Preparation and proton conductivity of WO3·2H2O/epoxy composite films

Proton conductivities were examined for WO3·2H2O (0–40 vol.%)/epoxy resin composite films prepared by the precursor mixing method (i.e., precursor mixing and precipitation of WO3·2H2O after film shaping). The composite films with 16–40 vol.% WO3·2H2O had large primary and secondary particles of WO3·2H2O compared with WO3·2H2O powders obtained by hydrolysis of Na2WO4 solution. The proton conductivity at 50 °C under saturated water vapor pressure increased abruptly with WO3·2H2O content, reaching the value of WO3·2H2O powder compact at 16 vol.%. The conductivity of the film with 40 vol.% WO3·2H2O was 6.3×10−4 S cm−1, which is higher than that of WO3·2H2O powder compact. The bulk conduction mechanism through the hydrogen bond network of WO3·2H2O was suggested to be dominant above 40 °C. The large primary particles and fully connected secondary particles of WO3·2H2O were assumed to contribute effectively to proton migration in the composite films.