DE102012018243A1 - Method and system for operating an electrolyzer - Google Patents

Abstract

The invention relates to a method and a system for operating an electrolyzer (1) with at least one electrolyzer cell (2) which at least partially lies in the interior (8) of a container (3) under pressure (p3) and is closed with respect to the interior (8) The electrolytic cell (2) comprises two pole plates (4, 5), between which a membrane electrode unit (6) is arranged such that the electrolytic cell (2) is divided into a first half cell (4a) and an anode a second half cell (5a) forming a cathode is divided. The pole plates (4, 5) are pressed against the membrane electrode assembly (6) by the pressure (p3) in the container (3). When the electrolytic cell (2) is operating in the first half-cell (4a), oxygen is generated and in the second half-cell (5a) hydrogen, which is passed via a respective outlet of the electrolytic cell (2) into a pressure accumulator (9, 10). The pressure (p1) in the first half cell (4a) and the pressure (p2) in the second half cell (4b) are kept essentially the same and the pressure (p3) in the container (3) the pressure (p1, p2) in the Half cells (4a, 5a) tracked.

Description

The present invention relates to a method and a system for operating an electrolyzer with at least one electrolyzer cell which at least partially rests in the interior of a pressurized container and is closed to the interior, the electrolyzer cell comprising two pole plates between which a membrane electrode Unit is arranged such that the electrolyzer cell is divided into a first, an anode-forming half-cell and a second, forming a cathode half-cell, wherein the pole plates are pressed by the pressure in the container against the membrane-electrode assembly, and in operation of the electrolyzer cell In the first half-cell oxygen and in the second half-cell hydrogen is generated, which is passed via in each case one output of the electrolyzer cell in each case a pressure accumulator.

Electrolysis cells of the aforementioned type are known. They convert electrical energy into chemical energy by applying a DC voltage to split distilled water into hydrogen and oxygen between electrodes, which is commonly known as electrolysis. For example, the German patent application describes DE 10 2009 057 494 A1 a device with a plurality of individual cells, which form a so-called stack and which can be used as electrolyzer cells.

The membrane-electrode assembly of a Elektrolyseurzelle of the aforementioned type consists of an ion-conductive polymer (PEM - polymer electrolyte membrane), on both sides of each a thin, porous and electrically conductive layer is applied. These layers form the electrodes. During operation, a DC voltage of at least 1.23 V is applied between the electrodes, so that one electrode acts as an anode and the other as a cathode. This means that the ion-conducting polymer is between the electrodes, with the membrane separating the electrolyzer cell into two half-cells. Each of the two pole plates surrounds the membrane electrode facing it, d. H. Electrode-forming layer on the membrane. The membrane is gas-tight and proton-permeable when wet. In most cases, the layers are additionally provided with a catalyst, it being possible to use platinum on the cathode side and noble metals such as iridium, ruthenium, platinum or metal oxides of the metals mentioned on the anode side.

For a better supply and removal of hydrogen and oxygen, porous, electrically conductive layers, also referred to as diffusion layers, can lie between the pole plates and the membrane electrodes. In this case, each half-cell is formed by a pole plate, the surface of the membrane facing this pole plate and the diffusion layer located therebetween. Since said diffusion layers are conductive and abut the respective membrane electrode, they form part of the corresponding electrode. The same applies to the respective pole plate, the z. B. of metal or graphite and in turn rests on the corresponding diffusion layer.

At least on the anode side of the electrolyzer cell water is supplied to the anode in elementary oxygen and positively charged hydrogen ions d. H. Protons is decomposed. The elemental oxygen immediately combines with molecular oxygen, the protons diffuse through the proton-conducting membrane to the cathode, where they first recombine with supplied electrons to form elementary hydrogen, which then combines to form hydrogen molecules.

The reaction equations for this electrochemical process are 2H ₂ O → 4H ⁺ + 4e ^- + 2O on the anode side; 2O → O ₂ and correspondingly on the cathode side 4H ⁺ + 4e ^- → 4H; 4H → 2H ₂ . Consequently, in the two half cells of the electrolyzer cell, oxygen collects in the anode half cell and hydrogen in the cathode half cell. An electrolyzer can thus be used specifically for the production of hydrogen and oxygen.

Essentially, the pressure on the pole plates causes them to be pressed flat against the membrane-electrode assembly, so that the electrical losses are reduced and the electrical contact between the individual layers of the electrolyzer cell is optimal. The pressure on the pole plates significantly affects the efficiency of the electrolysis by reducing the electrical losses.

There are different methods known to realize the necessary surface pressure within the half-cells. For example, two end plates can be used, between which the electrolyzer cell or a stack formed from a plurality of such cells is arranged, and which are clamped together by tie rods or threaded bolts. The two end plates transmit the surface pressure to the intervening electrolyzer cells / electrolyzer cell stack. By using solid end plates, the force introduced selectively at the tie rods can be distributed fairly uniformly over the entire surface of the membrane-electrode assembly, so that this force is pressed largely homogeneously. To increase the uniformity is from the patent application DE 1 930 116 A a technical construction known in which special cavities are provided in which z. B. Gas- or liquid-filled pressure pad are arranged. Also known are cavities which are filled with an incompressible pressure medium or which have special spring arrangements, see for example DE 100 03 528 A1 ,

Furthermore, the compression can also be done hydraulically. In this embodiment, the housing of the electrolyzer forms a pressure vessel in which a pressurized medium, such as a liquid or a gas is filled. The Elektrolyseurzelle lies at least partially in the medium, so that the medium transfers the pressure on the pole plates when building up an overpressure in the pressure vessel. This represents a "hydraulic compression" of the cells and is also in the DE 10 2009 017 779 A1 and DE 10 2009 057 494 A1 described. Such pressure exerted externally on the pole plates then causes a corresponding pressure of the pole plates on the membrane electrode assembly. It is also known to arrange the electrolyzer cell (s) in elastic pockets so that the medium exerts its pressure first on these pockets which attach to the pole plates and then transfer the pressure to the pole plates.

As already stated, the anode side and cathode side of an electrolyzer cell each form a half cell, in which the correspondingly formed gas can be collected, wherein the half cells are separated from each other by the gas-tight polymer membrane of the membrane electrode assembly.

Gases are usually stored and transported in pressure bottles.

For the production of hydrogen and oxygen, each half-cell can be connected to a mechanical compressor which compresses the corresponding gas into a pressure accumulator. The half cell itself remains essentially unpressurized, so as not to damage the sensitive membrane, as otherwise the membrane may crack and fracture. The pressure is accordingly built up only behind the compressor.

In a further embodiment, electrolyzers are known which discharge the oxygen produced in the electrolysis of water without pressure into the atmosphere, so that a low pressure gradient is established across the membrane, which the membrane must withstand. For this purpose, the membrane must have a certain mechanical stability, which is usually achieved by a thicker membrane.

A thicker membrane results in a lower efficiency of the electrolyzer cell as the path the proton must travel through the membrane increases, and thus the membrane resistance, which must be compensated by raising the electrolysis voltage. The efficiency of the overall system for hydrogen and oxygen production is also significantly reduced by the compressor power required for the compression of the gases.

It is an object of the present invention to provide a method and system for operating a PEM electrolyzer that allows for the direct production of hydrogen and oxygen above atmospheric conditions, such that a compressor for compressing the gases to be in a downstream pressure vessel can be omitted, the membrane of the electrolyzer cell is still to be thin.

This object is achieved by a method according to claim 1 and a system according to claim 11. Advantageous developments of the method and the system are specified in the corresponding subclaims.

According to the invention, a method for operating an electrolyzer with at least one electrolyzer cell is proposed which rests at least partially in the interior of a pressurized container and is closed relative to the interior, the electrolyzer cell comprising two pole plates, between which a membrane-electrode assembly is arranged in that the electrolyzer cell is divided into a first half-cell forming an anode and a second half-cell forming a cathode, the pole plates being pressed against the membrane-electrode assembly by the pressure in the container, and in operation the electrolyzer cell in the first half-cell Oxygen and in the second half-cell hydrogen is generated, which is passed via in each case one output of the electrolyzer cell in each case a pressure accumulator, wherein the pressure in the first half-cell and the pressure in the second half-cell are kept substantially the same, and the pressure in the containerPressure is tracked in the half-cells.

In this case, the pressure is tracked in particular proportionally so that a pressure difference between the interior and the half-cells necessary for pressing the pole plates against the membrane-electrode assembly is kept essentially constant.

This method allows the use of an electrolyzer for oxygen and hydrogen production, with direct storage of the hydrogen and oxygen without an additional compressor for compression is possible because the half-cells put the two gases directly ready above the atmospheric pressure. If the two half cells of the electrolyzer cell are connected to corresponding pressure accumulators, they continuously supply gas, the gas already generated being increasingly compressed as gas generation progresses, since the total volume consisting of a half cell, the corresponding line to the pressure accumulator and the pressure accumulator itself remains constant. This automatically results in a compression of the hydrogen and the oxygen in the respective pressure accumulator. The electrolyzer according to the invention can thus supply directly compressed oxygen and hydrogen.

Since the pressure in the two half-cells is kept at the same level, there is no or only a low pressure difference due to the adjustment over the membrane of the electrolysis cell. That is, a thinner membrane than usual for high pressure electrolyzers can be selected, resulting in reducing the membrane resistance. By using a thin membrane is thus possible to operate the electrolyzer cell with a higher efficiency.

The equalization of the pressures in the half-cells can in principle be carried out by control technology, the pressures being measured and the pressure being regulated in accordance with the other pressure serving as setpoint specification.

This can be done, for example, by a volume-displacing actuator which changes the volume of a half-cell, the connecting lines connected thereto and / or the pressure accumulator. Alternatively, the volume of both half-cells can simultaneously be oppositely influenced.

Too high a pressure in one of the half-cells are further degraded by the fact that the corresponding gas is discharged in a controlled manner, for example in the atmosphere or another connected pressure vessel. This is a particularly simple solution, in particular for the oxygen produced, to bring about a pressure equalization, provided that the pressure in the first half cell is greater than the pressure in the second half cell. Because in the gas extraction process by electrolysis of hydrogen is the valuable gas.

In another embodiment variant, the pressures in the half-cells can be matched to one another by means of an external hydraulic pressure compensation device, into which the outlets of the electrolyzer cell flow. Hereby, a quick pressure equalization can be achieved so that dynamic pressure changes such as pressure pulses and rapid pressure fluctuations on one side, for example as a result of a valve position change, can be compensated immediately. The load on the membrane is thereby reduced.

For example, the pressure compensating means may be a container having two spaces separated by an elastic membrane. A line coming from the one half cell opens into the one room area, while a line coming from the other half cell opens into the other room area. Through the membrane pressure equalization between the space areas and thus between the half cells is achieved immediately. Pressure pulses are intercepted. Furthermore, the hydraulic pressure compensation device has the advantage that can be dispensed with an electronic control with sensors, actuators and control lines. However, it may also be provided that the automatic pressure compensation device and the electronic pressure control are used in parallel.

Preferably, the electrolyzer cell can be operated at a pressure between 0 bar and 300 bar. Since the two process gases are separated by the membrane, the pressure can theoretically be increased on both sides with adequate pressure maintenance and monitoring. Physically, however, the housing components and connection points of the pole plates and cables are a limiting factor.

In general, to increase the storage density of the hydrogen consuming to compress. An additional compression stage, which is usually downstream of an electrolyzer, increases the system losses, which is undesirable. These losses are significant and amount to about 10% in relation to the remaining system components in the case of a compaction to 200 bar. Due to the fact that according to the invention the electrolyzer can be operated at a higher system pressure, in particular up to 300 bar, an additional compression stage is no longer necessary or can be considerably smaller.

For an operating pressure of the order of 20 bar and more, increased demands have to be placed on all system components. For example, the piping can be done with stainless steel pipes. Likewise, the cell housing of the electrolyzer cell, the pump for the supply of water, any valves, sensors and pressure vessels must also meet the increased pressure requirements, in particular with regard to the respective connection points.

In the electrolyzer according to the invention, the half-cells, ie the pole plates, are compressed by the pressure in the container surrounding the electrolyzer cell. If the pressure in the electrolyzer cell, ie in the two half cells, increases, the pressure difference between the cell is reduced and the container interior, so that the compression is no longer guaranteed. The pressure difference can even become negative, causing the cell to inflate into the container. The compression and thus the functionality of the cell are no longer given. For this reason, a proportional tracking of the pressure in the container is proposed according to the invention, so that the container pressure is always higher than the cell internal pressure.

Thus, the pressure in the housing can be increased as the pressure within the half-cells increases. Further, the pressure in the housing can be reduced when the pressure within the half-cells decreases. In particular, this tracking can be carried out such that always a constant, preferably predetermined pressure difference between the pressure in the container and the pressure between the half-cells or at least a predetermined pressure difference range is maintained.

The tracking of the pressure in the container is possible in various ways, for example by changing the internal volume of the container or by introducing further medium into the container, so that a stronger compression of the medium in the container (gas or liquid) takes place, the pressure on the electrolyzer cell transfers.

According to an advantageous embodiment, the pressure tracking in the container can be achieved by changing its internal volume. For example, the volume of the interior can be reduced as the pressure in the half cells increases. Accordingly, the volume of the internal space can be increased as the pressure in the half-cells decreases. It is of particular advantage if the pressure in the container is tracked regulated, with a predetermined pressure difference between the interior of the container and the half-cells should be maintained as the desired value. The pressure difference is required for the compression of the cell. The control can be done by measuring the internal pressure of the container by means of at least one sensor.

The change in the volume of the interior of the housing can be changed by means of a mechanical adjusting means, which is preferably controlled by a control. Such an actuator may be, for example, a motor-operated screw or a piston, which is moved into the interior of the container by its outer wall and thereby reduces the internal volume of the container.

Alternatively or additionally, a volume change can be made as follows. The container may have an auxiliary chamber, which is connected to the interior of the container via an opening closed by an elastic membrane element. The interior of the secondary chamber is communicatively connected to one of the half cells so that, during operation of the electrolyzer, gas is introduced from the corresponding half cell into this secondary chamber becomes. Thus, the pressure in the secondary chamber corresponds to the pressure in this half-cell. If the pressure in the half-cell increases, the pressure in the secondary chamber also increases. This causes the membrane element to expand into the interior of the container; the volume of the secondary chamber increases, whereas the volume in the interior of the container is reduced. As a result, the medium in the container is compressed more and the pressure in the container increases. Since the pressure in the interior of the container must be greater than the pressure in the half-cells to compress the half-cells, it is necessary to bias the membrane element. This can be achieved by a bias generating means, for example a spring pressing against the membrane element in the direction of the interior of the container. In this case, the bias is determined by the spring constant. However, it can also be used a means that generates a variable bias. For example, a pin pushing against the diaphragm can be used here, which is held movably in a guide and, together with the guide, is supported on a wall of the secondary chamber, in particular on the wall opposite the membrane element.

Preferably, the auxiliary chamber is connected to the first half-cell. Since both oxygen and water escape from this, which can be fed back to the electrolysis process as starting material, the secondary chamber can simultaneously serve as a collecting container for this water and media separation (oxygen, water) and as an intermediate container between a water reservoir and the electrolyzer. So can be pumped from this reservoir water in the secondary chamber and pumped from the secondary chamber water in the first half-cell. Alternatively, the secondary chamber may be connected to the second half cell. Since only hydrogen escapes from this, the secondary chamber can also serve as a tank.

According to the invention, a system for operating an electrolyzer with at least one electrolyzer cell is proposed, which lies at least partially in the interior of a pressurized container and comprises two pole plates, between which a membrane-electrode assembly is arranged such that the electrolyzer cell is transformed into a first, an anode forming half-cell and a second, forming a cathode half-cell is divided, wherein the pole plates are pressed by the pressure in the container against the membrane-electrode assembly, and in operation of the electrolyzer cell in the A half-cell oxygen and hydrogen in the other half-cell can be generated, which in each case via an output of the half-cells in each pressure accumulator is introduced, and wherein the device further comprises means for equalizing the pressure in or between the half-cells and means for tracking the pressure in the interior of the container as a function of the pressure in the half-cells.

Preferably, the means for equalizing the pressure between the half-cells are formed by a pressure equalizing tank having two space portions, each opening a pressure line from the pole plates into one of the space portions, and the space portions are separated from each other by an elastic membrane.

Further, the means for tracking the pressure in the container at least a first means for detecting the pressure in one of the half-cells, at least a second means for detecting the pressure in the interior of the container, at least one adjusting means for changing the volume of the interior of the container and thus the Pressure in a half-cell, and a control device for adjusting the actuating means in dependence on the pressure difference between the pressure in the container and the pressure in the half-cells include.

Furthermore, as already explained with regard to the method according to the invention, the container may have an auxiliary chamber which has an opening to the container interior, which is closed by an elastic membrane element which can move into the container interior as a result of its extensibility. The secondary chamber is communicatively connected to one of the half cells, so that gas of this half cell can be introduced into the secondary chamber. Furthermore, a means for generating a bias against the membrane may be present to obtain a higher pressure in the container than in the secondary chamber during normal operation of the electrolyzer.

Further features and advantages of the invention will be explained below with reference to three specific embodiments and the accompanying figures. The same reference numerals mean the same or at least functionally identical parts.

Show it:

1 : Schematic representation of the structure of an electrolyzer according to the invention

2 : Schematic representation of the structure of a system according to the invention with electrolyzer

3 : Schematic representation of the structure of a system according to the invention with electrolyzer, integrated gas collecting container and pressure tracking.

1 shows a schematic representation of an electrolyzer 1 comprehensively by way of example an electrolyzer cell 2 in the interior 8th a pressurized container 3 completely inserted. However, there may also be two, three or more such electrolyzer cells 2 in the container 3 be arranged, with the individual cells 2 then electrical are connected in parallel or in series and the supply and disposal ports are parallel. Furthermore, it is also possible that the cell 2 in the container only partially rests, wherein at least the active part of the cell 2 ie the part in which the electrolysis takes place in the container 3 protrudes.

The electrolyzer cell 2 is a closed system that comes from a housing 11 is formed, in which the active component of the cell 2 einliegen. The active components comprise two pole plates 4 . 5 of which the first pole plate 4 forming part of the anode and the second pole plate 5 forms a part of the cathode. Between the pole plates 4 . 5 is a gas-tight, proton-permeable membrane-electrode unit 6 (PEM, polymer electrolyte membrane) arranged. This consists of a polymer membrane, which is coated on both sides with an electrically conductive layer, which also acts as an electrode. Furthermore, lies between this PEM 6 and the corresponding pole plate 4 . 5 each an electrically conductive diffusion layer 7 , It should be noted that the two diffusion layers 7 can consist of different materials. Contrary to the purely illustrative representation in 1 lie the pole plates 4 . 5 at the diffusion layers 7 which in turn on the membrane electrode assembly 6 issue. Electrically, a pole plate, a diffusion layer and the layer facing it on the polymer membrane consequently each form a unit, ie an electrode wherein the electrodes are separated from each other only by the electrically insulating polymer membrane.

At the same time, the polymer membrane divides the membrane-electrode assembly 6 the electrolyzer cell in a first, the anode forming half cell 4a and a second half-cell forming the cathode 5a , The first half cell 4a consists of the first pole plate 4 , the facing half of the membrane electrode assembly 6 and the diffusion layer lying between them 7 whereas the second half cell 5a from the second pole plate 5 , the facing half of the membrane electrode assembly 6 and the diffusion layer lying between them 7 consists. The introduction of the current is via the pole plates 4 . 5 even, with sufficiently high conductivity of the pole plates 4 . 5 or over to the pole plates 4 . 5 flat fitting plates, z. Gilded. Achieved copper plates.

The pole plates 4 . 5 have a channel structure, not shown, in which collects the corresponding gas and through which the gas is passed to an output. About these outputs is the electrolyzer, each with a pressure vessel 9 . 10 connected, see 2 , However, such a channel structure is not mandatory. Alternatively, the pole plates may have channel-like depressions on their sides facing the gas diffusion layer, through which the gases are conducted upwards. Such a structure can be used, for example, when the gas diffusion layers consist of a tile.

In the container 3 , which is filled with liquid, is an internal pressure p3 through which the pole plates 4 . 5 against the membrane-electrode unit 6 be pressed, or initially against the gas diffusion layers 7 and these against the membrane, leaving the pole plates 4 . 5 Press indirectly against the membrane. This compression concept represents a hydraulic compression.

The pole plates 4 . 5 can in this embodiment directly a part of the cell wall 11 form so that the pressure p3 in the container 3 is exercised directly on them. At its edge are the pole plates 4 . 5 then electrically isolated from each other and encapsulate the membrane-electrode assembly 6 and the diffusion layers 7 in this way. Alternatively, the cell wall may consist of a flexible plastic, in particular an elastomer, which completely encloses the electrolyzer cell. According to another alternative, an open concept for the pole plates 4 . 5 be used where the area between the pole plates 4 . 5 is open at the top, bottom and sides and in which the pole plates are in an elastic pocket, which is the cell wall 11 So the case of the cell 2 forms. For example, the bag concept used in the DE 10 2009 057 494 A1 is described.

Hydrogen production by means of electrolysis of water requires electrical energy and heat energy for the separation of water. The energy required results from the reaction enthalpy of water at the operating temperature of the electrolyzer 1 , It follows: water + energy → hydrogen + oxygen. The energy is provided in the form of electrical energy, which is then converted into heat energy and chemical energy.

A galvanic cell based on polymer electrolyte membranes is generally divided into two cell halves, of which the pole plates 4 . 5 each form a part. For the electrolysis of water, on one side (anode) water is to be supplied, which is decomposed into oxygen and hydrogen cations and electrons: 2H ₂ O → O ₂ + 4H ⁺ + 4e ^- .

The hydrogen cations pass through the membrane 6 on the other side, the cathode, transports and recombines with externally supplied electrons to form hydrogen: 4H ⁺ + 4e ^- → 2H ₂ .

A cell voltage on the pole plates 4 . 5 of the electrolyzer 1 at the connections 20 is created (see 2 ) results from the minimum required cell voltage, which is derived from the principles of thermodynamics, and the overvoltages (including activation overvoltage, overvoltage due to ohmic resistances). The part of the overvoltage that is due to the membrane electrode unit used 6 is directly dependent on the membrane thickness. The following equation illustrates that a lower overvoltage due to membrane resistance requires a lower cell voltage. E = E _eq + η _act + η _{R_el} + η _{R_Mem} , where E is the cell voltage, E _{eq is} the required cell voltage under the prevailing ambient conditions, η _{act is} the activation overvoltage and η _{R_el is} the overvoltage through ohmic resistors and η _{R_Mem is} the overvoltage through the membrane resistor.

When operating a Elektrolyseurzelle the result is to create a higher voltage than a minimum is mathematically necessary for the decomposition of water. The overvoltages resulting from the internal losses can be significantly reduced by the inventive measures in comparison to conventional designs. In this case, the optimum compression pressure, in which the ohmic contact resistance is minimized and nevertheless sufficient media supply and removal is ensured, reduces the ohmic losses in the cell, and the pressure reduction in the two half cells allows the use of a thin membrane with reduced membrane resistance.

By exploiting the principles of Nernst, it is possible to adjust the outlet pressure of the gases produced within the framework of the mechanical properties of the components. This principle of isothermal compression has energy advantages over mechanical compression.

In operation of the electrolyzer cell 2 to 1 becomes in the second half-cell according to the above statements 5a (Cathode) hydrogen H ₂ and in the first half-cell 4a (Anode) oxygen O ₂ generated, each in an accumulator ( 9 . 10 ) is directed (see 2 ). Together with the oxygen O ₂ , undissolved water H ₂ O also comes out of the one half cell 4a out.

2 shows a system according to the invention, in which the electrolyzer 1 according to 1 is integrated.

About a pump 15 becomes the electrolyzer cell 2 Water, which is split by this into hydrogen H ₂ and oxygen O ₂ . The resulting hydrogen H ₂ collects in the channel structure of the cathode pole plate, not shown 5 , which at its exit over an appropriate piping with a pressure vessel 9 , For example, a conventional gas cylinder, is in communication, in which the hydrogen H _{2 is} introduced. In the said piping is a shut-off valve 16b , which is usually part of the gas cylinder fitting. In the second half cell 5a , the piping and the gas cylinder prevails the pressure p2, which is via a sensor 17b is measured.

Furthermore, the resulting oxygen O ₂ accumulates in a channel structure, not shown, of the anode pole plate 4 , which also has at its output via a corresponding piping to a container. In this case, not only the resulting oxygen O ₂ but also the unused water H ₂ O is conveyed through this channel structure. Behind the exit therefore follows a media separation in a container 30 in which the water 14 is collected. As in 2 shown, can from this container 30 the water 14 through the pump 15 the electrolyzer cell 2 be made available again. The oxygen O ₂ accumulates in the container 30 above the water and is via a valve 16a in another pressure vessel 10 introduced, which can also be a conventional gas cylinder here, for example. In the first half cell 4a , the piping to the tank 30 , in the upper part of the container 30 as well as in the gas bottle 10 the pressure p1 prevails, which via a first sensor 17a is monitored. From a separate storage container 21 will water over a valve 16c in the container 30 directed.

According to the invention, the pressure p1 is now in the first half-cell 4a and the pressure p2 in the second half cell 5a essentially the same. For this purpose, the container is used 30 as a surge tank. To achieve pressure equalization, the container is 30 in an upper room area 30a and a lower room area 30b divided, this separation by an elastic membrane 13 is reached. The upper room area 30a is communicating with the first half cell 4a , the lower room area 30b is communicating with the second half cell 5a connected so that in the upper room area 30a the pressure p1 in the anode half cell 4a and in the lower room area 30b the pressure p2 in the cathode half cell 5a is present.

Alternative to the elastic membrane 13 can also be used a balloon, as is commonly known in heating systems as hydraulic compensation. If the pressure p2, for example, in the cathode half-cell 5a soar, leaving the membrane-electrode unit 6 between the pole plates 4 . 5 to the anode pole plate 4 is pressed, the membrane would be the same 13 in the surge tank 30 in the upper room area 30a be pressed so that the pressure p1 in the upper room area 30a and thus in the anode half cell 4a is increased. As a result, a bulge of the membrane-electrode unit 6 to the anode pole plate 4 counteracted.

In the embodiment according to 2 In addition, the pressure p3 in the container 3 depending on the leveled pressure p1, p2 in the half cells 4a . 5a tracked by a control engineering pressure control. This is done as follows:
For the functionality and high efficiency of the electrolyzer cell 2 it is necessary that the half cells 4a . 5a be pressed, ie the pole plates 4 . 5 against the membrane-electrode unit 6 to press. This is done by the pressure p3 in which the electrolyzer cell 2 surrounding container 3 is always higher than the pressure p1, p2 in the half cells 4a . 5a is. Otherwise, the pole plates would 4 . 5 from the membrane-electrode unit 6 loosen and inflate into the container. If the pressure p1, p2 in the half cells increases 4a . 5a must therefore the pressure p3 in the container 3 be tracked. This is done by control technology via a corresponding pressure control unit 19 ,

At the same time, the pressure p3 in the interior becomes 8th of the container 3 by means of a sensor 17c and one of the pressures p1, p2 in the half cells 4a . 5b by means of at least one further sensor 17a and or 17b measured. Since the pressures p1, p2 in the half cells 4a . 5a are held equal, it is not necessary to measure both pressures p1, p2. Nevertheless, for security reasons, the pressure in the corresponding other half cell can be monitored. As in 2 shown, the pressure control 19 the measured pressure p2 in the cathode half cell 5a and the measured pressure p3 in the container interior 8th fed. Depending on the difference between these pressures p2, p3 performs the pressure control 19 the pressure p3 in the tank 3 to, so that a predetermined pressure difference .DELTA.p is maintained or at least a pressure difference range is maintained.

The change in the pressure p3 in the container is made by an actuating means 12 that of the pressure control 19 is controlled. The adjusting agent 12 acts as a volume displacement system and includes a servomotor, a piston or a screw in the interior 8th of the container 3 moved in and thus reduces its volume. This leads to an increase in pressure. The screw is partly in a bore in the container wall and is guided by a thread of the bore, being partially in the container 3 protrudes. Will this screw in the interior 8th of the container 3 screwed into it, its volume decreases and the internal pressure p3 increases. The screw is operated by the servo motor electric motor, wherein the electric motor adjusts the position of the screw. The appropriate control is via electrical connections 18 , please refer 1 ,

3 shows a further embodiment of the system according to the invention. The container 3 here has a side chamber 40 on top of one of an elastic membrane element 42 closed opening 41 with the interior 8th of the container 3 connected is. The membrane element 42 gets into the interior 8th of the container 3 pushed. The interior of the side chamber 40 is communicating with the first half cells 4a connected. In operation of the electrolyzer 1 becomes oxygen from the first half cell 4a in the side chamber 40 initiated. This corresponds to the pressure p4 in the secondary chamber 40 the pressure p1 in this half cell 4a , Now increases the pressure p1 in the half cell 4a , the pressure p4 in the secondary chamber also increases 40 , This causes the membrane element 42 in the interior 8th of the container 3 expands. The volume of the secondary chamber 40 increases thereby, whereas the volume in the interior 8th of the container 3 is reduced. As a result, the medium in the container interior 8th more compressed and the pressure p3 in the container interior 8th increases. Since this pressure p3 against the pressure p1, p2 in the half cells 4a . 5a must be larger, around the half-cells 4a . 5a it is necessary to press the membrane element 42 pretension. This is done by a compression spring 43 with a corresponding spring force FF, which is at the membrane element 42 opposite inner wall of the secondary chamber 40 supports and the membrane element 42 in the direction of the interior 8th of the container 3 suppressed. On the membrane element 42 then lies on one side in the secondary chamber 40 the power of the spring 43 and the pressure p4, which corresponds to the pressure p1, on and on the other side in the interior 8th of the container 3 the pressure p3 on. It is FF + p4 · A1 = p3 · A2, where A1, the side chamber side surface of the membrane element 42 and A2, the area of the membrane element 42 is, on which the pressure p3 acts. The two surfaces are in 3 almost the same size.

The secondary chamber 40 is with the first half cell 4a connected. Since both oxygen O ₂ and water H ₂ O exit from this, which is fed back into the electrolysis process as starting material, the secondary chamber serves 40 at the same time as a collecting container for this water and for separating media (oxygen, water) as well as an intermediate container between the water reservoir 21 and the electrolyzer cell 2 , It is from this reservoir 21 Water in the side chamber 40 pumped and from the side chamber 40 Water in the first half cell 4a pumped.

In the manner described above, the hydrogen H ₂ can be provided at a pressure level above atmospheric conditions without using an additional mechanical compressor stage. By the pressure balance between the half cells 4a . 5a Thinner membranes with more favorable properties for water electrolysis can be used. In addition, the integrated pressing of the electrolyzer cell makes it possible to increase the gas pressure of the generated process gases almost arbitrarily. A downstream additional mechanical compression of the gases can be omitted.

In accordance with the invention, therefore, the pressure p1 of the anode side is initially determined via an intelligent, cascaded control 4a and the pressure p2 of the cathode side 5a monitored and regulated, so that in both cell halves 4a . 5a the same pressure is set, p1 = p2. Based on this, the pressure p3 in the pressure vessel 3 that the single cells 4a . 5a encloses, with an adjusting agent 12 tracked, which is designed as a regulated mechanical volume displacement system. The tracking takes place in such a way that a defined predetermined pressure gradient Δp is set according to Δp = p3-p1 or Δp = p3-p2, if p1 = p2. This will ensure that the cell 2 continues to be squeezed when the pressure p1, p2 in the half-cells 4a . 5a increases. The pressure gradient or differential pressure Ap is to be selected (depending on the components used up to 10 bar), that optimum pressing of the pole plates 4 . 5 with the membrane-electrode unit 6 over the entire load and operating range of the electrolyzer 1 is guaranteed.

With this principle it is possible to use the electrolyser 1 Achieve achievable process gas pressure as desired. Limiting factor here is the mechanical stability of the pressure vessel 3 , the piping, the pump 15 , the pressure compensation device 30 and the pressure vessel 10 and 9 ,

• 1. Die über der Zellmembran anliegende Druckdifferenz zwischen Anode und Kathode, die so gering wie möglich gehalten wird, ermöglicht den Einsatz dünnerer Membranen als allgemein bei Elektrolyseuren üblich, die Wasserstoff bei einem Druckniveau oberhalb atmosphärischer Bedingungen bereitstellen. Die Membranstärke d ist neben der Stromdichte i und dem Wassergehalt der Membran λ maßgeblich für die parasitären Überspannungen und damit einhergehenden Verluste verantwortlich (η_CCM = η(d, λ, i)). λ ist ein Maß für die Befeuchtung der Membran. Bei der beschriebenen Ausführungsvariante ist eine Seite der Zelle mit Wasser geflutet und damit die Befeuchtung der Membran stets 100%.
• 2. Durchgeführte Beispielrechnungen zeigen, dass gerade bei kleinen Baugrößen bei der hier beschriebenen Kompressionstechnik höhere Wirkungsgrade erzielt werden können als bei der Verwendung von nachgeschalteten, mechanischen Kompressoren.
• 3. Der erfindungsgemäße Elektrolyseur besitzt eine kompakte Bauweise, da die Elektrolyseurzelle und das Stellmittel zur Erhöhung des Drucks im Behälter gemeinsam in diesem Behälter integriert sind.
• 4. Es wird kein Kompressor benötigt.
• 5. Die Anlage kann geräuschlos betrieben werden.
• 6. Druckspeicher die für unterschiedliche Drücke ausgelegt sind können direkt betankt werden.

The method according to the invention of increasing the pressure in direct combination with the process gas pressures affords the following advantages over conventional electrolyzer concepts with additionally connected mechanical and / or chemical compression stages:

• 1. The pressure differential across the cell membrane between anode and cathode, which is kept as low as possible, allows the use of thinner membranes than is common in electrolysers that provide hydrogen at a pressure level above atmospheric conditions. The membrane thickness d is in addition to the current density i and the water content of the membrane λ significantly responsible for the parasitic overvoltages and associated losses (η _CCM = η (d, λ, i)). λ is a measure of the humidification of the membrane. In the described embodiment, one side of the cell is flooded with water and thus the humidification of the membrane is always 100%.
• 2. Example calculations performed show that higher efficiency can be achieved with the compression technique described here, especially with small sizes, than with the use of downstream mechanical compressors.
• 3. The electrolyzer according to the invention has a compact design, since the Elektrolyseurzelle and the adjusting means for increasing the pressure in the container are integrated together in this container.
• 4. No compressor is needed.
• 5. The system can be operated noiselessly.
• 6. Accumulators are designed for different pressures can be refueled directly.

LIST OF REFERENCE NUMBERS

1

electrolyzer

2

Elektrolyseurzelle

3

Tank / pressure vessel

4

Pole plate, anode

4a

first half cell, anode side

5

Pole plate, cathode

5a

first half cell, anode side

6

Membrane-electrode assembly

7

Gas diffusion layer

8th

Interior of the container 3

9

Pressure accumulator for hydrogen

10

Pressure accumulator for oxygen

11

elastic sheathing of the electrolyzer cell

12

actuating means

13

membrane

14

water

15

pump

16a, 16b, 16c

valves

17a, 17b, 17c

pressure sensors

18

electrical connections of the actuator

19

Pressure control unit

20

electrical connections of the electrolyzer

21

reservoir

30

Pressure compensator

30a

Upper space area of the pressure compensation device

30b

lower area of the pressure compensation device

40

secondary chamber

41

opening

42

membrane element

43

Biasing means, spring

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102009057494 A1 [0002, 0009, 0050]
• DE 1930116 A [0008]
• DE 10003528 A1 [0008]
• DE 102009017779 A1 [0009]

Claims (18)

Method for operating an electrolyzer ( 1 ) with at least one electrolyzer cell ( 2 ) in the interior ( 8th ) of a container under pressure (p3) ( 3 ) at least partially rests and with respect to the interior ( 8th ), the electrolyzer cell ( 2 ) two pole plates ( 4 . 5 ) between which a membrane-electrode unit ( 6 ) is arranged such that the electrolyzer cell ( 2 ) in a first, an anode forming half-cell ( 4a ) and a second, a cathode forming half-cell ( 5a ), the pole plates ( 4 . 5 ) by the pressure (p3) in the container ( 3 ) against the membrane electrode assembly ( 6 ) and in operation of the electrolyzer cell ( 2 ) in the first half cell ( 4a ) Oxygen and in the second half cell ( 5a ) Hydrogen is generated, which in each case via an outlet of the electrolyzer cell ( 2 ) in each case an accumulator ( 9 . 10 ), characterized in that the pressure (p1) in the first half cell ( 4a ) and the pressure (p2) in the second half cell ( 4b ) are kept substantially the same, and that the pressure (p3) in the container ( 3 ) the pressure (p1, p2) in the half cells ( 4a . 5a ) is tracked. Method according to claim 1, characterized in that the equalization of the pressures (p1, p2) in the half cells ( 4a . 5a ) is carried out by control technology, wherein the pressures (p1, p2) are measured and the one pressure is adjusted in accordance with the other pressure serving as setpoint specification. A method according to claim 1 or 2, characterized in that the pressures (p1, p2) (in the half-cell 4a . 5a ) by means of an external hydraulic pressure compensation device ( 30 ), with which the outputs of the electrolyzer cell ( 2 ) communicate, be aligned. Method according to one of the preceding claims, characterized in that the pressure (p3) in the container ( 3 ) is increased when the pressure (p1, p2) in the half cells ( 4a . 5a ) increases and / or is reduced when the pressure (p1, p2) in the half-cells ( 4a . 5a ) sinks. Method according to one of the preceding claims, characterized in that the pressure (p3) in the container ( 3 ) by changing the volume of its interior ( 8th ) is changed. Method according to one of the preceding claims, characterized in that a pressure equalization between the half-cells ( 4a . 5a ) is achieved by reducing a higher pressure in the one half-cell by controlled discharge of gas from this half-cell. Method according to one of the preceding claims, characterized in that the pressure (p3) in the container ( 3 ) by changing the amount in the container ( 3 ) existing medium is set. Method according to one of the preceding claims, characterized in that the pressure (p3) in the container ( 3 ) is controlled proportionally such that a predetermined pressure difference (Δp) between the pressure (p3) in the container ( 3 ) and the pressure (p1, p2) in the half cells ( 4a . 5a ) is maintained, or that a predetermined pressure difference range is maintained. Method according to one of the preceding claims, characterized in that the hydrogen and the oxygen without an additional compressor in the corresponding pressure accumulator ( 9 . 10 ). Method according to one of claims 5 to 9, characterized in that the volume of the interior ( 8th ) of the container ( 3 ) by means of a volume-displacing mechanical actuator ( 12 ) is set. System for operating an electrolyzer ( 1 ) with at least one electrolyzer cell ( 2 ) in the interior ( 8th ) of a container under pressure (p3) ( 3 ) at least partially rests and two pole plates ( 4 . 5 ) between which a membrane-electrode unit ( 6 ) is arranged such that the electrolyzer cell ( 2 ) in a first, an anode forming half-cell ( 4a ) and a second, a cathode forming half-cell ( 5a ), the pole plates ( 4 . 5 ) by the pressure (p3) in the container ( 3 ) against the membrane electrode assembly ( 6 ) and in operation of the electrolyzer cell ( 2 ) in the first half cell ( 4a ) Oxygen and in the second half cell ( 5a ) Hydrogen is generated, which in each case via an output of the half-cells ( 4a . 5a ) in each case an accumulator ( 9 . 10 ), characterized by - means ( 30 ) for equalizing the pressure (p1, p2) in the half cells ( 4a . 5a ) and - means ( 12 . 17a . 17b . 17c ; 40 . 42 ) for tracking the pressure (p3) in the housing ( 3 ) as a function of the pressure (p1, p2) in at least one of the half cells ( 4a . 5a ). System according to claim 11, characterized in that the means ( 30 ) for equalizing the pressure (p1, p2) between the half-cells ( 4a . 5a ) through a surge tank ( 30 ) with two spatial areas ( 30a . 30b ) are formed, wherein in each case a pressure line from the half-cells ( 4a . 5a ) in one of the room areas ( 30a . 30b ) and the room areas ( 30a . 30b ) by an elastic membrane ( 13 ) are separated from each other. System according to claim 11 or 12, characterized in that the means for tracking the pressure (p3) in the container ( 3 ) - at least a first means ( 17a ) for detecting the pressure (p1, p2) in one of the half cells ( 4a . 5a ), - at least a second means ( 17b ) for detecting the pressure (p3) in the interior ( 8th ) of the container ( 3 ), - at least one actuating means ( 12 . 43 ) for changing the pressure (p3) in the interior ( 8th ) of the housing ( 3 ) and - a control device ( 19 ) for adjusting the actuating means ( 12 ) as a function of the pressure difference (Δp) between the pressure (p3) in the container ( 3 ) and the pressure (p1, p2) in the half cells ( 4a . 5a ). System according to claim 13, characterized in that the actuating means ( 12 ) is adapted to volume of the interior ( 8th ) of the container ( 3 ) to displace. System according to one of claims 11 to 14, characterized in that the means ( 40 . 42 ) for tracking the pressure (p3) in the housing ( 3 ) from a secondary chamber ( 40 ) of the container ( 3 ) and an elastic membrane element ( 43 ), wherein the secondary chamber ( 40 ) via a closed by the membrane element opening ( 41 ) with the interior ( 8th ) of the container ( 3 ), and the interior of the secondary chamber ( 40 ) communicating with one of the half-cells ( 4a . 5a ) connected is. System according to claim 15, characterized in that in the secondary chamber means ( 43 ) for biasing the membrane element ( 42 ) are arranged. System according to claim 15 or 16, characterized in that the first half cell ( 4a ) with the secondary chamber ( 40 ) is communicatively connected. System according to claim 15 or 16, characterized in that the second half cell ( 5a ) with the secondary chamber ( 40 ) is communicatively connected.

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