Membrane stability, fuel cell technology

The membrane in a membrane fuel cell fulfils several important functions as stated in the introduction. Nafion was the first commercially available membrane, which lead to a breakthrough in fuel cell technology. Today, various companies are engaged in membrane development especially for this purpose, aiming at improved material properties. The goals are less sensitivity towards elevated temperature and dry operation, better chemical and mechanical stability and reduced methanol crossover for DMFC operation. A significant improvement of the mechanical stability was achieved by incorporation of a PTFE porous sheet as mechanical support for the membrane material [13,14]. 

With respect to fuel-cell technology itself, the small portable units use commercially available membrane electrode assemblies (MEA) and gas diffusion layers (GDL). As the operating temperature of small fuel-cell stacks usually lies below 50 °C, the requirements with respect to material stability of MEA and GDL, but also of sealing gaskets and bipolar plates are comparable lower than for other applications. For example, it is well known that metallic bipolar plates show significantly lower corrosion below 50 °C than at typical operation temperature of 80 °C [6,7], so that a sufficient lifetime for portable applications can be achieved with stainless steel. 

As it has been pointed out in past years [1], the most critical concerns of the alkaline membrane fuel cell technology were the low conductivity and the poor stability of the early anion exchange membranes. In past years, significant advances were achieved [3, 4], promoting the development of the alkaline membrane fuel cell technology. 

In summary, the improvement of AAEMs is an ongoing area of research and development There is no one membrane of choice currently and the conductivity and stability of some membranes are still an issue. However, there are signs that good AAEM performance is close and so catalyst development for the AAEM fuel cell is required to match performance and cost of the current PEM fuel cell technology. 

The emergence of commercial fuel cell cars will depend on developments in membrane technology, which are about one third of the fuel cell cost. Improvements are desired in fuel crossover from one side of a membrane to the other, the chemical and mechanical stability of the membrane, undesirable side reactions, contamination from fuel impurities and overall costs. 

Uranous nitrate [U(N03)4] solution is used for the quantitative reduction of plutonium from loaded tributyl phosphate (TBP) phase [8]. Membrane cell technology was investigated for the production of 100% uranous nitrate solution [9], which is to be used in the partition cycle of the PUREX process in the fuel reprocessing plant. The membranes used hitherto have suffered from mechanical instability. A study was carried out at the BARC to obtain 100% uranous nitrate solution using a membrane-based electrolytic cell. The membrane used in this study was a thin polymer film reinforced with a Teflon fabric. The film was used as a separator between the anolyte and catholyte chambers, which are made of perfluorinated polymers, thus offering high thermal and chemical stability. 

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