Membrane electrode assembly design

Since the membrane in the middle of the MEA expands and contracts with the change of temperature and hydration level, it is important to control the MEA thickness to avoid possible physical failure. As mentioned in the GDL design section, this is usually achieved by proper control of the compression force. Other methods to control the MEA thickness after compression include using proper seal (Steck et al., 1995 Barton et al., 2000 Bonk et al., 2002), bonded layer (Schmid et al., 2000), plastic spaces (Kelland et al., 1992), and metal shims (Jiao et al., 2010). These methods aU provide physical supports against the compression between bipolar plates to optimize the compression level of the GDL. 

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The development of commercially viable proton exchange membrane (PEM) fuel cell systems powered by hydrogen or hydrogen-rich reformate faces a significant number of materials and MEA (membrane electrode assembly) design-related performance and durability challenges, which need to be addressed via ... 

In the design of membrane-type fuel cell stacks (batteries), membrane-electrode assemblies (MEAs) are used, which consist of a sheet of membrane and of the two electrodes (positive and negative) pressed onto it from either side. 

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. 

The main advantage of the GDE technique is that the electrode structure is similar to the fuel cell membrane electrode assembly. Therefore, the obtained results may be closer to those tested in a real fuel cell. However, the GDE technique is still rarely used in fuel cell studies due to the complicated design of the electrochemical cell, as well as the instability and poor-repeatability of the results. Furthermore, prior to the electrochemical measurements, the GDE needs to... 

The theoretical power density of a DMFC at 0.5 V is about 1600 Wh per kg of methanol fuel, but in practice, small DMFCs for portable applications have achieved much less. If small DMFCs are designed like conventional PEM cells, including a membrane-electrode assembly (MEA), two gas diffusion layers, fuel and air channels with forced flows and current collectors, they may achieve power densities of about 0.015-0.050 W cm at temperatures in the range of 23-60°C (Lu et al., 2004), consistent with the value found at 85°C in Fig. 3.53. 

Figure 3.54. Direct methanol fuel cell designed for passive operation (no forced flows), with two membrane-electrode assemblies MEA) and a central fuel container.

The fuel cell is basically a two-scale system. The small and large scales are determined, respectively, by membrane-electrode assembly (MEA) thickness and by the length of the feed channel. The Q3D model is designed to investigate the interplay of small- and large-scale processes in PEFC/DMFC, so that the fully 3D model of the cell is split into a model of a cell cross section (internal model) and a model of the flow in the channel (channel model). The two models are coupled via the local current density along the channel and the overall Q3D solution is obtained by iterations. 

The PEM cell design chosen for tlie current work employs a significantly different geometry than the Westinghouse cell. The PEM electrolyzer consists of a membrane electrode assembly (MEA) inserted between two flow fields. Behind each flow field is a back plate, copper current collector and stainless steel end plates. The MEA consists of a Nafion proton-exchange-membrane with catalyst-coated gas diffusion electrodes bonded on either side. 

Membrane electrode assemblies (MEAs) are typically five-layer structures, as shown in Figure 10.1. The membrane is located in the center of the assembly and is sandwiched by two catalyst layers. The membrane thickness can be from 25 to 50 pm and, as mentioned in Chapter 10, made of perfluorosulfonic acid (Figure 11.3). The catalyst-coated membranes are platinum on a carbon matrix that is approximately 0.4 mg of platinum per square centimeter the catalyst layer can be as thick as 25 pm [12], The carbon/graphite gas diffusion layers are around 300 pm. Opportunities exist for chemists to improve the design of the gas diffusion layer (GDF) as well as the membrane materials. The gas diffusion layer s ability to control its hydrophobic and hydrophilic characteristics is controlled by chemically treating the material. Typically, these GDFs are made by paper processing techniques [12],... 

Design and demonstrate a reformate-capable fuel cell stack, utilizing CO-tolerant membrane electrode assemblies (MEAs) and low cost bipolar collector plates. 

Design and optimize membrane-electrode assemblies (MEAs) to enhance cell performance. 

The Jet Propulsion Laboratory (JPL) has researched the stated objectives by investigating sputter-deposition (SD) of designed anode and cathode nanostructures of Pt-alloys, and electronic structures and microstructures of sputter-deposited catalyst layers. JPL has used the information derived from these investigations to develop novel catalysts and membrane electrode assemblies (MEAs) that... 

There are multiple transport and reaction steps in a fuel cell. Many of these reaction and transport processes are discussed in other chapters. PEM fuel cell designs have been heuristically derived to achieve high power output. Many proprietary methods of membrane-electrode assemblies have been developed, as well as complex structures of the flow fields, to provide the... 

We describe here an experimental approach to design PEM fuel cell reactors where the complexities of macroscopic design parameters are chosen to obtain data in the least ambiguous form, not to optimize the overall power output. The fuel cell designs presented here can be used with virtually any membrane-electrode assembly these are fuel cell test stations. The fuel cell reactors described here can be thought of as building blocks for more complex fuel cells designs. 

Supply the water required for the methanol oxidation in the anode by transporting water from the cathode, so that the fuel cell can be operated with pure methanol and with minimum flooding at the cathode. This can be achieved by innovation in the design of the membrane electrode assembly. 

Small milliliter-scale fuel cells are mostly used with a membrane electrode assembly (MEA), which means that the conductive electrode material is coated on a membrane. This has led to a one-chamber design that contains the anode compartment. The cathode electrode is open to the air [47, 48]. 

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