Electrochemical cell

Abstract

An electrochemical cell (1), particularly for binding carbon dioxide (CO2), comprising a layered structure with at least one bipolar plate (2) and a first electrode (3) and a second electrode (4) as a layer (5). The first electrode (3) has a surface that can be brought into contact with a gas and / or the second electrode (4) has a surface that can be brought into contact with an electrolyte. According to the invention, the surface(s) that can be brought into contact with the gas and / or the surface that can be brought into contact with the electrolyte are formed by an inner wall surface (6) which defines a continuous cavity volume (7) within the respective electrode (3, 4), forming flow paths (8) for the gas and / or the electrolyte.

Description

[0001] The present invention relates to an electrochemical cell with the features of the preamble of claim 1. The electrochemical cell can in particular be a cell for binding gases, especially carbon dioxide (CO2).

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

[0003] Electrochemical cells used for carbon dioxide capture typically consist of two coated electrodes that are electrically connected. At the first electrode, located on the cathode side, a gas, such as carbon dioxide, is bound from a gas mixture through chemical processes. A second electrode, located on the anode side, provides the electrons necessary for the capture reaction. An electrolyte serves to balance the charges, preventing the reaction from stalling due to the rising potential. A membrane is located between the two electrodes. This membrane is permeable to ions, thus ensuring charge balance within the cell while simultaneously providing electrical isolation between the two electrodes. Bipolar plates are adjacent to the electrodes, and in a series connection, the electrons flow between these plates from the first to the second cell.In a parallel circuit, they serve as contacts and, together with the membrane, ensure charge balance in the electrochemical cell. The bipolar plates have flow channels and / or paths that supply the gas and / or electrolyte to the surface of the cathode-side and / or anode-side electrodes, respectively.

[0004] The electrodes typically have an electrically conductive substrate on whose surface a coating suitable for the specific function of the electrode is applied. The cathode-side electrode is usually coated with a polymer that can bind gases, such as carbon dioxide, from a gas stream. Gas deposition is controlled by temperature, pressure, or electrical regulation. It is reversible, meaning that a change in temperature or pressure back to the initial state, or the removal / reversal of the voltage, leads to the release of the bound gases. The anode-side electrode is usually coated with a polymer capable of releasing electrons.

[0005] In practical applications, several electrochemical cells are typically stacked and electrically coupled. A cell stack coupled in this way is called a stack and features supply channels through which a gas is fed to the stack on the cathode side and distributed evenly across its surface via flow channels in a bipolar plate located against the cathode-side electrode. A design has become established in which the bipolar plates form flow channels and chambers on their surfaces. The flow channels facing the cathode-side electrode serve—as previously described—to supply the gas flow. The chambers facing the anode-side electrode serve to maintain a steady electrolyte.However, this shape of the bipolar plates leads to a certain height of the electrochemical cells, which, given a specific overall height of the stack, limits the number of cells and thus the amount of bound gas during operation of the stack.

[0006] The present invention is concerned with the objective of providing an electrochemical cell that minimizes the described limitations in order to increase, in particular, the volumetric and gravimetric efficiency of the electrochemical cell. Disclosure of the invention

[0007] To solve the problem, the electrochemical cell with the features of claim 1 is proposed. Advantageous embodiments of the invention are described in the dependent claims. An electrochemical cell, particularly for binding carbon dioxide (CO2), is proposed, comprising a layered structure with at least one bipolar plate and a first electrode and a second electrode as a layer and / or layer. The first electrode has a surface that can be brought into contact with a gas and / or the second electrode has a surface that can be brought into contact with an electrolyte. According to the invention, the surface(s) that can be brought into contact with the gas and / or the surface that can be brought into contact with the electrolyte are formed by an inner wall surface that defines a continuous cavity volume within the respective electrode, forming flow paths for the gas and / or the electrolyte.

[0008] The flow paths formed by the electrode eliminate the need for flow channels typically created by the bipolar plate adjacent to the electrode. By eliminating these flow channels, the bipolar plate can be made flat—at least on the side facing the electrode—thus reducing its overall height. This reduced height of the bipolar plate allows for a decrease in the overall height of the electrochemical cell and / or an increase in the electrode's volume fraction. This saves space and material costs and / or enables the absorption of more gas per electrochemical cell. Simultaneously, the gas absorption process is shortened because the inner wall surface, which defines the cavity volume, provides a larger surface area for gas absorption. The shortened process time allows for the absorption of a greater quantity of gas, thereby increasing the efficiency of the electrochemical cell.

[0009] Alternatively or additionally, the flow channels adjacent to the anode-side electrode for transporting the electrolyte can be omitted. These can be replaced by the flow paths formed by the anode-side electrode. This results in a bipolar plate that is flat on one or both sides, which further reduces the component height of the electrochemical cell and / or increases the volume fraction of the electrode.

[0010] Preferably, the first electrode and / or the second electrode has a base body to form the continuous cavity volume. - expanded metal, - sintered carbon fibers and / or - a metal foam.

[0011] The base body serves to receive a functional coating, which is applied to the inner wall surface that defines the cavity volume. The aforementioned materials are characterized by their inherently large, contiguous cavity volume. This means that the inner wall surface of these materials, which defines the cavity volume, is also large. Expanded metal has the additional advantage of being particularly cost-effective due to its simple manufacturing process. Sintered carbon fibers exhibit high strength and chemical resistance. They also possess high electrical conductivity while being relatively lightweight. Metal foams, on the other hand, have a very regular and, in particular, consistently reproducible pore structure. This allows for the production of metal foams of consistently high quality with minimal variations in pore structure.Furthermore, the pore size of the metal foams can be adjusted very precisely and can thus be adapted to the requirements of the electrochemical cell.

[0012] Regardless of whether the base body is that of the first or second electrode, it preferably has a coating. The coating is applied, in particular, to the inner wall volume that defines the cavity volume, so that it lines the cavity volume. The gas and / or electrolyte thus flows along the flow paths past the coated inner wall surfaces.

[0013] Furthermore, the base body of the first electrode preferably has a coating of a gas-absorbing polymer, preferably a polymer from the quinone group, which forms the surface area exposed to the gas. Gas-absorbing polymers have a particularly high affinity for binding gases, and especially carbon dioxide (CO2). Quinones, in particular, are able to bind large quantities of carbon dioxide. This can increase the efficiency of the electrochemical cell.

[0014] Preferably, the base body of the second electrode has a coating of an electron-releasing polymer, preferably a polymer from the ferrocene group, which forms the surface that can be brought into contact with the electrolyte. The release of electrons supports electrochemical gas binding at the cathode-side electrode. Electron-releasing materials, and in particular ferrocenes, are able to efficiently and reversibly provide larger quantities of electrons, thus further improving the efficiency of the electrochemical cell.

[0015] In a further development of the invention, it is proposed that the base body of the first electrode and / or the second electrode has macroscopic pores that form the continuous cavity volume of the respective electrode. The macroscopic pores, i.e., those visible to the naked eye, enable optimal gas distribution along the flow paths. As the size of the pores increases, so does the size of the inner wall surface on which the electrochemical reaction can take place. The macroscopic pores thus promote the efficiency of the electrochemical cell.

[0016] Preferably, the macroscopic pores have a pore size of 100 µm to 5000 µm. Above a pore size of 5000 µm, turbulence occurs, which negatively affects the flow rate. Below a pore size of 100 µm, flow obstructions occur, which impair the flow rate through the electrode.

[0017] In a preferred embodiment of the invention, the coating of the first electrode and / or the second electrode has microscopic pores, which increase the surface area of ​​the respective electrode. The pore size correlates with the size of the reaction surface, thus accelerating the electrochemical bonding of the gas. Furthermore, this allows larger quantities of gas to be stored.

[0018] Preferably, the microscopic pores have a pore size of 0.1–100 µm. Pores of this size, in particular, result in a suitably high carbon dioxide loading per volume. To prevent inhibition of the reactions by excessively small pores, a pore size of 0.1 µm should not be undercut.

[0019] The macroscopic pores of the base body and the microscopic pores of the coating create an electrode with a multimodal pore structure. This multimodal pore structure increases the efficiency of the electrochemical cell because it facilitates gas binding. This is achieved through the formation of a flow-through macroscopic pore network within which a smaller, microscopic pore network can develop, further supporting gas binding.

[0020] In a preferred embodiment of the proposed electrochemical cell, the at least one bipolar plate has a flat surface in contact with the first or second electrode. The flat surface of the bipolar plate reduces the overall height of the electrochemical cell or—with the overall height remaining the same—increases the volume fraction of the respective electrode(s). This improves the efficiency of the electrochemical cell and also reduces material costs.

[0021] Preferably, the at least one bipolar plate is designed as a plate with flat sides. The flat design of the bipolar plate further enhances the advantageous effects described above. A plate with flat sides is also particularly easy to manufacture, resulting in further cost savings.

[0022] Preferred embodiments of the invention are described in more detail below with reference to the figures. These show: Fig. 1 a schematic cross-section through several electrochemical cells according to a preferred embodiment of the invention, and Fig. 2 a schematic cross-section through an electrode of an electrochemical cell according to the invention in a preferred embodiment. Detailed description of the drawings

[0023] Fig. Figure 1 shows a schematic cross-section through several electrochemical cells 1 according to the invention for binding carbon dioxide (CO2). Each electrochemical cell 1 has several layers and / or layers 5, which are stacked on top of each other. These include, in particular, a first electrode 3 on the cathode side, a second electrode 4 on the anode side, and at least one bipolar plate 2. A membrane 11, which is always located between the first electrode 3 on the cathode side and the second electrode 4 on the anode side, separates the electrodes 3 and 4 from each other and serves to equalize the charge. The electrodes 3 and 4 each have a base body 9, which is coated with a functional polymer. The coating 10 of the first electrode 3 on the cathode side is typically a gas-binding polymer. During operation, it is in contact with a gas via a surface and is able to selectively bind a component of the gas by means of an electrochemical reaction.The second electrode 4 on the anode side, on the other hand, is coated with an electron-releasing polymer and provides the electrons required for the reaction at the first electrode 2.

[0024] In the cell stack shown in the figure, the individual electrochemical cells 1 are each separated from one another by a bipolar plate 2. The bipolar plates 2 have a laterally projecting area beyond the electrodes 3, 4. Sealing elements 11 are arranged between the bipolar plates 2 in this area. A stack is formed by stacking several electrochemical cells 1.

[0025] Fig. Figure 2 shows a schematic cross-section through an electrode 3, 4 of an electrochemical cell 1 according to the invention. The electrode 3, 4 can be the first electrode 3 on the cathode side or the second electrode 4 on the anode side. The electrode 3, 4 has a base body 9 that forms a continuous cavity volume 7. The cavity volume 7 is bounded by an inner wall surface 6 with a functional coating 10. The cavity volume 7 of the base body 9 is formed by macroscopic pores. The functional coating 10 applied to the inner wall surface 6 has microscopic pores. This results in a multimodal pore structure of the electrode 3, 4. The macroscopic pores of the base body 9 form flow paths 8 for the respective gas or electrolyte, depending on whether it is the cathode-side electrode 3 or the anode-side electrode 4.The flow paths 8 replace flow channels, which are usually formed by structuring the bipolar plate 2 adjacent to the electrode 3, 4. The elimination of the flow channels allows the bipolar plate 2 to be designed as a flat plate, as exemplified in . Fig. Figure 1 shows that this allows the overall height to be reduced and / or the volume fraction of the electrodes 3, 4 within an electrochemical cell 1 to be increased.

Claims

[1] Electrochemical cell (1), in particular for binding carbon dioxide (CO2), comprising a layered and / or layered structure with at least one bipolar plate (2), a first electrode (3) and a second electrode (4) and an intermediate membrane (11) as a layer and / or layer (5), wherein the first electrode (3) has a surface that can be brought into contact with a gas and / or the second electrode (4) has a surface that can be brought into contact with an electrolyte, characterized by , that the surface that can be brought into contact with the gas and / or the surface that can be brought into contact with the electrolyte is formed by an inner wall surface (6) which within the respective electrode (3, 4) defines a continuous cavity volume (7) that forms flow paths (8) for the gas and / or the electrolyte. [2] Electrochemical cell (1) according to claim 1, characterized by, that the first electrode (3) and / or the second electrode (4) form a base body (9) from to create the connected cavity volume (7) - expanded metal, - sintered carbon fibers and / or - contains a metal foam. [3] Electrochemical cell (1) according to claim 2, characterized by , that the base body (9) of the first electrode (3) has a coating (10) made of a gas-absorbing polymer, preferably a polymer from the group of quinones, which forms the surface that can be brought into contact with the gas. [4] Electrochemical cell (1) according to claim 2 or 3, characterized by , that the base body (9) of the second electrode (4) has a coating (10) made of an electron-releasing polymer, preferably a polymer from the group of ferrocenes, which forms the surface that can be brought into contact with the electrolyte. [5] Electrochemical cell (1) according to any one of claims 2 to 4, characterized by , that the base body (9) of the first electrode (3) and / or the second electrode (4) has macroscopic pores that form the continuous cavity volume (7) of the respective electrode (3, 4), wherein the macroscopic pores have a pore size of preferably 100 µm to 5000 µm. [6] Electrochemical cell (1) according to any one of claims 2 to 5, characterized by , that the coating (10) of the first electrode (3) and / or the second electrode (4) has microscopic pores which increase the surface area of ​​the respective electrode (3, 4), wherein the microscopic pores have a pore size of preferably 0.1 µm to 100 µm. [7] Electrochemical cell (1) according to any one of the preceding claims, characterized by, that the at least one bipolar plate (2) has a flat surface adjacent to the first electrode (3) or second electrode (4). [8] Electrochemical cell (1) according to any one of the preceding claims, characterized by , that the at least one bipolar plate (2) is designed as a plate that is flat on both sides.

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