The Re-former

Figure 23. Depiction of the components of a complete fuel cell system including the re-former and power conditioning unit.

If the CO is left untreated, it would reach the anode at a concentration of 0.5-4% within the mixture from the re-former. The preferred approach is to oxidize the CO further to C02. This oxidation must be made preferential to CO and avoid any oxidation of H2, the fuel. The overall setup is shown in Fig. 13.25. 

The difference between the two extremes is essentially that, in the former, the Re retains its valence electrons in its d orbitals whereas in the latter it loses 6 of them to delocalized ligand orbitals. In either case paramagnetism is anticipated since rhenium has an odd number of valence electrons. The magnetic moment of 1.79 BM corresponding to 1 unpaired electron, and esr evidence showing that this electron is situated predominantly on the ligands, indicates that an intermediate oxidation state is involved... 

The coordination of the dienophile to a Lewis acid (in the calculations a proton was used as the Lewis acid) leads also to an increase in regioselectivity. The re-gioselectivity of reactions of electron-rich, or conjugated dienes, with electron-deficient dienophiles is also controlled hy the diene HOMO-dienophile LUMO interaction. From Fig. 8.2 it appears that the difference in magnitudes of the LUMO coefficients at carhon atoms 1 and 2 of acrolein (Ci -C2 = 0.20) is smaller than the same difference for protonated acrolein (Ci -C2 = 0.30-0.43) so that the reaction of the latter should he considerable more regioselective than the former in accordance with the experimental results [3]. 

Efforts directed to develop HTSs to commercial products are confined to the RE-123 compounds, where RE = rare earth element, Y, Nd, Sm, etc., and the Bi-based materials. As far as the former type is concerned the discussion is confined to YBCO, the most prominent of the RE-123 family. YBCO has the advantage of a higher Jc value at 77K than the Bi-based materials ( 1010 Am-2 compared to 109 Am-2) although the comparison is not an easy one to make since the values are so dependent on specimen form, doping, applied field, etc. More importantly, the Bi-based powders have a flat, clay-like morphology and this is very significant when it comes to fabrication. In contrast YBCO particles tend to be equiaxed. 

If sufficiently cheap hydrogen from the solar-driven photoproduction of hydrogen were available, the hydrogen could be stored on board in lightweight cylinders or as a liquid (no re-former ). 

Fig. 13.25. Preferential oxidation and re-former-shifter test bench experiment. (Reprinted with permission from Research and Development of Proton-Exchange-Membrane (PEM) Fuel Cell System for Transportation Applications, Phase I, Final Report, prepared for the U.S. Dept, of Energy by General Motors, 1996, Fig. 2.2.3.1.)...

Emissions of NO, CO, and S02 in the fuel cell (steam re-former) scheme would be zero, whereas for battery-powered cars, the electricity-producing plants would emit these pollutants in substantial quantities. 14The fuel cell-electric motor combination is termed the electrochemical engine. ... 

The reason certain amino acids are essential in human diets is because the carbon skeletons cannot be synthesized. It was reasoned formerly that the re-... 

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