Electrolysis device and method for operating electrolysis device

Abstract

The invention relates to an electrolysis device for the decomposition of water into hydrogen (H2) and oxygen (O2) by means of an electric current, comprising a plurality of electrolysis cells (2), which are divided into electrolysis stacks, each electrolysis cell (2) having a proton-permeable polymer membrane (4), on both sides of which electrodes (6, 8) are present, to which an external voltage is applied during operation, a first water supply line (10) for supplying water to the anode chamber (12) is provided on the anode side, to which an oxygen product line (14) for drawing off the generated oxygen (O2) from the anode chamber (12) is coupled, and a hydrogen product line (16) for drawing off the generated hydrogen (H2) from the cathode chamber (18) is provided on the cathode side, and a control system (22) for controlling the operation of the electrolysis stack. In order to ensure safe operation of the electrolysis device and to minimize the negative effects of membrane damage during operation of the electrolysis device, the control system (22) is designed to set the pressure (pa) in the anode chamber (12) higher than the pressure (pa) in the cathode chamber (18), the pressure (pa) in the anode chamber (12) being 2 to 20 times, in particular 4 to 7 times, of the pressure (pk) in the cathode chamber (18).

Description

Technical Field

[0001] The present invention relates to an electrolysis device for decomposing water into hydrogen and oxygen by using electric current, wherein the electrolysis device comprises a plurality of electrolysis cells, wherein the plurality of electrolysis cells form a plurality of electrolysis stacks, wherein each electrolysis cell has a proton-permeable polymer membrane, and electrodes are provided on both sides of the proton-permeable polymer membrane, and an external voltage is applied to the electrodes during operation, wherein a water supply pipeline for supplying water to the anode chamber is provided on the anode side, an oxygen product pipeline for drawing out the generated oxygen from the anode chamber is connected, and a hydrogen product pipeline for drawing out the generated hydrogen from the cathode chamber is provided on the cathode side, and the electrolysis device also comprises a control system for controlling the operation of the electrolysis stack.

[0002] The invention also relates to a method for operating an electrolysis device for decomposing water into hydrogen and oxygen using an electric current, the electrolysis device comprising a plurality of electrolysis cells, the plurality of electrolysis cells forming a plurality of electrolysis stacks, wherein each electrolysis cell has a proton-permeable polymer membrane, electrodes are present on both sides of the proton-permeable polymer membrane, an external voltage being applied to the electrodes during operation, wherein on the anode side water is added to the anode chamber and the produced oxygen is removed from the anode chamber, and on the cathode side the produced hydrogen is removed from the cathode chamber via a hydrogen product line. Background Art

[0003] Hydrogen is currently produced, for example, by PEM electrolysis. The components of a PEM electrolyser are a proton-permeable polymer membrane (proton exchange membrane) which is in contact with porous platinum electrodes (anode and cathode) on both sides. An external voltage is applied to the porous platinum electrodes and water is added to the anode side of the electrolyser. The water is decomposed on the anode side by the catalytic action of the platinum. This produces oxygen, free electrons and positively charged hydrogen ions H + . Hydrogen ion H + The hydrogen ions diffuse across the proton conducting membrane to the cathode side where they combine with electrons from the external circuit to form hydrogen molecules H2.

[0004] The above-mentioned electrolytic cells are combined into a stack. Water is introduced into the stack under direct voltage, and after passing through the electrolytic cells, two product streams consisting of water and gas bubbles (i.e. oxygen or hydrogen) appear. Here, the inherent feature of the system is that in the product stream of one product gas, the other product gas is only present in a small amount. In fact, the oxygen stream contains a small amount of hydrogen, and the hydrogen stream also contains a small amount of oxygen. The amount of the corresponding impurity gas depends on the electrolytic cell design and is also affected by the current density, catalyst composition, aging and the membrane material in the PEM electrolysis device. Here, in some cases, it may be necessary to reduce the impurity gas concentration, that is, directly at the electrolytic cell or electrolytic stack or directly downstream of the electrolytic cell or electrolytic stack, for example in a gas separation device connected downstream of the electrolysis device. In partial load operation and in the case of membrane aging, this problem becomes more serious and leads to limited operation.

[0005] Therefore, a gas separation must then be carried out. In this case, a plurality of electrolysis cells and also a plurality of electrolysis units are usually connected to one another via pipelines and the corresponding gas-water mixture formed is conveyed to a central gas separator. For example, an advantageous embodiment for this is known from WO 2020 / 020611 A1. Summary of the invention

[0006] It is therefore an object of the present invention to ensure safe operation of an electrolysis device and to minimize the negative consequences of membrane damage during operation of the electrolysis device.

[0007] According to the invention, this object is achieved by an electrolysis device for decomposing water into hydrogen and oxygen using electric current, the electrolysis device comprising a plurality of electrolysis cells, the plurality of electrolysis cells being divided into an electrolysis stack, wherein each electrolysis cell has a proton-permeable polymer membrane, electrodes are present on both sides of the proton-permeable polymer membrane, an external voltage is applied to the electrodes during operation, wherein a first water supply line for supplying water to the anode chamber is provided on the anode side, an oxygen product line for drawing out the produced oxygen from the anode chamber is connected, and a hydrogen product line for drawing out the produced hydrogen from the cathode chamber is provided on the cathode side, the electrolysis device further comprising a control system for controlling the operation of the electrolysis stack, wherein the control system is configured to set the pressure in the anode chamber to be higher than the pressure in the cathode chamber, wherein the pressure in the anode chamber is 2 to 20 times, in particular 4 to 7 times, the pressure in the cathode chamber.

[0008] According to the invention, the object is also achieved by a method for operating an electrolysis device, which uses an electric current to decompose water into hydrogen and oxygen, the electrolysis device comprising a plurality of electrolysis cells, which are divided into an electrolysis stack, wherein each electrolysis cell has a proton-permeable polymer membrane, electrodes are present on both sides of the proton-permeable polymer membrane, and an external voltage is applied to the electrodes during operation, wherein on the anode side, water is added to the anode chamber via a first water supply pipeline, and the produced oxygen is led from the anode chamber via an oxygen product pipeline, and on the cathode side, the produced hydrogen is led from the cathode chamber via a hydrogen product pipeline, and the electrolysis device also includes a control system for controlling the operation of the electrolysis stack, wherein the pressure in the anode chamber is set higher than the pressure in the cathode chamber by the control system, wherein the pressure in the anode chamber is 2 to 20 times, in particular 4 to 7 times, the pressure in the cathode chamber.

[0009] The advantages and preferred embodiments listed below with respect to the electrolysis device can be transferred analogously to the method for operating the electrolysis device.

[0010] According to the invention, it is proposed to operate each electrolysis with a differential pressure. In this case, the pressure on the anode side is set higher than the pressure on the cathode side. The pressure ratio between the anode side and the cathode side is 2 to 20, in particular 4 to 7. This means that if there is a pressure of, for example, 5 bar in the cathode space, then in the anode space a pressure of, in particular, 20 bar is set.

[0011] The lower pressure on the cathode side compared to the anode side brings several advantages. On the one hand, this supports the migration of water molecules through the membrane. On the other hand, if the membrane ruptures, less foreign gas passes through. Last but not least, the foreign gas concentration is improved during operation.

[0012] According to a preferred design, the control system is set up so that the water in the anode chamber can circulate. Preferably, the oxygen outlet line is also used as the water outlet line. If water circulates only on the anode side, there is a humidified pool on the hydrogen side. It is simpler to operate a PEM electrolyzer with only one water circuit than to operate a PEM electrolyzer with two circuits.

[0013] According to another preferred design, the control system is set up so that the water in the cathode chamber can circulate. Here, the hydrogen product pipeline is also used in particular to lead out water. The inherent safety of the electrolytic cell is improved by the water circulation. The circulation rate in the cathode chamber is particularly smaller than the circulation rate in the anode chamber. The ratio of water circulation on the hydrogen side to the oxygen side is 0.9 to 0.01. If the membrane ruptures, the oxygen passing through will usually mix with the hydrogen and a reactive gas mixture can be formed. Therefore, it is very advantageous that discrete, smaller volumes are formed here by the hydrogen-oxygen mixture, which are embedded in the water as bubbles, for example. Since the total reaction volume is smaller, the energy release is also lower.

[0014] Preferably, there is a horizontal cell structure, in which the anode chamber is arranged above the cathode chamber. Alternatively, the cell can also be oriented vertically.

[0015] With regard to particularly high safety in the electrolysis process, according to a preferred embodiment, a composite catalyst for the recombination of hydrogen and oxygen to form water is integrated in the hydrogen product line. The composite catalyst prevents the reactive product gas mixture from reaching downstream gas separators or downstream regions, such as compressors, due to the oxygen content in the hydrogen product stream.

[0016] Preferably, the control system is set up to detect at least one temperature value in the hydrogen product pipeline, and the temperature value or the temperature related to the temperature value is compared with a threshold value, and if it exceeds the threshold value, the hydrogen product pipeline is blocked and the bypass line is opened. The detected temperature value can be, for example, an absolute temperature in or downstream of the composite catalyst, a temperature change over time, an inlet temperature and an outlet temperature relative to the composite catalyst, or a difference between two temperature values ​​of the hydrogen product pipeline. An exothermic reaction occurs in the composite catalyst, wherein the temperature rises. Therefore, if the temperature in the composite catalyst or another temperature rise in the hydrogen product pipeline exceeds a predetermined threshold value, this indicates that there is a particularly large amount of impurity oxygen in the hydrogen product stream. This in turn indicates that the membrane is defective. Therefore, when exceeding the threshold value, the hydrogen product pipeline must be blocked to prevent entry into the gas separator, and a bypass line is opened, which derives the reaction mixture consisting of oxygen and hydrogen from other components of the electrolysis device.

[0017] Preferably, the control system is configured to cut off the current flowing to the electrolysis stack when a threshold value is exceeded, thereby preventing an increase in the concentration of impurity oxygen on the hydrogen side in a timely manner.

[0018] Advantageously, as a further safety measure, the control system is configured to introduce an inert gas into the cathode chamber of the switched-off electrolysis stack. In particular, nitrogen is used to flush the cathode side of the electrolysis stack. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Embodiments of the invention are explained in more detail with reference to the accompanying drawings. In the drawings, in a schematic and highly simplified manner:

[0020] Figure 1 A first embodiment of an electrolytic cell is shown in a vertical orientation;

[0021] Figure 2 A second embodiment of an electrolytic cell is shown in a horizontal orientation;

[0022] Figure 3 A third embodiment of an electrolytic cell is shown in a horizontal orientation;

[0023] Figure 4A fourth embodiment of an electrolytic cell is shown in a horizontal orientation;

[0024] Figure 5 A fifth embodiment of an electrolytic cell is shown in a horizontal orientation; and

[0025] Figure 6 A vertically oriented electrolytic cell and downstream components are shown.

[0026] The same reference numerals in the figures have the same meaning. DETAILED DESCRIPTION

[0027] Figure 1 A vertically oriented electrolysis cell 2 is shown, which is part of an electrolysis device (not shown here) for decomposing water into hydrogen H2 and oxygen O2 by means of electric current. A plurality of such electrolysis cells 2 are connected in series to form an electrolysis stack. Each electrolysis cell 2 has a proton-permeable polymer membrane 4, on both sides of which there are electrodes 6, 8, to which an external voltage is applied during operation. A first water supply line 10 for supplying water to the anode chamber 12 is provided on the anode side. The oxygen O2 produced in the electrolysis cell 2 is led from the anode chamber 12 via an oxygen product line 14. A hydrogen product line 16 for leading the produced hydrogen from the cathode chamber 18 is provided on the cathode side. In addition, according to Figure 1 A second water supply line 20 is also connected to the cathode side. Therefore, water circulates not only through the anode chamber 12 but also through the cathode chamber 16.

[0028] Furthermore, a control system 22 is provided for controlling the operation of the electrolysis stack, which is symbolically represented by a block 22. With the aid of the control system 22, the pressure p in the anode space 12 is set to a is set higher than the pressure p in the cathode chamber 18 k , where the pressure on the anode side is a is the pressure on the cathode side p k Preferably, the pressure p in the anode chamber 12 is about 2 to 20 times greater than that in the anode chamber 12. a In particular, the pressure p in the cathode chamber 18 k In this way, the negative consequences of membrane damage during operation of the electrolyzer are minimized, since less foreign gas can pass through in the event of a rupture of the membrane 4 .

[0029] Figure 2 The electrolytic cell 2 in has a horizontal structure, wherein the anode chamber 12 is arranged above the cathode chamber 18. The cathode chamber 18 is only partially filled here, i.e., although water is introduced into the cathode chamber 18 via the second water supply line 20, the chamber is not completely filled with water.

[0030] according to Figure 3 The level of the electrolytic cell 2 with Figure 2The electrolytic cell 2 in FIG. 1 is different only in that the anode chamber 12 and the cathode chamber 18 are not of the same size, but the anode chamber 12 is larger than the cathode chamber 18 , ie, an asymmetrical arrangement of the electrodes 6 , 8 is present via the polymer membrane 4 .

[0031] and Figure 2 The difference is that in Figure 4 In the embodiment of the present invention, liquid water is not supplied to the cathode chamber 18, but water vapor is supplied to the cathode chamber 18, so that a humidified half cell is present on the cathode side.

[0032] In accordance with Figure 5 In the embodiment of the electrolytic cell 2, there is also a humidified half cell on the cathode side, which is also connected with Figure 3 Likewise, the anode chamber 12 is larger than the cathode chamber 16 .

[0033] according to Figure 2 , Figure 3 , Figure 4 and Figure 5 The embodiments shown in connection with a horizontally oriented electrolysis cell 2 can also be transferred to a vertically oriented electrolysis cell 2 and vice versa.

[0034] Figure 6 Other components of the electrolysis device and their interactions during operation are shown. A composite catalyst 24 for recombination is integrated in the hydrogen product pipeline 16, in which hydrogen H2 and oxygen O2 recombine to form water. In the embodiment shown, temperature sensors 26 and 28 are installed upstream and downstream of the composite catalyst 22, and the temperature sensors detect the temperature values ​​T1 and T2 in the hydrogen product pipeline 16 respectively. The temperature values ​​T1 and T2 are provided to the control system 22, and the control system 22 forms a temperature difference ΔT based on the temperature difference, and compares the temperature difference with the predetermined threshold value T S Instead of the temperature difference ΔT, a measured temperature value (eg, T2) or another temperature related to the temperature value T2 may be used directly. In this way, the temperature development of the exothermic reaction in the composite catalyst 24 is monitored.

[0035] When the temperature difference △T exceeds the threshold T S When the hydrogen product pipeline 16 is blocked by the valve 30, the bypass valve 32 is opened so that the mixture of hydrogen H2 and oxygen O2 is discharged through the bypass pipeline 34. S In the case of a shutdown, the current flowing to the corresponding electrolytic stack is also cut off for safety reasons. In addition, the nitrogen valve 36 installed in the second water supply line 20 is opened so that nitrogen N2 or other inert gas is introduced into the cathode chamber 18 of the shut-off electrolytic stack.

Claims

1. An electrolysis device for decomposing water into hydrogen (H2) and oxygen (O2) by means of electric current, the electrolysis device comprising a plurality of electrolysis cells (2), the plurality of electrolysis cells being divided into electrolysis stacks, wherein: Each electrolytic cell (2) has a proton-permeable polymer membrane (4), electrodes (6, 8) are present on both sides of the proton-permeable polymer membrane, and an external voltage is applied to the electrodes during operation, wherein a first water supply pipeline (10) for supplying water to the anode chamber (12) is provided on the anode side, an oxygen product pipeline (14) for leading the generated oxygen (O2) from the anode chamber (12) is connected, and a hydrogen product pipeline (16) for leading the generated hydrogen (H2) from the cathode chamber (18) is provided on the cathode side, and the electrolysis device also includes a control system (22) for controlling the operation of the electrolytic stack, The control system (22) is configured to adjust the pressure (p a ) is set higher than the pressure in the cathode chamber (18), wherein the pressure in the anode chamber (12) (p a ) is the pressure (p k ), 2 to 20 times, especially 4 to 7 times.

2. The electrolysis device according to claim 2, characterized in that: The control system (22) is set up to enable the water in the anode chamber (12) to circulate.

3. An electrolysis device according to any one of the preceding claims, characterized in that The control system (22) is set up to enable the water in the cathode chamber (18) to circulate.

4. An electrolysis device according to any one of the preceding claims, characterized in that There is a horizontal cell structure, in which the anode chamber (12) is arranged above the cathode chamber (18).

5. An electrolysis device according to any one of the preceding claims, characterized in that A composite catalyst (24) for combining hydrogen (H2) and oxygen (O2) into water is integrated in the hydrogen product pipeline (16).

6. An electrolysis device according to any one of the preceding claims, characterized in that The control system (22) is configured to detect at least one temperature value (T1, T2) in the hydrogen product pipeline (16) and compare the temperature value (T1, T2) or a temperature (ΔT) related to the temperature value (T1, T2) with a threshold value (T S ) is compared, and when the threshold value (T S ) when the hydrogen product pipeline (16) is blocked and the bypass line (34) is opened.

7. The electrolysis device according to claim 6, characterized in that: The control system (22) is configured to S ) cuts off the current flowing to the corresponding electrolytic stack.

8. The electrolysis device according to claim 6 or 7, characterized in that: The control system (22) is configured to introduce an inert gas (N2) into the cathode chamber (18) of the shut-down electrolysis stack.

9. A method for operating an electrolysis device for decomposing water into hydrogen (H2) and oxygen (O2) by means of an electric current, the electrolysis device comprising a plurality of electrolysis cells (2) which are divided into electrolysis stacks, wherein: Each electrolysis cell (2) has a proton-permeable polymer membrane (4), on both sides of which electrodes (6, 8) are present, to which an external voltage is applied during operation, wherein, on the anode side, water is added to the anode chamber (12) via a first water supply line (10), and the generated oxygen (O2) is led out of the anode chamber (12) via an oxygen product line (14), and on the cathode side, the generated hydrogen (H2) is led out of the cathode chamber (18) via a hydrogen product line (16), and the electrolysis device also includes a control system (22) for controlling the operation of the electrolysis stack, The invention is characterized in that the pressure (p a ) is set higher than the pressure in the cathode chamber (18), wherein the pressure in the anode chamber (p a ) is the pressure in the cathode chamber (p k ), in particular 4 to 7 times.

10. The method for operating an electrolysis device according to claim 9, characterized in that Water is circulated through the anode chamber (12).

11. Method for operating an electrolysis device according to any one of claims 9 or 10, characterized in that Water is circulated through the cathode chamber (18).

12. Method for operating an electrolysis device according to any one of claims 9 to 11, characterized in that A composite catalyst (24) is integrated in the hydrogen product pipeline (16), and hydrogen (H2) and oxygen (O2) are combined in the composite catalyst to generate water.

13. The method for operating an electrolysis device according to claim 12, characterized in that At least one temperature value (T1, T2) is detected in the hydrogen product pipeline (16), and the temperature value (T1, T2) or a temperature (ΔT) related to the temperature value is compared with a threshold value (T S ) is compared, and when the threshold value (T S ), the hydrogen product line (16) is blocked and the bypass line (34) is opened.

14. The method for operating an electrolysis device according to claim 13, characterized in that When the threshold value (T S ), the current flowing to the corresponding electrolytic stack is cut off.

15. Method for operating an electrolysis device according to claim 14, characterized in that An inert gas (N2) is introduced into the cathode chamber (18) of the switched-off electrolysis stack.

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