Influence of the size and shape of silica nanoparticles on the properties and degradation of a PBI-based high temperature polymer electrolyte membrane

The life time stability of membrane material is one of the major parameters regarding reliability of high temperature polymer electrolyte membrane fuel cells. Present work has improved fuel cell durability and chemical stability by incorporating cross-linked silica particles in phosphoric acid doped poly(2,2′-m-phenylene-5,5′-bibenzimidazole) membranes. Three different silica particle contents were generated in membranes by in-situ sol–gel reaction from the precursor tetraethoxy silane and cross-linked to the polymer chains by using (3-glycidoxypropyl)-methyldiethoxysilane. The size, shape and distribution of the silica nanoparticles were examined by transmission electron microscopy. The amorphous characteristics and the chemical composition of the silica particles were investigated using X-ray diffraction, electron diffraction and energy dispersive X-ray spectroscopy. Detailed statistical analysis showed that by increasing the tetraethoxy silane content, the particle size was reduced while the amount of particles was increased. Ex-situ membrane characterization and in-situ membrane electrode assembly testing revealed a high influence of the silica content on the mechanical stability and start–stop-cycling behavior. The improved lifetime durability of the organic–inorganic composite membrane was proven in comparison to the pure polybenzimidazole membrane in membrane electrode assemblies over 1300 h under constant fuel cell operation in reformate.