Electric response and conductivity mechanism reciprocity in H3PO4-doped Polybenzimidazole-4N-ZrO2 nanocomposite membranes

The electrical response of zirconia composite polybenzimidazole membranes [PBI4N(ZrO2)x](H3PO4)y is studied by Broadband Electrical Spectroscopy (BES), and correlated with our previous Dynamic Mechanical Analysis (DMA) and Modulated Differential Scanning Calorimetry (MDSC) measurements. The presence of nanofiller in the PBI4N polymer matrix is shown to plasticize the membrane, with a maximum effect observed at a nanofiller loading level of x ≈ 0.13. The disrupting effect of the nanofiller on the interchain dipole interactions modulates the overall electrical response of the materials. Following acid doping, a marked increase in conductivity is observed as new chemistry is installed at the interfaces between polymer and nanofiller that facilitates dipolar fluctuations and segmental motions of the polymer chains. In these composite membranes, two mechanisms of conductivity are postulated based on BES analysis; i) proton hopping between binding sites, and ii) proton hopping at the interfaces between HnPBI4Nn+/HnPBI4Nn+ and HnPBI4Nn+/HmZrO2m+. The results here presented demonstrate the effect of zirconia nanofiller and subsequent acid doping on the conductivity properties of composite PBI4N membranes. Of note, at 100 °C for [PBI4N(ZrO2)0.132](H3PO4)11, conductivity as high as 0.035 S/cm is achieved.