Ion transport studies in PEO:NH₄ClO₄ polymer electrolyte and its composite with Al₂O₃

Composition, temperature and humidity dependence of ionic conductivity in polyethylene oxide (PEO):NH₄ClO₄ polymer electrolyte composite obtained by the dispersal of Al₂O₃ is reported. The dispersal of Al₂O₃ introduces significant changes in the conductivity vs. composition isotherm. The conductivity of the composite peaks at two concentrations of Al₂O₃ is ~2 × 10⁻⁵ S cm⁻¹. For studying ion dynamics, motional narrowing of ¹H NMR line with temperature is also reported. In PEO:NH₄ClO₄ (without dispersed Al₂O₃), two ¹H frequency-shifted NMR lines are seen (one of these have been assigned to the ¹H belonging to –CH₂–CH₂– chain of the polymer and the other to NH₄ ⁺ complexed with the chain). For the (PEO:NH₄ClO₄) + Al₂O₃ composites, however, one additional narrow peak is also seen at temperatures higher than 40 °C. This has been interpreted in terms of some hopping H⁺ ions getting loosely bonded to Al₂O₃, forming Al(OH)₃, which possibly releases an additional mobile protonic species (OH⁻).