U.S. patent application number 10/555893 was filed with the patent office on 2007-04-12 for electrode for electrochemical cell and electrochemical cell.
This patent application is currently assigned to Japan Science and Technology Agency. Invention is credited to Tatsuya Kawada, Hiroshige Matsumoto, Junichiro Mizusaki, Hitoshi Takamura, Keiji Yashiro.
Application Number | 20070080058 10/555893 |
Document ID | / |
Family ID | 34631423 |
Filed Date | 2007-04-12 |
United States Patent
Application |
20070080058 |
Kind Code |
A1 |
Matsumoto; Hiroshige ; et
al. |
April 12, 2007 |
Electrode for electrochemical cell and electrochemical cell
Abstract
To provide low-overpotential electrodes for an electrochemical
cell including a proton-conductive electrolyte and an
electrochemical cell including the electrodes. The following
reaction occurs at the interface between a gas phase and an anode
3: H.sub.2.fwdarw.2H.sup.++2e.sup.- At this time, the resultant
protons (H.sup.+) and electrons (e.sup.-) exist in the anode 3. The
subsequent electrode reaction is completed after the protons travel
to an electrolyte 2 and the electrons travel to a lead 5. The
reverse reaction occurs at a cathode 4 to generate hydrogen
gas.
Inventors: |
Matsumoto; Hiroshige;
(Fukuoka-Shi, JP) ; Takamura; Hitoshi;
(Sendai-Shi, JP) ; Mizusaki; Junichiro;
(Sendai-Shi, JP) ; Kawada; Tatsuya; (Sendai-Shi,
JP) ; Yashiro; Keiji; (Sendai-Shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
Japan Science and Technology
Agency
1-8, Honmachi 4-chome
Kawaguchi-shi, Saitama
JP
332-0012
|
Family ID: |
34631423 |
Appl. No.: |
10/555893 |
Filed: |
November 17, 2004 |
PCT Filed: |
November 17, 2004 |
PCT NO: |
PCT/JP04/17100 |
371 Date: |
October 11, 2006 |
Current U.S.
Class: |
204/291 ;
420/900 |
Current CPC
Class: |
Y02E 60/50 20130101;
C01B 3/501 20130101; C01B 3/0005 20130101; H01M 4/9033 20130101;
H01M 4/8605 20130101; C01B 2203/0405 20130101; H01M 8/1231
20160201; C25B 11/04 20130101; Y02E 60/32 20130101 |
Class at
Publication: |
204/291 ;
420/900 |
International
Class: |
C25B 11/04 20060101
C25B011/04 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 25, 2003 |
JP |
2003-393252 |
Claims
1. Electrodes for an electrochemical cell including a
proton-conductive electrolyte, the electrodes being an anode and a
cathode, the anode and/or the cathode comprising a solid having
hydrogen permeability.
2. The electrodes according to claim 1, wherein the
proton-conductive electrolyte has a perovskite structure
represented by the general formula ABxO3-d (wherein 0.8 .English
Pound..times..English Pound.1.2; and d is a deviation from the
nominal value of oxygen, namely 3); and the B-site elements include
zirconium (Zr).
3. The electrodes according to claim 2, wherein the content of
zirconium (Zr) is 20 mole percent or more.
4. The electrodes according to claim 1, wherein the solid having
hydrogen permeability is a mixed proton-electron conductor.
5. The electrodes according to claim 4, wherein the mixed
proton-electron conductor is a mixed proton-electron conductive
ceramic material having the perovskite structure.
6. The electrodes according to claim 1, wherein the solid having
hydrogen permeability is a hydrogen storage alloy.
7. The electrodes according to claim 6, wherein the hydrogen
storage alloy comprises palladium (Pd).
8. The electrodes according to claim 7, wherein the hydrogen
storage alloy comprises 10% or more of palladium (Pd).
9. The electrodes according to claim 1, wherein the solid having
hydrogen permeability is a mixture of a mixed proton-electron
conductor and a hydrogen storage alloy.
10. The electrodes according to claim 9, wherein the mixed
proton-electron conductor is a mixed proton-electron conductive
ceramic material having the perovskite structure; and the hydrogen
storage alloy comprises palladium (Pd).
11. An electrochemical cell comprising the proton-conductive
electrolyte and the electrodes according to claim 1.
12. The electrodes according to claim 2, wherein the solid having
hydrogen permeability is a mixed proton-electron conductor.
13. The electrodes according to claim 3, wherein the solid having
hydrogen permeability is a mixed proton-electron conductor.
14. The electrodes according to claim 2, wherein the solid having
hydrogen permeability is a hydrogen storage alloy.
15. The electrodes according to claim 3, wherein the solid having
hydrogen permeability is a hydrogen storage alloy.
16. The electrodes according to claim 2, wherein the solid having
hydrogen permeability is a mixture of a mixed proton-electron
conductor and a hydrogen storage alloy.
17. The electrodes according to claim 3, wherein the solid having
hydrogen permeability is a mixture of a mixed proton-electron
conductor and a hydrogen storage alloy.
18. An electrochemical cell comprising the proton-conductive
electrolyte and the electrodes according to claim 2.
19. An electrochemical cell comprising the proton-conductive
electrolyte and the electrodes according to claim 3.
20. An electrochemical cell comprising the proton-conductive
electrolyte and the electrodes according to claim 3.
Description
TECHNICAL FIELD
[0001] The present invention relates to electrodes for an
electrochemical cell including a proton-conductive electrolyte and
electrochemical cells, and particularly relates to electrodes and
electrochemical cells suitable for high-temperature
proton-conductive electrolytes.
BACKGROUND ART
[0002] Hydrogen has recently come under the spotlight as an energy
source for fuel cells etc. in view of global environment
conservation and energy saving. Accordingly, as is well known,
proton-conductive electrolytes have been widely researched as
electrochemical devices useful for hydrogen separation, which is an
essential technology for the production of hydrogen, and fuel
cells.
[0003] Proton-conductive electrolytes are electrolyte materials
containing positive hydrogen ions, namely protons, as a mobile ion
species. Protons can move in the electrolytes when a voltage is
applied. If, therefore, gas electrodes are provided on a
proton-conductive electrolyte (hereinafter referred to as a
proton-conductive cell), a direct current may be allowed to flow
through the cell to achieve hydrogen separation or hydrogen fuel
cell power generation according to the type of gas in contact with
the electrodes.
[0004] Gas electrodes of a proton-conductive cell serve to produce
hydrogen-involved electrode reactions. The voltage required as the
driving force for the electrode reactions is called electrode
overpotential. A lower electrode overpotential allows the
proton-conductive cell to operate more efficiently; therefore,
materials with lower electrode overpotentials are demanded to
achieve higher-performance gas electrodes.
[0005] Examples of conventional materials for gas electrodes
include porous electron-conductive materials and cermets of
electron-conductive materials and electrolytes. Such electrodes are
designed exclusively to transfer electrons. For example, techniques
for hydrogen separation devices having some type of
high-temperature proton conductor as a proton-conductive
electrolyte have been proposed (for example, Hiroyasu Iwahara,
Solid State Ionics, 125, 271-278(1999)).
[0006] Non-Patent Document 1: Hiroyasu Iwahara, Solid State Ionics,
125, 271-278(1999)
[0007] According to this technique, the electrodes used are porous
platinum electrodes. In this case, it is obvious that platinum is
used as an electron-conductive material. If electrodes that serve
only to transfer electrons are used for proton-conductive
electrolytes, some electrolytes, unfortunately, cause slow
hydrogen-involved electrode reactions which result in high
electrode overpotential; that is, they require a large electrical
energy in order to cause the electrode reactions. In fact,
perovskite proton conductors containing zirconium (Zr) that have
conventional porous platinum electrodes exhibit extremely poor
electrode properties, as shown in Examples below as comparative
examples.
DISCLOSURE OF INVENTION
Problems to be Solved by the Invention
[0008] To solve the above problem, the present invention provides
low-overpotential electrodes for electrochemical cells including a
proton-conductive electrolyte and an electrochemical cell including
the electrodes.
Means for Solving the Problems
[0009] As a result of intensive studies, the present inventor has
found and confirmed by experiment that a lower electrode
overpotential can be achieved using electrodes that function not
only to transfer electrons but also to include protons or hydrogen,
thereby completing the following invention:
[0010] (1) Electrodes for an electrochemical cell including a
proton-conductive electrolyte. The electrodes are an anode and a
cathode, and the anode and/or the cathode is made of a solid having
hydrogen permeability.
[0011] The reactions at gas electrodes are the reactions among
hydrogen or a hydrogen-containing compound in a gas, protons, and
electrons. These electrode reactions proceed at sites where the
three components coexist. Such reaction sites are called
three-phase interfaces since the three components usually exist
separately as a gas phase, an electrolyte phase, and an electron
conductor phase, respectively.
[0012] Although the three-phase interfaces should extend only in
one dimension in view of their components, the reaction sites where
the electrode reactions can occur must extend in at least two
dimensions. Accordingly, it is considered that the reaction sites
where the electrode reactions can occur actually have some
extension at the interface between the gas phase and the electron
conductor phase and/or the interface between the gas phase and the
electrolyte phase in the vicinity of the three-phase interfaces.
For the former combination, some reaction intermediate associated
with hydrogen occurs at the interface between the gas phase and the
electron conductor phase, and the electrode reactions can proceed
through the intermediate. For the latter, on the other hand, the
electrode reactions occur probably because the electrolyte phase,
which has no inherent electron permeability, exhibits electron
permeability to some extent locally at the interface with the gas
phase in the vicinity of the electron conductor phase.
[0013] The performance of gas electrodes (that is, the magnitude of
electrode overpotential) depends on the quantity (area) of
three-phase interfaces and the smoothness of the electrode
reactions occurring at the three-phase interfaces in a particular
quantity (catalytic properties). The performance of the gas
electrodes should therefore be achieved by increasing the
three-phase interfaces and/or the catalytic properties per unit
three-phase interface.
[0014] According to the present invention, the anode and/or the
cathode is made of the "solid having hydrogen permeability" so that
it can function not only to transfer electrons but also to include
protons or hydrogen. This allows the interfaces between the
electrodes and the gas phase to function as electrode reaction
sites and thus provide a lower electrode overpotential.
[0015] (2) The electrodes according to Item (1). In this item, the
proton-conductive electrolyte has a perovskite structure
represented by the general formula AB.sub.xO.sub.3-d (wherein
0.8.ltoreq.x.ltoreq.1.2); and the B-site elements include zirconium
(Zr).
[0016] Although the electrodes according to the present invention
may in principle be used in combination with any type of
proton-conductive electrolyte, they are effective particularly for
electrolytes having a perovskite structure including zirconium (Zr)
as a B-site element.
[0017] High-temperature proton conductors are broadly divided into
cerates including Ce as a B-site element and zirconates including
Zr as a B-site element. In general, cerate-based electrolytes
feature high conductivity but exhibit poor chemical stability and
mechanical strength while zirconate-based electrolytes exhibit
lower conductivity than cerates but feature excellent stability and
strength. Although the introduction of Zr as a B-site element
increases the resistance of the electrolyte, it allows the
electrolyte to have a smaller thickness because of the high
mechanical strength.
[0018] (3) The electrodes according to Item (2) above. In this
item, the content of zirconium (Zr) in the B-site elements is 20
mole percent or more.
[0019] As described above, the chemical stability of
proton-conductive electrolytes increases with increasing content of
zirconium. It is known that, if proton-conductive electrolytes
including barium (Ba) as an A-site element, particularly, contain
20 mole percent or more of zirconium, they are stable with no
reaction even against 100% carbon dioxide.
[0020] (4) The electrodes according to any of Items (1) to (3). In
this item, the solid having hydrogen permeability is a mixed
proton-electron conductor.
[0021] The "solid having hydrogen permeability" used may be the
"mixed proton-electron conductor." The use of the mixed
proton-electron conductor allows the electrodes to function not
only to transfer electrons but also to include protons.
[0022] FIG. 1 is a schematic diagram of electrode reactions in the
case where a mixed proton-electron conductor is used for the
electrodes for an electrochemical cell 1. The following reaction
occurs at the interface between a gas phase and an anode 3:
H.sub.2.fwdarw.2H.sup.++2e.sup.- At this time, the resultant
protons (H.sup.+) and electrons (e.sup.-) exist in the anode 3. The
subsequent electrode reaction is completed after the protons travel
to an electrolyte 2 and the electrons travel to a lead 5. The
reverse reaction occurs at a cathode 4 to generate hydrogen gas.
These actions allow the interfaces between the electrodes and the
gas phase to function as electron reaction sites and thus provide a
lower electrode overpotential.
[0023] (5) The electrodes according to Item (4). In this item, the
mixed proton-electron conductor is a mixed proton-electron
conductive ceramic material having the perovskite structure.
[0024] Naturally, electrodes and electrolytes are made of different
materials. Many combinations of them cause problems, including
delamination due to differences in physical properties, such as
thermal expansion coefficient, and degraded electrode performance
due to chemical properties, such as mutual reactivity and
differences in oxidation-reduction properties. Such incompatibility
between electrodes and electrolytes can empirically often be
minimized using the same structure for them. The use of an
electrolyte having a perovskite structure in combination with
electrodes having the same structure is extremely effective.
[0025] (6) The electrodes according to any of Items (1) to (3)
above. In this item, the solid having hydrogen permeability is a
hydrogen storage alloy.
[0026] The "solid having hydrogen permeability" used may be the
"hydrogen storage alloy." The use of the hydrogen storage alloy
allows the electrodes to function not only to transfer electrons
but also to include atomic hydrogen.
[0027] FIG. 2 is a schematic diagram of electrode reactions in the
case where a hydrogen storage alloy is used for the electrodes for
an electrochemical cell 20. The following reaction occurs at the
interface between a gas phase and an anode 23: H.sub.2.fwdarw.2H At
this time, hydrogen (H) exists in the anode 23 (probably in atomic
form). The resultant hydrogen undergoes the following reaction at
the interface between the anode 23 and an electrolyte 22:
2H.fwdarw.2H.sup.++2e.sup.- The subsequent electrode reaction is
completed after the protons travel to the electrolyte 22 and the
electrons travel to a lead 25. The reverse reaction occurs at a
cathode 24 to generate hydrogen gas. These electrodes are provided
not only with the function of transferring electrons but also with
the function of including protons or hydrogen. These actions allow
the interfaces between the electrodes and the gas phase to function
as electron reaction sites and thus provide a lower electrode
overpotential.
[0028] (7) The electrodes according to Item (6). In this item, the
hydrogen storage alloy contains palladium (Pd).
[0029] Palladium can store hydrogen, as is well known, and can also
provide stable electrode properties since it is a noble metal, that
is, a stable metal with high resistance to oxidation.
[0030] (8) The electrodes according to Item (7). In this item, the
hydrogen storage alloy contains 10% or more of palladium (Pd).
[0031] The above-described hydrogen storage ability and stability
of palladium can also be achieved for an alloy containing the above
amount of palladium, and thus the alloy can provide stable
electrode properties.
[0032] (9) The electrodes according to any of claims 1 to 3. In
this item, the solid having hydrogen permeability is a mixture of a
mixed proton-electron conductor and a hydrogen storage alloy.
[0033] The "solid having hydrogen permeability" used may be a
mixture of the "mixed proton-electron conductor" and the "hydrogen
storage alloy." The two materials, as described above, function not
only to transfer electrons but also to include protons or hydrogen,
and thus the mixture thereof has the same functions.
[0034] The mixing ratio between the two materials may be suitably
selected according to the type of proton-conductive
electrolyte.
[0035] (10) The electrodes according to Item (9) above. In this
item, the mixed proton-electron conductor is a mixed
proton-electron conductive ceramic material having the perovskite
structure, and the hydrogen storage alloy contains palladium
(Pd).
[0036] (11) An electrochemical cell including the proton-conductive
electrolyte and the electrodes according to any of Items (1) to
(10) above.
Advantages
[0037] The use of the electrodes according to the above invention
in combination with a proton-conductive electrolyte can achieve an
electrochemical cell with low electrode overpotential.
BEST MODE FOR CARRYING OUT THE INVENTION
[0038] Examples of the present invention will now be specifically
described.
EXAMPLE 1
[0039] Hydrogen pumping was performed using a proton-conductive
cell including electrodes made of a mixed proton-electron
conductive ceramic material to evaluate its hydrogen separation
performance. FIG. 3 is a schematic diagram of a performance
evaluation apparatus.
[0040] The electrolyte used was a proton-conductive ceramic
material having the composition SrZr.sub.0.9Y.sub.0.1O.sub.3-a
(wherein a indicates the amount of loss of oxygen). This
electrolyte was disc-shaped and had a diameter of about 13.5 mm and
a thickness of 0.5 mm. A mixed proton-electron conductive ceramic
material (SrZr.sub.0.85Y.sub.0.1Ru.sub.0.05O.sub.3-a) was then
deposited in the center of each side of the disc-shaped electrolyte
31 by pulsed laser deposition (PLD) to form an anode 32 and a
cathode 33 that were circular and had a diameter of 8 mm and a
thickness of about 0.2 to 0.5 .mu.m. The anode 32 and the cathode
33 were connected to leads 38a and 38b, respectively, through
platinum nets for current collection and a platinum paste (neither
is shown). A platinum electrode (not shown) was connected to the
outside of the disc-shaped electrolyte 31 as a reference electrode.
Thus an electrochemical cell including the electrolyte 31, the
anode 32, and the cathode 33 was formed. The reference electrode
was provided as a standard for measuring the potentials of the
anode 32 and the cathode 33; it does not directly affect the
electrochemical function of the proton-conductive cell. The
electrochemical cell 34 was held vertically between ceramic tubes
36 and 37 with annular sealing members 39 disposed therebetween to
define an anode chamber 36a and a cathode chamber 37a. The ceramic
tube 36 had a gas-feeding tube 36b and a gas outlet 36c, and the.
ceramic tube 37 had a gas-feeding tube 37b and a gas outlet
37c.
[0041] The electrochemical cell 34 was placed in an electric
furnace 35 which was kept at 800.degree. C. to carry out a hydrogen
pumping test described below. Pure hydrogen and an argon gas
containing 1% hydrogen were fed into the anode 32 and the cathode
33, respectively, at a gas flow rate of 30 mL/min. These gases were
wetted with saturated steam at 17.degree. C. (the partial pressure
of the steam was about 1,900 Pa) to prevent the reduction of the
electrolyte 31. The anode gas serves to supply the hydrogen to be
pumped to the electrochemical cell while the cathode gas serves to
sweep the hydrogen generated in the cathode chamber by hydrogen
pumping. The cathode sweep gas contained 1% hydrogen for
convenience of potential measurement.
[0042] While the gases were fed as described above, a DC power
supply was connected to the leads 38a and 38b to supply a
predetermined current from the anode 32 to the cathode 33. The
concentration of hydrogen in the gas from the cathode gas outlet
37c was measured by gas chromatography to determine the rate of
hydrogen pumped from the anode chamber 36a to the cathode chamber
37a by supplying the current, namely the rate of hydrogen generated
at the cathode 33.
[0043] The electrode properties of the anode 32 and the cathode 33
were measured by current interruption. The measurement procedure is
as follows. The potentials of the anode 32 and the cathode 33
relative to that of the reference electrode were measured under
open-circuit conditions (with no current flowing) and with a
predetermined current flowing. The overpotential (ohmic loss) due
to the resistance of the electrolyte, which was measured by current
interruption, was deducted from the differences between the
potentials at the individual electrodes with the current flowing
and those at the individual electrodes under the open-circuit
conditions to determine the anode overpotential and the cathode
overpotential.
[0044] The evaluation results are shown in FIGS. 4 to 6.
[0045] FIG. 4 is a graph showing a comparison of the overpotential
of the anode made of the mixed proton-electron conductive ceramic
material and that of a conventional porous platinum electrode under
the same conditions. FIG. 5 is a graph showing a similar comparison
of cathode overpotentials. The two graphs show that the electrodes
made of the mixed proton-electron conductive ceramic material
exhibited a lower overpotential than the conventional porous
platinum electrodes.
[0046] FIG. 6 is a graph showing a comparison of the rates of
hydrogen generated, plotted against current densities, for the
above electrodes. The theoretical rate of hydrogen generated,
indicated by the dashed line in the graph, was calculated according
to Faraday's law, that is, the rate of hydrogen generated when all
current flowing is utilized for hydrogen pumping. The electrolyte
used as a proton-conductive electrolyte in this example,
SrZr.sub.0.9Y.sub.0.1O.sub.3-a, can pump hydrogen only at limited
current densities depending on the performance of the electrodes
used. If any larger current is applied, a current caused by
electron conduction flows through the electrolyte. This current,
however, does not contribute to hydrogen pumping. For this reason,
the rate of hydrogen generated when the conventional porous
platinum electrodes were used already started to deviate from the
theoretical rate of hydrogen generated at a current density of 13
mA/cm.sup.2. On the other hand, the measured rate of hydrogen
generated when the electrodes made of the mixed proton-electron
conductive ceramic material were used coincided with the
theoretical rate of hydrogen generated even at a current density of
16 mA/cm.sup.2 because the electrode performance was improved, as
shown in FIGS. 4 and 5.
[0047] The above results clearly proved that the electrodes made of
the mixed proton-electron conductive ceramic material were superior
to the conventional electrodes.
EXAMPLE 2
[0048] Next, hydrogen storage alloy electrodes and the same
apparatus as in Example 1 were used to evaluate the hydrogen
separation performance. Example 2 is different from Example 1 in
that the gas electrodes used were made of palladium, which can
store hydrogen. Palladium was deposited in the center of each side
of a disc-shaped electrolyte by sputtering to form the anode 32 and
the cathode 33, which were circular and had a diameter of 0.8 mm
and a thickness of about 1 .mu.m. The other parts of the apparatus
and the evaluation method used are not described since they are the
same as in Example 1.
[0049] The evaluation results are shown in FIGS. 7 to 9.
[0050] FIG. 7 is a graph showing a comparison of the overpotential
of the palladium anode and that of a conventional porous platinum
electrode under the same conditions. FIG. 8 is a graph showing a
similar comparison of cathode overpotentials. The two graphs show
that the palladium electrodes exhibited a lower overpotential than
the conventional porous platinum electrodes.
[0051] FIG. 9 is a graph showing a comparison of the rates of
hydrogen generated, plotted against current densities, for the
above electrodes. The theoretical rate of hydrogen generated,
indicated by the dashed line in the graph, is the same as in
Example 1. The rate of hydrogen generated when the conventional
porous platinum electrodes were used, as shown in Example 1,
already started to deviate from the theoretical rate of hydrogen
generated at a current density of 13 mA/cm.sup.2. On the other
hand, the measured rate of hydrogen generated when the palladium
electrodes were used coincided with the theoretical rate of
hydrogen generated even at a current density of 180 mA/cm.sup.2
because the electrode performance was improved, as shown in FIGS. 7
and 8.
[0052] The above results proved the superiority of the hydrogen
storage alloy electrodes.
INDUSTRIAL APPLICABILITY
[0053] The present invention can be widely applied to
electrochemical devices used for hydrogen separation for hydrogen
production and fuel cells.
BRIEF DESCRIPTION OF THE DRAWINGS
[0054] FIG. 1 is a schematic diagram of electrode reactions in the
case where a hydrogen storage alloy mixed proton-electron conductor
is used for the electrodes for a proton-conductive electrolyte.
[0055] FIG. 2 is a schematic diagram of electrode reactions in the
case where a hydrogen storage alloy is used for the electrodes for
a proton-conductive electrolyte.
[0056] FIG. 3 is a diagram of an evaluation apparatus in Example
1.
[0057] FIG. 4 is a graph showing anode overpotentials according to
the results of hydrogen separation performance evaluations in
Example 1.
[0058] FIG. 5 is a graph showing cathode overpotentials according
to the results of the hydrogen separation performance evaluations
in Example 1.
[0059] FIG. 6 is a graph showing the rates of hydrogen generated
according to the results of the hydrogen separation performance
evaluations in Example 1.
[0060] FIG. 7 is a graph showing anode overpotentials according to
the results of hydrogen separation performance evaluations in
Example 2.
[0061] FIG. 8 is a graph showing cathode overpotentials according
to the results of the hydrogen separation performance evaluations
in Example 2.
[0062] FIG. 9 is a graph showing the rates of hydrogen generated
according to the results of the hydrogen separation performance
evaluations in Example 2.
REFERENCE NUMERALS
[0063] 1, 20, and 34: electrochemical cell [0064] 2, 22, and 31:
electrolyte [0065] 3, 23, and 32: anode [0066] 4, 24, and 33:
cathode [0067] 35: electric furnace [0068] 36a: anode chamber
[0069] 36b: gas-feeding tube [0070] 37a: cathode chamber [0071]
37c: cathode gas outlet
* * * * *