The influence of carbon nanotubes and graphene oxide sheets on the morphology, porosity, surface characteristics and thermal and electrical properties of polysiloxane derived ceramics

Abstract

Graphene oxide (GO) and multi-walled carbon nanotubes (MWCNT) were incorporated into a SiOC composite ceramic matrix using a simple roll-mixing method followed by thermal cross-linking and pyrolysis. The structure, morphology, porosity, surface characteristics, and thermal properties of polysiloxane are analysed using scanning electron microscopy, BET specific surface area, mercury intrusion porosimetry, water vapour and n-heptane adsorption, and Raman spectroscopy, respectively. The electrical conductivity, conduction mechanism, and percolation behavior of the composite ceramics are investigated by electrical impedance spectroscopy in the temperature range of 25–250 °C. Free-rising composite ceramic foams are generated, incorporating both nanofillers into the SiOC ceramic matrix. Both nanofillers show a positive effect on the thermal stability of the SiOC ceramics. The room temperature DC conductivity value of pure SiOC ceramics shows ∼2.97 × 10⁻⁹ S cm⁻¹, which increases by three to four orders of magnitude after the incorporation of 5 wt% conductive nanofillers (∼2.5 × 10⁻⁶ S cm⁻¹ for 5 wt% GO and ∼2.08 × 10⁻⁵ S cm⁻¹ for 5 wt% MWCNT). The calculated activation energy from the Arrhenius plot for composite ceramics is found to be lower (0.10 eV for 5 wt% GO and 0.07 eV for 5 wt% MWCNT) compared to the same SiOC ceramics without nanofillers (0.22 eV). The conduction mechanism studies of composite ceramics suggest a non-Debye type distribution of relaxation in SiOC. Thus the nanofiller-enhanced SiOC ceramics are highly promising materials for rechargeable batteries, high-temperature fuel cells, gas sensors, display devices etc.