Composite polymer electrolytes based on metal oxides

8 Composite polymer electrolytes based on metal oxides 

The characteristics of composite membranes depend not only on the type of metal oxide, but also on surface area, size, concentration and surface chemical modification of the metal oxide, and on the type of polymer matrix. The primary method for characterising membranes is to compare the current-voltage response of the cell as a function of membrane chemical characteristics and cell humidity/temperature. 

Antonucci et attributed the enhanced performance of the composite membrane to the hygroscopic properties of silica. Watanabe et investigated silica- and titania-impregnated Nation composite membranes in H2/O2 proton-exchange membrane fuel cells operating at 100 °C with minimal external humidification. They reported that the silica particles were superior to titania particles in terms of water retention qualities within the Nafion membrane, and attributed this to the higher water sorption properties of silica. Adjemian et reported that the performances of silica and titania composites at 130 °C and 75% RH are comparable (0.33 Qcm and 0.35 Qcm cell resistivities) while recast Nafion -based composites present high cell resistivity (0.9 Qcm ). 

Some authors have suggested that improved cell behaviour is not related to water retention or the acidity of the metal oxide component, but rather to the effect of the metal oxide particles on the temperature-dependent structure of the polymer matrix. 

Proton conductivity increased with silica content in all temperature conditions. This suggests that the silica doped into the membrane enhanced the formation of proton conduction pathways due to molecular water absorption. Thus, the probable mechanism for new proton conduction due to the presence of silica is proton hopping between Si-OH and water molecules.  

---