1. Malaviya National Institute of Technology,
Enzymatic Biofuel Cells
Presented by:
Gurmeet singh
2013PCY7013
Jaipur
2. INTRODUCTION
Fuel cells are devices that convert chemical energy into
electrical energy. Biofuel cells are a subset of fuel cells
that employ biocatalysts. The main types of biofuel cells
are defined by the type of biocatalyst. Microbial biofuel
cells employ living cells to catalyze the oxidation of the
fuel, whereas enzymatic biofuel cells use enzymes for this
purpose.
3. Continued…
Enzymatic biofuel cells typically possess orders of magnitude
higher power densities but can only partially oxidize the fuel
and have limited lifetimes (typically 7–10 days).Enzymes
have the added advantage of specificity, which can eliminate
the need for a membrane separator. A conventional
enzymatic fuel cell and the polymer electrolyte membrane
(PEM) shown is standard, but if there are selective enzymes
on both the cathode and the anode then the PEM is
unnecessary.
5. What would it be like if you could recharge your
cell phone battery instantly by pouring your soft
drink into it?
6. Technical challenges surrounding a fuel cell that will run on such
simple sugars as those found in our everyday foodstuffs. Most fuel
cells in the world today run on hydrogen. However, as the fuel
gets more complex, this oxidation process becomes vastly more
complicated
Researchers are turning to the natural world in an effort to see
how sugars are oxidized by animals to produce power. Using
enzymes (nature’s catalysts) seems to be the answer, since they
do not suffer from the contamination problems that more
traditional metallic catalysts suffer from.
7. Action……….
In animals, enzymes are floating freely in the cells of
the body, but to work in a fuel cell, they have to be put in
a specific place and stay there, a process that scientists
call immobilizing the enzymes.
They are also “selective,” a word that scientists use to
describe an enzyme’s ability to work with a very specific
fuel, and only that fuel, so that the byproduct of one
oxidation step could be the fuel for another enzyme.
8. A schematic of a generic biofuel cell oxidizing glucose as
fuel at the bioanode and reducing oxygen to water at the
biocathode.
9. History
Biofuel cells were first introduced in 1911 when Potter
cultured yeast and E. Coli cells on platinum electrodes, but
it was not until 1962 that the enzymatic biofuel cell was
invented employing the enzyme glucose oxidase to oxidize
glucose at the anode. Over the last 45 years, many
improvements have been made in enzymatic biofuel cells
and those can be found in several review articles.
10. Recent advances in enzymatic
biofuel cells
One of the most significant advances in biofuel cells
has been the development of biocathodes and bioanodes
that employ direct electron transfer(DET) instead of
mediated electron transfer (MET).
Enzymes are proteins that typically have short
lifetimes (8 h to 2 days) in buffer solution,but Recently,
active lifetimes have even been extended beyond 1 year
through encapsulation in micellar polymers.
11. Principles of biofuel cell design indicting the maximum oxidation
potentials for glucose and the corresponding thermodynamic potential
for oxygen reduction at neutral pH. Redox potentials of several
enzymes and their corresponding co-factors are shown along with the
potential “zone” containing the redox potentials of the usual
mediators. Polarization curves depict typical current performances for
direct and mediated electron transfer in biofuel cell electrodes.
12. Fluorescence
The entrapment of enzymes within polymer
networks has found numerous applications in the design of
bioelectrochemical devices, primarily owing to the simplicity
and mild conditions of the procedure and its ability to
preserve the catalytic activity of biomolecules.In the context
of biosensor and biofuel cell development, electrochemistry
has generally been the method of choice when
characterizing the performance of polymer- immobilized
enzymes. Other methods, such as scanning electron
microscopy , infrared spectroscopy, X-ray diffraction ,
atomic force microscopy.
13. Fluorescently tagged enzymes in polymer films.
Alcohol dehydogenase in an Eastman AQ membrane as
shown (a) in a single plane and (b) in three-dimensions.
14. Alcohol dehydogenase in a Nafion membrane
(c) in a single plane and (d) in three dimensions
shown
15. Applications for Biofuel Cells and Their
Desirable Features
Applications Fuel/type of catalyst ; Desirable Features
Implantable - glucose/02/using human derived
enzymes;
biocompatible.
Developing countries - carbohydrates or agricultural
and municipal wastes/using microorganisms; robust, low-cost
components.
Portable - methanol or ethanol/using thermophilic
enzymes; high activity (to achieve high power density).
Space - human waste/microbial; simplicity in
regeneration of catalysts,dual use in environmental
management and power generation.
Waste Control - waste/microbial; able to handle a
large range of feeds.
16. Conclusions
Enzyme-based biofuel cells have many
advantages over traditional fuel cells and primary batteries,
they remain limited by short lifetimes, catalytic
inefficiencies,low fuel utilization, and low power densities.
Recently, working solutions to short lifetimes and catalytic
inefficiencies have been introduced, but similar advances in
improved fuel utilization and power density are needed.
Improvements in these areas will require electrochemical
characterization in standardized test geometries, and the use
of additional spectroscopic procedures that can be coupled to
classic electrochemical measurements.
