U.S. patent application number 16/735317 was filed with the patent office on 2020-11-05 for self-regulating electrolytic gas generator and implant system comprising the same.
The applicant listed for this patent is Giner Life Sciences, Inc.. Invention is credited to Melissa Schwenk, Simon G. Stone, Linda A. Tempelman.
Application Number | 20200348113 16/735317 |
Document ID | / |
Family ID | 1000004974657 |
Filed Date | 2020-11-05 |
United States Patent
Application |
20200348113 |
Kind Code |
A1 |
Stone; Simon G. ; et
al. |
November 5, 2020 |
SELF-REGULATING ELECTROLYTIC GAS GENERATOR AND IMPLANT SYSTEM
COMPRISING THE SAME
Abstract
Self-regulating electrolytic gas generator and implant system
including the same. In one embodiment, the electrolytic gas
generator is a water electrolyzer and includes a polymer
electrolyte membrane with an anode on one side and a cathode on the
other side. Anode and cathode seals surround the peripheries of the
anode and cathode and include inlets for water and outlets for
oxygen and hydrogen, respectively. A cathode current collector is
placed in contact with the cathode, and an anode current collector,
which may be an elastic, electrically-conductive diaphragm, is
positioned proximate to the anode. The anode current collector is
reversibly deformable between a first state in which it is in
direct physical and electrical contact with the anode and a second
state in which it distends, due to gas pressure generated at the
anode, so that it is not in physical or electrical contact with the
anode, causing electrolysis to cease.
Inventors: |
Stone; Simon G.; (Arlington,
MA) ; Tempelman; Linda A.; (Lincoln, MA) ;
Schwenk; Melissa; (Waltham, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Giner Life Sciences, Inc. |
Newton |
MA |
US |
|
|
Family ID: |
1000004974657 |
Appl. No.: |
16/735317 |
Filed: |
January 6, 2020 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
15814124 |
Nov 15, 2017 |
10557691 |
|
|
16735317 |
|
|
|
|
62422420 |
Nov 15, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F42B 3/04 20130101; A61M
2005/14204 20130101; A61M 2005/006 20130101; C25B 9/10 20130101;
A61M 37/00 20130101; A61K 48/0075 20130101; A61M 2202/0208
20130101; A61M 5/14276 20130101; A61M 2205/7536 20130101; A61M
31/002 20130101; C25B 9/04 20130101 |
International
Class: |
F42B 3/04 20060101
F42B003/04; C25B 9/04 20060101 C25B009/04; A61K 48/00 20060101
A61K048/00; A61M 5/142 20060101 A61M005/142; A61M 31/00 20060101
A61M031/00 |
Goverment Interests
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was made with government support under Grant
Number 1R43DK113536-01, awarded by NIH-NIDDK. The government has
certain rights in the invention.
Claims
1. An electrolytic gas generator for electrolyzing a reactant to
generate at least a first gas, the electrolytic gas generator
comprising: (a) a polymer electrolyte membrane, the polymer
electrolyte membrane having opposing first and second faces; (b) a
first electrode, the first electrode being electrically coupled to
the first face of the polymer electrolyte membrane; (c) a second
electrode, the second electrode being electrically coupled to the
second face of the polymer electrolyte membrane; (d) a first
current collector, the first current collector being
electrically-conductive and being reversibly deformable between a
first state in which the first current collector is electrically
coupled to the first electrode and a second state in which the
first current collector is at least partially electrically
disconnected from the first electrode; (e) a second current
collector, the second current collector being
electrically-conductive and being electrically coupled to the
second electrode; and (f) a power source, the power source being
electrically coupled to the first current collector and to the
second current collector; (g) whereby, when the first current
collector is in the first state and the reactant is supplied to the
electrolytic gas generator, a first gas is generated at the
interface of the first electrode and the polymer electrolyte
membrane.
2. The electrolytic gas generator as claimed in claim 1 wherein the
electrolytic gas generator is a water electrolyzer.
3. The electrolytic gas generator as claimed in claim 1 wherein the
first current collector is in direct physical and electrical
contact with the first electrode in the first state and is
completely physically and electrically disconnected from the first
electrode in the second state or is partially physically and
electrically disconnected from the first electrode in the second
state.
4. (canceled)
5. The electrolytic gas generator as claimed in claim 1 wherein the
first electrode is an anode and wherein the second electrode is a
cathode or further comprising a resiliently-compressible member
engaged with the first current collector to bias the first current
collector towards the first state.
6. (canceled)
7. The electrolytic gas generator as claimed in claim 5 wherein the
resiliently-compressible member comprises a block of foam.
8. The electrolytic gas generator as claimed in claim 7 wherein the
foam is open-cell foam or is closed-cell foam.
9. (canceled)
10. The electrolytic gas generator as claimed in claim 1 wherein
the first current collector is elastic.
11. The electrolytic gas generator as claimed in claim 1 wherein
the first current collector comprises a non-porous,
gas-impermeable, electrically-conductive diaphragm or comprises a
non-porous, gas-permeable, electrically-conductive diaphragm.
12. (canceled)
13. The electrolytic gas generator as claimed in claim 1 wherein
the first current collector comprises an electrically-conductive
diaphragm and a ring terminal or wherein the second current
collector comprises at least one pore.
14. (canceled)
15. The electrolytic gas generator as claimed in claim 1 further
comprising a first fluid inlet for admitting outside fluid into the
electrolytic gas generator to be electrolyzed or further comprising
a first fluid outlet for discharging from the electrolytic gas
generator a first gas generated thereby.
16. (canceled)
17. An electrolytic gas generator for electrolyzing water to
generate oxygen and hydrogen gases, the electrolytic gas generator
comprising: (a) a polymer electrolyte membrane, the polymer
electrolyte membrane having opposing first and second faces; (b) a
first electrode, the first electrode being electrically coupled to
the first face of the polymer electrolyte membrane; (c) a second
electrode, the second electrode being electrically coupled to the
second face of the polymer electrolyte membrane; (d) a first
current collector, the first current collector being
electrically-conductive and being reversibly deformable, when
subjected to gas pressure, between a first state in which the first
current collector is electrically coupled to the first electrode
and a second state in which the first current collector is at least
partially electrically disconnected from the first electrode; (e) a
second current collector, the second current collector being
electrically-conductive and being electrically coupled to the
second electrode; (f) a first seal, the first seal being disposed
around a periphery of the first electrode, the first seal
comprising a fluid outlet for discharging one of hydrogen and
oxygen generated at the first electrode; (g) a second seal, the
second seal being disposed around a periphery of the second
electrode, the second seal comprising a fluid outlet for
discharging the other of hydrogen and oxygen generated at the
second electrode; (h) a first endplate, the first current collector
being positioned between the first endplate and the polymer
electrolyte membrane; (i) a second endplate, the second current
collector being positioned between the second endplate and the
polymer electrolyte membrane; (j) wherein at least one of the first
seal, the second seal, the first endplate and the second endplate
has at least one inlet for admitting outside water; and (k) a power
source, the power source being electrically coupled to the first
current collector and to the second current collector; (l) whereby,
when the first current collector is in the first state and water is
supplied to the electrolytic gas generator, one of hydrogen and
oxygen gas is generated at the interface of the first electrode and
the polymer electrolyte membrane and the other of hydrogen and
oxygen is generated at the interface of the second electrode and
the polymer electrolyte membrane.
18. The electrolytic gas generator as claimed in claim 17 wherein
the first current collector is in direct physical and electrical
contact with the first electrode in the first state and is
completely physically and electrically disconnected from the first
electrode in the second state or is partially physically and
electrically disconnected from the first electrode in the second
state.
19. (canceled)
20. The electrolytic gas generator as claimed in claim 17 wherein
the first electrode is an anode and wherein the second electrode is
a cathode or further comprising a resiliently-compressible member
positioned between and engaged with the first endplate and the
first current collector to bias the first current collector towards
the first state.
21. (canceled)
22. The electrolytic gas generator as claimed in claim 20 wherein
the resiliently-compressible member comprises a block of foam.
23. The electrolytic gas generator as claimed in claim 22 wherein
the first current collector comprises an elastic, non-porous,
gas-impermeable, electrically-conductive diaphragm or wherein the
first current collector comprises an elastic, non-porous,
gas-permeable, electrically-conductive diaphragm, wherein the foam
is open-cell foam, and wherein the first endplate comprises at
least one pore.
24. (canceled)
25. The electrolytic gas generator as claimed in claim 23 further
comprising an ultrafiltration membrane positioned within the at
least one pore of the first endplate.
26. The electrolytic gas generator as claimed in claim 17 wherein
the second current collector comprises at least one pore and
wherein the second endplate comprises at least one pore or wherein
at least one of the first seal and the second seal has a fluid
inlet for admitting outside water.
27. The electrolytic gas generator as claimed in claim 26 further
comprising a liquid-permeable, gas-impermeable interface layer
positioned between the second current collector and the second
endplate.
28. (canceled)
29. An implant system comprising: (a) the electrolytic gas
generator of claim 1; (b) a container for holding implantable one
or more cells and/or tissues; and (c) a first tubing for conducting
the first gas generated by the electrolytic gas generator to the
container.
30. An implant system comprising: (a) the electrolytic gas
generator of claim 17; (b) a container for holding implantable one
or more cells and/or tissues; and (c) a first tubing for conducting
one of hydrogen and oxygen generated by the electrolytic gas
generator to the container; and (d) a second tubing for conducting
the other of hydrogen and oxygen generated by the electrolytic gas
generator to the container.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 15/814,124, inventors Simon G. Stone et al.,
filed Nov. 15, 2017, which, in turn, claims the benefit under 35
U.S.C. 119(e) of U.S. Provisional Patent Application No.
62/422,420, inventors Simon G. Stone et al., filed Nov. 15, 2016,
the disclosures of all of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0003] The present invention relates generally to electrolytic gas
generators and relates more particularly to a novel electrolytic
gas generator and to an implant system comprising the same.
[0004] The controlled generation of one or more types of gases at
point-of-use is of significance to a multitude of industrial and
medical applications. Electrolysis is a common technique for
generating such gases and typically involves converting a feedstock
(which is often a low cost, stable reactant) to a useful commodity
(which is often a high cost or unstable product) using an
electrical current. Electrolysis is favored as a production
technique due to its high process efficiency, its product
selectivity, and its inherent ability to control production rate by
controlling the applied current. Devices designed to generate one
or more gases using electrolysis are sometimes referred to as
electrolytic gas generators. Electrolytic gas generators for
hydrogen production, for instance, are used frequently in
analytical laboratories to supply high purity hydrogen, on-demand,
for use as carrier and detector gases in gas chromatographs.
Electrolytic gas generators for oxygen production, for example,
have been used to generate oxygen in situ at skin wounds to improve
the healing process for severe burns and diabetic ulcers. Such
electrolytic gas generators typically require several basic system
components to govern performance and safety, and these basic system
components generally include current control (e.g., a DC power
supply for maintaining generation rate and voltage efficiency),
downstream pressure and gas purity monitoring (e.g., for process
and environmental safety), and fluid management (e.g., water
reactant feed pump and gas-liquid separation units). However, as
can be appreciated, such components can increase the size, cost,
and complexity of the overall system and can make the overall
system more difficult to maintain. Also, although hydrogen and
oxygen are two of the more common gases produced by electrolytic
gas generators, electrolytic gas generators can be used to produce
other gases, such as, but not limited to, carbon dioxide, chlorine,
ozone, hydrogen peroxide, chlorine dioxide, nitric oxide, sulfur
dioxide, hydrogen sulfide, carbon monoxide, ammonia, hydrogen
chloride, hydrogen bromide, and hydrogen cyanide.
[0005] An emerging medical application for in situ gas generation
is in the provision of gaseous oxygen to cells and/or tissues that
are located under the skin or that are included as part of a
subdermal implant device. Subdermal implant devices are useful
implements for the in situ generation and dissemination of
therapeutics to a patient in need thereof for the treatment of
various diseases, disorders, and/or conditions. Typically, such
implant devices comprise cells and/or tissues that are encapsulated
within a suitable implantable container. The implantable container
is typically designed to allow the cells and/or tissues to produce
the desired therapeutic and for the dissemination of the produced
therapeutic to the patient while, at the same time, limiting an
immunological response. As can be appreciated, the delivery of
essential gases (e.g., oxygen) and nutrients to implant devices is
important for the viability and function of the cells and/or
tissues contained therein. Regarding the delivery of gases to the
implant device, it is especially important to the safety of the
patient that excessive gas pressures be prevented and/or mitigated
so as to obviate the risk of pain, infection, tissue damage, or
embolism in the patient.
[0006] In U.S. Patent Application Publication No. US 2015/0112247
A1, inventors Tempelman et al., which was published Apr. 23, 2015,
and which is incorporated herein by reference in its entirety,
there is disclosed a system for gas treatment of a cell implant.
According to the aforementioned publication (hereinafter "the '247
publication"), the system enhances the viability and function of
cellular implants, particularly those with high cellular density,
for use in human or veterinary medicine. The system utilizes a
miniaturized electrochemical gas generator subsystem that
continuously supplies oxygen and/or hydrogen to cells within an
implantable and immunoisolated cell containment subsystem to
facilitate cell viability and function at high cellular density
while minimizing overall implant size. The cell containment
subsystem is equipped with features to allow gas delivery through
porous tubing or gas-only permeable internal gas compartments
within the implantable cell containment subsystem. Furthermore, the
gas generator subsystem includes components that allow access to
water for electrolysis while implanted, thereby promoting long-term
implantability of the gas generator subsystem. An application of
the system is a pancreatic islet (or pancreatic islet analogue)
implant for treatment of Type I diabetes (T1D) that would be
considered a bio-artificial pancreas.
[0007] In U.S. Pat. No. 7,892,222 B2, inventors Vardi et al., which
issued Feb. 22, 2011, and which is incorporated herein by reference
in its entirety, there is disclosed an implantable device
comprising a chamber for holding functional cells and an oxygen
generator for providing oxygen to the cells within the chamber.
According to the aforementioned patent (hereinafter "the '222
patent"), functional cells are loaded into the chamber of the
device that is then implanted in the body. The device comprises an
oxygen generator, i.e., an element that can produce oxygen and make
it available to the functional cells, so that the functional cells
do not suffer from hypoxia. The oxygen generator thus produces
oxygen and typically releases the oxygen in the cell's vicinity. In
one embodiment, the oxygen generator comprises a pair of
electrodes. When an electric potential is applied across the
electrodes, oxygen is released by electrolysis of ambient water
molecules present within the chamber. The electrodes are connected
to a power source, typically a rechargeable battery. The chamber
may further comprise an oxygen sensor that determines the oxygen
concentration in the vicinity of the functional cells. A
microprocessor may be provided to turn on the oxygen generator when
the sensor detects that the oxygen concentration is below a
predetermined minimum and to turn it off when the oxygen
concentration is above a predetermined maximum.
[0008] In U.S. Pat. No. 6,368,592 B1, inventors Colton et al.,
which issued Apr. 9, 2002, and which is incorporated herein by
reference in its entirety, there is disclosed a method of
delivering oxygen to cells by electrolyzing water. According to the
aforementioned patent (hereinafter "the '592 patent"), oxygen is
supplied to cells in vitro or in vivo by generating oxygen with an
oxygen generator that electrolyzes water to oxygen and hydrogen.
Oxygen can be generated substantially without generating free
hydrogen using a multilayer electrolyzer sheet having a proton
exchange membrane sandwiched by an anode layer and a cathode layer.
The oxygen generator may be used to supply oxygen to cells
contained by a culture plate, a culture flask, a microtiter plate
or an extracorporeal circuit, or to cells in an encapsulating
chamber for implanting in the body such as an immunoisolation
chamber bounded by a semipermeable barrier layer that allows
selected components to enter and leave the chamber. A bioactive
molecule may be present with the cells. Oxygen can be delivered in
situ to cells within the body such as by implanting the oxygen
generator in proximity to cell-containing microcapsules in an
intraperitoneal space, or by implanting a system containing the
oxygen generator in proximity to an immunoisolation chamber
containing cells. The oxygen generator may be connected to a
current control circuit and a power supply.
[0009] One shortcoming that has been identified by the present
inventors with electrolytic gas generators of the type
conventionally used with subdermal implant devices is that such
electrolytic gas generators either are configured to continuously
generate a gas (which, in most cases, is oxygen) or are equipped
with some external mechanism, such as a gas sensor and a current
control device, to control actuation of the electrolytic gas
generator. However, the continuous generation of gas may be
undesirable for a subdermal implant device, especially if the rate
of gas generation exceeds the rate at which the generated gas is
consumed by cells and/or tissues of the implant device, as excess
gas can lead to damage to the implant and/or the patient. On the
other hand, external mechanisms for controlling gas generation can
increase the size of the implant, which is undesirable, as well as
adding to the cost and complexity of the implant.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to provide a novel
electrolytic gas generator.
[0011] It is another object of the present invention to provide an
electrolytic gas generator as described above that addresses at
least some of the shortcomings associated with existing
electrolytic gas generators.
[0012] It is still another object of the present invention to
provide an electrolytic gas generator as described above that is
compact, has a minimal number of parts, is inexpensive to
manufacture, and is easy to operate.
[0013] Therefore, according to one aspect of the invention, there
is provided an electrolytic gas generator for electrolyzing a
reactant to generate at least a first gas, the electrolytic gas
generator comprising (a) a polymer electrolyte membrane, the
polymer electrolyte membrane having opposing first and second
faces; (b) a first electrode, the first electrode being
electrically coupled to the first face of the polymer electrolyte
membrane; (c) a second electrode, the second electrode being
electrically coupled to the second face of the polymer electrolyte
membrane; (d) a first current collector, the first current
collector being electrically-conductive and being reversibly
deformable between a first state in which the first current
collector is electrically coupled to the first electrode and a
second state in which the first current collector is at least
partially electrically disconnected from the first electrode; (e) a
second current collector, the second current collector being
electrically-conductive and being electrically coupled to the
second electrode; and (f) a power source, the power source being
electrically coupled to the first current collector and to the
second current collector; (g) whereby, when the first current
collector is in the first state and the reactant is supplied to the
electrolytic gas generator, a first gas is generated at the
interface of the first electrode and the polymer electrolyte
membrane.
[0014] In a more detailed feature of the invention, the
electrolytic gas generator may be a water electrolyzer.
[0015] In a more detailed feature of the invention, the first
current collector may be in direct physical and electrical contact
with the first electrode in the first state and may be completely
physically and electrically disconnected from the first electrode
in the second state.
[0016] In a more detailed feature of the invention, the first
current collector may be in direct physical and electrical contact
with the first electrode in the first state and may be partially
physically and electrically disconnected from the first electrode
in the second state.
[0017] In a more detailed feature of the invention, the first
electrode may be an anode, and the second electrode may be a
cathode.
[0018] In a more detailed feature of the invention, the
electrolytic gas generator may further comprise a
resiliently-compressible member engaged with the first current
collector to bias the first current collector towards the first
state.
[0019] In a more detailed feature of the invention, the
resiliently-compressible member may comprise a block of foam.
[0020] In a more detailed feature of the invention, the foam may be
an open-cell foam.
[0021] In a more detailed feature of the invention, the foam may be
a closed-cell foam.
[0022] In a more detailed feature of the invention, the first
current collector may be elastic.
[0023] In a more detailed feature of the invention, the first
current collector may comprise a non-porous, gas-impermeable,
electrically-conductive diaphragm.
[0024] In a more detailed feature of the invention, the first
current collector may comprise a non-porous, gas-permeable,
electrically-conductive diaphragm.
[0025] In a more detailed feature of the invention, the first
current collector may comprise an electrically-conductive diaphragm
and a ring terminal.
[0026] In a more detailed feature of the invention, the second
current collector may comprise at least one pore.
[0027] In a more detailed feature of the invention, the
electrolytic gas generator may further comprise a first fluid inlet
for admitting outside fluid into the electrolytic gas generator to
be electrolyzed.
[0028] In a more detailed feature of the invention, the
electrolytic gas generator may further comprise a first fluid
outlet for discharging from the electrolytic gas generator a first
gas generated thereby.
[0029] According to another aspect of the invention, there is
provided an electrolytic gas generator for electrolyzing water to
generate oxygen and hydrogen gases, the electrolytic gas generator
comprising (a) a polymer electrolyte membrane, the polymer
electrolyte membrane having opposing first and second faces; (b) a
first electrode, the first electrode being electrically coupled to
the first face of the polymer electrolyte membrane; (c) a second
electrode, the second electrode being electrically coupled to the
second face of the polymer electrolyte membrane; (d) a first
current collector, the first current collector being
electrically-conductive and being reversibly deformable, when
subjected to gas pressure, between a first state in which the first
current collector is electrically coupled to the first electrode
and a second state in which the first current collector is at least
partially electrically disconnected from the first electrode; (e) a
second current collector, the second current collector being
electrically-conductive and being electrically coupled to the
second electrode; (f) a first seal, the first seal being disposed
around a periphery of the first electrode, the first seal
comprising a fluid outlet for discharging one of hydrogen and
oxygen generated at the first electrode; (g) a second seal, the
second seal being disposed around a periphery of the second
electrode, the second seal comprising a fluid outlet for
discharging the other of hydrogen and oxygen generated at the
second electrode; (h) a first endplate, the first current collector
being positioned between the first endplate and the polymer
electrolyte membrane; (i) a second endplate, the second current
collector being positioned between the second endplate and the
polymer electrolyte membrane; (j) wherein at least one of the first
seal, the second seal, the first endplate and the second endplate
has at least one inlet for admitting outside water; and (k) a power
source, the power source being electrically coupled to the first
current collector and to the second current collector; (l) whereby,
when the first current collector is in the first state and water is
supplied to the electrolytic gas generator, one of hydrogen and
oxygen gas is generated at the interface of the first electrode and
the polymer electrolyte membrane and the other of hydrogen and
oxygen is generated at the interface of the second electrode and
the polymer electrolyte membrane.
[0030] In a more detailed feature of the invention, the first
current collector may be in direct physical and electrical contact
with the first electrode in the first state and may be completely
physically and electrically disconnected from the first electrode
in the second state.
[0031] In a more detailed feature of the invention, the first
current collector may be in direct physical and electrical contact
with the first electrode in the first state and may be partially
physically and electrically disconnected from the first electrode
in the second state.
[0032] In a more detailed feature of the invention, the first
electrode may be an anode, and the second electrode may be a
cathode.
[0033] In a more detailed feature of the invention, the
electrolytic gas generator may further comprise a
resiliently-compressible member positioned between and engaged with
the first endplate and the first current collector to bias the
first current collector towards the first state.
[0034] In a more detailed feature of the invention, the
resiliently-compressible member may comprise a block of foam.
[0035] In a more detailed feature of the invention, the first
current collector may comprise an elastic, non-porous,
gas-impermeable, electrically-conductive diaphragm.
[0036] In a more detailed feature of the invention, the first
current collector may comprise an elastic, non-porous,
gas-permeable, electrically-conductive diaphragm, the foam may be
an open-cell foam, and the first endplate may comprise at least one
pore.
[0037] In a more detailed feature of the invention, the
electrolytic gas generator may further comprise an ultrafiltration
membrane positioned within the at least one pore of the first
endplate.
[0038] In a more detailed feature of the invention, the second
current collector may comprise at least one pore, and the second
endplate may comprise at least one pore.
[0039] In a more detailed feature of the invention, the
electrolytic gas generator may further comprise a liquid-permeable,
gas-impermeable interface layer positioned between the second
current collector and the second endplate.
[0040] In a more detailed feature of the invention, at least one of
the first seal and the second seal has a fluid inlet for admitting
outside water.
[0041] It is another object of the present invention to provide an
implant system comprising the above-described electrolytic gas
generator.
[0042] Therefore, according to one aspect of the invention, there
is provided an implant system, the implant system comprising (a) at
least one of the types of electrolytic gas generators described
above; (b) a container for holding implantable one or more cells
and/or tissues; and (c) a first tubing for conducting a gas
generated by the electrolytic gas generator to the container.
[0043] According to another aspect of the invention, there is
provided an implant system, the implant system comprising (a) at
least one of the types of electrolytic gas generators described
above; (b) a container for holding implantable one or more cells
and/or tissues; (c) a first tubing for conducting hydrogen
generated by the electrolytic gas generator to the container; and
(d) a second tubing for conducting oxygen generated by the
electrolytic gas generator to the container.
[0044] For purposes of the present specification and claims,
various relational terms like "top," "bottom," "proximal,"
"distal," "upper," "lower," "front," and "rear" may be used to
describe the present invention when said invention is positioned in
or viewed from a given orientation. It is to be understood that, by
altering the orientation of the invention, certain relational terms
may need to be adjusted accordingly.
[0045] Additional objects, as well as aspects, features and
advantages, of the present invention will be set forth in part in
the description which follows, and in part will be obvious from the
description or may be learned by practice of the invention. In the
description, reference is made to the accompanying drawings which
form a part thereof and in which is shown by way of illustration
various embodiments for practicing the invention. The embodiments
will be described in sufficient detail to enable those skilled in
the art to practice the invention, and it is to be understood that
other embodiments may be utilized and that structural changes may
be made without departing from the scope of the invention. The
following detailed description is, therefore, not to be taken in a
limiting sense, and the scope of the present invention is best
defined by the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] The accompanying drawings, which are hereby incorporated
into and constitute a part of this specification, illustrate
various embodiments of the invention and, together with the
description, serve to explain the principles of the invention.
These drawings are not necessarily drawn to scale, and certain
components may have undersized and/or oversized dimensions for
purposes of explication. In the drawings wherein like reference
numeral represent like parts:
[0047] FIG. 1 is a schematic section view of a first embodiment of
an electrolytic gas generator constructed according to the present
invention, the electrolytic gas generator being shown in an
operating (or "on") state;
[0048] FIG. 2 is a schematic section view of the electrolytic gas
generator of FIG. 1, the electrolytic gas generator being shown in
a non-operating (or "off") state;
[0049] FIG. 3 is a schematic section view of a second embodiment of
an electrolytic gas generator constructed according to the present
invention, the electrolytic gas generator being shown in an
operating (or "on") state;
[0050] FIG. 4 is a schematic section view of the electrolytic gas
generator of FIG. 3, the electrolytic gas generator being shown in
a non-operating (or "off") state;
[0051] FIG. 5 is a schematic section view of an alternate anode
current collector constructed according to the present invention,
the alternate anode current collector being suitable for use in
either the electrolytic gas generator of FIG. 1 or the electrolytic
gas generator of FIG. 3, the alternate current collector being
shown with its electrically-conductive diaphragm in a flattened
state as would be the case when the electrolytic gas generator is
in an operating (or "on") state;
[0052] FIG. 6 is a schematic section view of the alternate anode
current collector of FIG. 5, with its electrically-conductive
diaphragm being shown in a distended state as would be the case
when the electrolytic gas generator is in a non-operating (or
"off") state;
[0053] FIG. 7 is a schematic section view of a third embodiment of
an electrolytic gas generator constructed according to the present
invention, the electrolytic gas generator being shown in a
fully-operating state;
[0054] FIG. 8 is a schematic section view of the electrolytic gas
generator of FIG. 7, the electrolytic gas generator being shown in
a partially-operating state;
[0055] FIG. 9 is a schematic perspective view of a first embodiment
of an implant system constructed according to the present
invention;
[0056] FIG. 10 is a schematic perspective view of a second
embodiment of an implant system constructed according to the
present invention;
[0057] FIG. 11 is a graph depicting current and voltage as a
function of time for the electrolytic gas generator described in
Example 1; and
[0058] FIG. 12 is a graph depicting current, pressure, and oxygen
flow rate as a function of time for the electrolytic gas generator
described in Example 2.
DETAILED DESCRIPTION OF THE INVENTION
[0059] The present invention is directed, in part, at a novel
electrolytic gas generator and is also directed, in part, at an
implant system comprising said novel electrolytic gas
generator.
[0060] Without reducing the present invention to a singular
principle, an important concept of the present invention is the
design of an electrolytic gas generator that automatically
undergoes one or more mechanical changes, such as a physical
deformation of one or more components, during the course of
electrolysis. More specifically, as current passes through the
electrolytic gas generator of the present invention, products are
generated at the anode and/or at the cathode, and electrolyte may
also be transferred from one electrode to the other via
electro-osmosis. In the case of water electrolysis, one or both of
the gaseous products of hydrogen and oxygen that are generated by
electrolysis may accumulate within the electrolytic gas generator
if they do not exit the generator as quickly as they are generated.
The accumulation of such gases within the electrolytic gas
generator may result in an increased pressure in one or both
electrode compartments, and this increase in pressure may, in turn,
cause a mechanical change in certain components within the
electrolytic gas generator. This electrolysis-induced mechanical
change may then be taken advantage of to limit the extent of
further electrolysis, as the mechanical change may be engineered to
cause two electrically-conductive elements in the electrolytic gas
generator that were in physical contact with one another to become
partially or completely disconnected from one another. This
disconnection may reduce or stop current flow, at which point the
generated gas or gases may remain in their respective cell
compartments until either they exit the electrolytic gas generator
through their respective outlet ports and/or they diffuse through
one or more permeable layers in the electrolytic gas generator to
the surrounding environment. Thereafter, when the gas pressure in
the affected cell compartment decreases, the mechanical change may
automatically reverse, and the electrically-conductive elements
that had become disconnected may become electrically reconnected,
whereby further electrolysis may ensue. In such a way, the
electrolytic gas generator of the present invention may be capable
of maintaining a constant gas activity in its vicinity so as to
maintain cytoprotective, respiratory, and/or metabolic function of
vicinal tissue or another implant and may do so with only a
connection to an electrical source, such as a source of constant DC
current. The constant DC current source, such as a battery, may be
co-implanted with the electrolytic gas generator or may be
maintained outside the body and wired to the electrolytic gas
generator percutaneously. Such a system could optionally be fitted
with a secondary control system which, upon detection that the
electrolytic gas generator has been de-actuated (i.e., by use of a
current sensor), either slows the re-actuation process or prevents
it entirely (i.e., latches the circuit open) to satisfy performance
or safety criteria.
[0061] The electrolytic gas generator of the present invention is
particularly amenable to a fully implanted medical device where
oxygen is delivered by diffusion (i.e., via gas-permeable
membranes) to cells or tissue in one or more implanted,
immunoisolated capsules at rates governed by the metabolic
consumption rate of said cells or tissue. In these scenarios, it is
important to control oxygen pressure to accurately control dose, to
mitigate the possible effects of hypoxia and hyperoxia, and to
minimize power consumption and system complexity of a fully
implanted system. It shall be readily appreciated that the
principles taught in the present application are equally applicable
to an electrolytic gas generator wherein the gas generated under
intrinsic pressure control is hydrogen at the cathode, or moreover,
any anodically or cathodically produced electrolytic product
gas.
[0062] The intrinsic pressure management capability of the present
invention is preferred or complementary in critical applications,
such as implanted medical devices, to other pressure control
methods, including but not limited to closed-loop process
controller (pressure sensor plus current controller), external
pressure switch, or pressure relief valve, due to the ability to
control gas generation at its source (thereby precluding the risk
of gas pressure buildup in the electrolytic gas generator in the
case of a gas blockage in tubing intervening between said generator
and these example extrinsic pressure management solutions). It will
be readily appreciated that elimination of a pressure sensor and
process controller, or any additional electronic component,
comprises a simplification of an overall system which may result in
smaller size, lower cost, and higher reliability. It will also be
readily appreciated that the use of pressure relief valves is
generally precluded in implanted (or otherwise partially enclosed)
applications, as there is not a readily convenient or safe location
to shunt excess gas generated during valve actuation. It will
additionally be appreciated that the present invention affords an
additional advantage over other methods of gas generation in
implanted or otherwise partially contained applications, in that it
may safely account for variations in ambient (i.e., barometric)
pressure that would otherwise potentially put implant, subject, or
host device at risk due to excessive pressure differential. To
these ends, the present invention is an improvement for implanted
medical and many other applications, as it enables these
simplifications without unduly compromising safety, reliability,
size, cost or effectiveness.
[0063] Beyond the aforementioned implantable device use, any
application requiring in situ pressure-controlled generation of gas
reagents in a small, intrinsically-safe, and/or reliable device may
benefit from the teachings of this invention. Such alternative
applications may include, for instance, corrosion inhibition or
acceleration, odor control, cleansing and/or sanitization of
surfaces or enclosed spaces, life support of immobilized or
enclosed organisms, and reagent production for miniature
sensors.
[0064] Referring now to FIGS. 1 and 2, there are shown schematic
section views of a first embodiment of an electrolytic gas
generator constructed according to the present invention, the
electrolytic gas generator being represented generally by reference
numeral 11. (For simplicity and clarity, certain components of
electrolytic gas generator 11 that are not critical to an
understanding of the present invention are either not shown or
described herein or are shown and/or described herein in a
simplified manner.)
[0065] Electrolytic gas generator 11, which may be in the form of a
water electrolyzer, may comprise a solid polymer electrolyte
membrane (PEM) 13 (also known in the art as a proton exchange
membrane). Polymer electrolyte membrane 13 is preferably a
non-porous, ionically-conductive, electrically-non-conductive,
liquid-permeable and substantially gas-impermeable membrane.
Polymer electrolyte membrane 13 may consist of or comprise a
homogeneous perfluorosulfonic acid (PFSA) polymer. Said PFSA
polymer may be formed by the copolymerization of
tetrafluoroethylene and perfluorovinylether sulfonic acid. See
e.g., U.S. Pat. No. 3,282,875, inventors Connolly et al., issued
Nov. 1, 1966; U.S. Pat. No. 4,470,889, inventors Ezzell et al.,
issued Sep. 11, 1984; U.S. Pat. No. 4,478,695, inventors Ezzell et
al., issued Oct. 23, 1984; and U.S. Pat. No. 6,492,431, inventor
Cisar, issued Dec. 10, 2002, all of which are incorporated herein
by reference in their entireties. A commercial embodiment of a PFSA
polymer electrolyte membrane is manufactured by The Chemours
Company FC, LLC (Fayetteville, N.C.) as NAFION.TM. extrusion cast
PFSA polymer membrane.
[0066] Polymer electrolyte membrane 13 may be a generally planar
unitary structure in the form of a continuous film or sheet. In the
present embodiment, when viewed from above or below, polymer
electrolyte membrane 13 may have a generally circular shape.
Moreover, the overall shape of electrolytic gas generator 11, when
viewed from above or below, may correspond generally to the shape
of polymer electrolyte membrane 13. However, it is to be understood
that polymer electrolyte membrane 13, as well as electrolytic gas
generator 11 as a whole, is not limited to a generally circular
shape and may have a generally rectangular shape or other suitable
shape.
[0067] Electrolytic gas generator 11 may further comprise an anode
15 and a cathode 17. Anode 15 and cathode 17 may be positioned
along two opposing major faces of polymer electrolyte membrane 13.
In the present embodiment, anode 15 is shown positioned along the
top face of polymer electrolyte membrane 13, and cathode 17 is
shown positioned along the bottom face of polymer electrolyte
membrane 13; however, it is to be understood that the positions of
anode 15 and cathode 17 relative to polymer electrolyte membrane 13
could be reversed.
[0068] Anode 15 may comprise an anode electrocatalyst layer 19 and
an anode support 21. Anode electrocatalyst layer 19 may be
positioned in direct contact with polymer electrolyte membrane 13
and, in the present embodiment, is shown as being positioned
directly above and in contact with the top of polymer electrolyte
membrane 13. Anode electrocatalyst layer 19 defines the
electrochemically active area of anode 15 and preferably is
sufficiently porous and electrically- and ionically-conductive to
sustain a high rate of surface oxidation reaction. Anode
electrocatalyst layer 19, which may be an anode electrocatalyst
layer of the type conventionally used in a PEM-based water
electrolyzer, may comprise electrocatalyst particles in the form of
a finely divided electrically-conductive (and, optionally,
ionically-conductive) material (e.g., a metal powder) which can
sustain a high rate of electrochemical reaction. The
electrocatalyst particles are distributed within anode
electrocatalyst layer 19 along with a binder, which is preferably
ionically-conductive, to provide mechanical fixation.
[0069] Anode support 21, which may be an anode support of the type
conventionally used in a PEM-based water electrolyzer and may be,
for example, a film or sheet of porous titanium, preferably is
sufficiently porous to allow fluid (gas and/or liquid) transfer
between anode electrocatalyst layer 19 and the anode-side gas port
to be discussed below. To this end, anode support 21 may have pore
sizes on the order of, for example, approximately 0.001-0.5 mm.
Anode support 21 may also contain macroscopic channel features, for
example, on the order of 0.2-10 mm to further assist in fluid
distribution. In addition, anode support 21 is
electrically-conductive to provide electrical connectivity between
anode electrocatalyst layer 19 and the anode-side current collector
to be discussed below, and anode support 21 is also preferably
ionically-non-conductive. Anode support 21 may be positioned in
direct contact with anode electrocatalyst layer 19 and, in the
present embodiment, is shown as being positioned directly on top of
anode electrocatalyst layer 19 such that anode electrocatalyst
layer 19 may be sandwiched between and in contact with polymer
electrolyte membrane 13 and anode support 21. Anode support 21 may
be dimensioned to entirely cover anode electrocatalyst layer 19,
and, in fact, anode 15 may be fabricated by depositing anode
electrocatalyst layer 19 on anode support 21.
[0070] Cathode 17 may comprise a cathode electrocatalyst layer 23
and a cathode support 25. Cathode electrocatalyst layer 23 may be
positioned in direct contact with polymer electrolyte membrane 13
and, in the present embodiment, is shown as being positioned
directly below and in contact with polymer electrolyte membrane 13.
Cathode electrocatalyst layer 23 defines the electrochemically
active area of cathode 17 and preferably is sufficiently porous and
electrically- and ionically-conductive to sustain a high rate of
surface reduction reaction. Cathode electrocatalyst layer 23, which
may be a cathode electrocatalyst layer of the type conventionally
used in a PEM-based water electrolyzer, may comprise
electrocatalyst particles in the form of a finely divided
electrically-conductive (and, optionally, ionically-conductive)
material (e.g., a metal powder) which can sustain a high rate of
electrochemical reaction. The electrocatalyst particles are
distributed within cathode electrocatalyst layer 23 along with a
binder, which is preferably ionically-conductive, to provide
mechanical fixation. The reactants and products involved at anode
15 and cathode 17 implicate ionic species which are mobile
throughout the electroactive surface; therefore, an
ionically-conductive medium comprising polymer electrolyte membrane
13 and optionally one or more ionically-conductive catalyst binders
in electrocatalyst layers 19 and 23 couples the two electrodes and
allows ions to flow in support of the overall reaction
electrochemistry.
[0071] Cathode support 25, which may be a cathode support of the
type conventionally used in a PEM-based water electrolyzer and may
be, for example, a film or sheet of porous carbon, preferably is
sufficiently porous to allow fluid (gas and/or liquid) transfer
between cathode electrocatalyst layer 23 and the cathode-side gas
port to be discussed below. To this end, cathode support 25 may
have pore sizes on the order of, for example, approximately
0.001-0.5 mm. Cathode support 25 may also contain macroscopic
channel features, for example, on the order of 0.2-10 mm to further
assist in fluid distribution. In addition, cathode support 25 is
electrically-conductive to provide electrical connectivity between
cathode electrocatalyst layer 23 and the cathode-side current
collector to be discussed below, and cathode support 25 is also
preferably ionically-non-conductive. Cathode support 25 may be
positioned in direct contact with cathode electrocatalyst layer 23
and, in the present embodiment, is shown as being positioned
directly below and in contact with cathode electrocatalyst layer 23
such that cathode electrocatalyst layer 23 may be sandwiched
between and in contact with polymer electrolyte membrane 13 and
cathode support 25. Cathode support 25 may be dimensioned to
entirely cover cathode electrocatalyst layer 23, and, in fact,
cathode 17 may be fabricated by depositing cathode electrocatalyst
layer 23 on cathode support 25.
[0072] The combination of polymer electrolyte membrane 13, anode
15, and cathode 17 or the combination of polymer electrolyte
membrane 13, anode electrocatalyst layer 19, and cathode
electrocatalyst layer 23 may be regarded collectively as a
membrane-electrode assembly (MEA).
[0073] Electrolytic gas generator 11 may further comprise an anode
seal 31 and a cathode seal 33. Anode seal 31, which may be an anode
seal of the type conventionally used in a PEM-based water
electrolyzer, may be a generally annular or frame-like member
mounted around the periphery of anode 15 in a fluid-tight manner.
Anode seal 31, which may be made of TEFLON.TM.
polytetrafluoroethylene, ethylene-propylene-diene-monomer (EPDM)
rubber, or another similarly suitable material, may be
ionically-non-conductive and electrically-non-conductive. Anode
seal 31 may also be non-porous and fluid-impermeable, except for a
fluid port extending radially outwardly from the inner periphery of
anode seal 31 to the outer periphery of anode seal 31. In the
present embodiment, the aforementioned fluid port in anode seal 31
may be an oxygen outlet 35. Oxygen outlet 35 may be fluidically
connected to a location in need of oxygen via suitable tubing (not
shown), which tubing may be equipped with features like
sterilization filters and/or check valves to prevent electrolytic
gas generator 11 from becoming contaminated by contents of the
tubing or from having condensate flow backwards into electrolytic
gas generator 11. Where, for example, electrolytic gas generator 11
is implanted in a body, such tubing may be used to fluidically
connect oxygen outlet 35 to a container holding implanted cells
and/or tissue. Alternatively, such tubing may be eliminated if the
container holding implanted cells and/or tissue is permeable to gas
and the container is positioned against or sufficiently proximate
to oxygen outlet 35.
[0074] Anode seal 31 may additionally include a second fluid port
extending radially outwardly from the inner periphery of anode seal
31 to the outer periphery of anode seal 31, which second fluid port
may be used as a water inlet 36 to supply water to anode 15 from a
source external to electrolytic gas generator 11. For example, a
water reservoir (not shown), which may be external to electrolytic
gas generator 11, may be fluidically connected to water inlet 36
via suitable tubing (not shown) so as to supply water to anode 15.
Such tubing may be equipped with features like sterilization
filters and/or check valves. Where electrolytic gas generator 11 is
implanted in a body, such a water reservoir may also be implanted
in the body, or the water reservoir may be positioned external to
the body. Alternatively, instead of using a water reservoir,
ambient water in the local environment outside of electrolytic gas
generator 11 may be supplied to electrolytic gas generator 11
through water inlet 36; however, in this case, it may be desirable
to place one or more filters (not shown) over the exterior of water
inlet 36 to keep select contaminants in the ambient water from
entering water inlet 36 and to prevent anode-generated gas from
exiting through water inlet 36.
[0075] Cathode seal 33, which may be a cathode seal of the type
conventionally used in a PEM-based water electrolyzer, may be a
generally annular or frame-like member mounted around the periphery
of cathode 17 in a fluid-tight manner. Cathode seal 33, which may
be made of TEFLON.TM. polytetrafluoroethylene,
ethylene-propylene-diene-monomer (EPDM) rubber, or another
similarly suitable material, may be ionically-non-conductive and
electrically-non-conductive. Cathode seal 33 may also be non-porous
and fluid-impermeable, except for two fluid ports extending
radially outwardly from the inner periphery of cathode seal 33 to
the outer periphery of cathode seal 33. In the present embodiment,
one of the two fluid ports in cathode seal 33 may be a water inlet
37, which may be used to supply water to cathode 17 from a source
external to electrolytic gas generator 11. For example, a water
reservoir (not shown), which may be external to electrolytic gas
generator 11, may be fluidically connected to water inlet 37 via
suitable tubing (not shown) so as to supply water to cathode 17.
Such tubing may be equipped with features like sterilization
filters and/or check valves. Where electrolytic gas generator 11 is
implanted in a body, such a water reservoir may also be implanted
in the body, or the water reservoir may be positioned external to
the body. Alternatively, instead of using a water reservoir,
ambient water in the local environment outside of electrolytic gas
generator 11 may be supplied to electrolytic gas generator 11
through water inlet 37; however, in this case, it may be desirable
to place one or more filters or flow control valves (not shown)
over the exterior of water inlet 37 to keep select contaminants in
the ambient water from entering water inlet 37 and to prevent
cathode-generated gas from exiting through water inlet 37.
[0076] In the present embodiment, the other of the two fluid ports
in cathode seal 33 may be a hydrogen outlet 39. Hydrogen outlet 39
may be fluidically connected via suitable tubing (not shown) to a
location in need of hydrogen or, if hydrogen is not needed, to a
location where hydrogen may be safely expelled. Such tubing may be
equipped with features like sterilization filters and/or check
valves. Where, for example, electrolytic gas generator 11 is
implanted in a body and it is desired to treat implanted or native
cells and/or tissue with hydrogen, such tubing coupled to hydrogen
outlet 39 may be used to deliver hydrogen to a container holding
the implanted cells and/or tissue or may be used to deliver
hydrogen to a location proximate to native cells and/or tissue.
Where hydrogen treatment is not needed, such tubing can be used to
deliver hydrogen to a part of the body where it can be safely
expelled; alternatively, if electrolytic gas generator 11 is
implanted at a location in a body where hydrogen can safely diffuse
from electrolytic gas generator 11 and be expelled from the body
without requiring any tubing, such tubing can be omitted.
[0077] In the present embodiment, anode 15 and anode seal 31 may be
dimensioned to jointly match the footprint of the top surface of
polymer electrolyte membrane 13, and cathode 17 and cathode seal 33
may be dimensioned to jointly match the footprint of the bottom
surface of polymer electrolyte membrane 13. Notwithstanding the
above, it is to be understood that the footprints of the foregoing
components may be varied from what is described above.
[0078] Electrolytic gas generator 11 may further comprise an anode
current collector 51. Anode current collector 51, which may be a
unitary structure in the form of a continuous film or sheet, may be
a non-porous, electrically-conductive, flexible, diaphragm-like
member capable of being reversibly deformed (for example, when
subjected to gas pressure) from a generally planar state to a
bulging or distended state. When viewed from above, anode current
collector 51 may have a footprint that substantially matches the
collective footprints of anode 15 and anode seal 31, except that
anode current collector 51 may additionally comprise a tab 55 that
may extend radially outwardly a short distance beyond the footprint
of anode seal 31 and that may be used as a terminal. In the present
embodiment, anode current collector 51 is preferably substantially
gas-impermeable. In addition, in the present embodiment, anode
current collector 51 is preferably elastic but need not be.
Examples of materials that may be suitable for use as anode current
collector 51 include, but are not limited to, silicones films or
sheets with metallic (e.g., silver) or other
electrically-conductive particles dispersed therein and non-porous,
electrically-conductive, liquid-permeable, substantially
gas-impermeable membranes of the type disclosed in U.S. Pat. No.
9,595,727 B2, inventors Mittelsteadt et al., which issued Mar. 14,
2017, and which is incorporated herein by reference in its
entirety.
[0079] More specifically, according to the aforementioned patent
(hereinafter "the '727 patent"), such a non-porous,
electrically-conductive, liquid-permeable, substantially
gas-impermeable membrane may comprise, for example, a solid polymer
electrolyte into which electrically-conductive materials are
dispersed. Examples of materials suitable for use as the solid
polymer electrolyte may include (i) polymer compositions that
contain metal salts; (ii) polymeric gels that contain electrolytes;
and (iii) ion exchange resins. More specifically, the solid polymer
electrolyte may be, for example, a cation exchange ionomer membrane
where the cation exchange group may be, but is not limited to,
--SO.sub.3.sup.-, --SO.sub.2NH.sup.+, --PO.sub.3.sup.2-, or
--CO.sub.2.sup.- or may be, for example, an anion exchange ionomer
membrane where the anion exchange group may be, but is not limited
to, --NH.sub.2.sup.+. A preferred material for use as the solid
polymer electrolyte may be a perfluorosulfonic acid (PFSA)
membrane, such as is manufactured by The Chemours Company FC, LLC
(Fayetteville, N.C.) as NAFION.TM. extrusion cast PFSA polymer
membrane. Examples of other materials that may be used in place of
NAFION.TM. PFSA are disclosed in U.S. Pat. No. 7,947,405 B2,
inventors Mittelsteadt et al., which issued May 24, 2011, and which
is incorporated herein by reference in its entirety.
[0080] Examples of materials that may be suitable for use as the
dispersed, electrically-conductive materials of the above-described
membrane may include high-aspect-ratio, electrically-conductive,
non-particulate materials, such as carbon nanotubes, carbon
nanofibers, metal nanowires, or combinations thereof. Carbon
nanotubes that may be suitable for use in the membrane may have a
diameter of about 0.20 nm to about 100 nm, may have a length of
about 0.50 .mu.m to about 200 .mu.m, and may have an aspect ratio
(i.e., length/diameter) in the range of about 5 to about 1,000,000.
Additionally, carbon nanotubes that may be suitable for use in the
membrane may be non-functionalized or may include one or more
functional groups, such as, but not limited to, --COOH,
--PO.sub.4.sup.-, --SO.sub.3H, --SH, --NH.sub.2, tertiary amines,
quaternary amines, --CHO, --OH, --NO.sub.2, and --PO.sub.3.sup.2-.
Moreover, carbon nanotubes that may be suitable for use in the
membrane may include single-walled carbon nanotubes, double-walled
carbon nanotubes, multi-walled carbon nanotubes, or combinations
thereof.
[0081] Carbon nanofibers that may be suitable for use in the
membrane may be non-functionalized or may include one or more
functional groups, such as, but not limited to, --COOH,
--PO.sub.4.sup.-, --SO.sub.3H, --SH, --NH.sub.2, tertiary amines,
quaternary amines, --CHO, --OH, --NO.sub.2, and --PO.sub.3.sup.2-.
In addition to including dispersed, non-particulate,
electrically-conductive materials or instead of such materials, the
membrane may comprise dispersed, electrically-conductive particles,
such as, but not limited to, carbon black, metal particles (e.g.,
niobium particles, platinum particles, titanium particles, or
combinations thereof), supported metal particles, or combinations
thereof.
[0082] The above-described membrane may be prepared by adding the
electrically-conductive materials to the ionomer while the ionomer
is in suspension form and then drying the suspension.
[0083] Electrolytic gas generator 11 may further comprise an anode
endplate 61. Anode endplate 61, which may be a unitary structure
made of a rigid material of the type conventionally used in
PEM-based water electrolyzers, such as a suitably strong metal or
polymer, may have the shape of an inverted canister and may
comprise a top wall 63 and a side wall 65 jointly defining an
interior chamber 67 with an open bottom. Anode endplate 61 may be
appropriately dimensioned so that an outer surface 69 of side wall
65 may be substantially aligned with an outer surface 71 of anode
seal 31. In addition, anode endplate 61 may be further dimensioned
so that an inner surface 73 of side wall 65 may be spaced radially
outwardly relative to an inner surface 75 of anode seal 31. A
vascularizing membrane (not shown), such as disclosed in U.S.
Patent Application Publication No. US 2015/0112247 A1, may be
applied to one or more exposed surfaces of anode endplate 61.
[0084] The bottom of side wall 65 of anode endplate 61 may be
positioned directly on top of anode current collector 51 and may be
used to secure a peripheral portion 77 of anode current collector
51 between anode endplate 61 and anode seal 31 (peripheral portion
77 of anode current collector 51 being positioned directly on top
of anode seal 31). In this manner, peripheral portion 77 of anode
current collector 51 may be kept immobile between anode endplate 61
and anode seal 31 whereas a central portion 79 of anode current
collector 51 may be free to flex upwardly away from anode 15 when a
particular anodic gas pressure is reached between anode current
collector 51 and anode 15, as will be discussed further below. As
can readily be appreciated, when central portion 79 of anode
current collector 51 flexes upwardly away from anode 15
sufficiently that anode current collector 51 and anode 15 are no
longer in electrical contact with one another, electrolytic gas
generator 11 stops electrolyzing.
[0085] Electrolytic gas generator 11 may further comprise a
resiliently-compressible member 81. Resiliently-compressible member
81 may be a structure designed to permit central portion 79 of
anode current collector 51 to deform or to distend upwardly away
from and out of contact with anode 15 when the gas pressure between
anode current collector 51 and anode 15 exceeds a certain threshold
gas pressure and to cause or to bias central portion 79 of anode
current collector 51 to flatten or to deflate downwardly back into
contact with anode 15 when the gas pressure between anode current
collector 51 and anode 15 falls below a certain threshold gas
pressure. The threshold gas pressure at which
resiliently-compressible member 81 may permit central portion 79 to
flex away from anode 15 and the threshold gas pressure at which
resiliently-compressible member 81 may cause central portion 79 to
flex back into contact with anode 15 may be the same or may be
different. In some cases, it may be advantageous for the threshold
gas pressure at which resiliently-compressible member 81 allows
central portion 79 to flex away from anode 15 to be significantly
greater than the threshold gas pressure at which
resiliently-compressible member 81 forces central portion 79 to
flex back into contact with anode 15. Consequently, in such a case,
once the operation of electrolytic gas generator 11 has stopped, it
will not resume until the gas pressure between central portion 79
and anode 15 has dropped significantly. In this manner,
electrolytic gas generator 11 may be prevented from undesirably
stuttering back and forth between its operating and off states.
[0086] In the present embodiment, resiliently-compressible member
81 may comprise a block or disc of foam that may be disposed within
interior chamber 67 of anode endplate 61. Such a foam may be a
closed-cell foam or an open-cell foam. Examples of suitable foams
may include, but are not limited to, polyurethane foams and
silicone rubber foams, such as an open-cell silicone rubber foam.
Resiliently-compressible member 81 may be appropriately dimensioned
to have a first surface 83 engaged with an inner surface 85 of top
wall 63 of anode endplate 61 and a second surface 87 engaged with
anode current collector 51. In the present embodiment,
resiliently-compressible member 81 may be dimensioned so that, when
in its uncompressed state, it substantially fills the entire volume
of interior chamber 67 of anode endplate 61; however, it is to be
understood that resiliently-compressible member 81 need not be so
dimensioned.
[0087] Although, in the present embodiment,
resiliently-compressible member 81 may be a block of foam,
resiliently-compressible member 81 is not limited thereto and may
be any type of resiliently-compressible structure, such as, but not
limited to, a coil spring, a Belleville spring, an enclosed gas
pocket, a gas pocket with an externally referenceable gas filling
port, or combinations thereof.
[0088] Also, it is to be understood that, if anode current
collector 51 is sufficiently inherently resilient, it may be
possible to omit resiliently-compressible member 81.
[0089] Electrolytic gas generator 11 may further comprise a cathode
current collector 91, which may be a cathode current collector of
the type conventionally used in a PEM-based water electrolyzer and
may be, for example, a platinum-coated titanium sheet. When viewed
from below, cathode current collector 91 may have a footprint that
substantially matches the collective footprints of cathode 17 and
cathode seal 33, except that cathode current collector 91 may
additionally comprise a tab 93 that may extend radially outwardly a
short distance beyond the footprint of cathode seal 33 and that may
be used as a terminal.
[0090] Electrolytic gas generator 11 may further comprise a cathode
endplate 95, which may be a cathode endplate of the type
conventionally used in a PEM-based water electrolyzer. Cathode
endplate 95 may be appropriately dimensioned so that a side wall 97
thereof may be substantially aligned with an outer surface 98 of
cathode seal 33. A top wall 99 of cathode endplate 95 may be
positioned directly below cathode current collector 91 and may be
used to keep cathode current collector 91 in direct contact with
cathode 17 and with cathode seal 33. A vascularizing membrane (not
shown), such as disclosed in U.S. Patent Application Publication
No. US 2015/0112247 A1, may be applied to one or more exposed
surfaces of cathode endplate 95.
[0091] Electrolytic gas generator 11 may further comprise a power
source 101. Power source 101, which may be, for example, a DC
battery (which may be rechargeable), may be electrically connected
by a wire 103 to tab 55 of anode current collector 51 and by a wire
105 to tab 93 of cathode current collector 91. Where, for example,
electrolytic gas generator 11 is implanted in a patient, power
source 101 may also be implanted in the patient; alternatively,
power source 101 may be positioned external to the patient.
[0092] Electrolytic gas generator 11 may further comprise other
components commonly found in conventional PEM-based water
electrolyzers. For example, the static forces upon electrolytic gas
generator 11 that may be required to compress
resiliently-compressible member 81, to sustain good electrical
contact of the serial components of electrolytic gas generator 11,
and to achieve good sealing of the cell perimeter may be
established and maintained using a variety of conventional
fixturing or joining implements and techniques about the internal
or external periphery of the assembly. Such implements may include,
for instance, fasteners (e.g., screws, rivets, etc.) which may
clamp the endplates 61 and 95 together, or adhesives, cements or
welds which cohere the elements together in the seal region. Such
implements and techniques are considered to be known to those of
ordinary skill in the art.
[0093] Referring now specifically to FIG. 1, it can be seen that
electrical contact is established across the combination of anode
current collector 51, anode 15, polymer electrolyte membrane 13,
cathode 17, and cathode current collector 91. As a result,
electrolytic gas generator 11 forms a closed electrical circuit,
and electrolytic gas generator 11 is in an operating (or "on")
state for the electrolysis of water. Water may be introduced into
electrolytic gas generator 11 through water inlet 36 of anode seal
31 and/or water inlet 37 of cathode seal 33, and such water may be
electrolyzed in the conventional manner at the electroactive
interfaces of electrolytic gas generator 11, with oxygen gas being
generated at the interface of polymer electrolyte membrane 13 and
anode electrocatalyst layer 19 and with hydrogen gas being
generated at the interface of polymer electrolyte membrane 13 and
cathode electrocatalyst layer 23. The thus-generated oxygen gas may
then exit electrolytic gas generator 11 through oxygen outlet 35,
and the thus-generated hydrogen gas may then exit electrolytic gas
generator 11 through hydrogen outlet 39. If the rate at which
oxygen gas may exit electrolytic gas generator 11 is greater than
or approximately equal to the rate at which oxygen gas is generated
by electrolytic gas generator 11, very little, if any, oxygen gas
may build up between anode support 21 and anode current collector
51, and the upwardly-directed gas pressure exerted on anode current
collector 51 may be less than the downwardly-directed mechanical
pressure exerted on anode current collector 51 by
resiliently-compressible member 81. As a result, electrical contact
may be maintained between anode current collector 51 and anode
support 21, and gas generation may continue.
[0094] On the other hand, if the rate at which oxygen gas may exit
electrolytic gas generator 11 is less than the rate at which oxygen
gas is generated by electrolytic gas generator 11, oxygen gas may
build up between anode support 21 and anode current collector 51,
and, eventually, the upwardly-directed gas pressure exerted on
anode current collector 51 may be greater than the
downwardly-directed mechanical pressure exerted on anode current
collector 51 by resiliently-compressible member 81. As a result, as
seen in FIG. 2, anode current collector 51 may flex or distend away
from anode support 21, thereby breaking any electrical contact
between anode current collector 51 and anode support 21. As a
result, electrolytic gas generator 11 may stop electrolyzing water.
Thereafter, at least some of the oxygen gas that has accumulated
between anode support 21 and anode current collector 51 may exit
electrolytic gas generator 11 through oxygen outlet 35 until the
gas pressure between anode support 21 and anode current collector
51 decreases sufficiently for anode current collector 51 to be
brought back into contact with anode support 21, thereby permitting
electrolysis to resume.
[0095] As can be appreciated, the foregoing scenario may take place
in the context of a cell implant system in which the oxygen
produced by electrolytic gas generator 11 is conducted by tubing to
a closed container holding implanted cells and/or tissue. If the
implanted cells and/or tissue cannot consume the oxygen that is
delivered thereto at a rate that exceeds or is substantially equal
to the rate at which the generated oxygen is delivered or if there
is some restriction to flow downstream of oxygen outlet 35, oxygen
may accumulate in the electrolytic gas generator 11 as described
above. If the amount of oxygen that accumulates within electrolytic
gas generator 11 is sufficient to create a pressure that exceeds a
predetermined threshold, electrolytic gas generator 11 stops
generating oxygen. In this manner, electrolytic gas generator 11
may be regarded as being self-regulating. As can be appreciated,
such a self-regulating electrolytic gas generator is advantageous
for at least the reason that it does not require external sensors
or feedback mechanisms.
[0096] Referring now to FIGS. 3 and 4, there are shown schematic
section views of a second embodiment of an electrolytic gas
generator constructed according to the present invention, the
electrolytic gas generator being represented generally by reference
numeral 111. (For simplicity and clarity, certain components of
electrolytic gas generator 111 that are not critical to an
understanding of the present invention are either not shown or
described herein or are shown and/or described herein in a
simplified manner.)
[0097] Electrolytic gas generator 111, which may be in the form of
a water electrolyzer, may be similar in many respects to
electrolytic gas generator 11. Accordingly, electrolytic gas
generator 111 may comprise a polymer electrolyte membrane 113,
which may be identical to polymer electrolyte membrane 13. In
addition, electrolytic gas generator 111 may also comprise an anode
115 comprising an anode electrocatalyst layer 119 and an anode
support 121, wherein anode 115, anode electrocatalyst layer 119,
and anode support 121 may be identical to anode 15, anode
electrocatalyst layer 19, and anode support 21, respectively, of
electrolytic gas generator 11. Moreover, electrolytic gas generator
111 may further comprise a cathode 117 comprising a cathode
electrocatalyst layer 123 and a cathode support 125, wherein
cathode 117, cathode electrocatalyst layer 123 and cathode support
125 may be identical to cathode 17, cathode electrocatalyst layer
23, and cathode support 25, respectively, of electrolytic gas
generator 11.
[0098] Electrolytic gas generator 111 may further comprise an anode
seal 131 and a cathode seal 133. Anode seal 131 may be similar in
most respects to anode seal 31, with a principal difference between
the two anode seals being that, whereas anode seal 31 may comprise
oxygen outlet 35 and water inlet 36, anode seal 131 may comprise an
oxygen outlet 135 but need not include a water inlet. In fact, it
may even be possible, in certain cases, for anode seal 131 not to
include oxygen outlet 135. Cathode seal 133 may be similar in most
respects to cathode seal 33, with a principal difference between
the two cathode seals being that, whereas cathode seal 33 may
comprise water inlet 37 and hydrogen outlet 39, cathode seal 133
may comprise a hydrogen outlet 139 but need not include a water
inlet.
[0099] Electrolytic gas generator 111 may further comprise an anode
current collector 151. Anode current collector 151 may be similar
in most respects to anode current collector 51, with a principal
difference between the two anode current collectors being that,
whereas anode current collector 51 may be substantially
gas-impermeable, anode current collector 151 is gas-permeable.
Anode current collector 151 is also preferably
liquid-permeable.
[0100] Electrolytic gas generator 111 may further comprise an anode
endplate 161. Anode endplate 161 may be similar in most respects to
anode endplate 61, with a principal difference between the two
endplates being that, whereas anode endplate 61 may be made of a
non-porous, fluid-impermeable material, anode endplate 161 may
comprise a porous or fluid-permeable material. For example, in the
present embodiment, anode endplate 161 may comprise one or more
pores 163. Pores 163 may permit the passage of gas or liquid from
the external environment of anode endplate 161 to the internal
chamber of anode endplate 161 or vice versa. (In addition, pores
163 may allow pressure equalization with the local external
pressure.) For example, outside water may be introduced into the
anode side of electrolytic gas generator 111 through pores 163, and
oxygen gas generated at anode 115 may be expelled from electrolytic
gas generator 111 through pores 163. An ultrafiltration membrane
165 or other suitable membrane or filter may be positioned within
pores 163 to keep select contaminants from passing from the
exterior of electrolytic gas generator 111 through pores 163 into
the interior chamber of anode endplate 161. (It is to be understood
that, instead of or in addition to having ultrafiltration membrane
165 positioned within pores 163, ultrafiltration membrane 165 may
be positioned across pores 163 along the exterior or interior
surface of anode endplate 161.) A vascularizing membrane (not
shown), such as disclosed in U.S. Patent Application Publication
No. US 2015/0112247 A1, may be applied to one or more exposed
surfaces of anode endplate 161.
[0101] Where, for example, electrolytic gas generator 111 is
implanted in a patient, oxygen gas expelled through pores 163 may
be delivered to a desired destination via one or more tubes coupled
to pores 163. Alternatively, electrolytic gas generator 111 may be
positioned near or at a desired destination, and expelled gas may
simply diffuse to the desired destination without the use of
tubing. In fact, according to one embodiment, a gas-permeable wall
of a container holding implanted cells and/or tissue may be
directly contacted with the exterior of anode endplate 161 so that
oxygen expelled from pores 163 may pass directly into the container
holding implanted cells and/or tissue.
[0102] Electrolytic gas generator 111 may further comprise a
resiliently-compressible member 181. Resiliently-compressible
member 181 may be similar in most respects to
resiliently-compressible member 81, with a principal difference
between the two resiliently-compressible members being that,
whereas resiliently-compressible member 81 need not be porous or
gas-permeable, resiliently-compressible member 181 is preferably
porous or gas-permeable to enable oxygen gas generated at anode 115
to pass therethrough. Therefore, for example,
resiliently-compressible member 181 may be a suitable open-cell
foam.
[0103] Electrolytic gas generator 111 may further comprise a
cathode current collector 191. Cathode current collector 191 may be
similar in most respects to cathode current collector 91, with a
principal difference between the two cathode current collectors
being that, whereas cathode current collector 91 need not be
porous, cathode current collector 191 may comprise one or more
pores 192. As will become apparent below, pores 192 may be used to
facilitate the passage of outside water to cathode 117.
[0104] Electrolytic gas generator 111 may further comprise an
interface layer 193. Interface layer 193, which is positioned below
and in direct contact with cathode current collector 191, may
comprise a liquid-permeable, gas-impermeable material. In this
manner, interface layer 193 may facilitate the passage of outside
water therethrough to pores 192 of cathode current collector 191
while excluding contaminants (such as biomolecules in said outside
water where, for example, electrolytic gas generator 111 is
implanted in a patient) and may prevent gas generated at cathode
117 from egressing therethrough. A sealing gasket 194 may be
positioned around the periphery of interface layer 193.
[0105] Electrolytic gas generator 111 may further comprise a
cathode endplate 195. Cathode endplate 195 may be similar in most
respects to cathode endplate 95, with a principal difference
between the two cathode endplates being that, whereas cathode
endplate 95 need not be porous, cathode endplate 195 may comprise
one or more pores 196, which may be used to communicate with the
local environment and to facilitate the ingress of outside water
into electrolytic gas generator 111 for delivery to cathode 117.
Where, for example, electrolytic gas generator 111 is implanted in
a patient, the outer surfaces of cathode endplate 195 and interface
layer 193 may be treated to promote vascular ingrowth and tissue
integration. A vascularizing membrane (not shown), such as
disclosed in U.S. Patent Application Publication No. US
2015/0112247 A1, may be applied to one or more exposed surfaces of
cathode endplate 195.
[0106] Electrolytic gas generator 111 may further comprise a power
source 201, which may be identical to power source 101. Power
source 201 may be electrically connected by a wire 203 to anode
current collector 151 and by a wire 205 to cathode current
collector 191.
[0107] Like electrolytic gas generator 11, electrolytic gas
generator 111 may further comprise other components commonly found
in conventional PEM-based water electrolyzers.
[0108] In use, referring now specifically to FIG. 3, it can be seen
that electrical contact is established across the combination of
anode current collector 151, anode support 121, anode
electrocatalyst layer 119, polymer electrolyte membrane 113,
cathode electrocatalyst layer 123, cathode support 125, and cathode
current collector 191. As a result, electrolytic gas generator 111
forms a closed electrical circuit, and electrolytic gas generator
111 is in an operating (or "on") state for the electrolysis of
water. Water may be introduced into electrolytic gas generator 111
by passing first through pores 163 of anode endplate 161, then
through resiliently-compressible member 181, and then through anode
current collector 151. In addition, water may also be introduced
into electrolytic gas generator 111 by passing through pores 196 of
cathode endplate 195, then through interface layer 193, then
through pores 192 of cathode current collector 191. Such water may
then be electrolyzed in the conventional manner at the
electroactive interfaces of electrolytic gas generator 111, with
oxygen gas being generated at the interface of polymer electrolyte
membrane 113 and anode electrocatalyst layer 119 and with hydrogen
gas being generated at the interface of polymer electrolyte
membrane 113 and cathode electrocatalyst layer 123. The
thus-generated hydrogen gas may then exit electrolytic gas
generator 111 through hydrogen outlet 139.
[0109] With respect to thus-generated oxygen gas, a first portion
may exit electrolytic gas generator 111 through oxygen outlet 135,
a second portion may diffuse through anode current collector 151,
then pass through resiliently-compressible material 181, and then
pass through pores 163 of anode endplate 161, and a third portion
may accumulate between anode current collector 151 and anode
support 121. If the gas pressure of the third portion does not
exceed the combination of the pressure applied by
resiliently-compressive member 181 and the environmental pressure,
anode current collector 151 may remain in contact with anode
support 121, and electrolysis may continue. On the other hand, if
the gas pressure of the third portion exceeds the combination of
the pressure applied by resiliently-compressive member 181 and the
environmental pressure, anode current collector 151 may be bent out
of contact with anode support 121, as seen in FIG. 4, thereby
breaking any electrical contact between anode current collector 151
and anode support 121. As a result, electrolytic gas generator 111
may stop electrolyzing water. Thereafter, at least some of the
oxygen gas that has accumulated between anode support 121 and anode
current collector 151 may dissipate until the gas pressure between
anode support 121 and anode current collector 151 decreases
sufficiently for anode current collector 151 to be brought back
into contact with anode support 121, thereby permitting
electrolysis to resume.
[0110] Referring now to FIGS. 5 and 6, there are shown schematic
section views of an alternate anode current collector constructed
according to the present invention, the alternate anode current
collector being represented generally by reference numeral 251.
[0111] Anode current collector 251, which may be suitable for use
in electrolytic gas generator 11, electrolytic gas generator 111,
or other electrolytic gas generators operating on similar
principles, may be similar in most respects to anode current
collector 51 or to anode current collector 151 and may be used
similarly to such anode current collectors. A principal difference
between anode current collector 251 and anode current collector 51
or anode current collector 151 may be that, whereas anode current
collector 51 or 151 may be a one-piece structure, anode current
collector 251 may comprise the combination of an
electrically-conductive diaphragm 253 and a ring terminal 255.
Electrically-conductive diaphragm 253 may be similar in composition
to anode current collector 51 or to anode current collector 151.
Ring terminal 255, which may be an electrically-conductive member,
may be bonded or otherwise fixed to electrically-conductive
diaphragm 253. As can be seen in FIG. 5, when in its relaxed state,
electrically-conductive diaphragm 253 lies substantially flat.
Consequently, with electrically-conductive diaphragm 253 in such a
flattened state, anode current collector 251 may be used to
maintain an electrolytic gas generator in an operating (or "on"
state). By contrast, as can be seen in FIG. 6,
electrically-conductive diaphragm 253 may become distended, for
example, when subjected to gas pressure and may extend though an
opening 257 in ring terminal 255. Consequently, with
electrically-conductive diaphragm 253 in such a distended state,
anode current collector 251 may move out of electrical contact with
its anode, thereby causing the respective electrolytic gas
generator to be switched to a non-operating (or "off") state.
Thereafter, when electrically-conductive diaphragm 253 is no longer
subjected to such gas pressure or when the gas pressure decreases
to a certain threshold, electrically-conductive diaphragm 253, due
to a biasing force from resiliently-compressible member 81 or 181
and/or due to its own inherent resiliency, may once again assume a
flattened state.
[0112] Referring now to FIGS. 7 and 8, there are shown schematic
section views of a third embodiment of an electrolytic gas
generator constructed according to the present invention, the
electrolytic gas generator being represented generally by reference
numeral 311. (For simplicity and clarity, certain components of
electrolytic gas generator 311 that are not critical to an
understanding of the present invention are either not shown or
described herein or are shown and/or described herein in a
simplified manner.)
[0113] Electrolytic gas generator 311 may be similar in most
respects to electrolytic gas generator 111. A principal difference
between the two electrolytic gas generators may be that, whereas
electrolytic gas generator 111 may be configured so that anode
current collector 151 makes no physical/electrical contact with
anode support 121 when the gas pressure between anode current
collector 151 and anode support 121 exceeds the combination of the
pressure applied by resiliently-compressive member 181 and the
environmental pressure, electrolytic gas generator 311 may comprise
an anode support 321 and an anode current collector 351 that, under
analogous pressure conditions, are configured to maintain some
physical/electrical contact with one another, albeit to a
diminished extent. Such a state, which may be regarded as a
"partially on" condition, results in reduced current through
electrolytic gas generator 311, due to the added series resistance
imposed by the longer and/or more tortuous conduction path. As a
result of such a reduction in current, a reduction in gas
production may ensue.
[0114] As can be appreciated, an important feature of the present
invention is the anode current collector, which sustains variable
physical-13 and, therefore, variable electrical-13 contact with the
anode support in response to differences in pressure on opposing
faces of the anode current collector. In opposition to the
generated gas pressure, a resiliently-compressible member (e.g.,
rubber foam) may be implemented on the side of the anode current
collector opposite to the side where electrolytic gas generation
occurs. The essential components of the electrolytic gas generator
may be improved by modification of the current collection scheme to
enable a responsiveness to changes in either environmental pressure
or the pressure of the generated gas. Physical contact, and,
therefore, electrical conductivity, is maintained along the
following electrical path: anode current collector to anode support
to anode electrocatalyst layer to polymer electrolyte membrane to
cathode electrocatalyst layer to cathode support and finally to
cathode current collector. This state is considered "on" because
the application of electrical power to the two collectors of the
cell causes electrolytic gas generation. This gas generation ceases
(the "off" state) if any electrical or ionic pathway is opened
(i.e., disconnected) and is reduced if any component in the series
circuit develops a high resistance, as current is thereby
attenuated (a "partially on" state). By way of the present
invention, the "off" state may be achieved by influence of the
applied electrolytic current and the differential pressure between
the gas electrolytically produced and the combination of
environmental pressure communicated to the reference region within
the anode endplate and the compression of the
resiliently-compressible member. The pressure differential (dP)
across the anode current collector may be expressed as:
dP=P.sub.e+P.sub.c-P.sub.g
wherein P.sub.e is the environmental pressure, P.sub.c is the
pressure applied by the resiliently-compressible member, and
P.sub.g is the gas pressure in the gas region. When the pressure in
the gas region exceeds the combined pressure in the reference
region (P.sub.e+P.sub.c), the dP value becomes negative, and the
anode current collector deflects into the resiliently-compressible
member and moves away from the anode support, causing mechanical
separation and opening of the electrical circuit. The
reestablishment of the "on" state may be part of the normal
operation of the self-regulating electrolytic gas generator and is
ensured by the judicious selection of the resiliently-compressible
member such that the mechanical energy stored therein results in a
force upon the active area of the electrolyzer sufficient to
restore mechanical contact between the anode current collector and
the anode support. Similarly, in a case where the environmental
pressure (i.e., the barometric pressure or blood pressure of a
subject having a cell implant utilizing the generated gas) changes,
there will be a respective change in the displacement of the anode
current collector so as to properly regulate the generation of gas
and, thereby, adjust the pressure of the gas-treated implant.
[0115] While the "on"-"off" function may be suitable for general
control of generated gas pressure, it may be preferable to regulate
the current to a lower, non-zero value in order to achieve the
finest pressure control. A "partially on" condition may be effected
when the gas pressure P.sub.g and reference region pressure (sum of
the resiliently-compressible member compression P.sub.c and
environmental pressure P.sub.e) have equalized and current
continues to flow at a reduced rate proportional to the steady
state rate of gas delivery to the application. Under constant power
or voltage control of the electrolytic gas generator, current
through the cell is reduced, in this case, by the added series
resistance imposed by the longer and/or more tortuous conduction
path. Referring to FIG. 8, which shows the "partially on" state, it
can be seen that the anode current collector and the anode support
are not in complete contact. As a result, current flowing through
the cell must take a longer path through the anode support, and
there is greater contact resistance due to the smaller area of
contact and the reduced contact pressure between the anode current
collector and the anode support.
[0116] In engineering the self-regulating electrolytic gas
generator component properties for a desired current attenuation
function in the correct pressure range, the mechanical properties
of the resiliently-compressible member and the anode current
collector, the contact and sheet resistivity properties of the
anode current collector and the anode support, and the amount of
compression of the resiliently-compressible member achieved should
be taken into account. For the "on" state, where the gas pressure
(P.sub.g) and the reference region pressure (P.sub.e+P.sub.c)
produce a zero or positive differential pressure (dP), the endplate
cavity depth and resiliently-compressible member thickness should
be selected such that the compressed thickness of the
resiliently-compressible member, when the endplate is fully
compressed against the gaskets in the perimeter seal region, is
storing the desired P.sub.c. This may be derived from the
compressibility of the resiliently-compressible member, which is
preferably selected from within the elastic deformation region of
the material's stress-strain property in compression.
[0117] Although the electrolytic gas generator of the present
invention has been described herein in certain embodiments as
comprising, amongst other things, a reversibly distensible anode
current collector and a resiliently-compressible member configured
to bias the reversibly distensible anode current collector to a
flattened state, it is to be understood that, in accordance with
the present invention, one could modify such an electrolytic gas
generator to instead have a reversibly distensible cathode current
collector and a resiliently-compressible member configured to bias
the reversibly distensible cathode current collector to a flattened
state. Moreover, it is to be understood that, in accordance with
the present invention, it may be desirable in certain instances for
an electrolytic gas generator to comprise, amongst other things, a
reversibly distensible anode current collector, a
resiliently-compressible member configured to bias the reversibly
distensible anode current collector to a flattened state, a
reversibly distensible cathode current collector, and a
resiliently-compressible member configured to bias the reversibly
distensible cathode current collector to a flattened state.
[0118] As can be appreciated, the electrolytic gas generator of the
present invention may be incorporated into a multi-cell stack,
either made up exclusively of multiple units of the electrolytic
gas generator of the present invention or in combination with
conventional and/or novel electrolytic gas generators or other
electrochemical cells.
[0119] The extension of the above-described principles to an
all-liquid system--wherein a liquid-phase or dissolved product is
delivered to the application by means of diffusion, and the
auto-regulation of the electrolysis reaction is achieved in the
identical circuit-breaking manner (as governed by increase or
decrease in electrolyte volume and, therefore, pressure during the
course of electrolysis)--is an additional feature of the
self-regulating principle described here.
[0120] Referring now to FIG. 9, there is shown a first embodiment
of an implant system constructed according to the present
invention, the implant system being represented generally by
reference numeral 411. (For simplicity and clarity, certain
components of implant system 411 that are not critical to an
understanding of the present invention are either not shown or
described herein or are shown and/or described herein in a
simplified manner.)
[0121] Implant system 411 may comprise an electrolytic gas
generator 413. Electrolytic gas generator 413, in turn, may
comprise any of the electrolytic gas generators described above
encased within a housing top 415 and a housing bottom 417.
Electrolytic gas generator 413 may further comprise a battery lid
419 under which the battery (not shown) for powering the
electrolytic gas generator may be disposed.
[0122] Implant system 411 may further comprise a container 421 for
holding implanted cells and/or tissues. Container 421 may be, for
example, a conventional container for holding implanted cells
and/or tissues or may be, for example, a container of the type
disclosed in U.S. Patent Application Publication No. US
2015/0112247 A1.
[0123] Implant system 411 may further comprise tubing 431 for
fluidically connecting electrolytic gas generator 413 to container
421. More specifically, one end of tubing 431 may be fluidically
coupled to the oxygen outlet of electrolytic gas generator 413 and
the other end of tubing may be fluidically coupled to the interior
of container 421. (Alternatively, tubing 431 could be used to
fluidically couple the hydrogen outlet of electrolytic gas
generator 413 to the interior of container 421.)
[0124] Referring now to FIG. 10, there is shown a second embodiment
of an implant system constructed according to the present
invention, the implant system being represented generally by
reference numeral 511. (For simplicity and clarity, certain
components of implant system 511 that are not critical to an
understanding of the present invention are either not shown or
described herein or are shown and/or described herein in a
simplified manner.)
[0125] Implant system 511 may be similar in most respects to
implant system 411, a principal difference between the two implant
systems being that, whereas implant system 411 may comprise tubing
431 for fluidically coupling either the oxygen outlet or the
hydrogen outlet of electrolytic gas generator 413 to the interior
of container 421, implant system 511 may comprise a first tubing
513 for fluidically coupling the oxygen outlet of electrolytic gas
generator 413 to the interior of a container 515 and a second
tubing 517 for fluidically coupling the hydrogen outlet of
electrolytic gas generator 413 to the interior of container 515.
Container 515 may be, for example, a container of the type
disclosed in U.S. Patent Application Publication No. US
2015/0112247 A1. Container 515 may optionally include a separate
interface to the implanted tissue for diffusion of one or the other
electrolytically generated gas away from the implant and into the
body, instead of into the cells or tissues encapsulated in
container 515.
[0126] The following examples are provided for illustrative
purposes only and are in no way intended to limit the scope of the
present invention:
EXAMPLE 1
[0127] A pre-existing, small electrolysis cell was adapted for use
as a self-regulating electrolytic gas generator. The cell used
machined poly(etheretherketone) plastic endplates and stainless
steel fasteners to maintain a constant mechanical load to the
active and seal areas of the cell.
[0128] The membrane-electrode assembly (MEA) at the heart of the
cell utilized Solvay Aquivion.RTM. E79-04SX perfluorosulfonic acid
(PFSA) film as the proton-exchange membrane (PEM) and utilized
platinum black catalysts (Engelhard, 4 mg/cm.sup.2) for the
electrocatalysts. The electrocatalysts were blended with
Aquivion.RTM. PFSA solution (Solvay Specialty Polymers) and applied
to the PEM by decal transfer at 1000 psi and 175.degree. C. to
unitize the MEA. The anode electrocatalyst contained iridium for
improved voltage efficiency.
[0129] The circular active catalyst area (2 cm.sup.2) of the MEA
was electrically contacted and mechanically reinforced on both
sides with porous, conductive media comprising supports. The
cathode support was porous carbon (Toray TGPH-090), and the anode
support was porous titanium (ADMA Products). The border of the MEA
was sealed with an adhesive-backed vinyl gasket.
[0130] The cathode current collector was a platinum-coated titanium
sheet with a tab for edge collection. The anode current collector
(diaphragm collector) was a WaMM.TM. membrane (Giner, Inc., Newton,
Mass.) comprising a carbon nanotube/PFSA blend fabricated per
Example 8, Build 2, of U.S. Pat. No. 9,595,727 B2. The WaMM.TM.
membrane was selected due to its high selective permeability of
water vapor and good electrical conductivity, which are required
for good cell performance. The WaMM.TM. membrane was cut to extend
to the outer edge of the seal area and included a tab for current
collection. The cylindrical volume defined by the anode face of the
MEA, the inside wall of the anode side gasket, and the face of
WaMM.TM. membrane contacting the anode support comprised the
internal volume at high relative pressure.
[0131] The WaMM.TM. membrane was supported on the face opposite the
anode support by a 1/16'' thick, resiliently-compressible,
open-cell silicone rubber foam material (density--12 lbs/ft.sup.3)
cut to the same diameter as the active area. In this section of the
assembly, the seal area of the cell comprised a 1/16'' thick
square-profile, Buna-N rubber O-ring which resided peripherally
about the foam. A small hole in the face of the anode side endplate
allowed for communication of the region defined by the foam to the
outside environment at low relative pressure.
[0132] The application of 2.5 volts from a DC power supply to the
cathode and anode collector tabs of this self-regulating
electrolytic gas generator caused an immediate increase in cell
current to about 8 mA, followed by a steady drop to about 1.5 mA
over about 10 minutes. Referring to the chart of FIG. 11, after
this steady decrease, the cell was observed to begin oscillating in
current indefinitely, with jumps from 1 mA to about 4 mA at
approximately 20 second intervals. The rate of gas generation was
thus decreasing at gas pressure maxima (approximately 20 psig in
this case) and restored after a period of time sufficient for
pressure to be relieved by mass transfer from the high relative
pressure side of the diaphragm collector to the extent that the
degree of electrical contact between the anode support and the
diaphragm collector necessary for high current operation could be
restored. Restoration of this current allowed renewed pressure
differential at constant applied voltage, thereby causing another
pressure-current-time cycle.
EXAMPLE 2
[0133] A pre-existing, small electrolysis cell was adapted for use
as a self-regulating electrolytic gas generator. The cell used
machined poly(etheretherketone) plastic endplates and stainless
steel fasteners to maintain a constant mechanical load to the
active and seal areas of the cell. Registration pin holes were
added to maintain alignment of the gaskets and oxygen port.
[0134] The membrane-electrode assembly (MEA) at the heart of the
cell utilized Solvay Aquivion.RTM. E79-05S perfluorosulfonic acid
(PFSA) film as the proton-exchange membrane (PEM) and utilized
platinum black catalysts (Engelhard, 4 mg/cm.sup.2) for the
electrocatalysts. The electrocatalysts were blended with
Aquivion.RTM. PFSA solution (Solvay Specialty Polymers) and applied
to the PEM by decal transfer at 1000 psi and 175.degree. C. to
unitize the MEA. The anode electrocatalyst contained iridium for
improved voltage efficiency.
[0135] The circular active catalyst area (1 cm.sup.2) of the MEA
was electrically contacted and mechanically reinforced on both
sides with porous, conductive media comprising supports. The
cathode support was porous carbon (Toray TGPH-090), and the anode
support was porous titanium (ADMA Products). The border of the MEA
was sealed with polytetrafluoroethylene gaskets on the periphery of
both anode and cathode faces.
[0136] The cathode current collector was a platinum-coated titanium
sheet with a tab for edge collection. The anode current collector
was a platinum-coated titanium annulus with a tab for edge
collection. Between the MEA and the anode current collector were a
non-conductive annulus with a port for gas collection (contacting
the MEA) and a conductive diaphragm made of Cho-Seal 1215 elastomer
(a conductive material made of silver-plated copper filler in a
silicone binder, a product of Parker Chomerics, Woburn, Mass.)
which lay between the non-conductive annulus and the anode current
collector. The Cho-Seal 1215 was selected due to its good
electrical conductivity and elastic mechanical properties. The
cylindrical volume defined by the anode face of the MEA, the inside
walls of the anode side gasket and non-conductive port, and the
face of the conductive diaphragm contacting the anode support
comprised the internal volume at high relative pressure.
[0137] The conductive diaphragm was supported on the face opposite
the anode support by a 1/8'' thick, open-cell polyurethane
polyether foam material (Formulation 1034 fabricated by New England
Foam Products, LLC, Hartford, Conn.; density--0.9 lb/ft.sup.3) cut
to a diameter slightly larger than the active area diameter. In
this section of the assembly, the seal area of the cell comprised a
0.07'' thick, square-profile, polytetrafluoroethylene gasket which
resided peripherally about the foam. A small hole in the center of
the anode side endplate face allowed for communication of the
region defined by the foam to the outside environment at low
relative pressure. A second hole through the face of the anode side
endplate allowed for gas generated at the MEA and collected through
the non-conductive port to be routed out of the cell.
[0138] The electrolytic gas generator so described was fitted to a
test system having a DC power supply to provide current to the
cell, a flowmeter (Alicat Scientific M-0.5SCCM-D) and a pressure
transducer (IFM PX3238) on the oxygen outlet, and flow restricting
valve venting to the atmosphere. Application of more than 1.5 VDC
from a DC power supply between the cathode and anode collector tabs
of this self-regulating electrolytic gas generator caused an
immediate increase in cell current to about 10 mA, followed by
current oscillation, where the lower limit slowly decreased from 4
mA to 2 mA as the pressure in the cell rose. Referring to FIG. 12,
after this steady decrease in the lower limit, the cell was
observed to begin oscillating in current indefinitely between about
2 mA to about 10 mA at approximately 10 second intervals. The rate
of gas generation (oxygen gas flow rate in standard cubic
centimeters per hour, scch) was also oscillating in accordance with
the self-regulation of the cell current and a constant regulated
gas pressure of about 1.2 psig was observed between the outlet of
the cell and the flow restricting valve.
[0139] The embodiments of the present invention described above are
intended to be merely exemplary and those skilled in the art shall
be able to make numerous variations and modifications to it without
departing from the spirit of the present invention. All such
variations and modifications are intended to be within the scope of
the present invention as defined in the appended claims.
* * * * *