U.S. patent application number 15/594094 was filed with the patent office on 2017-12-21 for gas diffusion layer and electrochemical hydrogen pump.
The applicant listed for this patent is Panasonic Intellectual Property Management Co., Ltd.. Invention is credited to ATSUO OKAICHI, YUUICHI YAKUMARU.
Application Number | 20170362718 15/594094 |
Document ID | / |
Family ID | 58715110 |
Filed Date | 2017-12-21 |
United States Patent
Application |
20170362718 |
Kind Code |
A1 |
YAKUMARU; YUUICHI ; et
al. |
December 21, 2017 |
GAS DIFFUSION LAYER AND ELECTROCHEMICAL HYDROGEN PUMP
Abstract
A gas diffusion layer includes a laminate made up of sheets each
having a plurality of through-holes through which gas passes. One
or a plurality of the sheets in the laminate includes communication
paths to communicate the through-holes in another sheet adjacent to
the one sheet or one of the plurality of sheets with each other or
to communicate the through-holes in another sheet adjacent to the
one sheet or one of the plurality of sheets with the through-holes
in the other adjacent sheet, the through-holes being separated from
and being not communicated with the other through-holes in the same
sheet.
Inventors: |
YAKUMARU; YUUICHI; (Osaka,
JP) ; OKAICHI; ATSUO; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Panasonic Intellectual Property Management Co., Ltd. |
Osaka |
|
JP |
|
|
Family ID: |
58715110 |
Appl. No.: |
15/594094 |
Filed: |
May 12, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25B 15/02 20130101;
C25B 9/10 20130101; B01D 53/228 20130101; B01D 2257/504 20130101;
H01M 8/0256 20130101; B01D 2257/502 20130101; C25B 11/035 20130101;
Y02E 60/36 20130101; H01M 8/0656 20130101; C25B 1/10 20130101; H01M
8/0258 20130101; C25B 1/02 20130101; B01D 2256/16 20130101; Y02E
60/50 20130101; Y02P 20/151 20151101; B01D 53/326 20130101; B01D
53/62 20130101; C25B 13/08 20130101 |
International
Class: |
C25B 1/10 20060101
C25B001/10; C25B 13/08 20060101 C25B013/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 16, 2016 |
JP |
2016-119602 |
Claims
1. A gas diffusion layer including a laminate made up of sheets
each having through-holes through which gas passes, wherein one or
a plurality of sheets in the laminate includes communication paths
to communicate the through-holes in another sheet adjacent to the
one sheet or one of the plurality of sheets with each other or to
communicate the through-holes in another sheet adjacent to the one
sheet or one of the plurality of sheets with the through-holes in
the other adjacent sheet, the through-holes being separated from
and being not communicated with the other through-holes in the same
sheet.
2. The gas diffusion layer according to claim 1, wherein a number
of the communication paths in one of the plurality of sheets in the
laminate, the one sheet being in contact with a catalyst layer, is
smaller than a number of the communication paths in another sheet
of the plurality of sheets.
3. The gas diffusion layer according to claim 1, wherein adjacent
two of the sheets in the laminate are bonded to each other.
4. The gas diffusion layer according to claim 1, wherein the
through-holes and the communication paths are formed in same one
principal surface of the one sheet or each of the plurality of
sheets.
5. The gas diffusion layer according to claim 1, wherein respective
opening areas of the through-holes and the communication paths in
same one principal surface of the one sheet or each of the
plurality of sheets are different from each other.
6. The gas diffusion layer according to claim 5, wherein the
opening area of the communication paths is larger than the opening
area of the through-holes in the same one principal surface of the
one sheet or each of the plurality of sheets.
7. The gas diffusion layer according to claim 1, wherein respective
numbers of the through-holes and the communication paths in same
one principal surface of the one sheet or each of the plurality of
sheets are different from each other.
8. The gas diffusion layer according to claim 7, wherein the number
of the through-holes is larger than the number of the communication
paths in the same one principal surface of the one sheet or each of
the plurality of sheets.
9. The gas diffusion layer according to claim 1, wherein an area of
a region of the sheet where the through-holes are not opened is
larger than an opening area of the through-holes in a zone of same
one principal surface of the sheet, the zone being positioned in an
overlapped relation to a catalyst layer to which the gas diffusion
layer is adjacent.
10. An electrochemical hydrogen pump comprising: an electrolyte
membrane having a pair of principal surfaces; a cathode catalyst
layer disposed on one of the principal surfaces of the electrolyte
membrane; an anode catalyst layer disposed on the other principal
surface of the electrolyte membrane; a cathode gas diffusion layer
disposed in contact with the cathode catalyst layer; an anode gas
diffusion layer disposed in contact with the anode catalyst layer;
a first plate including a gas flow channel through which anode gas
flows; a second plate including a gas flow channel through which
cathode gas flows; and a voltage applying unit that applies a
voltage between the cathode catalyst layer and the anode catalyst
layer, wherein the anode gas diffusion layer includes the gas
diffusion layer according to claim 1.
11. The electrochemical hydrogen pump according to claim 10,
wherein the communication path communicates one of the
through-holes in the laminate, the one through-hole being
positioned on a line perpendicularly extending from the gas flow
channel in the first plate, with another one of the through-holes
in the laminate, the other through-hole being positioned on a line
perpendicularly extending from a portion of the first plate where
the gas flow channel is not provided.
12. The electrochemical hydrogen pump according to claim 10,
wherein the cathode gas diffusion layer includes a single sheet
including a plurality of ventilation holes.
Description
BACKGROUND
1. Technical Field
[0001] The present disclosure relates to a gas diffusion layer and
an electrochemical hydrogen pump.
2. Description of the Related Art
[0002] Due to environmental problems such as global warming and
energy problems such as depletion of oil resources, attention has
recently been focused on hydrogen gas as a clean alternate energy
source that is to be substituted for fossil fuel. Hydrogen gas is
expected as clean energy for the reason that, when the hydrogen gas
is burnt, only water is released while carbon dioxide, nitrogen
oxides, etc., which may cause global warming, are not discharged.
Devices utilizing hydrogen gas as fuel are fuel cells, for example.
The fuel cells have been developed and have become popular for use
in automotive power supplies and private power generation in homes.
In future hydrogen society, it is to be demanded not only to
produce hydrogen gas, but also to develop techniques with which the
hydrogen gas can be stored at high density and transported or
utilized in a small capacity and at a low cost. Moreover, promotion
of the infrastructure for fuel supply is necessary to realize
further widespread use of the fuel cells. In view of such
situations, various proposals have been made to refine and
pressurize high-purity hydrogen gas.
[0003] As illustrated in FIG. 9, in Japanese Patent No. 4733380,
for example, a support member 30 for an electrolyte membrane of a
high differential-pressure electrochemical cell is used as a gas
diffusion layer that is held in contact with the electrolyte
membrane. More specifically, a plurality of rectangular recesses is
formed in one surface of the support member 30, and a plurality of
rhombic recesses is formed in the other surface. Overlapped
portions of both the recesses constitute triangular through-holes
31 through which a fluid passes. The above structure makes it
possible to suppress clogging of fluid flow channels, which may be
caused in a prior-art gas diffusion layer of mesh type, and to
ensure rigidity endurable against a differential pressure between
the high pressure side and the lower pressure side of the
electrochemical cell. Accordingly, such a deformation as giving
rise to a breaking point in the electrolyte membrane is suppressed
with the support member 30 supporting the electrolyte membrane.
SUMMARY
[0004] However, diffusivity of gas flowing in the gas diffusion
layer is not sufficiently taken into consideration in the related
art.
[0005] One non-limiting and exemplary embodiment provides a gas
diffusion layer in which more consideration is paid to diffusivity
of gas than in the related art. Another non-limiting and exemplary
embodiment provides an electrochemical hydrogen pump including the
gas diffusion layer.
[0006] In one general aspect, the techniques disclosed here feature
a gas diffusion layer including a laminate made up of sheets each
having a plurality of through-holes through which gas passes,
wherein one or a plurality of the sheets in the laminate includes
communication paths to communicate the through-holes in another
sheet adjacent to the one sheet or one of the plurality of sheets
with each other or to communicate the through-holes in another
sheet adjacent to the one sheet or one of the plurality of sheets
with the through-holes in the other adjacent sheet, the
through-holes being separated from and being not communicated with
the other through-holes in the same sheet.
[0007] According to the one general aspect, the gas diffusion layer
is obtained in which more consideration is paid to diffusivity of
gas than in the related art.
[0008] Additional benefits and advantages of the disclosed
embodiments will become apparent from the specification and
drawings. The benefits and/or advantages may be individually
obtained by the various embodiments and features of the
specification and drawings, which need not all be provided in order
to obtain one or more of such benefits and/or advantages.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1A illustrates an example of a gas diffusion layer
according to a first embodiment;
[0010] FIG. 1B illustrates an example of a gas diffusion layer
according to a modification of the first embodiment;
[0011] FIG. 2A illustrates an example of a sheet in a laminate of
the gas diffusion layer according to the first embodiment;
[0012] FIG. 2B illustrates an example of a sheet in the laminate of
the gas diffusion layer according to the first embodiment;
[0013] FIG. 2C illustrates an example of a sheet in the laminate of
the gas diffusion layer according to the first embodiment;
[0014] FIG. 3 illustrates an example of a gas diffusion layer
according to First Example of the first embodiment;
[0015] FIG. 4 illustrates an example of a gas diffusion layer
according to Third Example of the first embodiment;
[0016] FIG. 5 illustrates an example of a gas diffusion layer
according to Fourth Example of the first embodiment;
[0017] FIG. 6 illustrates an example of an electrochemical hydrogen
pump according to a second embodiment;
[0018] FIG. 7 illustrates an example of the electrochemical
hydrogen pump according to the second embodiment;
[0019] FIG. 8 illustrates an example of a gas diffusion layer in an
electrochemical hydrogen pump according to Example of the second
embodiment; and
[0020] FIG. 9 illustrates an example of a prior-art gas diffusion
layer.
DETAILED DESCRIPTION
First Embodiment
[0021] The following points have been found as a result of
intensive studies on diffusivity of gas flowing in a gas diffusion
layer.
[0022] FIG. 9 representing the related art illustrates that, on the
front (one) side of the support member 30, the adjacent triangular
through-holes 31 are communicated with each other in a lattice
pattern forming the rhombic recesses. It is also illustrated that,
on the rear (other) side of the support member 30, the adjacent
triangular through-holes 31 are communicated with each other in a
lattice pattern forming the rectangular recesses. Stated in another
way, the through-holes 31 formed in the same single sheet of the
support member 30 are not separated, but are communicated with each
other. When the through-holes 31 are communicated with each other
in the same single sheet as described above, biasing of gas
diffusion is reduced and uniformity of the gas diffusion is
improved.
[0023] When the support member 30 in Japanese Patent No. 4733380 is
constituted, for example, such that gas is supplied to flow into
the through-holes 31 of the support member 30 from a gas flow
channel of an appropriate flow channel member, the gas is not
directly supplied, from the gas flow channel, to those
through-holes 31 that are each positioned on a line perpendicularly
extending from a portion of the support member 30 where the gas
flow channel of the flow channel member is not provided. In the
support member 30, however, because the through-holes 31 are
communicated with each other in the same single sheet as described
above, the through-holes 31 to which the gas is not directly
supplied from the gas flow channel are also indirectly supplied
with the gas via those through-holes 31 which are each positioned
on a line perpendicularly extending from a portion of the support
member 30 where the gas flow channel of the flow channel member is
provided, and to which the gas is directly supplied from the gas
flow channel.
[0024] On the other hand, when the through-holes are not
communicated with each other in the same single sheet unlike the
support member 30, the through-holes that are each not positioned
on the line perpendicularly extending from the gas flow channel are
even indirectly not supplied with the gas via the other
through-holes. Hence gas diffusion becomes not uniform in the gas
diffusion layer. Non-uniformity of the gas diffusion may lead to
such a possibility in an electrochemical cell, for example, that
the reaction overpotential increases, namely that the power
consumption increases.
[0025] Taking the above point into account, the inventors have
attained an idea of, in a laminate of sheets each having a
plurality of through-holes, forming communication paths to
communicate through-holes with each other, which are separated from
and are not communicated with the other through-holes in the same
single sheet, in a sheet adjacent to the former sheet.
[0026] In more detail, a gas diffusion layer according to a first
aspect of the present disclosure includes a laminate made up of
sheets each having a plurality of through-holes through which gas
passes, wherein one or a plurality of the sheets in the laminate
includes communication paths to communicate the through-holes in
another sheet adjacent to the one sheet or one of the plurality of
sheets with each other or to communicate the through-holes in
another sheet adjacent to the one sheet or one of the plurality of
sheets with the through-holes in the other adjacent sheet, the
through-holes being separated from and being not communicated with
the other through-holes in the same sheet.
[0027] With the features described above, the gas diffusion layer
according to the first aspect can make gas diffused more uniformly
than in the case of not forming the communication paths in the
adjacent sheet. More specifically, since the adjacent sheet
includes the communication paths, the gas passing through the
laminate from an appropriate flow channel member can be delivered
not only in a sheet stacking direction, but also in any desired
direction. Thus, by stacking, as the laminate, the sheets including
the communication paths in different layout patterns, a flow
direction of the gas in the laminate can be set optionally. As a
result, diffusivity of the gas in the gas diffusion layer is
improved.
[0028] Assuming, for example, the case of supplying gas to flow
into the through-holes in the laminate via a gas flow channel of a
flow channel member, if the laminate does not include the
above-described communication paths, the gas does not flow into
those ones of the through-holes in the laminate, those
through-holes being each positioned on a line perpendicularly
extending from a portion of the flow channel member where the gas
flow channel of the flow channel member is not provided. This leads
to a possibility that diffusion of the gas in the gas diffusion
layer becomes not uniform. In the gas diffusion layer according to
the first aspect, however, since the gas can be caused to flow into
those through-holes in the laminate as well via the communication
paths, non-uniformity of the gas diffusion can be suppressed.
[0029] According to a second aspect of the present disclosure, in
the gas diffusion layer according to the first aspect, the number
of the communication paths in one of the plurality of sheets in the
laminate, the one sheet being in contact with a catalyst layer, may
be smaller than the number of the communication paths in another
sheet of the plurality of sheets.
[0030] With the feature described above, uniformity of the gas
diffusion is improved. Usually, the through-holes and the
communication paths have different shapes and hence have different
opening areas. The different opening areas generate different fluid
resistances and cause different levels of gas fluidity between the
through-holes and the communication paths, thus causing
non-uniformity of the gas diffusion. By reducing the number of the
communication paths, the gas can be supplied more uniformly over
the entirety of the catalyst layer.
[0031] According to a third aspect of the present disclosure, in
the gas diffusion layer according to the first aspect or the second
aspect, adjacent two of the sheets in the laminate may be bonded to
each other.
[0032] With the feature described above, a relative displacement
between the sheets in the laminate is reduced even under conditions
where high pressure is applied to the gas diffusion layer. This
reduces a possibility that diffusivity of the gas lowers due to the
relative displacement between the through-holes in the adjacent
sheets.
[0033] According to a forth aspect of the present disclosure, in
the gas diffusion layer according to any one of the first to third
aspects, the through-holes and the communication paths may be
formed in the same one principal surface of the one sheet or each
of the plurality of sheets.
[0034] With the feature described above, the gas can be diffused
more uniformly than in the case of forming only the through-holes
in the sheet. Furthermore, an amount of the gas diffusing in a
surface direction of the sheet is reduced and an amount of the gas
leaking in the surface direction of the sheet through a gap between
the sheets is also reduced in comparison with the case of forming
only the communication paths in the sheet.
[0035] According to a fifth aspect of the present disclosure, in
the gas diffusion layer according to any one of the first to the
forth aspects, respective opening areas of the through-holes and
the communication paths in the same one principal surface of the
one sheet or each of the plurality of sheets may be different from
each other.
[0036] According to an sixth aspect of the present disclosure, in
the gas diffusion layer according to the first to the fifth
aspects, the opening area of the communication paths may be larger
than the opening area of the through-holes in the same one
principal surface of the one sheet or each of the plurality of
sheets.
[0037] With the features described above, diffusion resistance of
the gas is reduced in comparison with the case of setting the
opening area of the communication paths to be smaller than the
opening area of the through-holes.
[0038] According to a seventh aspect of the present disclosure, in
the gas diffusion layer according to the first to the sixth
aspects, the respective numbers of the through-holes and the
communication paths in the same one principal surface of the one
sheet or each of the plurality of sheets may be different from each
other.
[0039] According to a eighth aspect of the present disclosure, in
the gas diffusion layer according to the seventh aspect, the number
of the through-holes may be larger than the number of the
communication paths in the same one principal surface of the one
sheet or each of the plurality of sheets.
[0040] With the features described above, the amount of the gas
diffusing in the surface direction of the sheet is reduced and the
amount of the gas leaking in the surface direction of the sheet
through the gap between the sheets is also reduced in comparison
with the case of setting the number of the through-holes to be
smaller than the number of the communication paths.
[0041] According to an ninth aspect of the present disclosure, in
the gas diffusion layer according to the first to the eighth
aspects, an area of a region of the sheet where the through-holes
are not opened may be larger than an opening area of the
through-holes in a zone of the same one principal surface of the
sheet, the zone being positioned in an overlapped relation to a
catalyst layer to which the gas diffusion layer is adjacent.
[0042] With the feature described above, the provision of the
communication paths contributes to improving the gas diffusivity to
a larger extent than in the case of setting, as in the related art,
the opening area of the through-holes to be larger than the area of
the region of the sheet where the through-holes are not opened. The
reason is as follows. If the sheet is displaced in the surface
direction, an overlapped area between the through-holes in the
adjacent sheets is reduced and the gas diffusivity is reduced. On
that occasion, when a total opening area of the plurality of
through-holes formed in the sheet is relatively small, the
overlapped area between the through-holes in the adjacent sheets is
reduced, thus causing a larger reduction in the gas diffusivity
than in the case where the total opening area of the through-holes
is relatively large. This is because, for example, when the opening
area of the through-holes is relatively large, a reduction rate of
the opening area is relatively small even with the displacement of
the sheet in the surface direction causing a reduction of the
overlapped area between the through-holes in the adjacent sheets,
but when the opening area of the through-holes is relatively small,
the reduction rate is increased even at the same amount of
reduction in the opening area of the through-holes. Thus, the
reduction in the gas diffusivity is suppressed with the provision
of the communication paths.
[0043] An electrochemical hydrogen pump according to a tenth aspect
of the present disclosure includes an electrolyte membrane having a
pair of principal surfaces, a cathode catalyst layer disposed on
one of the principal surfaces of the electrolyte membrane, an anode
catalyst layer disposed on the other principal surface of the
electrolyte membrane, a cathode gas diffusion layer disposed in
contact with the cathode catalyst layer, an anode gas diffusion
layer disposed in contact with the anode catalyst layer, a first
plate including a gas flow channel through which anode gas flows, a
second plate including a gas flow channel through which cathode gas
flows, and a voltage applying unit that applies a voltage between
the cathode catalyst layer and the anode catalyst layer, wherein
the anode gas diffusion layer includes the gas diffusion layer
according to any one of the first to the ninth aspects.
[0044] With the features described above, the gas diffusion layer
used in the electrochemical hydrogen pump according to the twelfth
aspect can made the gas diffused more uniformly than in the case of
not forming the through-holes in the adjacent sheet.
[0045] According to a eleventh aspect of the present disclosure, in
the gas diffusion layer used in the electrochemical hydrogen pump
according to the tenth aspect, the communication path may
communicate one of the through-holes in the sheet, the one
through-hole being positioned on a line perpendicularly extending
from the gas flow channel in the first plate, with another one of
the through-holes in the sheet, the other through-hole being
positioned on a line perpendicularly extending from a portion of
the first plate where the gas flow channel is not provided.
[0046] With the feature described above, the gas flowing through
one of the through-holes in the sheet, the one through-hole being
positioned on the line perpendicularly extending from the gas flow
channel in the first plate, flows into another one of the
through-holes in the sheet, the other through-hole being positioned
on the line perpendicularly extending from the portion of the first
plate where the gas flow channel is not provided, via the
communication path. Therefore, uniformity of the gas diffusivity is
improved.
[0047] According to a twelfth aspect of the present disclosure, in
the gas diffusion layer used in the electrochemical hydrogen pump
according to the tenth aspect, the cathode gas diffusion layer may
include a single sheet including a plurality of ventilation
holes.
[0048] Here, the above-mentioned single sheet is not such a
laminate made up of a plurality of sheets as constituting the anode
gas diffusion layer. The above-mentioned single sheet may be, for
example, a metal steel plate including a plurality of through-holes
formed therein, or may be a sintered body of metal powder or a
sintered body of metal fibers, the sintered body including a
plurality of ventilation formed therein.
[0049] Embodiments of the present disclosure will be described in
detail with reference to the drawings. It is to be noted that the
embodiments described below represent non-exclusive or specific
examples. Numerical values, shapes, materials, components, and
layout positions and connection forms of the components, which are
described in the following embodiments, are merely illustrative,
and they are not purported to limit the present disclosure. Among
the components in the following embodiments, those ones not stated
in independent claims, which define the most significant concepts,
are described as optional components.
Device Configuration (Layer Structure)
[0050] FIG. 1A illustrates an example of a section of a gas
diffusion layer according to a first embodiment. FIGS. 2A, 2B and
2C each illustrate, as a plan view, an example of a sheet in a
laminate of the gas diffusion layer according to the first
embodiment.
[0051] As illustrated in FIG. 1A, a gas diffusion layer 100
includes a laminate 20. The laminate 20 includes sheets 22 each
having a plurality of through-holes 21 through which gas passes.
Each of the through-holes 21 is separated from and is not
communicated with the other through-holes 21 in the same single
sheet 22. In addition, at least one of the sheets 22 in the
laminate 20 includes communication paths 23 to communicate the
through-holes 21 in another sheet 22 adjacent to the at least one
sheet with each other, those through-holes being separated from and
being not communicated with the other through-holes 21 in the
adjacent same one sheet 22. The structure of the laminate 20 may be
optionally selected insofar as the laminate 20 includes the sheets
22 each having the plurality of through-holes 21 and at least one
of the sheets 22 in the laminate 20 includes the communication
paths 23 to communicate the through-holes 21 with each other.
[0052] In the example illustrated in FIG. 1A, the laminate 20
includes gas flow channels (hereinafter referred to as "reference
gas flow channels") that extend in a direction penetrating the
laminate 20, and that are constituted by the through-holes 21 and
respective opposite end portions of the communication paths 23, and
gas flow channels that are each branched from one of the reference
gas flow channels so as to extend in a direction parallel to a
principal surface of the laminate 20 up to the adjacent reference
gas flow channel, and that are constituted by the communication
paths 23. With such a structure, the communication paths 23
communicate the through-holes 21 in another sheet 22 adjacent to
the sheet 22 in which the communication paths 23 are formed, those
through-holes being separated from and being not communicated with
the other through-holes 21 in the other adjacent sheet 22. An
alternate example of the gas diffusion layer 100 (specifically, the
laminate 20) will be described later as a modification.
[0053] As illustrated in FIG. 2A, for example, when looking at the
laminate 20 in a plan view, a plurality of through-holes 21A may be
formed in a rectangular metal sheet 22A, which constitutes the
sheet 22 in the laminate 20, in a matrix (lattice) pattern with
equal pitches in the vertical and horizontal directions. The
through-holes 21A may have any suitable shape. The through-holes
21A may be each, for example, a circular hole with a diameter of
about several ten microns (e.g., about 50 .mu.m). The metal sheet
22A can be made of, e.g., stainless steel or titanium, but
materials of the metal sheet 22A are not limited to those examples.
It is to be noted that the metal sheet 22A illustrated in FIG. 2A
does not include the above-mentioned communication paths. FIG. 2A
is a plan view when looking at the metal sheet 22A with one
principal surface positioned on the upper side.
[0054] As illustrated in FIG. 2B, for example, a plurality of
through-holes 21B may be formed in a rectangular metal sheet 22B,
which constitutes the sheet 22 in the laminate 20, at equal pitches
in the vertical and horizontal directions. The through-holes 21B
may have any suitable shape. The through-holes 21B may be each, for
example, a circular hole with a diameter of about several ten
microns (e.g., about 50 .mu.m). The metal sheet 22B can be made of,
e.g., stainless steel or titanium, but materials of the metal sheet
22B are not limited to those examples. FIG. 2B is a plan view when
looking at the metal sheet 22B with one principal surface
positioned on the upper side.
[0055] In the example illustrated in FIG. 2B, the through-holes 21B
are arrayed in the vertical and horizontal directions in such a
pattern that a rhombic shape S denoted by two-dot-chain lines is
defined when respective centers of the adjacent through-holes 21B
are interconnected. In the illustrated example, communication paths
23B are each formed so as to define an opening that obliquely
interconnects respective centers PB of the adjacent rhombic shapes
S. It can be said that each of the communication paths 23B extends
in a direction parallel to a first direction in which the
through-holes 21B are communicated with each other without
intersecting the communication path 23B. It can also be said that
the communication paths 23B are each formed so as to define an
opening which interconnects respective midpoints (PB) of linear
lines interconnecting those ones of the adjacent through-holes 21B
(namely, of the through-holes 21B adjacent to each other in the
vertical and horizontal directions), those ones being adjacent to
each other in a direction different from the first direction and
having a longer spacing distance. Furthermore, the through-holes
21B and the communication paths 23B are arrayed, for example, such
that when the metal sheet 22B and the metal sheet 22A are stacked,
some of the through-holes 21A are overlapped with the through-holes
21B and the other through-holes 21A are overlapped with opposite
end portions of the communication paths 23B. In this case,
therefore, the communication paths 23B can communicate the
through-holes 21A with each other.
[0056] The communication paths 23B may have any suitable shape. For
example, when the through-holes 21B are each a circular hole with a
diameter of about several ten microns (e.g., about 50 .mu.m), the
communication paths 23B may be each a slit with a width of about
several ten microns (e.g., about 50 .mu.m).
[0057] Alternatively, as illustrated in FIG. 2C, a plurality of
through-holes 21C may be formed in a rectangular metal sheet 22C
that constitutes the sheet 22 in the laminate 20. The through-holes
21C may have any suitable shape. The through-holes 21C may be each,
for example, a circular hole with a diameter of about several ten
microns (e.g., about 50 .mu.m). The metal sheet 22C can be made of,
e.g., stainless steel or titanium, but materials of the metal sheet
22C are not limited to those examples. FIG. 2C is a plan view when
looking at the metal sheet 22C with one principal surface
positioned on the upper side.
[0058] In the example illustrated in FIG. 2C, the through-holes 21C
are arrayed in the vertical and horizontal directions in such a
pattern that an oblique linear line L denoted by a two-dot-chain
line is defined when respective centers of the adjacent
through-holes 21C are interconnected without intersecting the
communication path 23C. In this example, the communication paths
23C are each formed so as to define an opening that horizontally
interconnects two intermediate points PC resulting from dividing a
linear line, which interconnects the through-holes 21C adjacent to
each other in the horizontal direction, into equal three parts.
Furthermore, the through-holes 21C and the communication paths 23C
are arrayed, for example, such that when the metal sheet 22A and
the metal sheet 22C are stacked, some of the through-holes 21A are
overlapped with the through-holes 21C and the other through-holes
21A are overlapped with opposite end portions of the communication
paths 23C. In this case, therefore, the communication paths 23C can
communicate the through-holes 21A with each other.
[0059] The communication paths 23C may have any suitable shape. For
example, when the through-holes 21C are each a circular hole with a
diameter of about several ten microns m (e.g., about 50 .mu.m), the
communication paths 23C may be each a slit with a width of about
several ten microns (e.g., about 50 .mu.m).
[0060] With the features described above, the gas diffusion layer
100 according to this embodiment can make gas diffused more
uniformly than in the prior art. More specifically, since the
laminate 20 of the gas diffusion layer 100 includes the
communication paths 23, the gas passing through the laminate 20 can
be delivered not only in one direction, but also in any desired
direction. Thus, by stacking, as the laminate 20, the sheets 22
including the communication paths 23 in different layout patterns,
a flow direction of the gas in the laminate 20 can be set
optionally. As a result, diffusivity of the gas in the gas
diffusion layer 100 is improved.
[0061] The sheets 22 including the communication paths 23 in
different layout patterns can be combined with each other in any
suitable way. For example, a metal sheet having a different layout
pattern from the metal sheet 22C may be a metal sheet including the
communication paths 23C at positions horizontally deviated from
those in the metal sheet 22C, or may be the metal sheet 22B.
[0062] In the case of, for example, supplying gas to flow into the
through-holes 21 of the laminate 20 from a gas flow channel of an
appropriate flow channel member not illustrated, there is a
possibility that, if the laminate 20 does not include the
above-described communication paths, the gas does not flow into
those through-holes 21, which are each positioned on a line
perpendicularly extending from a portion of the flow channel member
where the gas flow channel of the flow channel member is not
provided, and that diffusion of the gas in the laminate 20 becomes
not uniform. In the gas diffusion layer 100 according to this
embodiment, however, the gas can be supplied to flow into the
above-mentioned through-holes 21 in the laminate 20 via the
communication paths 23, and hence non-uniformity of the gas
diffusion can be suppressed.
[0063] Additionally, the following points are understood from the
metal sheet 22B and the metal sheet 22C illustrated respectively in
FIGS. 2B and 2C. First, the through-holes and the communication
paths are formed in the same one principal surface of the sheet.
Furthermore, respective opening areas of the through-holes and the
communication paths in the same one principal surface of the sheet
are different from each other. In particular, the opening area of
the communication paths is larger than that of the through-holes in
the same one principal surface of the sheet. Moreover, the
respective numbers of the through-holes and the communication paths
in the same one principal surface of the sheet are different from
each other. In particular, the number of the through-holes is
larger than that of the communication paths in the same one
principal surface of the sheet.
[0064] It is to be noted that the above-mentioned shapes and sizes
of the through-holes 21 and the communication paths 23 are to be
taken as illustrative only, and not limiting the present
disclosure.
Modification
[0065] FIG. 1B illustrates an example of a gas diffusion layer
according to a modification of the first embodiment.
[0066] As illustrated in FIG. 1B, a gas diffusion layer 100
includes a laminate 20. The laminate 20 includes sheets 22 each
having a plurality of through-holes 21 through which gas passes. In
addition, at least one of the sheets 22 in the laminate 20 includes
communication paths 23 to communicate the through-holes 21 with
each other.
[0067] In the example illustrated in FIG. 1B, the laminate 20
includes the through-holes 21 that constitute penetration paths of
gas flow channels (hereinafter referred to as "stepwise gas flow
channels") each extending in a step-like shape, the penetration
paths extending in a direction penetrating the laminate 20, and the
communication paths 23 each of which communicates the penetration
paths of the stepwise gas flow channels with each other. With such
a structure, the communication paths 23 communicate the
through-holes 21 in other sheets 22 adjacent to the sheet 22 in
which the communication paths 23 are formed.
[0068] Practical exemplary configurations of the metal sheet
constituting the sheet 22 in the laminate 20 when looking at the
laminate 20 in a plan view are the same as those described in the
above first embodiment, and hence are not described here.
[0069] With the features described above, the gas diffusion layer
100 according to this modification can make gas diffused more
uniformly than in the prior art. Details of the operation and the
advantageous effects of the gas diffusion layer 100 according to
this modification are similar to those of the gas diffusion layer
100 according to the first embodiment, and hence are not described
here.
[0070] The gas diffusion layer 100 according to this modification
may be constituted in a similar structure to that of the gas
diffusion layer 100 according to the first embodiment except for
the above-described features.
FIRST EXAMPLE
[0071] FIG. 3 illustrates an example of a gas diffusion layer
according to First Example of the first embodiment.
[0072] A gas diffusion layer 100 according to First Example is
featured in that, in the gas diffusion layer 100 according to the
first embodiment or the modification of the first embodiment, the
number of communication paths 23 in a sheet 22 (hereinafter
referred to as a "contact layer 22" in some cases), which is in
contact with an anode catalyst layer 3A of the laminate 20, is
smaller than that in other sheets. While FIG. 3 illustrates an
example in which the contact layer 22 is disposed in the laminate
20 illustrated in FIG. 1A, the contact layer 22 may be disposed in
the laminate 20 illustrated in FIG. 1B.
[0073] While the metal sheet constituting the contact layer 22 may
be the metal sheet 22A, illustrated in FIG. 2A, not including the
communication paths, the present disclosure is not limited to such
a case. Furthermore, while a metal sheet different from the contact
layer 22 may be at least one of the metal sheet 22B illustrated in
FIG. 2B and the metal sheet 22C illustrated in FIG. 2C, the present
disclosure is not limited to such a case. In addition, as
illustrated in FIGS. 2A to 2C, an area of a region of the metal
sheet where the through-holes are not opened is larger than an
opening area of the through-holes in the metal sheet. Accordingly,
the area of the region of the metal sheet where the through-holes
are not opened is larger than the opening area of the through-holes
in a zone of the same one principal surface of the sheet, the zone
being positioned in an overlapped relation to the catalyst layer to
which the gas diffusion layer is adjacent.
[0074] The sheet 22 in the laminate 20 has a larger contact area
between the anode catalyst layer 3A and the sheet 22 as the number
of the communication paths 23 reduces. Thus, since a contact area
between the contact layer 22 and the anode catalyst layer 3A is
larger than that in the case where the anode catalyst layer 3A is
held in contact with a different sheet, contact resistance between
the contact layer 22 and the anode catalyst layer 3A can be
reduced.
[0075] When the number of the communication paths 23 in the sheet
22 of the laminate 20 increases, a variation of fluid resistance in
a plane of the sheet 22 tends to increase. For example, when a
region including a larger number of the communication paths and a
region including a smaller number of the communication paths are
both present in the plane of the sheet 22, the fluid resistance in
the former region is lower than that in the latter region because
the communication path 23 has a larger opening area than the
through-hole 21. Thus, gas is more apt to flow through the former
region than through the latter region. Therefore, if the sheet 22
including the communication paths 23 in a larger number is held in
contact with the anode catalyst layer 3A, there is a possibility of
impeding even supply of the gas to the entirety of the anode
catalyst layer 3A from the laminate 20. In the gas diffusion layer
100 according to First Example, however, such a possibility is
reduced because the contact layer 22 including the communication
paths 23 in a smaller number is held in contact with the anode
catalyst layer 3A.
[0076] The gas diffusion layer 100 according to First Example may
be constituted in a similar structure to that of the gas diffusion
layer 100 according to the first embodiment or the modification of
the first embodiment except for the above-described features.
SECOND EXAMPLE
[0077] A gas diffusion layer 100 according to Second Example is
featured in that, in the gas diffusion layer 100 according to any
one of the first embodiment, the modification of the first
embodiment, and First Example of the first embodiment, adjacent two
of the sheets 22 in the laminate 20 are bonded to each other. For
example, metal sheets constituting the adjacent sheets 22 are
welded through sintering, whereby the adjacent sheets 22 are
properly bonded to each other.
[0078] The gas diffusion layer 100 according to Second Example may
be constituted in a similar structure to that of the gas diffusion
layer 100 according to any one of the first embodiment, the
modification of the first embodiment, and First Example of the
first embodiment except for the above-described features.
THIRD EXAMPLE
[0079] FIG. 4 illustrates an example of a gas diffusion layer
according to Third Example of the first embodiment.
[0080] A gas diffusion layer 100 according to Third Example is
featured in that, in the gas diffusion layer 100 according to any
one of the first embodiment, the modification of the first
embodiment, and First and Second Examples of the first embodiment,
a communication path 23 communicates a through-hole 21LD and a
through-hole 21RD with each other, the through-holes 21LD and 21RD
being formed in the same single sheet 22D adjacent to a sheet 22 in
which the communication path 23 is formed. In other words, the
communication path 23 communicates the through-hole 21LD at the
left and the through-hole 21RD at the right with each other, the
through-holes 21LD and 21RD being formed in the same single sheet
22D on the lower side of the sheet 22 in which the communication
path 23 is formed. The through-hole 21LD and the through-hole 21RD
are deviated from each other through a distance corresponding to a
length of the communication path 23 in a direction parallel to a
principal surface of the laminate 20.
[0081] Furthermore, as illustrated in FIG. 4, a sheet 22U on the
upper side of the sheet 22 in which the communication path 23 is
formed may have a through-hole 21U just above the through-hole
21LD. In this case, the communication path 23 communicates the
through-hole 21U and the through-hole 21RD with each other.
Alternatively, the sheet 22U on the upper side of the sheet 22 in
which the communication path 23 is formed may have a through-hole
(not illustrated) just above the through-hole 21RD. In this case,
the communication path 23 communicates the through-hole just above
the through-hole 21RD and the through-hole 21LD with each
other.
[0082] Since the laminate 20 includes the communication paths 23,
the gas passing through the laminate 20 can be delivered not only
in the direction penetrating the laminate 20, but also in the
direction parallel to the principal surface of the laminate 20. As
a result, diffusivity of the gas in the gas diffusion layer 100 is
improved.
[0083] The gas diffusion layer 100 according to Third Example may
be constituted in a similar structure to that of the gas diffusion
layer 100 according to any one of the first embodiment, the
modification of the first embodiment, and First and Second Examples
of the first embodiment except for the above-described
features.
FOURTH EXAMPLE
[0084] FIG. 5 illustrates an example of a gas diffusion layer
according to Fourth Example of the first embodiment.
[0085] A gas diffusion layer 100 according to Fourth Example is
featured in that, in the gas diffusion layer 100 according to any
one of the first embodiment, the modification of the first
embodiment, and First to Third Examples of the first embodiment, a
communication path 23 communicates a through-hole 21U and a
through-hole 21D with each other, the through-holes 21U and 21D
being formed respectively in different sheets, i.e., a sheet 22U
and a sheet 22D, adjacent to a sheet 22 in which the communication
path 23 is formed. In other words, the communication path 23
communicates the through-hole 21U in the sheet 22U on the upper
side of the sheet 22 in which the communication path 23 is formed
and the through-hole 21D in the sheet 22D on the lower side thereof
with each other. The through-hole 21U and the through-hole 21D are
deviated from each other through a distance corresponding to a
length of the communication path 23 in a direction parallel to a
principal surface of the laminate 20.
[0086] Since the laminate 20 includes the communication paths 23,
the gas passing through the laminate 20 can be delivered not only
in a direction penetrating the laminate 20, but also in the
direction parallel to the principal surface of the laminate 20. As
a result, diffusivity of the gas in the gas diffusion layer 100 is
improved.
[0087] The gas diffusion layer 100 according to Fourth Example may
be constituted in a similar structure to that of the gas diffusion
layer 100 according to any one of the first embodiment, the
modification of the first embodiment, and First to Third Examples
of the first embodiment except for the above-described
features.
Second Embodiment
[0088] An electrochemical hydrogen pump according to a second
embodiment includes an electrolyte membrane having a pair of
principal surfaces, a cathode catalyst layer disposed on one of the
principal surfaces of the electrolyte membrane, an anode catalyst
layer disposed on the other principal surface of the electrolyte
membrane, a cathode gas diffusion layer disposed in contact with
the cathode catalyst layer, an anode gas diffusion layer disposed
in contact with the anode catalyst layer, a first plate including a
gas flow channel through which anode gas flows, a second plate
including a gas flow channel through which cathode gas flows, and a
voltage applying unit that applies a voltage between the cathode
catalyst layer and the anode catalyst layer. The anode gas
diffusion layer includes the gas diffusion layer according to any
one of the first embodiment, the modification of the first
embodiment, and First to Fourth Examples of the first
embodiment.
[0089] With the features described above, the anode gas diffusion
layer used in the second embodiment can reliably provide rigidity
at a level endurable against pressing exerted on the electrolyte
membrane under high pressure, and can make anode gas diffused more
uniformly than in the related art. More specifically, since the
anode gas diffusion layer includes the communication paths, the
anode gas passing through the anode gas diffusion layer from the
first plate can be delivered not only in one direction, but also in
any desired direction. Thus, by stacking, in the anode gas
diffusion layer, the sheets including the communication paths in
different layout patterns, a flow direction of the anode gas in the
anode gas diffusion layer can be set optionally. As a result,
diffusivity of the anode gas in the anode gas diffusion layer is
improved, whereby an increase in the reaction overpotential of the
electrochemical hydrogen pump can be suppressed. In other words, an
increase in the reaction resistance (reaction overpotential) in a
dissociation process of hydrogen in the anode gas into a proton and
an electron, namely an increase in the power consumption necessary
for an operation of compressing hydrogen in the electrochemical
hydrogen pump, can be suppressed in comparison with the related
art.
Device Configuration
[0090] FIGS. 6 and 7 each illustrate an example of an
electrochemical hydrogen pump 16 according to the second
embodiment.
[0091] The electrochemical hydrogen pump 16 includes an electrolyte
membrane 4, a cathode catalyst layer 3C, an anode catalyst layer
3A, a cathode gas diffusion layer 2C, an anode gas diffusion layer
2A, a first plate 1A, a second plate 1C, and a voltage applying
unit 13.
[0092] As illustrated in FIG. 7, the electrolyte membrane 4 has a
pair of principal surfaces 4U and 4D. The one principal surface 4U
of the electrolyte membrane 4 is an upper surface (front surface),
and the other principal surface 4D of the electrolyte membrane 4 is
a lower surface (rear surface).
[0093] The electrolyte membrane 4 is a proton-conducting polymer
membrane through which protons (H.sup.+) are permeable. The
electrolyte membrane 4 can be made of any type of proton-conducting
polymer membrane. The electrolyte membrane 4 may be, for example, a
fluorine-based polymer electrolyte membrane. In particular, Nafion
(registered trademark, made by Du Pont) or Aciplex (trade name,
made by Asahi Kasei Corporation), for example, can be used.
[0094] The cathode catalyst layer 3C is disposed on the one
principal surface 4U of the electrolyte membrane 4. The cathode
catalyst layer 3C contains, for example, platinum as a catalyst
metal, but the present disclosure is not limited to such a
case.
[0095] The anode catalyst layer 3A is disposed at the other
principal surface 4D of the electrolyte membrane 4. The anode
catalyst layer 3A contains, for example, RulrFeOx as a catalyst
metal, but the present disclosure is not limited to such a
case.
[0096] Regarding the cathode catalyst layer 3C and the anode
catalyst layer 3A, a catalyst preparation method is not limited to
particular one because the catalyst can be prepared by various
methods. A catalyst carrier may be, for example, conductive porous
material powder or carbon-based powder. The carbon-based powder may
be, for example, powder of graphite, carbon black, or activated
carbon having electrical conductivity. A method of supporting a
catalyst metal, such as platinum or the like, on the carrier made
of, e.g., carbon is not limited to particular one. For example, a
powder mixing method or a liquid-phase mixing method may be used.
In one example of the latter liquid-phase mixing method, the
carrier made of, e.g., carbon is dispersed in a solution of a
colloidal catalyst component, thus causing the catalyst component
to be adsorbed on the carrier. When necessary, it is also possible
to use an active oxygen removing material as a carrier, and to
support a catalyst metal, such as platinum or the like, on the
carrier in a manner similar to that described above. A supported
state of the catalyst metal, such as platinum, on the carrier is
not limited to particular one. In one example, the catalyst metal
may be atomized into micro-particles and supported on the carrier
in a high dispersion state.
[0097] The cathode gas diffusion layer 2C is disposed in contact
with the cathode catalyst layer 3C. The cathode gas diffusion layer
2C may be in the form of a single sheet instead of such a laminate
made up of a plurality of sheets as constituting the anode gas
diffusion layer 2A described below. The cathode gas diffusion layer
2C may be made of, e.g., a sheet-like porous material that is
obtained, for example, by plating platinum on surfaces of
high-modulus graphitized carbon fibers or a surface of a sintered
body of titanium powder. In the case of employing the graphitized
carbon fibers, carbon fibers are subjected to heat treatment at,
e.g., 2000.degree. C. or higher, thereby causing graphite crystals
to be developed for transformation to graphite fibers.
[0098] The anode gas diffusion layer 2A is disposed in contact with
the anode catalyst layer 3A. The anode gas diffusion layer 2A needs
to have rigidity at a level endurable against pressing exerted on
the electrolyte membrane 4 under high pressure. The anode gas
diffusion layer 2A may be any type of layer insofar as the layer
exhibits rigidity at a level endurable against pressing exerted on
the electrolyte membrane 4 under high pressure. In this embodiment,
the anode gas diffusion layer 2A includes the gas diffusion layer
100. As described above, the gas diffusion layer 100 includes the
laminate 20. By employing, e.g., a metal sheet or the like as each
of the sheets 22 in the laminate 20, the gas diffusion layer 100
can be reliably given with the rigidity at a level endurable
against pressing exerted on the electrolyte membrane 4 under high
pressure. Because the gas diffusion layer 100 used in this
embodiment is similar to the gas diffusion layer 100 according to
any one of the first embodiment, the modification of the first
embodiment, and First to Fourth Examples of the first embodiment,
detailed description of the gas diffusion layer 100 is omitted
here.
[0099] Thus, a membrane electrode assembly (MEA) 15 includes the
electrolyte membrane 4, the cathode catalyst layer 3C and the anode
catalyst layer 3A disposed respectively on the pair of principal
surfaces 4U and 4D of the electrolyte membrane 4, the cathode gas
diffusion layer 2C disposed on an upper surface of the cathode
catalyst layer 3C, and the anode gas diffusion layer 2A disposed at
a lower surface of the anode catalyst layer 3A. Individual sheets
constituting those layers are joined together in a multilayered
state.
[0100] The first plate 1A includes a gas flow channel 14A through
which the anode gas flows. In other words, the first plate 1A
serves as a member for supplying the anode gas to the anode gas
diffusion layer 2A. More specifically, the gas flow channel 14A
having, e.g., a serpentine shape in a plan view is formed in the
first plate 1A, and the first plate 1A is arranged such that a
region where the gas flow channel 14A is formed is held in contact
with the lower surface of the anode gas diffusion layer 2A.
[0101] Drying of the electrolyte membrane 4 may lead to a
possibility of not only increasing the film resistance (IR loss)
and the reaction resistance (reaction overpotential) in a
dissociation process of hydrogen into a proton and an electron, but
also making the electrolyte membrane 4 more susceptible to
breakage. Therefore, the anode gas contains at least hydrogen gas
and water molecules (water vapor). The anode gas may be, for
example, reformed gas containing hydrogen or hydrogen-containing
gas produced with a water electrolysis method.
[0102] The second plate 1C includes a gas flow channel 14C through
which cathode gas flows. In other words, the cathode gas incoming
from the cathode gas diffusion layer 2C flows through the gas flow
channel 14C in the second plate 1C. More specifically, the gas flow
channel 14C having, e.g., a serpentine shape in a plan view is
formed in the second plate 1C, and the second plate 1C is arranged
such that a region where the gas flow channel 14C is formed is held
in contact with the upper surface of the cathode gas diffusion
layer 2C. The cathode gas may be, for example, high-purity hydrogen
gas.
[0103] A unit cell of the electrochemical hydrogen pump 16 is
obtained by arranging the first plate 1A and the second plate 1C
respectively in contact with upper and lower surfaces of the MEA 15
in a sandwiching relation.
[0104] The voltage applying unit 13 applies a voltage between the
cathode catalyst layer 3C and the anode catalyst layer 3A. More
specifically, a plus terminal of the voltage applying unit 13 is
connected to the conductive first plate 1A, and a minus terminal of
the voltage applying unit 13 is connected to the conductive second
plate 1C. The voltage applying unit 13 may be of any type insofar
as it is able to apply a voltage between the cathode catalyst layer
3C and the anode catalyst layer 3A.
[0105] Here, the cathode gas diffusion layer 2C and the anode gas
diffusion layer 2A serve as power feeders in a cathode and an anode
of the MEA 15, respectively. In other words, the cathode gas
diffusion layer 2C and the anode gas diffusion layer 2A have roles
of supplying electric power between the second plate 1C and the
cathode catalyst layer 3C and between the first plate 1A and the
anode catalyst layer 3A, respectively.
[0106] Furthermore, the cathode gas diffusion layer 2C and the
anode gas diffusion layer 2A have roles of diffusing gases between
the gas flow channel 14C in the second plate 1C and the cathode
catalyst layer 3C and between the gas flow channel 14A in the first
plate 1A and the anode catalyst layer 3A, respectively. For
example, the anode gas flowing through the gas flow channel 14A in
the first plate 1A is caused to diffuse over the surface of the
anode catalyst layer 3A through the anode gas diffusion layer
2A.
[0107] When necessary, a stack made up of plural unit cells of the
electrochemical hydrogen pumps 16 may be constituted by disposing,
e.g., a cooler in association with the unit cell of the
electrochemical hydrogen pump 16, and by stacking two or more unit
cells in a multilayered state.
[0108] As illustrated in FIG. 6, the electrochemical hydrogen pump
16 includes an anode chamber 8 and a the cathode chamber 7.
[0109] The inside of the anode chamber 8 is communicated with an
anode inlet pipe 11 and is also communicated with the gas flow
channel 14A in the first plate 1A through not-illustrated fluid
flow channels (such as a pipe and a manifold). Thus, the anode gas
flowing through the anode inlet pipe 11 flows into the anode
chamber 8 and is then supplied to the gas flow channel 14A in the
first plate 1A.
[0110] The inside of the cathode chamber 7 is communicated with a
cathode outlet pipe 12 and is also communicated with the gas flow
channel 14C in the second plate 1C through not-illustrated fluid
flow channels (such as a pipe and a manifold). Thus, the cathode
gas (hydrogen gas) having passed through the MEA 15 flows through
the gas flow channel 14C in the second plate 1C and further flows
into the cathode chamber 7. Thereafter, the cathode gas is supplied
to the cathode outlet pipe 12. An on-off valve 9 (such as a
solenoid valve) is disposed in the cathode outlet pipe 12, and the
cathode gas is stored in a high-pressure tank 10 by opening and
closing the on-off valve 9 at proper timings. The cathode gas thus
stored is used, for example, as fuel of a not-illustrated apparatus
utilizing hydrogen (such as a fuel battery car).
[0111] With the features described above, the anode gas diffusion
layer 2A used in this embodiment can reliably provide rigidity at a
level endurable against pressing exerted on the electrolyte
membrane 4 under high pressure, and can make the anode gas diffused
more uniformly than in the related art. More specifically, since
the anode gas diffusion layer 2A includes the communication paths
23, the anode gas passing through the anode gas diffusion layer 2A
from the first plate 1A can be delivered not only in one direction,
but also in any desired direction. Thus, by stacking, in the anode
gas diffusion layer 2A, the sheets including the communication
paths 23 in different layout patterns, a flow direction of the
anode gas in the anode gas diffusion layer 2A can be set
optionally. As a result, diffusivity of the anode gas in the anode
gas diffusion layer 2A is improved, whereby an increase in the
reaction overpotential of the electrochemical hydrogen pump 16 can
be suppressed. In other words, an increase in the reaction
resistance (reaction overpotential) in a dissociation process of
hydrogen in the anode gas into a proton and an electron, namely an
increase in the power consumption necessary for an operation of
compressing hydrogen in the electrochemical hydrogen pump 16, can
be suppressed in comparison with the related art.
Operation
[0112] The operation of the electrochemical hydrogen pump according
to the second embodiment will be described below with reference to
FIGS. 6 and 7.
[0113] Part or the whole of the operation described below may be
executed in accordance with a control program installed in a
controller (not illustrated). The controller may be of any type
insofar as it has a suitable control function. The controller
includes, for example, an arithmetic circuit and a storage circuit
storing the control program. The arithmetic circuit may be, for
example, an MPU or a CPU. The storage circuit may be, for example,
a memory. The controller may be constituted by a single controller
that executes centralized control, or by a plurality of controllers
that execute decentralized control under cooperation.
[0114] First, the voltage applying unit 13 applies a voltage
between the anode and the cathode of the MEA 15.
[0115] Then, the anode gas is supplied to the anode chamber 8
through the anode inlet pipe 11. Hydrogen in the anode gas
dissociates an electron and becomes a proton (H.sup.+) (formula
(1)) at the anode. The dissociated electron moves to the cathode
via the voltage applying unit 13.
[0116] On the other hand, the proton permeates through the
electrolyte membrane 4 while entraining a water molecule, and comes
into contact with the cathode. At the cathode, a reduction reaction
occurs between the proton having permeated through the electrolyte
membrane 4 and the electron supplied from the cathode gas diffusion
layer 2C, and the cathode gas (hydrogen gas) is produced (formula
(2)).
[0117] Thus, the anode gas containing impurities, such as CO.sub.2
gas, is purified with high efficiency. In other words, the
impurities, such as CO.sub.2 gas, are removed in the MEA 15. The
anode gas contains, as one of the impurities, CO gas in some cases.
In those cases, because the CO gas reduces catalyst activity of the
anode catalyst layer 3A and so on, it is preferable to remove the
CO gas by a not-illustrated CO remover (such as a transformer or a
CO selective oxidizer).
[0118] When the on-off valve 9 is closed, a pressure of the cathode
gas in the cathode chamber 7 rises, and a cathode gas pressure
becomes high. More specifically, a relation among a gas pressure P1
at the anode, a gas pressure P2 at the cathode, and a voltage E of
the voltage applying unit 13 is formulated by the following formula
(3).
Anode:
H.sub.2 (low pressure).fwdarw.2H.sup.++2e.sup.- (1)
Cathode:
2H.sup.++2e.sup.-.fwdarw.H.sub.2 (high pressure) (2)
E=(RT/2F) In(P2/P1)+ir (3)
[0119] In the formula (3), R denotes the gas constant (8.3145
J/Kmol), T denotes the temperature (K) of the MEA 15, F denotes the
Faraday constant (96485 C/mol), P2 denotes the cathode gas
pressure, P1 denotes the anode gas pressure, i denotes the current
density (A/cm.sup.2), and r denotes the cell resistance
(.OMEGA.cm.sup.2).
[0120] From the formula (3), it is easily understood that the
cathode gas pressure P2 can be raised by increasing the voltage E
applied from the voltage applying unit 13.
[0121] Thus, in the electrochemical hydrogen pump 16 according to
the second embodiment, the cathode gas pressure in the cathode
chamber 7 is raised by closing the on-off valve 9 and by increasing
the voltage E applied from the voltage applying unit 13. When the
cathode gas pressure rises to a predetermined pressure or above,
the on-off valve 9 is opened such that the cathode gas in the
cathode chamber 7 is filled into the high-pressure hydrogen tank 10
through the cathode outlet pipe 12. On the other hand, when the
cathode gas pressure in the cathode chamber 7 lowers beyond a
predetermined pressure, the on-off valve 9 is closed to cut off the
communication between the cathode chamber 7 and the high-pressure
hydrogen tank 10. Therefore, the cathode gas in the high-pressure
hydrogen tank 10 is suppressed from flowing backward to the cathode
chamber 7.
[0122] In such a manner, the pressure of the cathode gas (hydrogen
gas) is boosted to a desired target pressure by the electrochemical
hydrogen pump 16, and the pressurized cathode gas is filled in the
high-pressure hydrogen tank 10.
EXAMPLE
[0123] FIG. 8 illustrates an example of a gas diffusion layer in an
electrochemical hydrogen pump according to Example of the second
embodiment.
[0124] An electrochemical hydrogen pump 16 according to this
Example is featured in that, in the electrochemical hydrogen pump
16 according to the second embodiment, a communication path 23
communicates a through-hole 21D in the laminate 20, the
through-hole 21D being positioned on a line perpendicularly
extending from the gas flow channel 14A in the first plate 1A, with
a through-hole 21U in the laminate 20, the through-hole 21U being
positioned on a line perpendicularly extending from a portion
(hereinafter referred to as a "rib LB") of the first plate 1A where
the gas flow channel 14A is not provided. The through-hole 21U and
the through-hole 21D are deviated from each other through a
distance corresponding to a length of the communication path 23 in
a direction parallel to a principal surface of the laminate 20.
[0125] This Example has such a configuration that the anode gas is
supplied to flow into the through-hole 21D in the laminate 20 via
the gas flow channel 14A in the first plate 1A. Accordingly, if the
laminate 20 does not include the above-described communication
path, the anode gas does not flow into the through-hole 21U in the
laminate 20, the through-hole 21U being positioned on the line
perpendicularly extending from the rib LB of the first plate 1A
where the gas flow channel 14A is not provided. This leads to a
possibility that diffusion of the anode gas in the gas diffusion
layer 100 becomes not uniform.
[0126] When a horizontal size of the rib LB of the first plate 1A
is about several hundred microns (e.g., about 500 .mu.m), for
example, a diameter of each of the through-hole 21D and the
through-hole 21U needs to be set to about several ten microns
(e.g., about 50 .mu.m) from the viewpoint of preventing breakage of
the electrolyte membrane 4 under high pressure. In such a case,
unless the laminate 20 includes the communication path, the anode
gas does not flow into the through-hole 21U that is positioned on
the line perpendicularly extending from the rib LB.
[0127] In this Example, since the above-described structure allows
the anode gas to flow into the through-hole 21U in the laminate 20
as well via the communication path 23 in the gas diffusion layer
100, the above-mentioned non-uniformity of diffusion of the anode
gas can be suppressed.
[0128] The electrochemical hydrogen pump 16 according to this
Example may be constituted in a similar configuration to that of
the electrochemical hydrogen pump 16 according to the second
embodiment except for the above-described features. The
above-described shapes and sizes of the through-holes 21 and the
rib LB are merely illustrative examples, and the present disclosure
is not limited to those examples.
[0129] From the above description, a variety of improvements and
other embodiments of the present disclosure are apparent to those
skilled in the art. Accordingly, the above description is to be
construed in an illustrative sense and is provided with intent to
teach the best mode for carrying out the present disclosure to
those skilled in the art. Details of the structure and/or the
function of the present disclosure can be substantially modified
without departing from the gist of the present disclosure.
[0130] One aspect of the present disclosure provides, for example,
a gas diffusion layer capable of making gas diffused more uniformly
than in the prior art. Accordingly, the one aspect of the present
disclosure can be utilized in an electrochemical hydrogen pump, for
example.
* * * * *