Cell for an electrochemical energy converter

Abstract

The present invention relates to a cell (100) for an electrochemical energy converter (300), the cell (100) comprising: - a membrane electrode assembly (MEA) (101), - a frame (103) encompassing the MEA, - a terrace seal (105), wherein the frame (103) comprises a frame body (107) and a frame terrace (109), wherein a height of the frame terrace (109) is smaller than a height of the frame body (107), wherein the terrace seal (105) is arranged at the frame terrace (109), wherein the MEA (101) comprises: - a porous transport layer (PTL) (111), - a gas diffusion layer (GDL) (113), - a membrane (115) arranged between the PTL (111) and the GDL (113), wherein the PTL (111) comprises a first part (117) having a first porosity and a second part (119) having a second porosity, wherein the second porosity is smaller than the first porosity, and wherein at least a part of the second part (119) overlies the terrace seal (105).

Description

[0001] R.414902

[0002] - 1 -

[0003] Description

[0004] Title

[0005] Cell for an electrochemical energy converter

[0006] The present invention relates to a cell for an electrochemical energy converter, a method for producing a cell for an electrochemical energy converter, and an electrochemical energy converter.

[0007] State of the art

[0008] A stack, i.e. a series arrangement of electrochemical cells, such as a fuel cell or an electrolysis stack, is well known in the art

[0009] Each cell in the stack has a layered construction, typically comprising an electrically insulating and chemically separating, but ion conducting composite polymer membrane with a respective (cathode and anode) electrode / catalyst layer provided on either side thereof, at which the actual electrochemical reaction takes place, such as H2O oxidation (OER: oxygen evolution reaction) at the anode and IT reduction (HER: hydrogen evolution reaction) at the cathode in case of electrolysis of water.

[0010] The anode and cathode catalyst layers comprise catalyst nano particles mixed with binder and support materials, typically an ionomer. This layered assembly of the membrane and the electrodes is often referred to catalyst coated membrane (CCM), which latter naming refers to the conventional production process of coating the membrane with the electrode catalyst mixture dissolved in a volatile solvent.

[0011] Further, the layered construction comprises a porous transport layer (PTL) or gas diffusion layer (GDL) on either (i.e. anode & cathode) side of the CCM for R.414902

[0012] - 2 - carrying electric currents? to or away from the electrodes, while allowing electrolyte and / or the electrochemical reactants and products to be supplied to or carried away from a respective electrode of the CCM.

[0013] The PTL / GDL can be provided as a metal open-celled foam, sintered metal powder or pellets or fibres or whiskers, woven or non-woven carbon fibres and the like.

[0014] Further, the layered construction comprises a metal “bipolar” plate (BPP) shared between and mutually chemically separating adjacent cells for coupling electric current out of, resp. into these cells, which plate can be corrugated such that it defines a fluid supply and distribution area and a fluid flow-field for the transport of the electrolyte, the reactant, the product and / or a cooling medium across the active area of the cell.

[0015] Disclosure of the invention

[0016] According to a first aspect, the present invention relates to a cell for an electrochemical energy converter.

[0017] The cell comprises a membrane electrode assembly (MEA), a frame encompassing the MEA, and a terrace seal, wherein the frame comprises a frame body and a frame terrace, wherein a height of the frame terrace is smaller than a height of the frame body, wherein the terrace seal is arranged at the frame terrace.

[0018] The MEA comprises a porous transport layer (PTL), a gas diffusion layer (PTL), and a membrane arranged between the PTL and the GDL.

[0019] The PTL comprises a first part having a first porosity and a second part having a second porosity, wherein the second porosity is smaller than the first porosity, and wherein at least a part of the second part overlies the terrace seal.

[0020] In the context of the present invention a porosity is to be understood as a value quantifying a number or density of pores in a volume. R.414902

[0021] - 3 -

[0022] The PTL is preferably made from sintered titanium.

[0023] The present invention is based on a PTL, in particular an anode PTL, that has a surface section in its second part of lesser porosity compared to its first part or no porosity. The second part is extending along at least a substantial part of its circumference on at least one side of the PTL that faces the membrane in the cell and at least opposite the terrace seal in the cell.

[0024] The second part of the PTL, which is a surface section, for example, is preferably non-porous, i.e. provides a continuous or solid flat surface.

[0025] By the at least less porous, preferably non-porous surface section of the second part of the PTL, a sealing force acting on the terrace seal is more evenly distributed compared to the first part of the PTL pressing in the terrace seal.

[0026] Moreover, the second part of the PTL has an increased stiffness compared to the first part of the PTL. As a consequence, the effectiveness of the terrace seal can be improved and a gas leakage from one side of the cell to another side, in particular a hydrogen leakage, is minimized.

[0027] According to an embodiment, the second part of the PTL extends fully to its side edge and continuously along its entire circumference. In particular, the second part of the PTL encompasses the first part of the PTL.

[0028] A second part that encompasses the first part may only be provided at the side edges of the PTL that overlie the terrace seal. Thus, a large first part is provided that is energy efficient for a chemical reaction taking place in the cell during operation of an electrochemical energy converter.

[0029] According to an embodiment, a surface of the second part is non-porous.

[0030] A non-porous may be provided by a coating or a filler filled in the pores of the second part of the PTL. R.414902

[0031] - 4 -

[0032] According to an embodiment, more pores in the second part of the PTL are filled with a filler than in the first part of the PTL.

[0033] In particular by adjusting a sintering rate with a sinter metal as filler, the filling of the pores of the PTL may be controlled and adjusted such that more pores in the second part of the PTL are filled with a filler than in the first part of the PTL

[0034] According to an embodiment, a density of the second part of the PTL is greater than a density of the first part of the PTL.

[0035] The density of the second may be enhanced compared to the density of the first part, by compression of the second part.

[0036] According to an embodiment, the second part comprises a rim element having a planar surface and / or non-porous surface.

[0037] An additional rim element, such as a plastic or metal block, can be used to set the second porosity in the second part of the PTL smaller than the first porosity in the first part of the PTL. Such a rim element may pressed and / or glued and / or welded on the second part of the PTL.

[0038] According to a second aspect, the present invention relates to a method for producing a cell for an electrochemical energy converter.

[0039] The method comprises providing a PTL comprising a first part having a first porosity and a second part having a second porosity, wherein the second porosity is smaller than the first porosity, combining a membrane and the PTL with a GDL to form a MEA, and combining the MEA with a frame, wherein the frame comprises a frame body and a frame terrace, wherein a height of the frame terrace is smaller than a height of the frame body, wherein a terrace seal is arranged at the frame terrace, and wherein at least a part of the second part of the PTL overlies the terrace seal. R.414902

[0040] - 5 -

[0041] According to an embodiment, the PTL is provided by filling, at least partially, more pores in the second part of the PTL with a filler than in the first part of the PTL

[0042] By filling more pores with a filler, a more stable and more flat surface is generated.

[0043] According to an embodiment, the PTL is provided by varying a filling density of a sinter medium in a PTL-sintering process, wherein the filling density is higher in the second part of the PTL than in the first part of the PTL.

[0044] At least in water electrolysis, the anode PTL is typically made of sintered titanium. In a sintering process, the porosity resulting after sintering can be locally varied by varying the filling density of the sinter medium, such as a powder, pellets or fibers in the PTL sintering mold before sintering. In particular, the sinter mold filling density may be set higher in the second part of the PTL than in the first part of the PTL.

[0045] According to an embodiment, the PTL is provided by compression of the PTL, wherein the second part of the PTL is compressed with a stronger compression force than the first part of the PTL.

[0046] The porosity of the PTL can be locally varied, i.e. reduced or removed by locally compressing the PTL after sintering. Hereby, the PTL pores are locally compressed and closed and the PTL is locally provided with a flatter, i.e. more planar surface section facing the membrane of the unit cell and the terrace seal located on the opposite side thereof.

[0047] By compression of the PTL, the free porous space between the material forming the PTL is minimized. Thus, the porosity of the PTL is reduced. By varying the local compression force, the porosity of the PTL can locally varied.

[0048] According to an embodiment, the PTL is compressed using one at least stepshaped anvil that forms a step shaped edge at the second part of the PTL. R.414902

[0049] - 6 -

[0050] A step shaped anvil causes a first area providing a first compression force and a second area providing a second compression force, wherein the first compression is different, in particular greater than the second compression force. Thus, in the first area, the PTL is compressed stronger, resulting in a less porous first part of the PTL.

[0051] According to an embodiment, the PTL has a greater thickness in the second part of the PTL than in the first part of the PTL, before compression.

[0052] A step pressed into the PTL can be disadvantageous, because the membrane is bent around the corner of the edge of such step upon assembly and / or operation of the cell. This may limit the minimal thickness of the membrane that can be used to provide it with sufficient mechanical strength. Therefore, i.e. to minimize the step height in the PTL on the membrane-side thereof in relation to the PTL edge compression amount, the PTL can also be compressed from both sides, by halving the step height on the membrane side of the PTL, for example.

[0053] Alternatively or additionally to minimize the step or steps in the PTL formed by the edge compression thereof, the PTL can be pre-manufactured, in particular sintered with a thicker edge section, i.e. second part on one side or on two sides, which thicker edge section is then compressed, ideally to the extent that the surface thereof lies flush with a central, main surface of the PTL.

[0054] According to an embodiment, a rim element is inserted in the second part of the PTL, wherein the rim element is flush with the first part of the PTL.

[0055] A gap formed by compressing the PTL with a step shaped anvil can be filled-in with an additional rim element, in particular a plastic or a metal, such as titanium, rim element.

[0056] The rim element can be provided as a single, integral “window frame” part or as composed of 2 L-shaped sections or 4 linear sections, for example. R.414902

[0057] - 7 -

[0058] According to a third aspect, the present invention relates to an electrochemical energy converter, wherein the electrochemical energy converter comprises a stack of a number of possible embodiments of the cells disclosed herein.

[0059] Because of the cells disclosed herein, the electrochemical energy converter disclosed herein is very gas-tight and, therefore, very energy efficient.

[0060] According to an embodiment, the electrochemical energy converter, is a fuel-cell system or an electrolysis system.

[0061] BRIEF DESCRIPTION OF THE DRAWINGS

[0062] The foregoing and other features and advantages of the invention will become further apparent from the following detailed description read in conjunction with the accompanying drawings. In the drawings, like reference numerals refer to like elements.

[0063] Figure 1 shows a cell according to an embodiment of the invention disclosed herein,

[0064] Figure 2 shows a PTL of the cell according to Fig. 1 in detail,

[0065] Figure 3 shows a method for producing a cell for an electrochemical energy converter, according to an embodiment of the invention disclosed herein,

[0066] Figure 4 shows an embodiment of the method according to Fig. 3 in detail,

[0067] Figure 5 shows another embodiment of the method according to Fig. 3 in detail,

[0068] Figure 6 shows a raw material for carrying out the method according to Fig. 3, R.414902

[0069] - 8 -

[0070] Figure 7 shows an embodiment of the electrochemical energy converter disclosed herein.

[0071] In Fig. 1 , a cell 100 for an electrochemical energy converter 300 is shown.

[0072] The cell 100 comprises a membrane electrode assembly (MEA) 101 , a frame 103 encompassing the MEA 101 , and a terrace seal 105.

[0073] The frame 103 comprises a frame body 107 and a frame terrace 109, wherein a height of the frame terrace 109 is smaller than a height of the frame body 107, and wherein the terrace seal 105 is arranged at the frame terrace 109, in a recess formed by the frame terrace 109 or a step formed by the frame terrace 109, for example.

[0074] The MEA 101 comprises a porous transport layer (PTL) 111 , a gas diffusion layer (GDL) 113, a membrane 115 arranged between the PTL 111 and the GDL 113.

[0075] The PTL 111 comprises a first part 117 having a first porosity and a second part 119 having a second porosity, wherein the second porosity is smaller than the first porosity. As can be seen in Fig. 1 , the second part 119 overlies the terrace seal 105.

[0076] Due to the less porous second part 119, a sealing force acting on the terrace seal 105 by the second part 119 is much greater compared to a PTL having an evenly distributed porosity. Thus, a leakage of gas, in particular of hydrogen, from one side of the membrane 115 to the other, is minimized.

[0077] Further, the higher porosity in the first part 117 provides for optimal conditions for electrochemical reactions within an active area of the cell.

[0078] Further, an optional Mesh 121 is shown in Fig. 1 to reduce costs of the cell 100 by requiring a thinner PTL 111 and to improve water flow across the cell 100 by providing larger and straighter channels for such flow compared to the pores in the PTL 111 , as indicated by arrows 123. R.414902

[0079] - 9 -

[0080] The membrane 115 is coated with catalyst layers 125 for improving the energetic efficiency of chemical reactions in the cell 100.

[0081] In the frame 103 delta channels 127 are formed for guiding fluid out of the cell or into the cell, as indicated by arrows 129 and 121 , respectively.

[0082] In Fig. 2, the PTL 111 is shown in detail. Here, it can be seen that the less porous second part 119 forms a frame around the more porous first part 117.

[0083] In the cell 100, the first part 117 is part of an active area of the cell 100, thereby allowing a stream of fluid to reach the catalyst coated areas of the membrane 115 due to its high porosity.

[0084] In Fig. 3, a method 200 for producing a cell 100 for an electrochemical energy converter 300 is shown.

[0085] The method 200 comprising a providing step 201 , in which a PTL 111 comprising a first part 117 having a first porosity and a second part 119 having a second porosity, wherein the second porosity is smaller than the first porosity, is provided, a first combination step 203, in which a membrane 115 and the PTL 111 are combined with a GDL 113 to form a MEA 101 , and a second combination step 205, in which the MEA 101 is combined with a frame 103, wherein the frame 103 comprises a frame body 107 and a frame terrace 109, wherein a height of the frame terrace 109 is smaller than a height of the frame body 107, wherein a terrace seal 105 is arranged at the frame terrace 109, and wherein at least a part of the second part 119 of the PTL 111 overlies the terrace seal 205.

[0086] In Fig. 4, an anvil 401 is shown that is used for compression of raw material 403 for forming the PTL 111.

[0087] The anvil 401 is pressed against a barrier 411 , as indicated by arrow 413. Optionally the barrier 411 may be pressed against the anvil 401 .

[0088] The anvil 401 is step formed at its edges 405, such that a higher compression force is acting on the raw material 403 at the edges 405, compared to a center R.414902

[0089] - 10 - area 407. Thus, a resulting PTL 111 becomes denser and, therefore, less porous at the edges, which form second parts 119, compared to a first part 117 between the second parts 119. An abutment surface 409 is limiting the compression at the second parts 119.

[0090] In Fig. 5 a press 501 is used, by which the raw material 403 is compressed from both sides, as indicated by arrows 503. Thus, a halving of the step height is achieved, compared to the arrangement shown in Fig. 4, which results in a lower minimal thickness of the cell 100.

[0091] In Fig. 6 different raw material 601 , 603 are shown for production of the PTL 111.

[0092] Raw material 601 has thicker section 605 on one side of its edge, which, when compressed by the arrangement according to Fig. 4, becomes flush with the central first part 117 of the PTL 111.

[0093] Raw material 603 has thicker sections 607 on both sides of its edge, which, when compressed by the arrangement according to Fig. 5, become flush with the central first part 117 of the PTL 111.

[0094] In Fig. 7, an electrochemical energy converter 300 in form of a fuel-cell system is shown. The energy converter 300 comprises a stack 301 of fuel-cells 100 according to Fig. 1 , for example.

Claims

R.414902- 11 -Claims1 . Cell (100) for an electrochemical energy converter (300), the cell (100) comprising: a membrane electrode assembly (MEA) (101), a frame (103) encompassing the M EA, a terrace seal (105), wherein the frame (103) comprises a frame body (107) and a frame terrace (109), wherein a height of the frame terrace (109) is smaller than a height of the frame body (107), wherein the terrace seal (105) is arranged at the frame terrace (109), wherein the MEA (101) comprises: a porous transport layer (PTL) (111), a gas diffusion layer (GDL) (113), a membrane (115) arranged between the PTL (111) and the GDL (113), wherein the PTL (111) comprises a first part (117) having a first porosity and a second part (119) having a second porosity, wherein the second porosity is smaller than the first porosity, and wherein at least a part of the second part (119) overlies the terrace seal (105).

2. Cell (100) according to claim 1 , characterized in that, the second part (119) of the PTL (111) encompasses the first part (117) of the PTL (111).

3. Cell (100) according to claim 1 or 2, characterized in that, a surface of the second part (119) is non-porous.R.414902- 12 -4. Cell (100) according to any of the preceding claims, characterized in that, more pores in the second part (119) of the PTL (111) are filled with a filler than in the first part (117) of the PTL (111).

5. Cell (100) according to any of the preceding claims, characterized in that, a density of the second part (119) of the PTL (111) is greater than a density of the first part (117) of the PTL (111).

6. Cell (100) according to any of the preceding claims, characterized in that, the second part (119) comprises a rim element (121) having a planar surface and / or non-porous surface.

7. Method (200) for producing a cell (100) for an electrochemical energy converter (300), the method (200) comprising: providing (201) a PTL (111) comprising a first part (117) having a first porosity and a second part (119) having a second porosity, wherein the second porosity is smaller than the first porosity combining (203) a membrane (115) and the PTL (111) with a GDL (113) to form a MEA (101), combining (205) the MEA (101) with a frame (103), wherein the frame (103) comprises a frame body (107) and a frame terrace (109), wherein a height of the frame terrace (109) is smaller than a height of the frame body (107), wherein a terrace seal (105) is arranged at the frame terrace (109), and wherein at least a part of the second part (119) of the PTL (111) overlies the terrace seal (205).R.414902- 13 -8. Method (100) according to claim 7, characterized in that, the PTL (111) is provided by filling, at least partially, more pores in the second part (119) of the PTL (111) with a filler than in the first part (117) of the PTL (111).

9. Method (100) according to claim 7, characterized in that, the PTL (111) is provided by varying a filling density of a sinter medium in a PTL-sintering process, wherein the filling density is higher in the second part (119) of the PTL (111) than in the first part (117) of the PTL (111).

10. Method (100) according to any of claims 7 to 9, characterized in that, the PTL (111) is provided by compression of the PTL (111), wherein the second part (119) of the PTL (111 ) is compressed with a stronger compression force than the first part (117) of the PTL (111).11 . Method (100) according to claim 10, characterized in that, the PTL (111) is compressed using one at least step-shaped anvil that forms a step shaped edge at the second part (119) of the PTL (111).

12. Method (100) according to claim 10 or 11 , characterized in that, the PTL (111) has a greater thickness in the second part (119) of the PTL (111) than in the first part (117) of the PTL (111) before compression.

13. Method (100) according to claim 11 or 12, characterized in that, a rim element (121 ) is inserted in the second part (119) of the PTL (111), wherein the rim element (121) is flush with the first part (117) of the PTL (111).R.414902- 14 -14. Electrochemical energy converter (300), wherein the electrochemical energy converter (300) comprises a stack (301) of a number of cells (100) according one of claims 1 to 6.

15. Electrochemical energy converter (300) according to claim 14, characterized in that, the electrochemical energy converter (300), is a fuel-cell system or an electrolysis system.

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