Exo-Cellular Electron Transfer

Schematic representation of bacterial membrane respiration. Note that the number of components of the electron transport chain varies with species. 

As mentioned above, free electrons are transferred during respiratory via a respiratory chain in which their energy gradually decreases, and are subsequently transferred to an externally terminal electron acceptor. The change of free energy under biological standard conditions (AG ) during this process can be expressed as 

for a given substrate (the electron donor), the more positive the redox potential of a terminal electron acceptor, the higher the energy gain for an organism. In the anodes of MFCs, exoelectrogens (facultative or obligate 

Facultative anaerobes microorganisms that make adenosine triphosphate (ATP) by aerobic respiration if oxygen is present, but are also capable of growing by fermentation in the absence of oxygen. 

Biological Standard Potentials of Some Biological Electron Donors and Electron Acceptors 

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The anodic electron transfer mechanism in MFC is a key issue in understanding how MFCs work. As discussed above, the redox active species at the end of the electron transfer chain links the solid electrode in MFCs anodes, completing the exo-cellular electron transfer (Figure 2.3). These linking species, for example, may be a soluble redox shuttle, an outer membrane redox protein or a pili (nanowire). For an efficient electron transfer, the linking species must fulfill the following requirements [6] ... 

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