A Four-Enzyme Methanol-Oxidizing Anode

In 1998, Palmore et al. reported a methanol-oxygen fuel ceU that carried out the full six-electron oxidation of methanol to carbon dioxide in its anode compartment (Equation 9.18) [29]  

A multienzyme pathway accomplished the multistep oxidation of methanol as follows  

In this case, the NAD /NADH couple is operating as anatural mediator, with aredox potential of E ad -0.59 V versus SCE, which is approximatelyE = —0.32 V versus SHE. However, the oxidation of NADH at an electrode surface is a kinelically hindered reaction, requiring a of approximately 1V [117-121]. Thus, relying on 

FIGURE 9.7 A methanol-oxygen biological fuel cell with mediators and enzymes freely diffusing in solution. This cell used an enzyme cascade of ADH ALDH FDH to completely oxidize methanol to carbon dioxide. (Reproduced with permission from Ref. [29]. Copyright 1998, Elsevier.) 

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