Comparison of sol–gel derived carbon xerogels synthesized from different phenolic precursors and solvents: electrical conductivity and dielectric relaxation

Carbon xerogels based on resorcinol/formaldehyde (R/F) and pyrogallol/formaldehyde (P/F) were synthesized via a sol–gel route using hydrochloric acid as catalyst, with distilled water or acetone as solvent, in order to perform a comparative study of precursor and solvent effects on their structural and electrical properties. Scanning electron microscopy reveals that all samples exhibit a nanospheres-based morphology, while FTIR spectroscopy confirms the presence of characteristic functional groups associated with the phenolic precursors. Nitrogen adsorption–desorption measurements at 77 K indicate a predominantly mesoporous texture with relatively low specific surface areas. The AC electrical conductivity follows Jonscher’s universal power law, characteristic of charge transport in disordered materials. A decrease in conductivity is observed at low temperatures, followed by a thermally activated increase above a critical temperature that depends on the precursor–solvent combination. The dielectric permittivity decreases with increasing temperature at low temperatures and tends to stabilize below the critical temperature. Analysis using the electric modulus formalism reveals two distinct relaxation processes. The high-frequency relaxation mode exhibits a temperature dependence similar to that of the electrical conductivity, with comparable activation energies, suggesting a common charge transport mechanism. The low-frequency relaxation is attributed to electrode–sample interfacial polarization effects. These results highlight the significant role of sol–gel synthesis parameters, particularly precursor nature and solvent choice, in tailoring the dielectric relaxation and electrical conductivity of carbon xerogels.