Electrochemical cell stack and method for operating an electrochemical cell stack
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-03-12
- Publication Date
- 2026-03-11
AI Technical Summary
Existing electrochemical cell stacks face challenges in manufacturing and sealing, particularly in maintaining effective seals under high differential pressures, which limits their efficiency in applications like hydrogen production.
The electrochemical cell stack design features a multi-part support frame with frame elements of different widths, overlapping multi-layer film arrangements, and offset seals that contact both the film and bipolar plates, creating a static sealing effect and enabling operation under high pressures over 100 bar.
This design allows for efficient hydrogen production under high pressures, reducing the effort for subsequent hydrogen compression and enhancing sealing efficacy, enabling the production of hydrogen at pressures over 100 bar while maintaining effective sealing.
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Abstract
Description
[0001] Electrochemical cell stack and method for operating an electrochemical cell stack
[0002] The invention relates to an electrochemical cell stack, in particular an electrolysis cell stack. Furthermore, the invention relates to a method for operating such a stack of electrochemical cells.
[0003] An electrolysis cell stack is known, for example, from WO 2018 / 078157 A1. The known electrolysis cell stack, i.e., electrolyzer, comprises a plurality of bipolar plates arranged in a stacked fashion, with membranes and porous transport layers, also commonly referred to as porous transport layers (PTLs), located between the bipolar plates. According to WO 2018 / 078157 A1, the bipolar plates each have a layer of Ir, Ru, Rh, Os, their oxides, or mixtures thereof. This layer is intended to function as a corrosion protection layer within the electrochemical system.
[0004] DE 10 2021 203 983 A1 discloses a single-cell arrangement for a fuel cell stack. A framed membrane electrode arrangement comprises an electrochemically active region made of two gas diffusion layers and a catalyst-coated membrane, which are bonded to a frame. Furthermore, the arrangement according to DE 10 2021 203 983 A1 comprises a bipolar plate having flow distribution and guiding elements in a flow region corresponding to the electrochemically active region. In an edge region of the bipolar plate surrounding the flow region, a sealing groove for receiving a seal between the frame and the bipolar plate is formed on at least one of the surfaces of the bipolar plate.
[0005] Another membrane assembly, which separates an anode chamber from a cathode chamber within a fuel cell stack, is described in DE 10 2009 039 905 A1. The membrane of the arrangement according to DE 10 2009 039 905 A1 has an elongated rectangular shape, with several channels, generally also referred to as ports, for the passage of working gases, i.e., operating media, located on both narrow sides of the rectangular membrane. The membrane is assigned to an MEA plate, which is surrounded by an auxiliary assembly section designed as a dimensionally stable support frame. Within a connecting section, which connects the MEA plate to the support frame, there is, among other things, a seal designed as a sealing bead.
[0006] An arrangement for a fuel cell disclosed in DE 10 2008 028 117 A1 comprises a bipolar plate in the form of a flat component to which a sealing element is positively attached. The sealing element is essentially U-shaped.
[0007] Further design options for seals in stacked arrangements of electrochemical cells can be found, for example, in the documents EP 3 039 734 B1, DE 10 2006 058 335 A1, DE 11 2015 002 427 T5 and WO 2021 / 104812A1.
[0008] EP 3 356 575 B1 discloses a high-pressure or differential-pressure electrolysis cell comprising an electrochemical cell with a high-pressure side and a low-pressure side. The electrochemical cell comprises two flow-field plates and a membrane arranged between the flow-field plates and having a first side on the low-pressure side and a second side on the high-pressure side. Furthermore, the electrolyzer according to EP 3 356 575 B1 comprises a first porous support arranged between the first side of the membrane and the first flow-field plate, which is relatively incompressible compared to other materials arranged between the plates. A first seal surrounds the first porous support, forming a gap between the first porous support and the seal. A second seal is arranged between the second side of the membrane and the second flow-field plate.Furthermore, the device according to EP 3 356 575 B1 comprises a second porous support arranged on the second side of the membrane, which is more compressible than the first porous support. The electrolyzer according to EP 3 356 575 B1 is intended to be operable at a pressure difference between the high-pressure side and the low-pressure side of at least 40 bar.
[0009] EP 3 496 194 B1 describes a membrane electrode assembly with a circumferential seal. In this case, a sealing frame is constructed in three parts, with a sealing material being displaced in a defined manner by pressing individual parts of the sealing frame together.
[0010] The invention is based on the object of further developing electrochemical systems constructed in stack form compared to the aforementioned prior art, in particular with regard to manufacturing and sealing technology.
[0011] This object is achieved according to the invention by an electrochemical cell stack which can be used in particular for hydrogen production and which has the features of claim 1. The object is also achieved by a method for operating an electrochemical cell stack according to claim 10. The embodiments and advantages of the invention explained below in connection with the operating method also apply mutatis mutandis to the device, i.e. the stack of electrochemical cells, and vice versa.
[0012] The cell stack according to the application comprises a plurality of electrochemical cells, in particular electrolysis cells, which are separated from each other by bipolar plates in a basic concept known per se, wherein
[0013] - each electrochemical cell is formed from two half-cells which have a membrane as a common component, which is held by a multi-part support frame,
[0014] - the multi-part support frame is constructed from two frame elements of different widths, each assigned to a half-cell, which are stacked on top of one another by inserting a multi-layer foil arrangement overlapping the membrane, - on the inside of each frame element facing the interior of the respective half-cell, there is a seal contacting a bipolar plate,
[0015] - the two seals, which are offset from each other due to the different cross-sectional shape of the frame elements, each contact an outer layer of the film arrangement.
[0016] Thus, each of the two seals attached to a frame element is in contact with a layer of the foil assembly and with one of the two bipolar plates between which the electrochemical cell, in particular the electrolysis cell, is formed. The foil assembly represents a sealing component that acts both between the two stacked frame elements and, together with the seals attached to the frame elements and facing the active field, provides a static seal.
[0017] The different widths of the frame elements mean that the distance between the inside and outside of the frame is different for both frame elements. The outside of the frame can be aligned. On the inside of the frame, however, the two frame elements form a step. This means that the area enclosed by one frame element, which is often rectangular, is larger than the area enclosed by the other frame element.
[0018] Each half-cell of the electrochemical cell can contain two superimposed, distinguishable porous transport layers. Differences can arise, for example, in the porosity and / or electrical conductivity of the various transport layers. Generally, an inner transport layer contacting the membrane can be distinguished from a comparatively thick outer transport layer contacting one of the bipolar plates. The film arrangement, which encloses the membrane and overlaps it, can, in particular, be constructed in three layers, with the thickness of the entire film arrangement corresponding to the sum of the thickness of the membrane and the total thickness of the two inner, thin transport layers.
[0019] According to various possible embodiments, an equally flat intermediate region consisting of the membrane and the two outer layers of the film arrangement is formed between the flat arrangement, which is made up of the membrane and the two inner transport layers, and the three-layer film arrangement. This means that the intermediate region represents the overlap between the membrane and the multi-layer film arrangement. Thus, three adjacent surface regions of equal thickness can exist. At least one of the two seals attached to the frame elements can contact the flat intermediate region. In particular, one of the two seals can rest on the top side and the other seal on the bottom side of the flat intermediate region. A section of each of the two outer transport layers can rest on the flat intermediate region.
[0020] Regardless of the presence and possible design of the flat intermediate area, the two seals can be offset from each other without overlap. In this case, one of the two seals rests on the frame element associated with the other half-cell, while the other seal is supported by the outer transport layer surrounded by the first seal. In this configuration in particular, the cell stack can be operated with high differential pressures, for example, pressures of more than 100 bar, between the anode and cathode sides. This applies even in cases where hydrogen must be sealed.
[0021] The frame element that supports one of the two seals is the wider frame element. Due to the wider cross-section of this frame element, together with the attached seal, it defines a space available for the installation of the outer transport layer that is smaller than the space enclosed by the narrower frame element including the seal. The outer transport layer enclosed by the latter frame element may have less elastic compliance than the transport layer enclosed by the wider frame element. Each frame element represents a stable border for the associated seal.
[0022] Both frame elements are primarily metal parts, and the seals can be integrally bonded to the corresponding frame element, for example, by injection molding. The seals can thus be designed as edge-bonded seals.
[0023] The cell stack is particularly useful as an electrolyzer for producing hydrogen from water. In general, the cell stack offers the possibility of operating the half-cells enclosed by the narrower frame elements at a higher pressure than the half-cells enclosed by the wider frame elements. In this way, in the case of electrochemical hydrogen production, hydrogen can be directly produced at a pressure of over 100 bar, which drastically reduces the effort required for subsequent compression of the hydrogen compared to conventional processes.
[0024] An embodiment of the invention is explained in more detail below with reference to a drawing. In the drawings:
[0025] Fig. 1 shows a section of an electrochemical cell stack for the production of hydrogen,
[0026] Fig. 2 shows a detail of the cell stack according to Fig. 1, namely an arrangement of a catalytically coated membrane and foils located thereon,
[0027] Fig. 3 shows a bipolar plate of the cell stack, Fig. 4 shows the cell stack in a perspective view with some components separated in the manner of an exploded view.
[0028] An electrochemical cell stack, designated overall by the reference numeral 1, is designed as an electrolyzer for producing hydrogen. The cell stack 1 comprises a plurality of electrochemical cells 2, i.e., electrolysis cells, each composed of a first half-cell 3 and a second half-cell 4. Bipolar plates 5 separate a half-cell 3 of a first electrochemical cell 2 from a half-cell 4 of another electrochemical cell 2. The two half-cells 3, 4 of each electrochemical cell 2 are separated from one another by a proton-permeable membrane 6. The membrane 6 is located in a multi-part support frame 7, which is sandwiched between two parallel bipolar plates 5. For the supply and discharge of operating and cooling media, the cell stack 1 has ports 23, which can be seen in each bipolar plate 23 and, in the present case, each have a circular cross-section.
[0029] The support frame 7 encloses an active field 8 of the electrolysis cell 2. Outside the active field 8, in which the desired electrochemical reactions take place, are the ports 23 already mentioned, visible in Figures 3 and 4. Within each electrochemical cell 2, the operating media of the cell stack 1 flow, among other things, through porous transport layers 10, 11, 12, 13, which are located in the half-cells 3, 4.
[0030] The two half-cells 3, 4 have different widths. Without loss of generality, in the present case, the anode-side half-cell 3 is referred to as the upper half-cell and the cathode-side half-cell 4 as the lower half-cell. The anode-side half-cell 3 contains a fluid mixture comprising water and oxygen. Hydrogen is produced in the cathode-side half-cell 4. When the electrolyzer 1 is in the steady state, a differential pressure in the range of 30 bar to 100 bar exists between the two half-cells 3, 4. In each half-cell 3, 4, an inner porous transport layer 10, 11 can be distinguished from an outer porous transport layer 12, 13. The characterization as “inner” or “outer” layer refers to the proximity to the center plane of the respective electrochemical cell 2 defined by membrane 6. The anode-side inner porous transport layer 10, like the cathode-side inner porous transport layer 11, is located on the surface of the membrane 6.The much thicker outer porous transport layers 12, 13, i.e. the anode-side outer porous transport layer 12 and the cathode-side outer porous transport layer 13, lie on the inner porous transport layers 10, 11 and each contact a bipolar plate 5.
[0031] As can be seen from Fig. 1, the anode-side outer porous transport layer 12 projects beyond the cathode-side outer porous transport layer 13. The two inner porous transport layers 10, 11, however, are of the same dimensions in the exemplary embodiment.
[0032] The larger surface area of the anode-side outer porous transport layer 12 corresponds to a stepped cross-sectional shape of the multi-part support frame 7. The support frame 7 comprises a frame element 16 located at the top in the arrangement according to Fig. 1 and a frame element 17 located at the bottom, which is wider in the cross-section shown, so that overall a stepped shape of the support frame 7 is achieved. The outer contours of both frame elements 16, 17 coincide with each other.
[0033] Seals 14, 15 are located on the inner contours surrounding the active field 8 on the frame elements 16, 17. In this case, the seals 14, 15 are designed as edge-bonding seals. The offset between the seals 14, 15, together with the stepped shape of the multi-part support frame 7 and the stability of the anode-side outer porous transport layer 12, contributes significantly to preventing the accumulation of hydrogen in the gap-shaped area between the edge of the outer porous transport layer 12 and the seal 14 located on the frame element 16. The seals 14, 15 are made of a virtually incompressible elastomeric material. The sealing effect is initially generated by the vertical pressure—relative to the arrangement shown in Fig. 1—acting on the seals 14, 15.The media pressure, which presses the seals 14, 15 against the corresponding frame elements 16, 17, reinforces this effect, so that one can speak of the effect of a self-sealing.
[0034] Between the two superimposed, metal frame elements 16, 17 there is a multi-layer foil arrangement 9 which comprises a first foil 18, a second foil 19 and a third foil 20 as layers 18, 19, 20 of equal thickness in the exemplary embodiment. The foil arrangement 9 does not completely fill the gap between the frame elements 16, 17. Rather, the membrane 6 extends into the aforementioned gap and lies there between the two outer layers 18, 20 of the foil arrangement 9. This forms a flat intermediate region 21, to which the three-layer arrangement comprising the membrane 6 and the two inner porous transport layers 10, 11 adjoins inwards, within the active field 8. The film arrangement 9, constructed from the three films 18, 19, 20, namely plastic films, adjoins the outer edge of the flat intermediate region 21 located within the support frame 7.
[0035] The thickness of the film arrangement 9 corresponds to the thickness of the intermediate region 21 as well as to the thickness of the arrangement comprising the membrane 6 and the inner porous transport layers 10, 11 applied thereto.
[0036] Thus, there are three flat, adjacent areas, which on the anode side border the outer porous transport layer 12, the seal 14 and the narrower frame element 16 and on the cathode side contact the outer porous transport layer 13, the seal 15 and the wider frame element 17:
[0037] - a first three-layer arrangement of the membrane 6 and the two inner porous transport layers 10, 11,
[0038] - an intermediate region 21, also a three-layer arrangement consisting of the membrane 6 and the two outer films 18, 20,
[0039] - the film arrangement 9 formed from the three plastic films 18, 19, 20. Each of the seals 14, 15 rests on the intermediate region 21. Forces F acting in the normal direction of the flat elements of the cell stack 1 are partially absorbed by the seals 14, 15. The anode-side seal 14 is supported on the wider frame element 17. The cathode-side seal 15, in contrast, transmits a force F into the anode-side outer porous transport layer 12, which is significantly stiffer than the cathode-side outer porous transport layer 13.
[0040] The membrane 6 is provided with a catalyst layer 22 on both sides. The structure of the membrane 6, illustrated in Fig. 2, is uniform up to the intermediate region 21. This means that in the intermediate region 21, the foils 18, 20 each contact a catalyst layer 22, which has no catalytic function in the corresponding region 21. The foils 18, 20 compensate for micro- and macro-roughness of the catalyst layers 22 and thus fulfill a sealing function in addition to their electrically insulating function.
[0041] List of reference symbols electrochemical cell stack electrochemical cell, electrolysis cell half cell
[0042] Half-cell
[0043] Bipolar plate
[0044] membrane
[0045] Support frame, multi-part
[0046] Active field
[0047] Foil arrangement inner porous transport layer, anode side inner porous transport layer, cathode side outer porous transport layer, anode side outer porous transport layer, cathode side Seal
[0048] seal
[0049] Frame element, narrow
[0050] Frame element, wide
[0051] Foil, first layer
[0052] Foil, second layer
[0053] Foil, third layer
[0054] Intermediate area
[0055] Catalyst layer
[0056] port
Claims
Patent claims 1 . Electrochemical cell stack (1) comprising a plurality of electrochemical cells (2) separated from one another by bipolar plates (5), wherein - each electrochemical cell (2) is formed from two half-cells (3, 4) which have a membrane (6) as a common component, which is held by a multi-part support frame (7), - the multi-part support frame (7) is constructed from two frame elements (16, 17) of different widths, each associated with a half-cell (3, 4), which are stacked on top of one another with the insertion of a multi-layer foil arrangement (9) overlapping the membrane (6), - a seal (14, 15) contacting a bipolar plate (5) is located on the inside of each frame element (16, 17) facing the interior of the respective half-cell (3, 4), - the two seals (14, 15) which are offset from one another due to the different cross-sectional shape of the frame elements (16, 17) each contact an outer layer (18, 20) of the film arrangement (9).
2. Cell stack (1) according to claim 1, characterized in that in each half-cell (3, 4) there are two superimposed porous transport layers (10, 12; 11, 13), namely an inner transport layer (10, 11) contacting the membrane (6) and a comparatively thick outer transport layer (12, 13) contacting one of the bipolar plates (5), wherein the film arrangement (9) which encloses the membrane (6) and overlaps it, is constructed in three layers, wherein the thickness of the film arrangement (9) corresponds to the sum of the thickness of the membrane (6) and the total thickness of the two inner transport layers (10, 11).
3. Cell stack (1) according to claim 1, characterized in that the overlap between the membrane (6) and the film arrangement (9) forms a flat intermediate region (21), which is formed from the membrane (6) and the two outer layers (18, 20) of the film arrangement (9), wherein at least one of the two seals (14, 15) contacts the flat intermediate region (21).
4. Cell stack (1) according to claim 3, characterized in that the flat intermediate region (21) contacts the two outer transport layers (12, 13).
5. Cell stack (1) according to one of claims 2 to 4, characterized in that the outer transport layer (12) which is enclosed by the narrower frame element (16) has a lower elastic flexibility than the transport layer (13) enclosed by the wider frame element (17).
6. Cell stack (1) according to one of claims 1 to 5, characterized in that the two seals (14, 15) are offset from one another without overlapping.
7. Cell stack (1) according to one of claims 1 to 6, characterized in that the frame elements (16, 17) are designed as metal frames.
8. Cell stack (1) according to claim 7, characterized in that the seals (14, 15) are each integrally connected to the associated frame element (16, 17).
9. Use of a cell stack (1) according to one of claims 1 to 8 for producing hydrogen by electrolysis.
10. A method for operating an electrochemical cell stack (1) according to one of claims 1 to 8, wherein the half-cell (3) enclosed by the narrower frame element (16) is operated under a higher pressure than the half-cell (4) enclosed by the wider frame element (17).