:1. We also observed that the conductivities of these samples typically increased with increasing temperatures. The analysis of the temperature dependence of σdc for all the samples suggest the conduction mechanism perhaps follows a thermally activated Arrhenius type mechanism with activation energies ~10-2 eV. We also found that the AC conductance (σ (ω)) for all the temperatures studied obeys “universal” ac power law with σ (ω) ~ ωs, where ‘s’ is the power exponent. We found that the value of s is > 1 (indicating a super linear nature) and is weakly dependent on temperature. These results indicate that perhaps the AC transport in biochar polymer composites studied follows a quantum mechanical tunnelling phenomena.