Membrane and electrode assembly

Staudt, R. and J. Boyer, Development of polybenzimidazole-based, high temperature membrane and electrode assemblies for stationary and automotive applications, U.S. DOE 2004 Annual Program Review Proceedings, Philadelphia, PA, May 2004. 

There is some question of whether higher utilization of the catalyst is needed even though new research has resulted in the loading being reduced to less than 1 mg/cm. Some researchers cite a need for higher utilization of catalysts, while others state that because only 10% of the cell materials cost is tied up in catalyst, it is better to concentrate on the design of an effective membrane and electrode assembly at this time (27). 

The membrane and electrode assembly used for the detection of oxides of nitrogen is similar to that used for CO detection, except that the sensing electrode is fabricated from a graphite Teflon mix. 

Figure 9. A 2.5 ft2 active area membrane and electrode assembly...

Previously, the common approach to fabricating membrane and electrode assemblies for proton exchange membrane fuel cells involves hot-pressing a mixture of platinum powder and polytetrafluoroethylene (PTFE) on both sides of a proton exchange membrane. This method has resulted in hydrogen-oxygen fuel cells capable of high power densities. 

W. G. Grot, G. Rajendran (E. 1. du Pont de Nemours and Company) Membranes containing inorganic fillers and membrane and electrode assemblies and electrochemical cells employing same. US Patent 5919583, July 1999. 

R. Staudt, Development of Polybenzimid-azole-based High-temperature Membrane and Electrode Assemblies for Stationary and Transportation Applications, DoE Hydrogen, Fuel Cells and Infrastructure Technologies, 2005, pp. 771-776. 

BASF Fuel Cells (formerly PEMEAS or Celanese Ventures) produces polybenzimidazole (PBI)-based high-temperature membrane and electrode assemblies sold under the brand name Celtec . These MEAs operate at temperatures between 120 °C and 180 °C. One of the distinct advantages of high-temperature PEMFCs is exhibited in their high tolerance toward fuel gas impurities, such as CO (up to 3%), H2S (up to 10 ppm), NH3, or methanol (up to several percent), compared to low-temperature PEMFCs. Additionally, waste heat can be effectively used and, therefore, the overall system efficiency is increased. 

The membrane and electrode assembly (MEA) is the heart of the PEMFC. Its structure and composition are of vital importance ... 

Staudt R (2005) Development of Polybenzimidazole-based High Temperature Membrane and Electrode Assemblies for Stationary and Automotive Applications, 2005 DOE Hydrogen, Fuel Cells Infrastructure Technologies. 

MEAs used in this study were prepared in the following procedure [5]. The diffusion backing layers for anode and cathode were a Teflon-treated (20 wt. %) carbon paper (Toray 090, E-Tek) of 0.29 mm thickness. A thin diffusion layer was formed on top of the backing layer by spreading Vulcan XC-72 (85 wt. %) with PTFE (15 wt. %) for both anode and cathode. After the diffusion layers were sintered at a temperature of 360 C for 15 min., the catalyst layer was then formed with Pl/Ru (4 mg/cm ) and Nafion (1 mg/cm ) for anode and with Pt (4 mg/cm ) and Nafion (1 mg/cm ) for cathode. The prepared electrodes were placed either side of a pretreated Nafion 115 membrane and the assembly was hot-pressed at 85 kg/cm for 3 min. at 135 C. 

Macrocyclic ionomers consisting of fullerenes containing grafted Nafion acidic termini, (11), were prepared by Wudl [2] and used in composites for conducting membranes. Rao [3], however, used Nafion directly in membranes in electrode assemblies in fuel cells. 

In practice, commercial pH meters employing a glass electrode and a reference electrode are used to make pH measurements. The E value (potential) of the glass electrode does not result from an oxidation-reduction reaction but rather from the transfer of H ions through a thin glass membrane. The electrode assembly is shown in Figure 3-3. 

Composite Ion exchange Membranes and Electrode Catalysts (MEA, Membrane Electrode Assembly), and Water Electrolysis... 

This introductory chapter provides a brief outline and history of the PEFC technology, and important requirements and aspects in the development of polymer membranes for fuel cells. To obtain materials that meet specific requirements, the relationship of composition/structure and the properties has to be estabUshed. For the preparation of the membrane electrode assembly, it is important to understand the interfacial properties between membrane and electrodes. 

Figure 2 Composition of a transfer sandwich with plate electrodes at the top and bottom. The polyacrylamide gel is placed onto the membrane, and the assembly is tightly compressed using ScotchBrite sponge pads to ensure ciose contact of the gei and membrane. The transfer sandwich is then submerged in a tank of buffer for electrophoretic transfer of proteins from the gel on the cathode side to the membrane on the anode side.

Vengatesan, S., Kim, H.J., Lee, S.Y., Gho, E., Ha, H.Y., Oh, I.H., Lim, T.H. 2007 Operation of a proton exchange membrane fuel cell under non-humidified conditions using a membrane-electrode assemblies with composite membrane and electrode. Journal of Power Sources, 167,325-329. 

In this chapter, the electrode construction of a high temperature (HT) polymer electrolyte membrane (PEM) electrode assembly (MEA) will be explained. The different functionalities of the electrode layers like the gas diffusion layer (GDL), the micro porous layer (MPL), and the... 

FIGURE 5.2 A scanning electron microphotograph of a MEA (left), and a PTL/MPL assembly (right). The thick membrane and electrodes in the MEA are typical of direct alcohol applications. The structural differences between the GDL and PTL are clearly visible on the right. (From Fraunhofer Institute for Solar Energy Systems. With permission.)... 

The concept of the reversed fuel cell, as shown schematically, consists of two parts. One is the already discussed direct oxidation fuel cell. The other consists of an electrochemical cell consisting of a membrane electrode assembly where the anode comprises Pt/C (or related) catalysts and the cathode, various metal catalysts on carbon. The membrane used is the new proton-conducting PEM-type membrane we developed, which minimizes crossover. 

To measure the e.m.f. the electrode system must be connected to a potentiometer or to an electronic voltmeter if the indicator electrode is a membrane electrode (e.g. a glass electrode), then a simple potentiometer is unsuitable and either a pH meter or a selective-ion meter must be employed the meter readings may give directly the varying pH (or pM) values as titration proceeds, or the meter may be used in the millivoltmeter mode, so that e.m.f. values are recorded. Used as a millivoltmeter, such meters can be used with almost any electrode assembly to record the results of many different types of potentiometric titrations, and in many cases the instruments have provision for connection to a recorder so that a continuous record of the titration results can be obtained, i.e. a titration curve is produced. 

This presentation reports some studies on the materials and catalysis for solid oxide fuel cell (SOFC) in the author s laboratory and tries to offer some thoughts on related problems. The basic materials of SOFC are cathode, electrolyte, and anode materials, which are composed to form the membrane-electrode assembly, which then forms the unit cell for test. The cathode material is most important in the sense that most polarization is within the cathode layer. The electrolyte membrane should be as thin as possible and also posses as high an oxygen-ion conductivity as possible. The anode material should be able to deal with the carbon deposition problem especially when methane is used as the fuel. 

The slurries of electro-catalysts were prepared by mixing together the catalysts and appropriate amount of 5wt % Nafion solution(Du Pont) including some kinds of dispersant[8]. The electrodes were made by spraying method with these well mixed inks. Two electrodes and Nafion 112 membrane were hot pressed with the condition of 50kgf/cm, 120°C for 3min to fabricate MEAs(Membrane Electrode Assembly). 

---