Membrane electrode assembly evaluation

These selection and evaluation criteria were applied systematically to four technological fields, three of which contribute to new energy-efficient solutions. Passive houses, for example, with their major components of insulation solutions, window systems, ventilation and control techniques are close to market diffusion within the next ten years. Fuel cells for mobile uses in vehicles, however, are still a long way from market introduction, for instance, because of unresolved problems regarding the deactivation of the membrane electrode assembly (MEA) and the need for cost reductions by about one order of magnitude. Other types of fuel cells for stationary uses may be closer to market introduction, owing to less severe technical bottlenecks and better economic competitiveness. 

The main activities for the remaining part of this program will focus on optimization of the promising membrane-electrode assembly, scale-up to nominal 300 cm and validation in single cells followed by short stack evaluation. The program is scheduled to be completed in February 2003. 

Evaluate new membrane electrode assembly (MEA) fabrication protocols to enhance catalyst utilization and overall fuel cell efficiency. 

Electrodes were fabricated with catalyst layers containing platinum-ruthenium alloys and platinum-ruthenium oxide. Membrane electrode assemblies were fabricated with such cells, and the performance was evaluated in a full cell configuration. Although ruthenium oxide is a proton conductor and is expected to enhance the rate of proton transport from the interface during methanol oxidation, no noticeable improvement in activity of the catalyst layer was observed by addition of ruthenium oxide. The role of other metal oxides such as tungsten oxide will be investigated next year, along with evaluation of non-noble metal catalysts based on nickel, titanium, and zirconium. 

Solutions of DMM, TMM and methanol were evaluated in single cells and a 5-cell stack supplied by Giner, Inc. The cells were operated at temperatures ranging from 25 °C to 90 °C and were heated at the ceil block and the anode fuel reservoir, which was equipped with a condenser to prevent evaporation but allow CO2 rejection from the system. In the present study, the membrane electrode assembly (manufactured by Giner Inc.) consisted of electrocatalytic Pt-Ru (50/50 atom %) and R fine metal powders (surface area 30-70 m /g) bonded to either side of a Nafion -117 polymer electrolyte membrane. The... 

Recent intensive studies have, however, been reported to lead to AEMs with high ionic conductivities, reportedly comparable to Nalion . These promising AEMs [11, 45-51] are still to be evaluated in AMFCs. Most hydrocarbon AEMs are soluble in various solvents, which is potentially useful for the formulation of alkaline ionomers required for the preparation of high-performance membrane electrode assemblies (MEAs). If the conductive properties reported can be translated into high power outputs, then AMEC performances comparable to those of PEMFCs can be expected in the near future. 

The molecular weight of PBI strongly influences the membrane properties and the lifetime of the membrane electrode assembly (MEA), as shown by Yang et al. [1]. Due to the poor solubility of PBI in common solvents such as tetrahydrofurane (THF) or acetonitrile, the most common method to evaluate the molecular weight of PBI is to measure the viscosity dissolved in 96 % sulfuric acid. Care needs to be taken not to heat sulfuric acid-based PBI solutions and not to store them for a long time, to avoid possible side reactions like suUbnation or cross-linking. Also, viscosity depends on temperature, and a strict control of the temperature is necessary. Impurities like dust should be removed by filtration. 

Aromatic polyimides (Genies et al., 2001, 2001a, Guo et al., 2002, Besse et al., 2002) show high levels of conductivity, but the hydrolytic stability is reported to be very sensitive to the chemical structure of the polyimide main-chain. A membrane-electrode assembly based on a sulfonated polyimide evaluated in a fuel cell at 70-80°C, was found to have a performance similar to Nation. 

Therefore, another type of planar glucose biosensor with Pt electrodes on a sihcon substrate has therefore been developed for in vivo measurements [61]. The enzyme glucose oxidase was immobilized by the well known GDA-BSA method and the whole sensor was covered subsequently by a polyurethane membrane. This sihcon chip has to be sawed and assembled on a flexible carrier for in vivo application, the assembled catheter was successfully evaluated in rats [79]. This sensor gives encouraging results in aqueous solutions and subcutaneous apphcations. Drawbacks of this include the complicated mounting and assembling procedures which are difficult and cumbersome. 

A half-cell is often used to evaluate an electrode. Figure 11.3 illustrates the structure of a half-cell. An electrode is bonded onto one side of a piece of Nafion membrane and the resulting assembly is placed in a fixture in such a way that the Nafion membrane faces the electrolyte solution and the electrode backing side faces a gas chamber. Since the Nafion membrane is permselective, it allows only cations such as protons to pass through. Anions such as S04 should not be able to... 

Middelman E (2002) Improved PEM fuel cell electrodes by controlled self-assembly. Fuel Cells Bulletin, November 2002, pp. 9-12 Miyake N, Wainright J S, Savinell R F (2001) Evaluation of a sol-gel derived NaEon silica hybrid membrane for proton electrolyte membrane fuel cell applications-I. Proton conductivity and water content. J... 

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