Electrocatalyst supports graphitization

Pt (5 wt%) supported on platelet and ribbon graphite nanofibers exhibited similar activities to those observed by Pt (25 wt°/o) on carbon black [138], This phenomenon was attributed to the crystallographic orientations adopted by the catalyst particles dispersed on graphitic nanofiber structures [139]. Also, the electrocatalysts supported on CNFs were less susceptible to CO poisoning than Pt supported on carbon black. 

In fuel cells, carbon (or graphite) is an acceptable material of construction for electrode substrates, electrocatalyst support, bipolar electrode separators, current collectors, and cooling plates. 

There are many considerations that must be taken into account when choosing a particular carbon, or carbon structure, as an electrocatalyst support. In hot phosphoric acid at cathodic potentials, the carbon surface is capable of being oxidized to carbon dioxide. The degree of oxidation will depend on the pretreatment of the carbon (for instance, the degree of graphitization), on the carbon precursor, and the provenance. There are two important parameters that will govern the primary oxidation rate for any given carbon material in an electrochemical environment. These are electrode potential (the carbon corrosion is an electrochemical process and therefore will increase rapidly as the electrode potential is raised) and temperature. 

Finally, the understanding of the chemistry of carbon and its stability in hot phosphoric acid in relation to its use as electrocatalyst supports, has led to the use of highly graphitic carbons, where the fundamental electrochemistry now is well defined. 

Carbon constitutes the most abundant element of the different FC components. Setting aside the membrane, which is a polymer with a carbon backbone, all the other components, i.e. the CL, GDL and current collector plates (bipolar plates) are made almost entirely of graphitic carbon. The electrocatalyst support of the CL is commonly carbon black in the form of fine powder. GDLs are thin porous layers formed by carbon fibers interconnected as a web or fabric, while current collector plates are carbon monoliths with low bulk porosity. As explained above each of these components has a particular function within the fuel cell and in particular in the triple phase boundary. The structure and properties of the carbon in each of the different FC components will determine the whole performance of the cell. 

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... 

Gunnar RD and Langer SH. Comparisons of Ebonex and graphite supports for platinum and nickel electrocatalysts. Electrochim Acta 1998 44 437 44. 

Carbon and graphite are often used as supports for electrocatalysts, but they also have an electrocatalytic function in electrode reactions such as oxygen reduction in alkaline electrolytes, chlorine alkali industry, and SOCI2 reduction in lithium-thionyl chloride batteries. 

At present, electrocatalysts generally are supported on high-surface-area carbon blacks (CBs) with a high-mesoporous distribution and graphite characteristics, and Vulcan XC-72 carbon blacks (Cabot International) are the most commonly used carbon support because of their good compromise between electronic conductivity and Brunauer-Emmett-Teller s (BET s) surface area. However, the effect of the surface characteristics of the various carbon materials had not been fully studied to our best knowledge. 

Proietti E, Rugger S, Dodelet J-P (2008) Fe-based electrocatalysts for oxygen reduction in PEMFCs using ball-milled graphite powder as a carbon support. J Electrochem Soc 155 B340-B348... 

A variant of the enhanced reaction zone concept is to utilize as catalyst support various porous three-dimensional electrodes with thickness between 200 to 2,000 pm. Thus, the electric contact resistance between the individual layers is eliminated. The three-dimensional matrix (such as various graphite felts, reticulated vitreous carbon, metal mesh, felt, and foam) supporting uniformly dispersed electrocatalysts (nanoparticles or thin mesoporous coating) could assure an extended reaction zone for fuel (methanol, ethanol, and formie aeid) electrooxidation, providing an ionic conductor network is established to link the catalytically active sites and the proton exchange membrane. The patent by Wilkinson et al. also suggests such electrode configurations (e.g., carbon foam, expended metal and reticulated metal) but experimental results were not provided [303]. 

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