Electrochemical cell and electrolyzer with a stack of electrochemical cells

Abstract

An electrochemical cell (1), comprising - a cell frame (2) surrounding an interior space (3) of the cell (1), - a first electrode and a second electrode, - a bipolar separating plate (5), which is arranged in the interior space (3) and in its outermost edge region is secured on the cell frame (2), wherein the cell frame (2) is formed from a fibre-reinforced plastic.

Description

[0001] Electrochemical cell and electrolyzer with a stack of electrochemical cells

[0002] Description:

[0003] The present invention relates to an electrochemical cell and an electrolyzer with a stack of electrochemical cells, in particular an alkaline electrolyzer.

[0004] With the increasing use of renewable energies, technologies for storing the generated electrical energy are gaining in importance. One possibility is storage in the form of hydrogen, which is produced using an electrolyzer. Depending on their design, such electrolyzers can consist of stacks of electrochemical cells. Typically, each cell has a steel frame, which can be circular or rectangular, surrounding the electrochemical cell and holding the bipolar separator plate, also made of steel or ceramic, which separates adjacent cells. Similar electrochemical cells are also used in fuel cells.

[0005] Manufacturing and finishing such cell frames with a diameter of, for example, 1.6 m requires expensive lathes. Mass production of cell stacks is not yet practical.

[0006] It is an object of the present invention to provide a cell frame for an electrolyzer with a stack of electrochemical cells that is particularly easy to manufacture and also reliably withstands pressure and heat loads.

[0007] This problem is solved by the subject matter of the independent claim. Advantageous embodiments and further developments are the subject matter of the dependent claims. According to one aspect of the invention, an electrochemical cell is provided, comprising a cell frame surrounding an interior space of the cell, as well as a first electrode and a second electrode arranged in the interior space of the cell. Furthermore, the electrochemical cell comprises a bipolar separator plate arranged in the interior space and held at its outermost edge by the cell frame. The cell frame is made of a fiber-reinforced plastic. The electrochemical cell according to the invention can be an electrochemical cell of an electrolyzer or another electrochemical cell, such as a fuel cell.

[0008] Preferably, the cell frame has a coefficient of thermal expansion cd that is slightly larger, in particular at most 20% larger, than a coefficient of thermal expansion 02 of the bipolar separating plate.

[0009] The electrochemical cell has the advantage that the cell frame and the bipolar separator exhibit essentially the same expansion behavior when heated. Due to the slightly higher coefficient of thermal expansion of the cell frame, it expands the bipolar separator somewhat and "smooths it out" when the cell is heated to operating temperature. This slightly higher coefficient of thermal expansion of the cell frame means that it expands somewhat more than the bipolar separator when heated. As a result, when heated, the cell frame exerts an outward force on the circumference of the bipolar separator, causing it to stretch and smooth out.

[0010] To prevent excessive mechanical stresses that could potentially lead to damage, the difference in the coefficient of thermal expansion is preferably no more than 20%. More preferably, the coefficient of thermal expansion of the cell frame ai is no more than 15% greater, and particularly preferably no more than 5% or between 5% and 10% greater, than the coefficient of thermal expansion 02 of the bipolar partition plate.

[0011] For example, the coefficient of thermal expansion of the cell frame ai is 1 T10' 6 1 / K < a < 15- 10' 61 / K (at 20°C). The bipolar separator plate is preferably made of a metal, for example, steel. The electrochemical cell has the advantage that the cell frame is particularly easy to manufacture, as it is made of plastic and can be produced using a casting or lamination process, for example, by lamination winding, and can be mass-produced with minimal effort. Due to the fiber reinforcement, the plastic exhibits the necessary stability even under pressure and temperature stress. If the coefficient of thermal expansion of the cell frame is, for example, 1 T10' 6 1 / K < ai < 15- 10' 6With a thermal conductivity of 1 / K, it is only slightly larger than that of the bipolar separator plate, so that no excessive mechanical stresses occur under temperature load. The electrochemical cell thus has the advantage of being particularly easy to mass-produce and can simultaneously withstand high operating pressures and temperatures.

[0012] According to one embodiment of the invention, the bipolar partition plate is positively connected to the cell frame. For this purpose, the bipolar partition plate can have a profile for positive anchoring in the cell frame, particularly in its outermost edge region where it is held against the cell frame. This profile can consist of areas of the partition plate bent out of the plane of the partition plate, forming undercuts in the cell frame and thus anchoring the partition plate in the cell frame.

[0013] Such a separating plate can be inserted into the mold during the production of the cell frame and, after the cell frame has been formed, is anchored in the plastic mass of the cell frame by the profile in its outermost edge area.

[0014] This embodiment has the advantage that a robust connection between the partition plate and the cell frame can be created in a simple manner. This positive-locking connection is preferably still stable even when the cell frame, due to its slightly higher coefficient of thermal expansion, exerts an outward force on the bipolar partition plate when heated.

[0015] According to one embodiment, the bipolar separating plate, also called a bipolar plate, has a strain structure in an area adjoining the outermost edge region to the inside. In particular, the strain structure can be designed as a circumferential folded area of ​​the separating plate.

[0016] According to this embodiment, the partition plate can absorb mechanical stresses in the cell frame even if it exhibits a different coefficient of thermal expansion than the cell frame. Differences in thermal expansion can then be compensated for by the expansion structure. For example, if the partition plate, which can be positively anchored in the cell frame, is stretched or pulled flat by the cell frame when heated, the expansion structure can expand slightly. This helps to avoid excessive mechanical stresses due to differing coefficients of thermal expansion between the bipolar partition plate and the cell frame.

[0017] A circumferential folded region of the partition plate, as used here and in the following, refers to a region extending over the entire circumference of the partition plate in which the partition plate is locally bent out of its main plane and then back into it, so that it is partially folded. Such an accordion-like expansion structure can be introduced into the bipolar partition plate by simple forming processes and has the advantage that stress equalization between the bipolar partition plate and the cell frame is possible in all directions. In particular, multiple circumferential folds can also be provided in the bipolar partition plate.

[0018] According to a preferred embodiment, the coefficient of thermal expansion of the cell frame is cd 13-10 -6 1 / K < ai < 15- 10 -61 / K. Such a coefficient of thermal expansion, cu, is very similar to that of steel. The coefficient of thermal expansion can be adjusted by a suitable selection of the plastic, the fibers, and the filler content, i.e., the proportion of fibers in the composite material. Alternatively or additionally, the coefficient of thermal expansion can be adjusted by a suitable choice of fiber orientation within the cell frame. In particular, the fibers can be arranged within the cell frame such that they extend primarily in the direction in which particularly low thermal expansion is desired. Specifically, the fibers preferably extend radially with respect to a surface normal of the plane spanned by the frame.

[0019] The plastic can be in the form of an epoxy resin or vinyl ester. It can also be glass fiber reinforced, for example, with E-glass fibers. E-glass fibers are particularly temperature-resistant and also resistant to many chemicals, making them especially suitable for use in the electrochemical cells of electrolyzers.

[0020] According to a further aspect of the invention, an electrolyzer with a stack of the described electrochemical cells is provided. The electrolyzer has the advantages already described in connection with the electrochemical cell.

[0021] Embodiments of the invention are described below by way of example with reference to schematic drawings.

[0022] Figure 1 shows a cross-section through an electrochemical cell according to a first embodiment of the invention,

[0023] Figure 2 shows a cross-section through an electrochemical cell according to a second embodiment of the invention and

[0024] Figure 3 shows a cross-section through an electrochemical cell according to a third embodiment of the invention.

[0025] Figure 1 shows a section of an electrochemical cell 1, for example an alkaline electrolyzer, with a cell frame 2 in a sectional view. The cell frame 2 has a frame body that surrounds an interior space 3 of the electrochemical cell 1. The cell frame 2 is made of glass fiber reinforced plastic. A bipolar partition 5 of the electrochemical cell 1 is mounted on the cell frame 2. The partition 5 is embedded in the cell frame 2 with its edge region 6.

[0026] The bipolar partition plate 5 is made of a metal, in particular steel. Its coefficient of thermal expansion largely corresponds to that of the cell frame 2, or is slightly lower. To absorb mechanical stresses resulting from minor differences in the coefficients of thermal expansion, the partition plate 5 has an expansion structure 7 in an area adjoining the edge region 6 inwards. The expansion structure 7 is designed as a circumferential, folded area of ​​the partition plate 5. If the cell frame 2 expands more than the partition plate 5, the connection between the cell frame 2 and the partition plate 5 in the edge region 6 of the partition plate 5 is relieved by the partition plate 5 being able to expand along the expansion structure 7.

[0027] Other elements of cell 1, in particular the electrodes, are not shown in the figures for the sake of clarity.

[0028] Figure 2 shows another embodiment of the electrochemical cell 1. This differs from the embodiment shown in Figure 1 in that it does not have an expansion structure 7 on the partition plate 5. However, the connection between the partition plate 5 and the cell frame 2 is particularly robust, since the partition plate 5 has a profile 8 in its edge region 6 for a positive-locking connection with the cell frame 2. Due to the profile 8, the partition plate 5 is positively locked and particularly securely anchored in the cell frame 2.

[0029] Figure 3 shows another embodiment of the electrochemical cell 1. In this embodiment, a profile 8 of the partition plate 5 is provided in its edge region 6 for positive-locking anchoring in the cell frame 2, as well as an expansion structure 7 in the partition plate 5 for compensating mechanical stresses. Reference numeral list:

[0030] 1 cell

[0031] 2 cell frames

[0032] 3 Interior

[0033] 5 Dividing plate

[0034] 6 Edge area

[0035] 7. Expansion structure 8. Profile

Claims

Patent claims:

1. Electrochemical cell (1) comprising - a cell frame (2) surrounding an interior space (3) of the cell (1), - a first electrode and a second electrode, - a bipolar partition plate (5) arranged in the interior (3) and held at its outermost edge on the cell frame (2), wherein the cell frame (2) is made of a fiber-reinforced plastic.

2. Electrochemical cell (1) according to claim 1 , wherein the cell frame (2) has a coefficient of thermal expansion ai which is slightly larger than a coefficient of thermal expansion 02 of the bipolar separating plate (5).

3. Electrochemical cell (1) according to claim 1 or 2, wherein the cell frame (2) has a coefficient of thermal expansion ai with 1 T 10' 6 1 / K< ai < 15-10 -6 exhibits 1 / K.

4. Electrochemical cell (1) according to one of the preceding claims, wherein the bipolar separating plate (5) is positively connected to the cell frame (2).

5. Electrochemical cell (1) according to claim 4, wherein the bipolar separating plate (5) has a profile (8) in its outermost edge region for a form-fitting anchoring in the cell frame (2).

6. Electrochemical cell (1) according to any one of claims 1 to 5, wherein the bipolar separating plate (5) has a strain structure (7) in an area adjoining the outermost edge region to the inside.

7. Electrochemical cell (1) according to claim 6, wherein the expansion structure (7) is formed as a circumferential folded region of the bipolar separating plate (5).

8. Electrochemical cell (1) according to one of claims 1 to 7, wherein 13-10' 6 1 / K < ai < 15-10 6 1 / K applies.

9. Electrochemical cell (1) according to any one of claims 1 to 8, the plastic is in the form of epoxy resin or vinyl ester.

10. Electrochemical cell (1) according to any one of claims 1 to 9, the plastic is glass fiber reinforced and contains an E-glass fiber.

11. Electrolyzer with a stack of electrochemical cells (1 ) according to any one of claims 1 to 10.

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