Carbon-ceramic composite electrodes CCEs

Amperometric detection has been widely used for sol-gel biosensing and many devices have been described (Lev, 1997 Wang, 1999 CoUinson, 2000 Przybyt, 2002). These methods are very convenient, but silica is not electronically conductive (Willner, 2000). Therefore carbon-ceramic composite electrodes (CCE) in which an enzyme-loaded carbon powder is mixed to the sol-gel solution have been developed (Gun, 1996 Sampath, 1996a Wang, 1997). 

Carbon-ceramic composite electrodes (CCEs) and the closely related metal-sihcate electrodes are comprised of carbon or metal dispersion in sol-gel derived silicates or Or-mocers. In this construction the silicate serves as a porous binder for the conductive dispersion. The conductive component is added as powders, nanoparticles, or nanotubes whose particle size ranges between sub-millimeter and a few nanometers. The initial intention was to provide improved conductivity by the interconnected conductive powder, but soon, other favorable attributes of the metal-sihcate hybrids were discovered, including improved catalytic reactivity, biological compatibility, and control of the thickness of the wetted section of the electrodes in aqueous electrolyte. Since the metal silicate and graphite silicate call for different preparation protocols they are addressed separately. 

Figure 16-8. Scheme of a 3-electrode fuel cell with details of the hydrophobic carbon ceramic composite electrode. The inserts show unwetted (left) and flooded (middle) sections of the CCE. The active section of a wetted channels electrode is shown in the right insert (after Rabinovich and Lev, 2001). 

Ferrocene doping provides an electrochemical probe of the material during gelation, reporting in particular on the mobility of the probe as measured by the diffusion coefficient.133,134 If necessary the sol-gel material can be loaded with carbon powder to confer electrical conductivity (composite ceramic carbon electrodes, CCEs).135 Single-walled nanotubes in vanadia aerogels exhibit high capacities for lithium intercalation.136... 

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