Isomeric influences of naphthalene based sulfonated poly(arylene ether sulfone) membranes for energy generation using reverse electrodialysis and polymer electrolyte membrane fuel cell

Sulfonated poly(arylene ether sulfone) (SPAES) copolymers possessing three different dihydroxynaphthalene isomers and a biphenol (BP) moiety were synthesized as membranes for energy generation. Membrane samples of three different weight-based ion exchange capacities (IECw, 1.42, 1.82 and 2.2 meq g(-1)) were evaluated through a thermal, mechanical and electrochemical analysis. In order to investigate the isomeric effects of naphthalene and BP units in a polymer matrix, their ion transport properties were studied for potential energy generation applications, exemplified by reverse electrodialysis (RED) and polymer electrolyte membrane fuel cell (PEMFC) applications. Interestingly, the prepared polymeric membranes comprised of three different naphthalene isomers or BP exhibited considerably disparate ion transport properties in both RED and PEMFC applications. In RED applications, 2,6-dihydroxynaphthalene containing SPAES showed high Na+ ion permselectivity and low membrane resistance due to the dense membrane structure and linear conformation of the resulting membrane. In addition, despite having the same IECw, a large difference in the electrochemical performance of the membranes was observed due to isomeric effects in the naphthalene containing polymer backbone. Moreover, in PEMFC single cell tests at 80 degrees C under RH 100% and H-2/air feed conditions, the membrane composed of 1,5-dihydroxynaphthalene (IECw=2.2 meq g(-1)), which had a helical conformation, achieved a promising current density (614 mA cm(-2) at 0.6 V) among the tested membranes.