Investigating frequency dependent ionic and electronic transport in porous media.

This thesis presents the development and application of frequency-dependent characterisation techniques for extracting transport parameters from porous media. A custom data acquisition framework was implemented using the Zurich Instruments MFLI lock-in amplifier and its MATLAB API, enabling programmable frequency sweeps, time- and voltage-automated measurements, real-time visualisation, and systematic data organisation. Complementary data analysis programmes were developed to fit experimental spectra to theoretical models by minimising normalised residuals, extracting physically-meaningful parameters with errors. The accuracy and reliability of the measurement and fitting protocols were validated through multiple approaches, including preliminary tests on circuits with known impedances, comparison of parameter results with values reported in the literature for a PEDOT:PSS channel, and general measures of fit quality. These methods were then applied to a series of organic mixed ionic-electronic conductors (OMIECs) with a variety of additive formulations. Analysis employed a distributed transmission line model, based on de Levie theory, revealing insights into chemical and structural properties, including electronic and ionic transport, and capacitive coupling. Additionally, a preliminary study was conducted on surface-treated cellulose discs to assess the suitability of impedance spectroscopy for evaluating water resistance, using an equivalent circuit modelling approach. The combined experimental and computational framework enabled robust characterisation of complex porous systems. Extracted parameters revealed structure-property relationships, critical to the optimisation of materials for applications in bioelectronics, sensing, and sustainable materials development.