DE102023111278A1 - Electrochemical cell stack and method for operating an electrochemical cell stack - Google Patents

Abstract

An electrochemical cell stack (1) comprises several electrochemical cells (2) which are separated from each other by bipolar plates (5), whereby
- 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 film 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).

Description

The invention relates to an electrochemical cell stack, in particular an electrolysis cell stack. The invention further relates to a method for operating such a stack of electrochemical cells.

An electrolysis cell stack is, for example, made from WO 2018/078157 A1 The known electrolysis cell stack, i.e. electrolyzer, comprises a plurality of bipolar plates arranged in a stack, with membranes and porous transport layers, which are also generally referred to as porous transport layers (PTL), being located between the bipolar plates. According to the 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 act as a corrosion protection layer within the electrochemical system.

The DE 10 2021 203 983 A1 discloses a single cell arrangement for a fuel cell stack. Here, 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 the DE 10 2021 203 983 A1 a bipolar plate which has flow distribution and guide 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.

Another membrane assembly, which separates an anode compartment from a cathode compartment within a fuel cell stack, is in the DE 10 2009 039 905 A1 The membrane of the arrangement according to the DE 10 2009 039 905 A1 has an elongated rectangular shape, with several channels, also generally referred to as ports, for the passage of working gases, i.e. operating media, on both narrow sides of the rectangular membrane. The membrane is part of an MEA plate, which is surrounded by an auxiliary assembly section, which is 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.

One in the DE 10 2008 028 117 A1 The arrangement for a fuel cell disclosed 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.

Further design options for seals in stacked arrangements of electrochemical cells are given, 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 out.

The EP 3 356 575 B1 discloses a high or differential pressure electrolysis cell, which has an electrochemical cell with a high pressure side and a low pressure side. The electrochemical cell comprises two flow field plates and a membrane, which is arranged between the flow field plates and has a first side on the low pressure side and a second side on the high pressure side. Furthermore, the electrolyzer according to the EP 3 356 575 B1 a first porous support arranged between the first side of the membrane and the first flow field plate and which is relatively incompressible compared to other materials arranged between the plates. A first seal surrounds the first porous support, with a gap being formed 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. The device according to the invention further comprises EP 3 356 575 B1 a second porous carrier arranged on the second side of the membrane, which is more compressible than the first porous carrier. The electrolyzer after the EP 3 356 575 B1 shall be operable at a pressure difference between the high pressure side and the low pressure side of at least 40 bar.

The EP 3 496 194 B1 describes a membrane electrode unit with a circumferential seal. In this case, a sealing frame is constructed in three parts, whereby a sealing material is to be displaced in a defined manner by pressing individual parts of the sealing frame together.

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 aspects.

This object is achieved according to the invention by an electrochemical cell stack which can be used in particular for hydrogen production and has the features of claim 1. The object is also achieved by a method for operating an electrochemical cell stack according to claim 10. In the following in connection with The embodiments and advantages of the invention explained in the operating methods also apply mutatis mutandis to the device, i.e. the stack of electrochemical cells, and vice versa.

• - jede elektrochemische Zelle aus zwei Halbzellen gebildet ist, welche eine Membran als gemeinsame Komponente aufweisen, die von einem mehrteiligen Trägerrahmen gehalten ist,
• - der mehrteilige Trägerrahmen aus zwei unter Einfügung einer mehrlagigen, mit der Membran überlappenden Folienanordnung aufeinander gestapelten, unterschiedlich breiten, jeweils einer Halbzelle zugeordneten Rahmenelementen aufgebaut ist,
• - sich an der dem Inneren der jeweiligen Halbzelle zugewandten Innenseite eines jeden Rahmenelementes eine jeweils eine Bipolarplatte kontaktierende Dichtung befindet,
• - die beiden aufgrund der unterschiedlichen Querschnittsform der Rahmenelemente gegeneinander versetzten Dichtungen jeweils eine äußere Lage der Folienanordnung kontaktieren.

The cell stack according to the application comprises a plurality of electrochemical cells, in particular electrolysis cells, which are separated from one another by bipolar plates in a basic concept known per se, whereby

• - 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,
• - 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 with the insertion of a multi-layer foil arrangement overlapping the membrane,
• - there is a seal contacting a bipolar plate on the inside of each frame element facing the interior of the respective half-cell,
• - 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.

Thus, each of the two seals attached to a frame element is in contact with one layer of the foil arrangement and with one of the two bipolar plates between which the electrochemical cell, in particular the electrolysis cell, is formed. The foil arrangement represents a sealing component which is effective both between the two frame elements stacked on top of one another and also acts as a static seal together with the seals attached to the frame elements facing the active field.

The different widths of the frame elements mean that the distance between the inside and outside of the frame is different for the two frame elements. The outside of the frame can be flush with each other. 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.

Each half-cell of the electrochemical cell can contain two porous transport layers that are arranged one on top of the other and can be distinguished from one another. Differences can be found, for example, in the porosity and/or electrical conductivity of the various transport layers. In general, an inner transport layer that contacts the membrane can be distinguished from a comparatively thick outer transport layer that contacts one of the bipolar plates. The film arrangement that encloses the membrane, overlapping the membrane, 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.

According to various possible designs, an equally flat intermediate region made up 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.

Regardless of the presence and possible design of the flat intermediate area, the two seals can be offset from each other without overlapping. In this case, one of the two seals is supported on the frame element associated with the other half-cell, while the other seal is supported by the outer transport layer that is surrounded by the first-mentioned seal. In this design in particular, the cell stack can be operated with high differential pressures, for example pressures of more than 100 bar, between the anode side and the cathode side. This applies even in cases where hydrogen is to be sealed.

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, this, together with the seal attached to it, limits a space available for the installation of the outer transport layer, which is smaller than the space enclosed by the narrower frame element including the seal. The outer transport layer enclosed by the latter frame element can have a lower elastic flexibility than the transport layer enclosed by the wider frame element. Each frame element represents a stable border for the associated seal.

Both frame elements are metal parts, whereby the seals can be bonded to the associated frame element in a material-locking manner, for example by injection molding. The seals can therefore be designed as edge bonding seals.

The cell stack can be used in particular 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 under 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 produced directly at a pressure of over 100 bar, which drastically reduces the effort required for subsequent compression of the hydrogen compared to conventional processes.

• 1 ausschnittsweise einen elektrochemischen Zellenstapel zur Produktion von Wasserstoff,
• 2 ein Detail des Zellenstapels nach 1, nämlich eine Anordnung aus einer katalytisch beschichteten Membran und hierauf befindlichen Folien,
• 3 eine Bipolarplatte des Zellenstapels,
• 4 den Zellenstapel in perspektivischer Ansicht mit teilweise in der Art einer Explosionsdarstellung vereinzelten Komponenten.

An embodiment of the invention is explained in more detail below with reference to a drawing. In the drawing:

• 1 section of an electrochemical cell stack for the production of hydrogen,
• 2 a detail of the cell stack after 1 , namely an arrangement of a catalytically coated membrane and foils located thereon,
• 3 a bipolar plate of the cell stack,
• 4 the cell stack in perspective view with some components separated in the manner of an exploded view.

An electrochemical cell stack, which is identified overall by the reference number 1, is designed as an electrolyzer for producing hydrogen. The cell stack 1 comprises a plurality of electrochemical cells 2, i.e. electrolysis cells, which are each made up 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 positioned like a sandwich between two bipolar plates 5 that are parallel to one another. For the supply and removal 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.

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 already mentioned 3 and 4 visible ports 23. 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.

The two half-cells 3, 4 are of different widths. Without restricting generality, in the present cases 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 that includes water and oxygen. Hydrogen is produced in the cathode-side half-cell 4. When the electrolyzer 1 is in the stationary state, there is a differential pressure between the two half-cells 3, 4 in the range of 30 bar to 100 bar.

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 an “inner” or “outer” layer refers to the proximity to the center plane of the respective electrochemical cell 2, which is given by the membrane 6. The anode-side inner porous transport layer 10, as well as the cathode-side inner porous transport layer 11, are 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.

As from 1 As can be seen, 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 dimension in the embodiment.

The larger surface area of the anode-side outer porous transport layer 12 corresponds to a stepped cross-section of the multi-part support frame 7. The support frame 7 comprises a 1 upper frame element 16 and a lower frame element 17 which is wider in the cross-section shown, so that overall a stepped shape of the support frame 7 is given. The outer contours of both frame elements 16, 17 coincide with each other.

On the inner contours that enclose the active field 8, there are seals 14, 15 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 accumulations of hydrogen in the gap-shaped area between the edge of the outer porous transport layer 12 and the seal 14, which is located on the frame element 16. The seals 14, 15 are made of an almost incompressible elastomer material. The sealing effect is initially achieved by the vertical pressure - based on the arrangement according to 1 - which acts on the seals 14, 15. The media pressure, which presses the seals 14, 15 against the associated frame elements 16, 17, reinforces this effect, so that one can speak of the effect of self-sealing.

Between the two superimposed frame elements 16, 17 made of metal there is a multi-layer film arrangement 9 which comprises a first film 18, a second film 19 and a third film 20 as layers 18, 19, 20 of equal thickness in the exemplary embodiment. The film arrangement 9 does not completely fill the gap between the frame elements 16, 17. Rather, the membrane 6 extends into the gap and lies there between the two outer layers 18, 20 of the film arrangement 9. This forms a flat intermediate region 21, to which the three-layer arrangement of the membrane 6 and the two inner porous transport layers 10, 11 adjoins inwards, within the active field 8. The film arrangement 9, which is 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.

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 consisting of the membrane 6 and the inner porous transport layers 10, 11 applied thereto.

• - eine erste dreilagige Anordnung aus der Membran 6 und den beiden inneren porösen Transportlagen 10, 11,
• - eine als Zwischenbereich 21 ausgebildete, ebenfalls dreilagige Anordnung aus der Membran 6 und den beiden äußeren Folien 18, 20,
• - die aus den drei Kunststofffolien 18, 19, 20 gebildete Folienanordnung 9.

Thus, there are three flat, adjacent areas which, on the anode side, border on the outer porous transport layer 12, on the seal 14 and on 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:

• - a first three-layer arrangement of the membrane 6 and the two inner porous transport layers 10, 11,
• - an intermediate region 21, also a three-layer arrangement consisting of the membrane 6 and the two outer films 18, 20,
• - 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, which act 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, on the other hand, introduces 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.

The membrane 6 is provided with a catalyst layer 22 on both sides. 2 The structure of the membrane 6 illustrated is uniform up to the intermediate region 21. This means that in the intermediate region 21 the films 18, 20 each contact a catalyst layer 22, which has no catalytic function in the corresponding region 21. The films 18, 20 compensate for micro and macro roughnesses of the catalyst layers 22 and thus also fulfill a sealing function in addition to their electrically insulating function.

list of reference symbols

1

electrochemical cell stack

2

electrochemical cell, electrolysis cell

3

half-cell

4

half-cell

5

bipolar plate

6

membrane

7

support frame, multi-part

8

active field

9

foil arrangement

10

inner porous transport layer, anode side

11

inner porous transport layer, cathode side

12

outer porous transport layer, anode side

13

outer porous transport layer, cathode side

14

seal

15

seal

16

frame element, narrow

17

frame element, wide

18

foil, first layer

19

foil, second layer

20

foil, third layer

21

intermediate area

22

catalyst layer

23

port

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• WO 2018078157 A1 [0002]
• DE 102021203983 A1 [0003]
• DE 102009039905 A1 [0004]
• DE 102008028117 A1 [0005]
• EP 3039734 B1 [0006]
• DE 102006058335 A1 [0006]
• DE 112015002427 T5 [0006]
• WO 2021104812 A1 [0006]
• EP 3356575 B1 [0007]
• EP 3496194 B1 [0008]

Claims (10)

Electrochemical cell stack (1) comprising a plurality of electrochemical cells (2) which are separated from one another by bipolar plates (5), whereby - 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 which are stacked on top of one another with the insertion of a multi-layer film arrangement (9) overlapping the membrane (6), - on the inside of each frame element (16, 17) facing the interior of the respective half-cell (3, 4) there is a seal (14, 15) which contacts a bipolar plate (5), - 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 have an outer layer (18, 20) of the foil arrangement (9). Cell stack (1) after 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 therewith 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). Cell stack (1) after 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). Cell stack (1) after claim 3 , characterized in that the flat intermediate region (21) contacts the two outer transport layers (12, 13). Cell stack (1) according to one of the Claims 2 until 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). Cell stack (1) according to one of the Claims 1 until 5 , characterized in that the two seals (14, 15) are offset from one another without overlap. Cell stack (1) according to one of the Claims 1 until 6 , characterized in that the frame elements (16, 17) are designed as metal frames. Cell stack (1) after claim 7 , characterized in that the seals (14, 15) are each materially connected to the associated frame element (16, 17). Use of a cell stack (1) according to one of the Claims 1 until 8 for the production of hydrogen by electrolysis. Method for operating an electrochemical cell stack (1) according to one of the Claims 1 until 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).

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