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High Polymer Content 3,5‐Pyridine‐Polybenzimidazole Copolymer Membranes with Improved Compressive Properties
Author(s) -
Molleo M. A.,
Chen X.,
Ploehn H. J.,
Fishel K. J.,
Benicewicz B. C.
Publication year - 2014
Publication title -
fuel cells
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.485
H-Index - 69
eISSN - 1615-6854
pISSN - 1615-6846
DOI - 10.1002/fuce.201300202
Subject(s) - membrane , copolymer , phosphoric acid , materials science , polymer , polymer chemistry , chemical engineering , proton exchange membrane fuel cell , pyridine , polymerization , solubility , chemistry , composite material , organic chemistry , metallurgy , biochemistry , engineering
Three series of polybenzimidazole (PBI) copolymers (3,5‐pyridine‐r‐2OH‐PBI, 3,5‐pyridine‐r‐ para ‐PBI, and 3,5‐pyridine‐r‐ meta ‐PBI) were polymerized and cast into membranes by the polyphosphoric acid (PPA) process. Monomer pairs with high and low solubility characteristics were used to define phase stability‐processing windows for preparing membranes with high temperature membrane gel stability. Creep compliance of these membranes (measured in compression at 180 °C) generally decreased with increasing polymer content. Membrane proton conductivities decreased linearly with increasing membrane polymer content. Fuel cell performances of some high‐solids 3,5‐pyridine‐based copolymer membranes (up to 0.66 V at 0.2 A cm –2 following break‐in) were comparable to para ‐PBI (0.68 V at 0.2 A cm –2 ) despite lower phosphoric acid (PA) loadings in the high solids membranes. Long‐term steady‐state fuel cell studies showed 3,5‐pyridine‐r‐ para ‐PBI copolymers maintained a consistent fuel cell voltage of >0.6 V at 0.2 A cm –2 for over 2,300 h. Phosphoric acid that was continuously collected from the long‐term study demonstrated that acid loss is not a significant mode of degradation for these membranes. The PBI copolymer membranes' reduced high‐temperature creep and long‐term operational stability suggests that they are excellent candidates for use in extended lifetime electrochemical applications.