KOH-doped polybenzimidazole for alkaline direct glycerol fuel cells

• Published in: Journal of membrane science Vol. 486; pp. 239 - 247
• Main Authors: Couto, Rafaela Nunes, Linares, José J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.07.2015
• Subjects: Alkaline membrane; Glycerol; Membrane characterization; Polybenzimidazole; Glycerol; Membrane characterization; Polybenzimidazole; Alkaline membrane
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2015.03.031

This study addresses the physico-chemical characterization of KOH-doped polybenzimidazole (PBI, poly[2,2-(m-phenylene)-5,5-bibenzimidazole]) membranes for application in alkaline direct glycerol fuel cells. The KOH-doped membranes present a large affinity for water and gradually replace the acid hydrogens in the imidazole rings with K. Only at KOH concentrations above 4molL−1 are “free” KOH molecules present in the membrane structure, along with a small fraction of glycerol molecules. These behaviours impact on the membrane dimensions. At KOH concentrations below 4molL−1, the membrane dimensions become enlarged. However, at higher concentrations, the cross-sectional area shrinks, whereas the thickness expands significantly. This result is confirmed by x-ray diffraction, where an enlargement in the inter-chain distances is evidenced. The infrared spectra support the interaction of KOH and PBI at alkali concentrations of 4molL−1 or higher, though reveal some membrane degradation processes. The KOH-doped PBI membranes present thermal stabilities up to 573K, a coefficient of permeability to glycerol of around 10−7cm2 s−1, and OH− conductivities above 0.01Scm−1 at temperatures between 303 and 348K. The combination of these parameters configures a suitable alkaline membrane capable of producing a maximum power density of 34.2mWcm−2 for 1molL−1 glycerol and 4molL−1 KOH at 348 K. •KOH-impregnated PBI is a suitable candidate for Direct Glycerol Fuel Cells.•The membrane swells and absorbs KOH, water and glycerol after impregnation.•The membrane presents low glycerol permeability and suitable thermal stability.•The OH− conductivity is not significantly affected by the presence of glycerol.•A maximum power density of 34.2mWcm−2 is obtained in the single cell.