U.S. patent application number 11/558698 was filed with the patent office on 2007-05-03 for fuel cartridge for fuel cells.
This patent application is currently assigned to SOCIETE BIC. Invention is credited to Paul Adams.
Application Number | 20070095860 11/558698 |
Document ID | / |
Family ID | 32770877 |
Filed Date | 2007-05-03 |
United States Patent
Application |
20070095860 |
Kind Code |
A1 |
Adams; Paul |
May 3, 2007 |
Fuel Cartridge for Fuel Cells
Abstract
A versatile fuel cartridge for storing methanol and water,
methanol/water mixture or methanol/water mixtures of varying
concentrations is disclosed. The present invention utilizes a
filler insert preferably occupying a small portion of the volume of
the fuel cartridge, so that the fuel cartridge may hold more fuel
to ensure a longer life. The filler insert is capable of wicking
and transporting the fuel to the MEA. Additionally, the filler
insert remains in physical contact with the fuel in any orientation
of the fuel cartridge and at any fuel level in the fuel cartridge.
The fuel cartridge may have more than one chamber, and preferably
each chamber contains a different concentration of fuel.
Optionally, the fuel cartridge may include a pump to initiate fuel
flow from the fuel reservoir. The pump may regulate the flow of
fuel and importantly to shut off the flow of fuel, when
necessary.
Inventors: |
Adams; Paul; (Monroe,
CT) |
Correspondence
Address: |
THE H.T. THAN LAW GROUP
WATERFRONT CENTER SUITE 560
1010 WISCONSIN AVENUE NW
WASHINGTON
DC
20007
US
|
Assignee: |
SOCIETE BIC
14 rue Jeanne d'Asnieres
Clichy Cedex
FR
92611
|
Family ID: |
32770877 |
Appl. No.: |
11/558698 |
Filed: |
November 10, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10356793 |
Jan 31, 2003 |
7147955 |
|
|
11558698 |
Nov 10, 2006 |
|
|
|
Current U.S.
Class: |
222/187 ;
239/145 |
Current CPC
Class: |
Y02T 90/40 20130101;
H01M 8/04208 20130101; H01M 2250/20 20130101; H01M 8/1011 20130101;
H01M 8/04186 20130101; H01M 8/04216 20130101; Y02E 60/50
20130101 |
Class at
Publication: |
222/187 ;
239/145 |
International
Class: |
B67D 3/00 20060101
B67D003/00; A01G 27/00 20060101 A01G027/00 |
Claims
1-76. (canceled)
77. A fuel cartridge containing fuel suitable for use with a fuel
cell comprising a plurality of chambers, wherein each chamber has a
predetermined concentration of fuel and wherein each chamber
comprises a filler insert made from an absorbent material capable
of wicking fuel contained within the chamber by capillary action,
and wherein the filler insert is substantially in contact with the
fuel at any orientation of the chamber and at any fuel level.
78. The fuel cartridge of claim 77, wherein the concentrations of
fuel in the chambers are different from each other.
79. The fuel cartridge of claim 78, wherein the concentration of
fuel range from about 100% fuel and 0% water to about 0% fuel and
100% water.
80. The fuel cartridge of claim 77, wherein the chambers are either
arranged side-by-side, or end-to-end.
81. (canceled)
82. The fuel cartridge of claim 77, wherein at least one chamber
comprises a first free space portion and a second space portion,
wherein the filler insert occupies the second space portion.
83-85. (canceled)
86. The fuel cartridge of claim 77, wherein each chamber comprises
an outlet port.
87. The fuel cartridge of claim 82, wherein the filler insert of
said at least one chamber comprises a connecting column and at
least two disks.
88. The fuel cartridge of claim 82, wherein the filler insert of
said at least one chamber comprises a shell covering at least a
portion of the inner surface of the cartridge.
89. The fuel cartridge of claim 82, wherein the filler insert of
said at least one chamber comprises a connecting column and a
plurality of spokes, and optionally comprises a plurality of rings
wherein the spokes connect the connecting column to the rings.
90. (canceled)
91. The fuel cartridge of claim 77, wherein the absorbent material
is made from either polymeric fibers or plant-based fibers.
92. (canceled)
93. The fuel cartridge of claim 77 further comprising at least one
air vent.
94. The fuel cartridge of claim 77 further comprising at least one
refillable valve.
95. The fuel cartridge of claim 77, wherein the fuel cartridge is
connectable to a microelectromechanical pump to control the flow of
fuel.
96. The fuel cartridge of claim 95, wherein the fuel in at least
one chamber is pumped out of the chamber by the
microelectromechanical pump.
97. The fuel cartridge of claim 96, wherein the fuel in each
chamber is pumped at a different rate.
98. The fuel cartridge of claim 96, wherein the fuels from the
chambers are mixed after being pumped from the chambers.
99. The fuel cartridge of claim 95, wherein the
microelectromechanical pump is a field-induced pump.
100. The fuel cartridge of claim 99, wherein the
microelectromechanical pump comprises an electrical field applied
to the fuel to pump the fuel.
101. The fuel cartridge of claim 95, wherein the
microelectromechanical pump comprises an electrohydrodynamic pump
and an electro-osmotic pump
102. The fuel cartridge of claim 95, wherein the
microelectromechanical pump is an electro-osmotic pump.
103. The fuel cartridge of claim 95, wherein the
microelectromechanical pump is a membrane-displacement pump.
104. The fuel cartridge of claim 77, wherein the fuel cartridge is
connectable to a pump to control the flow of fuel.
105. The fuel cartridge of claim 77, wherein at least a portion of
one filler insert is covered by a fluid impermeable film.
106-110. (canceled)
111. The fuel cartridge of claim 77 further comprising at least one
shut-off valve.
112. The fuel cartridge of claim 82 wherein the at least one
chamber comprises a shut-off valve.
113. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a division of co-pending,
commonly-owned U.S. patent application Ser. No. 10/356,793, which
was filed on Jan. 31, 2003.
FIELD OF THE INVENTION
[0002] This invention generally relates to fuel cartridges for fuel
cells, and more particularly this invention relates to disposable
and refillable fuel cartridges. This invention also relates to fuel
cartridges for direct methanol fuel cells.
BACKGROUND OF THE INVENTION
[0003] Fuel cells are devices that directly convert chemical energy
of reactants, i.e., fuel and oxidant, into direct current (DC)
electricity. For an increasing number of applications, fuel cells
are more efficient than conventional power generation, such as
combustion of fossil fuel and more efficient than portable power
storage, such as lithium-ion batteries.
[0004] In general, fuel cell technologies include a variety of
different fuel cells, including alkali fuel cells, polymer
electrolyte fuel cells, phosphoric acid fuel cells, molten
carbonate fuel cells and solid oxide fuel cells. Today's more
important fuel cells can be divided into three general categories,
namely fuel cells utilizing compressed hydrogen (H.sub.2) as fuel,
proton exchange membrane (PEM) fuel cells that use methanol
(CH.sub.3OH) reformed into hydrogen as fuel, and PEM fuel cells
that use methanol (CH.sub.3OH) fuel directly ("direct methanol fuel
cells" or DMFC). Compressed hydrogen is generally kept under high
pressure, and is therefore difficult to handle. Furthermore, large
storage tanks are typically required, and cannot be made
sufficiently small for consumer electronic devices. On the other
hand, fuel cells using methanol reformats require reformers and
other vaporization and auxiliary systems thereby increasing the
size and complexity of methanol-reformat based fuel cells. DMFC is
the simplest and potentially smallest fuel cell, and holds the most
promising power application for consumer electronic devices.
[0005] DMFC for relatively larger applications typically comprises
a fan or compressor to supply an oxidant, typically air or oxygen,
to the cathode electrode, a pump to supply a water/methanol mixture
to the anode electrode and a membrane electrode assembly (MEA). The
MEA typically includes a cathode, a PEM and an anode. During
operation, the water/methanol fuel liquid mixture is supplied
directly to the anode, and the oxidant is supplied to the cathode.
The chemical-electrical reaction at each electrode and the overall
reaction for the fuel cell are described as follows:
[0006] Reaction at the anode:
CH.sub.3OH+H.sub.2O.fwdarw.CO.sub.2+6H.sup.++6e.sup.-
[0007] Reaction at the cathode:
O.sub.2+4H.sup.++4e.sup.-.fwdarw.2H.sub.2O
[0008] The overall fuel cell reaction:
CH.sub.3OH+1.5O.sub.2.fwdarw.CO.sub.2+2H.sub.2O
[0009] Due to the migration of the hydrogen ions (H.sup.+) through
the PEM from the anode through the cathode and due to the inability
of the free electrons (e.sup.-) to pass through the PEM, the
electrons must flow through an external circuit, which produces an
electrical current through the external circuit. The external
circuit may be any useful consumer electronic devices, such as
mobile or cell phones, calculators, personal digital assistants and
laptop computers, among others. DMFC is discussed in U.S. Pat. Nos.
5,992,008 and 5,945,231, which are incorporated by reference in
their entireties. Generally, the PEM is made from a polymer, such
as Nafion.RTM. available from DuPont, which is a perfluorinated
material having a thickness in the range of about 0.05 mm to about
0.50 mm. The anode is typically made from a Teflonized carbon paper
support with a thin layer of catalyst, such as platinum-ruthenium,
deposited thereon. The cathode is typically a gas diffusion
electrode in which platinum particles are bonded to one side of the
membrane.
[0010] One of the most important features for DMFC application is
fuel storage. Another important feature is to regulate the
transport of fuel out of the fuel cartridge to the MEA. To be
commercially useful, DMFC systems must have the capability of
storing sufficient fuel to satisfy the consumers' normal usage. For
example, for mobile or cell phones, for notebook computers, and for
personal digital assistants (PDAs), fuel cells need to power these
devices for at least as long as the current batteries, and
preferably much longer. Additionally, the DMFC should have easily
replaceable or refillable fuel tanks to minimize or obviate the
need for lengthy recharges required by today's rechargeable
batteries.
[0011] The patent literature contains no specific discussion of
non-pressurized portable fuel tank or fuel storage for fuel cells.
United States patent application publication no. US 2002/0127451A1
discloses a compact PEM fuel cell that stores methanol fuel in
upstanding circular tank(s) and vents the by-product CO.sub.2 back
into the tank to pressurize same. This fuel tank further comprises
a release valve to prevent the over-pressurization of the tank and
a fuel intake valve to add fuel. The fuel tank comprises a porous
layer to wick the water/methanol fuel mixture by capillary action
to the anode terminal of the PEM. However, this porous layer cannot
remain in contact with the fuel in positions other than vertical or
at a slight angle from vertical. Hence this fuel tank cannot be
used in all orientations.
[0012] Similarly, United States patent application publication no.
2001/0051293 A1 discloses a wicking structure made from an
absorbent material in fluid communication with a refillable fuel
reservoir. The wicking structure's function is to bring fuel to the
PEM by capillary action in regulated amounts. However, this
reference does not describe the method for regulating fuel flow, or
how the wicking structure maintains contact with the fuel when the
fuel level is less than full for capillary action to work.
[0013] U.S. Pat. No. 6,326,097 B1 discloses, among other things,
fuel ampoules that can be filled with fuel permeable materials that
allow the fuel to be communicated via capillary action in any
orientation to a fuel needle to be wicked to the PEM. These fuel
ampoules cannot store a sufficient amount of fuel, because for
capillary action to work properly the spacing within the permeable
materials is necessarily small. Hence, the fuel permeable materials
take up most of the space in the ampoules, thereby reducing the
storage capability. This reference also discloses a hand-operated
pump, i.e., a dimpled area on the ampoules, for the user to push to
pump fuel. This pump is also impractical since it requires the user
to pump before power can be supplied to the electronic devices, and
may require the user to continually pump the fuel cell to maintain
the flow of fuel to the PEM. Additionally, each hand pumping action
may send a surge of fuel to the PEM, and may cause an undesirable
surge in the electrical output from the fuel cell to the electronic
devices. Importantly, the '097 reference provides no teaching as to
how the unused fuel absorbed by the permeable materials can be
transported to the PEM.
[0014] United States patent application publication no.
2002/0018925 A1 discloses a cavity in an electronic device, where a
balloon containing fuel is stored or where an absorbing solid
containing fuel is stored for use with a fuel cell. Similar to the
'097 reference, this absorbing material would take up most of the
space in the fuel tank and would retain fuel within the absorbing
materials, thereby reducing effective fuel storage capacity.
[0015] U.S. Pat. No. 6,447,941 B1 discloses a plurality of
horizontal fuel permeating layers that are in contact with fuel in
a fuel tank, and the fuel is communicated by capillary action from
the fuel storage to the fuel permeating layers. The fuel is then
evaporated in fuel evaporating layers before reaching the anode
terminal. This fuel tank does not have any internal structure to
aid in the transport of fuel.
[0016] U.S. Pat. No. 6,460,733 B2 discloses a multi-walled fuel
container comprising an inner container of a methanol fuel disposed
inside an outer container. The inner container may have rigid walls
or may be a distensible bladder. The plenum area between the two
containers comprises agents or additives that neutralize the
methanol fuel in case of breakage or before disposal. The fuel is
fed to a fuel reservoir or directly to the anode electrode by
gravity or by a pressurized gas source located within the outer
reservoir. An external pump is provided to communicate the fuel to
the PEM.
[0017] U.S. Pat. Nos. 5,709,961 and 6,268,077 B1 disclose
pressurized fuel tanks to communicate fuel to the fuel cell.
[0018] Hence, there remains a need for a fuel storage device that
possesses high storage capacity and does not require a pressurized
source to transport the fuel to the PEM from the storage
device.
SUMMARY OF THE INVENTION
[0019] Hence, the present invention is directed to a fuel cartridge
adapted for use with a fuel cell.
[0020] The present invention is also directed to a fuel cartridge
adapted for use with a direct methanol fuel cell.
[0021] The present invention is also directed to a single use fuel
cartridge and also to a refillable fuel cartridge.
[0022] The present invention is also directed to stackable fuel
cartridges or fuel cartridges having multiple fuel chambers.
[0023] A preferred embodiment of the present invention is directed
to a fuel cartridge containing fuel suitable for use with a fuel
cell. The fuel cartridge comprises a free space portion and a
filler insert. The filler insert comprises an absorbent material
capable of wicking fuel contained within the cartridge by capillary
action, and the filler insert is substantially in contact with the
fuel at any orientation of the cartridge and at any fuel level. The
filler insert comprises preferably less than about 67%, more
preferably less than about 50% and even more preferably less than
about 33% of the volume of the cartridge.
[0024] In accordance with one aspect of this embodiment, the filler
insert comprises a connecting column and at least two disks. The
disks are preferably located at the ends of the connecting column.
The connecting column and/or at least one disk are preferably
covered by a fluid impermeable film. Preferably, the filler insert
further comprises an outlet port for fuel to leave the cartridge.
The outlet port may be made from absorbent material, or may
comprise a capillary needle or a bundle of capillary tubes.
Alternatively, the filler insert comprises a connecting column and
a plurality of spokes, and may further comprise a plurality of
rings, wherein the spokes connect the connecting column to the
rings.
[0025] In accordance with another aspect of this embodiment, the
filler insert comprises a shell covering at least a portion of the
inner surface of the cartridge and an outlet port. The filler
insert may further comprise at least one disk and/or a connecting
column. The shell may also cover the entire inner surface of the
cartridge.
[0026] The absorbent material of the filler insert can be made from
polymeric fibers, such as polyester, polyethylene, polyolefin,
polyacetal, or polypropylene fibers, or from plant-based fibers,
such as hemp, cotton, or cellulose acetate.
[0027] The cartridge may further comprise an air vent and a
refillable valve. The air vent prevents a partial vacuum from
forming within the cartridge, as fuel is withdrawn. The air vent
may be an air valve or an opening covered by a hydrophobic
micro-membrane. The air vent may also allow vapors or gases to vent
from the cartridge.
[0028] In accordance with another aspect of this embodiment, the
fuel cartridge is operatively connectable to a pump to control the
flow of fuel from the cartridge. Preferably, the pump is a
microelectromechanical system (MEMS) pump. The MEMS pump can be
either a field-induced pump or a membrane-displacement pump. A
field-induced pump has an AC or DC electrical field or magnetic
field applied to the fuel to pump the fuel. Suitable field-induced
pumps include, but are not limited to, electrohydrodynamic pump,
magnetohydrodynamic pump and electro-osmotic pump. The
electrohydrodynamic pump and an electro-osmotic pump can be used
together. A membrane-displacement pump comprises a membrane and a
force is applied to the membrane causing the membrane to move or
vibrate to pump the fuel. Suitable membrane-displacement pumps
include, but are not limited to, electrostatic pump and
thermopneumatic pump. The MEMS pump controls the speed of the flow
of fuel and reverses the flow, as well as stopping the flow.
[0029] Another preferred embodiment of the present invention is
directed to a fuel cartridge containing fuel suitable for use with
a fuel cell comprising a filler insert and a MEMS pump to control
the flow of fuel. The filler insert comprises an absorbent material
capable of wicking fuel contained within the cartridge by capillary
action, and wherein the filler insert is substantially in contact
with the fuel at any orientation of the cartridge and at any fuel
level.
[0030] In accordance with one aspect of this embodiment, the fuel
cartridge further comprises a first free space portion and a second
space portion, wherein the filler insert occupies the second space
portion. The filler insert comprises preferably less than about
67%, more preferably less than about 50% and even more preferably
less than about 33% of the volume of the cartridge.
[0031] In accordance with another aspect of this embodiment, the
filler insert may have any of the structures discussed above. The
absorbent material of the filler insert can be made from polymeric
fibers or plant-based fibers. The cartridge may further comprise an
air vent and a refillable valve. The MEMS pump can be either a
field-induced pump or a membrane-displacement pump, as discussed
above.
[0032] Another preferred embodiment of the present invention is
directed to a fuel cartridge containing fuel suitable for use with
a fuel cell, wherein the cartridge comprises a plurality of
chambers. Each chamber has a predetermined concentration of fuel,
and each chamber comprises a filler insert made from an absorbent
material capable of wicking fuel contained within the chamber by
capillary action. The filler insert is substantially in contact
with the fuel at any orientation of the chamber and at any fuel
level.
[0033] The concentrations of fuel in the chambers are preferably
different from each other. The concentration of fuel range from
about 100% fuel and 0% water to about 0% fuel and 100% water. The
chambers may be positioned side-by-side or end-to-end to each
other.
[0034] In accordance with one aspect of this embodiment, at least
one chamber comprises a first free space portion and a second space
portion, wherein the filler insert occupies the second space
portion. The filler insert comprises preferably less than about
67%, more preferably less than about 50% and even more preferably
less than about 33% of the volume of the chamber.
[0035] In accordance with another aspect of this embodiment, the
filler insert may have any of the structures discussed above. The
absorbent material of the filler insert can be made from polymeric
fibers or plant-based fibers. The cartridge may further comprise an
air vent and a refillable valve. The MEMS pump can be either a
field-induced pump or a membrane-displacement pump, as discussed
above. The fuel in each chamber is preferably pumped at a different
rate, and preferably the fuels from the chambers are mixed after
being pumped from the chambers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] In the accompanying drawings, which form a part of the
specification and are to be read in conjunction therewith and in
which like reference numerals are used to indicate like parts in
the various views:
[0037] FIG. 1 is a front view of a preferred fuel cartridge
oriented in an arbitrary position in accordance with the present
invention;
[0038] FIG. 2 is a front view of the fuel cartridge of FIG. 1
orientated in another arbitrary position;
[0039] FIG. 3(a) is a front view of a preferred embodiment of the
filler insert in accordance with the present invention; FIGS.
3(b)-3(d) are various views of another preferred embodiment of the
filler insert; and FIGS. 3(e)-3(g) are various views of another
preferred embodiment of the filler insert;
[0040] FIG. 4(a) is a front view with a partial cutaway of another
preferred embodiment of the filler insert in accordance with the
present invention; FIGS. 4(b) and 4(c) are various views of another
preferred embodiment of the filler insert; and FIGS. 4(d) and 4(e)
are front views of other preferred embodiments of the filler
insert;
[0041] FIGS. 5(a), 5(b) and 6 are alternative embodiments of the
fuel cartridge shown in FIGS. 1 and 2;
[0042] FIGS. 7(a)-7(b) are schematic views of alternative
embodiments of an electro-osmotic pump controlling or regulating
the flow of methanol fuel and/or water from the fuel cartridge(s)
to the MEA;
[0043] FIGS. 8(a)-8(b) are schematic views of the electro-osmotic
pump with reversed polarity to stop the flow of fuel, and being
electrically isolated from the fuel cartridge, respectively;
[0044] FIG. 9 is another preferred embodiment of the fuel cartridge
of the present invention with details omitted for clarity having a
plurality of fuel chambers;
[0045] FIG. 10 is another preferred embodiment of the fuel
cartridge of the present invention with details omitted for clarity
having a plurality of fuel chambers schematically connected to an
optional diffuser/mixing element and to the MEA; and
[0046] FIG. 11 is an alternative embodiment of the filler insert
shown in FIGS. 1 and 2 with protective sheathing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0047] As illustrated in the accompanying drawings and discussed in
detail below, the present invention is directed to a versatile fuel
cartridge for storing fuel cell fuels such as methanol and water,
methanol/water mixture, methanol/water mixtures of varying
concentrations or pure methanol. The fuel cartridge may contain
other types of fuel cell fuels, such as ethanol, or other chemicals
that may improve the performance or efficiency of fuel cells, and
the present invention is not limited to any type of fuels or
liquids contained in the cartridge. The term "fuel" as used herein
includes all fuels that can be reacted in fuel cells, and includes
all of the above suitable fuels, liquids, and/or chemicals and
mixtures thereof. The present invention utilizes a filler insert,
which preferably occupies a small portion of the volume of the fuel
cartridge, so that the fuel cartridge may hold more fuel to ensure
a long life of the fuel cartridge, and to minimize the retention of
fuel in the cartridge at the end of the useful life of the
cartridge. The filler insert is capable of wicking and transporting
the fuel to the MEA. Additionally, the filler insert remains
substantially in physical contact with the fuel in any orientation
of the fuel cartridge and at any fuel level in the fuel
cartridge.
[0048] Optionally, the fuel cartridge may also include a pump to
initiate, maintain and/or control fuel flow from the fuel
reservoir. The pump may also regulate the flow of fuel to the MEA
to increase or decrease the electrical current output from the MEA,
and importantly to shut off the flow of fuel, when necessary.
Alternatively, a shut-off valve may be used to ensure that the flow
of fuel is shut off when the electronic device is shut-off or when
the cartridge is separated from the device. The pump or pumps may
also mix pure methanol with water before pumping the mixture to the
MEA. The pump may also selectively pump methanol/water mixture from
different reservoirs having varying methanol concentrations.
[0049] Preferably, the pump is adapted for use with low liquid flow
rate, and preferably is available in small sizes for use with
consumer electronic devices. Preferably, the pump has a minimal
number of moving parts or more preferably no moving part to
minimize breakage. Preferably, suitable pumps include
microelectromechanical systems (MEMS) pumps, such as those used to
pump ink in inkjet printers or those used in drug delivery systems
or those used to cool micro integrated circuit chips, among others.
More specifically, suitable MEMS pumps include field-induced flow
pumps and membrane-displacement pumps. Field induced pumps utilize
an electrical or magnetic field to produce flow. A suitable
field-induced pump is an electro-osmotic pump, which is capable of
moving liquid in small spaces, such as capillary spaces, by
applying a direct circuit (DC) potential across at least a portion
of a capillary column. The direction of fluid flow in the capillary
column can also be reversed or stopped by reversing the direction
of the DC potential. Other suitable field-induced pumps include,
but are not limited to, electrohydrodynamic pumps and
magnetohydrodynamic pumps. Membrane-displacement pumps utilize a
force, e.g., an electrical charge, applied to a membrane, causing
the membrane to move or vibrate to propel the fluid-to-be-pumped.
Suitable membrane-displacement pumps include, but are not limited
to electrostatic pumps and thermopneumatic pumps.
[0050] As shown in FIG. 1, fuel cartridge 10 comprises a free space
portion and a portion occupied by filler insert 12. Free space
portion indicates that the space may be occupied by fuel or gas
when the fuel level is less than full, but otherwise not occupied
by other substances or materials. Insert 12 is preferably made from
an absorbent material. Suitable absorbent materials include, but
are not limited to, sponges and fibrous polymers such as polyester,
polyethylene, polyolefin, polyacetal, polypropylene fibers, or from
natural fibers such as hemp, cotton, or cellulose acetate or other
plant-based fibers. Preferably, if polymeric fibers are used, these
fibers are either thermoset or thermoplastic with high softening or
melting temperature to withstand potentially high internal
temperatures that may exist inside the fuel cells or inside the
electronic devices. Filler materials of any porosity or
permeability can be used, so long as the filler materials can wick
fuel at a sufficient flow rate. Insert 12 preferably comprises two
bases or disks 14 and a connecting column 16. Insert 12 preferably
occupies less than about 67% of the internal volume of cartridge
10, more preferably less than about 50% and even more preferably
less than about 33%, so that the free space portion and the
interstitial volume within insert 12 may be used to hold fuel 20.
Alternatively, insert 12 may occupy all of the internal volume of
cartridge 10, preferably when cartridge 10 is utilized with a MEMS
pump.
[0051] In FIG. 1, cartridge 10 is shown arbitrarily in the
horizontal position to replicate an electronic device, such as a
calculator or PDA, being used. In this position, liquid fuel 20,
which is shown as partially empty, may make contact with filler
insert 12, so that fuel 20 may be communicated to insert 12 at
contact points 22 for wicking to the MEA. Fuel is then transferred
out of cartridge 10 via outlet port 24. Outlet port 24 may contain
the same filler material as insert 12, so that fuel 20 may be
continually wicked out of cartridge 10. Alternatively, outlet port
24 may comprise a single capillary needle or a bundle of capillary
tubes. More preferably, outlet port 24 comprises a material more
suitable with the selected pump to optimize flow from the cartridge
and to control same. For example, if an electro-osmotic pump is
used, outlet port 24 preferably comprises glass or fused-silica
capillary tubes or beads.
[0052] As illustrated in FIG. 2, cartridge 10 can also be
arbitrarily positioned at any tilt angle and fuel 20 would
substantially maintain its contact with filler insert 12 at contact
point(s) 22. Similarly, when cartridge 10 is positioned vertically,
such that outlet port 24 is positioned either at the top or bottom,
the fuel remaining in cartridge 10 substantially maintains contact
with disk 14 of filler insert 12.
[0053] Alternatively, as shown in FIG. 3(a), filler insert 12 may
comprise additional disk(s) 26 located between disks 14. Disk 26
may have any orientation, including but are not limited to, being
parallel to disks 14. Disk 26 may be positioned diagonally between
disks 14. For additional structural support, connecting column 16
may be covered by a thin plastic film 25, as shown in FIG. 11.
Advantageously, such thin film improves the flow of liquid through
insert 12 by preventing air or other gases from entering the filler
material. Alternatively, thin plastic film 25 may also at least
partially cover disk 14, 26, and seals 27 may be provided where the
film covering column 14 intersects the film covering disk 14,
26.
[0054] FIG. 3(b) illustrates another variation of filler insert 12,
which comprises column 16 and a plurality of spokes 28. FIG. 3(c)
is a cross-sectional view of FIG. 3(b) showing a preferred fuel
flow path within the insert. Spokes 28 may be aligned in straight
lines as shown in FIGS. 3(b) and 3(c) or may be unaligned as shown
in FIG. 3(d). FIG. 3(e) illustrates another variation of filler
insert 12, which comprises column 16, spokes 28 and rings 29. FIG.
3(f) is a cross-sectional view of FIG. 3(e) showing a preferred
fuel flow path within the insert, FIG. 3(g) is a top view of FIG.
3(e). Spokes 28 can also be aligned or unaligned in this
embodiment.
[0055] In another preferred embodiment, filler insert 12 may
comprise outlet port 24, disks 14 and a shell 31. FIG. 4(a), shown
with a portion of shell 31 removed for clarity, illustrates this
embodiment. Since shell 31 and disks 14 would cover the entire
inside surface of cartridge 10, fuel 20 would always remain in
contact with insert 12 at any fuel level and at any orientation of
the cartridge. It is important to note that it is not necessary for
shell 31 and disks 14 to completely cover the inside surface of
cartridge 10 for fuel 20 to substantially maintain contact with
insert 12. For example, as shown in FIGS. 4(d) and 4(e), shell 31
may have a spiral shape or may comprise a plurality of spaced-apart
strips, respectively, and partially covers the inner surface of the
cartridge. As shown in FIGS. 4(d) and 4(e), insert 12 may also have
outlet port 24 and one disk 14. Alternatively, this embodiment may
also have second disk 14 and connecting column 16. Furthermore, as
shown in FIG. 4(b), filler insert 12 comprises outlet port 24,
column 16, disk 14 and shell 31 connected serially in the manner
shown. FIG. 4(c) is a cross-sectional view of FIG. 4(b) showing the
preferred fuel flow path within the insert.
[0056] Advantageously, filler insert 12 may be used with other
cartridges such as cartridge 30, which have outer surfaces with
varying curvature, e.g., the hourglass-shaped cartridge shown in
FIG. 5(a) or the bottle-shaped cartridge shown in FIG. 5(b). As
illustrated, the filler insert shown in FIGS. 1-2 is used with
cartridge 30 in FIG. 5(a) and the filler insert shown in FIGS.
4(b)-4(c) is shown with cartridge 30 in FIG. 5(b). Disks 14 and/or
rings 29 can also be modified to other shapes, such as hexagonal
disks 34, to be utilized in cartridge 32 shown in FIG. 6. Hence, as
used herein, the term "disk" or "ring" is not limited to any
particular shape and includes circular and non-circular shapes as
well as regular and irregular shapes.
[0057] As fuel is withdrawn from cartridge 10, 30 or 32, a partial
vacuum may be created within the cartridge. This partial vacuum
tends to force the fuel to flow back into the cartridge or it may
pull water from the fuel cell reaction into the cartridge. This
effect can work against the capillary effect of filler insert 12 to
draw fuel out of the cartridge. To overcome this effect, when the
electronic consumer device is not in used, air or CO.sub.2 produced
by the fuel cell reaction may be allowed to flow into the cartridge
through outlet port 24 to eliminate the partial vacuum. In
applications where outlet port 24 is connected in an airtight
manner to the MEA or where the fuel cell is used continuously for a
long period of time, a vent 36 may be provided to allow air to
enter the cartridge to equalize the internal pressure of the
cartridge to the external pressure. Vent 36, shown schematically in
FIG. 6, can be a one-way valve that only allows air to enter but
does not allow fuel or other liquids to exit. Alternatively, vent
36 is an opening covered by a hydrophobic membrane, such that
methanol, water or other liquids cannot pass through but air is
allowed to enter the cartridge. Hydrophobic membranes can be made
from polytetrafluoroethylene (PTFE), nylon, polyamides,
polyvinylidene, polypropylene, polyethylene or other polymeric
membrane. A commercially available hydrophobic PTFE microporous
membrane can be obtained from W.L Gore Associates, Inc.
Additionally, a refill valve 38 may be provided to add fuel to
cartridge 10, 30, 32 when necessary. It is important to note that
while air vent 36 and valve 38 are illustrated in connection with
FIG. 6, these devices are applicable to all cartridge embodiments
shown and claimed herein.
[0058] To ensure that the fuel flow from outlet port 24 of the fuel
cartridge to the MEA is regulated, an optional pump is provided.
Any pump can be used so long as fuel can be pumped from the
cartridge in a regulated manner. Preferably, the pump is a MEMS
pump to minimize the size of the pump. Electro-osmotic pump is one
of the MEMS pumps usable with the present invention. As shown in
FIGS. 7(a)-7(c), an electro-osmotic pump 39 is provided.
Electro-osmotic pump 39 contains no moving parts and is capable of
moving fluids through tight spaces. Electro-osmotic pump
advantageously can move fluid with low conductivity. An
electro-osmotic flow is created when a DC potential is applied
across a porous media. The liquid in the porous media is driven
from the anode or positive electrode to the cathode or negative
electrode, when exposed to the DC electrical field. Electro-osmotic
pump is particularly useful in micro-channels, such as those within
filler insert 12 or outlet port 24, and in slow and controlled
flow, which is very useful in DMFC. Electro-osmotic flow is
discussed in details in U.S. Pat. No. 3,923,426 entitled,
"Electroosmotic Pump and Fluid Dispenser Including Same," issued on
Dec. 2, 1975, in "Electroosmotic flow pumps with polymer frits" by
S. Zeng, C. Chen, J. Santiago, J. Chen, R. Zare, J. Tripp, F. Svec
and J. Frechet, published in Sensors and Actuators B Chemical
Journal, vol. 82, pp. 209-212 (2002), and in "A Large Flowrate
Electroosmotic Pump with Micron Pores," by S. Yao, D. Huber, J.
Mikkelsen and J. Santiago, proceedings of IMECE, 2001 ASME
International Mechanical Engineering Congress and Exposition, Nov.
11-16, 2001, New York, N.Y., among other references. These
references are incorporated by reference herein in their
entireties.
[0059] As shown in FIG. 7(a), a DC potential can be applied across
entire insert 12 to ensure that the fuel flow out of cartridge 10
is regulated. More preferably, a DC potential is applied across
only outlet port 24, since less voltage is required and once the
fuel begins to flow through outlet port 24 momentum is transferred
to the remaining fuel through viscous interaction. Battery 40 is
selected to have any potential necessary to induce fuel flow. One
or more batteries 40 can be stacked in series to increase the
applied DC potential, as shown in FIGS. 7(b) and 7(c).
Alternatively, a DC-DC converter can be used to increase the DC
potential output. The DC-DC converter converts low voltage DC to
alternating current (AC) voltage (or to electrical pulses), and
then transforms the low AC voltage to higher AC voltage before
reconverting it to DC voltage. Advantageously, DC-DC converters are
available in small sizes. When the fuel stored in the free space of
the fuel cartridge is used up, electro-osmotic pump 39 can pump
fuel out of insert 12 to render most of this fuel usable. To
minimize the draw from battery 40, the electrical potential from
the fuel cell can be used to power the electro-osmotic flow once
the fuel cell is operational. Preferably, controller 42 is provided
to control the potential and/or to invert the polarity of battery
40.
[0060] In accordance with one aspect of the present invention,
battery 40 is rechargeable so that the current from the fuel cell,
when it is in operation, may recharge battery 40. Advantageously,
battery 40 can be continually recharged to prolong battery life,
and the consumer may not realize that a battery is used within the
fuel cell. In accordance with another aspect of the present
invention, a manual pump 44, such as a hand-operated air pump, can
be provided to manually pump the fuel to activate the MEA when the
battery 40 is run down, or after a long period of inactivity the
fuel is drained from outlet port 24 or from most of insert 12, or
when the capillary spacing is blocked.
[0061] Another advantage of electro-osmotic pump 39 is that when
the MEA needs to be shut down, controller/inverter 42 can reverse
the polarity of battery 40 so that fuel is forced to flow away from
the MEA to stop the fuel cell reaction to disengage the electrical
circuit, as shown in FIG. 8(a). Alternatively, a shut-off valve 45,
as shown in FIG. 6, may be provided to isolate the fuel from the
MEA. Shut-off valve 45 can also help prevent the unintended
discharge of fuel from the fuel cartridge, when the cartridge is
separated from the electronic device. Shut-off valve can be
positioned either above or below refill valve 38. Shut-off valve 45
can be a normally opened valve or a normally closed valve, as
discussed in commonly-owned U.S. Pat. No. 5,520,197. The '197
patent is hereby incorporated by reference in its entirety.
[0062] After the fuel cell's electrical production is stopped, a
manual or electronic switch 44 is opened to remove any DC potential
across filler insert 12 or outlet port 24. Controller 42, for
example, can be operatively connected to the on/off switch of the
consumer electronic device, such that when the device is turned on,
a DC potential is applied across insert 12 or outlet port 24. When
the device is turned off, the DC potential is reversed and then
disconnected. Controller 42 may also control the rate of fuel flow
from the fuel cartridge by varying the DC potential applied. One
method of varying the DC potential is described below.
[0063] Battery 40 and controller/inverter 42 may be located on the
fuel cartridge, preferably when the cartridge is refillable, or may
be located in the fuel cell so that the costs for producing the
fuel cartridges may be reduced to make the fuel cartridge
disposable after a single-use.
[0064] In accordance with another aspect of the invention, fuel
cartridge 10 may comprise two or more chambers. As shown in FIG. 9,
fuel cartridge 10 may have chambers 46 and 48, where one chamber is
located on top of the other chamber. Preferably, one contains
methanol and the other contains water. A filler insert is included
in each chamber. In the embodiment shown in FIG. 9, the connecting
column 50 of chamber 48 is disposed concentrically inside
connecting column 52 of chamber 46. Preferably, column 50 is
isolated from column 52 by a waterproof film. As shown, each column
is connected to disks to ensure that the liquid contained therein
is wicked out of the chambers. Alternatively, the chambers can be
positioned side-by-side, such as chambers 54 and 56 illustrated in
FIG. 10. Each chamber 54, 56 contains a filler insert comprising a
connecting column 58, 60, respectively, and disks to wick the
liquids out of the chambers. In the embodiments shown in FIGS. 9
and 10, the methanol and water streams need to be combined or mixed
before reaching the MEA. Preferably, the liquids are mixed in
diffuser or mixing zone 62. Preferably zone 62 is filled with the
same filler material as insert 12 to spread the fuel mixture by
capillary action before reaching the MEA. Additionally, a
pre-mixing chamber may be provided upstream of diffuser or mixing
zone 62, so that the liquids may be thoroughly mixed before
reaching the diffuser 62.
[0065] Different fuel cells may require different concentrations of
methanol to water in the fuel mixture for operation. This can be
accomplished by the electro-osmotic pump shown schematically in
FIG. 7(c). The same DC potential can be applied to chambers 46, 48
or 54, 56. Due to the different viscosity and surface tensions of
methanol and water, the flow rate of methanol and water may be
different. Controller/inverter 42 may have multiple outputs, and
each output may have a different voltage to regulate the flows out
of the chambers. Alternatively, in one preferred embodiment, each
output may have a variable resistor 64 to adjust the voltage of the
output as illustrated in FIG. 7(b). Alternatively, the variable
resistor can be located in series with the chamber to adjust the
voltage applied to the chamber, as illustrated in FIG. 7(c).
[0066] Alternatively, chambers 46, 48 or 54, 56 may contain fuel
mixtures of different concentrations or compositions, and
electro-osmotic pump 39 can selectively pump the fuel mixture out
of one or the other chamber depending on the power consumption
requirements. This can be accomplished by increasing the resistance
in resistor 64 connected with the unneeded chamber, so that it is
significantly higher than the impedance or resistance of the filler
insert in the chamber. When the resistance of resistor 64 is
sufficiently high, the DC potential across the filler insert is
insignificantly small thereby effectively stopping the flow from
the unneeded chamber and only allowing the flow to come from the
selected chamber. The fuel mixtures in the two or more chambers may
be mixed together before reaching the MEA, as explained above.
Alternatively, each chamber may have its own pump to regulate or
control the flow of fuel therefrom.
[0067] In accordance with other embodiments of the invention, other
pumps can be utilized with fuel cartridges 10, 30, 32 or other fuel
cartridges. As stated above, other suitable pumps include, but are
not limited to, field-induced pumps such as electrohydrodynamic
pumps and magnetohydrodynamic pumps. Other suitable pumps include
membrane-displacement pumps, such as electrostatic pumps and
thermopneumatic pumps.
[0068] An electrohydrodynamic pump applies an AC voltage field to a
fluid-to-be-pumped. An example of an electrohydrodynamic pump is
disclosed in U.S. Pat. No. 4,316,233, entitled "Single Phase
Electrohydrodynamic Pump," issued on Feb. 16, 1982. The '233 patent
is hereby incorporated by reference in its entirety. An
electrohydrodynamic pump generally works by the attractive and
repulsive forces exerted on the fluid by an electric field through
Coulombic reaction. Since the electrical field acts on the fluid
and not through mechanical pressure, the internal pressure within
the fluid does not increase significantly due to the pumping. An
electrohydrodynamic pump is particularly suitable for liquid with
low electrical conductivity. As disclosed in and shown in the
figures of the '233 patent, an AC charge is applied to a flow
conduit, wherein the flow conduit comprises a plurality of internal
projections of semi-insulating material hanging from the conduit
wall. This flow conduit advantageously can be outlet port 24 of
filler insert 12. The projections are made from different materials
having different electrical relaxation times, such that the
electrical charge for each projection reaches its peak at different
times. This creates an AC electrical field in the fluid. For
example, if the AC charge is a sinusoidal voltage, the voltages at
the tips of the projections cause a sinusoidal electrical field to
pump the fluid in a desired direction. Alternatively, the
projections can be made from the same materials but have different
dimensions to have different relaxation times. The projections may
be spaced apart or positioned adjacent to each other. The
projections may also have any geometrical shapes.
[0069] It is known that electrohydrodynamic flow can be used in
combination with electro-osmotic flow to pump fluid, and it has
also been reported that electrohydrodynamic and electro-osmotic
pumps can be used together to pump methanol and ethanol through
capillary tubes.
[0070] A magnetohydrodynamic pump, on the other hand, applies a
magnetic field to a working fluid to move the working fluid in any
desired direction. The flow of working fluid can be reversed by
reversing the magnetic field. An example of a magnetohydrodynamic
pump is disclosed in U.S. Pat. No. 6,241,480, entitled
"Micro-magnetohydrodynamic Pump and Method for Operation of the
Same," issued on Jun. 5, 2001. The '480 patent is incorporated
herein by reference in its entirety. Any conductive liquid can be
the working fluid. Preferably, the working fluid is a highly
viscous, liquid metal, such as mercury or gallium alloys. In a
preferred embodiment, the magnetohydrodynamic pump comprises a
chamber having an inlet and an outlet with a mass of the liquid
metal acting as a piston. A magnetic field generated by permanent
magnet, electromagnet or an array of spiral magnetic inductors is
applied to the working fluid to move the working fluid away from
the inlet to draw the fluid-to-be-pumped into the chamber. The
magnetic field is then reversed to pump the fluid out of the
chamber through the outlet. The magnetohydrodynamic pump may have
an additional chamber for holding the liquid to be pumped. Each of
the inlet and outlet preferably has a check valve to control the
flow of the fluid-to-be-pumped. The inlet is preferably in fluid
communication with outlet port 24 and the outlet is preferably in
fluid communication with the MEA to transport the fluid to the
MEA.
[0071] An electrostatic pump is a membrane-displacement pump, which
is different than the field-induced pumps discussed above. Instead
of applying an electrical or magnetic field (or both) to a fluid
and pumping the fluid, a membrane-displacement pump typically
includes a membrane or diaphragm and a force applied to the
membrane or diaphragm to pump the fluid. In an electrostatic pump,
an electrical potential is applied to a membrane or diaphragm
causing the membrane or diaphragm to move or to vibrate to pump the
fluid. An electrostatic pump is disclosed in U.S. Pat. No.
6,485,273, entitled "Distributed MEMS Electrostatic Pumping
Devices," issued on Nov. 26, 2002. The '273 patent discloses, among
other things, a MEMS pump, which has a movable membrane attached in
a cantilevered manner to a substrate. The membrane is biased at the
free end away from the substrate. When an electrostatic voltage is
applied across a first electrode in the movable membrane and a
second electrode in the substrate, the movable membrane moves
toward the substrate. Such movement pumps any fluid-to-be-pumped
located between the free end of the movable membrane and the
substrate. When the electrostatic force is removed, the movable
membrane is biased back to its original position. This cycle may be
repeated to continually pump the fluid. Another electrostatic pump
is disclosed in U.S. Pat. No. 5,336,062, entitled
"Microminiaturized Pump," issued on Aug. 9, 1994. The '062 patent
discloses, among other things, an electrostatic pump having at
least one membrane. When an AC voltage is applied to the membrane
through its "ohmic" contact, the membrane vibrates to pump fluid.
The '062 patent also discloses a two membrane embodiment, where two
AC voltages having different phases and voltages are applied to the
membranes, such that the membranes may vibrate in opposite phase to
one another to pump fluid. The disclosure of the '273 patent and
the '062 patent are incorporated herein by reference in their
entireties.
[0072] A thermopneumatic pump is another membrane-displacement
pump. In this pump a heating element, e.g., a resistive heating
element, is disposed in a pressure chamber and the pressure chamber
is operatively connected to the membrane. Enclosed in the chamber
is a quantity of either working gas or working liquid that expands
when heated. Suitable working liquids include fluorinated
hydrocarbon liquids available from 3M. Such thermal expansion
generates a force against the membrane and moves the membrane. The
movement of the membrane pumps the fluid-to-be-pumped. A reduction
in temperature of the enclosed working gas or liquid contracts the
membrane. Thermopneumatic pump and other membrane displacement
micropumps are disclosed in U.S. Pat. No. 6,069,392, entitled
"Microbellows Actuator," issued on May 30, 2000 and U.S. Pat. No.
6,326,211, entitled "Method of Manipulating a Gas Bubble in a
Microfluidic Device" issued on Dec. 4, 2001. These references are
incorporated by reference in their entireties.
[0073] The fuel cartridges 10, 30, 32 described above can be used
with DMFC, or can be incorporated with a reformat to convert the
methanol to hydrogen to be used with methanol reformat fuel
cells.
[0074] While it is apparent that the illustrative embodiments of
the invention disclosed herein fulfill the objectives of the
present invention, it is appreciated that numerous modifications
and other embodiments may be devised by those skilled in the art.
Additionally, feature(s) and/or element(s) from any embodiment may
be used singly or in combination with other embodiment(s).
Therefore, it will be understood that the appended claims are
intended to cover all such modifications and embodiments, which
would come within the spirit and scope of the present
invention.
* * * * *