U.S. patent application number 11/071075 was filed with the patent office on 2005-07-21 for enzymatic fuel cell.
This patent application is currently assigned to PowerZyme, Inc.. Invention is credited to Bindra, Chetna, Fan, Zhonghui Hugh, Hozer, Leszek, Kumar, Rajan, Liberatore, Michael James, Sreeram, Attiganal Narayanaswamy.
Application Number | 20050158618 11/071075 |
Document ID | / |
Family ID | 27536829 |
Filed Date | 2005-07-21 |
United States Patent
Application |
20050158618 |
Kind Code |
A1 |
Liberatore, Michael James ;
et al. |
July 21, 2005 |
Enzymatic fuel cell
Abstract
Provided is a battery comprising a first compartment, a second
compartment and a barrier separating the first and second
compartments, wherein the barrier comprises a proton transporting
moiety.
Inventors: |
Liberatore, Michael James;
(Jersey City, NJ) ; Hozer, Leszek; (West Windsor,
NJ) ; Sreeram, Attiganal Narayanaswamy; (Edison,
NJ) ; Kumar, Rajan; (Robbinsville, NJ) ;
Bindra, Chetna; (Piscataway, NJ) ; Fan, Zhonghui
Hugh; (Plainsboro, NJ) |
Correspondence
Address: |
LERNER, DAVID, LITTENBERG,
KRUMHOLZ & MENTLIK
600 SOUTH AVENUE WEST
WESTFIELD
NJ
07090
US
|
Assignee: |
PowerZyme, Inc.
Monmouth Junction
NJ
|
Family ID: |
27536829 |
Appl. No.: |
11/071075 |
Filed: |
March 3, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11071075 |
Mar 3, 2005 |
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10226841 |
Aug 23, 2002 |
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10226841 |
Aug 23, 2002 |
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09376792 |
Aug 18, 1999 |
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6500571 |
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60097277 |
Aug 19, 1998 |
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60118837 |
Feb 5, 1999 |
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60126029 |
Mar 25, 1999 |
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60134240 |
May 14, 1999 |
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Current U.S.
Class: |
429/105 ;
429/50 |
Current CPC
Class: |
H01M 8/16 20130101; H01M
14/00 20130101; Y02E 60/50 20130101; H01M 14/005 20130101 |
Class at
Publication: |
429/105 ;
429/050 |
International
Class: |
H01M 008/20; H01M
010/44 |
Claims
What is claimed:
1. A battery comprising a first compartment, a second compartment
and a barrier separating the first and second compartments, wherein
the barrier comprises a proton transporting moiety.
2. A battery comprising: a first compartment; a second compartment;
a barrier separating the first compartment from the second
compartment; said barrier having a proton transporting moiety; a
first electrode; a second electrode; a redox enzyme in the first
compartment in communication with the first electrode to receive
electrons therefrom; an electron carrier in the first compartment
in chemical communication with the redox enzyme; and an electron
receiving composition in the second compartment in chemical
communication with the second electrode, wherein, in operation, an
electrical current flows along a conductive pathway formed between
the first electrode and the second electrode.
3. The battery of claim 2, wherein the first electrode is further
associated with an electron transfer mediator that transfers
electrons from the redox enzyme to the first electrode.
4. The battery of claim 2, wherein the proton transporting protein
comprises at least a portion of the redox enzyme.
5. The battery of claim 2, adapted to operate at the first
electrode at a temperature of about 60.degree. C. or less.
6. The battery of claim 2, further comprising a reservoir for
supplying to the vicinity of at least one of the electrodes a
component consumed in the operation of the battery and a pump for
drawing such component to that vicinity.
7. The battery of claim 6, further comprising a controller which
receives data on the operation of the battery and controls the pump
in response to the data.
8. The battery of claim 2, wherein a light-driven proton pump
protein comprises at least a portion of the proton transporting
protein, and further comprising: a source of light for powering the
light-driven proton pump protein.
9. The battery of claim 2, further incorporating in the barrier a
second protein, distinct from the first, adapted to facilitate
reverse proton pumping when the battery is operated in recharge
mode.
10. A method of operating a battery with a first compartment and a
second compartment comprising: enzymatically oxidizing an electron
carrier and delivering the electrons to a first electrode in
chemical communication with the first compartment; catalyzing the
transfer of protons from the first compartment to the second
compartment; and reducing an electron receiving molecule with
electrodes conveyed through a circuit from the first electrode to a
second electrode located in the second compartment.
11. The method of claim 10, wherein the catalytic transfer of
protons occurs in conjunction with the enzymatic oxidation of the
electron carrier.
12. The method of claim 10, wherein at least a portion of the
transfer of protons is driven by a light-driven proton pump
protein, and the method further comprises: directing light to the
light-driven proton pump.
13. The method of claim 12, further comprising monitoring the pH of
the first compartment and controlling the amount of light directed
to the light-driven proton pump such that relatively more light is
directed at lower pH values.
14. The method of claim 10, further comprising: applying a voltage
to the electrodes of a polarity opposite that generated by the
normal operation of the battery to recharge the battery.
15. The method of claim 14, further comprising: enzymatically
transporting protons from the second chamber to the first chamber
in connection with the applying the recharge voltage.
16. The method of claim 15, wherein at least a portion of the
enzymatic transport in recharge mode is accomplished by an enzyme
distinct from an enzyme catalyzing the majority of proton transport
in a power producing mode.
17. A battery comprising: a first compartment; a second
compartment; a barrier separating the first compartment from the
second compartment; a first electrode; a second electrode; a redox
enzyme in the first compartment in communication with the first
electrode to receive electrons therefrom, the redox enzyme
incorporated in a lipid composition; an electron carrier in the
first compartment in chemical communication with the redox enzyme;
and an electron receiving composition in the second compartment in
chemical communication with the second electrode, wherein, in
operation, an electrical current flows along a conductive pathway
formed between the first electrode and the second electrode.
18. A method of operating a battery with a first compartment and a
second compartment comprising: enzymatically oxidizing, with an
enzyme incorporated into a lipid composition, an electron carrier
and delivering the electrons to a first electrode in chemical
communication with the first compartment; and reducing an electron
receiving molecule with electrodes conveyed through a circuit from
the first electrode to a second electrode located in the second
compartment.
Description
[0001] The present invention relates to batteries, including fuel
cells and re-chargeable fuel cells, for use in powering electrical
devices.
[0002] Batteries such as fuel cells are useful for the direct
conversion of chemical energy into electrical energy. Fuel cells
are typically made up of three chambers separated by two porous
electrodes. A fuel chamber serves to introduce a fuel, typically
hydrogen gas, which can be generated in situ by "reforming"
hydrocarbons such as methane with steam, so that the hydrogen
contacts H.sub.2O at the first electrode, where, when a circuit is
formed between the electrodes, a reaction producing electrons and
hydronium (H.sub.3O.sup.+) ions is catalyzed.
2H.sub.2O+H.sub.22H.sub.3O.sup.++2e.sup.- (1)
[0003] A central chamber can comprise an electrolyte. The central
chamber acts to convey hydronium ions from the first electrode to
the second electrode. The second electrode provides an interface
with a recipient molecule, typically oxygen, found in the third
chamber. The recipient molecule receives the electrons conveyed by
the circuit.
2H.sub.3O.sup.++1/2O.sub.2+2e.sup.-3H.sub.2O (2)
[0004] The electrolyte element of the fuel cell can be, for
example, a conductive polymer material such as a hydrated polymer
containing sulfonic acid groups on perfluoroethylene side chains on
a perfluoroethylene backbone such as Nafion.TM. (du Pont de
Nemours, Wilmington, Del.) or like polymers available from Dow
Chemical Co., Midland, Mich. Other electrolytes include alkaline
solutions (such as 35 wt %, 50 wt % or 85 wt % KOH), acid solutions
(such as concentrated phosphoric acid), molten electrolytes (such
as molten metal carbonate), and solid electrolytes (such as solid
oxides such as yttria (Y.sub.2O.sub.3)-stabilized zirconia
(ZrO.sub.2)). Liquid electrolytes are often retained in a porous
matrix. Such fuel cells are described, for example, in "Fuel
Cells," Kirk-Othmer Encyclopedia of Chemical Technology, Fourth
Edition, Vol. 11, pp. 1098-1121.
[0005] These types of fuel cells typically operate at temperatures
from about 80.degree. C. to about 1,000.degree. C. The shortcomings
of the technology include short operational lifetimes due to
catalyst poisoning from contaminants, high initial costs, and the
practical restrictions on devices that operate at relatively high
to extremely high temperatures.
[0006] The present invention provides a fuel cell technology that
employs molecules used in biological processes to create fuel cells
that operate at moderate temperatures and without the presence of
harsh chemicals maintained at high temperatures, which can lead to
corrosion of the cell components. While the fuel used in the fuel
cells of the invention are more complex, they are readily available
and suitably priced for a number of applications, such as power
supplies for mobile computing or telephone devices. It is
anticipated that fuel cells of the invention can be configured such
that a 300 cc cell has a capacity of as much as 80
W.multidot.h--and thus can have more capacity than a comparably
sized battery for a laptop computer--and that such cells could have
still greater capacity. Thus, it is believed that the fuel cells of
the invention can be used to increase capacity, and/or decrease
size and/or weight. Moreover, the compact, inert energy sources of
the invention can be used to provide short duration electrical
output. Since the materials retained within the fuel cells are
non-corrosive and typically not otherwise hazardous, it is
practical to recharge the fuel cells with fuel, with the recharging
done by the consumer or through a service such as a mail order
service.
[0007] Moreover, in certain aspects, the invention provides fuel
cells that use active transport of protons to increase sustainable
efficiency. Fuel cells of the invention can also be electrically
re-charged.
SUMMARY OF THE INVENTION
[0008] In one aspect, the invention provides a fuel cell comprising
a first compartment, a second compartment and a barrier separating
the first and second compartments, wherein the barrier comprises a
proton transporting moiety.
[0009] In another aspect, the invention provides a fuel cell a
first compartment; a second compartment; a barrier separating the
first compartment from the second compartment; a first electrode; a
second electrode; a redox enzyme in the first compartment in
communication with the first electrode to receive electrons
therefrom, the redox enzyme incorporated in a lipid composition; an
electron carrier in the first compartment in chemical communication
with the redox enzyme; and an electron receiving composition in the
second compartment in chemical communication with the second
electrode, wherein, in operation, an electrical current flows along
a conductive pathway formed between the first electrode and the
second electrode.
BRIEF DESCRIPTION OF THE DRAWING
[0010] FIG. 1 displays a perspective view of the interior of a fuel
cell with three chambers.
[0011] FIG. 2 illustrates a fuel cell exhibiting certain preferred
aspects of the present invention.
[0012] FIGS. 3A, 3B and 3C illustrate a similar fuel cell with
scavenger-containing segment.
[0013] FIGS. 4A and 4B show a top view of a fuel cell with two
chambers.
[0014] FIG. 5A shows a top view of a fuel cell with two chambers,
while FIG. 5B shows a side view.
[0015] FIG. 6 shows a fuel cell where the fluids bathing the two
electrodes are segregated.
[0016] FIG. 7 shows a fuel cell with incorporated light regulation
and a sensor.
DEFINITIONS
[0017] The following terms shall have, for the purposes of this
application, the respective meaning set forth below.
[0018] electron carrier: An electron carrier is a composition that
provides electrons in an enzymatic reaction. Electron carriers
include, without limitation, reduced nicotinamide adenine
dinucleotide (denoted NADH; oxidized form denoted NAD or
NAD.sup.+), reduced nicotinamide adenine dinucleotide phosphate
(denoted NADPH; oxidized form denoted NADP or NADP.sup.+), reduced
nicotinamide mononucleotide (NMNH; oxidized form NMN), reduced
flavin adenine dinucleotide (FADH.sub.2; oxidized form FAD),
reduced flavin mononucleotide (FMNH.sub.2; oxidized form FMN),
reduced coenzyme A, and the like. Electron carriers include
proteins with incorporated electron-donating prosthetic groups,
such as coenzyme A, protoporphyrin IX, vitamin B 12, and the like
Further electron carriers include glucose (oxidized form: gluconic
acid), alcohols (e.g., oxidized form: ethylaldehyde), and the like.
Preferably the electron carrier is present in a concentration of 1
M or more, more preferably 1.5 M or more, yet more preferably 2 M
or more.
[0019] electron-receiving composition: An electron-receiving
composition receives the electrons conveyed to the cathode by the
fuel cell.
[0020] electron transfer mediator: An electron transfer mediator is
a composition which facilitates transfer to an electrode of
electrons released from an electron carrier.
[0021] redox enzyme: An redox enzyme is one that catalyzes the
transfer of electrons from an electron carrier to another
composition, or from another composition to the oxidized form of an
electron carrier. Examples of appropriate classes of redox enzymes
include: oxidases, dehydrogenases, reductases and oxidoreductases.
Additionally, other enzymes, will redox catalysis as their
secondary property could also be used e.g., superoxide
dismutase.
[0022] composition. Composition refers to a molecule, compound,
charged species, salt, polymer, or other combination or mixture of
chemical entities.
DETAILED DESCRIPTION
[0023] FIG. 1 illustrates features of an exemplary battery such as
a fuel cell 10. The fuel cell 10 has a first chamber 1 containing
an electron carrier, with the textured background fill of the first
chamber 1 illustrating that the solution can be retained within a
porous matrix (including a membrane). Second chamber 2 similarly
contains an electrolyte (and can be the same material as found in
the first chamber) in a space, which space can also be filled with
a retaining matrix, intervening between porous first electrode 4
and porous second electrode 5. A face of second electrode 5
contacts the space of third chamber 3, into which an electron
receiving molecule, typically a gaseous molecule such as oxygen, is
introduced. First electrical contact 6 and second electrical
contact 7 allow a circuit to be formed between the two
electrodes.
[0024] The optional porous retaining matrix can help retain
solution in, for example, the second chamber 2 and minimize
solution spillover into the third chamber 3, thereby maintaining a
surface area of contact between the electron receiving molecule and
the second electrode 5. In some embodiments, the aqueous liquid in
the first chamber 1 and second chamber 2 suspends non-dissolved
reduced electron carrier, thereby increasing the reservoir of
reduced electron carrier available for use to supply electrons to
the first electrode 4. In another example, where the chambers
include a porous matrix, a saturated solution can be introduced,
and the temperature reduced to precipitate reduced electron carrier
within the pores of the matrix. Following precipitation, the
solution phase can be replaced with another concentrated solution,
thereby increasing the amount of electron carrier, which electron
carrier is in both solid and solvated form.
[0025] It will be recognized that the second chamber can be made up
of a polymer electrolyte, such as one of those described above.
[0026] The reaction that occurs at the first electrode can be
exemplified with NADH as follows:
H.sub.2O+NADHNAD.sup.++H.sub.3O.sup.++2e.sup.- (3)
[0027] Preferred enzymes relay the electrons to mediators that
convey the electrons to the anode electrode. Thus, if the enzyme
normally conveys the electrons to reduce a small molecule, this
small molecule is preferably bypassed. The corresponding reaction
at the second electrode is:
2H.sub.3O.sup.++1/2O.sub.2+2e.sup.-3H.sub.2O (2)
[0028] Using reaction 2, preferably the bathing solution is
buffered to account for the consumption of hydrogen ions, or
hydrogen ion donating compounds must be supplied during operation
of the fuel cell. This accounting for hydrogen ion consumption
helps maintain the pH at a value that allows a useful amount of
redox enzymatic activity. To avoid this issue, an alternate
electron receiving molecule with an appropriate oxidation/reduction
potential can be used. For instance, periodic acid can be used as
follows:
H.sub.3O.sup.++H.sub.5IO.sub.6+2e.sup.-IO.sub.3.sup.-+4H.sub.2O
(4)
[0029] The use of this reaction at the cathode results in a net
production of water, which, if significant, can be dealt with, for
example, by providing for space for overflow liquid. Such
alternative electron receiving molecules are often solids at
operating temperatures or solutes in a carrier liquid, in which
case the third chamber 3 should be adapted to carry such
non-gaseous material. Where, as with periodic acid, the electron
receiving molecule can damage the enzyme catalyzing the electron
releasing reaction, the second chamber 2 can have a segment, as
illustrated as item 8 in fuel cell 10' of FIG. 2, containing a
scavenger for such electron receiving molecule.
[0030] In a preferred embodiment, the electrodes comprise
metallizations on each side of a non-conductive substrate. For
example, in FIG. 3A the metallization on a first side of dielectric
substrate 42 is the first electrode 44, while the metallization on
the second side is the second electrode 45. Perforations 49
function as the conduit between the anode and cathode of the fuel
cell, as discussed further below. The illustration of FIG. 3A, it
will be recognized, is illustrative of the relative geometry of
this embodiment. The thickness of dielectric substrate 42 is, for
example, from 15 micrometer (.mu.m) to 50 micrometer, or from 15
micrometer to 30 micrometer. The width of the perforations is, for
example, from 20 micrometer to 80 micrometer. Preferably,
perforations comprise in excess of 50% of the area of any area of
the dielectric substrate involved in transport between the
chambers, such as from 50 to 75% of the area. In certain preferred
embodiments, the dielectric substrate is glass or an polymer, such
as polyvinyl acetate or soda lime silicate.
[0031] FIG. 3B illustrates the electrodes framed on a perforated
substrate in more detail. The perforations 49 together with the
dielectric substrate 42 provide a support for lipid bilayers (i.e.,
membranes) spanning the perforations. Such lipid bilayers can
incorporate at least a first enzyme or enzyme complex (hereafter
"first enzyme") 62 effective (i) to oxidize the reduced form of an
electron carrier, and preferably (ii) to transport, in conjunction
with the oxidation, protons from the fuel side 41 to the product
side 43 of the fuel cell 50. Preferably, the first enzyme 62 is
immobilized in the lipid bilayer with the appropriate orientation
to allow access of the catalytic site for the oxidative reaction to
the fuel side and asymmetric pumping of protons. However, as the
fuel is substantially isolated on the fuel side 41, an enzyme
inserted into the lipid bilayer with the opposite orientation is
without an energy source.
[0032] Examples of particularly preferred enzymes providing one or
both of the oxidation/reduction and proton pumping functions
include, for example, NADH dehydrogenase (e.g., from E. coli. Tran
et al., "requirement for the proton pumping NADH dehydrogenase I of
Escherichia coli in respiration of NADH to fumarate and its
bioenergetic implications," Eur. J. Biochem 244: 155, 1997), NADPH
transhydrogenase, proton ATPase, and cytochrome oxidase and its
various forms. Methods of isolating such an NADH dehydrogenase
enzyme are described in detail, for example, in Braun et al.,
Biochemistry 37: 1861-1867, 1998; and Bergsma et al., "Purification
and characterization of NADH dehydrogenase from Bacillus subtilis,"
Eur. J. Biochem. 128: 151-157, 1982. The lipid bilayer can be
formed across the perforations 49 and enzyme incorporated therein
by, for example, the methods described in detail in Niki et al.,
U.S. Pat. No. 4,541,908 (annealing cytochrome C to an electrode)
and Persson et al., J. Electroanalytical Chem. 292: 115, 1990. Such
methods can comprise the steps of: making an appropriate solution
of lipid and enzyme, where the enzyme may be supplied to the
mixture in a solution stabilized with a detergent; and, once an
appropriate solution of lipid and enzyme is made, the perforated
dielectric substrate is dipped into the solution to form the
enzyme-containing lipid bilayers. Sonication or detergent dilution
may be required to facilitate enzyme incorporation into the
bilayer. See, for example, Singer, Biochemical Pharmacology 31:
527-534, 1982; Madden, "Current concepts in membrane protein
reconstitution," Chem. Phys. Lipids 40: 207-222, 1986; Montal et
al., "Functional reassembly of membrane proteins in planar lipid
bilayers," Quart. Rev. Biophys. 14: 1-79, 1981; Helenius et al.,
"Asymmetric and symmetric membrane reconstitution by detergent
elimination," Eur. J. Biochem 116: 27-31, 1981; Volumes on
biomembranes (e.g. Fleischer and Packer (eds.)), in Methods in
Enymology series, Academic Press.
[0033] Using enzymes having both the oxidation/reduction and proton
pumping functions, and which consume electron carrier, the
acidification of the fuel side caused by the consumption of
electron carrier is substantially offset by the export of protons.
Net proton pumping in conjunction with reduction of an electron
carrier can exceed 2 protons per electron transfer (e.g., up to 3
to 4 protons per electron transfer). Accordingly, in some
embodiments care must be taken to buffer or accommodate excess
de-acidification on the fuel side or excess acidification of the
product side. Alternatively, the rate of transport is adjusted by
incorporating a mix of redox enzymes, some portion of which enzymes
do not exhibit coordinate proton transport. In some embodiments,
care is taken especially on the fuel side to moderate proton export
to match proton production. Acidification or de-acidification on
one side or another of the fuel cell can also be moderated by
selecting or mixing redox enzymes to provide a desired amount of
proton production. Of course, proton export from the fuel side is
to a certain degree self-limiting, such that in some embodiments
the theoretical concern for excess pumping to the product side is
of, at best, limited consequence. For example, mitochondrial matrix
proteins which oxidize electron carriers and transport protons
operate to create a substantial pH gradient across the inner
mitochondrial membrane, and are designed to operate as pumping
creates a relatively high pH such as pH 8 or higher. (In some
embodiments, however, care is taken to keep the pH in a range
closer to pH 7.4, where many electron carriers such as NADH are
more stable.) Irrespective of how perfectly proton production is
matched to proton consumption, the proton pumping provided by this
embodiment of the invention helps diminish loses in the electron
transfer rate due to a shortfall of protons on the product
side.
[0034] In some embodiments, proton pumping is provided by a
light-driven proton pump such as bacteriorhodopsin. Recombinant
production of bacteriorhodopsin is described, for example, in
Nassal et al., J. Biol. Chem. 262: 9264-70, 1987. All trans retinal
is associated with bacteriorhodopsin to provide the light-absorbing
chromophore. Light to power this type of proton pump can be
provided by electronic light sources, such as LEDs, incorporated
into the fuel cell and powered by a (i) portion of energy produced
from the fuel cell, or (ii) a translucent portion of the fuel cell
casing that allows light from room lighting or sunlight to impinge
the lipid bilayer. For example, illustrated in FIG. 7 is a fuel
cell 400 in which light control devices 71 are incorporated. These
light control devices 71 contain, for example, LEDs or liquid
crystal shutters. Liquid crystal shutters have a relatively opaque
and a relatively translucent state and can be electronically
switched between the two states. An eternal light source, such as
the light provided by room lighting or sunlight can be regulated
through the use of liquid crystal shutters or other shuttering
device. In some embodiments, the light control devices are
individually regulated or regulated in groups to aid in regulating
the amount of light conveyed to the proton pump protein.
Preferably, the light control devices 71 have lenses to direct the
light to focus primarily at the dielectric substrate 42,
particularly those portions containing lipid bilayers incorporating
the proton pumps. A monitoring device 72 can operate to monitor a
condition in the fuel cell, such as the pH or the concentration of
electron carrier, and relay information to a controller 73 which
operates to moderate an aspect of the operation of the fuel cell
should monitored values dictate such action. For example, the
controller 73 can moderate the level of light conveyed by the light
control devices 71 depending upon the pH of the fuel side 41. Note
that in one embodiment an external light source is allowed to
energize the proton pump without the use of any light-regulating
devices.
[0035] In another embodiment, redox enzyme is deposited on or
adjacent to the first electrode, while a proton transporter is
incorporated into the lipid bilayers of the perforations.
[0036] In another embodiment, a second enzyme 63 is incorporated
into the fuel cell, such as into the lipid bilayer or otherwise on
the first electrode or in the first chamber, to facilitate proton
transport or generation in the first chamber during recharge mode,
thereby adding protons to the fuel side. The second enzyme can be
the same as, or distinct from, the enzyme that transports protons
during forward operation. An example of this second enzyme include
transporting proteins with lower redox potential relative to, for
example, NAD succinate dehydrogenase in conjunction with the
CoQH.sub.2-cyt c reductase complex. Also useful are lactate
dehydrogenase and malate dehydrogenase, both enzymes isolated from
various sources available from Sigma Chemical Co., St. Louis, Mo.
For example, bacteriorhodopsin can also be used with an orientation
appropriate for this use in the recharge mode.
[0037] In some embodiments, the recharge mode operates to
regenerate NADH, but does not reverse pump protons.
[0038] The perforations 49 are illustrated as openings. However,
these can also comprise porous segments of the dielectric substrate
42. Alternatively, these can comprise membranes spanning the
perforations 49 to support the lipid bilayer. Preferably, the
perforations encompass a substantial portion of the surface area of
the dielectric substrate, such as 50%. Preferably, enzyme density
in the lipid bilayer is high, such as
2.times.10.sup.12/mm.sup.2.
[0039] The orientation of enzyme in the lipid bilayer can be
random, with effectiveness of proton pumping dictated by the
asymmetric presence of substrate such as protons and electron
carrier. Alternatively, orientation is established for example by
using antibodies to the enzyme present on one side of the membrane
during formation of the enzyme-lipid bilayer complex.
[0040] The perforations 49 and metallized surfaces (first electrode
44 and second electrode 45) of the dielectric substrate 42 can be
constructed, for example, with masking and etching techniques of
photolithography well known in the art. Alternatively, the
metallized surfaces (electrodes can be formed for example by (1)
thin film deposition through a mask, (2) applying a blanket coat of
metallization by thin film then photo-defining, selectively etching
a pattern into the metallization, or (3) Photo-defining the
metallization pattern directly without etching using a metal
impregnated resist (DuPont Fodel process, see, Drozdyk et. al.
"Photopatternable Conductor tapes for PDP applications" Society for
Information Display 1999 Digest, 1044-1047; Nebe et al., U.S. Pat.
No. 5,049,480). In one embodiment, the dielectric substrate is a
film. For example, the dielectric can be a porous film that is
rendered non-permeable outside the "perforations" by the
metallizations. The surfaces of the metal layers can be modified
with other metals, for instance by electroplating. Such
electroplatings can be, for example, with chromium, gold, silver,
platinum, palladium, nickel, mixtures thereof, or the like,
preferably gold and platinum. In addition to metallized surfaces,
the electrodes can be formed by other appropriate conductive
materials, which materials can be surface modified. For example,
the electrodes can be formed of carbon (graphite), which can be
applied to the dielectric substrate by electron beam evaporation,
chemical vapor deposition or pyrolysis. Preferably, surfaces to be
metallized are solvent cleaned and oxygen plasma ashed.
[0041] As illustrated in FIG. 3C, electrical contact 54 connects
the first electrode 44 to a prospective electrical circuit, while
electrical contact 55 connects the second electrode 45.
[0042] In one embodiment, the product side of the fuel cell is
comprised of an aqueous liquid with dissolved oxygen. In an
embodiment, at least a portion of the wall retaining such aqueous
liquid is oxygen permeable, but sufficiently resists transmission
of water vapor to allow a useful product lifetime with the aqueous
liquid retained in the fuel cell. An example of an appropriate
polymeric wall material is an oxygen permeable plastic. In
contrast, the fuel side is preferably constructed of material that
resists the incursion of oxygen. The fuel cell can be made
anaerobic by flushing to purge oxygen with an inert gas such as
nitrogen or helium. In some rechargeable embodiments, the
electron-receiving composition is regenerated during recharging
mode, thereby eliminating or reducing the need for an outside
supply of such electron-receiving composition.
[0043] The fuel cell of the invention can preferably be recharged
by applying an appropriate voltage to inject electrons into the
fuel side to allow the first enzyme to catalyze the reverse
reaction. In particularly preferred embodiments, the first enzyme
has both the oxidation/reduction and proton pumping functions and
operates to reverse pump protons from the product side to the fuel
side during recharging. Thus, the reverse pumping supplies the
protons consumed in generating, for example, NADH from (i)
NAD.sup.+ and (ii) the injected electrons and protons. Note that in
reverse operation the injected electrons act first to reduce any
oxygen resident in the fuel side, as this reaction is energetically
favored. Once any such oxygen is consumed, the electrons can
contribute to regenerating the reduced electron carrier.
[0044] The above discussion of the embodiments using proton
transport focus on the use of both faces of a substrate to provide
the electrodes, thereby facilitating a more immediate transfer of
protons to the product side where the protons are consumed in
reducing the electron-receiving composition. However, it will be
recognized that in this embodiment structures such as a porous
matrix can be interposed between the fuel side and the product
side. Such an intervening structure can operate to provide
temperature shielding or scavenger molecules that protect, for
example, the enzymes from reactive compounds.
[0045] The fuel cell operates within a temperature range
appropriate for the operation of the redox enzyme. This temperature
range typically varies with the stability of the enzyme, and the
source of the enzyme. To increase the appropriate temperature
range, one can select the appropriate redox enzyme from a
thermophilic organism, such as a microorganism isolated from a
volcanic vent or hot spring. Nonetheless, preferred temperatures of
operation of at least the first electrode are about 80.degree. C.
or less, preferably 60.degree. C. or less, more preferably
40.degree. C. or 30.degree. C. or less. The porous matrix is, for
example, made up of inert fibers such as asbestos, sintered
materials such as sintered glass or beads of inert material.
[0046] The first electrode (anode) can be coated with an electron
transfer mediator such as an organometallic compound which
functions as a substitute electron recipient for the biological
substrate of the redox enzyme. Similarly, the lipid bilayer of the
embodiment of FIG. 3 or structures adjacent to the bilayer can
incorporate such electron transfer mediators. Such organometallic
compounds can include, without limitation, dicyclopentadienyliron
(C.sub.10H.sub.10Fe, ferrocene), available along with analogs that
can be substituted, from Aldrich, Milwaukee, Wis., platinum on
carbon, and palladium on carbon. Further examples include
ferredoxin molecules of appropriate oxidation/reduction potential,
such as the ferredoxin formed of rubredoxin and other ferredoxins
available from Sigma Chemical. Other electron transfer mediators
include organic compounds such as quinone and related compounds.
The electron transfer mediator can be applied, for example, by
screening or masked dip coating or sublimation. The first electrode
can be impregnated with the redox enzyme, which can be applied
before or after the electron transfer mediator. One way to assure
the association of the redox enzyme with the electrode is simply to
incubate a solution of the redox enzyme with electrode for
sufficient time to allow associations between the electrode and the
enzyme, such as Van der Waals associations, to mature.
Alternatively, a first binding moiety, such as biotin or its
binding complement avidin/streptavidin, can be attached to the
electrode and the enzyme bound to the first binding moiety through
an attached molecule of the binding complement.
[0047] The redox enzyme can comprise any number of enzymes that use
an electron carrier as a substrate, irrespective of whether the
primary biologically relevant direction of reaction is for the
consumption or production of such reduced electron carrier, since
such reactions can be conducted in the reverse direction. Examples
of redox enzymes further include, without limitation, glucose
oxidase (using NADH, available from several sources, including
number of types of this enzyme available from Sigma Chemical),
glucose-6-phosphate dehydrogenase (NADPH, Boehringer Mannheim,
Indianapolis, Ind.), 6-phosphogluconate dehydrogenase (NADPH,
Boehringer Mannheim), malate dehydrogenase (NADH, Boehringer
Mannheim), glyceraldehyde-3-phosphate dehydrogenase (NADH, Sigma,
Boehringer Mannheim), isocitrate dehydrogenase (NADH, Boehringer
Mannheim; NADPH, Sigma), and .alpha.-ketoglutarate dehydrogenase
complex (NADH, Sigma).
[0048] The redox enzyme can also be a transmembrane pump, such as a
proton pump, that operates using an electron carrier as the energy
source. In this case, enzyme can be associated with the electrode
in the presence of detergent and/or lipid carrier molecules which
stabilize the active conformation of the enzyme. As in other
embodiments, an electron transfer mediator can be used to increase
the efficiency of electron transfer to the electrode.
[0049] Associated electron carriers are readily available from
commercial suppliers such as Sigma and Boehringer Mannheim. The
concentrations at which the reduced form of such electron carriers
can be as high as possible without disrupting the function of the
redox enzyme. The salt and buffer conditions are designed based on,
as a starting point, the ample available knowledge of appropriate
conditions for the redox enzyme. Such enzyme conditions are
typically available, for example, from suppliers of such
enzymes.
[0050] As illustrated for the fuel cell 100 in FIG. 4A (top view),
a source reservoir 111 can be provided to supply reduced electron
carrier via conduit 113, check-valve 112 and diffuser 114 to second
chamber 102. Note that fuel cell 100 lacks a first chamber as this
chamber often serves as a reservoir, which in fuel cell 100 is
provided by source reservoir 111. Diffuser 115, conduit 116, and
pump 117 provide the pathway and motive power for conveying spent
liquid containing the electron carrier (often merely having reduced
effectiveness in powering the fuel cell) to an output reservoir
118. Fuel cell 100 further has a first electrode 104, second
electrode 105, third chamber 103, air pump 121, air inlet 122, and
air outlet 123. The various pumps can be operated off of a battery,
which can be recharged and regulated using energy from the fuel
cell, or can come into operation after the fuel cell begins
generating current. As illustrated in FIG. 4B, voltage or current
monitor M can monitor the performance the fuel cell in providing
voltage to the circuit comprising resister(s) R. Monitor M can
relay information to the controller, which uses the information to
regulate operation of one or more of the pumps.
[0051] FIG. 5A illustrates a fuel cell 200 (top view) in which an
acid/base reservoir 231 serves to supply a source of a material
required to account for any material imbalances in the reaction
equations at the first and second electrodes. The acid/base
reservoir 231 is connected via conduit 232, first actuated valve
233, and diffuser 234 to a second chamber 202. Liquid from source
reservoir 211 is delivered via check valve 212A and second actuated
valve 212B. In one example of operation, second actuated valve 212B
is normally open, and first actuated valve 233 is normally closed.
These valve positions are reversed when the controller detects the
need for fluid from acid/base reservoir 231 (e.g., because of a
signal received from a pH monitor) and operates pump 117 (e.g., by
use of a stepper motor) to draw fluid into the second chamber
202.
[0052] It will be recognized that the pump and valve arrangements
in FIGS. 4A through 5B are for illustration only, as numerous
alternative arrangements will be recognized by those of ordinary
skill. The plumbing of the fuel cell can be arranged to maintain a
chamber less than atmospheric pressure, for instance to help reduce
fluid leakage through various porous materials. The pores in
various porous materials can be selected to allow such diffusion as
is needed while minimizing fluid flow across the porous materials,
such as bulk liquid flow into a chamber designed to bring gas into
contact with a porous electrode.
[0053] The chambers of fluid which the first and second electrodes
contact can be independent, as illustrated in FIG. 6. In fuel cell
300, the solution bathing the first electrode (anode) is fed
through conduit 313A, while that bathing the second electrode
(cathode) is supplied through conduit 313B. Flow is illustrated as
regulated by pumps 317A and 317B. In the illustrated fuel cell, the
bathing solutions are replenished as needed to account for the
necessary imbalance in the chemistries occurring in the segregated
cells.
[0054] Cells can be stacked, and electrodes arranged in a number of
ways to increase the areas of contact between electrodes and
reactants. These stacking and arranging geometries can be based on
well-known geometries used with conventional fuel cells.
[0055] It will be recognized that where the electron carrier has an
appropriate electrochemical potential relative to the
electron-receiving molecule, the cell can be operated so that the
oxidized form of the electron carrier receives the electrons
through an enzyme catalyzed event. For example, the electron
carrier and the electron-receiving molecule can both be of the
class exemplified for electron carriers, but with distinct
electrochemical potentials. Thus, both the fuel side and product
side reactions can be enzyme catalyzed. In fact, even with such
traditional electron-receiving composition as oxygen, the product
side reaction can be enzyme catalyzed.
[0056] In one embodiment of the invention, the fuel cell does not
incorporate a proton pump. Preferably, in this embodiment the redox
enzyme is associated with a lipid component, such as a composition
containing phospholipid, steroids (such as sterols), glycolipids,
sphinoglipids, triglyceride or other components typically
incorporated into intracellular or external cellular membranes,
while still being sufficiently associated with the electrodes to
convey electrons. The enzyme is preferably incorporated into a
lipid bilayer. The barrier can be separating component such as is
used in a typical fuel cell, which preferably conveys protons
between the first and second chambers, though without requiring
proton pumping.
[0057] The following examples further illustrate the present
invention, but of course, should not be construed as in any way
limiting its scope.
EXAMPLE
[0058] The test apparatus consisted of a 5 ml reaction vessel which
held the fuel and into which copper or other electrodes were
dipped. The electrodes were in turn connected to a high impedance
voltmeter for open circuit voltage measurements or to a low
impedance ammeter for short circuit current measurements. Various
test configurations were employed to establish a baseline with
which to measure performance of the cell. Testing was done by
dipping electrodes in the fuel solution and measuring current
and/or voltage as a function of time.
[0059] The reaction which drove the cell was the oxidation of
nicotinamide-adenine dinucleotide hydride (NADH) which is catalyzed
by the enzyme glucose oxidase (GOD) in the presence of glucose.
This reaction yielded NAD.sup.+, a proton (H.sup.+) and 2 free
electrons.
H.sub.2O+NADH=NAD.sup.++H.sub.3O.sup.++2e.sup.-
[0060] The reaction toke place at one electrode, which was a
metallized plastic strip coated with the enzyme GOD. This
half-reaction was coupled through an external circuit to the
formation of water or hydrogen peroxide from protons, dissolved
oxygen, and free electrons at the other electrode.
[0061] Fuels used were solutions of glucose, NADH or combinations
thereof, distilled deionized water or a 50 mM solution of Tris.TM.
7.4 buffer. (NADH is most stable in a pH 7.4 environment.)
Electrode materials were copper (as a reference) and metallized
plastic strips coated with GOD (a commercially available
product).
[0062] Test configurations employed as well as initial results were
as follows:
[0063] Configuration 1:
[0064] Electrode 1: Copper
[0065] Electrode 2: Copper
[0066] Solution: 50 mM tris 7.4 buffer
[0067] Voltage: -7.5 mV
[0068] Current: 3 .mu.A initially decaying to -2.2 .mu.A within 3
minutes, fairly constant thereafter.
[0069] Configuration 2:
[0070] Electrode 1: Copper
[0071] Electrode 2: GOD coated strip
[0072] Solution: 50 mM tris 7.4 buffer
[0073] Voltage: +350 mV
[0074] Current: >20 .mu.A (+) initially decaying to +4 .mu.A
within 2 minutes, fairly constant thereafter.
[0075] Configuration 3:
[0076] Electrode 1: Copper
[0077] Electrode 2: Copper
[0078] Solution: 10 mM glucose in 50 mM tris 7.4 buffer
[0079] Voltage: -6.3 mVCurrent: -1.7 .mu.A, fairly constant after
initial dropoff.
[0080] Configuration 4:
[0081] Electrode 1: Copper
[0082] Electrode 2: GOD coated strip
[0083] Solution: 10 mM glucose in 50 mM tris 7.4 buffer
[0084] Voltage: +350 mV
[0085] Current: >20 .mu.A (+) initially decaying to -+2 .mu.A
within 2 minutes, fairly constant thereafter.
[0086] Configuration 5:
[0087] Electrode 1: Copper
[0088] Electrode 2: Copper
[0089] Solution: 10 mM glucose+10 mM NADH in 50 mM tris 7.4
buffer
[0090] Voltage: -290 mV slowly increasing to -320 after 4
minutes
[0091] Current: -25 .mu.A, decaying to -21 .mu.A after 2
minutes.
[0092] Configuration 6:
[0093] Electrode 1: Copper
[0094] Electrode 2: GOD coated strip
[0095] Solution: 10 mM glucose+10 mM NADH in 50 mM tris 7.4
buffer
[0096] Voltage: +500 mV decaying to +380 after 2 minutes
[0097] Current: >+30 .mu.A, dropping rapidly to .about.+1 .mu.A
after 1 minute.
[0098] All publications and references, including but not limited
to patents and patent applications, cited in this specification are
herein incorporated by reference in their entirety as if each
individual publication or reference were specifically and
individually indicated to be incorporated by reference herein as
being fully set forth. Any patent application to which this
application claims priority is also incorporated by reference
herein in its entirety in the manner described above for
publications and references.
[0099] While this invention has been described with an emphasis
upon preferred embodiments, it will be obvious to those of ordinary
skill in the art that variations in the preferred devices and
methods may be used and that it is intended that the invention may
be practiced otherwise than as specifically described herein.
Accordingly, this invention includes all modifications encompassed
within the spirit and scope of the invention as defined by the
claims that follow.
* * * * *