Toward Improved Conductivity of Sulfonated Aromatic Proton Exchange Membranes at Low Relative Humidity

Abstract

Three sulfonated aromatic polymers with different sequence lengths were studied in order to better understand the relationship between molecular structure, morphology, and properties of proton exchange membranes as a function of relative humidity. A random copolymer with a statistical distribution of sulfonic acid groups had very small domain sizes, whereas an alternating polymer with sulfonic acid groups spaced evenly along the polymer chain was found to have larger, but quite isolated, domains. The multiblock copolymer studied herein showed highly phase-separated hydrophilic and hydrophobic domains, with good long-range connectivity. Scanning force microscopy as a function of relative humidity was used to observe water absorption and swelling of the hydrophilic domains in each of the three membranes. The conductivity, water sorption kinetics, and fuel cell performance, especially at low relative humidity, were found to be highly dependent upon the morphology. The multiblock copolymer outperformed both the random and alternating systems at 100°C and 40% RH fuel cell operating conditions and showed similar performance to Nafion.

Sulfonated hydrocarbon membranes for medium-temperature and low-humidity proton exchange membrane fuel cells (PEMFCs)

“…This could be advantageous in actual fuel cell systems operated under low humidified conditions by reducing the effect of dimensional miss-match between hydrocarbon PEM and PFSA ionomer-catalyst [121]. Multiblock copolymers exhibit proton conductivities that are less RH-dependent and higher than that of Nafion ® [124].…”

Enhanced thermo-oxidative stability of sulfophenylated poly(ether sulfone)s

“…1 H, 13 C and 2D NMR spectra were obtained on a Varian Unity Inova NMR spectrometer operating at frequencies of 399.95 MHz for 1 H and 100.575 MHz for 13 C. Deuterated dimethylsulfoxide (DMSO-d 6 ) and deuterated chloroform (CDCl 3 ) were selected as the solvents.…”

“…Although a great variety of structures has been made, there are still challenges to be met, such as complete property evaluation of PEMs, optimization and simplification of sulfonation reactions, controllability of DS (degree of sulfonation) and the site of sulfonation, and performance enhancement and microstructure improvement of PEMs by designing polymer chemical structures [12,13].…”

Enhanced proton transport in nanostructured polymer electrolyte/ionic liquid membranes under water-free conditions

“…Among the many kinds of ion-conducting polymers, proton-conducting polymers have been the subject of extensive study for their possible use in PEFCs, which offer the prospect of supplying clean energy for automotives. Significant efforts have been devoted to improving the transport properties of PEFCs so they can be operated at relatively lower temperatures below 90 °C [8][9][10][11][12][13][14] . However, the development of a commercial PEFCpowered vehicle that replaces a gasoline-powered vehicle still seems distant.…”