Cell catalyst characteristics

Transport properties of hydrated PFSA membranes strongly depend on nanophase-segregated morphology, water content, and state of water. In an operational fuel cell, these characteristics are indirectly determined by the humidity level of the reactant streams and Faradaic current densities generated in electrodes, as well as the transport properhes of catalyst layers, gas diffusion layers, and flow... 

The performance of a catalyst for a certain application depends on a number of important parameters. As noted earlier, the characteristics of the catalyst support chosen has a strong influence. Additionally, some other key factors coming from the preparation process determine the final performance, especially selectivity and activity. Those factors are the precious metal loading, the metal distribution of the precious metal crystallites, the size of the crystallites and their spatial distribution, the oxidation state of the metal, and the addition of modifiers. The mefal loading of a cafalysf is typically in the range 1 to 20% for precious metal powder catalysts. A fuel cell catalyst can have metal loadings of up to 60%. This parameter can easily be adjusted by the amount of precious metal used during catalyst preparation. 

From a practical standpoint, the two most important characteristics of an immobilized cell catalyst are its activity and its operational stability. The latter parameter is usually expressed in catalyst half-life. The amount of activity, say in International Units (I.U.), would be a function of cell-to-carrier ratio. As mentioned earlier, a 50% loading ratio has been found to be optimal. 

Antolini E, Gonzalez ER (2011) Effect of synthesis method and stmctural characteristics of Pt-Sn fuel cell catalysts rai the electro-oxidatirai of CH3OH and CH3CH2OH in acid medium. 

Anode Catalysts for Alkaline Direct Alcohol Fuel Cells and Characteristics of the Catalyst Layer... 

Table 4.3. Effect of three-dimensional support on the PtRu catalyst characteristics produced by galvanostatic elechodeposition from a colloidal media containing 25 vol% Triton X-lOOhsopropanol (1 4 v/v ratio) and 75 vol% aqueous phase (with 2.5x10 M H2PtCl6 and (NH4)2RuCl6 each). Deposition current density 20 A m, 120 min, 341 K [218]. RVC = reticulated viheous carbon, UGF = graphite felt (uncompressed). (With kind permission from Springer Science+Business Media Journal of Apphed Electrochemistry, Direct methanol fuel cells with reticulated vitreous carbon, uncompressed graphite felt and Ti mesh anodes, 38, 2008, 51-62, Cheng T, Gyenge E, table 3.)...

Figure 4.65. Performance comparison of DMFC equipped with extended reaction zone anode composed of pressed graphite felt with PtRu and PtRuMo, obtained by electrodeposition from a colloidal solution [86, 250], a) 333 K, b) 343, and 353 K. Anode catalyst characteristics are given in Table 4.4. Anolyte 1 M CH3OH - 0.5 M H2SO4, 5 mL min, ambient pressure. Cathode 4 mg cm Pt black, O2 flow rate 500 nil min at 2 atm (abs). [86]. (Reprinted from Journal of Power Sources, 167(2), Bauer A, Gyenge EL, Oloman CW, Direct methanol fuel cell with extended reaction zone anode PtRu and PtRuMo supported on graphite felt, 281-7, 2007, with permission from Elsevier.)...

XRF, XRE, and PIXE are three related methods based upon similar principles. When a material is bombarded with high-energy X-rays or gamma rays, a secondary characteristic X-ray is then emitted. Currently, this characteristic X-ray is widely used for chemical analysis. For liiel cell catalysts, this is an ideal nondestructive method for analysing bulk composition, instead of traditional wet chemical methods and their automated successors like atomic absorption and atomic emission spectroscopy. 

Xiao, Y, Dou, M., Yuan, J., Hou, M., Song, W. Sunden, B. Fabrication process simulation of a PEM fuel cell catalyst layer and its microscopic structure characteristics. J. Electrochem. Soc. 159 (2012), B308-B314. 

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