Carbon support materials, for

Wang, Y.-J., Wilkinson, D.P, and Zhang, J. (2011) Non-carbon support materials for polymer electrolyte membrane fuel cells. Chem. Rev., Ill, 7625-7651. 

A Study on the Role of Carbon Support Materials for Fuel-Cell Catalysts... 

Despite the advantages offered by CNTs and CNFs, there are still many obstacles (cost, synthesis methods) to overcome to allow large-scale production. Another type of catalyst support material is mesoporous carbon that provides high surface area and conductivity [100, 141]. It can be classified into ordered (OMC) and disordered (DOMC) mesoporous carbon [100], OMCs have been extensively used as catalyst support materials for fuel cells [140,142-146], The large surface area and 3D connected monodis-persed mesospheres facilitate diffusion of the reactants, making them very attractive materials as catalyst supports [100]. 

Fig. 14.22 (a) TGA curves of carbon-supported materials with or without cobalt obtained in nitrogen atmosphere (b) Chronoamperometry results for Ppy-C-Co, P3MT-C-CO and Ppy-C in 0.5 M H2S04 under oxygen (Reprinted from [221] with permission from Elsevier). 

Carbon black is the traditional support material for fuel cell cafalysfs for fhe following reasons ... 

Over the last decade, novel carbonaceous and graphitic support materials for low-temperature fuel cell catalysts have been extensively explored. Recently, fibrous nanocarbon materials such as carbon nanotubes (CNTs) and CNFs have been examined as support materials for anodes and cathodes of fuel cells [18-31], Mesoporous carbons have also attracted considerable attention for enhancing the activity of metal catalysts in low-temperature DMFC and PEMFC anodes [32-44], Notwithstanding the many studies, carbon blacks are still the most common supports in industrial practice. 

Another material has some importance for oxygen reduction, not as an electrocatalyst but because other properties make it a good supporting material for catalysts that is, carbon, graphite, used with dispersed platinum particles or adsorbed coordination compounds. The main reduction product on carbon itself... 

Poly(amino acids) are insoluble in common solvents, are difficult to fabricate due to high melting point, and absorb a significant amount of water when their acid content reaches over 50 mol%. To solve these problems, polyesters derived from amino acids and lactic acids [e.g., poly (lactic acid-co-lysine) PLAL] are developed. The PLAL system is further modified by reaction with lysine A-carboxyanhydride derivatives. Another modification of poly(amino acids) includes poly(iminocarbon-ates), which are derived from the polymerization of desaminotyrosyl tyrosine alkyl esters. These polymers are easily processable and can be used as support materials for cell growth due to a high tissue compatibility. Mechanical properties of tyrosine-derived poly(carbonates) are in between those of poly(orthoesters) and poly(lactic acid) or poly(gly-colic acid). The rate of degradation of poly(iminocarbonates) is similar to that of poly (lactic acid). 

Although the homogeneous catalyst systems have been successfully applied in commercial practice, some intrinsic problems associated with catalyst separation remain. This has led to considerable interest in the development of a suitable heterogeneous analog. Rhodium compounds have been heterogenenized on substrates such as carbon (197), alumina (198, 199), and synthetic polymers (200). More recently, zeolites have also attracted quite some attention as a support material for carbonylation catalysis, as is discussed later. 

A remarkable difference in the Pt spectra of oxide- and carbon-supported platinum is especially clear for the 2.5-nm sample the fuel cell material shows much less intensity at the bulk resonance position (1.138 G/kHz). A similar difference is shown by the spectrum for the 2.0-nm sample. In terms of the NMR layer model, this comparison means that the healing length is larger in the carbon-supported material. It is not clear whether this result is related to the conducting nature of the carrier or to the presence of the electrolyte comparisons between wet and dry samples are needed. 

Because carbon black is the preferred support material for electrocatalysts, the methods of preparation of (bi)metallic nanoparticles are somewhat more restricted than with the oxide supports widely used in gas-phase heterogeneous catalysis. A further requirement imposed by the reduced mass-transport rates of the reactant molecules in the liquid phase versus the gas phase is that the metal loadings on the carbon support must be very high, e.g., at least lOwt.% versus 0.1-1 wt.% typically used in gas-phase catalysts. The relatively inert character of the carbon black surface plus the high metal loading means that widely practiced methods such as ion exchange [9] are not effective. The preferred methods are based on preparation of colloidal precursors, which are adsorbed onto the carbon black surface and then thermally decomposed or hydrogen-reduced to the (bi)metallic state. This method was pioneered by Petrow and Allen [10], and in the period from about 1970-1995 various colloidal methods are described essentially only in the patent literature. A useful survey of methods described in this literature can be found in the review by Stonehart [11]. Since about 1995, there has been more disclosure of colloidal methods in research journals, such as the papers by Boennemann and co-workers [12]. 

Diamond has long been regarded as an inert material for chemical reactions. Recently, one of the present authors elucidated that the surface of diamond can be modified by chemical reactions, such as hydrogenation, oxidation, chlorination, etc. [1]. Activated carbon, composed of sp carbon atoms, has been utilized as a support material for catalyst. However, no carbon materials consisting of sp carbon atoms have been used as catalyst supports. Silicon oxide (or silica) is also a very popular support material to catalysts. Carbon belongs to the same group of elements as silicone, but no carbon oxide solid phase exists. 

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