U.S. patent application number 15/311705 was filed with the patent office on 2017-06-01 for electrolysis system.
This patent application is currently assigned to H2SG ENERGY PTE LTD. The applicant listed for this patent is H2SG ENERGY PTE LTD. Invention is credited to Alexey IZGORODIN, Ivan IZGORODIN.
Application Number | 20170152605 15/311705 |
Document ID | / |
Family ID | 56919389 |
Filed Date | 2017-06-01 |
United States Patent
Application |
20170152605 |
Kind Code |
A1 |
IZGORODIN; Ivan ; et
al. |
June 1, 2017 |
ELECTROLYSIS SYSTEM
Abstract
An electrolysis cell system (100) for producing hydrogen and
oxygen from water comprising: at least one electrolysis cell (101)
including a membrane electrode assembly (102) which comprises at
least one pair of gas permeable electrodes (107, 109) comprising an
anode (107) and a cathode (109), and an ion conductive electrolyte
(108) arranged between each pair of anode (107) and cathode (109);
an electrode gas space (104, 106) on the non-electrolyte side of
each electrode (107, 109) comprising an anode gas space (104) and a
cathode gas space (106), at least one electrode gas space (104)
including an inlet (130) and an outlet (132); a recirculating loop
(143) for recirculating at least a portion of produced oxygen
product gas from the outlet (132) of at least one electrode gas
space (104) to the inlet (130) of the respective electrode gas
space (104) and through the respective electrode gas space (104); a
water supply vessel (142) in fluid communication with the
recirculating loop (143), the water supply vessel (142) vaporising
water from a water supply (144) utilising heat of vaporisation
provided by the respective product gas in the recirculating loop
(143) and feeding said water vapour into the recirculating loop
(143); and a heat transfer arrangement (105) for transferring heat
between the membrane electrode assembly (102) and gas in the anode
gas space (104) located in the electrode gas space (104) fluidly
connected to the recirculating loop through the inlet and outlet
thereof, wherein the heat transfer arrangement (105) is in contact
with the membrane electrode assembly (102) and also allows for gas
circulation between the membrane electrode assembly (102) and the
respective gas space (104).
Inventors: |
IZGORODIN; Ivan; (Ivanovo,
RU) ; IZGORODIN; Alexey; (Singapore, SG) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
H2SG ENERGY PTE LTD |
Singapore |
|
SG |
|
|
Assignee: |
H2SG ENERGY PTE LTD
Singapore
SG
|
Family ID: |
56919389 |
Appl. No.: |
15/311705 |
Filed: |
March 13, 2015 |
PCT Filed: |
March 13, 2015 |
PCT NO: |
PCT/SG2015/000077 |
371 Date: |
November 16, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25B 1/10 20130101; C25B
15/02 20130101; C25B 9/00 20130101; C25B 9/10 20130101; Y02E 60/36
20130101; C25B 15/08 20130101; Y02E 60/366 20130101 |
International
Class: |
C25B 15/02 20060101
C25B015/02; C25B 9/10 20060101 C25B009/10; C25B 15/08 20060101
C25B015/08; C25B 1/10 20060101 C25B001/10 |
Claims
1.-26. (canceled)
27. An electrolysis cell system for producing hydrogen and oxygen
product gas from water comprising: at least one electrolysis cell
including a membrane electrode assembly which comprises at least
one pair of gas permeable electrodes comprising an anode and a
cathode, and an ion conductive electrolyte arranged between each
pair of anode and cathode; an electrode gas space on the
non-electrolyte side of each electrode at least one electrode gas
space including an inlet and an outlet; a recirculating loop for
recirculating at least a portion of at least one of the produced
oxygen or hydrogen product gas from the outlet of the respective
electrode gas space to the inlet of the respective electrode gas
space; a water supply vessel in fluid communication with the
recirculating loop, the water supply vessel vaporising water from a
water supply utilising heat of vaporisation provided by the product
gas and introducing said water vapour into the recirculating loop;
and a heat transfer arrangement for transferring heat between the
membrane electrode assembly and gas in the gas space located in the
electrode gas space fluidly connected to the recirculating loop
through the inlet and outlet thereof, wherein the heat transfer
arrangement is in contact with the membrane electrode assembly and
also allows for gas circulation between the membrane electrode
assembly and the respective electrode gas space.
28. The electrolysis cell system of claim 27, wherein the heat
transfer arrangement comprises a heat sink in direct physical
contact with the respective anode or cathode.
29. The electrolysis cell system of claim 28, wherein the heat sink
is in abutting contact or is physically connected to at least one
portion of the respective anode or cathode.
30. The electrolysis cell system of claim 27, wherein the heat
transfer arrangement comprises at least one of: a mesh, preferably
a corrugated mesh section; a perforated sheet; or a sheet or a
plate.
31. The electrolysis cell system of claim 27, wherein the heat
transfer arrangement is gas permeable, preferably in a direction
parallel to the longitudinal axis of the membrane electrode
assembly.
32. The electrolysis cell system of claim 27, wherein the heat
transfer arrangement is formed from metal, preferably nickel or
stainless steel, more preferably corrosion resistant stainless
steel.
33. The electrolysis cell system of claim 27, wherein the electrode
gas space including the inlet and the outlet fluidly connected to
the recirculating loop is the electrode gas space of the anode and
the product gas comprises oxygen.
34. The electrolysis cell system of claim 27, wherein the electrode
gas space including the inlet and the outlet fluidly connected to
the recirculating loop is the electrode gas space of the cathode
and the product gas comprises hydrogen.
35. The electrolysis cell system of claim 27, wherein the water
supply vessel comprises a humidifier.
36. The electrolysis cell system of claim 35, wherein the
humidifier directly mixes the product gas and water supplied into
and flowing through the humidifier.
37. The electrolysis cell system of claim 35, wherein the
recirculated oxygen or hydrogen product gas passes through the
humidifier and entrains water vapour therein.
38. The electrolysis cell system of claim 27, wherein the heat of
vaporisation for water vaporisation is provided by the product gas
in the recirculating loop.
39. The electrolysis cell system of claim 27, wherein water is
supplied to the water supply vessel at a rate needed to replenish
water used in the system by electrolysis.
40. The electrolysis cell system of claim 27, wherein the electrode
gas space is housed in an electrode chamber having inlet and outlet
openings are located along a gas flow axis which is orientated
perpendicular to longitudinal axis of the membrane electrode
assembly of the respective electrolysis cell.
41. The electrolysis cell system of claim 27, including at least
two electrolysis cells stacked together.
42. A process of producing hydrogen and oxygen from water using at
least one electrolysis cell including a membrane electrode assembly
which comprises at least one pair of gas permeable electrodes
comprising an anode and a cathode, and an ion conductive
electrolyte arranged between each pair of anode and cathode, the or
each gas permeable electrodes including an electrode gas space on
the non-electrolyte side thereof, at least one of the electrode gas
spaces of the anode and cathode including an inlet and an outlet,
said process comprising: supplying current and water vapour to the
membrane electrode assembly to produce hydrogen gas from the
cathode and oxygen gas from the anode; recirculating a portion of
at least one of the produced oxygen gas or hydrogen gas from the
outlet of the respective electrode gas space through a
recirculating loop to the inlet of said respective gas space and
through said respective gas space; vapourising water supplied into
the recirculating loop from a water supply utilising energy
provided by at least a portion of the respective oxygen or hydrogen
product gas in said recirculating loop to provide the requisite
heat of vaporisation; and transferring heat between the membrane
electrode assembly and product gas in said respective electrode gas
space using a heat transfer arrangement located in said respective
electrode gas space which is in contact with the membrane electrode
assembly and also allows for gas circulation between the membrane
electrode assembly and said respective electrode gas space.
43. The process of claim 42, wherein the step of vapourising water
occurs in a humidifier.
44. The process of claim 42, wherein the step of vapourising water
includes mixing water into the recirculating a portion of produced
oxygen gas thereby transferring heat from the produced oxygen
product gas to water in said mixture for water vaporisation.
45. The process of claim 42, wherein said respective gas space is
the electrode gas space of the anode and the product gas comprises
oxygen.
46. The process of claim 42, wherein said respective gas space is
the electrode gas space of the cathode and the product gas
comprises hydrogen.
Description
TECHNICAL FIELD
[0001] The invention generally relates to an electrolysis process
and apparatus for carrying out said electrolysis process to produce
clean gases such as hydrogen and oxygen. The invention is
particularly applicable for low temperature gas electrolysis cell
systems for electrolysing water and it will be convenient to
hereinafter disclose the invention in relation to that exemplary
application. However, it is to be appreciated that the invention is
not limited to that application and could be used in other
electrolysis applications.
BACKGROUND OF THE INVENTION
[0002] The following discussion of the background to the invention
is intended to facilitate an understanding of the invention.
However, it should be appreciated that the discussion is not an
acknowledgement or admission that any of the material referred to
was published, known or part of the common general knowledge as at
the priority date of the application.
[0003] Low temperature gas electrolysis cell systems have a
substantial amount of heat generated in the membrane electrode
assembly (particularly on the anode side) as a result of the
exothermic reaction in water electrolysis under operational
conditions. Cooling systems must therefore be used to maintain the
low operational temperature of the membrane electrode assembly and
overall electrolysis cell.
[0004] One water electrolysing apparatus that utilises a heat
exchange system is taught in U.S. Pat. No. 3,917,520 (Katz et al.)
and U.S. Pat. No. 3,905,884 (Edmund et al.) and is illustrated in
FIG. 1. As shown in FIG. 1, the apparatus includes an electrolysis
cell that comprises a porous matrix 18 sandwiched between a cathode
14 and an anode 16, and filled with an aqueous electrolyte. Heat
removal from the cell is through porous backup plate 20 (which also
includes an electrolyte storage matrix) adjacent the anode 16, and
thermal exchange portion 22. The cell also includes gas spaces 24,
26 on the nonelectrolyte side of the cathode and anode
respectively.
[0005] During operation an electric potential is applied by the
power source 30 causing electrolysis of the water and liberating
oxygen on the anode side of the cell into gas space 26 and hydrogen
on the cathode side of the cell into gas space 24 and through
outlet 32. The gases are removed using conduits 34 and 36
respectively. Pressure regulating means are used to maintain
substantially equivalent pressure in the gas spaces 24 and 26. A
portion of the hydrogen gas is recirculated through the cell by a
pump 39 and re-enters the cell the gas space 24 at the inlet
38.
[0006] Heat is removed from the cell by a pump 46 recirculating a
coolant fluid through a loop 41 which passes through thermal
exchange portion 22 using coolant inlet 42 and coolant outlet 44.
The loop 41 also includes bypass loop 48 with bypass control valve
50, thermal element 52 and radiator 54. The coolant is circulated
through the cell in counter current flow direction to the
recirculating hydrogen gas.
[0007] Water from a storage compartment 56 is supplied to the
recirculating hydrogen stream using metering device 58 in an amount
sufficient to replace the water used by the cell and the water
which exits with gases through conduits 34, 36. The water is
vaporized using evaporator 60 with the heat of evaporation provided
by the hot liquid coolant leaving thermal exchange portion 22.
[0008] The water electrolysis cell system apparatus of U.S. Pat.
Nos. 3,905,884 and 3,917,520 therefore includes a separate heat
exchange section to be attached to the electrolysis cell. This
section has to be isolated from the anode chamber to avoid gas
crossover. Resultingly, this system has the following
disadvantages:
(A) A separate thermal exchange portion is required to be attached
to the cell introducing additional complexity to the overall system
and introducing thermal losses through the connection materials;
(B) High cost and complexity of the cell heat management system
that includes thermal sensors and control equipment that provides
circulation and maintains temperature of the liquid coolant at
various operating conditions; and (C) Low reliability due to water
condensation within the gas recirculation loop. The heat from the
cell is removed using the liquid coolant loop and is released
through the bypass loop or used to vaporise water in the
evaporator. The system maintains a constant temperature of the
liquid coolant entering the cell. The recirculated hydrogen gas is
used to transport the water in a vapour form from the evaporator to
the cell. However, the described system does not have means to
maintain substantially constant temperature in the gas
recirculation loop. It should be appreciated that to transmit
substantial amount of water in a vapour form the process should be
conducted at elevated temperature. With temperature variations
within the gas recirculation loop, a portion of the water can
condense locally within the gas recirculation loop. Water supply is
limited by the amount of water leaving the cell. Thus, such
temperature variations can eventually lead to the electrolyte
drying out and subsequent failure of the device.
[0009] It would therefore be desirable to provide an alternate
and/or improved method and apparatus for carrying out an
electrolytic process to produce clean gases such as hydrogen and
oxygen. Such a system would preferably reduce cost and complexity
of cell heat management and control equipment required to operate
the apparatus.
SUMMARY OF THE INVENTION
[0010] The present invention provides a new electrolysis system,
preferably a low temperature gas electrolysis cell system, for
producing hydrogen and oxygen from water.
[0011] A first aspect of the present invention provides an
electrolysis cell system for producing hydrogen and oxygen product
gas from water comprising:
[0012] at least one electrolysis cell including a membrane
electrode assembly which comprises at least one pair of gas
permeable electrodes comprising an anode and a cathode, and an ion
conductive electrolyte arranged between each pair of anode and
cathode;
[0013] an electrode gas space on the non-electrolyte side of each
electrode at least one electrode gas space including an inlet and
an outlet;
[0014] a recirculating loop for recirculating at least a portion of
at least one of the produced oxygen or hydrogen product gas from
the outlet of the respective electrode gas space to the inlet of
that electrode gas space;
[0015] a water supply vessel in fluid communication with the
recirculating loop, the water supply vessel vaporising water from a
water supply utilising heat of vaporisation provided by the product
gas and introducing said water vapour into the recirculating loop;
and
[0016] a heat transfer arrangement for transferring heat between
the membrane electrode assembly and gas in the gas space located in
the electrode gas space fluidly connected to the recirculating loop
through the inlet and outlet thereof, wherein the heat transfer
arrangement is in contact with the membrane electrode assembly and
also allows for gas circulation between the membrane electrode
assembly and the respective electrode gas space.
[0017] Unlike prior art electrolysis cell configurations (for
example discussed above), the present invention includes a heat
transfer arrangement in the electrode gas space of either the
cathode or the anode which is in contact, preferably physical
contact, with the membrane electrode assembly to allow for
efficient heat transfer between the respective hydrogen or oxygen
product gas and membrane electrode assembly. The respective product
gas circulates through electrode gas space over the heat transfer
arrangement to remove heat from that electrode gas space.
[0018] The water required to maintain electrolysis is supplied in
vapour form with the recirculating product gas. The water vapour is
fed to the membrane electrode assembly via the fluidly connected
electrode gas space. Advantageously, the recirculating loop enables
the heat generated during water electrolysis to be used to
evaporate water (from the water supply) needed for electrolysis in
the membrane electrode assembly. It should be appreciated that the
remainder of the heat generated during water electrolysis is
utilised to maintain and where required, increase the temperature
in the electrolysis cell system.
[0019] It should be appreciated that the efficiency of an
electrolysis cell increases with increasing operational
temperature. Thus, as the temperature in the system increases, at a
constant rate of hydrogen production (i.e. a constant current
supply), the electrolysis cell will generate less heat. As a
result, equilibrium will be reached where the heat generated during
electrolysis will be used to maintain elevated temperature within
the system and provide energy to evaporate water required for
electrolysis in the electrolysis cell.
[0020] The heat transfer arrangement can comprise any suitable
body, system or arrangement which can transfer heat from the
membrane electrode assembly to the gas in the electrode gas space
housing the heat transfer arrangement. In some embodiments, the
heat transfer arrangement comprises a heat sink in direct physical
contact with the respective anode or cathode. More preferably, the
heat sink is in abutting contact or is physically connected to at
least one portion of the respective anode or cathode. Suitable heat
transfer arrangements preferably include apertures or openings,
preferably multiple apertures/openings for gas flow between the
respective electrode gas space and the membrane electrode assembly.
The heat transfer arrangement is therefore gas permeable,
preferably in direction parallel to the longitudinal axis of the
membrane electrode assembly. Suitable heat transfer arrangement
includes a mesh, preferably a corrugated mesh section or a
perforated sheet. Heat transfer arrangements of this type typically
have a sheet or a plate form. The heat transfer arrangement may
also in some embodiments be electrically conductive. The heat
transfer arrangement is therefore preferably formed from a
conductive metal, for example nickel or stainless steel. Corrosion
resistance is also preferred, particularly for certain corrosive
electrolytes. Accordingly, in some embodiments the heat transfer
arrangement is preferably formed from a corrosion resistant metal,
preferably corrosion resistant stainless steel. This corrosion
resistance may result from alloy composition, corrosion resistance
coating or the like.
[0021] The membrane electrode assembly can comprise any number of
configurations. For example, in one embodiment each electrolysis
cell contains a pair of gas porous electrodes pressed on each side
of the electrolyte. The electrolyte preferably comprises any
suitable electrolytic composition having a lower saturated water
pressure over its surface compared to that of pure water at
identical temperature and pressure. In some embodiments, the
electrolyte may comprise a solid ion exchange membrane or a liquid
electrolyte embedded in a variety of porous matrixes. The
electrodes for the anode and the cathode are preferably composed of
materials well known to catalyse water oxidation and reduction, in
either acidic or alkaline medium depending on the type of the
electrolyte. A variety of suitable materials are well known in the
art.
[0022] Depending on the desired electrolysis cell configuration,
either the electrode gas space of the anode or the electrode gas
space of the cathode can include the heat transfer arrangement and
be fluidly connected to the recirculating loop. Thus in some
embodiments, the electrode gas space including the inlet and the
outlet fluidly connected to the recirculating loop is the electrode
gas space of the anode and the product gas comprises oxygen. In
such embodiments, oxygen product gas is circulated through the
recirculating loop and provides heat of vaporisation for
vaporisation of water fed into the humidifier. In other
embodiments, the electrode gas space including the inlet and the
outlet fluidly connected to the recirculating loop is the electrode
gas space of the cathode and the product gas comprises hydrogen. In
such embodiments, hydrogen product gas is circulated through the
recirculating loop and provides heat of vaporisation for
vaporisation of water fed into the humidifier.
[0023] The water supply vessel comprises any vessel in which
heat/energy can be transferred from a gaseous phase (the
recirculated gas flow) to a liquid phase (supply water) so to
vaporise the water. Various heat transfer arrangements are
possible. In preferred embodiments, the water supply vessel
comprises a humidifier. The humidifier preferably directly mixes
the product oxygen or hydrogen gas in the recirculating loop and
water supplied into and flowing through the humidifier. The
recirculated oxygen or hydrogen product gas can therefore passes
through the humidifier and entrains water vapour therein. In such
embodiments, the heat of vaporisation for water vaporisation is
provided by the product gas in the recirculating loop.
[0024] The humidifier, and more particularly the outlet of the
humidifier, is preferably located close to the inlet of the fluidly
connected electrode gas space. Close proximity between the
humidifier and inlet of the fluidly connected electrode gas space
minimises heat loss between the humidifier and electrode gas space
and the possibility of condensation in any fluid connection
therebetween.
[0025] The system is preferably a low temperature electrolysis
system, and is therefore preferably operated at a temperature of
between 0 to 300.degree. C., preferably between 100 and 200.degree.
C., more preferably between 120 and 160.degree. C.
[0026] Water is used in the system in electrolysis to produce
hydrogen and oxygen. Water is preferably supplied to the water
supply vessel at a rate needed to replenish water used in the
system by electrolysis. In this respect, a control system can be
used to control the amount of water fed to the water supply vessel.
In such embodiments, the amount of water that is equivalent to the
amount used during the electrolysis as sensed (for example by an
ammeter or other appropriate sensor) plus the amount of water lost
from the cell with the gases through the outlet of the respective
electrode gas space and with the recirculated product gas and a
suitable/equivalent amount is fed to the water supply vessel.
[0027] In embodiments of the invention, the electrode gas space is
housed in an electrode chamber having inlet and outlet openings
which are located along a gas flow axis which is orientated
perpendicular to longitudinal axis of the membrane electrode
assembly of the respective electrolysis cell. The inlet and outlet
openings are preferably sized to maintain a sufficient gas flow
through the electrode gas space and respective electrode chamber.
In some embodiments, the ratio between the total active planar
surface area of the membrane electrode assembly perpendicular to
the longitudinal axis of the membrane electrode assembly and the
planar area of each of the inlet and outlet openings of the
electrode chamber is between 1 and 5.
[0028] The size of the inlet and outlet openings of the electrode
chamber facilitate gas flowing and being circulated through the
electrode gas space at a preferred velocity of between 0.1 to 20
m/s, preferably between 1 and 20 m/s, more preferably between 5 and
20 m/s. A lower circulation velocity can be used at high operating
temperature and pressure of the gas in the system, in which smaller
volumes of the circulated gas are required to provide effective
heat transfer and supply a sufficient amount of water as a
feedstock for electrolysis. A higher velocity is required to
maintain a desired system efficiency at lower temperature and gas
pressure.
[0029] In some embodiments, the system includes at least two
electrolysis cells stacked together. In some embodiments, the
system includes multiple electrolysis cells stacked together. Such
a system comprises a cell stack, with the stacked electrolysis
cells functioning in parallel to produce the desired product gases
from the fed water.
[0030] A second aspect of the present invention provides a process
of producing hydrogen and oxygen from water using at least one
electrolysis cell including a membrane electrode assembly which
comprises at least one pair of gas permeable electrodes comprising
an anode and a cathode, and an ion conductive electrolyte arranged
between each pair of anode and cathode, the or each gas permeable
electrodes including an electrode gas space on the non-electrolyte
side thereof, at least one of the electrode gas spaces of the anode
and cathode including an inlet and an outlet, said process
comprising:
[0031] supplying current and water vapour to the membrane electrode
assembly to produce hydrogen gas from the cathode and oxygen gas
from the anode;
[0032] recirculating a portion of at least one of the produced
oxygen gas or hydrogen gas from the outlet of the respective
electrode gas space through a recirculating loop to the inlet of
said respective gas space and through said respective gas
space;
[0033] vapourising water supplied into the recirculating loop from
a water supply utilising energy provided by at least a portion of
the respective oxygen or hydrogen product gas in said recirculating
loop to provide the requisite heat of vaporisation; and
[0034] transferring heat between the membrane electrode assembly
and product gas in said respective electrode gas space using a heat
transfer arrangement located in said respective electrode gas space
which is in contact with the membrane electrode assembly and also
allows for gas circulation between the membrane electrode assembly
and said respective electrode gas space.
[0035] As discussed above, depending on the desired configuration,
either the electrode gas space of the anode or the electrode gas
space of the cathode can include the heat transfer arrangement and
be fluidly connected to the recirculating loop. Thus in some
embodiments, said respective gas space is the electrode gas space
of the anode and the product gas comprises oxygen. In other
embodiments, said respective gas space is the electrode gas space
of the cathode and the product gas comprises hydrogen.
[0036] Similarly, as discussed above, the step of vapourising water
preferably occurs in a humidifier. In this step, water is
preferably mixed into the recirculating a portion of produced
oxygen gas thereby transferring heat from the produced oxygen
product gas to water in said mixture for water vaporisation.
[0037] It should be appreciated that the process according to the
second aspect of the present invention can be performed using a
system according to the first aspect of the present invention.
Accordingly, the features discussed in relation to the first aspect
of the present invention equally apply to the second aspect of the
present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] The present invention will now be described with reference
to the Figures of the accompanying drawings, which illustrate
particular preferred embodiments of the present invention,
wherein:
[0039] FIG. 1 is a view of the electrolysis cell system
corresponding to the prior art and as described in the introduction
to the specification.
[0040] FIG. 2 is a view of the electrolysis cell system
corresponding to the invention.
[0041] FIG. 3 provides a general design schematic of the oxygen
chamber of an electrolysis cell according to one embodiment of the
present invention.
[0042] FIG. 4 shows a perspective view of a portion of an
electrolysis cell according to one embodiment of the present
invention without oxygen chamber (shown in FIG. 3).
[0043] FIG. 5 shows a perspective view of the assembled
electrolysis cell according to the embodiment shown in FIGS. 3 and
4.
[0044] FIG. 6 provides a perspective view of a number of
electrolysis cells as shown in FIG. 5 forming a cell stack.
DETAILED DESCRIPTION
[0045] The present invention provides an electrolysis cell which
produced hydrogen and oxygen product gases from a water supply. The
electrolysis cell of the present invention generally includes a
membrane electrode assembly containing an anode, a cathode and
electrolyte therebetween.
[0046] One development provided by the present invention is the use
of a heat transfer arrangement that facilitates efficient heat
transfer between the membrane electrode assembly and either the
oxygen gas or hydrogen product gas produced by the membrane
electrode assembly. The heat transfer arrangement of the present
invention is housed in an electrode gas chamber on the
non-electrolyte side of the anode or cathode depending on the
desired configuration of the electrolysis cell. The heat transfer
arrangement is physically connected to the respective anode or
cathode. Product oxygen or hydrogen product gas circulates through
electrode gas chamber over the heat transfer arrangement to remove
heat from the chamber and supply water for the electrolysis. A
portion of this heated product gas is recirculated through a
recirculation loop connected between an outlet and inlet of the
electrode gas chamber. The recirculation loop includes a humidifier
into which supply water is feed in sufficient quantity to maintain
electrolysis. The humidifier utilises the heat of the product gas
in the recirculation loop to supply the required energy (heat of
vaporisation) to vaporise the supplied water. The water required
for electrolysis is therefore supplied to the membrane electrode
assembly in vapour form from the recirculation loop with
recirculating product gas.
[0047] FIGS. 2 to 6 show one form of an electrolysis cell system or
electrolyser 100 according to the present invention.
[0048] Referring firstly to FIG. 2, which shows a process schematic
of one electrolysis cell system 100 according to an embodiment of
the subject invention. The illustrated electrolysis cell system 100
comprises at least one electrolysis cell 101. Each electrolysis
cell 101 includes a membrane electrode assembly 102 having gas
permeable electrodes comprising an anode 107 and a cathode 109
which are arranged on either side of an ion conductive electrolyte
108. The membrane electrode assembly 102 is constructed by means
well known in the art. For example, in one embodiment of the
present invention the electrolysis cell 101 contains a pair of gas
porous electrodes pressed on each side of the electrolyte 108.
[0049] The electrolyte 108 is preferably either a solid ion
exchange membrane (a commercially available proton exchange
membrane, for example NAFION.RTM. or an anion exchange membrane,
for example Tokuyama's A201 available from Tokuyama America:
Arlington Heights, Ill. 60005, United States of America) or a
liquid electrolyte embedded in a variety of porous matrixes (for
example as described in the U.S. Pat. Nos. 5,843,297 and 4,895,634
the contents of which should be understood to be incorporated into
the specification by this reference). The main requirement for the
electrolyte 108 is to have a lower saturated water pressure over
its surface compared to that of pure water at identical temperature
and pressure.
[0050] The electrodes for the anode 107 and the cathode 109 are
preferably composed of materials well known to catalyse water
oxidation and reduction, in either acidic or alkaline medium
depending on the type of the electrolyte. For example, the
electrodes for the anode 107 and the cathode 109 may either form
nanoparticles dispersed on the surface of an ion exchange membrane
(as for example described in Energy Environ. Sci., 2011, 4, 2993
the contents of which should be understood to be incorporated into
the specification by this reference), or be manufactured as a
perforated sheet or mesh (for example as described in Int. Journal
of Hydrogen Energy 37 (2012) 10992-11000 the contents of which
should be understood to be incorporated into the specification by
this reference).
[0051] The electrolysis cell 101 uses gas spaces 104, 106 on the
non-electrolyte side of the cathode 109 and the anode 107. Oxygen
gas produced by electrolysis is collected in anode gas space 104.
Hydrogen produced by electrolysis is collected in cathode gas space
107. The produced oxygen and hydrogen gases exit the respective gas
spaces 104, 106 via outlets 132 and 132A. As explained below, the
anode gas space 104 also include water vapour used to supply water
to the electrolysis cell 101 for electrolysis. The cell gas spaces
104, 106 are formed in the cell by a cathode chamber 128 and anode
chamber 129, as shown in FIGS. 3 and 4. The anode chamber 129 has
an inlet 130 and an outlet 132.
[0052] The cathode chamber 128 can be manufactured by any
well-known means that allows for electric current to be supplied to
the cathode 109 and preferably contains a plurality of channels on
the electrolyte side (not illustrated) for the hydrogen gas to be
removed from the system 100 as for example described in Energy
Environ. Sci., 2011, 4, 2993 the contents of which should be
understood to be incorporated into the specification by this
reference.
[0053] One embodiment of an electrolysis cell 101 according to the
present invention is shown in FIGS. 3 to 6. A general design of the
anode chamber 129 used in this embodiment of the presented
invention is shown in FIG. 3. The illustrated anode chamber 129
consists of a thin hollow plate with two openings comprising inlet
130 and an outlet 132 on opposing sides 131A and 131B to allow for
gas circulation in and out of the anode chamber 129 and an opening
133 on the base 131C, to which the membrane electrode assembly 102
(including the anode) is mounted via the anode 107.
[0054] A heat transfer arrangement comprising heat exchanger or
heat sink 105 is located within the anode gas space 104. Heat sink
105 is in direct physical contact with the anode 107 while
maintaining a gas circulation/gas diffusion between the anode 107
and the gas in the anode gas space 104. Heat sink 105 can comprise
a metal perforated plate or mesh section. However, it should be
appreciated that the heat sink 105 can be have any suitable
construction able to maintain high volumes of gas circulation and
provide an efficient heat transfer from the anode 107 to the gas in
the anode gas space 104.
[0055] A portion of this embodiment of the electrolysis cell 101
illustrated without the anode chamber 129 is shown in FIG. 4. Heat
sink 105 is used to remove heat from the anode 107 and is pressed
onto the anode 107 of the membrane electrode assembly 102 that is
placed over the cathode chamber 128. In the preferred embodiment,
the heat sink 105 can be made from a metal sheet or metal mesh. In
the illustrated embodiment, the heat sink 105 comprises a
corrugated metal plate (square corrugations) having a perforated
contact area 107A with the anode 107 and solid corrugated fins
107B. The area of the heat sink 105 in contact with the anode 107
of the membrane electrode assembly 102 has a number of openings 145
to allow for heat and water transfer between the membrane electrode
assembly 102 and oxygen product gas in the anode chamber 129. The
heat sink 105 can be made of nickel or corrosion resistant
stainless steel in the case of an alkaline membrane or stainless
steel with corrosion resistant coating (for example the carbon
coating taught in JP 2013082985 A Watanabe et al. 9 May 2013, the
contents of which should be understood to be incorporated into the
specification by this reference) in the case of an acidic
membrane.
[0056] The heat sink 105 may have various designs to enhance heat
transfer between the membrane electrode assembly 102 and the gas
circulating in the anode chamber 129. Electrical current can be
directly supplied to the anode 107 or alternatively through the
heat sink 105 if a conductive material is being used.
[0057] A full cell assembly 101 is shown in FIG. 5. In the
preferred embodiment the anode chamber 129 (the outer side thereof)
has a direct electrical contact with the anode 107, while the
cathode chamber 128 (the outer side thereof) has a direct
electrical contact with the cathode 109.
[0058] The inlet 130 and outlet 132 openings of the anode chamber
129 are located on the side of the anode chamber 129 with the inlet
openings orientated perpendicular to the longitudinal axis X-X of
the electrolysis cell 101. The flow of gas through the inlet 130
and outlet 132 of the anode chamber 129 are located along a flow
axis which is orientated perpendicular to longitudinal axis X-X of
the membrane electrode assembly 102. The inlet 130 and outlet 132
openings are sized to maintain a sufficient gas flow through the
anode chamber 129. For this purpose, it is preferred for the ratio
between the active surface of the membrane electrode assembly 102
(the planar surface area of the electrodes, electrolyte and the
like perpendicular to the longitudinal axis X-X) and the inlet area
A of the inlet 130 and outlet 132 to the anode chamber 129 is
preferably between 1 and 5.
[0059] During operation of the system 100, an electric potential is
applied between each cathode 109 and anode 107 from a power source
113 causing the electrolysis of the fraction of the water retained
in the electrolyte 108, thus liberating oxygen into the anode gas
space 104 and hydrogen into the cathode gas space 106. The oxygen
and hydrogen product gases are removed from the system 100 while
maintaining substantially equivalent pressure within the gas spaces
104 and 106 through the pressure control outlet 115. Due to
inefficiencies of the water oxidation process, most of the heat is
generated at the interface between the anode 107 and the
electrolyte 108 during electrolysis. The generated heat from the
electrolyte 108 is transferred through the anode 107 into the heat
sink 105.
[0060] A portion of the oxygen gas produced from electrolysis in
the electrolysis cell 101 is recirculated by a pump 111 within the
electrolysis cell 101 and is used to remove heat from the heat sink
105. The recirculating oxygen leaves the electrolysis cell 101 at
the outlet 146 of the anode gas space 104 and re-enters the
electrolysis cell 101 at the inlet 148.
[0061] The gas is circulated through the anode chamber 129 and
anode gas space 104 therein at a velocity between 0.1 to 20 m/s. A
lower circulation velocity can be used at high operating
temperature and pressure of the gas in the system, in which smaller
volumes of the circulated gas are required to provide effective
heat transfer and supply a sufficient amount of water as a
feedstock for electrolysis. A higher velocity is required when it
is important to maintain the system 100 efficiency at lower
temperatures and gas pressures.
[0062] It should be noted that a higher ratio between the active
surface of the membrane electrode assembly 102 (the planar surface
area perpendicular to the longitudinal axis X-X) and the inlet area
A of the inlet 130 and outlet 132 to the anode chamber will require
a higher circulation velocity of the gas to maintain effective heat
transfer and supply a sufficient amount of water as a feedstock for
electrolysis.
[0063] A portion of the produced oxygen and hydrogen gas is
circulated from the outlet of the anode gas space 104 through
humidifier 142 and back to the inlet of the anode gas space 104 via
recirculating loop 143. The humidifier 142 is fluidly connected to
the recirculating loop 143, with the oxygen product gas (from
electrolysis) flowing therethrough. The humidifier 142 is also fed
water from a water supply 144. The supplied water is vaporised
(i.e. transferred the requisite energy (heat of vaporisation) and
thereby heated to the requisite temperature) in the humidifier 142
using the energy provided by the heated oxygen product gas stream
in the recirculating loop 143 and therefore flows from the outlet
of the humidifier 142 in a vapour form entrained the oxygen product
gas. The recirculated oxygen therefore passes through the
humidifier 142 and entrains water vapour therein. Water vapour is
resultingly feed into the anode gas space 104 of each electrolysis
cell 101 from the recirculating loop 143.
[0064] The water is supplied to the system 100 from the water
supply at a rate needed to replenish water used the system 100 by
electrolysis. A portion of the produced oxygen and hydrogen gas is
circulated from the outlet of the anode gas space 104 through
humidifier 142 and back to the inlet of the anode gas space 104 via
recirculating loop 143. The humidifier 142 is fluidly connected to
the recirculating loop 143, with the oxygen product gas (from
electrolysis) flowing therethrough. The humidifier 142 is also fed
water from the water supply 144 which is vaporised in the
humidifier 142 using the energy/heat provided by the heated oxygen
product gas stream in the recirculating loop 143. Water vapour
therefore flows from the outlet of the humidifier 142 entrained the
oxygen product gas. Water vapour is resultingly feed into the anode
gas space 104 of each electrolysis cell 101 from the recirculating
loop 143. The water is supplied to the system 100 from the water
supply at a rate needed to replenish water used the system 100 by
electrolysis.
[0065] A control system (not illustrated) can be used to control
the flow of water into the humidifier 142 from the water supply
144. The control system ensures that the amount of water that is
equivalent to the amount used during the electrolysis as sensed by
the ammeter 152 plus the amount of water lost from the cell with
the gases through outlet 115 (i.e. not cycling through the
recirculation loop 143) is fed into the humidifier 142 and then
vaporised into the recirculated oxygen. Dotted line 149 shows the
general control line between the ammeter 152 and water supply 144.
It should be appreciated that water supply 144 would include a
control valve or similar flow limiting/control device which can
control the amount of water being fed to the humidifier 142.
[0066] The energy of vaporisation for vapouring the water fed into
the humidifier 142 is provided by the temperature/heat of the
recirculated oxygen. If there is insufficient heat available from
the circulated product oxygen gas, it will not be able to vaporise
water in the humidifier 142. Thus, water vapour in excess of energy
levels of the system 100 cannot enter the recirculation loop 143,
and thus condensation of such water vapour in the recirculation
loop 143 does not occur.
[0067] The heat generated during water electrolysis in the
electrolysis cell 101 is used to evaporate water needed for
electrolysis with the remainder increasing the temperature in the
electrolysis cell system 100. As the temperature of the
electrolysis cell 101 increases, the efficiency of the process will
increase and, thus, the heat generated by the electrolysis cell 101
will become sufficient for the water vaporisation, whereby
compensating for the heat loss within the system 100. It is well
known that efficiency of an electrolysis cell increases with
increasing operational temperature. Thus, as the temperature in the
system increases, at a constant rate of hydrogen production (i.e. a
constant current supply), the cell will generate less heat. As a
result, equilibrium will be reached where the heat generated during
the electrolysis will be used to maintain elevated temperature
within the system 100 and provide energy to evaporate water
required for electrolysis. Additionally, the electrolysis cell 101
is maintained at a higher temperature compared to that of the
humidifier 142 to allow for the heat transfer through the
recirculated oxygen. Overall, the system 100 can be operational
between 0 to 300.degree. C., with preferred mode of operation being
between 120 and 160.degree. C.
[0068] The electrolysis cell 101 operates at a substantially equal
pressure between the oxygen and hydrogen gases. Depending on the
type of the membrane and required purity of gases, the system 100
can operate from ambient pressure to high pressure exceeding 30
bar.
[0069] It is noted that in the illustrated system, the heat sink
105 is located in anode gas space 104. However, it should be
appreciated that in other embodiments the heat sink 105 could
alternatively be located in the cathode gas space 106 with the
cathode gas space 106 fluidly connected to the recirculating loop
143. In such embodiments, the configuration of the electrolysis
cell system 100 would be similar to that illustrated in FIG. 2,
with the cathode 109 and anode 107 interchanged or swapped position
within the membrane electrode assembly 102 and the corresponding
electrical connections interchanged accordingly. This would result
in hydrogen product gas circulating through recirculating loop 143.
Similarly, the configuration of the anode chamber 129 could equally
be used for the cathode chamber in this alternate embodiment. It
should be understood that the discussion of the illustrated
embodiment equally applies to this embodiment, with the above
alternations or variations.
[0070] Several cells 101 according to the invention can be
connected in a series and stacked with one another to form a stack.
For example, individual cells 101 can be stacked together in a cell
stack 160 as shown in FIG. 6. The openings 162 of each cell
(comprising has inlets 130 and outlets 132 to the anode chambers
129) can comprise a significant portion of surface area of the
stacked sides 164 of the cells 101. The ratio between the total
area of the sides 164 and the area of the openings 130, 131 on/in
those sides 164 is typically between 1 and 5.
[0071] Those skilled in the art will appreciate that the invention
described herein is susceptible to variations and modifications
other than those specifically described. It is understood that the
invention includes all such variations and modifications which fall
within the spirit and scope of the present invention.
[0072] Where the terms "comprise", "comprises", "comprised" or
"comprising" are used in this specification (including the claims)
they are to be interpreted as specifying the presence of the stated
features, integers, steps or components, but not precluding the
presence of one or more other feature, integer, step, component or
group thereof.
* * * * *