Ionomer Membrane and MEA Development for DMFC

Abstract

Membrane-electrode assemblies (MEAs) have been prepared from different acid-base-blends consisting of different sulfonated arylene main-chain polymers and polybenzimidazole PBI and a microphase-separated arylene main-chain block copolymer consisting of a sulfonated and proton-conducting and a hydrophobic microphase. The MEAs have been prepared using 4 different methods: Method A: The membrane has been prepared first as a free film, and the electrodes have subsequently been coated onto the membrane; Method B: The membrane has been prepared first as a polyester-supported film, and the electrodes have thereafter been coated onto the membrane; Method C: The MEA has been built up from the anode; Method D: The MEA has been built up from the cathode. The MEAs have been tested under different temperatures and different meOH concentrations. Three different polyacid-PBI blend membranes could be identified which showed comparable or even better DMFC performance than Nafion®105: a sulfonated polyethersulfone-PBI blend membrane, a sulfonated polyetherketone-PBI blend membrane, and a partially fluorinated sulfonated polyether-PBI blend membrane. The proton-conducting block co-ionomer membrane initially showed an excellent DMFC performance due to reduced meOH permeability, compared to the polyacid-PBI blend membranes, which however degraded with time of the DMFC operation probably being due to irreversible morphology changes. Among all tested MEAs the MEAs prepared by Method B showed the best DMFC performance. The DMFC performance of the MEAs prepared by Method C and Method D was slightly worse than that of the MEAs made via Method B. The DMFC performance of a MEA from the sulfonated polyetherketone-PBI blend membrane which was built up using Method D improved steadily during 4 weeks of DMFC operation.

Keywords:

• blend membranes
• DMFC
• MEA

Notes

^a 0.3 g/dL in NMP, at 25°C.

^b Determined from TGA-FTIR coupling experiment, appearance of traces of SO2 in TGA gaseous decomposition products.

^c The swelling of this ionomer was, due to its high IEC, extremely high and could not be determined properly.

^a measured in the DMFC during operation, temperature 60°C.

^b values taken from Table 1, for comparison.