Biomedical Engineering Reference
In-Depth Information
its high glucose content (
30 mM). The biocatalytic fuel cell performance depended
on O 2 transport. In the O 2 -defi cient grape center the power density was 47
Wcm 2
µ
Wcm 2 , with an oper-
ating voltage of 0.52 V for both cases. Further improvement in output for this biofuel
cell was achieved by increasing the redox site density of the anode redox polymer,
resulting in a glucose fl ux-limited current density increase of 20% and an overpoten-
tial decrease of 50 mV [98]. This optimized biocatalytic fuel cell operated at
whereas near the better oxygenated grape skin it reached 240
µ
0.60 V
Wcm 2 power density in pH 7.2 phosphate buffer containing 0.1 M NaCl,
15 mM glucose at 37.5ºC, losing about 8% of its power each day of operation.
with a 480
µ
12.7 CONCLUSIONS
It seems that using and developing the different strategies discussed above, biocatalytic
fuel cells with power densities and operating voltage high enough to power low energy
microdevices are now at hand. Indeed, a tremendous improvement has been shown
from the initial units of
Wcm 2 for the cell power density and tens of millivolts for
the operating voltage, to achieve outputs approaching mWcm 2 and operating voltages
of
µ
0.5 V. Biocatalytic fuel cell optimization to date has mostly dealt with attempts to
achieve direct electron transfer to the biocatalyst, and with matching the redox poten-
tial of the mediator with the biocatalytic elements. An important factor to consider,
addressed by some, in the biocatalytic fuel cell refi nement process is the nature of the
electrode. The introduction of solid nanoparticles and fi bers, for example of gold or car-
bon, in the biocatalytic electrodes can further improve current and power densities, while
opening up the possibility of direct electron transfer with the biocatalytic active site.
A remaining crucial technological milestone to pass for an implanted device
remains the stability of the biocatalytic fuel cell, which should be expressed in months
or years rather than days or weeks. Recent reports on the use of BOD biocatalytic
electrodes in serum have, for example, highlighted instabilities associated with the
presence of O 2 , urate or metal ions [99, 100], and enzyme deactivation in its oxi-
dized state [101]. Strategies to be considered include the use of new biocatalysts with
improved thermal properties, or stability towards interferences and inhibitors, the use
of nanostructured electrode surfaces and chemical coupling of fi lms to such surfaces,
to improve fi lm stability, and the design of redox mediator libraries tailored towards
both mediation and immobilization.
12.8 REFERENCES
1. A. Heller, AIChE Journal 51 , 1054 (2005).
2. Useful reviews for an introduction to this area are: (a) S.C. Barton, J. Gallaway, and P. Atanassov,
Chem. Rev. 104 , 4867 (2004). (b) E. Katz, A.N. Shipway, and I. Willner, in Handbook of Fuel Cells -
Fundamentals, Technology and Applications (W. Vielstich, H.A. Gasteiger, and A. Lamm, eds), Vol. 1,
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