Supported Metals for Application in

Sergio Rojas, Marfa Victoria Martfnez-Huerta and M.A. Pena 

Instituto de Catdlisis y Petroleoquimica, CSIC, C/Marie Curie, Cantoblanco, 28049 Madrid, Spain 

An FC is an electrochemical device that allows the transformation of the chemical energy of a fuel directly into electrical energy. 

Since the working conditions (temperature and electrolyte environment) are very different depending on the type of FC, the used materials are very also varied. One of these materials is the electrocatalyst that is used in the electrodes, anode and cathode. A catalyst is necessary in the surface of the electrode for an efficient rate of the electrochemical half-reactions of oxidation and reduction occurring in anode and cathode. From the different types of FCs, PEMFCs have been intensely studied during the last years, and they are the clearest candidates for transportation and portable applications. The catalyst used in the electrodes of this family of 

FCs is a supported metal catalyst. Throughout this chapter, the different electrocatalysts that are used in PEMFCs will be described. We will see that PEMFC electrocatalysts are supported metals of high loading, usually higher than 30 wt%, but they should maintain a high metal dispersion, with a metal particles size typically below 4 nm and an active surface area (ASA) for the metal in the range of 70-120 We will see that, depending on the electrode and 

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Rojas, S., Martinez-Huerta, M.V Pena, M.A. Supported metals for application in fuel-cells. In J.A. Anderson and M. Fernandez Garcia (eds) Supported metals in catalysis. Imperial College Press, London, UK, 2012, pp. 407 91. 

An important question frequently raised in electrochemical promotion studies is the following How thick can a porous metal-electrode deposited on a solid electrolyte be in order to maintain the electrochemical promotion (NEMCA) effect The same type of analysis is applicable regarding the size of nanoparticle catalysts supported on commercial supports such as Zr02, Ti02, YSZ, Ce02 and doped Zr02 or Ti02. What is the maximum allowable size of supported metal catalyst nanoparticles in order for the above NEMCA-type metal-support interaction mechanism to be fully operative ... 

Although hydrotalcites are relahvely stable (up to circa 500 °C), they are also of potential applicahon as precursors of mixed metal oxide catalysts, for example Reference [66]. Dehydrahon-rehydration equilibria account for the switching between hydrotalcites and mixed/supported metal oxides, which is somehmes termed the memory effect [67-69]. Recent advances have seen attempts to prepare highly dispersed LDH systems, such as those dispersed within mesoporous carbon [70]. Owing to widespread interest in their application, hydrotalcite catalysts have been the subject of a number of reviews, for example References [71-75]. Other layered-based systems have also attracted attention for application in catalysis, for example Reference [76]. 

The insertion of catalytically active guests, such as transition metal ions, is an example of the potentialities of zeolite membranes for applications in catalytic membrane reactors. The well-known catalytic properties of supported vanadium oxides for selective oxidations have recently prompted a number of studies on the possibility of inserting vanadium in the framework of crystalline microporous silica and aluminosilicate powders. " ... 

Lambert reviews the role of alkali additives on metal films and nanoparticles in electrochemical and chemical behavior modihcations. Metal-support interactions is the subject of the chapter by Arico and coauthors for applications in low temperature fuel cell electrocatalysts, and Haruta and Tsubota look at the structure and size effect of supported noble metal catalysts in low temperature CO oxidation. Promotion of catalytic activity and the importance of spillover are discussed by Vayenas and coworkers in a very interesting chapter, followed by Verykios s examination of support effects and catalytic performance of nanoparticles. In situ infrared spectroscopy studies of platinum group metals at the electrode-electrolyte interface are reviewed by Sun. Watanabe discusses the design of electrocatalysts for fuel cells, and Coq and Figueras address the question of particle size and support effects on catalytic properties of metallic and bimetallic catalysts. 

The work was supported by the Ministry of Science and Technological Development of the Republic of Serbia under the research projects Deposition of ultrafine powders of metals and alloys and nanostructured surfaces by electrochemical techniques (No. 142032G) and Modification of metal and nonmetal materials by electroconductive polymer for application in new technologies (No. 142044). 

Carbon is inert in nature and bears a high surface area making it highly suitable as a support for catalysts. The surface characteristics and porosity of carbon could be easily tailored for different applications. Acid treatment is often applied to modify the surface chemistry of carbon for specific applications. Typically, active metal species are immobilized on carbon for application in catalysis. 

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