Andreas Chromik

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.

Low retaining force optical viewport seal.

We report on the experimental realization of an ultrahigh vacuum (UHV) indium sealing between a conflat knife edge and an optical window. The sealing requires a very low clamping force and thus allows for the use of very thin and fragile windows.

Narrow bandwidth electromagnetically induced transparency in optically trapped atoms

We demonstrate electromagnetically induced transparency (EIT) in a sample of rubidium atoms, trapped in an optical dipole trap. Mixing a small amount of σ − -polarized light to the weak σ + -polarized probe pulses, we are able to measure the absorptive and dispersive properties of the atomic medium at the same time. Features as small as 4 kHz have been detected on an absorption line with 20 MHz line width. (Some figures in this article are in colour only in the electronic version)

Sulfonated Low-Cost Ionomers as Acidic Cross-Linkers for High-Temperature PBIOO Membranes

The low-cost polymers poly(styrene) and poly(α-methylstyrene) have been sulfonated in a first step. Then both sulfonated ionomers have been blended with PBIOO® (30 wt% sulfonated ionomer, 70 wt% PBIOO), the sulfonated ionomer serving as acidic cross-linker which enhances the PBIOO stability. Both membrane types were treated with Fentons Reagent to investigate their oxidative stability. Of particular interest was whether the poly(α-methylstyrene) ionomer was more stable against radical attack. It was indeed found that the PBIOO-sulfonated poly(α-methylstyrene) blend membrane showed less weight loss during and after Fenton Test than the respective poly(styrene sulfonic acid) PBIOO-containing membrane. The macromolecules are partially degrading by radical attack to the main chain of the sulfonated poly(α-methylstyrene) polymers but still remain in the blend membrane matrix due to acid-base interactions. Since the PBIOO/sulfonated poly(α-methylstyrene) blend membranes conserved their integrity even after Fentons Test they can be regarded as interesting low-cost high-T fuel cell membranes.