U.S. patent application number 12/045625 was filed with the patent office on 2008-11-13 for high rate electrochemical devices.
Invention is credited to Robert Brian Dopp.
Application Number | 20080277287 12/045625 |
Document ID | / |
Family ID | 39968549 |
Filed Date | 2008-11-13 |
United States Patent
Application |
20080277287 |
Kind Code |
A1 |
Dopp; Robert Brian |
November 13, 2008 |
HIGH RATE ELECTROCHEMICAL DEVICES
Abstract
A device and system useful for highly efficient chemical and
electrochemical reactions is described. The device comprises a
preferably porous electrode and a plurality of suspended
nanoparticles diffused within the void volume of the electrode when
used within an electrolyte. The device is suitable within a system
having a first and second chamber preferably positioned vertically
or in other special arrangements with respect to each other, and
each chamber containing an electrode and electrolyte with suspended
nanoparticles therein. When reactive metal particles are diffused
into the electrode structure and suspended in electrolyte by
gasses, a fluidized bed is established. The reaction efficiency is
increased and products can be produced at a higher rate. When an
electrolysis device can be operated such that incoming reactants
and outgoing products enter and exit from opposite faces of an
electrode, reaction rate and efficiency are improved. Ideally, this
device and system can be used to rapidly produce significant
quantities of high purity hydrogen gas with minimal electricity
cost.
Inventors: |
Dopp; Robert Brian;
(Marietta, GA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET, FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
39968549 |
Appl. No.: |
12/045625 |
Filed: |
March 10, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11716375 |
Mar 9, 2007 |
|
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12045625 |
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Current U.S.
Class: |
205/348 ;
204/242; 204/270; 204/278; 204/279; 205/637 |
Current CPC
Class: |
C25B 9/40 20210101; C25B
11/031 20210101; Y02E 60/36 20130101; C25B 1/04 20130101 |
Class at
Publication: |
205/348 ;
204/279; 204/242; 204/278; 204/270; 205/637 |
International
Class: |
C25B 1/02 20060101
C25B001/02; C25B 9/00 20060101 C25B009/00; C25B 9/18 20060101
C25B009/18 |
Claims
1. A device suitable for use in an electrochemical and/or catalytic
application, the device comprising a first component and a second
component, said first component being at least partially exposed to
a reaction medium during use, the second component comprising a
plurality of reactive metal nanoparticles suspended in the reaction
medium and diffused into the first component when the device is in
use.
2. The device of claim 1, wherein the first component comprising a
metal having a substantial void volume.
3. The device of claim 1, wherein at least a substantial portion of
the plurality of reactive metal particles comprises particles have
an average diameter of less than about 100 nm.
4. The device of claim 1, wherein at least a portion of the
reactive metal particles comprise nanoparticles having an oxide
shell.
5. The device of claim 1, wherein the plurality of reactive metal
particles comprise one or more of the metals from groups 3-16,
lanthanides, combinations thereof, and alloys thereof.
6. The device of claim 2, wherein the first component is a sintered
porous metal plate.
7. The device of claim 2, wherein the first component is a
reticulate metal plate.
8. The device of claim 1, wherein the first component comprises one
or more of the metals from groups 3-16, lanthanides, combinations
thereof, and alloys thereof.
9. The device of claim 1, wherein the device comprises an
electrolysis cell whereby reaction products are produced when
energy is applied.
10. The device of claim 9, wherein the device is configured to
generate hydrogen from water.
11. An electrochemical system, comprising: a first chamber
comprising an electrode, electrolyte, and metal catalyst particles
arranged such that, when in operation, a zone in the nature of a
fluidized bed may be established in the electrolyte and gaseous
products produced by the supply of electricity to the system may be
removed from the first chamber;
12. The electrochemical system of claim 11, further comprising: a
second chamber, the first chamber being partitioned from the second
chamber by a separator, the second chamber comprising an electrode,
electrolyte, and metal catalyst particles arranged such that, when
in operation, a fluidized bed may be established, and gaseous
products are removed from the second chamber.
13. The electrochemical system of claim 12, wherein the first and
second chambers are arranged with the first chamber at least
partially above the second chamber, at least partially around the
second chamber, at least partially displaced laterally with respect
to the second chamber, or at least partially coiled around the
second chamber.
14. The electrochemical system of claim 13, wherein the first
chamber is positioned at least partially above the second chamber,
the second chamber having an inlet and an outlet and being
configured such that electrolyte circulated through the second
chamber when in use may flow from the inlet past the second chamber
electrode to the outlet in a generally transverse direction and,
when in use, reactants may flux in the first chamber and gases
generated in the first chamber may move upwardly for
collection.
15. The electrochemical system of claim 14, further comprising a
pump to circulate at least a portion of the electrolyte in the
second chamber.
16. The electrochemical system of claim 13, wherein the system is
configured and adapted to permit useful operation while being
oriented such that the first chamber is positioned at least
partially horizontally displaced from the second chamber.
17. The electrochemical system of claim 11, wherein the electrolyte
in the first chamber is generally confined to that space.
18. The electrochemical system of claim 14, further comprising a
plurality of reactive metal particles in the upper chamber suitably
sized to permit particle diffusion into voids within one or both of
the electrodes.
19. The system of claim 11, wherein at least a substantial portion
of the reactive metal particles have an average diameter of less
than one micrometer.
20. The system of claim 19, wherein the nanoparticles have an
average diameter of less than about 100 nm.
21. The system of claim 11, wherein the plurality of reactive metal
particles comprises a metal selected from the group consisting of
metals from groups 3-16, lanthanides, combinations thereof, and
alloys thereof.
22. The system of claim 3, wherein the separator comprises a
membrane formed from an ionically conductive material.
23. The system of claim 22, wherein the separator membrane
comprises multiple layers of ionically conductive material to
increase mechanical, chemical, and electrochemical durability.
24. The system of claim 22, wherein the separator membrane is
capable of at least 5 A/cm.sup.2 flux.
25. The system of claim 14, wherein the electrolyte flow channel of
the second chamber contains a deflector to aid in transport to the
separator surface.
26. The system of claim 3, wherein the first chamber electrode is
configured to generate hydrogen from water and the second chamber
electrode is configured to generate oxygen from water.
27. An electrochemical system, comprising: a first chamber and a
second chamber, the first chamber being disposed within the second
chamber when the system is oriented such that it can be used in at
least one useful purpose, the first chamber comprising an
electrode, electrolyte, and metal catalyst particles arranged such
that, when in operation, a fluidized bed may be established, and
gaseous products may be removed from the upper portion of the first
chamber; the second outer chamber comprising an electrode,
electrolyte, and metal catalyst particles arranged such that, when
in operation, a fluidized bed may be established, and gaseous
products are removed from the upper portion of the second
chamber.
28. The system of claim 27, further comprising a separator membrane
disposed between the first and second chambers.
29. The system of claim 27, further comprising electrical contacts
on the first and second electrodes to permit the flow of
electricity therebetween.
30. The system of claim 27, wherein the electrolyte in the first
chamber is generally confined to that space.
31. The system of claim 27, wherein the electrolyte in the second
chamber is generally confined to that space.
32. The system of claim 27, wherein at least a substantial portion
of the reactive metal particles have an effective diameter of less
than one micrometer.
33. The system of claim 27, wherein the particles have a diameter
of less than about 100 nm.
34. The system of claim 27, wherein the plurality of reactive metal
particles comprises a metal selected from the group consisting of
metals from groups 3-16, lanthanides, combinations thereof, and
alloys thereof.
35. The system of claim 28, wherein the separator membrane
comprises an ionically conductive material.
36. The system of claim 35, wherein the separator membrane
comprises multiple layers of ionically conductive material to
increase mechanical, chemical, and electrochemical durability.
37. The system of claim 27, wherein the first chamber electrode is
configured to generate hydrogen from water and the second chamber
electrode is configured to generate oxygen from water.
38. The system of claim 27, wherein a multiple of first inner
chambers are placed within a single outer chamber, and where each
inner chamber is electrically connected in a circuit with the outer
chamber.
39. The system of claim 38, wherein the first chamber electrode is
configured to generate hydrogen from water and the second chamber
electrode is configured to generate oxygen from water.
40. An electrochemical system, comprising: a first chamber and a
second chamber, the first chamber being separated from the second
chamber by a separator membrane when the system is oriented such
that it can be used in at least one useful purpose, the first
chamber comprising a current collector, electrolyte, and metal
catalyst particles arranged such that, when in operation, a
fluidized bed may be established, and gaseous products may be
removed from the upper portion of the first chamber; the second
outer chamber comprising an electrode, electrolyte, and metal
catalyst particles arranged such that, when in operation, a
fluidized bed may be established, and gaseous products are removed
from the upper portion of the second chamber.
41. The system of claim 40, further comprising electrical contacts
on the first and second electrodes to permit the flow of
electricity therebetween.
42. The system of claim 40, wherein the current collector and
separator is wound into a spiral.
43. The system of claim 40, wherein the electrolyte in the first
chamber is generally confined to that space.
44. The system of claim 40, wherein the electrolyte in the second
chamber is generally confined to that space.
45. The system of claim 40, wherein the separator is
microporous.
46. The system of claim 40, wherein the separator is nonporous and
ion-conducting.
47. The system of claim 40, wherein the separator membrane
comprises multiple layers of ionically conductive material to
increase mechanical, chemical, and electrochemical durability.
48. The system of claim 40, wherein the separator is capable of
permitting the transport of at least 5 A/cm.sup.2 current flux.
49. The system of claim 40, wherein the current collector is
generally horizontal and the separator is generally vertical.
50. The system of claim 40, wherein the current collector and
separator are generally vertical.
51. The system of claim 40, wherein the current collector and
separator are conical.
52. The system of claim 40, further comprising an insulating
sheet.
53. The system of claim 40, wherein the current collector is porous
or reticulate.
54. The system of claim 40, wherein the current collector protrudes
into the fluidized bed.
55. The system of claim 40, wherein at least a substantial portion
of the reactive metal particles have an average diameter of less
than one micrometer.
56. The system of claim 40, wherein the particles have an average
diameter of less than about 100 nm.
57. The system of claim 40, wherein the plurality of reactive metal
particles comprises a metal selected from the group consisting of
metals from groups 3-16, lanthanides, combinations thereof, and
alloys thereof.
58. The system of claim 40, wherein the first chamber electrode is
configured to generate hydrogen from water and the second chamber
electrode is configured to generate oxygen from water.
59. A method of operating an electrochemical cell, which cell
comprises an anode chamber containing electrolyte and an anode, a
cathode chamber containing electrolyte and a cathode, which method
comprises suspending reactive metal particles in the anode chamber
and/or the cathode chamber electrolyte, and applying electricity
such that a circuit is formed.
60. A method of claim 59, comprising suspending reactive
nanoparticles in at least the cathode chamber and forming in the
electrolyte in the cathode chamber a reaction zone in the nature of
a fluidized bed to increase the effective area of the cathode and
transport gas produced by the reaction from the chamber.
61. A method of claim 59, comprising also suspending reactive
nanoparticles in the anode chamber and forming therein a reaction
zone in the nature of a fluidized bed to transport gas formed in
the anode chamber from the chamber.
62. A method of claim 60, wherein the electrolyte comprises an
aqueous salt solution and the method comprises producing hydrogen
in the cathode chamber and forming in that chamber from the
hydrogen, electrolyte and particles a system akin to a fluidized
bed whereby the hydrogen bubbles upwardly through the electrolyte,
the method further comprising collecting the hydrogen so
produced.
63. A method of claim 59, wherein the particles have an average
diameter of less than about 100 nm.
64. A method of claim 59, wherein the particles have an average
diameter of less than about 50 nm.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of application
Ser. No. 11/716,375, filed on Mar. 9, 2007.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The inventions disclosed herein generally relate to improved
electrochemical systems and their use and, in particular, to water
electrolysis devices for the production of high purity hydrogen and
oxygen, and catalysts for these devices which promote increased
electrical and cost efficiency, and methods of using such devices
and for the production of hydrogen and oxygen.
[0004] 2. Related Art
[0005] Hydrogen is a renewable fuel that produces zero emissions
when used in a fuel cell. In 2005, the Department of Energy (DoE)
developed a new hydrogen cost goal and methodology, namely to
achieve $2.00-3.00/gasoline U.S. gallon equivalent (gge, delivered,
untaxed, by 2015), independent of the pathway used to produce and
deliver hydrogen. The principal method to produce hydrogen is by
stream reformation. Nearly 95% of the hydrogen currently being
produced is made by steam reformation, where natural gas is reacted
on metallic catalyst at high temperature and pressure. While this
process has the lowest cost, four pounds of the greenhouse gasses
carbon monoxide (CO) and carbon dioxide (CO.sub.2) are produced for
every one pound of hydrogen. Without further costly purification to
remove CO and CO.sub.2, the hydrogen fuel cell cannot operate
efficiently.
[0006] Alternatively, 5% of hydrogen production is from water
electrolysis. This reaction is the direct splitting of water
molecules to produce hydrogen and oxygen. Note that greenhouse
gasses are not produced in these reactions. In this process,
electrodes composed of catalyst particles are submersed in water
and energy is applied to them. Using this energy, the electrodes
split water molecules into hydrogen and oxygen. Hydrogen is
produced at the cathode electrode which accepts electrons and
oxygen is produced at the anode electrode which liberates
electrons. The amount of hydrogen and oxygen produced by an
electrode is dictated by the current supplied to the electrodes.
The efficiency depends upon the voltage between the two electrodes,
and is proportional to the reciprocal of that voltage. That is to
say; efficiency increases as the voltage decreases. A more
catalytic system will have a lower voltage for any one current, and
therefore be more efficient in producing hydrogen and oxygen. If
the catalyst is highly efficient, there will be minimal energy
input to achieve a maximum hydrogen output. Unfortunately, this
process is currently too expensive to compete with steam
reformation due low efficiency and the use of expensive catalysts
in the electrodes.
[0007] Devices that are configured to electrochemically convert
reactants into products when energy is applied are generally known
as electrolyzers. For an electrolyzer to operate with high
efficiency, the amount of product produced during reaction should
be maximized relative to the amount of energy input. In many
conventional devices, low catalyst utilization in the electrodes,
cell resistance, inefficient movement of electrolyte, and
inefficient collection of reaction products from the electrolyte
stream contribute to significant efficiency loss. In many cases,
low efficiency is compensated for by operating the cell at a low
rate (current). This strategy does increase efficiency, however, it
also lowers the amount of products that can be produced at a given
time. The electrolyzer described in the preferred embodiments can
operate both at high rates and efficiencies.
[0008] Fluidized bed reactors (FBRs) have been designed to carry
out chemical reactions that take place between materials of the
same or different phases (solids, liquids and/or gasses). In an FBR
that contains catalyst particles, a gas or liquid is passed
upwardly through the FBR with enough flow rate to cause suspension
of the catalyst particles. While FBRs have been used in the
chemical industry because of their positive heat and mass transfer
characteristics, use of FBRs remain unexplored in conjunction with
electrochemical cells.
SUMMARY OF THE INVENTION
[0009] In one aspect of the invention, there is provided a device
suitable for use in an electrochemical and/or catalytic
application, the device comprising a metal component, preferably
having substantial void volume, a reaction medium to which the
metal component is at least partially exposed during use, and a
plurality of reactive metal nanoparticles suspended in the reaction
medium when the device is in use and diffused into the metal
component when the metal component preferably has said substantial
void volume and when the device is in use. The reaction medium is
preferably an electrolyte, with metal components comprising an
anode and a cathode to form an electrochemical cell.
[0010] The invention thereby provides a high-surface area
electrode. In one embodiment, the electrode comprises a porous or
reticulate metal plate combined with catalytic metal particles,
preferably at the nanoscale. The plate preferably includes some
void volume to allow infusion of a plurality of metal
nanoparticles. More preferably, the plates are porous, such as
sintered or reticulate, and most preferably they comprise metal
foams.
[0011] When immersed within an electrolyte, the metal particles can
float freely and can substantially infuse into the
porous/reticulate metal plate to create an electrode with extremely
high surface area.
[0012] The electrodes in this invention can be applied to a variety
of devices, including a hydrogen generation electrode in a water
electrolyzer system. In such an embodiment, the electrode can
function as a fluidized bed. At least one advantage is that the
electrode can be operated at currents (rates) exceeding 1
A/cm.sup.2 and efficiencies in excess of 65% (measured by
voltammetric or galvanometric electrochemical testing.), which in
turn means that large amounts of hydrogen can be produced using
less electricity. Typical electrodes have a far lower surface area
and thus cannot operate at rates significant enough to produce
large quantities of hydrogen. Other advantages may include,
depending upon the configuration, circumstances, and environment,
the ability to scale the electrode to a wide variety of sizes, a
high rate of hydrogen production, and the ability to minimize
agglomeration by using nano-sized particles. The fluidized bed
reactor of the invention preferably produces from about 0.1 to
about 3, more preferably from about 1 to about 3 gge/hr/m.sup.2 of
hydrogen. A gge is a "U.S. gallon of gasoline equivalent"
[0013] One embodiment of the invention provides an electrochemical
system, comprising: a first chamber and a second chamber, the first
chamber being separated or partitioned from the second chamber by a
separator, such as a membrane, the first chamber comprising an
electrode, electrolyte, and metal catalyst particles arranged such
that, when in operation, a fluidized bed may be established and
gaseous products may be removed from the first chamber, such as
from an upper portion thereof, the second outer chamber comprising
an electrode, electrolyte, and metal catalyst particles arranged
such that, when in operation, a fluidized bed may be established,
and gaseous products may be removed from the second chamber, such
as from an upper portion thereof.
[0014] The chambers can be arranged in a variety of ways, such as
one at least partially above the other; one at least partially
surrounding the other; one laterally displaced with respect to the
other and one coiled at least partially around the other.
[0015] The reaction efficiency may be enhanced depending on the
metal nanoparticles chosen. Efficiencies of at least 75%,
preferably at least 85% may be achieved. Preferably, the plurality
of reactive metal particles have an oxide shell. The reactive
particles preferably comprise a metal selected from the group
consisting of metals from groups 3-16, lanthanides, combinations
thereof, and alloys thereof, and most preferably the metal
nanoparticles are nickel, iron, combinations thereof, and alloys
thereof.
[0016] The anode and cathode chambers may be filled with
electrolyte that preferably contains a plurality of reactive and
conductive metal nanoparticles. Preferably, the metal nanoparticles
are on average less than 100 nm in diameter Average particle size
is typically measured by TEM microscopy and GAA analysis, and is
more preferably less than 50 nm in diameter, such as from 10-30 nm.
The reaction efficiency may be enhanced depending on the metal
nanoparticles chosen. Nickel or iron is preferred.)
[0017] Preferably, the generated anode and cathode gasses flow
through the container in a manner that suspends the nanoparticles
within the fluid, creating a fluidized bed. Most preferably, the
bed is fluidized by the reaction products. At least some advantages
of this configuration include, (i) elimination of pumps via direct
extraction of gasses from the container, such as via upper vents,
and the self propagating nature of the fluidized bed, (ii) ease of
keeping hydrogen and oxygen gasses separated, (iii) ease of
controlling temperature and pressure, (iv) simple design, and (v)
less expensive per unit of hydrogen produced, to name a few.
[0018] The invention also provides a method of operating an
electrochemical cell, which cell comprises an anode chamber
containing electrolyte and an anode, a cathode chamber containing
electrolyte and a cathode, which method comprises suspending
reactive metal particles, preferably nanoparticles, in the anode
chamber and/or the cathode chamber electrolyte, applying electric
current to the anode and the cathode. Preferably, the suspension of
reactive nanoparticles is provided in at least the cathode chamber,
more preferably in both chambers, and the chambers are configured
so that, in use, the suspension(s) act in the nature of a fluidized
bed to transport gases from the chamber(s). Thus, the invention
provides a method of generating hydrogen from water by
electrolysis, comprising suspending reactive metal nanoparticles in
a chamber containing a cathode and electrolyte, applying electric
current to the cathode and to an anode in a chamber containing the
anode and electrolyte, producing hydrogen in the cathode chamber
and forming in that chamber from the hydrogen, electrolyte and
particles a system akin to a fluidized bed whereby the hydrogen
bubbles upwardly through the electrolyte, the method further
comprising collecting the hydrogen so produced. These methods are
applicable to the devices, systems, compositions and components
described herein in connection with other embodiments of the
invention.
[0019] In another aspect of the invention, a new electrochemical
device is provided, preferably a water electrolysis device. Unlike
traditional electrolyzers, such as that shown in FIG. 1, one
embodiment of the inventive electrochemical device system may be
oriented horizontally rather than vertically. With such an
arrangement, electrolyte may be moved through a lower chamber, with
oxygen being generated on a lower electrode. A deflector is
preferably placed in the electrolyte stream to ensure removal of
all generated oxygen from the system. Oxygen may be scrubbed from
the electrolyte before it is circulated back into the system. In at
least one embodiment, water generated from the reaction can move
through a separator membrane to the upper chamber. An upper chamber
electrode produces hydrogen gas. Because hydrogen gas is less dense
than the electrolyte, the hydrogen may bubble upwards and can then
be removed from the system. Preferably, a fluidized bed is
established in the upper chamber employing catalytic nanoparticles.
Contemporaneously, hydroxyl ions (OH--) are generated and may move
downwardly through the separator for consumption at the lower
chamber electrode. At least some advantages include, depending upon
the configuration, circumstances, and environment, (i) that only
half of the system may need pumping (unless the device is oriented
on an angle, in which case no pumping may be necessary) whereas
traditional systems need total pumping; (ii) half the pumping means
half the parasitic losses; (iii) there is no need for a gas
separator in the upper chamber; gas freely moves upward because it
is less dense, and (iv) ions move from the bottom of the electrode
while hydrogen escapes from the top, which gives a lower ionic
resistance.
[0020] In yet another aspect of the invention, a fluidized bed
electrolyzer may be provided that comprises a corrosion resistant
container that houses a cylindrical separator. In one embodiment,
porous anode and cathode electrodes may be disposed on the outer
and/or inner circumference of the separator.
[0021] In the preferred embodiments, the individual anode or
cathode electrodes in the cell may be fluidized, or both may be
fluidized. Preferably, both electrodes are fluidized. A number of
electrolyzer cells may be interconnected to function as an
electrolyzer stack, and preferably they are electrically connected
in a vertical orientation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a schematic representation of a typical
electrolysis device.
[0023] FIG. 2 is a schematic representation of one embodiment of an
improved electrolysis device in which first and second chambers are
oriented perpendicular with respect to each other.
[0024] FIG. 3A is a cross-sectional schematic view of one
embodiment of an improved electrolysis device showing first and
second chambers positioned concentrically in a vertical
orientation.
[0025] FIG. 3B is an end schematic view of the embodiment of FIG.
3A.
[0026] FIG. 4 is an end schematic of one alternative embodiment of
the device of FIG. 3A wherein there are multiple second chambers
positioned within a large diameter first chamber.
[0027] FIG. 5 is a detailed view of metal particles in the upper
chamber.
[0028] FIG. 6 plots the number of atoms on the surface of
nanoparticles relative to particle diameter.
[0029] FIG. 7 is a chronovoltammetric plot showing the effect of
metal particle addition.
[0030] FIG. 8 is a bar graph describing the change in voltage with
the addition of different sized metal particles.
[0031] FIG. 9 is a polarization curve illustrating system
performance at high current.
[0032] FIG. 10 is a bar graph illustrating comparing hydrogen
generation on a fluidized bed versus other electrodes.
[0033] FIG. 11 is a schematic end-on view of a fluidized bed
reactor in spiral orientation.
[0034] FIG. 12 is a schematic end-on view of a fluidized bed
wherein the electrode is substantially horizontal and the separator
is substantially vertical.
[0035] FIG. 13 is a schematic perspective view of a fluidized bed
wherein the electrodes and separators deviate from horizontal and
the insulator is substantially vertical.
[0036] FIG. 14 is a schematic end-on view of a fluidized bed
wherein the electrode and separator are conical.
[0037] FIG. 15 is a schematic end-on view of a fluidized bed
wherein the electrode and separator are substantially vertical.
[0038] The features mentioned above in the summary of the
invention, along with other features of the inventions disclosed
herein, are described below with reference to the drawings of some
preferred embodiments. The illustrated embodiments in the figures
listed below are intended to illustrate, but not to limit the
inventions.
DETAILED DESCRIPTION OF SOME PREFERRED EMBODIMENTS
[0039] FIG. 1 illustrates a traditional electrolysis system. The
main features of this system are pumps circulating at the anode and
cathode to remove resulting oxygen and hydrogen gasses,
respectively. The electrodes are typically oriented in a vertical
fashion and are substantially solid. Oxygen and hydrogen gasses are
scrubbed from the electrode before electrolyte returns to the cell.
Electrodes are typically solid metal or electrodeposited metal with
relatively low surface area.
[0040] Referring to FIG. 2, one embodiment of an inventive
electrolyzer configured to generate hydrogen and oxygen from water
can be described. Electrolyte 201, such as aqueous potassium
hydroxide (KOH), sodium hydroxide (NaOH), or a mixture of the two
may be placed in a first chamber 202 via inlet port 203. When
electricity is applied to cathode electrode 204 through electrical
contact 205, hydrogen gas is produced by
2H.sub.2O+2e.sup.-.fwdarw.H.sub.2+2OH.sup.-. Because hydrogen gas
is less dense than the electrolyte, it rises and leaves via port
206 to be collected or consumed. Hydroxyl ions produced in the
reaction permeate downward through separator membrane 207. In a
second chamber 208, electrolyte 201 is circulated parallel to anode
electrode 209 via inlet port 211 and outlet port 210. In a
preferred operative mode of at least one system embodiment, the
system is oriented such that the first chamber 202 is positioned
above the second chamber 208. Such an arrangement provides some
advantages as discussed herein. It is contemplated, however, that
another embodiment may comprise a system that is usefully oriented
in such a manner that the first chamber is horizontally displaced
relative to the second chamber, either in a side-by-side
arrangement, or at some angle between vertical and horizontal.
[0041] When electricity is applied to electrode 209 via electrical
contact 212, oxygen is produced pursuant to the following general
reaction: 2OH--.fwdarw.H.sub.2O+1/2O.sub.2+2e-. Oxygen is
eliminated from the electrolyte stream before the electrolyte is
returned to the cell. To ensure that all oxygen is being eliminated
from the upper surfaces of the lower chamber, angled deflector 213
is placed proximal to port 211 to ensure that deoxygenated
electrolyte is washing the separator 207. For some system
measurements, a side chamber containing separator mat 214 is filled
with electrolyte 201, and reference electrode 215 is placed to
measure electrochemical potential versus the upper chamber.
Additionally, working reference electrode 216 is placed in contact
with electrode 204.
[0042] The system configuration illustrated in FIG. 2 has several
distinct advantages compared to the traditional electrolyzer shown
in FIG. 1. In traditional electrolyzers, the entire volume of
electrolyte fed into the system requires pumping and removal of
hydrogen and oxygen gasses from the cathode and anode streams,
respectively, resulting in parasitic losses. In the disclosed
invention, the upper chamber acts on gravity and the electrolyte is
stationary; hydrogen gas escapes from the top surface and
inherently travels to the upper outlet port because it is less
dense than both the electrolyte and air. Only the lower chamber
requires electrolyte pumping to move oxygen out of the cell and
flush new electrolyte into the system, thus this system has only
half the parasitic loss of a traditional system.
[0043] The cathode electrode in the upper chamber has increased
efficiency relative to a conventional electrode, in that reacting
hydroxyl ions leave from the bottom of the electrode and resulting
gas leaves from the top of the electrode. This minimizes ionic
resistance in the device, as gas bubbles do not block catalyst
sites on the electrode to outgoing hydroxyl ions or incoming water
molecules.
[0044] In the lower chamber of the device, an angled deflector is
placed proximal to the electrolyte inlet port. Because the
electrolyte flows in a parallel fashion to the electrode surface
and product gas rises, it is possible for gas bubbles to become
lodged on the upper surface of the chamber proximal to the
separator membrane, which can impede both water and ionic
transport. By deflecting electrolyte to the upper surface of the
chamber, the increased flow force of the electrolyte on that
surface prevents gas bubbles from lodging and results in improved
system efficiency.
[0045] In some of the preferred embodiments, the upper chamber
features both an inlet and outlet port. One of the ports allows the
removal of hydrogen gas from the system, and the other allows for
direct injection of new electrolyte, compensatory water, or new
catalyst. This feature allows for both simple cleaning and
replenishment or replacement if catalyst and reactants.
[0046] Some of the preferred embodiments detail an increased
available reaction surface through the use of porous electrodes.
The electrodes can be prepared of networking metal particles, for
example reticulate nickel or nickel foam. In other embodiments, the
electrodes may be sintered metal plates, prepared such that the
electrode is highly porous with a relatively large void volume. The
electrodes are preferably prepared from metals, preferably selected
from the group of metals from groups 3-16, the lanthanide series
and combinations thereof and alloys thereof. More preferably, the
metals are transition metals, mixtures thereof, and alloys thereof
and their respective oxides. Most preferably, the metal or metals
are selected from the group consisting of nickel, iron, manganese,
cobalt, tin, and silver, or combinations, alloys, and oxides
thereof.
[0047] An aspect of at least some of the embodiments in this
invention includes the realization that a reticulate or porous
electrode's surface area can be increased significantly through the
use of free moving reactive metal particles within the electrolyte.
The electrolyte serves as both an ionic conductor and medium for
the particles. Because of the reticulate or porous nature of the
electrode, reactive metal particles can infuse into the electrode
surface and become diffuse throughout the void volumes in the
electrode. Preferably, the particles are less than one micron in
effective diameter, and more preferably less than 100 nanometers in
diameter. Most preferably, the reactive metal particles are less
than 50 nm in diameter such that substantial portion can infuse
into the electrode. Larger particles tend to agglomerate to the
extent that the void volume within the electrode can no longer
accommodate their size. This results in a significant loss in
efficiency.
[0048] Referring to FIGS. 3A and 3B, another embodiment that
comprises, in operation, a fluidized bed electrolysis reactor. The
reactor comprises a corrosion resistant container 301 having one or
several possible geometric configurations. The particular
embodiment shown is generally cylindrical, with a generally
cylindrical separator membrane 302 aligned, if so desired,
concentrically with the container 301. The membrane 302 defines two
chambers, an anode chamber and a cathode chamber. Porous or
reticulate electrodes are disposed on each side of the membrane
302. Anode electrode 303 is disposed on the outer surface and
cathode electrode 304 is disposed on the inner surface. Both the
anode chamber 305 and cathode chamber 306 are filled with ionically
conducting electrolyte 307, such as aqueous potassium hydroxide.
Electrolyte 307 contains a plurality of reactive metal
nanocatalysts particles 308 that are fluidized by the rising gasses
in each chamber. Catalytic nanoparticles suspended in both the
inner and outer chambers make contact with the electrodes through a
percolation pathway. This percolation pathway is established when a
plurality of the catalytic nanoparticles make contact with the
porous or reticulate electrode as well as indirect contact through
a chain of nanoparticles that ultimately make contact with the
electrode. Electricity is applied to the electrodes via cathode
electrical contact 311 and anode electrical contact 312. Oxygen is
generated in the anode chamber. Because the density of oxygen is
less than that of the electrolyte, it travels upward and leaves the
system via port 309. Hydrogen is generated in the cathode chamber.
Because hydrogen is less dense than the electrolyte, it travels
upward and leaves the system via port 310. The movement of these
resulting gas bubbles effectively fluidizes the reactive metal
nanoparticles in the electrolyte such that the fluidized bed is
self-propagating.
[0049] The system configuration illustrated in FIGS. 3A and 3B has
several distinct advantages compared to the traditional
electrolyzer shown in FIG. 1. In traditional electrolyzers, the
entire volume of electrolyte fed into the system requires pumping
and removal of hydrogen and oxygen gasses from the cathode and
anode streams, respectively, resulting in parasitic losses. In the
disclosed device, pumping is eliminated when a fluidized bed is
established. Once fluidization occurs, considerably larger amounts
of gas can be produced compared to a traditional electrolyzer. In
addition, the device could be scaled to any conceivable size.
[0050] Referring to FIG. 4, multiple cells described in FIG. 3 can
be connected for increased surface area and therefore increased
hydrogen and oxygen production. Ions travel only a short distance
through the separator, thus fluidized bed convection in both inner
chambers 401 and outside chamber 402 the individual cells is not
disturbed. Cathode electrode contacts 403 (negative terminals)
would preferably be connected in parallel to the negative terminal
of a power supply, and anode electrode contacts 404 (positive
terminals) would be connected to the positive terminal of the power
supply. Both the inside and outside volume of each cell contains a
plurality of metal catalyst nanoparticles suspended in a fluidized
bed when the device is operating. An additional advantage to
operating multiple cells in this configuration is that because
surface area is increased, internal resistance decreases and lowers
parasitic losses. In this configuration seven cells are shown,
however the configuration can be scaled with many more cells.
[0051] FIG. 5 illustrates an electrode infused with nanoparticles
and with nanoparticles suspended in electrolyte. Electrode 501 is
preferably a highly reticulate or porous, and can accommodate the
infusion of nanoparticles 502 (shown as dots) that can diffuse
throughout the void spaces within the interior of the electrode 503
and free moving in the electrolyte 504. When electricity 508 is
applied to the electrode 501, water in the electrolyte that comes
through separator 510 is split, producing hydrogen gas 505. The
hydrogen gas 505 may diffuse upwardly and out of the top surface of
the electrode 501, bubbling to the surface of the electrolyte to
escape the apparatus 506. This bubbling maintains fluidization
within the chamber. Meanwhile, hydroxyl ions 507 may move
downwardly and permeate the separator membrane 510.
[0052] An electrode with infused nanoparticles has a larger
reaction surface than the electrode alone. To illustrate the
concept, a catalytic nanoparticle 502 touches the surface of
electrode 501 and collects electrons 508, splitting two surrounding
water molecules within the interior of the electrolyte 504 into an
H.sub.2 molecule 505 and two hydroxyl ions 507. The gas lifts the
nanoparticle off the surface of the electrode 501, while a sister
particle 511 replaces it to repeat the reaction. When the system is
running at it's optimum, a fluidized bed is desirably established
between the electrolyte, nano-catalysts and the tiny hydrogen gas
bubbles. At least one aspect of the preferred embodiments includes
the realization that gas or liquid does not necessarily need to be
flowed into the bottom of the chamber once a fluidized bed has been
established. In the described embodiments, gasses released from
electrochemical reaction establish fluidization in-situ. A
significant energy savings is inherent by eliminating the need for
continuous pumping.
[0053] Unlike a traditional electrolyzer, whose efficiency
decreases as current increases, a fluidized bed electrolyzer
described in the preferred embodiments will increase in efficiency
as current is increased, until a limiting current is reached in
which further gas generation disrupts fluidization and the
percolation pathway, ultimately lowering efficiency. Nevertheless,
this limiting current at maximum efficiency is significantly higher
in the devices described in the preferred embodiments compared to a
traditional electrolysis system.
[0054] Additionally, reactive surface area is increased by order of
magnitude by operation with catalytic nanoparticles in the
fluidized bed. In addition to the surface area of the porous or
reticulate electrode, and nanoparticles infused into the electrode,
the system capitalizes on the additional surface area of the
fluidized catalytic nanoparticles. The increased catalytic behavior
of the reactive metal nanoparticles, compared to the surface of the
metal substrate alone, is high due to the very large number of
atoms on the surface of the nanoparticles, as shown in FIG. 6. By
way of demonstration, consider a 3 nanometer nickel particle as a
tiny sphere. Such a sphere would have 384 atoms on its surface and
530 within its interior, of the 914 atoms in total. This means that
58% of the nanoparticles would have the energy of the bulk material
and 42% would have higher energy due to the absence of neighboring
atoms. Nickel atoms in the bulk material have about 12 nearest
neighbors while those on the surface have nine or fewer. A 3 micron
sphere of nickel would have 455 million atoms on the surface of the
sphere, 913 billion in the low energy and isolated interior of the
sphere for a total of nearly one trillion atoms. That means that
only 0.05% of the atoms are on the surface of the 3 micron-sized
material compared to the 42% of the atoms at the surface of the
3-nanometer nickel particles.
[0055] The reactive metal particles can be formed through any known
manufacturing technique, including, for example, but without
limitation, ball milling, precipitation, plasma torch synthesis,
combustion flame, exploding wires, spark erosion, ion collision,
laser ablation, electron beam evaporation, and
vaporization-quenching techniques such as joule heating.
[0056] Another possible technique includes feeding a material onto
a heater element so as to vaporize the material in a
well-controlled dynamic environment. Such technique desirably
includes allowing the material vapor to flow upwardly from the
heater element in a substantially laminar manner under free
convection, injecting a flow of cooling gas upwardly from a
position below the heater element, preferably parallel to and into
contact with the upward flow of the vaporized material and at the
same velocity as the vaporized material, allowing the cooling gas
and vaporized material to rise and mix sufficiently long enough to
allow nano-scale particles of the material to condense out of the
vapor, and drawing the mixed flow of cooling gas and nano-scale
particles with a vacuum into a storage chamber. Such a process is
described more fully in U.S. patent Ser. No. 10/840,109, filed May
6, 2004, the entire contents of which is hereby expressly
incorporated by reference.
[0057] The chemical kinetics of catalysts generally depend on the
reaction of surface atoms. Having more surface atoms available will
increase the rate of many chemical reactions such as combustion,
electrochemical oxidation and reduction reactions, and adsorption.
Extremely short electron diffusion paths, (for example, 6 atoms
from the particle center to the edge in 3 nanometer particles)
allow for fast transport of electrons through and into the
particles for other processes. These properties give nanoparticles
unique characteristics that are unlike those of corresponding
conventional (micron and larger) materials. The high percentage of
surface atoms enhances galvanic events such as the splitting of
water molecules into its composite gasses of hydrogen and oxygen.
FIG. 3 shows this relationship well.
[0058] The reactive metal particles referenced herein are
preferably selected from the group of metals from groups 3-16, and
the lanthanide series. More preferably, the metals are transition
metals, mixtures thereof, and alloys thereof and their respective
oxides. Most preferably, the metal or metals are selected from the
group consisting of nickel, iron, manganese, cobalt, tin, and
silver, or combinations, alloys, and oxides thereof. The
nanoparticles may be the same as, substantially the same, or
entirely different materials from those chosen for the electrode.
Additionally, the nanoparticles may comprise a metal core and an
oxide shell having a thickness in the range from 5 to 100% of the
total particle composition, wherein the metal core may be an
alloy.
[0059] In other preferred embodiments, new fluidized bed
electrolyzer designs are shown. These designs improve performance
by enhancing reaction efficiency and reducing size. In some
designs, reaction efficiency may be maximized when ionic resistance
losses are reduced by minimizing the distance between the separator
membrane and electrode. In other designs, the electrodes may be
formed into a smaller area allowing for a smaller footprint.
[0060] Irrespective of design, a significant aspect of the
preferred embodiments is adequate composition of the membrane
separator. The separator should be able to operate at temperatures
up to 130.degree. C., permit an ion flux exceeding 5 A/cm.sup.2,
maintain stability in strongly alkaline solutions such as high
concentration potassium or sodium hydroxide, and prevent product
gas bubbles from permeating between cell chambers. The membrane may
be micro porous, such that electrolyte is permitted to move between
reaction chambers, or may be nonporous but ionically
conductive.
[0061] A spiral orientation of the fluidized bed reactor is
illustrated in FIG. 11, wherein porous negative and positive
electrodes 1101 and 1102, respectively are rolled between separator
1103. Catalytic particles are then injected into electrolyte 1104.
Electrically insulating material 1105 is employed at the center of
the spiral as well as at the electrode and separator outer
termination points. The advantage to this configuration is that
high surface area current collector electrodes can occupy less
volume and therefore a smaller device can be employed to produce
the amount of reaction products only achieved in a larger system.
To encapsulate the reactor, solid negative and positive electrodes
1106 and 1107, respectively, are used as the outer walls.
[0062] In another aspect of the preferred embodiments, a fluidized
bed reactor may be established wherein the current collector is in
a horizontal configuration and the separator membrane is in a
vertical orientation. Referring to FIG. 12, separator membrane 1201
serves as a partition between the anode and cathode sides of the
cell. Cathode and anode porous electrodes 1202 and 1203 are placed
at the bottom of the reaction vessel, and catalytic particles are
injected into electrolyte 1204 in both the anodic and cathodic
chambers. The catalytic particles are suspended by the gasses they
produce and form an electrically conductive mass in each chamber.
The resulting ions have only a short distance to travel to the
opposing chamber to complete the circuit.
[0063] Referring to FIG. 13, porous electrodes 1301 and 1302 may be
oriented away from horizontal position such that a space is
provided under the electrode. Separator 1303 is disposed on the
bottom face of the electrodes. This space may be filled with an
electrolyte 1304 such as KOH in gel form to serve as an ion bridge
between the two electrodes. Insulator 1305 serves to keep catalytic
particles and product gasses segregated. This configuration may be
advantageous in improving the establishment of a fluidized bed
since both current collectors are only degrees from horizontal.
Referring to FIGS. 14A and 14B, electrodes 1401 and 1402 with
separator 1403 disposed on the lower surface may be formed into a
cone configuration. Insulator 1405 bisects the cone through the
porous electrode and separator to maintain polarized reaction
zones, and liquid electrolyte 1406 serves as an ion conduction
medium for the addition of reactive catalytic particles. Electrical
contact leads may be connected to 1401 and 1402 to permit the flow
of electricity.
[0064] Additionally, the electrodes and separator may be oriented
vertically. Referring to FIG. 15, porous anode and cathode
electrodes 1501 an 1502 are proximally disposed on either face of
separator 1503. Catalytic particles are injected into electrolyte
1304. In this configuration, multiple cells may be connected in
series through repeating units or in series. Negative and positive
leads 1505 and 1506 are connected to electrodes 1501 and 1502 to
permit the flow of electricity.
[0065] The foregoing description is that of preferred embodiments
having certain features, aspects, and advantages in accordance with
the present inventions. Various changes and modifications also may
be made to the above-described embodiments without departing from
the spirit and scope of the inventions.
Example 1
Effect of Nanoparticle Addition to Upper (Cathode) Chamber
[0066] The water electrolysis device shown in FIG. 2 was used to
perform the experiment. FIG. 7 illustrates the effect of injecting
nano-catalyst into the upper chamber of the water electrolysis
device. The electrolyzer is allowed to reach a steady-state voltage
under 1 A/cm.sup.2, which is evident after about 60 seconds. At
time 701, nickel nanoparticles (QSI-Nano.RTM. Nickel, 5-30 nm, from
QuantumSphere Inc.) were added to the upper chamber of the
electrolyzer. An efficiency increase of 10% was observed after
addition of nickel nanoparticles 502. After about 15 minutes,
steady state efficiency improvement was about 20%.
Example 2
Comparison of Five Different Cathode Electrodes
[0067] FIG. 8 compares the performance of several different cathode
electrodes for a water electrolysis device. Electrodes compared are
Incofoam nickel metal foam (purchased from Inco), a sintered micron
nickel plate (a sintered, compressed electrode of 1-5 micron Ni
particles, purchased from Alfa Aesar), a sintered nickel plate of
nickel particles (Inco 123, purchased from Inco), a sintered
electrode of 5-30 nm nano-nickel from QuantumSphere Inc, and a
sintered plate prepared from 1-5 micron nickel particles, as above,
with 10 wt % 5-30 nm nickel from QuantumSphere Inc. injected into
the electrolyte. An improvement over the base electrode 801 with no
catalytic powders added was observed when micron particles were
added 802 on a 1 Amp/cm.sup.2 load. This combination, however,
agglomerated after less than an hour of running with significant
degradation. The addition of nano-catalyst 803 increased the
performance by nearly 4 times compared to the unanalyzed electrode
801. For reference, a 10% improvement line 804 is included in the
FIG. 5.
Example 3
High Rate Capability of Electrolysis Device
[0068] FIG. 9 illustrates the improved rate capability of the
electrolysis device described in the preferred embodiments relative
to a more traditional system. This figure shows the voltage and
current relationship of several electrode designs. Sets 901-904 are
of a design compressed powders, as shown in Example 2. Sets 905-906
show the preferred embodiment. Specifically, data sets 901/901'
show a carbon electrode, 902/902' show a smooth nickel electrode,
903/903' show a compressed micron sized nickel electrode, 904/904'
show a micron nickel with nano sized powders added then compressed,
905/905' show the preferred embodiment with no added catalyst, and
906/906' show the most preferred embodiment (a foam nickel
electrode with nano-nickel particles injected.) with nano-catalyst
added. A voltage difference of 2 volts is about 75% efficiency. The
last set of dots, 907, is a cell potential of 1,584 volts and
represents over 90% efficiency when calculating the energy in the
hydrogen divided by the energy it takes to electrolyze the water to
make that hydrogen. The best traditional electrolysis systems
operate at less than 75% efficiency when run higher than 0.5
A/cm.sup.2.
Example 4
Effect of Fluidized Bed
[0069] FIG. 10 shows the performance of five experiments with the
most preferred embodiment to the right. Performance is expressed as
the amount of hydrogen (as gge or gallon of gas equivalents) per
hour per square meter of electrode surface. The set of comparisons
is a graphite electrode 1001, a micron nickel catalyzed electrode
1002, a nano nickel catalyzed electrode 1003, an electrode
catalyzed using three different nano sized catalysts 1004 and the
fluidized bed electrolyzer 1005. Another way to compare these would
be the amount of time it would take for a one square meter
electrode to produce one gge. Table 1 below summarizes that data.
The graphite produces hydrogen at 85% efficiency very slowly,
requiring 32 days to make one gge while the fluidized bed takes
just 25 minutes.
TABLE-US-00001 TABLE 1 Comparison of electrode rates from several
different electrode designs. Design Hr/gge/m{circumflex over ( )}2
Graphite (1001) 769 u Nickel (1002) 125 QSI nNi (1003) 25.0 3 QSI
nCatalysts (1004) 3.85 New with QSI Catalysts (1005) 0.412
* * * * *