Carbonaceous substrate

The oxidation of the carbonaceous substrate with oxygen cannot occur directly as the released energy would be converted into heat, but must proceed almost reversibly, through a number of poorly water-soluble redox... 

The theory of the accumulation of the Gibbs energy of oxidation of carbonaceous substrates in the form of the bond of the phosphate ion to... 

P. Mitchell (Nobel Prize for Chemistry, 1978) explained these facts by his chemiosmotic theory. This theory is based on the ordering of successive oxidation processes into reaction sequences called loops. Each loop consists of two basic processes, one of which is oriented in the direction away from the matrix surface of the internal membrane into the intracristal space and connected with the transfer of electrons together with protons. The second process is oriented in the opposite direction and is connected with the transfer of electrons alone. Figure 6.27 depicts the first Mitchell loop, whose first step involves reduction of NAD+ (the oxidized form of nicotinamide adenosine dinucleotide) by the carbonaceous substrate, SH2. In this process, two electrons and two protons are transferred from the matrix space. The protons are accumulated in the intracristal space, while electrons are transferred in the opposite direction by the reduction of the oxidized form of the Fe-S protein. This reduces a further component of the electron transport chain on the matrix side of the membrane and the process is repeated. The final process is the reduction of molecular oxygen with the reduced form of cytochrome oxidase. It would appear that this reaction sequence includes not only loops but also a proton pump, i.e. an enzymatic system that can employ the energy of the redox step in the electron transfer chain for translocation of protons from the matrix space into the intracristal space. 

Several studies have shown that the direct electron transfer between cat and graphite or carbon soot electrodes in deoxygenated solutions was sluggish, with large peak separations [157-159], Based on the consideration that CNTs might be the best candidate among the various carbonaceous substrates for promoting the electron transfer... 

The destmction of carbonaceous substrates during treatment resulted in significant (P=0.001) decreases of TS, VS, BODw, VFA (Table III) and COD (Fig 2) in every run. The destmction of VS and TS were very similar in each run being in the range 2-20%. COD destmction was higher, 21-38%, while BODw removal was 46-85%. Destmction of VFA was nearly total at 98-100%. Ethanoic acid was usually the only individual VFA found in the treated slurries. This was taken to be the residual ethanoic acid (6),... 

This section provides a comprehensive overview of recent efforts in physical theory, molecular modeling, and performance modeling of CLs in PEFCs. Our major focus will be on state-of-the-art CLs that contain Pt nanoparticle electrocatalysts, a porous carbonaceous substrate, and an embedded network of interconnected ionomer domains as the main constituents. The section starts with a general discussion of structure and processes in catalyst layers and how they transpire in the evaluation of performance. Thereafter, aspects related to self-organization phenomena in catalyst layer inks during fabrication will be discussed. These phenomena determine the effective properties for transport and electrocatalytic activity. Finally, physical models of catalyst layer operation will be reviewed that relate structure, processes, and operating conditions to performance. 

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 ... 

Polyhydroxyphenazine (pOPh) is investigated as an example of a polymer without conjugated 7i-systeia It is formed by anodic electropolymerization of hydroxyphenazine on noble metal or carbonaceous substrates (25-26) in a polymerization reaction... 

Figure 8.2. Illustration of structures and phenomena at multiple scales that control the performance of catalyst layers in PEFCs. Left Pt nanoparticle on carbonaceous substrate ( 3 nm) middle phase-segregation and agglomerate formation at mesoscale ( 50 nm) right the catalyst layer as a complex composite medium at the macoscopic scale ( 10 pm).

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