Anodes bioanodes

A construction of a biofuel cell is schematically illustrated in Fig. 23. A carbon felt sheet was used for both anode El and cathode E2. An anion-exchange membrane 180 /am thick was used for a separator membrane S. The contact area of S with the electrolyte in each compartment was 12.5 cm. Each compartment had an electrolyte solution (adjusted to pH 7.0 with NaH2P04 and Na2HP04) of 5 mL. The cell was used as a prototype biofuel cell to evaluate the performance of the fuel cell composed of a biocathode (ABTS / ABTS -B0D-02/H20) and a bioanode (MV /MV -Z). vulgaris (H)-2H /H2). The biofuel cell was operated with O2 and H2 gas bubbling in the cathode and anode compart-... 

In bioanodes, an (in)organic electron donor is oxidized by microorganisms with concomitant liberation of electrons and protons (Figure 6.1). The electrons produced are shuttled through the internal electron transport chain of the microorganisms and are deposited on the anode. The energy level of the electrons deposited on the electrode is dependent on the terminal electron transfer molecule. 

Second, biofllm thickness, structure, composition, and density affect the flux of substrates and products within the biofllm. The latter can result in large overpotentials, which have a negative impact on the performance of the system. In the case of bioanodes, higher power production was observed from thicker anodic biofilms [120]. Strikingly, the reverse effect has been observed in cathodic biofilms [35]. 

The OCP of a BFC is determined when there is no current flowing across the device C/max = 0) and thus, no bioelectrocatalysis is taking place at either the bioanode or the biocathode. As previously discussed, the use of an electron mediator requires a potential difference between the electron mediator and the enzyme s cofactor. This therefore can result in lower OCPs of BFCs, since the potential at both the bioanode and the biocathode is determined by the onset potential of the anodic electron mediator (F J and cathodic electron mediator (F ) 7). In... 

Addo et al. (2011) investigated a rechargeable alcohol biobattery. The anode compartment of this battery consisted of NAD-dependent alcohol dehydrogenase immobilized into a carbon composite paste. Ferrocene was added to the electrolyte to shuttle electrons to and from the electrode surface. In discharge mode the bioanode catalyzed the oxidation of ethanol to acetaldehyde. The cathode... 

To overcome the limitations of partial oxidation of fuel by EFCs and to enhance their power output, Minteer and co-workers [99-101] immobilised multiple enzymes of citric acid cycle or enzymes for complete oxidation of glycerol oti respective anodes. In one of the examples [101], they developed the enzymatic bioanode for complete oxidation of pyravate, where the bioanode contained the enzymes of the Kreb s cycle (Fig. 12A). Representative power curves for the five biofuel cells containing different numbers of dehydrogenase enzymes are shown in... 

The integration of cofactor-dependent enzymes as anodic catalysis clearly faces a number of technical hurdles that must be considered and addressed. To some extent, the stability of the NAD" /NADH couple has been addressed by introduction of electropolymerized polymers that has directly led to extended bioanode lifetimes. 

Improving bioanodes performances and efficiencies will be the most important task in future studies of enzymatic anodic catalysis. Based on research carried out in the past few years, trends for improving performance rely on better electron transport methods and higher enzyme loading. Electron transport could be improved, for example, by developing novel mediators and redox polymers for MET or by controlling orientation of enzymes to improve DET. Enzyme loading techniques could be improved to increase active enzyme concentration per unit of electrode area or volume. 

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