Cell stack with water reservoir and method for transporting and / or storing a cell stack

Abstract

The present invention relates to a cell stack (1) of electrochemical cells (2). The cell stack (1) is connected to a water tank (10), wherein a valve (13, 14) between the water tank (10) and an anode (3) and / or cathode (4) of the electrochemical cells (2) is open. The cell stack (1) is in a resting state.

Description

The present invention relates to a cell stack of electrochemical cells having a water storage and to a method for transporting and / or storing such a cell stack.Prior ArtElectrochemical energy converters such as fuel cell systems or electrolyzers are known in numerous different embodiments. The core component of these systems is usually a stack structure which has a plurality of electrochemical cells. More specifically, such a stack structure usually comprises bipolar plates (BPP) and membrane electrode assemblies (MEA) stacked alternately one above the other. The membrane is to allow only cations to pass to the cathode, i.e. generally H+lons, in the PEM electrolyser, in analogy to the PEM (proton exchange membrane) fuel cell. In the case of an alkaline AEM (anion exchange membrane) electrolyser which is operated on the anode side and / or on the cathode side with alkaline solution, for example a KOH solution, only anions pass, that is to say generally OH ions pass in the direction of the anode.For transport, cell stacks of electrochemical cells are often flooded with water and sealed, so that the membranes can be kept moist.It is an object of the present invention to improve the moisturizing of the membrane for storage and / or transport of the cell stack.Disclosure of the InventionFor this purpose, the cell stack of electrochemical cells is connected to a water tank. A valve between the water tank and an anode and / or a cathode of the electrochemical cells is opened. The cell stack is in the idle state. The idle state hereby expressly does not indicate an idle operation of the cell stack, but rather a completely shut-off cell stack, which is stored or transported. This is therefore a cell stack outside all operating states.The water tank filled with water ensures that, when the valve is open, the cell stack remains flooded during transport or during storage even in the event of a certain leak, so that the membranes of the electrochemical cells are kept moist. Drying of the membranes due to a certain leak in the cell stack is thus prevented even in the case of longer transport or storage times.The electrochemical cells preferably each have a membrane which is designed as an exchanger membrane, for example as a proton exchanger membrane. Such membranes, i.e. suitable either for cation transport or for anion transport, should be kept moist until the start of operation of the cell stack, in order to ensure optimum performance at the start of operation.The electrochemical cells are advantageously designed as electrolysis cells, for example as PEM electrolysis cells, AEM electrolysis cells or CO2 elektrolysezell cells.In advantageous refinements, the water tank has a fill level marking. As a result, at the beginning of the transport or at the beginning of the storage, a reference can be marked in the simplest way, with which a leak in the cell stack is determined at the end of the transport or at the end of the storage, by comparing this reference with the fill level which is then present.The water tank preferably alternatively or additionally has a fill level sensor. The fill level sensor can reliably output the volume of the water located in the cell stack, preferably in digital form.In advantageous refinements, the fill level sensor is connected to an evaluation unit by means of a data connection. The evaluation unit can thus ascertain, for example, a leak in the cell stack over time. The tightness of the cell stack can thereby preferably even be monitored online.The invention also relates to methods for storing and / or transporting a cell stack according to one of the above explanations. The cell stack is in the idle state during storage or transport. The anode and / or cathode of the electrochemical cells of the cell stack are supplied with water from the water tank. This prevents the membranes of the electrochemical cells from being dried out in a harmful manner. For this purpose, the electrochemical cells do not have to be rinsed with water, but rather the water can be present in a quasi-standing manner.In preferred refinements of the method, the cell stack has been subjected to a conditioning process for moistening membranes of the electrochemical cells before storage or before transport. This conditioning process advantageously took place with the application of electric current, so that ion transport through the membrane already took place. The water tank now provides sufficient water for moistening the membrane for the period of time between the conditioning process and the startup of the cell stack.In advantageous embodiments of the methods, the water tank has a fill level sensor. The fill level sensor is connected to an evaluation unit by means of a data connection. The evaluation unit monitors the tightness of the cell stack. Thus, for example, a leakage quantity per time [mm 3 / h] for the cell stack can be determined for the transport or for the storage.They show in each case schematically: FIG. 1 shows a schematic illustration of an electrochemical cell according to the prior art, only the essential regions being illustrated, FIG. 2 shows a cell stack according to the invention, only the essential regions being shown.In the following description of the embodiments of the invention, identical or similar elements are denoted by identical reference symbols, wherein a repeated description of these elements is omitted in individual cases. The figures only schematically represent the subject matter of the invention.FIG. 1 shows an electrochemical cell 2 in the form of a fuel cell or electrolysis cell. The electrochemical cell 2 has a membrane 21 as electrolyte. The membrane 21 separates an anode space or the anode 3 from a cathode space or the cathode 4 In the cathode space and in the anode space, an electrode 23, 24, a diffusion layer 25 and a bipolar plate 26 are arranged on the membrane 21, respectively. The combination of the membrane 21 and the electrodes 23, 24 forms a membrane-electrode unit 29.Media are supplied in or on the bipolar plates 26. In the case of electrolysis cells 2, water is fed to the anode 3 and, if appropriate, also to the cathode. This diffuses through the corresponding diffusion layer 25 substantially homogeneously to the membrane electrode unit 29.For a stack of a plurality of electrochemical cells 2, membrane electrode arrangements 29 and bipolar plates 26 are usually alternately stacked one above the other in a stacking direction z. A bipolar plate 26 thus functionally belongs to two adjacent electrochemical cells 2.FIG. 2 schematically shows a cell stack 1 according to the invention of electrochemical cells 2 embodied as electrolysis cells. The anode connection 30 is fluidically connected to the anodes 3 of the electrolysis cells 2. The cathode connection 40 is fluidically connected to the cathodes 4 of the electrolysis cells 2. The two connections 30, 40 can thereby represent an inlet and / or an outlet for the media during the operation of the cell stack 1.The anode connection 30 has a valve 13, which is preferably designed as a shut-off valve. The cathode connection 40 has a valve 14, which is preferably designed as a shut-off valve. Connected to the anode connection 30 and the cathode connection 40 via the valves 13, 14 is a water tank 10 from which water can be supplied to the anode 3 and the cathode 4, respectively. In alternative embodiments, a single water tank 10 is connected to both the anode 3 and the cathode 4. In further alternative embodiments, the water tank 10 is connected only to the anode 3 or only to the cathode 4.The water tank 10, which is connected to the connections 30, 40 on the anode side and / or on the cathode side, guarantees a controlled, continuous supply of water, which compensates for the leakage loss of water that has leaked out of the cell stack 1. This is advantageous in particular during transport or storage of the cell stack 1, i.e. outside operation, since the cell stack 1 is not supplied with product water in such idle states.By changing the fill level in the water tank 10, the tightness and quality of the cell stack 1 during transport and storage can be assessed. For this purpose, the water tank 10 preferably has a fill level marking 11 which is attached to the water tank 10 at the beginning of the storage or transport of the cell stack 1. Alternatively, a fill level sensor 12 with a data connection 16 can also be used.With the aid of the fill level sensor 12, the tightness or the water loss of the cell stack 1 can even be determined online over time. For this purpose, the fill level sensor 12 is connected to an evaluation unit 17 via the data connection 16. The data connection 16 can be designed, for example, as a cable or also as a Bluetooth connection. The evaluation unit 17 can be a computing unit, for example for determining a time-dependent tightness, or else a system which emits a warning signal from a certain tightness.The water tank 10 also guarantees, by supplying water to the electrochemical cells 2 of the cell stack 1, that the membranes 21 of the electrochemical cells 2 are kept moist. This may be very important for the function of starting the operation of the cell stack 1 after an initial conditioning of the cell stack 1 depending on the type of membranes 21, since the membranes 21 can transport ions only if they have sufficient moisture. This applies in particular if the membranes 21 are ion exchange membranes, in particular PEM membranes, i.e. "proton exchange membrane".This type of water supply to the membranes 21 is possible with minimal media contamination, since the connections of the cell stack 1 to the environment do not have to be opened for this; only the valve 13, 14 for the fluidic connection of the membranes 21 to the water tank 10 has to be opened. Advantageously, the system of cell stack 1 and water tank 10 is hermetically sealed from the outside.In addition to the embodiments shown, the invention allows further design principles. That is, the invention should not be considered limited to the exemplary embodiments explained with reference to the figures. As can be seen with reference to the figures, numerous further combination variants of the embodiments and methods shown are possible, which have not all been described in detail. These variations are not, of course, to be regarded as excluded from the scope of the claimed invention.

Claims

Cell stack (1) of electrochemical cells (2), wherein the cell stack (1) is connected to a water tank (10), wherein a valve (13, 14) is opened between the water tank (10) and an anode (3) and / or cathode (4) of the electrochemical cells (2), characterized in that the cell stack (1) is in the idle state.Cell stack (1) according to Claim 1da characterized in that the electrochemical cells (2) each have a membrane (21) which is designed as an exchanger membrane, preferably as a proton exchanger membrane.Cell stack (1) according to claim 1 or 2da characterized in that the electrochemical cells (2) are electrolytic cells.Cell stack (1) according to one of Claims 1 to 3da, characterized in that the water tank (10) has a filling level marking (11).Cell stack (1) according to one of Claims 1 to 4da characterized in that the water tank (10) has a fill level sensor (12).Cell stack (1) according to Claim 5da, characterized in that the fill level sensor (12) is connected to an evaluation unit (17) by means of a data connection (16).Method for storing or transporting a cell stack (1) according to one of the preceding claims, characterized in that the cell stack (1) is in the idle state and in that the anode (3) and / or cathode (4) of the electrochemical cells (2) are supplied with water from the water tank (10).Method according to claim 7 characterised in that prior to storage or before transport, the cell stacks (1) were subjected to a conditioning process for moistening membranes (21) of the electrochemical cells (2).Method according to Claim 7 or 8, wherein the water tank (10) has a fill level sensor (12), wherein the fill level sensor (12) is connected to an evaluation unit (17) by means of a data connection (16), characterized in that a tightness of the cell stack (1) is monitored by means of the evaluation unit (17).

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