Graphite substrates

Carbonaceous substrates (graphite and glassy carbon) are generally preferred because of their mechanical, chemical, and electrochemical properties. Excellent results are also obtained by chemically modified platinum (154,156,179) and tin(IV) oxide electrodes (155). For example, glucose oxidase has been successfully immobilized by cross-linking the enzyme with BSA and GA onto an electrochemically oxidized platinum surface, with silanization using 3-amino-propyltriethoxysilane ... 

One of the key technical issues is to select suitable material as the substrate. Graphite and silicate glass are widely used because graphite is easily oxidised in air at 700°C and silicate glass can be etched away by HF acid. Sometimes Mo, Ta, W, SiC and Si3N4 are also employed due to their superior stiffness at elevated temperatures and inertness to reactant gases. 

Microscopic particles of an alloy are distributed on a substrate (graphite) then exposed to silicon- and carbon-rich vapors. The presence of a liquid catalyst, such as a transition metal or usually an iron alloy, distinguishes this method from all other whisker preparation methods. 

Figures 2.4 and 2.5 show the SEM pictures of the laboratory prepared CMSM and the substrate graphite. Figure 2.4 depicts that the CMSM coated on top of the graphite support is crack-free. The thickness of the CMSM layer is 15 pm. Figure 2.5 shows that the surface of the CMSM and the graphite support. The CMSM layer is much smoother with a roughness within 0.02 pm. The pore size in the graphite support is 5-10 pm.

The focus of this section is on the corrosion phenomena of the GDL substrate graphite fibers driven by solid-liquid surface chemical interactions and surface energetics. Particular importance is assigned to uncoated areas of fibo s by hydrophobic fluoropolymer and interfacial zones between fiber and fluoropolymer. Since Teflon products such as PTFE and FEP are known to have excellent thermal resistance, electrochemical corrosion stability, chemical durability, and mechanical properties, the GDL and MPL fluoropolymer phase is not considered to be vulnerable in a PEFC operating enviromnent. 

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