Tuned Polymer Electrolyte Membranes Based on Aromatic Polyethers for Fuel Cell Applications

Abstract

Poly(arylene ether sulfone)-based ionomers containing sulfofluorenyl groups have been synthesized for applications to polymer electrolyte membrane fuel cells (PEMFCs). In order to achieve high proton conductivity and chemical, mechanical, and dimensional stability, the molecular structure of the ionomers has been optimized. Tough, flexible, and transparent membranes were obtained from a series of modified ionomers containing methyl groups with the ion-exchange capacity (IEC) ranging from 1.32 to 3.26 meq/g. Isopropylidene tetramethylbiphenylene moieties were more effective than the methyl-substituted fluorenyl groups in giving a high-IEC ionomer membrane with substantial stability to hydrolysis and oxidation. Dimensional stability was significantly improved for the methyl-substituted ionomer membranes compared to that of the non-methylated ones. This new ionomer membrane showed comparable proton conductivity to that of the perfluorinated ionomer membrane (Nafion 112) under a wide range of conditions (80-120 degrees C and 20-93% relative humidity (RH)). The highest proton conductivity of 0.3 S/cm was obtained at 80 degrees C and 93% RH. Although there is a decline of proton conductivity with time, after 10 000 h the proton conductivities were still at acceptable levels for fuel cell operation. The membranes retained their strength, flexibility, and high molecular weight after 10 000 h. Microscopic analyses revealed well-connected ionic clusters for the high-IEC membrane. A fuel cell operated using the polyether ionomer membrane showed better performance than that of Nafion at a low humidity of 20% RH and high temperature of 90 degrees C. Unlike the other hydrocarbon ionomers, the present membrane showed a lower resistance than expected from its conductivity, indicating superior water-holding capability at high temperature and low humidity.

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

“…Watanabe and co-workers studied various types of sulfonated PEMs with bulky fluorenyl groups such as SPIs [112], SPAES [113][114][115][116], and sulfonated poly(arylene ether sulfone ketone)s (SPAESKs) [117,118]. Based on the findings from the Litt group, SPIs with 4,4 ′ -(9-fluorenylidene) dianiline (FDA) were synthesized with increasing FDA compositions up to 60 mol%.…”

“…(Fig. 33) without sacrificing hydrolytic, oxidative, dimensional, and mechanical stability [115]. The researchers used a flow reactor for sul- fonation in order to overcome the poor solubility of the resulting sulfonated polymers.…”

Research and Development of Highly Active and Durable Electrocatalysts Based on Multilateral Analyses of Fuel Cell Reactions

“…126 The performances of the cathode CLs containing SPAE binder (SPAE-CL) were examined from 60 to 100% RH at 80°C. 65,66 The values of MA at 0.9 V (measure of the catalyst utilization) in air and O 2 at the SPAE-CL reached a maximum at 88% RH and decreased steeply below 78% RH.…”

Proton Conductive Areas on Sulfonated Poly(Arylene Ketone) Multiblock Copolymer Electrolyte Membrane Studied by Current-Sensing Atomic Force Microscopy

“…In recent years, membranes with sulfonated aromatic hydrocarbon (HC) structure have been extensively studied as an alternative to PFSA from the viewpoints of cost, high temperature operability, environmental friendliness, and low gas permeability, and the HCtype membranes have already demonstrated promising results. [4][5][6][7][8][9][10][11][12] Our group has reported a series of sulfonated poly(arylene ether sulfone) (SPE) multiblock copolymers with high proton conductivity, comparable to that of Nafion, at high temperature and low humidity. [13][14][15][16][17][18] Recently, we synthesized a novel HC-type membrane, sulfonated poly(arylene ketone) multiblock copolymer, or SPKbl-1, 19 which has the same hydrophobic group as in SPE-bl-1 16,17 but a different hydrophilic group (Fig.…”