US20040140202A1

US20040140202A1 - Electrolysis unit

Info

Publication number: US20040140202A1
Application number: US10/347,028
Authority: US
Inventors: Anwer Puthawala
Original assignee: Framatome ANP GmbH
Current assignee: Areva GmbH
Priority date: 2003-01-17
Filing date: 2003-01-17
Publication date: 2004-07-22

Abstract

An electrolysis unit having a plurality of membrane electrolytic cells connected in series suitable for use in a service station for supplying a motor vehicle with hydrogen as fuel. Each of the membrane electrolytic cells has a membrane provided on both sides with an appertaining contacting disk, especially a support mat made up of a large number of metal wires laid over each other and pressed together. In a service station, a gas cleaning unit is installed on the inlet side upstream from such an electrolysis unit.

Description

BACKGROUND

The present invention relates to an electrolysis unit with a number of membrane electrolytic cells electrically connected in series, each of which comprises a membrane surrounded by a pair of contact plates, whereby each contact plate has a channel system on its side facing the appertaining membrane for transporting water and/or gas. The present invention also relates to a service station for supplying a motor vehicle with hydrogen as fuel.

In an electrolysis device, a medium is electrolyzed by applying a supply voltage between an anode and a cathode. When water is used as the medium, hydrogen and oxygen are formed in this process. Such an electrolysis device can thus be used to generate hydrogen and/or oxygen as needed.

An electrolysis device can be configured as a so-called membrane electrolyzer. In this case, the electrolysis device comprises a number of membrane electrolytic cells in which the functioning principle is the opposite of that of a fuel cell as described, for example, in the German article titled “Brennstoffzellen für Elektrotraktion” [Fuel Cells for Electrotraction], by K. StraBer, VDI-Berichte [Reports of the German Engineering Association], No. 912 (1992), p. 125 ff. With such a membrane electrolytic cell, the water provided as the medium is conveyed to a membrane arranged between the anode and the cathode, especially to a cation exchanger membrane provided as the electrolyte. The membrane here is normally provided with a contact layer on both sides, whereby the first contact layer serves as the anode and the second contact layer serves as the cathode. Such a membrane electrolytic cell stands out for its especially compact design so that an electrolysis unit with a number of membrane electrolytic cells can be accommodated in a very small space. In order to feed the requisite media, especially the water to be electrolyzed, and in order to discharge the generated gas, the membrane in such a membrane electrolytic cell is normally provided on both sides with an appertaining contact plate that has a channel system for transporting the medium on its side facing the membrane.

The hydrogen that can be generated as needed in such an electrolysis unit is especially useful as a mobile fuel that could constitute an environmentally sound alternative to the widespread use of fossil fuels. In particular, the generated hydrogen, if necessary at an appropriate temperature in liquefied form, is especially suitable as a mobile and flexibly employable fuel for an environmentally sound use in motor vehicles of all kinds. Particularly with an eye towards efforts to reduce the global consumption of fossil fuels in supplying motor vehicles with power, a greater use of hydrogen as fuel for motor vehicles would be desirable.

In order for hydrogen to become more widespread as fuel for the operation of motor vehicles, however, there is a need to establish a sufficiently dense network of service stations in which the necessary hydrogen can be supplied in a simple and safe manner. For this purpose, flexible installations are needed in which the hydrogen can be generated at an adequate capacity and at an adequate rate while adhering to a high level of safety. A membrane electrolyzer is fundamentally well-suited for this purpose, although so far, the required capacities and production rates have only been achieved to an insufficient extent.

SUMMARY OF THE INVENTION

The present invention provides an electrolysis unit of the type described above with which a high production capacity of hydrogen can be achieved with relatively few resources and with simple means. Moreover, the present invention provides a service station for providing a reliable supply of hydrogen as fuel for a motor vehicle.

The electrolysis includes a contacting disk arranged between each contact plate and the appertaining membrane.

The production capacity of a membrane electrolyzer depends, among other things, on the total current that can be applied to the entire system in order to electrolyze the water to form hydrogen and oxygen. For material-related reasons, especially in view of the material properties of the membrane that is used in the membrane electrolytic cells, however, the current density in the individual membrane electrolytic cells is limited. Therefore, an increase in the total production capacities that can be achieved is attainable by increasing the active surface area provided per membrane electrolytic cell. However, increasing this surface area means that the reliable electric contacting of the sides of the membrane over a large surface area could become problematic, especially if the membrane used becomes unstable because the selected surface area was too large and then tends to become deformed due to the relatively high mechanical loads. Consequently, in order to ensure a reliable electrical contact over a large surface area between the contact plate and the membrane even when a large total surface area is selected, a contacting disk is provided between the contact plate and the membrane, whereby said contacting disk has a high electrical conductivity on the one hand and a high permeability to the medium on the other hand.

In order to also keep the mechanical stress on each membrane low in the case of such improved contacting, the mechanical properties of the contacting disk should be systematically configured so as to additionally support the membrane. Here, this support should be designed in such a way that the current flow in the entire system is minimally impeded. These criteria are met with a support that concurrently acts over a large surface area in that each contacting disk advantageously has a high conductivity and also a high porosity of up to about 50%.

With an eye towards the above-mentioned criteria, the contacting disk could be configured, for example, as a metal contact piece, especially made of titanium, which is provided with a large number of microfine bores having a diameter, for instance, of 100 μm. As an alternative, the contacting disk could also be in the form of a metallic sintered element that, in a sponge-like configuration, has a large number of cavities for whose formation, for example, suitable plastic can be used that is volatile at elevated temperatures. Advantageously, however, the contacting disk in question is configured as a support mat which, owing to its mechanical properties, especially a certain plasticity or deformability, ensures a particularly intense electrical contact over a large surface area when the membrane is affixed between the contact plates.

With such an arrangement, in order to ensure a sufficiently high conductivity of the entire system on the one hand and a sufficiently high porosity of the support vis-à-vis the medium flows on the other hand, the support mat or each support mat is advantageously made up of a large number of metal wires laid over each other and pressed together. The support mat, which thus has a felt-like appearance, is preferably made of titanium wires, in order to ensure sufficient resistance and a relatively long service life, even under conditions that are aggressive to the material. Particularly when titanium wires are used, a sufficiently high conductivity and corrosion resistance of the entire system can be achieved.

A high flexibility even when different numbers of membrane electrolytic cells are combined to form the electrolysis unit can also be achieved with a compact design in that the channel system of the contact plate or of each contact plate is advantageously connected to a feed or discharge channel for the medium by means of a shut-off valve that is integrated into each contact plate in such a way that it can be shut off. In particular, there can be a shared feed or discharge channel for the medium for all the contact plates, said channel being formed in each contact plate by an interconnected opening in the plane of the plate. When the contact plates are combined in order to form the electrolysis unit, in which process the contact plates are stacked on top of each other, these openings come to lie above each other, thus forming a medium channel that extends in the stacking direction of the contact plates. With this embodiment, the appertaining channel system of the contact plate can be connected to the appertaining media channel via a branch channel that extends in the plane of the plate, whereby the shut-off valve opens or closes the appropriate branch channel as needed via a suitable actuation from the outside.

In a flexible manner and with a relatively high production capacity, the electrolysis unit allows a decentralized production of hydrogen by electrolysis of water and it is thus well-suited for establishing a widespread supply network for motor vehicles. Therefore, in an advantageous embodiment, the electrolysis unit is part of a service station used for supplying motor vehicles.

The service station according to the present invention includes a pumping system connected on the inlet side via a gas cleaning unit to an electrolysis unit of the type described.

Here, it is firstly taken into account that the electrolysis unit of the type described should indeed ensure an adequately high production rate of hydrogen while having a relatively compact design, which is necessary for the reliable operation of a widespread supply network. Moreover, it is also taken into account that, in modern, hydrogen-based drive concepts for motor vehicles, as we move away from conventional combustion engine technology, more and more fuel cell-based concepts will be used. In such fuel cells, in a kind of reversal of the described electrolyzer concept, a systematic recombination of hydrogen with oxygen will be carried out making use of a suitable membrane or separating layer, a process in which electric power is liberated. This, in turn, can be used to power the motor vehicle. For the operation of such systems, which generally stand out for their relatively high efficiency and operational reliability, however, a high level of purity of about 99.99% is desirable for the supplied hydrogen. In order to supply hydrogen of such a high purity in an adequate quantity in the service station, the electrolysis unit of the type described above is combined with an appertaining gas cleaning unit. In this context, the gas cleaning unit is specially configured for removing oxygen from the gas flow.

In order to achieve a high operational reliability of the filling station and particularly of the electrolysis unit used therein, the contacting disk of one or of each membrane of the electrolysis unit is preferably electrically connected to an analyzer that determines the decay time of a voltage signal at this membrane when the current supply to a membrane is switched off. This is based on the insight that an operational failure of a membrane electrolytic cell can frequently be traced back to damage to its membrane, for example, as a result of hole formation. Such damage to a membrane due to hole formation can be detected especially easily by measuring at the membrane the course over time of the voltage that drops after the current supply has been switched off. This is because, in such a case, the membrane electrolytic cell to be examined should briefly behave like a fuel cell since there are still residues of the previously generated hydrogen or oxygen on both sides of the membrane. Therefore, if the membrane is intact, the voltage that drops at the membrane should briefly remain constant before the voltage signal decays. In contrast, if the membrane is damaged, the decay of the voltage signal sets in relatively sooner. Consequently, by determining the decay time of the voltage signal, a conclusion can be drawn about the condition of the membrane. Thus, a defective membrane electrolytic cell can be identified in a particularly simple manner.

In order to attain a high production rate of the electrolysis unit on the one hand, and a long service life of the electrolysis unit on the other hand, along with correspondingly little maintenance work, the membrane of each membrane electrolytic cell advantageously has a contact layer made of platinum as the cathode and a contact layer made of iridium as the anode.

In order to ensure a high quality of the hydrogen supplied by the service station, in an advantageous embodiment, the gas cleaning unit has a water separator and a dryer system connected in series with the latter on the gas flow side. Thus, any entrained residual water that might still be present in the generated gas flow can be separated from the gas flow. These dryers are advantageously configured for regeneration by back-washing, so that the operational and maintenance work can be kept especially simple, even in the case of “spent” active dryer components. For this purpose, in another advantageous embodiment, the dryer system comprises at least two dryers connected in parallel on the gas flow side, whereby each dryer is installed in a main gas line group as well as in a branch line group through which the flow can move in the opposite direction from that in the main gas line group.

The advantages achieved with the present invention consist especially in that, through the use of the contacting disks, especially the support mats, the requirements for a reliable generation of even relatively large quantities of hydrogen can be met in an advantageous manner. On the one hand, the contacting disks, due to their high porosity, allow exposure of each membrane over a large surface area to the necessary media, whereby on the other hand, with reliable electrical contacting over a large surface area, a reliable mechanical support of the membranes can be effectuated. This allows an enlargement of the active membrane surface area to a great extent so that, as a result of the available, relatively large active surface area, a correspondingly high production rate of hydrogen can be achieved. Therefore, through the combination of such an electrolysis unit with the other components, such as especially the gas cleaning installation, a service station can be provided which, with the relatively high specifications, allows a reliable and widespread network that can supply hydrogen as a possible mobile fuel for motor vehicles.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will be explained in greater depth with reference to the drawings, in which: [0020]
FIG. 1 shows a service station for a motor vehicle; [0021]
FIG. 2 shows a gas cleaning unit of the service station according to FIG. 1; [0022]
FIG. 3 shows an electrolysis unit in a longitudinal section; [0023]
FIG. 4 shows a section from FIG. 3 in an enlarged view; [0024]
FIG. 5 shows the electrolysis unit according to FIG. 3 in a cross section; [0025]
FIG. 6 shows a shut-off valve in a longitudinal section; and [0026]
FIGS. 7[0027] a, 7 b show the shut-off valve according to FIG. 6 in a closed and open position.
The same parts are marked with the same reference numerals in all of the Figures. [0028]

DETAILED DESCRIPTION

The [0029] service station 1 according to FIG. 1 serves to supply a motor vehicle 2 with hydrogen as fuel. For this purpose, there is a storage and filling system 4 that comprises a pumping system 6 for dispensing the fuel. On the fuel side, on the inlet side, the pumping system 6 is connected to a number of storage tanks 8 in which the hydrogen intended to be dispensed as the fuel is kept at a high pressure that is suitable for storage and dispensing.
The storage system [0030] 8, in turn—via a feed line 10 in which a compressor station 12 that is suitable for establishing the high pressure needed in the storage tanks 8 is installed—is connected on the inlet side to a system 14 that serves to generate the hydrogen intended as the fuel.
The [0031] system 14 is configured for generating hydrogen as needed by means of the electrolysis of water to form hydrogen and oxygen. For this purpose, the system 14 comprises a water circulation system 16 in which an electrolysis unit 20 is installed. Here, the electrolysis unit 20 is supplied on the inlet side with water at a suitably selected operating pressure of, for example, 5 to 30 bar, by pumps 22 installed in the water circulation system 1. The electrolysis unit 20 comprises a cathode 24 and an anode 26, which, during operation, are supplied with a suitably selected control voltage. Through the electrolysis of part of the water being fed in, hydrogen is generated at the cathode 24 and oxygen is generated at the anode 26.
The hydrogen generated at the [0032] cathode 24, together with the remaining water, is fed via a drain 28 to a gas/water separator 30. In the gas/water separator 30, which is connected on the gas side with the feed line 10, the entrained hydrogen is separated from the water. Analogously, the anode 26 is connected via a drain 32 to a gas/water separator 34 in which the entrained oxygen is removed from the water flow. On the gas side, the gas/water separator 34 is connected via a drain 36 to a drain system 38 for oxygen. On the water side, the water separators 30, 34 are connected by combined water lines to the inlet side of the pumps 22 so as to form a closed water circulation system 16. As an alternative, two independent water circulation systems could also be provided on the one hand for the cathode side and on the other hand for the anode side. In order to compensate as needed for the water that has been electrolyzed in the electrolysis unit 20, a water supply line group 40 is connected to the water circulation system 16, and a water treatment unit 42 as well as a supply pump 44 are installed in said water supply line group 40. In order to establish adequate operating conditions in the water circulation system 16, it also contains a number of additional functional components such as, for example, a heat exchanger 46, a catalyst arrangement 48 (not necessary with two separate water circulation systems) or a buffer tank 50.
In order to avoid the formation of explosive mixtures in the [0033] feed line 10 before starting up or after switching off the system 14, a purge gas line 51 is connected to the feed line 10. Via this purge gas line 51, a purge gas, especially nitrogen, can be fed into the feed line 10 if needed.
In the embodiment, the motor vehicle [0034] 2 is fitted for operation with fuel cells 52 that can be supplied with fuel via a hydrogen tank 54. Particularly when fuel cells are used for energy conversion, however, special requirements exist in terms of the quality and purity of the supplied hydrogen. In order to reliably comply with these requirements, the service station 1 has a gas cleaning unit 60 on the inlet side in the feed line 10 upstream from the pumping system 6. The gas cleaning unit 60 ensures that the hydrogen provided by the pumping system 6 has a purity, for instance, of 99.99%.
For this purpose, the [0035] gas cleaning system 60 is designed so as to consistently remove oxygen residues or water fractions that might have been entrained in the hydrogen flow. In order to achieve this, the gas cleaning unit 60 installed in the feed line 10, as schematically shown in FIG. 2, comprises a catalytic recombiner 62 in which, by means of a catalyst located there, for example, on the basis of palladium, any oxygen that might have been entrained in the gas flow is systematically recombined with hydrogen to form water. Downstream from the recombiner 62, there is a condenser 64 in which the gas flow that was heated up due to the exothermal reaction in the recombiner 62 is cooled off again. As a result of this cooling off, any moisture that might have been entrained then condenses out.
The condensed-out moisture is subsequently separated in a [0036] condensate trap 66 located downstream from the condenser 64.
In order to further dry the gas flow, downstream from the [0037] condensate trap 66, there is a drying system 68 that comprises essentially two dryers 70, 72 connected in parallel on the gas flow side. On the outlet side, the dryers 70, 72 are connected to the feed line 10 via appertaining outflow lines 74, 76 on the outlet side.
In addition or as an alternative, there could also be a catalytic recombiner installed in the [0038] drain 28 and said catalytic recombiner could be coated with catalytically active material such as, for example, a noble metal, in the area where its surfaces come into contact with the gas flow. This recombiner can already bring about a recombination of any oxygen that might still be entrained with hydrogen in a given gas flow, whereby the water generated in this process is also separated in the gas/water separator 30 that is downstream from this anyway. In this case, a reliable removal of possibly entrained oxygen can be effectuated with especially simple means. If necessary, the recombiner, which can have, for example, a space filled with packings having catalytically active surfaces as a catalytically active zone, can also be combined with a static mixer for thorough mixing of the gas fractions containing hydrogen and oxygen with each other.
The [0039] gas cleaning unit 60 is designed so as to allow a regeneration of the dryers 70, 72 by means of back-flushing as needed. For this purpose, each dryer 70, 72 has an appertaining back-flushing line 78, 80. Therefore, in conjunction with suitable branch lines 82, 84 and a back-flushing line 86, the dryer system 68 can be operated in such a way that one of the dryers 70, 72 is operated in the main flow direction, whereby regeneration gas R flows through the other dryer 72 or 70 in the opposite direction, regenerating it in the process. Thus, the affected dryer 70 or 72 can be regenerated without any interruption in the operation. Naturally, functional switch-over or shut-off valves are mounted at appropriate places in the above-mentioned lines.
All in all, the [0040] service station 1 is designed with an eye towards establishing a widespread supply network to supply vehicles 2 with hydrogen as fuel. For this purpose, especially the production capacity of the service station 1 to provide the requisite hydrogen is dimensioned accordingly high. In order to render this possible, the electrolysis unit 20 is specifically configured for a high production capacity for hydrogen while concurrently having a particularly compact design.
For this purpose, the [0041] electrolysis unit 20, as is shown in the longitudinal section in FIG. 3, is configured as a membrane electrolyzer and comprises a number of membrane electrolytic cells 90 electrically connected in series. In the embodiment according to FIG. 3, five membrane electrolytic cells 90 connected in series are shown; however, any desired number of membrane electrolytic cells 90 can be provided. As can be seen in the enlargement in FIG. 4, each membrane electrolytic cell 90 has a membrane 92 configured in the form of a cation exchanger membrane as an electrolyte for water as the medium to be electrolyzed. The membrane 92 of each membrane electrolytic cell 90, which can especially be configured as a fiber-reinforced PEM membrane of the type available under the description “Nation 424”, is provided on both sides with a contact layer (not shown here). The two contact layers of a membrane 92 serve as electrodes in the electrolysis procedure. In the embodiment, the contact layer of each membrane 92 provided as the cathode is made of platinum. In contrast, the contact layer of each membrane 92 provided as the anode is made primarily of iridium.
On each contact layer of each [0042] membrane 92, there is a contact plate 94. The supply of each membrane 92 with the electrolytic current needed for the electrolysis of the water on the one hand and with the media needed there on the other hand, especially water, is effectuated via the contact plate 94. The membrane electrolytic cells 90 consisting in each case of a membrane 92 and the appertaining contact plates 94 are in a stacked arrangement. Adjacent contact plates 94 can be electrically separated from each other by an insulator plate (not shown here), whereby the series connection of the membrane electrolytic cells 90 is effectuated by an external line system (not shown here). As an alternative, adjacent contact plates 94 of various membrane electrolytic cells 90 can also be directly in electrical contact with each other or can also be constructed in one piece. On the faces 100 of the stack formed by the membrane electrolytic cells 90, there are a number of screws that serve as fastening elements 102 for affixing the membrane electrolytic cells 90 to each other. In addition to that, the inside of each membrane electrolytic cell 90 can have force sensors, for example, strain gauges, that allow monitoring of the forces exerted on the individual components when the fastening elements 102 are affixed. In this manner, an overloading of the components can be avoided.
In order to ensure a high production rate of hydrogen, the [0043] electrolysis unit 20 is designed, on the one hand, for a high current density, particularly on the basis of the material properties of the membranes 92 and, on the other hand, for a generously dimensioned active surface of the membranes 92 with a diameter, for example, of 390 mm. Particularly in view of such a large dimensioning and of the relatively high operating pressures of about 5 to 30 bar that are conceivable during the operation of the electrolysis unit 20, the membranes 92, however, are exposed to a relatively high mechanical load during operation. In order to ensure a reliable electric contact of the membranes 92 over a large surface area under these conditions as well, and thus to keep the operational reliability of the electrolysis unit 20 especially high, each membrane 92 is provided with an appertaining contacting disk 104 on both sides, as can be seen in FIG. 4. On the cathode side of the membrane 92, on which the formation of the hydrogen gas can be expected, there is also a buffer element 106 between the membrane 92 and the contacting disk 104; in the embodiment, said buffer element 106 is made of carbonized paper that is about 0.35 mm thick. In each case, the contacting disk 104 is selected in such a way that on the one hand, it ensures a greater electric contact in the current flow direction, that is to say, from each contact plate 94 to the appertaining membrane 92. On the other hand, however, the contacting disk 104 is also selected in such a way that it greatly promotes the media flow from each contact plate 94 to the appertaining membrane 92. Media flow here refers, on the one hand, to the supply of water to the appertaining membrane 92 and, on the other hand, to the removal of the gases generated during the electrolysis, that is to say, especially hydrogen and oxygen. The buffer element 106, i.e. the carbonized paper in the embodiment, is somewhat deformable or compressible under pressure so that, even if there are uneven spots, a uniform contact over a large surface area is ensured.
In order to fulfill the above-mentioned requirements, the contacting [0044] disk 104 has a high electrical conductivity as well as a high porosity of up to about 50%. For this purpose, the contacting disk 104 in the embodiment is configured as a support mat, whereby each support mat is like a felted fabric consisting of a large number of titanium wires laid over each other and pressed together. As an alternative, however, the contacting disk 104 could also be in the form of a suitable metal piece, especially of titanium, that is provided with a large number of fine boreholes. As a result, it is especially ensured that the contacting disk 104 can be configured so as to be plane-parallel, thus promoting a flat and continuous, high-quality contact between each contact plate 94 and the appertaining membrane 92. In the embodiment as a support mat, the resultant elastic deformability makes it possible that, as a result of the fixation with the fastening screws 102, a close contact exists over a large surface area between each contact plate 94 and the appertaining membrane 92.
Each [0045] contact plate 94, as shown in FIG. 5 with reference to the electrolysis device 20 depicted in a cross sectional view, is designed so as to be virtually circular and it has a channel system 110 on its surface facing the appertaining contact layer. The channel system 110 is made up of indentations extending into each contact plate 94 and they are arranged in the form of concentric circle segments on the surface of each contact plate 94. The channel system 110 of each contact plate 94 serves to transport the medium to be electrolyzed to the appertaining membrane 92. For this purpose, the channel system 110 of each contact plate 94 is connected to a feed system for an electrolytic medium. Moreover, a discharge system for gas or for gas mixed with electrolytic medium is connected to the channel system 110 of each contact plate 94.
In order to form a shared feed and discharge system for the requisite electrolytic medium and/or for the gases generated during the electrolysis, the [0046] contact plates 94 are provided with a number of continuous passage openings 112 which completely penetrate the base plane of the appertaining contact plate 94, whereby each opening can be sealed vis-à-vis the environment by means of an encircling groove 114 with an O-ring. The openings 112 are arranged in such a way that, when several contact plates 94 are stacked one after the other to form the electrolysis unit 20, the corresponding openings 112 of each contact plate 94 come to lie behind each other, thus forming in their entirety a channel through which the media can flow in the lengthwise or stacking direction of the electrolysis unit 20.
In this manner, the [0047] openings 112 that are associated with each other form a number of shared feed or discharge channels for media for the entire electrolysis unit 20.
In order to be able to switch individual membrane [0048] electrolytic cells 90 on or off as needed, and thus, for example, to deactivate membrane electrolytic cells 90 that have become defective without having to switch off the entire system, the channel system 110 of each contact plate 94 is connected to the shared feed or discharge channels for media so that the former can be individually shut off. For this purpose, a number of shut-off valves 120 are integrated into each contact plate 94, whereby the integrated construction is selected in such a way that the overall height or the total thickness of the individual contact plates 94 does not change as a result of the shut-off valves 120. The interior of each opening 112 associated with the feed or discharge channel for the media is connected to the channel system 110 of each contact plate 94 via a branch channel 122, whereby the shut-off valve 120 opens or closes the appertaining branch channel 122 as needed.
An embodiment for the shut-off [0049] valve 120 is shown in FIG. 6. The shut-off valve 120 comprises a valve finger 123 that can be moved in its lengthwise direction and that opens up at the end into a widened valve head 124. The valve head 124 corresponds to a valve seat 122 on the end of the appertaining branch channel 126 on the outlet side. The valve finger 123 can be moved in its lengthwise direction by means of a control mechanism 128 that can be actuated, for example, electrically, hydraulically or electro-hydraulically. As can be seen in FIG. 6, all of the components of the shut-off valve 120 are dimensioned so as not to exceed the total prescribed thickness of the contact plate 94. Instead of the shut-off valve 120, a screw could be provided that can be applied with its thread onto the valve seat 126.
In FIG. 7, the shut-off [0050] valve 120 is shown in the closed (FIG. 7a) as well as in the open (FIG. 7b) position. As can be seen in the depiction of FIG. 7a, when the shut-off valve 120 is in the closed position, the valve head 124 is positioned in the appertaining valve seat 126, thus blocking the appertaining branch channel 122. Nevertheless, a cross section albeit reduced—remains free in the opening 112 for the appertaining medium to flow through, so that a systematic switching off of the appertaining branch channel 122 is possible without appreciably influencing the media flow in the actual feed or discharge system. In the open position (FIG. 7b), however, the valve finger 123 is completely retracted so that the medium can freely access the appertaining branch channel 122.
Therefore, by using the shut-off [0051] valves 120 on the medium flow side, individual membrane electrolytic cells 90 can be switched on and off relative to the overall system. As a result, individual membrane electrolytic cells 90 can be selectively checked for proper functioning, for example, by exposing them to a medium under excess pressure. If a membrane electrolytic cell 90 is recognized as being defective in this process, then this cell can be bypassed on the flow side as well as on the medium side.
In the [0052] service station 1 shown in FIG. 1, the electrolysis device 20 has an appertaining analyzer 130 which, as indicated by the arrows 132, is electrically connected to the contact layers of each membrane 92. For this purpose, after the power supply has been switched off, the analyzer 130 is designed so that it can determine the decay time of a voltage signal at this membrane 92. Then, on the basis of the decay time of the voltage signal, the analyzer 130, can provide information about the proper functioning of each membrane 92. Thus, if the membrane 92 is intact, then the appertaining membrane electrolytic cell 90 should still act as a fuel cell for a brief time after the power supply has been switched off, until the gases it had previously released have been transported away. Therefore, if the membrane 92 is intact, then the decaying voltage signal should at first be constant for a brief time before a decay sets in. In contrast, if the membrane 92 is defective, for example, because of hole formation, then the voltage should decay immediately after the power supply has been switched off, and in this manner, the analyzer 130 can distinguish an intact membrane 92 from a defective one.

Claims

What is claimed is:

1. An electrolysis unit including a plurality of membrane electrolytic cells electrically connected in series, each of the plurality of cells comprising:

a membrane;

two contact plates each disposed on an opposing side of the membrane and each including a channel system configured to transport at least one of a water and a gas on a side of the contact plate facing the membrane;

two contacting disks, each disposed between one of the two contact plates and the membrane.

2. The electrolysis unit as recited in claim 1, wherein each of the two contacting disks includes a support mat.

3. The electrolysis unit as recited in claim 1-, wherein each support mat includes a plurality of metal wires laid over each other and pressed together.

4. The electrolysis unit as recited in claim 2, wherein at least one supporting mat includes titanium.

5. The electrolysis unit as recited in claim 1, wherein each channel system includes a connection to a supporting channel and wherein each contact plate includes a shut-off valve for shutting off the connection.

6. The electrolysis unit as recited in claim 5, wherein the supporting channel includes one of a feed channel and a discharge channel.

7. A service station for supplying a motor vehicle with hydrogen as fuel comprising:

a pumping system having an inlet;

a gas cleaning unit; and

an electrolysis unit connected to the pumping unit at the inlet via the gas cleaning unit, wherein the electrolysis unit includes a plurality of membrane electrolytic cells electrically connected in series to each other, and wherein each of the cells includes a membrane, two contact plates, and two contacting disks, wherein each of the contacting plates is disposed on an opposing side of the membrane and includes a channel system configured to transport at least one of a water and a gas on a side of the contact plate facing the membrane, and wherein each contacting disk is disposed between one of the two contact plates and the membrane.

8. The service station as recited in claim 7, further comprising an analyzer electrically connected to at least one of the contacting disks of the electrolysis unit, the analyzer configured to determine a decay time of a voltage signal at the membrane when a power supply to the membrane is switched off.

9. The service station as recited in claim 7 wherein one of the two contact layers of each membrane is a cathode and includes platinum and the other of the two contact layers of each membrane is an anode and includes iridium.

10. The service station as recited in claim 7 wherein the gas cleaning unit includes a water separator and a dryer system connected in series on a gas flow side.

11. The service station as recited in claim 10, wherein the dryer system includes at least two dryers connected in parallel on an inlet side of the cleaning unit.

12. The service station as recited in claim 11 wherein each of the at least two dryers is installed in a main gas line group and in a branch line group, a flow of gas moving through the branch line group in an opposite direction as through the main gas line group.