Gas separation stack

Abstract

A stack (1), particularly for gas separation, comprising at least two electrochemical cells (2) is proposed. Each electrochemical cell (2) has several layers (3), in particular an anode (4), a cathode (5), and a separator (6) separating the anode (4) from the cathode (5). According to the invention, two electrochemical cells (2) each form a cell pair (7), the cells (2) of which are oriented such that either the cathodes (5) or the anodes (4) face each other, wherein a bipolar plate (8) is arranged between two cathodes (5) of a cell pair (7) or between the cathodes (5) of two stacked cell pairs (7), and a gas or gas mixture can be supplied via the two cathodes (5).

Description

[0001] The present invention relates to a stack for gas separation, comprising at least two electrochemical cells.

[0002] The preferred application area of ​​the invention is electrochemical systems or plants for carbon dioxide separation. State of the art

[0003] Electrochemical cells used for gas separation typically have two coated electrodes that are electrically connected and separated by a separator. Both the separator and at least one electrode are usually saturated with or surrounded by an electrolyte, which ensures charge balance within the electrochemical cell. During operation, the cells are supplied with a gas stream containing a gas to be separated, for example, carbon dioxide. The gas to be separated is bound to one of the two electrodes—specifically, the cathode-side electrode—in an electrochemical process. Gas separation can be initiated by a change in temperature, pressure, or electrical voltage. The process is reversible, meaning that returning to the initial state reverses the polarity, so that the cathode becomes the anode.the anode becomes the cathode, resulting in a controlled release of the previously bound gas.

[0004] In addition to the electrodes and the separator, electrochemical cells typically have bipolar plates as further layers. These form outer layers and have flow channels on both sides for supplying the gas mixture or electrolyte. The bipolar plates thus separate the cathode-side electrode of one cell from the anode-side electrode of an adjacent cell. To increase efficiency and the amount of bound gas, a large number of electrochemical cells are stacked in practical applications and electrically connected, particularly via the bipolar plates. Such a cell stack is also called a stack.

[0005] The high number of electrochemical cells in a stack leads to large dimensions and high weight. This, in turn, limits the stack's performance in systems with size and / or weight restrictions.

[0006] The present invention is therefore concerned with the objective of increasing the performance of a stack while maintaining the same dimensions or maintaining the performance while reducing dimensions.

[0007] To solve the problem, the stack with the features of claim 1 is proposed. Advantageous embodiments of the invention can be found in the dependent claims.

[0008] For the sake of simplicity, the electrode of an electrochemical cell, through which the gas to be deposited is bound during gas deposition, will be referred to as the "cathode" in the following text. The other electrode will be referred to as the "anode." This means that the terms do not change, even though during the polarity reversal phase, the electrode referred to as the "cathode" becomes the anode and vice versa. Disclosure of the invention

[0009] A stack, particularly for gas separation, comprising at least two electrochemical cells is proposed. Each electrochemical cell has several layers, in particular an anode, a cathode, and a separator separating the anode from the cathode. According to the invention, two electrochemical cells form a cell pair, the cells of which are oriented such that either the cathodes or the anodes face each other, and a bipolar plate is arranged between two cathodes of a cell pair or between the cathodes of two stacked cell pairs, through which a gas or gas mixture can be supplied.

[0010] In conventional stacks, the electrochemical cells are oriented such that the cathode of a first electrochemical cell faces the anode of an adjacent electrochemical cell, with a bipolar plate forming flow channels arranged between them. In contrast, the electrochemical cells of a stack according to the invention are oriented such that the layers of each cell pair are arranged in a mirror image of each other. That is, the layers of the electrochemical cells forming a cell pair are stacked in reverse order, so that either the cathodes or the anodes of the two cells face each other.

[0011] In cases where the cathodes face each other and are separated by an intermediate bipolar plate, both cathodes can be supplied with a gas or gas mixture via a single bipolar plate. This allows the number of bipolar plates per cell pair to be reduced, in particular halved. This leads to a significant reduction in the thickness of the electrochemical cells within a cell pair or of the entire stack. Furthermore, the weight of the stack is reduced. Both effects enable a higher number of electrochemical cells per stack with the same dimensions, thereby increasing the overall performance of the stack. Alternatively, space and / or weight can be saved while maintaining the same performance. In addition, costs are reduced.

[0012] The significant thickness reduction results primarily from the fact that bipolar plates are generally structured and / or embossed sheets, forming flow channels on both sides. By placing such a bipolar plate between two cathodes, the flow channels on both sides can be used to supply the gas or gas mixture required by the cathodes for gas deposition. In contrast, a conventional stack with at least two electrochemical cells and a bipolar plate between the cathode of the first cell and the anode of the second cell leaves a dead volume on the anode side due to the flow channels, which are generally unused and must be filled with electrolyte.

[0013] In cases where the anodes of the electrochemical cells in a cell pair face each other, a bipolar plate separating the anodes can be omitted, achieving the same effects described previously. This means that the number of bipolar plates is reduced, in particular halved, so that, with unchanged stack performance, space and / or weight can be saved, or, with unchanged dimensions, performance can be increased. A further advantage is that the elimination of the bipolar plate between the facing anodes removes the dead volume that would otherwise need to be filled with electrolyte. This also reduces the costs associated with electrolyte supply. Furthermore, reducing the amount of electrolyte decreases the risk of impurities being introduced via the electrolyte and accumulating in the electrochemical cells.This can increase the efficiency and lifespan of the electrochemical cells.

[0014] Preferably, a stack according to the invention comprises a plurality of electrochemical cells, wherein two cells form a cell pair.

[0015] In a further development of the invention, it is proposed that a separating layer be arranged between two anodes of a cell pair or between the anodes of two adjacent cell pairs to provide material, electrical, and ionic separation of the anodes. This separating layer prevents contact between the electrically conductive anodes and thus avoids unwanted current flows and / or short circuits. This ensures that the functionality of the electrochemical cells is maintained.

[0016] Preferably, the separating layer has an electrically conductive coating on both sides for connection to a voltage source, preferably a power electronics unit. The electrically conductive coatings of the separating layer enable the necessary electrical contact between the anodes located on both sides, which are simultaneously electrically insulated by the separating layer. This electrical contact is necessary to apply an electrical voltage and / or current, which controls the electrochemical reaction in the cells.

[0017] The separating layer between two anodes is preferably flat and coated on both sides with an electrically conductive material across its entire surface. This electrically conductive coating enables surface contact between the anodes. Unlike contact that is only partial or localized, this has the advantage that a constant voltage can be applied across the entire surface of the anodes. This results in a more homogeneous voltage distribution at the anodes and thus a faster and improved release of electrons from the anodes.

[0018] The voltage source is preferably a power electronics unit. In addition to its function as a voltage source, the power electronics unit controls the applied voltage. By controlling the applied voltage, the quantity and / or rate of the electrochemical reaction can be set and adjusted as needed. Furthermore, gas release can be initiated and controlled by reversing the polarity of the applied voltage.

[0019] Advantageously, an electrically conductive coating of a first separating layer and an electrically conductive coating of a second separating layer are connected to the voltage source via a common electrical conductor. This electrical conductor can be, in particular, a power cable, busbar, clamp, clip, and / or plug-in element, thus simplifying the connection with an electrically conductive coating. By connecting the electrically conductive coatings of two different separating layers, the electrical circuit can be simplified and material can be saved.

[0020] In a further development of the invention, it is proposed that at least one electrically conductive coating of a separating layer of a first cell pair is connected to the bipolar plate of another cell pair via a common electrical conductor. The electrical contact between the conductive coating of one cell pair and a bipolar plate of another cell pair enables charge equalization and, in particular, electrical contact between the individual electrochemical cells. The electrochemical cells of the stack can thus be electrically connected in a series or parallel circuit to allow current flow through all electrochemical cells.

[0021] Preferably, the separating layer arranged between two anodes has a lateral overhang relative to the anodes. This lateral overhang ensures that the anodes, which are located on both sides of the separating layer, do not come into contact. This prevents short circuits, which can lead to efficiency losses and failures of the electrochemical cell. Furthermore, the lateral overhang simplifies the assembly and handling of the electrochemical cell. For example, the cell can be gripped and positioned automatically thanks to the overhang. An electrical conductor can also be more easily attached to the lateral overhang.

[0022] Preferably, the anodes of two stacked cells or cell pairs are in contact with the common separating layer over a flat area. This flat arrangement further reduces dead volume, thus avoiding unused volume within the cells. Additionally, this flat arrangement enables flat contact between the anodes and the separating layer or the electrically conductive coatings applied thereto.

[0023] Furthermore, the bipolar plate arranged between two cathodes preferably has a lateral overhang relative to the cathodes. This lateral overhang of the bipolar plate offers similar advantages to the lateral overhang of the separating layer. In particular, the overhang simplifies the handling of the electrochemical cell and the electrical contacting of the bipolar plate with an electrical conductor.

[0024] According to a preferred embodiment of the invention, the bipolar plate forms flow channels on both sides for the gas or gas mixture to be supplied to the cathodes. In the area of ​​the flow channels, the bipolar plate has no contact with the cathodes on either side, so that the gas to be absorbed can reach the surfaces of the cathodes. By minimizing the contact areas between the bipolar plate and the adjacent cathodes, the cathode surface area available for gas deposition can be maximized.

[0025] Further measures improving the invention are described below together with the figures. These show: Fig. 1 a schematic cross-section through a stack according to the invention in the region of a cell pair according to a first preferred embodiment of the invention, Fig. 2 a schematic cross-section through a stack according to the invention in the region of a cell pair according to a second preferred embodiment of the invention and Fig. 3 a schematic cross-section through a stack according to the invention analogous to the Fig. 1 or the Fig. 2 including means for electrical power supply. Detailed description of the drawings

[0026] Fig. Figure 1 shows a stack 1 according to a first preferred embodiment with two stacked electrochemical cells 2, which together form a cell pair 7. Each electrochemical cell 2 has several layers 3. These include an anode 4, a cathode 5, and a separator 6 arranged between them. The two electrochemical cells 2 are oriented such that their layers 3 are arranged in a mirror-image fashion within the cell pair 7. The cathodes 5 face each other, so that they are located inside the cell pair 7. The anodes 4 are accordingly located outside. A bipolar plate 8 is arranged as a further layer 3 between the two cathodes 5. This forms flow channels 13 through which the cathodes 5 can be supplied with a gas or gas mixture. Thus, both cathodes 5 can be supplied via just one bipolar plate 8.Each anode 4 has an electrically non-conductive and impermeable separating layer 9 on its outer surface. This separating layer 9 has an electrically conductive coating 10, which serves for the electrical contact of the adjacent anode 4. Depending on the division of the stack 1 into cell pairs 7, either half of the separating layer 9 adjacent to the anodes 4 can be assigned to each cell pair 7, or a full separating layer 9 can be assigned to either the upper or lower anode 4.

[0027] During operation of stack 1, a gas or gas mixture is supplied to the cathodes 5 via the flow channels 13 of the intermediate bipolar plate 8. A voltage is also applied to the cathodes 5 via the bipolar plate 8, which initiates and controls the gas deposition. An electrical voltage is also applied to the anodes 4, leading to the release of electrons.

[0028] The shared bipolar plate 8 arranged between the cathodes 5 eliminates the need for a second bipolar plate, thus significantly reducing the thickness of the cell pair 7. This is particularly relevant because the bipolar plate 8 is quite thick due to the flow channels 13. Given a fixed stack height 1, the number of electrochemical cells 2 can therefore be increased, boosting the power output. Alternatively, space and weight can be saved while maintaining the same power output.

[0029] In the Fig. In the stack 1 shown, two superimposed electrochemical cells 2 also form a cell pair 7', with the anodes 4 of the two cells 2 facing each other. The basic structure of the cells 2 does not differ from that of the cells 2 of the Fig. 1, so that the description of the Fig. 1 is referred to. This means that here too, the layers 3 of the cells 2 grouped into a cell pair 7' are arranged in a mirror image. Between the two facing anodes 4, instead of a bipolar plate 8, an electrically non-conductive separating layer 9 is arranged, which electrically insulates the two anodes 4 from each other. For electrical contact of the anodes 4, the separating layer 9 has an electrically conductive coating 10 on both sides. The omission of the bipolar plate 8 leads analogously to the Fig. 1 leads to a significant reduction in the thickness of the stack 1, thus achieving the same advantages. Only one bipolar plate 8 is required per cell pair 7', which forms flow channels 13 for the adjacent cathodes 5, in this case the cathodes 5 of two adjacent cell pairs 7'.

[0030] How a stack 1 is subdivided into cell pairs 7, 7' is therefore irrelevant. What is relevant is only that two adjacent electrochemical cells 2 form a cell pair 7, 7', whereby within the cell pair 7, 7' the layers 3 of the two cells 2 are arranged in reverse order or as mirror images.

[0031] Fig. Figure 3 shows a stack 1 with several cell pairs 7, 7', which - depending on the subdivision - are analogous to the Fig. 1 or the Fig. 2 are formed. The separating layers 9 adjacent to each pair of anodes 4 each have an electrically conductive coating 10 on both sides. The coatings 10 are connected to a voltage source 11 via a common electrical conductor 12. This voltage source 11 can be, in particular, power electronics by means of which an electrical voltage can be applied to the anodes 4. The voltage source 11 is also connected to at least one bipolar plate 8, via which an electrical voltage can be applied to the adjacent cathodes 5. Furthermore, in the Fig. 3 two further bipolar plates 8 with the electrically conductive coatings 10 of two separating layers 9 connected.

[0032] The one in Fig. The illustrated wiring of the power electronics with the electrodes is merely an example. A parallel wiring configuration can also be used instead of the series wiring shown.

Claims

[1] Stack (1), in particular for gas separation, comprising at least two electrochemical cells (2), wherein each electrochemical cell (2) has several layers (3), in particular an anode (4), a cathode (5) and a separator (6) separating the anode (4) from the cathode (5), characterized by , that each pair of electrochemical cells (2) forms a cell pair (7) whose cells (2) are oriented such that either the cathodes (5) or the anodes (4) face each other, wherein a bipolar plate (8) is arranged between two cathodes (5) of a cell pair (7) or the cathodes (5) of two adjacent cell pairs (7), and a gas or gas mixture can be supplied via the two cathodes (5). [2] Stack (1) according to claim 1, characterized by , that between two anodes (4) of a cell pair (7) or the anodes (4) of two adjacent cell pairs (7) a separating layer (9) is arranged for material, electrical and ionic separation of the anodes (4). [3] Stack (1) according to claim 1 or 2, characterized by , that the separating layer (9) has an electrically conductive coating (10) on both sides for connection to a voltage source (11), preferably with power electronics. [4] Stack (1) according to claim 3, characterized by , that an electrically conductive coating (10) of a first separation layer (9) and an electrically conductive coating (10) of a second separation layer (9) are connected to the voltage source (11) via a common electrical conductor (12). [5] Stack (1) according to claim 3 or 4, characterized by , that at least one electrically conductive coating (10) of a separating layer (9) of a first cell pair (7) is connected to the bipolar plate (8) of another cell pair (7) via a common electrical conductor (12). [6] Stack (1) according to any of the preceding claims, characterized by, that the separating layer (9) arranged between two anodes (4) has a lateral projection relative to the anodes (4). [7] Stack (1) according to any of the preceding claims, characterized by , that the anodes (4) of two adjacent cells (2) or cell pairs (7) each lie flat against the common separation layer (9). [8] Stack (1) according to any of the preceding claims, characterized by , that the bipolar plate (8) arranged between two cathodes (5) has a lateral overhang relative to the cathodes (5). [9] Stack (1) according to any of the preceding claims, characterized by , that the bipolar plate (8) forms flow channels (13) on both sides for the gas or gas mixture to be supplied to the cathodes (5).

Images