US20060231386A1

US20060231386A1 - Solid polymer membrane-type water-electrolysis apparatus

Info

Publication number: US20060231386A1
Application number: US11/400,392
Authority: US
Inventors: Katsumi Kanematsu; Eiji Kato; Yasuo Ido
Original assignee: Daido Metal Co Ltd
Current assignee: Daido Metal Co Ltd
Priority date: 2005-04-14
Filing date: 2006-04-10
Publication date: 2006-10-19
Also published as: JP2006291329A

Abstract

A solid polymer membrane-type water-electrolysis apparatus according to the present invention includes a solid polymer electrolyte membrane, an oxygen electrode mounted in contact with one side of the solid polymer electrolyte membrane, a hydrogen electrode mounted in contact with the other side of the solid polymer electrolyte membrane, separator plates mounted adjacent the outsides of the oxygen electrode and the hydrogen electrode and serving as current collector plates having passages for water and generated gasses, fixing plates disposed outside the separator plates and made of a non-conductive material, and reservoirs disposed outside said fixing plates for storing water and the generated gasses. The fixing plates include pressing members build therein for pressing the oxygen electrode and the hydrogen electrode against the solid polymer electrolyte membrane, and flow passages are included in the pressing members. The reservoirs are fixed integrally by tie bolts by clamping the solid polymer electrolyte membrane, the oxygen electrode, the hydrogen electrode, the separator plates and the fixing plates together from outside the fixing plates. Further, the reservoirs have water supply bores provided at locations higher in level than the position of the water electrolysis level, and discharge bores for discharging the generated gasses. In this apparatus, storage tanks for the produced oxygen and hydrogen gasses are formed integrally into a compact structure. Thus, the apparatus is convenient for movement and preservation, and the oxygen and hydrogen gasses stored can be brought into a pressure equal to or higher than the atmospheric pressure and supplied to a remote place.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a water-electrolysis apparatus for producing hydrogen and oxygen gasses, and particularly, to a solid polymer membrane-type water-electrolysis apparatus having a compact structure and convenient for transportation and storage.

DESCRIPTION OF RELATED ART

There is a water-electrolysis apparatus using a solid polymer membrane to produce hydrogen and oxygen gasses, including an apparatus as shown in FIG. 3, which is intended for education and demonstration. This electrolysis apparatus includes a solid polymer membrane-type electrolytic cell 100 which comprises a solid polymer electrolyte membrane 1 interposed between an oxygen electrode 2 and a hydrogen electrode 3, separator plates 4 mounted outside the oxygen electrode 2 and the hydrogen electrode 3 and having passages for permitting generated gasses to pass therethrough, and fixing plates mounted outside the separator plates 4, so that these members are integrated together. A plurality of through-passages 62 are provided in each of the fixing plates 6 to communicate with the passages in each of the separators 4. An oxygen storage tank 20 adapted to store water from a water tank 22 and to store oxygen gas to discharge the latter through a discharge port 24 is mounted on the side of the oxygen electrode 2 in such a manner that it is connected in communication to the through-passages 62 through hoses 26, and a hydrogen storage tank 30 adapted to store water from a water tank 32 and to store hydrogen gas to discharge the latter through a discharge port 34 is mounted on the side of the hydrogen electrode in such a manner that it is connected in communication to the through-passages 62 through hoses 36.
There is also an apparatus for generating oxygen and hydrogen gasses by the electrolysis of water, including an apparatus using an ion-exchange membrane as described in JP-A-09-143778. This apparatus is formed as an electrolytic cell in which box-shaped partition walls are provided on opposite sides of the ion-exchange membrane; crosspieces for retaining a metal-coated surface formed by a metal coating treatment and the ion-exchange membrane are mounted inside the box-shaped partition walls, and gas outlets are provided above the crosspieces. In this apparatus, oxygen gas is generated in a chamber defined by the ion-exchange membrane and the partition wall connected to an anode of a power source device, and hydrogen gas is generated in a chamber defined by the ion-exchange membrane and the partition wall connected to a cathode of the power source device, and these gasses are removed from top portions of the partition walls.
There is further a conventionally proposed water-electrolysis apparatus also serving as a fuel cell, which uses a water-electrolyzing membrane-electrode assembly comprising a solid polymer electrolyte membrane and an oxygen electrode and a hydrogen electrode bonded on opposite sides of the solid polymer electrolyte membrane, as described in JP-A-2004-353033. An oxygen flow passage plate, a separator plate and an end plate are disposed in piles on the side of the oxygen electrode of the membrane-electrode assembly, and a separator plate and an end plate are disposed in piles on the side of the hydrogen electrode. These components are bonded together into an integral structure, which is immersed in water in a water tank.
In the water-electrolysis apparatus as shown in FIG. 3, the pressures of hydrogen and oxygen produced by this apparatus are ensured only up to substantially the atmospheric pressure, even if the discharge ports in the gas storage tanks 20 and 30 have been closed. Therefore, the amounts of hydrogen and oxygen stored are limited to the volume of the tanks. Even if these gasses are continuously generated, they are discharged through center pipes leading to the water tanks 22 and 32. For this reason, water in the water tanks 22 and 32 is overflowed and released into the atmosphere, and thus, it is substantially impossible to store these gasses in the storage tanks 20 and 30.
It is conceived that high-pressure gas cylinders are used for the storage of the oxygen and hydrogen gasses produced in the above manner. In this case, however, it is necessary to mount a regulator, resulting in increases in size and weight of the entire apparatus. Thus, the transportation and storage of the apparatus are limited.
The water-electrolysis apparatus described in JP-A-09-143778 suffers from the following problems: The oxygen and hydrogen gas chambers each divided into a number of sections are formed into an integral structure and for this reason, it is not only difficult to provide a force of close contact between the crosspiece and the ion-exchange membrane which are members defining such gas chamber, but also it is not easy to smoothly remove the gasses, because the gas chambers are divided into the sections.
Further, in water-electrolysis apparatus described in JP-A-2004-353033, essential portions of the apparatus are immersed in water and for this reason, the size of the apparatus itself is limited, but also the efficient removal, pressures and the like of the produced oxygen and hydrogen gasses are not taken into consideration, and it is necessary to mount other tanks for the storage of the gasses, as in the above-described prior art apparatus.

SUMMARY OF THE INVENTION

The present invention has been accomplished with the above problems in view, and it is an object of the present invention to provide a solid polymer membrane-type water-electrolysis apparatus, wherein tanks for storage of oxygen and hydrogen gasses produced are formed integrally to provide a compact structure for the entire apparatus, thereby facilitating the transportation or storage of the apparatus.
It is a further object of the present invention to provide a solid polymer membrane-type water-electrolysis apparatus, wherein the stored oxygen and hydrogen gasses can be brought into a pressure equal to or higher than the atmospheric pressure, and supplied to a remote place.
To achieve the above objects, according to the present invention, there is provided a solid polymer membrane-type water-electrolysis apparatus comprising a solid polymer electrolyte membrane, an oxygen electrode mounted in contact with one side of the solid polymer electrolyte membrane, a hydrogen electrode mounted in contact with the other side of the solid polymer electrolyte membrane, separator plates mounted adjacent the outsides of the oxygen electrode and the hydrogen electrode and serving as current collector plates having passages for water and generated gasses, fixing plates disposed outside the separator plates and made of a non-conductive material, and reservoirs disposed outside the fixing plates for storing water and the generated gasses, wherein
the fixing plates include pressing members build therein for pressing the oxygen electrode and the hydrogen electrode against the solid polymer electrolyte membrane, flow passages being included in the pressing members,
the reservoirs are fixed integrally by tie bolts by clamping the solid polymer electrolyte membrane, the oxygen electrode, the hydrogen electrode, the separator plates and the fixing plates together from outside the fixing plates, and
the reservoirs have water supply bores provided at locations higher in level than the position of the water electrolysis level, and release bores for releasing the generated gasses.
In the solid polymer membrane-type water-electrolysis apparatus, the oxygen electrode is formed by coating a solid polymer electrolyte membrane resin onto a porous sheet-shaped carbon material plated with iridium.
In the solid polymer membrane-type water-electrolysis apparatus, the hydrogen electrode is formed by coating a mixture including carbon and a solid polymer electrolyte membrane resin onto a porous sheet-shaped carbon material, and further coating a mixture including Pt (alloy) and Pt (alloy)-carrying carbon and a solid polymer electrolyte membrane resin onto the coated layer.
In the solid polymer membrane-type water-electrolysis apparatus, each of the separator plates is formed from a metal plate material coated with Pt or Au and provided with a plurality of through-bores.
In the solid polymer membrane-type water-electrolysis apparatus, each of the pressing members build in the fixing plates in contact with the separator plates is formed of a porous plastic material such as nylon having an elasticity.
In the solid polymer membrane-type water-electrolysis apparatus, the fixing plates are provided with through-bores serving as flow passages for water or the generated gasses.
In the solid polymer membrane-type water-electrolysis apparatus, the reservoirs have maintenance bores for drainage of water provided in their bottoms or in near their bottoms, in addition to the water supply bores and the generated-gas passages.
The solid polymer membrane-type water-electrolysis apparatus as described above according to the present invention comprises the solid polymer electrolyte membrane, the oxygen electrode mounted in contact with one side of the solid polymer electrolyte membrane, the hydrogen electrode mounted in contact with the other side of the solid polymer electrolyte membrane, the separator plates mounted adjacent the outsides of the oxygen electrode and the hydrogen electrode and serving as current collector plates having passages for water and generated gasses, the fixing plates disposed outside the separator plates and made of the non-conductive material, and the reservoirs disposed outside the fixing plates for storing water and the generated gasses, wherein the fixing plates include pressing members build therein for pressing the oxygen electrode and the hydrogen electrode against the solid polymer electrolyte membrane, the flow passages being included in the pressing members, and further, the reservoirs are fixed integrally by tie bolts by clamping the solid polymer electrolyte membrane, the oxygen electrode, the hydrogen electrode, the separator plates and the fixing plates together from outside the fixing plates. Therefore, the tanks of a pressure-resistant structure for storing oxygen and hydrogen can be mounted, thereby providing the water-electrolysis apparatus having a compact entire structure and convenient for movement and preservation.
In addition, the oxygen electrode and the hydrogen electrode are mounted in an opposed relation to and on the opposite sides solid polymer electrolyte membrane. The separator plates and the fixing plates are disposed in piles outside the oxygen electrode and the hydrogen electrode, and further, the reservoirs are fixed integrally outside the fixing plates by the tie bolts passed through these members. Therefore, the close contact of the separator plates to the oxygen electrode and the hydrogen electrode can be enhanced to ensure the efficient electrolysis. Despite this close contact, the generated oxygen and hydrogen gasses can be passed through the passages in the pressing members and hence, the supplying of the generated gasses can be conducted as needed. Further, the reservoirs have the water supply bores provided at the locations higher in level than the position of the water-electrolysis level, and the discharge bores for discharging the generated gasses. Therefore, if the water supply bores and the gas discharge bores are cut off, the generated gasses can be stored in the reservoirs under a pressure equal to or higher than the atmospheric pressure depending on the pressure resistance of the reservoirs, and the gasses having an increased pressure can be supplied to a place far away from the apparatus.
The oxygen electrode is formed by coating the solid polymer electrolyte membrane resin onto the porous sheet-shaped carbon material plated with iridium, and the hydrogen electrode is formed by coating the mixture including carbon and the solid polymer electrolyte membrane resin onto the porous sheet-shaped carbon material, and further coating the mixture including the Pt (alloy) and Pt (alloy)-carrying carbon and the solid polymer electrolyte membrane resin onto the coated layer. Therefore, the electrolysis using pure water can be achieved at a low voltage in such solid polymer membrane-type water-electrolysis apparatus.
In addition, in the solid polymer membrane-type water-electrolysis apparatus constructed as described above, each of the separator plates is formed from the metal plate material coated with Pt or Au and provided with the plurality of through-bores and hence, the produced oxygen gas and hydrogen gas can be passed through the through-bores into the reservoirs without any problem.
Additionally, in the solid polymer membrane-type water-electrolysis apparatus constructed as described above, the separator plates are pressed against the oxygen electrode and the hydrogen electrode by the pressing members which are made from the porous plastic material having the elasticity and which are build in the separators at the their sections having the through-bores, whereby a close contact force can be applied to these members, but also the flowing of the gasses can be achieved.
Yet additionally, in the solid polymer membrane-type water-electrolysis apparatus, the fixing plates are provided with the through-bores serving as the flow passages for the water or the generated gasses, and further, the reservoirs have the maintenance bores for drainage of water provided in their bottoms or in near their bottoms, in addition to the water supply bores and the passages for the generated gasses, and the through-bores serving as the gas flow passages are also provided in the fixing plates requiring the rigidity, and therefore, it is possible to achieve the smooth flowing of the generated gasses to the reservoirs. Moreover, the reservoirs have the water-draining bores and hence, the inside of each of the reservoirs can be easily washed.
The novel features, arrangement and effect of the present invention can be further understood from the accompanying drawings associated with the following description. In the drawings, the same reference characters indicate the same components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view for explaining a solid polymer membrane-type water-electrolysis apparatus according to one embodiment of the present invention;
FIG. 2A is a perspective view taken from an oxygen reservoir side and showing the solid polymer membrane-type water-electrolysis apparatus according to the embodiment of the present invention;
FIG. 2B is a side elevational view of the solid polymer membrane-type water-electrolysis apparatus, taken in a direction of an arrow B in FIG. 2A; and
FIG. 3 is a schematic sectional view of a conventional solid polymer membrane-type water-electrolysis apparatus.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will now be described with reference to FIGS. 1, 2A and 2B.
FIG. 1 is a sectional view for explaining a solid polymer membrane-type water-electrolysis apparatus according to an embodiment of the present invention; FIGS. 2A and 2B show one example of the same solid polymer membrane-type water-electrolysis apparatus. FIG. 2A is a perspective view and FIG. 2B is a side view taken in a direction of an arrow B in FIG. 2A. This solid polymer membrane-type water-electrolysis apparatus includes an electrolytic cell 100 comprising a solid polymer electrolyte membrane 1 made of a material of perfluorocarbon sulfonic acid polymer or the like, an oxygen electrode 2 which is disposed on one side of the solid polymer electrolyte membrane 1 and which is formed by forming a coated layer of a mixture including a resin for a solid polymer electrolyte membrane on a porous sheet-shaped carbon material plated with iridium, a hydrogen electrode 3 which is disposed on the other side of the solid polymer electrolyte membrane 1 and which is formed by coating a mixture of carbon and a resin for a solid polymer electrolyte membrane onto a surface of a porous sheet-shaped carbon material and further coating a mixture including Pt (alloy) and/or Pt (alloy)-carrying carbon and a resin for a solid polymer electrolyte membrane onto the surface of the coated layer, separator plates 4, 4 of a stainless steel which are disposed adjacent each other outside the oxygen electrode 2 and the hydrogen electrode 3 and which serve as current collector plates provided with water and gas flow passages, and fixing plates 6, 6 made of a resin and disposed outside the separator plates 4, 4. Further, preferably, each of the separator plates 4, 4 is coated with Pt or Au, thereby making it possible to ensure the electrolytic reaction of water permitting an enhanced corrosion resistance and stable over a long period.
Members 5 for pressing the oxygen electrode 2 and the hydrogen electrode 3 against the solid polymer electrolyte member 1 are build in the fixing plates 6, 6 of the electrolytic cell 100 at sections contacting with the oxygen electrode 2 and the hydrogen electrode 3. The pressing member 5 is made of a non-conductive material having water and gas flow passages, and a proper number of through-passages 62 for water and generated gasses are provided behind each of the pressing members 5 to extend to the outside. Further, an oxygen reservoir 20 and a hydrogen reservoir 30 having internal tanks 28 and 38 for reserving water and the generated gasses therein are integrally provided in the electrolytic cell 100, so that they are disposed adjacent outsides of the fixing plates 6, 6. The oxygen reservoir 20 and the hydrogen reservoir 30 are clamped and fixed integrally by a plurality of tie bolts 102 passed through bores made through the entire electrolytic cell 100 and a plurality of nuts 104. Packings are interposed between the fixing plates 6, 6 and the oxygen reservoir 20 and the hydrogen reservoir 30 to provide a sealed structure, so that the gas generated therein is prevented from being leaked even at more than the atmospheric pressure.
At least two bores such as a gas discharge bore 8 and a water supply bore 9 are provided in each of the oxygen reservoir 20 and the hydrogen reservoir 30 at locations higher than a water electrolysis level, so that they are opened into an upper surface of the electrolytic cell 100, for example, as shown in FIG. 2. A safety valve, a check valve or the like is mounted in the hydrogen or oxygen discharge bore 8, so that the pressure of the generated gas can be adjusted. An opening and closing valve is mounted in the water supply bore 9 to perform the supplement of water as needed, to that even if the gas stored is at a pressure more than the atmospheric pressure, the discharge of water is prevented. Maintenance bores 10 are provided for drainage of water or the like in the oxygen and hydrogen reservoirs 20 and 30 to permit the internal tanks 28 and 39 to communicate with the outside at locations closer to their bottoms, so that they are usually closed.
In the solid polymer membrane-type water-electrolysis apparatus of the above-described arrangement according to the embodiment of the present invention, water is injected through the water supply bore 9 into and filled in the oxygen and hydrogen reservoirs 20 and 30 and then permitted to flow through the through-bores 62 in the fixing plates 6, 6 and via the flow passages in the separator plates 4, 4 and the pressing plates 5 and the bores in the oxygen electrode 2 and the hydrogen electrode 3 to reach the solid polymer electrolytic member 1. In this state, a DC power source is connected to terminals of the separator plates 4, 4. In this state, the oxygen electrode 2 and the hydrogen electrode 3 are pressed against the solid polymer electrolytic member 1 with the separator plates 4, 4 interposed therebetween into close contact states by the pressing members 5 of the fixing plates 6, 6. Therefore, the flowing of electric current in the oxygen electrode 2 causes the water to be ion-separated into oxygen ions and hydrogen ions by the catalytic action of the plated iridium. The oxygen ions are robbed of electrons to form an oxygen molecule. The hydrogen ions are moved through the solid polymer electrolytic membrane 1 to the side of the hydrogen electrode 3 and receive electrons under the catalytic action of Pt to form a hydrogen gas.
The oxygen and hydrogen gasses generated at the oxygen electrode 2 and the hydrogen electrode 3 as described above are permitted to flow via the passages in the separator plates 4, the flow passages within the pressing members 5 and through the through-bores 62 in the fixing plates 6 into the internal tanks 28 and 38 of the oxygen gas reservoir 20 and the hydrogen gas reservoir 30. If the flowing of the generated gasses is continued as it is, as long as there is the water reaching the solid polymer electrolytic membrane 1, the oxygen gas is continuously stored in the oxygen reservoir 20. If the oxygen gas is retained in the oxygen reservoir 20 with its pressure adjusted in pressure by the safety valve, the check valve or the like mounted in the oxygen discharge bore 8 and the water supply bore 9, the oxygen gas accumulated therein is gradually brought into a state having a pressure higher than the atmospheric pressure. In this state, the hydrogen gas is likewise accumulated in a state having a pressure higher than the atmospheric pressure even in the hydrogen reservoir 30.
The oxygen and hydrogen gasses accumulated in the above manner are stored under higher pressures and hence, the oxygen or hydrogen gas can be introduced through the oxygen gas discharge bore or the hydrogen gas discharge bore to any place depending on the external application, e.g., even to a considerably remote place.
In addition, the water electrolysis apparatus 100 and the oxygen and hydrogen reservoirs 20 and 30 are entirely integrally fixed in the clamped manner by the tie bolts 102 and the nuts 104, as shown in FIGS. 2A and 2B. Therefore, not only a compact hydrogen/oxygen generating system is obtained, but also a highly pressure-resistant system is obtained. Thus, it is possible to provide an apparatus which is convenient for movement and preservation, thereby enabling the supplying of the generated gas to a remote place.
Further, in the polymer membrane-type water-electrolysis apparatus of the above-described arrangement, the oxygen electrode 2 and the hydrogen electrode 3 are placed in direct contact with the separator plates 4, 4. Further, not only the force of close contact between the separator plates 4, 4 and the oxygen electrode 2 and the hydrogen electrode 3 is increased, but also the gas flow passages are ensured, by virtue of the fixing plates 6 which have the through-bores 62 and which are properly disposed in such a manner that the pressing members 5 made of the porous plastic material having an elasticity are interposed therebetween from the outside of the separator plates 4, 4. Therefore, it is possible to carry out the electrolysis of water with a good efficiency.
Additionally, hydrogen and oxygen can be generated and supplied as needed, at any place wherever a power source exists therein, by the polymer membrane-type water electrolysis apparatus as described above. Therefore, it is unnecessary to store hydrogen or oxygen gas in a weighty container such as a bomb to transport it, and hence, the transportation of the apparatus is not limited. Thus, the hydrogen/oxygen generating system can be provided in the term of a portable apparatus.
Yet further, in the solid polymer membrane-type water-electrolysis apparatus of the above-described arrangement, the solid polymer electrolyte membrane is formed of the material of perfluorocarbon sulfonic acid polymer; the oxygen electrode 2 is formed by coating the resin for the solid polymer membrane onto the porous sheet-shaped carbon material plated with iridium; and the hydrogen electrode 3 is formed in the form of water electrolyzing membrane-electrode assembly by coating the mixture including carbon and the resin for the solid polymer electrolyte membrane onto the surface of the porous sheet-shaped carbon material to form the coated layer, coating the mixture including the Pt (alloy) and/or Pt (alloy)-carrying carbon and the resin for the solid polymer electrolyte membrane onto the coated layer, and pressing the resulting material integrally. Therefore, it is possible to carry out the electrolysis of water at a voltage equal to or higher than 1.6 V and to avoid the damage to carbon.
Further, because the maintenance bores 10 are provided at the locations closer to the bottoms of the oxygen gas reservoir 20 and the hydrogen gas reservoir 30, the water in each of the internal tanks 28 and 38 can be drained, and the insides of the tanks 28 and 38 can be washed at any time to avoid the clogging of the through-bores 62 in the fixing plates 6, 6. In this manner, the electrolysis of water with a good efficiency can be carried out.
As described above, it is obvious that the solid polymer membrane-type water-electrolysis apparatus according to the present invention can be carried out in a technical scope defined in claims without being limited to the above-described embodiment.

Claims

1. A solid polymer membrane-type water-electrolysis apparatus comprising a solid polymer electrolyte membrane, an oxygen electrode mounted in contact with one side of said solid polymer electrolyte membrane, a hydrogen electrode mounted in contact with the other side of said solid polymer electrolyte membrane, separator plates mounted adjacent the outsides of said oxygen electrode and the hydrogen electrode and serving as current collector plates having passages for water and generated gasses, fixing plates disposed outside said separator plates and made of a non-conductive material, and reservoirs disposed outside said fixing plates for storing water and the generated gasses, wherein

said fixing plates include pressing members build therein for pressing said oxygen electrode and said hydrogen electrode against said solid polymer electrolyte membrane, said pressing members including flow passages,

said reservoirs are fixed integrally by tie bolts by clamping the solid polymer electrolyte membrane, said oxygen electrode, said hydrogen electrode, said separator plates and the fixing plates together from outside said fixing plates, and

said reservoirs have water supply bores provided at locations higher in level than the position of the water electrolysis level, and release bores for releasing the generated gasses.

2. A solid polymer membrane-type water-electrolysis apparatus according to claim 1, wherein said oxygen electrode is formed by coating a solid polymer electrolyte membrane resin onto a porous sheet-shaped carbon material plated with iridium.

3. A solid polymer membrane-type water-electrolysis apparatus according to claim 1, wherein said hydrogen electrode is formed by coating a mixture including carbon and a solid polymer electrolyte membrane resin onto a porous sheet-shaped carbon material, and further coating a mixture including Pt (alloy) and Pt (alloy)-carrying carbon and a solid polymer electrolyte membrane resin onto the coated layer.

4. A solid polymer membrane-type water-electrolysis apparatus according to claim 1, wherein each of said separator plates is formed of a metal plate material coated with Pt or Au and provided with a plurality of through-bores.

5. A solid polymer membrane-type water-electrolysis apparatus according to claim 1, wherein each of said pressing members build in said fixing plates in contact with said separator plates is formed of a porous plastic material such as nylon having an elasticity.

6. A solid polymer membrane-type water-electrolysis apparatus according to claim 1, wherein said fixing plates are provided with through-bores serving as flow passages for water or the generated gasses.

7. A solid polymer membrane-type water-electrolysis apparatus according to claim 1, wherein said reservoirs have maintenance bores for drainage of water provided in their bottoms or in near their bottoms, in addition to the water supply bores and the generated-gas passages.