(163g) Gelation, Pore Structure, and Ionic Conductivity in Silico-Phosphate Proton Exchange Glass Membranes

Silico-phosphate glasses are an intriguing alternative to sulfonated fluoropolymer proton exchange membranes because they maintain conductivity over a wide range of temperature and humidity. Sol gel processing of the glass-former allows for the production of a robust membrane by tailoring the glass microstructure. The relationship between protonic transport through these amorphous, nano-scale phase-separated membranes and structure has not yet been fully established. To obtain a representative description of how these structures are affected by processing parameters, we monitor their structural developments during assembly of these materials under different processing conditions using concurrent Raman and Brillouin light scattering. We then measure protonic transport in the final product using dielectric impedance spectroscopy, and correlate the conductivity data with the structural information derived from the two light scattering probes, each probing a different length scale. We describe the details of the investigatory approach and discuss the information that can be derived from this novel structural probe. We present data for a series of silico-phosphate compositions and examine the relationship between the molar ratios of the phosphate and silica precursors, the thermal history during formation of the electrolytes and their application performance, both in terms of mechanical rigidity and proton conductivity.