Membrane electrolyte assembly

Based on the literature survey, no membranes or MEAs reported so far can achieve all the above required goals. This research is directed at developing novel high-temperature, composite proton exchange membrane-electrolyte assemblies for PEMFC for building applications. 

The most important components in a fuel cell are the Membrane Electrolyte Assembly (MEA) and the bipolar plates. The MEA usually consists of an electrolyte membrane, which is coated with catalytically active platinum-electrodes and a gas diffusion layer of hydrophobic graphite. As the electrolyte membrane cation exchange polymers are used. A crucial break-through was reached here by the employment of fluoridated polymers. The market leader here is Nation developed by the company Dupont. 

The three components of the fuel cell, anode, cathode, and electrolyte form a membrane-electrolyte assembly, as, by analogy with polymer electrolyte fuel cells, one may regard the thin layer of solid electrolyte as a membrane. Any one of the three membrane-electrode assembly components can be selected as the entire fuel cell s support and made relatively thick (up to 2 mm) in order to provide mechanical stability. The other two components are then applied to this support in a different way as thin layers (tenths of a millimeter). Accordingly, one has anode-supported, electrolyte-supported, and cathode-supported fuel cells. Sometimes though an independent metal or ceramic substrate is used to which, then, the three functional layers are applied. 

Membrane electrolyte assembly (MEA) testing - degradation experiment... 

In this connection it can be noted that Guha et al. (2010) investigated the influence of carbon support morphology on the behavior of a PEMFC membrane electrolyte assembly. Platinum electrocatalyst particles were deposited on lower-surface-area fibrous (carbon nanofibers) and particulate (carbon blacks) supports. The performance was shown to be independent of the carbon support morphology. 

Higher dimension fuel cell models can be considered to study PEM fuel cell performance. As shown previously, two-dimensional models can be used to characterize fuel cell performance along the channel length (x-z plane) or across channels (y-z plane). In the y-z plane, the model can focus on the membrane electrolyte assemble, or include the effect of gas transport in the porous diffusion layer and gas channel. In the y-z plane, several channels can be considered in order to investigate the effects such as gas mixing between the chaimels occurring in the diffusion layer. A three-dimensional model can be used to consider all the aforementioned phenomena, but computational hmitations often limit the model s fidelity. The equations are the same as those in 1-D and 2-D models, but all the differential equations are applied in all three directions. Consequently, the boundary conditions must be applied for all three dimensions. 

Sol-gel techniques have been successfidly applied to form fuel cell components with enhanced microstructures for high-temperature fuel cells. The apphcations were recently extended to synthesis of hybrid electrolyte for PEMFC. Although die results look promising, the sol-gel processing needs further development to deposit micro-structured materials in a selective area such as the triple-phase boundary of a fuel cell. That is, in the case of PEMFC, the sol-gel techniques need to be expanded to form membrane-electrode-assembly with improved microstructures in addition to the synthesis of hybrid membranes to get higher fuel cell performance. 

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 function of the electrolyte membrane is to facilitate transport of protons from anode to cathode and to serve as an effective barrier to reactant crossover. The electrodes host the electrochemical reactions within the catalyst layer and provide electronic conductivity, and pathways for reactant supply to the catalyst and removal of products from the catalyst [96], The GDL is a carbon paper of 0.2 0.5 mm thickness that provides rigidity and support to the membrane electrode assembly (MEA). It incorporates hydrophobic material that facilitates the product water drainage and prevents... 

Bose, A. B., Shaik, R., and Mawdsley, J. Optimization of the performance of polymer electrolyte fuel cell membrane electrode assemblies Roles of curing parameters on the catalyst and ionomer structures and morphology. Journal of Power Sources 2008 182 61-65. 

Hoshi, N., Uematsu, N., Saito, H., Hattori, M., Aoyagi, T. and Ikeda, M. 2005. Membrane electrode assembly for polymer electrolyte fuel cell. US Patent 2005130006. 

Endo, E., Terasono, S. and Haidiyanto, W. 2004. Solid polymer electrolyte membrane and membrane electrode assembly for solid polymer fuel cell. Japan Patent 2004247155. 

Figure 4.1 shows a schematic of a typical polymer electrolyte membrane fuel cell (PEMFC). A typical membrane electrode assembly (MEA) consists of a proton exchange membrane that is in contact with a cathode catalyst layer (CL) on one side and an anode CL on the other side they are sandwiched together between two diffusion layers (DLs). These layers are usually treated (coated) with a hydrophobic agent such as polytetrafluoroethylene (PTFE) in order to improve the water removal within the DL and the fuel cell. It is also common to have a catalyst-backing layer or microporous layer (MPL) between the CL and DL. Usually, bipolar plates with flow field (FF) channels are located on each side of the MFA in order to transport reactants to the... 

T. Erey and M. Linardi. Effects of membrane electrode assembly preparation on the polymer electrolyte membrane fuel cell performance. Electrochimica Acta 50 (2004) 99-105. 

Collection of in situ XAS data using a single cell fuel cell avoids problems associated with bubble formation found in liquid electrolytes as well as questions regarding the influence of adsorption of ions from the supporting electrolyte. However, the in situ study of membrane electrode assemblies (MEAs) in a fuel cell environment using transmission... 

In earlier investigations by the authors (2,3) solid sulfonic acid resins containing polyarylether and cyano substituents, (II) and (III), respectively, were prepared and used as proton-conductive membranes, electrode electrolytes, electrode paste, and in membrane electrode assemblies. 

A.Z. Weber, M.A. Hickner, Modeling and high-resolution-imaging studies of water-content profiles in a polymer-electrolyte-fuel-cell membrane-electrode assembly. Electrochimica. Acta. 53, 7668—7674 (2008)... 

Membrane electrode assemblies (MEA) with AEM were prepared with a single-sided ELAT electrode (20% Pt on Vulcan XC-72 and 0.5 mg/cm2 Pt loading) on the cathode side and carbon only electrode on the anode side. The electrodes were assembled on both sides of a membrane without a press procedure and the assembly was sealed in the electrolytic cell. 

In the proton-emitting membrane or proton electrolyte membrane (PEM) design, the membrane electrode assembly consists of the anode and cathode, which are provided with a very thin layer of catalyst, bonded to either side of the proton exchange membrane. With the help of the catalyst, the H2 at the anode splits into a proton and an electron, while Oz enters at the cathode. On the inside of the porous anode is a thin platinum catalyst layer. When H2 reaches this layer, it separates into protons (H2 ions) and electrons. One of the reasons why the cost of fuel cells is still high is because the cost of the platinum catalyst is rising. One ounce of platinum cost 361 in 1999 and increased to 1,521 in 2007. 

Figure 3.15. Schematic representation of the correlation between fuel cell impedance and polarization curve. (Modified from [23], with kind permission from Springer Science+Business Media Journal of Applied Electrochemistry, Characterization of membrane electrode assemblies in polymer electrolyte fuel cells using a.c. impedance spectroscopy, 32(8), 2002, 859-63, Wagner N. Figure 4.)...

Wagner N (2002) Characterization of membrane electrode assemblies in polymer electrolyte fuel cells using a.c. impedance spectroscopy. J Appl Electrochem 32(8) 859-63... 

The MCFC membrane electrode assembly (MEA) comprises three layers a porous lithiated NiO cathode structure and a porous Ni/NiCr alloy anode structure, sandwiching an electrolyte matrix (see detail below). To a first approximation, the porous, p-type semiconductor, nickel oxide cathode structure is compatible with the air oxidant, and a good enough electrical conductor. The nickel anode structure, coated with a granular proprietary reform reaction catalyst, is compatible with natural gas fuel and reforming steam, and is an excellent electrical conductor. As usual, the oxygen is the actual cathode and the fuel the anode. Hence the phrase porous electrode structure . 

Figure 12.1 is a schematic view of a typical PEM fuel cell. A membrane electrode assembly (MEA) usually refers to a five-layer structure that includes an anode gas diffusion layer (GDL), an anode electrode layer, a membrane electrolyte, a cathode electrode layer, and a cathode GDL. Most recently, several MEA manufacturers started to include a set of membrane subgaskets as a part of their MEA packages. This is often referred to as a seven-layer MEA. In addition to acting as a gas and... 

---