Polybenzimidazole‐Based Membranes as a Real Alternative to Nafion for Fuel Cells Operating at Low Temperature

Abstract

Acid-doped polybenzimidazole (PBI) membranes are considered as one of the most attractive alternatives to Nafion in polymer fuel cells (PEMFCs). [1][2][3] At present, however, their use at temperatures below $160 8C is impeded by the leaching of the free phosphoric acid from the membrane in presence of liquid water, which causes a drop in conductivity of many orders of magnitude during fuel cell operation. To overcome this problem, we investigated the suitability of silica derivatized with imidazole-based functionalities as fillers able to improve the acid retention capability of the membrane. We show that even small amounts ($10 wt %) of filler increase the permanent proton conductivity of the PBI composite membranes by a factor >10 3 in comparison with that of unfilled PBI. The preparation of PBI composite membranes with basic functionalities is a promising way to make possible their use in PEMFCs operating around 120 8C, that is, the temperature required for automotive applications. During the last ten years, polybenzimidazole-based separators have been widely investigated for what concerns polymer synthesis and casting process, [4] membrane thermal stability, [5]

Design and Synthesis of Cross-Linked Copolymer Membranes Based on Poly(benzoxazine) and Polybenzimidazole and Their Application to an Electrolyte Membrane for a High-Temperature PEM Fuel Cell

“…However, PEMs using perfluorinated sulfonic acid (PFSA) ionomers, such as Nafion (DuPont; 0.9 meq g −1 ), have several drawbacks, such as a limited operation temperature (generally <100 °C), high fuel crossover, and a high cost [50]. These shortcomings have hampered their wider commercialization and have triggered extensive research into alternative PEMSes that can perform at elevated temperatures (generally 120-200 °C) and in a low-humidity condition (relative humidity (RH) <50%) [51][52][53][54][55][56][57][58]. Among numerous material candidates, a significant body of literature is devoted to PBI and its derivatives when doped with phosphoric acid (PA) as a PEM in high-temperature fuel cell processes.…”

PBI Composite and Nanocomposite Membranes for PEMFCs: The Role of the Filler

“…The imidazole-containing silica (see Scheme 1) was synthesised by means of the standard basic hydrolysis/condensation process, starting from tetraethoxysilane (TEOS) and N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole in molar ratio 2:1, as described in details elsewhere [20]. Selected fractions with particle size ranging around 20 lm were used in the composite membrane preparation.…”

“…Recently, our group proposed an imidazole-functionalised silica to use in PBI membranes for the control of acid leaching, so allowing the use in PEMFCs at temperatures lower than 150°C [20].…”

Testing a Vapour‐fed PBI‐based Direct Ethanol Fuel Cell

“…For doping levels higher than two, the excess of acid is in the undissociated form, in equilibrium with the ionic species. Thus, some researchers are studying new PBI-based structures to increase the acid retention capability of the membranes [28]. To the author's knowledge, there is not much work about the lifetime test for direct ethanol high temperature fuel cells.…”