Introduction
Energy (obtained from food through
enzymatic reactions) is the basis of human movement. Enzymes are special
proteins that facilitate chemical reactions inside our bodies. Sony's Bio
Battery uses this same principle to produce electric energy. It is an extremely
safe form of energy production since the fuel (glucose) is a carbohydrate just
like bread or rice. Because glucose is a clean energy source---produced by
plants through photosynthesis (a process that involves the absorption of CO2)
---Bio Battery is also an eco-battery. Sony commenced Bio Battery R&D in
2001.
Technical Challenges of Bio-Fuel Cells
Bio-fuel cells are attracting
increased attention mainly due to promising advances from the research
laboratories around the world resolved before bio-fuel cells become
commercially viable for practical applications. The main challenges are: (1)
Nanostructured bioelectrocatalysis. (2) Immobilization of bioelectrocatalysts.
(3) Protein denaturation induced by CNT.
The Mechanism Behind Bio Battery
Like a conventional fuel cell
battery, Bio Battery basically consists of an anode, cathode, electrolyte and
separator. However, Bio Battery has certain specific characteristics. First,
biological enzymes are used as catalysts for the anode and cathode. Second,
enzymes and electronic mediators (which transfer electrons between enzymes, and
between enzymes and electrodes) are fixed on the anode and cathode.
Nanostructured Bioelectrocatalysis
Traditional direct hydrogen fuel
cells require noble metal catalysts both for hydrogen oxidation and oxygen
reduction.17 Similarly, the bio-fuel cells also need catalysts (bio-catalysts)
for the conversion of chemical to electrical energy. One approach is to use
microorganisms and/or enzymes as biological reactors for the fermentation of
raw materials to fuel products (similar hydrogen fuel reform- ers); the second
approach is to use the microorganisms and/or enzymes as catalysts directly in
the bio-fuel cells. The second approach, using purified redox enzymes for the
targeted oxidation and reduction of specific fuel and oxidizer substrates, is
more efficient for bio-fuel cells. Also, bio-catalysts are an attractive
renewable and less expensive alternative to transition metal catalysts for
mediated electron transfer (MET).18 MET-type bioelectrocatalyt based BFCs offer
the cur- rent density advantage over the direct electron transfer (DET) type,
but require that mediators and enzymes be immobilized on electrode surfaces.
The construction of DET-type bio-fuel cell is relatively simple as the sys- tem
is free from several restrictions concerning mediators.
The cell would not require separators because the crossover
of fuels (substrates) would not occur in principle due to enzymatic substrate
specificity as long as the enzymes are immobilized on electrodes and
dehydrogenases (that is, redox enzymes reacting with electron acceptors except
dioxygen) are utilized as anode catalysts. Kamitaka’s group have reported a
construction of sin- gle compartment bio-fuel cell, with no separators, using
D-fructose dehydrogenase (FDH) from Gluconobacter sp. and laccase from Trametes
sp. (TsLAC) as DET-type bio- electrocatalysts in the two-electron oxidation of
D-fructose and four-electron reduction of oxygen in the anode and cathode,
respectively.
Packaging Of Bio-Fuel Cells
One of the major challenges in
bionanotechnology is merging new nanoscale fabrication tools with classical
synthetic methods and delicate biomolecular building blocks to create materials
with unique biomedical properties. In order to address the packaging
requirement of the bio- fuel cells, it will be necessary to bridge the
disciplines of biology, chemistry, materials science, semiconductor technology
and engineering to find optimum packaging solutions for the challenges posed by
these devices. Biological packaging can be defined as the sum total of the
physical device, temperature regulating and monitoring systems, type of
preservation solution, and storage protocol(s) necessary to maintain cells or
tissues in a “state of suspended animation” during transport or storage.
The packaging issues connected with biological applications
pose different set of challenges. The materials used in the medical device
industry are extremely robust, and research shows that the failure rate is less
than one in one million packages.43 To achieve the performance levels of this
order, the reliability testing procedures for the devices has to be very stout,
which is an added cost of the product. The big difference, however, between
medical device packaging and other branches of the packaging industry is the
role the regulators play. Primarily the medical device industry for the last 30
years has been shaped by the FDA which oversees all aspects of medical device
packaging from material selection, design and manufacturing to label- ing and
sterilization.
Conclusion
Bio-fuel cells are energy-conversion
devises based on bio-electro catalysis leveraging on enzymes or microorganisms.
Chemical reactions can proceed by direct electron transfer (DET), in which case
the electron transfer occurs directly between enzymes and electrodes,5 or
through shuttle mediated electron transfer (MET), in which electron transfer
mediators shuttle the electron between enzymes and electrodes to reduce the
kinetic barrier in the electron transfer between enzymes and electrodes.
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