The Polymer Electrolyte Membrane PEM

The worst aspect of the Nation membrane is its high cost Massive R D efforts have been going on for years to develop low cost cation-selective membranes having a performance comparable to that of Nation, at a much lower price. This is a critical issue, because the commercial success or failure of the direct methanol fuel cell hinges on our ability to develop such membranes at (1-2)% of their present cost 

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Under normal operation of an H2/O2 fuel cell, anodic oxidation of IT2 (or other hydrocarbons or alcoholic fuels)—that is, H2 —> 2H+ -1- 2e —produces protons that move through the polymer electrolyte membrane (PEM) to the cathode, where reduction of O2 (i.e., O2 -1- 2H+ -1- 2e —> H2O) produces water. The overall redox process is H2 -1-O2 —> H2O. The electronically insulating PEM forces electrons produced at the anode through an external electric circuit to the cathode to perform work in stationary power units, drive trains... 

A fuel cell that has desirable features for transportation and portable power is the polymer electrolyte membrane (PEM) system. The core of this technology is a polymer membrane that conducts... 

Polymer electrolyte fuel cell (PEFC) is considered as one of the most promising power sources for futurist s hydrogen economy. As shown in Fig. 1, operation of a Nation-based PEFC is dictated by transport processes and electrochemical reactions at cat-alyst/polymer electrolyte interfaces and transport processes in the polymer electrolyte membrane (PEM), in the catalyst layers consisting of precious metal (Pt or Ru) catalysts on porous carbon support and polymer electrolyte clusters, in gas diffusion layers (GDLs), and in flow channels. Specifically, oxidants, fuel, and reaction products flow in channels of millimeter scale and diffuse in GDL with a structure of micrometer scale. Nation, a sulfonic acid tetrafluorethy-lene copolymer and the most commonly used polymer electrolyte, consists of nanoscale hydrophobic domains and proton conducting hydrophilic domains with a scale of 2-5 nm. The diffusivities of the reactants (02, H2, and methanol) and reaction products (water and C02) in Nation and proton conductivity of Nation strongly depend on the nanostructures and their responses to the presence of water. Polymer electrolyte clusters in the catalyst layers also play a critical... 

In Figure 1 the circuit of functional units traditional oxygen-hydrogen FC with clamping contacts)) is shown. Symmetrically on both sides of the polymer electrolyte membrane (PEM) (a position 1) the units included in anode and cathode electrodes are represented (positions 2-5, for simplicity units are numbered only on the one hand). 

The polymer electrolyte membrane (PEM) electrolysis operates at temperatures of 30-100 °C. The electrodes have platinum as a catalyst. A few industrial companies undertake strong efforts to develop this kind of electrolysis. To date, the efficiency of alkaline electrolysis has not been reached. It is expected that PEM electrolysis is suitable to build plants for small power units as well. 

Polymers are nsed in fnel cells. Those of particular interest are the polymer electrolyte membrane (PEM) and the phosphoric acid fuel cell (PAFC) designs. The latter design contains the liquid phosphoric acid in a Teflon bonded silicon carbide matrix. In March 2005 Ticona reported that it had bnilt the first fnel cell prototype made solely with engineering thermoplastics. They claimed that this approach rednced the cost of the fuel by at least 50% when compared with fuel cells fabricated from other materials. The 17-cell unit contains injection moulded bipolar plates of Vectra liquid crystal polymer and end plates of Fortron polyphenylene sulfide (PPS). These two materials remain dimensionally stable at temperatures up to 200 "C. The Vectra LCP bipolar plates contain 85% powdered carbon and are made in a cycle time of 30 seconds. 

If we only focus on the operation of membrane electrode assemblies (MEAs), E mainly includes irreversible voltage losses due to proton conduction in the polymer electrolyte membrane (PEM) and voltage losses due to transport and electrocatalytic activation of ORR in CCLs,... 

Fuel cells are currently at the early commercial stage for some applications. There are increasing numbers of units deployed in field trials for an increasing number of applicahons. The polymer electrolyte membrane (PEM) fuel cell is one of the most common types of fuel cells under development today. (They also are commonly referred to as proton exchange membrane fuel cells based on the key characteristic of the solid electrolyte membrane to transfer protons from the anode to the cathode.) With the experience gained through... 

Finally we come to the fuel cell itself. In addition to the original Grove fuel ceU and the alkaline and phosphoric acid fuel cells used in space technology, other types of ceU include the molten carbonate fuel ceU (with a molten Li2C03/Na2C03 electrol 4e), the soUd oxide fuel ceU (containing a sohd metal oxide electrol 4e) and the polymer electrolyte membrane (PEM) fuel cell. Both the molten carbonate and soUd oxide fuel cells... 

Direct methanol fuel cells (DMFCs) employ a polymer membrane as an electrolyte. The system is a variant of the polymer electrolyte membrane (PEM) cell however, the catalyst on the DMFC anode draws hydrogen from liquid methanol. This action eliminates the need for a fuel reformer and allows pure methanol to be used as a fuel. 

The electromotive force is maintained by keeping electrode compartments on anode and cathode sides of the polymer electrolyte membrane (PEM) at different chemical compositions. One electrode, the anode, is supplied with a fuel while the other electrode, the cathode, is supplied with an oxidant. Unless otherwise stated, this book assumes operation with hydrogen as the fuel and oxygen (air) as the oxidant. 

The polymer electrolyte membrane (PEM) is the heart of the polymer electrolyte fuel cell (PEFC). It separates the partial redox reactions at anode and cathode and, thereby, enables the fuel cell principle. 

A key element of the automotive fuel cell membrane electrode assembly is the proton exchange membrane (PEM), also referred to as the polymer electrolyte membrane (PEM), which is composed of a thermoplastic elastomer coated with a platinum catalyst. U.S. car-makers expect to have fuel cell-powered cars on the market by 2004. Polymer selection depends on, among other criteria, fuel selection such as Direct Methanol Fuel Cell (DMFC) or Direct Hydrogen Fuel Cell (DHFC). One prototype fuel cell vehicle is the product of the Partnership for a New Generation of Vehicles (PNGV), comprising U.S. automotive companies and the U.S. Department of Energy (DOE). ... 

Interfacial failure during DMFC operation seems to be closely related to water swelling of the ionomer. Typically, the dimensional change of the polymer electrolyte membrane (PEM) under hydration is greater than that of the electrode. As a result, mechanical stress at the membrane-electrode interface is likely to initiate local delamination, which then expands further over the time of DMFC operation. Good correlation between membrane water uptake and the gain in cell resistance was demonstrated (Kim and Pivovar 2005). 

K. Kordesch and M. Cifrain, A Comparison Between the Alkaline Fuel Cell (AFC) and the Polymer Electrolyte Membrane (PEM) Fuel CeU, in Handbook of Fuel Cells—Fundamentals, Technology and Applications, Vol. 4, W. Vielstich, A. Lamm, and H. A. Gasteiger, Eds., WUey, New York, 2003, pp. 789-793. 

It is well known that polyimides (Pis) are a class of thermally stable polymers that are related to their stiff aromatic backbones. In the past decades. Pis have been extensively studied owing to both scientific and industrial interests. In membrane-based technologies, PI membranes have been used for a long time for a wide variety of applications due to their excellent thermal stability, high mechanical strength and modulus, good film forming ability, and superior chemical resistance [1]. These merits are just what are required for the polymer electrolyte membrane (PEM) materials employed in fuel cell systems. 

In PEM fuel cells, the polymer electrolyte membrane (PEM) serves as a barrier to prevent the fuel and oxidizer from mixing without generating electricity. Ideally, electrons and protons from a fuel are liberated at a catalyst-coated anode and travel via separate routes to a cathode where they react with an oxidizer. Protons migrate through an electrolyte medium—the membrane—while electrons travel through an external circuit to provide electrical power. 

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