(381e) Properties, and Lifetime of Random and Multiblock Copolymer Anion Conducting Membranes for Direct Methanol Fuel Cells

Properties, and
Lifetime of Random and Multiblock Copolymer Anion
Conducting Membranes for Direct Methanol Fuel Cells

John M. Ahlfield, Doh-Yeon
Park, and Paul A. Kohl,

School of Chemical and
Biomolecular Engineering,

 Georgia Institute of Technology

 Atlanta, Georgia 30332, United States

kohl@gatech.edu

Introduction

Anionic fuel cells are of interest because they have the
potential to overcome cost and performance platinum usage issues with acid fuel
cells. In this study, a series of anion-conductive multiblock
copoly(arylene ether sulfone)s were
synthesized and compared to random copolymers in direct methanol fuel cells.
The block copolymer can create a nanochannel
structure for ion conduction. The corresponding random copolymers were less
effective at creating conductive channels in the polymer structure. The
lifetime of the polymers was evaluated by comparing their degradation in
accelerated ex-situ conditions. The effect of polymer backbone and pendant ion
group stability was evaluated. 

Results and discussion

A
series of anion conductive multiblock copolymers (mPES) with different block lengths containing quaternary
ammonium groups were synthesized by the polycondensation
of separately prepared OH- and F-terminated oligomers. The F-terminated oligomer
at which quaternary ammonium groups were attached become
an ion-conductive hydrophilic block.

The
ion exchange capacities, the ion conductivities, and the relaxation times were
evaluated as a function of degree of fluorination, and ion exchange capacity,
as shown in Table 1. The relaxation times correspond to water in the polymer
membranes rather than polymer protons, confirmed by the absence of peaks
belonging to the polymers and the high water content of the membranes.

Polymer lifetimes were evaluated by NMR analysis. The results show the
benefit of higher ion concentration, controlled water uptake, and optimized ion
channel size. The stability of the backbones materials was dependent on the
polymer backbone and type of conducting ion.

The
ion exchange capacities, the ion conductivities, and the relaxation times were
obtained. The relaxation times correspond to water in the polymer membranes
rather than polymer protons, confirmed by the absence of peaks belonging to the
polymers and the high water content of the membranes.