Method for operating an electrolysis device

Abstract

The invention proceeds from a method for operating an electrolysis device (10), in particular a solid oxide electrolyzer cell, having at least one reaction unit (12), which has at least two electrodes (14, 16), wherein, in at least one operating state, a cell voltage (18) is applied between the two electrodes (14, 16), by means of which hydrogen (38) is split off from water molecules (20) through an electrolysis process. It is proposed that, in at least one method step (30), one of at least three operating parameters (24, 26, 28) is set in such a way that a voltage increase of the cell voltage (18) as a result of degradation of the electrodes (14, 16) is counteracted.

Description

[0001] R.413640

[0002] - 1 -

[0003] Description

[0004] Method for operating an electrolysis device

[0005] State of the art

[0006] A method for operating an electrolysis device, in particular a solid oxide electrolyzer cell, with at least one reaction unit having at least two electrodes, has already been proposed, wherein in at least one operating state a cell voltage is applied between the two electrodes, by means of which hydrogen is split off from water molecules by electrolysis.

[0007] Disclosure of the invention

[0008] The invention relates to a method for operating an electrolysis device, in particular a solid oxide electrolyzer cell, with at least one reaction unit which has at least two electrodes, wherein in at least one operating state a cell voltage is applied between the two electrodes, by means of which hydrogen is split off from water molecules by electrolysis.

[0009] It is proposed that in at least one process step, one of at least three operating parameters is adjusted in such a way as to counteract an increase in cell voltage due to electrode degradation.

[0010] The inventive design of the method advantageously provides a long service life, since in particular the increase in cell voltage due to electrode degradation is counteracted. R.413640

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[0012] Advantageously, operation can be provided at low cost, particularly due to the exceptionally long service life of the electrolysis device. A long maintenance interval can also be advantageously provided, as the rate of electrode degradation is minimized.

[0013] Preferably, the electrolysis device is configured as a solid oxide electrolysis cell (SOEC). In particular, the electrolysis device is configured as an electrolysis stack with at least one, preferably a plurality, reaction units. Preferably, the at least one reaction unit is configured as an electrolysis cell. Preferably, water, in particular water vapor, is supplied to the reaction unit. Preferably, hydrogen is split from the water molecules in the at least one reaction unit by supplying electrical energy. Preferably, the at least one reaction unit has at least one electrode. Preferably, the at least one reaction unit has at least one further electrode. Preferably, the at least one electrode is configured as an anode. Preferably, the at least one further electrode is configured as a cathode.Preferably, a cell voltage is applied between the two electrodes during operation of the electrolysis device. Preferably, the cell voltage is used to decompose the water, in particular water vapor, into hydrogen (H₂) and oxygen (O₂). Preferably, the water is decomposed into hydrogen and oxygen by water electrolysis. Preferably, the water electrolysis is designed as an endothermic reaction. Preferably, the electrolysis device, in particular at least the reaction unit, is operated at an operating temperature of at least 250 °C, preferably at least 400 °C.

[0014] Preferably, degradation occurs in the reaction unit. Preferably, the degradation is long-term. The degradation could, for example, take the form of electrode aging. For example, sintering effects occur at at least one of the electrodes, particularly due to the high operating temperature. Preferably, electrical losses in the reaction unit are increased by the degradation. Preferably, the cell voltage is increased by the degradation. Preferably, the operating temperature increases with increasing cell voltage. Preliminary R.413640

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[0016] In some cases, the increasing cell voltage accelerates the progressive degradation. In particular, the lifespan of the electrolysis device is limited by the maximum flow rate of a fan used to generate a cooling airflow. Specifically, the fan begins to deliver more cooling air to cool at least one reaction unit as soon as the cell voltage rises above a thermoneutral voltage, in particular 1.28 V. Specifically, above a maximum cell voltage, in particular at least substantially above 1.6 V, the fan can no longer generate a sufficient cooling airflow, thus bringing the lifespan of the electrolysis device to an end. It is conceivable that, particularly from a technical perspective, hydrogen can continue to be produced after reaching the maximum cell voltage.However, it is conceivable that, particularly from an economic perspective, hydrogen production will cease altogether because the efficiency is too low and / or the electricity consumption during hydrogen production is too high, making economic operation no longer possible. "Degradation" in this context refers specifically to a change in at least one property, such as electrical resistance, electrical conductivity, or the like, over the operating life of a component.

[0017] Preferably, the electrolysis device is operated based on at least one operating parameter. Preferably, the cell voltage is set using at least one operating parameter. Preferably, the cell voltage can be set via at least one operating parameter. One of the three operating parameters could, for example, be a steam utilization rate. One of the three operating parameters could, for example, be an electrolysis stack temperature. One of the three operating parameters could, for example, be a hydrogen production rate. It is conceivable that further operating parameters, which appear useful to those skilled in the art, are taken into account. The steam utilization rate could, for example, be set via a fresh water flow rate. The electrolysis stack temperature could, for example, be set by an air flow rate of the cooling air stream.The cooling airflow could, for example, be expressed as a function of a fan speed. Alternatively or additionally, the stack temperature could be adjusted by an electric heating element. The hydrogen production rate could, for example, be controlled via a Stack-R.413640.

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[0019] The current is set at a DC rectifier. The phrase "setting an operating parameter" here refers specifically to the regular adjustment of the operating parameter at intervals, such as daily, hourly, or similar, to counteract, or preferably at least substantially compensate for, any increase in cell voltage. It is also conceivable that the at least one operating parameter is continuously adjusted. Alternatively, the cell voltage could be regulated to a substantially constant value using the at least one operating parameter.

[0020] Preferably, the voltage increase is at least substantially compensated by adjusting at least one of the at least three operating parameters. Preferably, the cell voltage is reduced by the voltage increase caused by degradation by adjusting at least one of the at least three operating parameters. Preferably, the voltage increase in the cell voltage is at least substantially compensated by adjusting the operating parameter. Preferably, the voltage increase is counteracted by adjusting at least the steam utilization rate, the electrolysis stack temperature, and / or the hydrogen production rate. Preferably, the cell voltage is kept constant until at least a limit value of at least one of the at least three operating parameters is reached. Preferably, the limit value of the operating parameter cannot be exceeded.Preferably, the cell voltage can no longer be counteracted by the operating parameter once the limit value is reached. Preferably, the cell voltage continues to rise due to progressive degradation once the operating parameter reaches the limit value. In particular, the increase in cell voltage can only be counteracted over a control period that extends over an operating period limited by the point at which the limit value is reached. "Counteracted" in this context means, in particular, that the voltage change is at least substantially balanced, preferably compensated. "At least substantially" in this context means, in particular, that the deviation from a predetermined value is less than 25%, preferably less than 10%, and most preferably less than 5% of the predetermined value. R.413640.

[0021] - 5 -

[0022] Preferably, the electrolysis device comprises at least one control unit. Preferably, the control unit retrieves and / or evaluates at least one measurement signal, for example, cell voltage, cell temperature, and / or the like. Preferably, the control unit sets at least one of the at least three operating parameters. Preferably, the electrolysis device comprises at least one actuator, for example, a fan, a valve, an electric heater, or the like, by means of which at least one of the at least three operating parameters can be set. Preferably, the at least one actuator is controlled by the control unit. A "control unit" is understood to mean, in particular, a unit with at least one control electronics module.The term "control electronics" refers in particular to a unit comprising a processor unit, a memory unit, and an operating program stored in the memory unit.

[0023] Furthermore, it is proposed that the increase in cell voltage be counteracted by adjusting at least two of at least three operating parameters. Advantageously, a long service life can be ensured, since the increase in cell voltage can be counteracted by adjusting at least two of the operating parameters. Preferably, the increase in cell voltage is counteracted until at least two of the at least three operating parameters have reached their respective limit values. The at least two of the at least three operating parameters can be adjusted simultaneously and / or sequentially to counteract the voltage increase. Preferably, once the at least two of the at least three operating parameters have reached their limit values, an increase in cell voltage can no longer be prevented by the at least two of the at least three operating parameters.

[0024] Furthermore, it is proposed that the increase in cell voltage be counteracted by adjusting at least three operating parameters. Advantageously, a long service life can be provided, since, in particular, the increase in cell voltage is counteracted by adjusting at least three operating parameters. Preferably, the R.413640

[0025] - 6 -

[0026] An increase in cell voltage is counteracted until at least three operating parameters reach their respective limit values. Preferably, an increase in cell voltage cannot be prevented once at least three operating parameters have reached their limit values. The limit value for the steam utilization rate could, for example, be a minimum steam utilization rate. The limit value for the electrolysis stack temperature could, for example, be a maximum electrolysis stack temperature. The limit value for the hydrogen production rate could, for example, be a minimum hydrogen production rate. It is conceivable that the limit value must not be exceeded in order to ensure the proper functioning of the electrolysis device.

[0027] Furthermore, it is proposed that the increase in cell voltage be at least substantially compensated. Advantageously, high precision can be provided, since the cell voltage is kept at least substantially constant. Preferably, the cell voltage is kept at least substantially constant. Preferably, the cell voltage is kept at least substantially constant by compensating for the voltage increase. Preferably, the cell voltage is kept at least substantially constant by adjusting at least one of the at least three operating parameters. Preferably, the voltage increase is compensated at least substantially by adjusting at least one of the at least three operating parameters. "Compensated" here is understood to mean, in particular, that a value is kept at least substantially constant by balancing out a deviation.

[0028] Furthermore, it is proposed that the electrolysis device be operated at least substantially at maximum efficiency by maintaining the cell voltage at a thermoneutral voltage, in particular 1.28 volts, by adjusting at least one of the at least three operating parameters. Advantageously, a high efficiency can be provided since the electrolysis device is operated at the thermoneutral voltage. Preferably, the maximum efficiency is achieved at the cell voltage corresponding to the thermoneutral voltage. The voltage increase of the cell voltage due to degradation can be counteracted.

[0029] - 7 -

[0030] This can be counteracted by taking at least one boundary condition into account. The boundary condition can, for example, include operation at maximum efficiency. Alternatively or additionally, it is conceivable that the boundary condition includes a hydrogen production quantity, a minimum service life, or another boundary condition that appears sensible to a person skilled in the art. Preferably, a cell voltage is determined taking the boundary condition into account, which is kept at least substantially constant by adjusting the operating parameters. A "thermoneutral voltage" is understood in particular to be a cell voltage at which the efficiency of the electrolysis device is maximized.

[0031] Furthermore, it is proposed that the increase in cell voltage be counteracted by adjusting at least two of the at least three operating parameters sequentially. Advantageously, this approach achieves low complexity, as the adjustment of at least two of the at least three operating parameters simplifies the adjustment or control process. Preferably, at least two of the at least three operating parameters are adjusted sequentially, with the subsequent parameter being adjusted only after the limit value of the preceding parameter has been reached. Preferably, the second operating parameter is adjusted to compensate for the voltage increase due to degradation only after the limit value of the first parameter has been reached.In particular, the second operating parameter is set as soon as the voltage increase can no longer be counteracted by the first operating parameter because its limit value has been reached. Preferably, the operating parameters are set sequentially to compensate for the voltage increase.

[0032] Furthermore, it is proposed that the increase in cell voltage be counteracted by setting at least two of the at least three operating parameters simultaneously. Advantageously, high flexibility can be provided, since in particular at least two of the at least three operating parameters can be set simultaneously. Preferably, at least two of the at least three operating parameters are set before one of the at least two operating parameters reaches its limit value. For example, at least two of the at least three operating parameters could be set simultaneously, R.413640

[0033] - 8 -

[0034] This allows for the consideration of multiple boundary conditions. It is also conceivable that the at least two operating parameters are only partially overlapping in time to compensate for the voltage increase. For example, another of the at least three operating parameters could be set as soon as another of the at least three operating parameters approaches its limit.

[0035] Furthermore, it is proposed that the operating parameters of the electrolysis device can be flexibly switched to counteract the increase in cell voltage. Advantageously, this provides a high degree of flexibility, particularly since the operating parameters can be switched flexibly, allowing, for example, a response to changes in user preference. The operating parameters can be flexibly adjusted to accommodate changes in boundary conditions. Specifically, the at least two operating parameters can be flexibly adjusted until at least one of them reaches its limit.

[0036] Furthermore, it is proposed that the electrolysis device can be flexibly operated in a way that allows switching between maximum lifetime operation with or without considering at least one boundary condition, for example, maximum efficiency operation. Advantageously, a high degree of flexibility can be provided, since it is particularly possible to switch between maximum lifetime operation with or without considering a boundary condition of maximum efficiency operation. Preferably, the cell voltage can be varied arbitrarily while simultaneously compensating for the voltage increase until the at least three operating parameters, and in particular all operating parameters, have reached their limit values.

[0037] The inventive method for operating an electrolysis device is not intended to be limited to the application and embodiment described above. In particular, the inventive method for operating an electrolysis device may, to achieve a functionality described herein, comprise a different number of individual elements, components, units, and process steps than the number mentioned herein. R.413640

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[0039] Furthermore, values ​​within the specified ranges of values ​​in this disclosure shall also be considered disclosed and freely usable.

[0040] drawing

[0041] Further advantages will become apparent from the following description of the drawing. The drawing illustrates an embodiment of the invention. The drawing, the description, and the claims contain numerous features in combination. A person skilled in the art will expediently consider the features individually and combine them into meaningful further combinations.

[0042] They show:

[0043] Fig. 1 shows a schematic representation of an electrolysis device with two electrodes,

[0044] Fig. 2 shows a schematic representation of a cell voltage diagram and

[0045] Fig. 3 shows a schematic flowchart of a method for operating the electrolysis device.

[0046] Description of the exemplary embodiment

[0047] Figure 1 shows a schematic representation of an electrolysis device 10. The electrolysis device 10 is designed as a solid oxide electrolysis cell (SOEC). The electrolysis device 10 is designed as a solid oxide electrolyzer cell. The electrolysis device 10 has a reaction unit 12. The reaction unit 12 is designed as an electrolysis cell. Water is supplied to the reaction unit 12. The water is supplied in liquid form. Alternatively, the water can also be supplied in gaseous form. The water consists of a multitude of water molecules 20. In the reaction unit 12, hydrogen is split off from the water molecules 20 by supplying electrical energy. The reaction unit 12 has an electrode 14R.413640.

[0048] - 10 -

[0049] Electrode 14 is designed as a solid-state electrode. The reaction unit 12 has a further electrode 16. The further electrode 16 is designed as a solid-state electrode. Electrode 14 is designed as an anode. The further electrode 16 is designed as a cathode. The reaction unit 12 has an electrolyte 66. The electrolyte 66 is designed as a solid-state electrolyte. The electrolyte 66 is arranged between electrode 14 and the further electrode 16. During operation of the electrolysis device 10, a cell voltage 18 is applied between the two electrodes 14 and 16. With the cell voltage 18, the water molecules 20 are decomposed into hydrogen (H2) 38 and oxygen (O2) 40. The water is decomposed into hydrogen 38 and oxygen 40 by water electrolysis. The water electrolysis is designed as an endothermic reaction. The electrolysis device 10 is operated at an operating temperature of at least 400 °C.The reaction unit 12 is operated at an operating temperature of at least 400 °C.

[0050] The electrolysis device 10 is operated using three operating parameters 24, 26, 28, see Fig. 2. One of the three operating parameters 24, 26, 28 is a steam utilization rate. The steam utilization rate is set via a fresh water flow rate. One of the three operating parameters 24, 26, 28 is an electrolysis stack temperature. The electrolysis stack temperature is set via an air flow rate of a cooling air stream. The cooling air stream is generated by a fan. The cooling air stream is expressed as a function of the fan speed. Alternatively or additionally, the electrolysis stack temperature could be set by an electrical heating power. One of the three operating parameters 24, 26, 28 is a hydrogen production rate. The hydrogen production rate is set via an electrolysis stack current at a DC rectifier.It is conceivable that other operating parameters, which appear sensible to the expert, are taken into account.

[0051] Figure 2 shows a schematic cell voltage diagram 42. The cell voltage diagram 42 has an ordinate 44. The ordinate 44 represents the cell voltage 18 between the two electrodes 14, 16. The cell voltage diagram 42 has an abscissa 46. The abscissa 46 represents a time period. The time period is defined as an operating time. The operating time is defined as a period from the commissioning 54 of the electrolysis device 10R.413640.

[0052] - 11 -

[0053] (Beginning of Life) up to the end of life 56 of the electrolysis device 10 (End of Life). Degradation of the electrodes 14, 16 occurs over the operating period. Degradation of the electrolyte 66 also occurs over the operating period. This degradation leads to an increase in the cell voltage 18. The voltage increase due to degradation can be counteracted by adjusting the three operating parameters 24, 26, 28. Alternatively, only one of the three operating parameters 24, 26, 28 can be adjusted. Alternatively, only two of the three operating parameters 24, 26, 28 can be adjusted. The cell voltage 18 can be reduced by increasing the electrolysis stack temperature. Increasing the electrolysis stack temperature reduces ohmic losses in the electrode 14, the other electrode 16, and / or the electrolyte 66.The reduced ohmic losses in electrode 14, the other electrode 16, and / or the electrolyte 66 decrease the cell voltage 18. The cell voltage 18 can be reduced by reducing the vapor utilization rate. Reducing the vapor utilization rate reduces the activation and concentration losses of the reaction unit 12, thereby reducing the cell voltage 18. The cell voltage 18 can also be reduced by reducing the hydrogen production rate. Reducing the hydrogen production rate reduces the cell current, thereby reducing the ohmic losses in electrode 14, the other electrode 16, and / or the electrolyte 66. Operating parameter 24 has a limit value of 48. Operating parameter 26 has a limit value of 50. Operating parameter 28 has a limit value of 52. One of the three operating parameters 24, 26, or 28 is adjusted until the limit values ​​48, 50, or 52 are reached.Then, one of the two remaining operating parameters 24, 26, 28 is set. The remaining operating parameter 24, 26, 28 is then set. The three operating parameters 24, 26, 28 are set sequentially. The three operating parameters 24, 26, 28 are set sequentially. When one of the operating parameters 24, 26, 28 reaches its limit value 24, 26, 28, one of the other operating parameters 24, 26, 28 is set. After the three operating parameters 24, 26, 28 have reached their limit values ​​48, 50, 52, the cell voltage 18 increases. The cell voltage 18 exhibits a curve. The curve of the cell voltage 18 has a slope of 64. The slope 64 occurs when all operating parameters 24, 26, 28 have reached their limit values ​​24, 26, 28. R.413640.

[0054] - 12 -

[0055] Cell voltage diagram 42 has a time interval of 58. Within this time interval, the voltage increase of cell 18 can be compensated by adjusting one of the three operating parameters 24, 26, or 28. Cell voltage diagram 42 has a time interval of 60. Within this time interval, the voltage increase of cell 18 can be compensated by adjusting one of the two remaining operating parameters 24, 26, or 28. Cell voltage diagram 42 has a time interval of 62. Within this time interval, the voltage increase of cell 18 can be compensated by adjusting the remaining of the three operating parameters 24, 26, or 28. The voltage increase of cell 18 is counteracted by adjusting two of the three operating parameters 24, 26, or 28 sequentially. The voltage increase of cell voltage 18 is counteracted by setting two of the three operating parameters 24, 26, 28 simultaneously.

[0056] The electrolysis device 10 has an efficiency. The efficiency depends on the cell voltage 18. A thermoneutral voltage 22 is shown on the ordinate 44. The efficiency is at its maximum when operating at the thermoneutral voltage 22.

[0057] Figure 3 shows a schematic flowchart of a method for operating the electrolysis device 10.

[0058] In process step 30, the electrolysis device 10 is operated. Hydrogen 38 is split off from the water molecules 20 by the cell voltage 18. Electrolysis is carried out by the cell voltage 18. During electrolysis, hydrogen 38 is split off from the water molecules 20. The water molecules 20 are split into hydrogen 38 and oxygen 40. In process step 30, one of the three operating parameters 24, 26, 28 is set such that an increase in the cell voltage 18 due to degradation of the electrodes 14, 16 is counteracted. The voltage increase in the cell voltage 18 is compensated. The voltage increase is counteracted until the limit value 48, 50, 52 of the operating parameter 24, 26, 28 is reached. By compensating for the voltage increase of cell voltage 18, the end of service life 56 of the electrolysis device 10 is postponed. R.413640

[0059] - 13 -

[0060] In process step 32, the voltage increase of cell 18 is counteracted by adjusting one of the two remaining operating parameters 24, 26, 28. The voltage increase of cell 18 is counteracted by adjusting two of the three operating parameters 24, 26, 28. The voltage increase of cell 18 is compensated by adjusting two of the three operating parameters 24, 26, 28. The voltage increase is counteracted until the limit value 48, 50, 52 of the operating parameter 24, 26, 28 is reached. One of the two remaining operating parameters 24, 26, 28 is adjusted in process step 32 if the previously adjusted of the three operating parameters 24, 26, 28 set in process step 30 has reached its limit value 48, 50, 52. The two of the three operating parameters 24, 26, 28 are set sequentially.

[0061] In process step 34, the voltage increase of cell 18 is counteracted by adjusting the remaining operating parameters 24, 26, 28. The voltage increase of cell 18 is counteracted by adjusting the three operating parameters 24, 26, 28. The voltage increase of cell 18 is compensated by adjusting the three operating parameters 24, 26, 28. The voltage increase is counteracted until the limit value 48, 50, 52 of the remaining operating parameter 24, 26, 28 is reached. The remaining operating parameter 24, 26, 28 is adjusted in process step 34 when two of the three operating parameters 24, 26, 28, which were previously set in process steps 30 and 32, have reached their limit values ​​48, 50, 52. The three operating parameters 24, 26, 28 are set sequentially.Once the limit values ​​48, 50, 52 of the three operating parameters 24, 26, 28 have been reached, the cell voltage 18 is no longer counteracted. Once the limit values ​​48, 50, 52 of the three operating parameters 24, 26, 28 have been reached, the reaction unit 12 is left to its own devices until the end of its service life 56 is reached.

[0062] In process step 36, a boundary condition can be considered when setting the operating parameters 24, 26, 28. This boundary condition takes efficiency into account. The electrolysis device 10 is operated at its maximum efficiency. The electrolysis device 10 is operated at the thermoneutral voltage 22. R.413640

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[0064] The three operating parameters 24, 26, 28 are set. By setting the three operating parameters 24, 26, 28, the cell voltage 18 is kept constant at the thermoneutral voltage 22. During operation of the electrolysis device 10, it is possible to flexibly switch between the operating parameters 24, 26, 28. During operation of the electrolysis device 10, it is possible to flexibly switch between operation at maximum lifetime with or without consideration of a boundary condition.

Claims

R.413640 - 15 - Claims 1. Method for operating an electrolysis device (10), in particular a solid oxide electrolyzer cell, with at least one reaction unit (12) which has at least two electrodes (14, 16), wherein in at least one operating state a cell voltage (18) is applied between the two electrodes (14, 16), by means of which hydrogen (38) is split off from water molecules (20) by electrolysis, characterized in that in at least one process step (30) one of at least three operating parameters (24, 26, 28) is adjusted in such a way as to counteract an increase in the cell voltage (18) as a result of degradation of the electrodes (14, 16).

2. Method according to claim 1, characterized in that the increase in cell voltage (18) is counteracted by adjusting at least two of at least three operating parameters (24, 26, 28).

3. Method according to claim 1 or 2, characterized in that the increase in cell voltage (18) is counteracted by adjusting the at least three operating parameters (24, 26, 28).

4. Method according to one of the preceding claims, characterized in that the voltage increase of the cell voltage (18) is at least substantially compensated.

5. A method according to one of the preceding claims, characterized in that the electrolysis device (10) is operated at least substantially at a maximum efficiency of the electrolysis device (10) by maintaining the cell voltage (18) at a thermoneutral voltage (22) by adjusting at least one of the at least three operating parameters (24, 26, 28). R.413640 - 16 - 6. Method according to one of claims 2 to 5, characterized in that the voltage increase of the cell voltage (18) is counteracted by adjusting at least two of the at least three operating parameters (24, 26, 28) sequentially.

7. Method according to one of claims 2 to 5, characterized in that the voltage increase of the cell voltage (18) is counteracted by setting at least two of the at least three operating parameters (24, 26, 28) simultaneously.

8. Method according to one of claims 2 to 7, characterized in that during operation of the electrolysis device (10) it is possible to flexibly switch between the operating parameters (24, 26, 28) by means of which the voltage increase of the cell voltage (18) is counteracted.

9. Method according to one of the preceding claims, characterized in that during operation of the electrolysis device (10) it is possible to flexibly switch between operation at maximum lifetime with or without consideration of at least one boundary condition, for example operation at maximum efficiency.

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