Ionic Liquid Composite Polybenzimidazol Membranes for High Temperature PEMFC Applications

Abstract

A series of proton exchange membranes based on polybenzimidazole (PBI) were prepared using the low cost ionic liquids (ILs) derived from 1-butyl-3-methylimidazolium (BMIM) bearing different anions as conductive fillers in the polymeric matrix with the aim of enhancing the proton conductivity of PBI membranes. The composite membranes prepared by casting method (containing 5 wt. % of IL) exhibited good thermal, dimensional, mechanical, and oxidative stability for fuel cell applications. The effects of anion, temperature on the proton conductivity of phosphoric acid-doped membranes were systematically investigated by electrochemical impedance spectroscopy. The PBI composite membranes containing 1-butyl-3-methylimidazolium-derived ionic liquids exhibited high proton conductivity of 0.098 S·cm−1 at 120 °C when tetrafluoroborate anion was present in the polymeric matrix. This conductivity enhancement might be attributed to the formed hydrogen-bond networks between the IL molecules and the phosphoric acid molecules distributed along the polymeric matrix.

Recent Progress in the Development of Composite Membranes Based on Polybenzimidazole for High Temperature Proton Exchange Membrane (PEM) Fuel Cell Applications

“…The resulting membrane showed a proton conductivity of 0.002 S/cm at 190 °C and the thermal stability in the range of 150–190 °C. Recently, our group prepared a series of PEMs based on PBI filled with 1-butyl-3-methylimidazolium (BMIM) bearing different anions (Cl, I, BF 4 , PF 6 , NCS, Br, NTf 2 , BF 4 ) [ 227 , 228 ]. Under PA doping conditions, these composite membranes with 5 wt.% of ILs exhibited the highest proton conductivity of 0.098 S/cm at 120 °C when BF 4 anion was present.…”

Fabrication of hybrid proton‐exchange membranes using a brandnew high temperature ionic liquid as charge transporting and clay modifier

“…9 The possibility of operating at elevated temperatures is desired, since it inhibits the catalytic poisoning that occurs at low temperatures, which is responsible for diminution of PEMFC performance. 10 According to the literature, charge transport from anode to cathode occurs as a synergic process that combines hopping and diffusion mechanisms, 11 diffusion of charge transporting agent through the solid involves the possibility of leaking, which has previously observed to be a threat for IL incorporation into PEMs, aiming device durability. 12,13 Several approaches have been proposed for the IL immobilization into PEM matrix, such as phosphoric acid doping of polybenzimidazole membranes, 14 grafting of ILs to titanate nanotubes, 15 grafting of imidazolium poly-ILs onto silica nanoparticles, 16 crosslinking of sPEEK with organometallic frameworks 17 or even the insertion of cross-links in the very structure of the polymer matrix as it was proposed by.…”

Synthesis and Properties of Phosphoric-Acid-Doped Polybenzimidazole with Hyperbranched Cross-Linkers Decorated with Imidazolium Groups as High-Temperature Proton Exchange Membranes

“…For ImOPBI-5, the proton conductivity reached 0.089 S cm −1 at 160 • C due to the increase in the phosphoric acid doping rate, which was higher or comparable to that based on PBI membranes [35][36][37]. With the increase in the cross-linking degree, although the phosphoric acid content of ImOPBI-10 and ImOPBI-15 decreased, more imidazolium groups were introduced into the membranes, which not only acted as a Bronsted base but also promoted phosphoric acid ionization to form ion pairs with phosphoric acid (Im…”