Aliphatic/Aromatic Polyimide Ionomers as a Proton Conductive Membrane for Fuel Cell Applications

Abstract

To produce a proton conductive and durable polymer electrolyte membrane for fuel cell applications, a series of sulfonated polyimide ionomers containing aliphatic groups both in the main and in the side chains have been synthesized. The title polyimide ionomers 1 with the ion exchange capacity of 1.78-2.33 mequiv/g were obtained by a typical polycondensation reaction as transparent, ductile, and flexible membranes. The proton conductivity of 1 was slightly lower than that of the perfluorinated ionomer (Nafion) below 100 degrees C, but comparable at higher temperature and 100% RH. The highest conductivity of 0.18 S cm(-)(1) was obtained for 1 at 140 degrees C. Ionomer 1 with high IEC and branched chemical structure exhibited improved proton conducting behavior without sacrificing membrane stability. Microscopic analyses revealed that smaller (<5 nm) and well-dispersed hydrophilic domains contribute to better proton conducting properties. Hydrogen and oxygen permeability of 1 was 1-2 orders of magnitude lower than that of Nafion under both dry and wet conditions. Fuel cell was fabricated with 1 membrane and operated at 80 degrees C and 0.2 A/cm(2) supplying H(2) and air both at 60% or 90% RH. Ionomer 1 membrane showed comparable performance to Nafion and was durable for 5000 h without distinct degradation.

Synthesis and properties of a polyimide containing pendant sulfophenoxypropoxy groups

“…The CÀ ÀS bonds are more likely to be thermally decomposed than the other side-chain bonds (e.g., CÀ ÀO bonds). These thermal properties are comparable to those of other sulfonated polyimides with shorter or longer aliphatic side chains, [18][19][20][21] and so we conclude that the phenylene rings introduced into the side chains do not practically affect the thermal stability.…”

“…Although the stability is not high enough for practical applications, these weightloss values are comparable to those of other side-chainsulfonated polyimides. [18][19][20] After these tests, 5 still remained a self-supporting and flexible membrane but was somewhat more brittle when bent. There are two possible degradation modes for the side-chain-sulfonated polyimides: imide linkage scission (mainchain degradation) and alkyl/aryl ether linkage scission (side-chain degradation), as clearly reported by Okamoto et al 14 Under operating fuel-cell conditions, however, the main-chain degradation seemed mainly to cause membrane brittleness for a similar sidechain-sulfonated polyimide membrane.…”

“…We have also investigated the effect of aliphatic groups in both the main and side chains to achieve excellent hydrolytic and oxidative stability. [18][19][20] However, because of the synthetic difficulties, the effect of the side-chain length has not been well examined. 21 In this article, we report the synthesis and properties of a novel polyimide electrolyte having longer pendant sulfophenoxypropoxy groups.…”

Aromatic Poly(ether ketone)s with Pendant Sulfonic Acid Phenyl Groups Prepared by a Mild Sulfonation Method for Proton Exchange Membranes

“…Two-phase separation morphology has been observed in the microstructure of Nafion and polyimide films. 45,46 Proton conductivity and dimensional stability of the membranes are closely related to their morphology. Wide ion channels formed by hydrophilic domains are helpful to the movement of protons but are possibly detrimental for mechanical properties and dimensional stability in hot water.…”

Sulphonated Biphenylated Poly(aryl ether ketone)s for Fuel Cell Applications

“…Although many series of polyarylether-type PEMs have been prepared as potential fuel cell materials, with the exception of sulphonated PEEK and a several other sulphonated polyarylene ether ketones and sulphones, only a few of them were successfully fabricated into MEAs and their data reported [21,22]. Among those which have modest water uptake, BiPh-SPEEKDK showed the best conductivity.…”