U.S. patent application number 11/743612 was filed with the patent office on 2008-05-29 for robust voltage management in electrochemical hydrogen cells.
This patent application is currently assigned to H2 Pump LLC. Invention is credited to Glenn A. Eisman, Michael David Gasda.
Application Number | 20080121532 11/743612 |
Document ID | / |
Family ID | 39462530 |
Filed Date | 2008-05-29 |
United States Patent
Application |
20080121532 |
Kind Code |
A1 |
Gasda; Michael David ; et
al. |
May 29, 2008 |
ROBUST VOLTAGE MANAGEMENT IN ELECTROCHEMICAL HYDROGEN CELLS
Abstract
Apparatus and operating methods are provided for integrated
electrochemical hydrogen separation and compression systems. In one
possible embodiment, an electrical potential is provided across an
electrochemical cell. A portion of the potential is shunted to an
electrical load when the potential is higher than a predetermined
threshold. As an example, a Zener diode can be used as a suitable
shunting mechanism. The invention can be used with individual cells
or stacks of cells. Various methods, features and system
configurations are discussed.
Inventors: |
Gasda; Michael David; (West
Sand Lake, NY) ; Eisman; Glenn A.; (Niskayuna,
NY) |
Correspondence
Address: |
H2 PUMP, LLC
11 NORTHWAY LANE NORTH
LATHAM
NY
12110
US
|
Assignee: |
H2 Pump LLC
Latham
NY
|
Family ID: |
39462530 |
Appl. No.: |
11/743612 |
Filed: |
May 2, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60797269 |
May 3, 2006 |
|
|
|
Current U.S.
Class: |
205/763 ;
204/242; 204/267 |
Current CPC
Class: |
H01M 16/00 20130101;
C25B 9/65 20210101; H01M 8/04 20130101; Y02E 60/50 20130101 |
Class at
Publication: |
205/763 ;
204/242; 204/267 |
International
Class: |
C25B 1/02 20060101
C25B001/02; C25B 9/00 20060101 C25B009/00; C25B 9/18 20060101
C25B009/18 |
Claims
1. A method of managing voltage across an electrochemical cell,
comprising: providing an electrical potential across an
electrochemical cell; and shunting a portion of the potential to an
electrical load when the potential is higher than a predetermined
threshold.
2. The method of claim 1, wherein the cell is a hydrogen pumping
cell.
3. The method of claim 1, wherein the cell has an anode in contact
with hydrogen, and a cathode in contact with hydrogen.
4. The method of claim 1, wherein the potential is shunted to the
electrical load through a diode.
5. The method of claim 1, wherein the potential is shunted to the
electrical load through a Zener diode.
6. The method of claim 1, wherein the electrical load is an
electrical grounding circuit.
7. The method of claim 1, wherein the electrical load is an second
electrochemical cell.
8. The method of claim 1, wherein the predetermined threshold is
0.6 volts.
9. The method of claim 1, wherein the predetermined threshold is
0.8 volts.
10. The method of claim 1, wherein the cell forms part of a stack
of cells electrically connected in series.
11. A method of managing voltage across an electrochemical cell,
comprising: providing an electrical potential across a first
electrochemical cell and a second electrochemical cell, wherein the
first cell and second cell are electrically connected in series;
connecting a diode in an electrically parallel configuration with
the first and second cells; and shunting a portion of the potential
through the diode to an electrical load when the potential is
higher than a predetermined threshold.
12. The method of claim 11, wherein the cell is a hydrogen pumping
cell.
13. The method of claim 11, wherein the cell has an anode in
contact with hydrogen, and a cathode in contact with hydrogen.
14. The method of claim 11, wherein the diode is a Zener diode.
15. The method of claim 11, wherein the electrical load is an
electrical grounding circuit.
16. The method of claim 11, wherein the electrical load is an
second electrochemical cell.
17. The method of claim 11, wherein the predetermined threshold is
0.6 volts.
18. The method of claim 11, wherein the predetermined threshold is
0.8 volts.
19. The method of claim 11, wherein the cell forms part of a stack
of cells electrically connected in series.
20. A voltage management system for electrochemical cells,
comprising: an electrochemical cell; a power supply adapted to
provide an electrical potential across the electrochemical cell;
and a shunting mechanism adapted to shunt a portion of the
potential to an electrical load when the potential is higher than a
predetermined threshold.
21. The system of claim 20, wherein the cell is a hydrogen pumping
cell.
22. The system of claim 20, wherein the cell has an anode in
contact with hydrogen, and a cathode in contact with hydrogen.
23. The system of claim 20, wherein the shunting mechanism is a
diode that is electrically connected in parallel to the cell.
24. The system of claim 20, wherein the shunting mechanism is a
Zener diode that is electrically connected in parallel to the
cell.
25. The system of claim 20, wherein the electrical load is an
electrical grounding circuit.
26. The system of claim 20, wherein the electrical load is an
second electrochemical cell.
27. The system of claim 20, wherein the predetermined threshold is
0.6 volts.
28. The system of claim 20, wherein the predetermined threshold is
0.8 volts.
29. The system of claim 20, wherein the power supply has a
potential limit that is higher than the predetermined
threshold.
30. The system of claim 20, wherein the cell forms part of a stack
of cells electrically connected in series.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 USC 119(e) from
U.S. Provisional Application Nos. 60/797,269, filed May 3, 2006,
naming Gasda and Eisman as inventors, and titled "PASSIVE CELL
PROTECTION SCHEME." This application is hereby incorporated herein
by reference in their entirety and for all purposes.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention relates to apparatus and operating
methods for electrochemical hydrogen separation and compression
systems. Various methods, features and system configurations are
discussed.
BACKGROUND
[0003] Electrochemical technologies are of increasing interest, due
in part to advantages provided in efficiency and environmental
impact over traditional mechanical and combustion based
technologies.
[0004] A variety of electrochemical fuel cell technologies are
known, wherein electrical power is produced by reacting a fuel such
as hydrogen in an electrochemical cell to produce a flow of
electrons across the cell, thus providing an electrical current.
For example, in fuel cells utilizing proton exchange membrane
technology, an electrically non-conducting proton exchange membrane
is typically sandwiched between two catalyzed electrodes. One of
the electrodes, typically referred to as the anode, is contacted
with hydrogen. The catalyst at the anode serves to divide the
hydrogen molecules into their respective protons and electrons.
Each hydrogen molecule produces two protons which pass through the
membrane to the other electrode, typically referred to as the
cathode. The protons at the cathode react with oxygen to form
water, and the residual electrons at the anode travel through an
electrically conductive path around the membrane to produce an
electrical current from anode to cathode. The technology is closely
analogous to conventional battery technology.
[0005] Electrochemical cells can also be used to selectively
transfer (or "pump") hydrogen from one side of the cell to another.
For example, in a cell utilizing a proton exchange membrane, the
membrane is sandwiched between a first electrode (anode) and a
second electrode (cathode), a gas containing hydrogen is placed at
the first electrode, and an electric potential is placed between
the first and second electrodes, the potential at the first
electrode with respect to ground (or "zero") being greater than the
potential at the second electrode with respect to ground. Each
hydrogen molecule reacted at the first electrode produces two
protons which pass through the membrane to the second electrode of
the cell, where they are rejoined by two electrons to form a
hydrogen molecule (sometimes referred to as "evolving hydrogen" at
the electrode).
[0006] Electrochemical cells used in this manner are sometimes
referred to as hydrogen pumps. In addition to providing controlled
transfer of hydrogen across the cell, hydrogen pumps can also be
used to separate hydrogen from gas mixtures containing other
components. Where the hydrogen is pumped into a confined space,
such cells can be used to compress the hydrogen, at very high
pressures in some cases.
[0007] There is a continuing need for apparatus, methods and
applications relating to electrochemical cells.
SUMMARY OF THE INVENTION
[0008] Apparatus and operating methods are provided for integrated
electrochemical hydrogen separation and compression systems. In one
possible embodiment, an electrical potential is provided across an
electrochemical cell. A portion of the potential is shunted to an
electrical load when the potential is higher than a predetermined
threshold. As an example, a Zener diode can be used as a suitable
shunting mechanism. The invention can be used with individual cells
or stacks of cells. Numerous optional features and system
configurations are provided.
[0009] Various aspects and features of the invention will be
apparent from the following Detailed Description and from the
claims.
DETAILED DESCRIPTION OF THE INVENTION
[0010] It will be appreciated that the apparatus, methods, and
applications of the invention can include any of the features
described herein, either alone or in combination.
[0011] Electrochemical cells such as fuel cells, hydrogen pumping
cells, electrolyzers, etc., often use carbon-supported precious
metal catalysts at the electrodes, particularly the anode. The
carbon support generally provides the advantage of lowering the
catalyst loading required for satisfactory performance of the cell.
However, the carbon support also provides a disadvantage in that it
can be oxidized under various conditions that can be periodically
encountered during cell operation, thereby degrading cell
performance, generally on a permanent basis.
[0012] For example, under a condition where electrical current is
supplied across a cell and insufficient hydrogen is present at the
anode (sometimes referred to as a "fuel starvation" condition), the
electrical potential across the cell can thereby increase to a
point where oxidation of the electrode occurs. The electrical
potential at which such oxidation can occur will depend on the
configuration of a given cell, but it typically occurs over a
threshold of 0.6 volts or 0.8 volts, as examples.
[0013] It is thus desirable to limit the potential that can be
placed across a given cell. The present invention is generally
discussed with respect to individual cells, but it will be
appreciated that the invention is also applicable to stacks of
cells. For example, an individual cell can form part of a stack of
cells. As well known in the art, stacks of cells are generally
configured such that they are connected in electrical series,
though other configurations are possible. The flow field plates of
cells in a stack are generally electrically conductive and stacked
adjacently to each other in a bi-polar relationship such that the
anode of one cell is adjacent to the cathode of another cell, and
so forth.
[0014] Sophisticated control schemes are often used to monitor the
voltage of each cell in a stack, and to remove or reduce the
potential across the cell if it becomes too high. As an example, a
cell can be shorted with a load contactor, or can be disconnected
from a power supply (as in the case of hydrogen pumping), or an
electrical load on the cell can be removed (as in the case of fuel
cells). Such voltage scanning systems can be expensive, cumbersome
and unreliable. They can also be undesirably slow to react. Another
disadvantage of scanning configurations for stacks can be that a
single cell failure can render the entire stack inoperable if the
cell is unable to be isolated from the stack. Under the present
invention, individual cells can be bypassed.
[0015] Under one possible embodiment of the present invention, a
method is provided for managing voltage across an electrochemical
cell, comprising at least the following steps: providing an
electrical potential across an electrochemical cell; and shunting a
portion of the potential to an electrical load when the potential
is higher than a predetermined threshold.
[0016] As previously discussed, the electrochemical cell can be any
type of electrochemical cell, such as a hydrogen pumping cell, a
fuel cell, an electrolyzer, etc. In the case of hydrogen pumping
cells, operation of a cell under such methods can be further
characterized wherein the cell has an anode in contact with
hydrogen, and a cathode in contact with hydrogen.
[0017] In the context of the present invention, "shunting" refers
to any means of reducing electrical potential, as is the case where
electrical charge or current is drained or diverted from a circuit
such as the electrodes of an electrochemical cell. For example, a
cell can be connected to an electrical load that will absorb
current flow between the electrodes thereby reducing the electrical
potential between them. "Electrical load" refers to any means of
absorbing electrical current or charge. For example, this can refer
to simply grounding or shorting a cell. It can also refer to a
circuit capable of storing electrical charge, such as a capacitor
or battery. It can also refer to other electrochemical cells,
including those adjacent to the shunted cell in a stack
configuration. For example, as discussed below, for an overly high
potential cell in a stack, current can be shunted around the cell
to the adjacent cells in the stack.
[0018] In one possible embodiment, a diode can be used as a
suitable shunting mechanism. In this context, a diode is a
component that restricts the direction of flow of electrical charge
carriers. It allows an electric current to flow in one direction,
but blocks it in the opposite direction. Thus, the diode can be
thought of as an electronic version of a check valve. A diode such
as a Zener diode can be selected that has a breakdown voltage that
allows reverse flow if the potential exceeds a particular
threshold. The diode can be wired in parallel with the cell such
that, while the voltage across the cell is below the breakdown
voltage of the diode, current is not allowed to pass through the
diode, and so it passes through the cell instead. However, when the
cell potential exceeds the breakdown voltage of the diode, current
will begin to flow through the diode, and the cell potential will
be thereby reduced until it is at or below the breakdown voltage of
the diode. The current flowing through the diode can be configured
to simply bypass the cell, or to flow to ground or any other
electrical load. A circuit configured to flow electrical current to
ground can be referred to as an electrical grounding circuit.
[0019] In such a configuration, if it is desired to limit the cell
to below 0.6 volts, as an example, a diode can be selected having a
breakdown voltage of 0.6 volts. As a further example, if there are
two cells in series and it is desired to keep the potential across
each below 0.6 volts, a diode having a breakdown voltage of 1.2
volts can be placed across both cells in parallel with the cells.
Diodes can thus be used in this manner to provide protection for
individual cells, or groups of cells.
[0020] In another possible embodiment, the invention provides a
method of managing voltage across an electrochemical cell,
comprising at least the following steps, which can be selectively
paired with any of the features described above, alone or in
combination: providing an electrical potential across a first
electrochemical cell and a second electrochemical cell, wherein the
first cell and second cell are electrically connected in series;
connecting a diode in an electrically parallel configuration with
the first and second cells; and shunting a portion of the potential
through the diode to an electrical load when the potential is
higher than a predetermined threshold.
[0021] In another possible embodiment, the invention provides a
voltage management system for electrochemical cells, comprising an
electrochemical cell; a power supply adapted to provide an
electrical potential across the electrochemical cell; and a
shunting mechanism adapted to shunt a portion of the potential to
an electrical load when the potential is higher than a
predetermined threshold. Any of the features described herein can
be used with such a system, either alone or in combination.
[0022] As previously discussed, the shunting mechanism can be any
means of reducing electrical potential across the cell. As an
example, a diode can be used as discussed above. As additional
examples, the shunting mechanism can include a physical switch or
electrical switch wired to divert current from the cell. Suitable
electrical switches can include transistors such as field effect
transistors, MOSFETs, etc. The system can include a controller
adapted to actuate such a switch on receipt of a control signal.
For example, the controller can measure the potential across a cell
and actuate a switch to short or isolate the cell if the potential
across the cell exceeds a predetermined threshold.
[0023] As another possible example, a diode can be configured as
described above, but to where reverse current across the diode is
communicated to a controller, indicating an over-voltage condition
(i.e., the potential across the cell is higher than a predetermined
threshold).
[0024] In another possible embodiment, the electrical load can
include a circuit configured to indicate any over-voltage condition
occurring at a cell or group of cells. For example, a diode can be
configured as described above, but to where reverse current across
the diode powers a condition indicator, such as a light emitting
device.
[0025] It will be appreciated that many other configurations are
possible.
[0026] The inventive concepts discussed in the claims build on
traditional electrochemical cells technologies that are well known
in the art. As examples, various suitable designs and operating
methods that can be used as a base to implement the present
invention are described in the teachings of U.S. Pat. Nos.
4,620,914; 6,280,865; 7,132,182 and published U.S. patent
application Ser. Nos. 10/478,852, 11/696,179, 11/737,730,
11/737,733, and 11/737,737 which are each hereby incorporated by
reference in their entirety.
[0027] While the invention has been shown or described in only some
of its forms, it should be apparent to those skilled in the art
that it is not so limited, but is susceptible to various changes
without departing from the scope of the invention.
* * * * *