Strategy for operating an electrolysis cell stack, electrolyzer, and electrolyzer unit

Abstract

The invention relates to a strategy for operating an electrolysis cell stack (10) of an electrolyzer or an electrolyzer unit (1), wherein the electrolysis cell stack (10) can be supplied and / or is supplied with electrical power (P) by a power electronics (100) over its lifetime (t), and an increasing electrical power requirement of the electrolysis cell stack (10) with increasing lifetime (t) is at least partially compensated by increasing an operating temperature level (T) of the electrolysis cell stack (10).

Description

[0001] The invention relates to a strategy or method for operating a stack of electrolysis cells of an electrolyzer or an electrolyzer assembly. Furthermore, the invention relates to an electrolyzer, an electrolyzer assembly, and an electrolyzer system. State of the art

[0002] For example, in a water electrolyzer of an electrolyzer unit (stationary or mobile), such as an electrolyzer system or electrolyzer plant, water undergoes an electrochemical conversion into hydrogen and oxygen using electrical energy, generating heat in the process. The electrolyzer unit comprises at least one membrane electrode assembly (a membrane with transport structures and electrodes positioned between them), such as an AEM (Anion Exchange Membrane) or a PEM (Proton Exchange Membrane). Typically, the electrolyzer unit consists of a stack of membrane electrode assemblies with bipolar plates positioned between them, forming what is known as an electrolysis cell stack, containing multiple individual electrolysis cells. Task

[0003] To provide the electrical power required for the electrochemical reaction in an electrolysis cell stack of an electrolyzer or electrolyzer unit, the power electronics of the electrolyzer or electrolyzer unit must be designed to efficiently adapt to the properties of the electrolysis cell stack. With increasing aging of the electrolysis cell stack, an increased power requirement is observed over its lifetime, assuming a substantially constant hydrogen production rate. Since power electronics are expensive, one object of the invention is to enable the use of comparatively cost-effective power electronics. Disclosure of the invention

[0004] The object of the invention is achieved by a strategy for operating a stack of electrolysis cells of an electrolyzer or an electrolyzer assembly; by means of an electrolyzer for an electrolyzer assembly and an electrolyzer assembly for an electrolyzer system; as well as by means of an electrolyzer system. Advantageous further developments, additional features and / or advantages of the invention will become apparent from the dependent claims and the following description.

[0005] An electrolysis cell stack of an exemplary state-of-the-art electrolyzer system requires a power output of, for example, approximately 1.2 MW at the beginning of its life (BoL) and approximately 1.5 MW at the end of its life (EoL) to maintain a substantially constant hydrogen production rate throughout its lifetime. The increase in power requirement of approximately 0.3 MW is due to the aging or degradation of the electrolysis cell stack, and electrolysis cell stacks can age considerably differently. Some show hardly any signs of aging in the first half of their lifespan, while others exhibit signs of aging from the very first day of operation.

[0006] In the prior art, based on the example above, the power electronics must be able to provide at least approximately 1.5 MW of maximum power at the beginning of the electrolysis cell stack's lifetime. In this example, the required power of the power electronics is approximately 20% greater when comparing the beginning with the end of the electrolysis cell stack's lifetime. Therefore, in the prior art, the power electronics must be significantly oversized for the beginning and often also for a portion of the electrolysis cell stack's lifetime. The invention addresses this problem of the necessary significant oversizing of the power electronics.

[0007] In the operating strategy according to the invention, an electrolysis cell stack can be supplied with electrical power by a power electronics unit throughout its lifetime, and / or is supplied to it, whereby an increasing electrical power requirement of the electrolysis cell stack with increasing lifetime is at least partially compensated by increasing an operating temperature level of the electrolysis cell stack. The power electronics can therefore be electrically undersized at least for a temporal mid- and / or end-phase of the electrolysis cell stack's lifetime and / or be designed to be electrically optimized (i.e., neither over- nor under-sized) for a temporal initial phase.

[0008] The strategy for operating the electrolysis cell stack can also be referred to as a strategy method and / or a method for operating an electrolysis cell stack. Furthermore, this method can also be referred to as a method for the global operation of an electrolysis cell stack. The lifetime can be, for example, a nominal lifetime, a useful lifetime, etc., of the electrolysis cell stack. The power electronics can be the sole power electronics responsible for this electrolysis cell stack or for a plurality of electrolysis cell stacks. The size of the electrolysis cell stack can range from a few watts to several megawatts. The invention is applicable, for example, to all water electrolyzers, in particular PEM and AEM electrolyzers.

[0009] The lifetime is, of course, the operating time during which hydrogen can be produced by the electrolysis cell stack. This means that downtime of the electrolysis cell stack is not included in the lifetime. The nominal lifetime is the active, accumulated operating time specified by the manufacturer of the electrolyzer or electrolyzer unit, and for which the electrolysis cell stack can typically be used. The useful lifetime is the active, accumulated operating time during which the electrolysis cell stack is actually used. The same applies to the other terms with "nominal" and "useful."

[0010] Aging or degradation of the electrolysis cell stack can be countered by influencing its operating temperature without increasing the electrical power supplied to it. This is achieved primarily by adjusting the cooling of the electrolysis cell stack, while otherwise keeping conditions the same (e.g., by reducing the cooling). Other measures for increasing the operating temperature of the electrolysis cell stack are, of course, also applicable. For example, an electric heating element could be used.

[0011] The electrolysis cell stack can be operated at a low operating temperature level during the initial phase of its service life and at a high operating temperature level (relative to the low operating temperature level) during the final phase. The electrolysis cell stack can also be operated at a medium operating temperature level during the middle phase of its service life, which lies between the low and high operating temperature levels. Furthermore, over the service life of the electrolysis cell stack, the course of a curve representing the operating temperature level can correlate with and / or causally correlate with the degradation rate of the electrolysis cell stack.

[0012] The low operating temperature level at the beginning of the service life is controlled and regulated to achieve a specific, ideally optimal, voltage (output voltage of the power electronics, stack voltage, (average) cell voltage, etc.) at a specific current (output current of the power electronics, stack current, current density, etc.). During operation of the electrolysis cell stack, the degradation of the stack gradually increases, which would lead to an increased voltage at a constant temperature and constant current. To maintain the ideally optimal voltage unchanged throughout the service life, the operating temperature level of the electrolysis cell stack is controlled and / or regulated according to the invention.

[0013] A decreasing hydrogen production rate of the electrolysis cell stack over its lifetime can be at least partially compensated for by increasing the operating temperature of the electrolysis cell stack. Preferably, this results in a substantially constant hydrogen production rate over the entire lifetime of the electrolysis cell stack. The additional electrical power requirement of the electrolysis cell stack that increases with its lifetime is either not supplied or only partially supplied by the power electronics. This additional electrical power requirement is, of course, the power required in addition to the original power requirement due to the aging of the electrolysis cell stack. Through power requirement compensation, a substantially constant power requirement of the electrolysis cell stack can be maintained throughout its lifetime.

[0014] The lower the operating temperature of an aged electrolysis cell stack, the higher its energy losses, leading to a higher resulting voltage at a given current. By adjusting or varying the operating temperature according to the invention, the electrical current, and thus the hydrogen production rate, as well as the electrical voltage, and thus the power requirement, can be kept essentially constant over the entire lifetime of the electrolysis cell stack. This results in significantly improved coordination between the power electronics and the electrolysis cell stack, avoiding significant oversizing of the power electronics. This, in turn, leads to improved electrolyzer efficiency, reduced investment costs, and lower hydrogen production costs.

[0015] Increasing the operating temperature level of the electrolysis cell stack over its increasing lifetime can be achieved in such a way that a predetermined electrical power of the power electronics is not substantially exceeded, a predetermined electrical power of the power electronics remains substantially constant, and / or an electrical current and voltage for the electrolysis cell stack remain substantially constant.

[0016] The operating temperature of the electrolysis cell stack at the beginning and / or during the initial phase can be at least approximately: 17 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, or 50 °C, each ±2 °C. The operating temperature of the electrolysis cell stack at the end and / or during the final phase can be at least approximately: 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, or 105 °C, each ±2 °C. Other operating temperatures are, of course, applicable where applicable.

[0017] In this operating strategy, one cathode side of the electrolysis cell stack can be operated relative to one anode side of the electrolysis cell stack with a fluid overpressure of approximately 20 bar, 25 bar, 30 bar, 35 bar, 40 bar, 45 bar, or 50 bar, each ± ​​2 bar. Naturally, the invention is also applicable from the low-pressure electrolysis range (fluid overpressures up to 0.5 bar) to the high-pressure electrolysis range (fluid overpressures exceeding 100 bar).

[0018] The operating strategy is feasible and / or can be implemented by an electrolyzer or electrolyzer assembly according to any of the following claims. A feature described below in the context of a device is naturally applicable to the method described above. Furthermore, a feature described above in the context of the method is naturally applicable to the device described below.

[0019] The electrolyzer or electrolyzer assembly according to the invention comprises an electrolysis cell stack and power electronics for supplying the electrolysis cell stack with electrical power, wherein, with respect to the hydrogen production rate of the electrolysis cell stack, the power electronics are electrically undersized at least for a temporal mid-term and / or end-term portion of the service life of the electrolysis cell stack. An electrolyzer assembly can, for example, comprise a plurality of electrolyzers. The hydrogen production rate can, for example, be a nominal hydrogen production rate, a usable hydrogen production rate, etc., of the electrolysis cell stack.

[0020] According to the invention, the power electronics of the electrolyzer or electrolyzer assembly are designed such that, without a compensation measure, they cannot maintain the hydrogen production rate during a significant portion of the electrolysis cell stack's service life, particularly in the middle and / or end phases. To ensure that the hydrogen production rate can be maintained despite the undersizing of the power electronics, a compensation mechanism for this undersizing is provided according to the invention.

[0021] The undersizing of the power electronics can be compensated for by means of a variable operating temperature level for the electrolysis cell stack. The electrolysis cell stack can be operated at a higher operating temperature level during the middle and / or end phases of its service life compared to the beginning phase. Similarly, the electrolysis cell stack can be operated at a lower operating temperature level during the beginning phase of its service life compared to the end phase.

[0022] A control unit for the electrolyzer or electrolyzer assembly enables and / or allows for the variable operating temperature level of the electrolysis cell stack. This control unit can be either internal or external to the electrolyzer or electrolyzer assembly.

[0023] The power electronics can be designed to be at least adequately dimensioned for the initial phase of the electrolysis cell stack's lifetime. The power electronics can be designed to be electrically neither significantly over-dimensioned nor substantially dimensioned for the initial phase of the electrolysis cell stack's lifetime, as is generally the case. The power electronics can be electrically under-dimensioned by approximately 5%, 10%, 15%, 20%, 25%, 30%, or 35% (with a tolerance of ±2.5%) for the middle and / or end phases of the electrolysis cell stack's lifetime.

[0024] The initial time period can be approximately 0%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, or 40%, each with a tolerance of ± 2-5% of the lifetime. This means that during the first approximately 0%-75% of the electrolysis cell stack's lifetime, no power compensation of the power electronics occurs. The final time period can be approximately 100%, 99%, 95%, 90%, 85%, 80%, 75%, 70%, 60%, 50%, or 40%, each with a tolerance of ± 2-5% of the lifetime. This means that during the last approximately 100%-25% of the electrolysis cell stack's lifetime, power compensation of the power electronics occurs via temperature compensation of the electrolysis cell stack. Other percentages for the initial and / or final time periods are, of course, applicable. The electrolysis cell stack can be designed such that its lifetime is approximately: 20 kh, 30 kh, 40 kh, 50 kh, 60 kh, 70 kh, 80 kh, 90 kh, 100 kh, 110 kh or 120 kh (kh: kilohours).

[0025] The power electronics can be designed such that they provide and / or supply a substantially constant electrical power output throughout their service life. This electrical power output can be, for example, the nominal power, the useful output, etc., of the electrolysis cell stack. It is preferred that the electrical voltage and / or current provided and / or supplied by the power electronics also remain substantially constant throughout their service life.

[0026] The hydrogen production rate can be essentially constant over the lifetime of the device. An operating strategy according to the invention can be implemented and / or carried out by means of the electrolyzer or electrolyzer assembly. The operating strategy can be implemented, for example, by the power electronics themselves, the control unit, a control device, etc. Brief description of the characters

[0027] The invention is explained in more detail below with reference to exemplary embodiments and the accompanying schematic drawing, which is not to scale. In the invention, a feature can be positive (i.e., present) or negative (i.e., absent). In this specification, a negative feature is not explicitly defined as a feature unless the invention specifically emphasizes its absence. That is, the actual invention, rather than one constructed by the prior art, consists of omitting this feature. The absence of a feature (negative feature) in an exemplary embodiment indicates that the feature may be optional (to a person skilled in the art). The figures in the drawing, which are merely examples, show: The Fig. 1 in a simplified block diagram an embodiment of an electrolyzer assembly with an electrochemical electrolysis cell stack for an electrolyzer system, and the Fig. 2 a schematic diagram for a strategy according to the invention for operating an electrolysis cell stack of an electrolyzer or an electrolyzer assembly according to the invention. Embodiments of the invention

[0028] The invention is described below with reference to an electrolyzer unit 1 (see the Fig. 1) with an electrolysis cell stack 10 for a water electrolyzer for converting water into hydrogen and oxygen, explained in more detail. The invention is applicable to a variety of electrolyzer units 1, such as an electrolyzer unit 1 with an acidic or alkaline (AEL) electrolyzer, a carbon dioxide electrolyzer for converting carbon dioxide and water into carbon monoxide and hydrogen, a solid oxide electrolyzer (SOEC), etc. (see also above).

[0029] The drawing shows only those sections of electrolyzer unit 1 of an electrolyzer system, e.g., an electrolyzer plant, that are necessary for understanding the invention. Although the invention is described and illustrated in detail by preferred embodiments, the invention is not limited by the disclosed embodiments.

[0030] Other variations can be derived from this without leaving the scope of protection of the invention.

[0031] The Fig. Figure 1 shows an electrolyzer assembly 1 according to a general embodiment, with at least one, and in particular a plurality, of electrochemical individual cells 11 (individual electrolysis cell 11) bundled into an electrolysis cell stack 10, which are housed in a preferably fluid-tight stacking housing 16. Each individual cell 11 comprises an electrode compartment 12 designed as an anode compartment 12 and an electrode compartment 13 designed as a cathode compartment 13, which are spatially and electrically separated from each other by a membrane of a membrane electrode assembly 15.

[0032] A membrane electrode assembly 15 comprises a membrane, two electrodes, and preferably two transport layers, wherein at least one electrode is provided on the membrane and / or at least one electrode is provided on a transport layer opposite the membrane. Naturally, both electrodes can also be provided on the membrane (membrane electrode assembly) or on the transport layers. The membrane or the membrane electrode assembly is preferably arranged in a sealing sleeve (sub-gasket) to which a bipolar plate 14 can be sealed. The respective transport layer is arranged in the fuel cell stack 10 in a corresponding anode compartment 12 or cathode compartment 13.

[0033] A bipolar plate 14 is arranged between two directly adjacent membrane electrode assemblies 15, 15, including a corresponding anode compartment 12 and a respective cathode compartment 13. This bipolar plate serves, among other things, to supply and discharge media 3 / 4, 6 into an anode compartment 12 of a first individual cell 11 and a cathode compartment 13 of a directly adjacent second individual cell 11, and also provides an electrically conductive connection between these individual cells 11, 11. The cathode compartments 13 and, if applicable, their common inlet area or their actual electrodes form a cathode 39, and the anode compartments 12 and, if applicable, their common inlet area or their actual electrodes form an anode 29 of the electrolysis cell stack 10.

[0034] In principle, a membrane electrode assembly 15 of the electrolysis cell stack 10 can have an AEM (Anion Exchange Membrane) or a PEM (Proton Exchange Membrane) in the form of a CCM (Catalyst Coated AEM / PEM). Furthermore, a membrane electrode assembly 15 preferably has transport structures (PTLs: Porous Transport Layers, sintered metal elements, fiber elements, flow fields and / or flow structures, etc.) on its large-area sides. The transport structures of the membrane electrode assemblies 15, which are not explicitly shown in the drawing, are located in the anode compartments 12 and the cathode compartments 13 of the electrolysis cell stack 10.

[0035] The electrolyzer system comprises, in addition to the electrolyzer unit 1, peripheral system components such as a control unit, which can be one of the electrolyzer units themselves, etc. To supply the electrolysis cell stack 10 with water 3 as a supply medium 3, the electrolyzer unit 1 has a water supply 20. And to extract the media 4, 6 from the electrolysis cell stack 10, the electrolyzer unit 1 has a media extraction port 30.

[0036] The water supply 20 comprises in particular: a water reservoir 23 for the water 3 (flowing in), a supply path 21 (medium path 21) and a water pumping device 26 on / in the supply path 21. - The medium extraction 30 has at least one disposal path 31 (medium path 31) for (cooling) water 4 or (cooling) water with oxygen 4 back into the water reservoir 23, possibly with a gas separator for oxygen, and / or in another direction (shown with dashed lines), e.g. into the environment 2.

[0037] A product medium 6 from the electrolyzer unit 1, i.e., the produced hydrogen 6, is transported through a product medium path 32 (medium path 32) from the medium outlet 30. A water separator 33 with a valve 34 can be installed in the product medium path 32 to separate water from the product medium path 32. The water separated in the water separator 33 can be returned to the water reservoir 23 or conveyed in another direction, e.g., to the surroundings 2 (gravitationally). The produced hydrogen 6 can, for example, be stored in a hydrogen storage tank 40, with the product medium path 32 potentially leading directly into the hydrogen storage tank 40. Other methods of transporting the hydrogen 6 are, of course, also possible.

[0038] Depending on the embodiment of the electrolyzer unit 1, the media flow within the electrolysis cell stack 10 can be configured differently. It is possible to provide a temperature control system that differs from the electrochemical function of the electrolysis cell stack 10, in particular water cooling, and / or to implement the temperature control system in conjunction with the electrochemical function of the electrolysis cell stack 10.

[0039] In particular, it is possible to configure a water supply of 3 exclusively on the anode side in membrane electrode devices 15 with A-EMs (dotted arrow at the anode 29). In this case, the water 3 can flow directly into the 'anode' 29. Furthermore, it is possible to configure a water supply of 3 exclusively on the cathode side 39 in membrane electrode devices 15 with PEMs (dotted arrow at the cathode 39). In this case, the water 3 can flow directly into the 'cathode' 39.

[0040] Within the scope of the invention (see, e.g., the Fig. 2) It was found that the higher the operating temperature level T of an electrolysis cell stack 10, the lower its polarization curve (voltage-current characteristic; see brackets above for voltage and current). If, with increasing lifetime t (BoL (Begin of Life) to EoL (End of Life)), the polarization curve 'moves upwards' due to aging (in particular an increase in voltage U), the polarization curve can be 'kept low' according to the invention by increasing the operating temperature level T.

[0041] The invention allows the 'height' of the polarization curve to be controlled and / or regulated (also) by means of an operating temperature level T, particularly from the point in time at which noticeable or significant degradation of the electrolysis cell stack 10 begins. This point in time often lies in a temporal middle and / or end section of the lifetime t of the electrolysis cell stack 10, but in some electrolysis cell stacks 10 it can already lie in an initial section (see below) of the lifetime t.

[0042] With proper tuning, the polarization curve can remain largely or essentially the same or constant over the lifetime t, and the power electronics 100 does not need to be designed to cover an 'upper' polarization curve from the prior art, thus avoiding oversizing the power electronics 100. This allows the power electronics 100 to be utilized essentially uniformly at all times / ranges within the lifetime t of the electrolysis cell stack 10.

[0043] According to the state of the art, the problem of designing a power electronics system 100 (see the Fig. 1) for an electrolysis cell stack 10 and / or vice versa in a significant increase in its electrical power requirement, usually from about the second half of its lifetime t, assuming a substantially constant hydrogen production rate m. Due to degradation of the electrolysis cell stack 10, a higher electrical voltage is required during the electrochemical water splitting process, which leads to an oversizing of the power electronics 100 with respect to the requirements at the beginning of the lifetime t of the electrolysis cell stack 10.

[0044] According to the invention, the operating temperature level T of the electrolysis cell stack 10 is influenced in such a way that over long periods of the lifetime t, in particular mainly or substantially over the entire lifetime t of the electrolysis cell stack 10: a mainly or substantially constant voltage V, a mainly or substantially constant current A, a mainly or substantially constant power P and / or a mainly or substantially constant hydrogen production rate is obtained.

[0045] In particular, the operating temperature level T of the electrolysis cell stack 10 is increased with increasing lifetime t, i.e., increasing degradation of the electrolysis cell stack 10; see a curve of the operating temperature level T in the Fig. 2. This allows, for example, a decrease in the hydrogen production rate m with increasing lifetime t to be at least partially compensated. Furthermore, it can alternatively or additionally at least partially compensate for an increasing electrical power requirement P of the electrolysis cell stack 10. This also means that the power electronics 100 can be electrically undersized, at least for the middle and / or end phases of the lifetime t of the electrolysis cell stack 10.

[0046] That is, without raising the operating temperature level T or without such power compensation of an undersized power electronics 100, the electrolysis cell stack 10 could not maintain a given hydrogen production rate m for the middle and / or end phases of its lifetime t. The power electronics 100 can be electrically dimensioned to a specific degree for the initial phase t, to be (partially) undersized to a specific degree for the middle phase t, and / or to be electrically undersized to a specific degree for the final phase t.

[0047] The operating temperature level T can be influenced, i.e., increased or decreased, particularly by cooling, preferably by (supply) water cooling of the electrolysis cell stack 10. For example, increasing the operating temperature level T can be achieved by reducing the supply water cooling, although other temperature levels (ambient temperature, etc.) should naturally be taken into account. Other measures for influencing the operating temperature level T are also applicable. In principle, this can be implemented by a control system and / or a regulation system.

[0048] The schematic diagram from the Fig. Figure 2 shows an example of such an operating temperature-controlled and / or regulated system, primarily or essentially: constant voltage V and constant current A, and thus also constant electrical power P; as well as an example degradation rate d of the electrolysis cell stack 10 over its lifetime t. In the short to medium term, but of course not in the long term (e.g., greater than 0.1 kh to 1 kh), the values ​​for hydrogen production rate m, voltage V, current A, and / or power P during the lifetime t may naturally fluctuate considerably, which may be due, for example, to a variable hydrogen production rate m.

[0049] The hydrogen production rate m, the voltage V, the current A, and / or the power P are ensured over the lifetime t of the electrolysis cell stack 10 mainly or substantially by means of power compensation, which influences the operating temperature level T of the electrolysis cell stack 10. The power compensation increases the operating temperature level T with increasing lifetime t; that is, globally over the lifetime t, the operating temperature level T is increased and not decreased.

[0050] Since aging or degradation is a continuous process that, in principle, begins with the first start-up of the electrolyzer unit 1, the power compensation for the potentially additional electrical power required by the power electronics 100 can, in principle, begin as early as the initial phase of the lifetime t of the electrolysis cell stack 10. If power compensation is already necessary at the beginning of the lifetime t, the power compensation is usually less than at the end of the lifetime t (see below).

[0051] In the initial phase of the lifetime t, the target power P can still be achieved at a low operating temperature T of the electrolysis cell stack 10. However, with increasing aging (middle and / or end phase of the lifetime t), the compensation due to the resulting increase in the operating temperature T of the electrolysis cell stack 10 also typically increases. Preferably, this compensation begins at a noticeable or significant degradation of the electrolysis cell stack 10.

[0052] The operating temperature level T can be in a range between approximately +20 °C and approximately +70 °C; other temperatures, such as approximately +20 °C to approximately +105 °C, are of course applicable. To remain below approximately 2.0 V per electrochemical cell 11 across the entire operating range, temperatures above approximately +20 °C are generally preferred. 2.0 V is a common value to avoid inefficient production, minimize overvoltages, and thereby slow the aging of the electrolysis cell stack 10. In general, the lower and upper operating temperature levels T are stack-specific.

[0053] If the operating temperature level T has a greater influence on the 'height' of the polarization curve, small temperature values ​​(ΔT) must be compensated for by power compensation. klein ) are added to the previous operating temperature level T (T + ΔT klein). Whereas with a smaller influence of the operating temperature level T due to power compensation, larger temperature values ​​(ΔT) are obtained. groß ) must be added (T + ΔT groß ), in order to keep the polarization curves at comparable 'levels'.

[0054] Since the degradation of the electrolysis cell stack 10 generally increases over its lifetime t, the temperature values ​​to be added per unit of time to reach an operating temperature level T will generally increase towards the end of the lifetime t of the electrolysis cell stack 10. However, if an electrolysis cell stack 10 ages significantly at the beginning of its lifetime t and then hardly or not at all towards the end of its lifetime t, then the temperature values ​​to be added per unit of time to reach the operating temperature level T will be larger at the beginning of the lifetime t. This all depends on the electrolysis cell stack 10, the power electronics 100, the electrolyzer unit 1, the electrolyzer system, etc.

[0055] For a mathematical mean of a multitude of electrolysis cell stacks 10, the following applies: initially, the controllable / controlled and / or regulated / regulated operating temperature level T is lower in order to obtain the desired polarization curve. With increasing lifetime t of the electrolysis cell stack 10 and the associated increasing aging, the operating temperature level T rises increasingly sharply towards the end of the lifetime t (in particular, the exponential curve of the operating temperature level T is initially flat (quasi-linear with a low slope) and then, as in the Fig. Figure 2 shows a progressively increasing temperature. Whether the increase begins after 10h, 100h, 1kH, 10kH, or later or even earlier depends on the stack, power electronics, unit, and / or system, etc. Exceptions to the set operating temperature level T can always occur, even with a single, specific electrolysis cell stack.

Claims

[1] Strategy for operating an electrolysis cell stack (10) of an electrolyzer or an electrolyzer unit (1), wherein the electrolysis cell stack (10) can be and / or is supplied with an electrical power (P) by a power electronics system (100) over its service life (t), characterized by , that an electrical power requirement of the electrolysis cell stack (10) which increases with increasing service life (t) is at least partially compensated by increasing an operating temperature level (T) of the electrolysis cell stack (10). [2] Operating strategy according to the previous claim, characterized by that the power electronics (100) is electrically under-dimensioned at least for a middle and / or end section of a service life (t) of the electrolysis cell stack (10) and / or is electrically dimensioned essentially specifically for an initial section. [3] Operating strategy according to one of the preceding claims, characterized by , that: • the electrolysis cell stack (10) is operable and / or operated at a low operating temperature level (T) in the initial phase (BoL =>) of its service life (t) and at a high operating temperature level (T) in the final phase (<= EoL) of its service life (t), • the electrolysis cell stack (10) in the middle section (BoL >=< EoL) of its service life (t) is operable and / or is operated at a medium operating temperature level (T) which lies between the low (T) and the high operating temperature level (T), and / or • over the service life (t) of the electrolysis cell stack (10), a course of a curve of the operating temperature level (T) correlates and / or causally relates to a degradation rate (d) of the electrolysis cell stack (10). [4] Operating strategy according to one of the preceding claims, characterized by , that: • a decreasing hydrogen production rate (m) of the electrolysis cell stack (10) with increasing service life (t) is at least partially compensated by increasing the operating temperature level (T) of the electrolysis cell stack (10), • an additional electrical power requirement of the electrolysis cell stack (10) with increasing service life (t) is not or only partially provided by the power electronics (100), and / or • the power requirement compensation sets an essentially constant power requirement of the electrolytic cell stack (10) over its service life (10). [5] Operating strategy according to one of the preceding claims, characterized by that the operating temperature level (T) of the electrolytic cell stack (10) is increased over the increasing service life (t) in such a way that: • a predetermined electrical power (P) of the power electronics (100) is essentially not exceeded, • a / the predetermined electrical power (P) of the power electronics (100) remains substantially constant, and / or • an electrical current (A) and an electrical voltage (V) for the electrolysis cell stack (10) remain substantially constant. [6] Operating strategy according to one of the preceding claims, characterized by , that • the operating temperature level (T) of the electrolysis cell stack (10) at the beginning (BoL) and / or in the initial time period (BoL =>) is at least approximately: 17 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C or 50 °C, in each case ± 2 °C, • the operating temperature level (T) of the electrolysis cell stack (10) at the end (EoL) and / or in the final time section (<= EoL) is at least approximately: 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, 85 °C, 90 °C, 95 °C, 100 °C or 105 °C, in each case ± 2 °C, and / or • the operating strategy can be carried out and / or is carried out by an electrolyzer or an electrolyzer unit according to one of the following claims. [7] Electrolyzer for an electrolyzer unit (1) or electrolyzer unit (1) for an electrolyzer system, with an electrolysis cell stack (10) and power electronics (100) for supplying the electrolysis cell stack (10) with electrical power (P), characterized by , that with respect to a hydrogen production rate (m) of the electrolysis cell stack (10), the power electronics (100) are designed to be electrically under-dimensioned at least for a middle and / or end section of a service life (t) of the electrolysis cell stack (10). [8] Electrolyzer or electrolyzer unit (1) according to the preceding claim, characterized by , that: • compensation for the under-dimensioning of the power electronics (100) is and / or will be realized by means of a variable operating temperature level (T) of the electrolysis cell stack (10), • the electrolysis cell stack (10) is operable and / or operated in the middle and / or final section of its service life (t) at a higher operating temperature level (T) than in the initial section of its service life (t), and / or • the variable operating temperature level (T) of the electrolysis cell stack (10) can be and / or will be realized by a control device for the electrolyzer or the electrolyzer unit (1). [9] Electrolyzer or electrolyzer unit (1) according to one of the preceding claims, characterized by , that: • the power electronics (100) are designed to be electrically dimensioned at least sufficiently for an initial period of the service life (t) of the electrolytic cell stack (10), • the power electronics (100) are not electrically significantly over-dimensioned for the initial period of the service life (t) of the electrolytic cell stack (10), or are essentially electrically specifically dimensioned, and / or • the power electronics (100) are electrically under-dimensioned for the middle and / or end section of the service life (t) of the electrolytic cell stack (10) by approximately: 5%, 10%, 15%, 20%, 25%, 30% or 35%, each ± ​​2.5%. [10] Electrolyzer or electrolyzer unit (1) according to one of the preceding claims, characterized by , that: • the initial time period is approximately: 0%, 1%, 5%, 10%, 15%, 20%, 25%, 30% or 40%, each ± ​​2 - 5% of the lifetime (t), • the final time period is approximately: 100%, 99%, 95%, 90%, 85%, 80%, 75%, 70%, 60%, 50% or 40%, each ± ​​2-5% of the lifetime (t), and / or • the electrolysis cell stack (10) is designed such that its service life (t) is approximately: 20 kh, 30 kh, 40 kh, 50 kh, 60 kh, 70 kh, 80 kh, 90 kh, 100 kh, 110 kh or 120 kh. [11] Electrolyzer or electrolyzer unit (1) according to one of the preceding claims, characterized by , that: • the power electronics (100) are designed in such a way that a substantially constant electrical power (P) can be made available and / or provided over the service life (t), • the hydrogen production rate (m) is a hydrogen production rate (m) that is essentially constant over the lifetime (t), and / or • an operating strategy according to one of the preceding claims can be and / or is carried out by means of the electrolyzer or the electrolyzer unit (1). [12] Electrolyzer system, characterized by , that Electrolyzer system an operating strategy according to one of the preceding claims is feasible and / or is carried out, and / or the electrolyzer system comprises an electrolyzer and / or an electrolyzer unit (1) according to one of the preceding claims.

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