Proton conductive composite membrane of phosphosilicate and polyvinyl alcohol

Proton conductive composite membranes were prepared by dispersing phosphosilicate colloidal particles into a polyvinyl alcohol (PVA) matrix. The synthesized membranes were flexible with film thickness between 80 and 200 μm. SEM micrographs show that the phosphosilicate particles are homogenously dispersed, whilst the PVA crosslinks with the inorganic phase and fills in the gaps between the particles. Proton conductivity increases by several orders of magnitude with increasing humidity, reaching a maximum of 0.02 S/cm at ambient temperature and 100% relativity humidity (RH). The activation energy is reduced to 7.3 kJ/mol with RH increasing to 90% in the tested temperature range 20–70 °C. From structural characterization and conductivity measurements, it is deduced that proton transport occurs by both the Grotthuss and diffusion mechanisms. The methanol permeability was found 5–10 times lower than Nafion 117. The composite membrane was tested in the direct methanol fuel cell (DMFC). The preliminary results show the membrane is a promising candidate for PEM for use in DMFC systems.