In Situ Characterizations of Porous Media for Applications in Biofuel Cells: Issues and Challenges - Porous Media: Applications in Biological Systems and Biotechnology - page 493

R

(a)

(c)

e e -

Glucose e -

e -

e -

e -

H 2 O

II

GOx I

BOD

O 2

Gluconolactone

Anode Cathode

(d)

2.6

O 2 / Bilirubin oxidase : E = +0.36 V

(b)

Cathode wire : E = +0.34 V

Cell
Potential
~0.52 V

1.3

Enzyme Active
Sites : + 0.72V

Anode wire : E = -0.19 V

0

Kinetic Losses

0 0.2 0.4

E / V

0.6 0.8

Glucose / Glucose oxidase
E = -0.36 V

FIGURE 13.2
(a) Photo of a sliced grape with an implanted glucose biofuel cell, (b) power
density output versus cell voltage when the air electrode is close to skin (bold)
or the inner part of the grape (thin), (c) schematic of the cell, (d) illustration
of the cell voltage as comprised by the electrode potentials. (Reprinted with
permission from Mano, N., Mao, F., and Heller, A., J. Am. Chem. Soc., 125,
2003. Copyright 2008 American Chemical Society.)

Kano (2001) provides a good discussion and introduction of the subject. In
the bioelectrocatalysis, the oxidation or reduction of the substrates by the
enzymatic redox reactions require the use of organic dyes or metal complexes
as electron acceptors or donors (mediators) to transfer the electrons to the
conductive electrode surface and be regenerated at such a surface. Figure 13.7
illustrates this important concept and shows how the enzymatic species and
mediators are regenerated in the bioelectrocatalysis.
Although the concept and a working model of the first fuel cell were
available in the mid-1800s, it was 100 years later that the hydrogen fuel
cell was developed for application in space explorations and other niche
applications. Since then the hydrogen fuel cell has been promised to be a
clean power source. Its potential, however, has been hampered by the high
costs of its components and fuel-related production, storage, and distribution
(Wu et al. 2008). The growing demand for cleaner power in conjunction
with the advent of biotechnology and the ability to produce a signifi-
cant amount of biocatalysts, spurred investigations into the biofuel cells
(Ikeda and Kano 2001; Katz et al. 2003; Chaudhuri and Lovley 2003; Liu