Electrodes proton exchange membrane

Proton exchange membrane fuel cells, also called polymer electrolyte fuel cell or solid polymer electrolyte fuel cells, use a proton exchange membrane, which acts as a solid electrolyte between the anode and cathode electrodes. Proton exchange membrane fuel cells are favored for use in automobiles, residential power as well as in portable devices such as laptops and cell phones. These fuel cells utilize hydrogen gas and air or oxygen to produce power. 

These main objectives can be reached only by modifying the structures and compositions of primarily the anode (methanol electrode) and secondarily the cathode (oxygen electrode) as discussed in Sections 111 and IV, respectively. In addition. Section IV discusses the conception of new proton exchange membranes with lower methanol permeability in order to improve the cathode characteristics. Section V deals with the progress in the development of DMFCs, while in Section VI the authors attempt to make a prognosis on the status of DMFC R D and its potential applications. 

Finally, a simple method for a rapid evaluation of the activity of high surface area electrocatalysts is to observe the electrocatalytic response of a dispersion of carbon-supported catalyst in a thin layer of a recast proton exchange membrane.This type of electrode can be easily obtained from a solution of Nafion. As an example. Fig. 11 gives the comparative... 

In this section, we summarize the kinetic behavior of the oxygen reduction reaction (ORR), mainly on platinum electrodes since this metal is the most active electrocatalyst for this reaction in an acidic medium. The discussion will, however, be restricted to the characteristics of this reaction in DMFCs because of the possible presence in the cathode compartment of methanol, which can cross over the proton exchange membrane. 

Following a period of slack, decisive improvements were made after 1990 in the area of PEMFCs. Modem models now achieve specific powers of over 600 to 800 mW/cm while using less than 0.4 mg/cm of platinum catalysts and offering a service fife of several tens of thousands of hours. These advances were basically attained by the combination of two factors (1) using new proton-exchange membranes of the Nafion type, and (2) developing ways toward much more efficient utilization of the platinum catalysts in the electrodes. 

In PEMFCs, the membrane electrode assembly (MEA, Eig. 15.2a) is a multilayer sandwich composed of catalytic layers (CLs) where electrochemical reactions take place, gas-diffusion media providing access of gases to the CLs, and a proton exchange membrane (PEM) such as Nafion . The CL is a multiphase multicomponent medium comprising ... 

Figure 15.2 Schematic representation of different electrochemical cell types used in studies of electrocatalytic reactions (a) proton exchange membrane single cell, comprising a membrane electrode assembly (b) electrochemical cell with a gas diffusion electrode (c) electrochemical cell with a thin-layer working electrode (d) electrochemical cell with a model nonporous electrode. CE, counter-electrode RE, reference electrode WE, working electrode.

Most automotive fuel cells use a thin, fluorocarbon-based polymer to separate the electrodes. This is the proton exchange membrane (PEM) that gives this type of fuel cell its name. The polymer provides the electrolyte for charge transport as well as the physical barrier to block the mixing... 

Hsieh, C.-T., Y.-Y. Liu, and A.K. Roy, Pulse etectrodeposited Pd nanoclusters on graphene-based electrodes for proton exchange membrane fuel cells. Electrochimica Acta, 2012. 64(0) p. 205-210. 

Another application of carbon and carbon hybrids is their use as electrode material in proton exchange membrane (PEM) electrochemical flow reactor for the production of hydrogen peroxide (H202). 

Protoadamantene, isomerization of, 25 146,147 Proton exchange membrane, gas diffusion electrodes, 40 142-144... 

T. Ralph, G. Hards, J. Keating, S. Campbell, D. Wilkinson, M. Davis, J. St. Pierre, M. Johnson, "Low Cost Electrodes for Proton Exchange Membrane Fuel Cells Performance in Single Cells and Ballard Stacks," J. Electrochemical Society, Volume 144, No. 11, November 1997. 

J. Srmivason, et al., "High Energy Efficiency and High Power Density Proton Exchange Membrane Fuel Cells - Electrode Kinetics and Mass Transport," Journal of Power Sources, p. 36, 1991. 

Figure 2.1 shows a schematic structure of the fuel cell membrane electrode assembly (MEA), including both anode and cathode sides. Each side includes a catalyst layer and a gas diffusion layer. Between the two sides is a proton exchange membrane (PEM) conducting protons from the anode to the cathode. 

There are two main types of thin-film catalyst layers catalyst-coated gas diffusion electrode (CCGDL), in which the CL is directly coated on a gas diffusion layer or microporous layer, and catalyst-coated membrane, in which the CL is directly coated on the proton exchange membrane. In the following sections, these catalyst layers will be further classified according to their composition and structure. 

Wang, C., Waje, M., Wang, X., Tang, J. M., Haddon, R. C., and Yan, Y. Proton exchange membrane fuel cells with carbon nanotube based electrodes. Nano Letters 2004 4 345-348. 

Saha, M. S., Li, R., Cai, M., and Sun, X. Nano wire-based three-dimensional hierarchical core/shell heterostructured electrodes for high-performance proton exchange membrane fuel cells. Journal of Power Sources 2008 185 1079-1085. 

Sasikumar, G., Ihm, J. W, and Ryu, H. Dependence of optimum Nation content in catalyst layer on platinum loading. Journal of Power Sources 2004 132 11-17. Taylor, E. J., Anderson, E. B., and Vilambi, N. R. K. Preparation of high-plat-inum-utilization gas diffusion electrodes for proton-exchange-membrane fuel cells. Journal of the Electrochemical Society 1992 139 L45-L46. 

Kim, C. S., Ghun, Y. G., Peck, D. H., and Shin, D. R. A novel process to fabricate membrane electrode assemblies for proton exchange membrane fuel cells. International Journal of Hydrogen Energy 1998 23 1045-1048. 

Hirano, S., Kim, J., and Srinivasan, S. High-performance proton exchange membrane fuel cells with sputter-deposited Pt layer electrodes. Electrochimica Acta 1997 42 1587-1593. 

Cha, S. Y., and Lee, W. M. Performance of proton exchange membrane fuel cell electrodes prepared by direct deposition of ultrathin platinum on the membrane surface. Journal of the Electrochemical Society 1999 146 4055 060. 

Nakakubo, T., Shibata, M., and Yasuda, K. Membrane electrode assembly for proton exchange membrane fuel cells prepared by sputter deposition in air and transfer method. Journal of the Electrochemical Society 2005 152 A2316-A2322. 

Kadjo, A. J. J., Brault, R, Caillard, A., Coutanceau, C., Gamier, J. R, and Martemianov, S. Improvement of proton exchange membrane fuel cell electrical performance by optimization of operating parameters and electrodes preparation. Journal of Power Sources 2007 172 613-622. 

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. R. Ralph, G. A. Hards, J. E. Keating, et al. Low cost electrodes for proton exchange membrane fuel cells. Journal of the Electrochemical Society 144 (1997) 3845-3857. 

K. F. Ghiu and K. W. Wang. Hydrophobic coatings on carbon electrodes for proton exchange membrane fuel cells. Surface and Coatings Technology 202 (2007) 1231-1235. 

W. He, G. Lin, and T. V. Nguyen. Diagnostic tool to detect electrode flooding in proton-exchange-membrane fuel cells. AIChE Journal 49 (2003) 3221-3228. 

New membrane materials for PEM fuel cells must be fabricated into a well-bonded, robust membrane electrode assembly (MEA) as depicted in Figure 1. In addition to the material requirements of the proton exchange membrane itself as outlined above, the ease of membrane electrode assembly fabrication and the resulting properties of the MEA are also... 

Like many other fluoropolymers, Nafion is quite resistant to chemical attack, but the presence of its strong perfluorosulfonic acid groups imparts many of its desirable properties as a proton exchange membrane. Fine dispersions (sometimes incorrectly called solutions) can be generated with alcohol/water treatments. Such dispersions are often critical for the generation of the catalyst electrode structure and the MEAs. Films prepared by simply drying these dispersions are often called recast Nafion, and it is often not realized that its morphology and physical behavior are much different from those of the extruded, more crystalline form. 

The principles of the fuel cell are illustrated in Figure 1.1. The electrochemical cell consists of two electrodes, an anode and a cathode, which are electron conductors, separated by an electrolyte [e.g. a proton exchange membrane (PEM) in a PEMFC or in a DAFC], which is an ion conductor (as the result of proton migration and diffusion inside the PEM). An elementary electrochemical cell converts directly the chemical... 

In addition, in a DAFC, the proton exchange membrane is not completely alcohol tight, so that some alcohol leakage to the cathodic compartment will lead to a mixed potential with the oxygen electrode. This mixed potential will decrease further the cell voltage by about 0.1-0.2 V. It turns out that new electrocatalysts insensitive to the presence of alcohols are needed for the DAFC. 

In PEMFCs working at low temperatures (20-90 °C), several problems need to be solved before the technological development of fuel cell stacks for different applications. This concerns the properties of the components of the elementary cell, that is, the proton exchange membrane, the electrode (anode and cathode) catalysts, the membrane-electrode assemblies and the bipolar plates [19, 20]. This also concerns the overall system vdth its control and management equipment (circulation of reactants and water, heat exhaust, membrane humidification, etc.). 

An additional problem arises from ethanol crossover through the proton exchange membrane. It results that the platinum cathode experiences a mixed potential, since both the oxygen reduction and ethanol oxidation take place at the same electrode. The cathode potential is therefore lower, leading to a decrease in the cell voltage and a further decrease in the voltage efficiency. 

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