Gas diffusion layer, electrochemical cell having such a gas diffusion layer, and electrolyzer

Abstract

A gas diffusion layer is arranged between a bipolar plate and an electrode of an electrochemical cell and includes at least two layers which are layered one on top of the other layer. At least one of the two layers is designed as a spring component having a progressive spring characteristic curve.

Claims

1. A gas diffusion layer arranged between a bipolar plate and an electrode of an electrochemical cell, said gas diffusion layer comprising: at least two separate layers formed as elements which are separate from each other, with one of the separate layers being layered on top of another one of the separate layers; and a spring component forming at least one of the at least two separate layers, said spring component having a progressive spring characteristic curve selected so as to achieve a deformation in a range of a normal contact pressure of 5-25 bars.

2. The gas diffusion layer of claim 1, wherein the gas diffusion layer has at least three separate layers formed as elements which are separate from each other and being layered on top of each other, said spring component forming an outer separate layer of the gas diffusion layer.

3. The gas diffusion layer of claim 1, wherein the at least two separate layers have different structure and/or composition.

4. The gas diffusion layer of claim 1, wherein the gas diffusion layer has at three layers, a first one of the layers configured as a contacting component, a second one of the layers configured as a diffusion component, and a third one of the layers configured as the spring component.

5. The gas diffusion layer of claim 1, wherein the spring characteristic curve of the spring component is divided into at least two regions of differing progression.

6. The gas diffusion layer of claim 1, wherein the spring characteristic curve of the spring component is divided into at least three regions of differing progression.

7. The gas diffusion layer of claim 1, wherein the spring component is deformed up to 60% of a maximum elastic deformation when a contact pressure of up to 5 bar is applied.

8. The gas diffusion layer of claim 1, wherein the spring component is deformed up to 80% of a maximum elastic deformation when a contact pressure of up to 5 bar is applied.

9. The gas diffusion layer of claim 1, wherein the spring component is deformed between 60% to 90% of a maximum elastic deformation when a contact pressure between 5 bar and 25 bar is applied.

10. The gas diffusion layer of claim 1, wherein the spring component is formed from an electrically conductive material.

11. The gas diffusion layer of claim 10, wherein the electrically conductive material is selected from the group consisting of steel, titanium, niobium, tantalum, nickel, and any combination thereof.

12. The gas diffusion layer of claim 1, wherein the spring component is formed as a profiled metal sheet.

13. The gas diffusion layer of claim 1, wherein the spring component is formed as a mesh.

14. The gas diffusion layer of claim 1, wherein the spring component comprises one or more spirals.

15. An electrochemical cell, comprising: a bipolar plate; an electrode; and a gas diffusion layer arranged between the bipolar plate and the electrode, said gas diffusion layer including at least two separate layers formed as elements which are separate from each other, with one of the layers being layered on top of another one of the layers, and a spring component forming at least one of the at least two separate layers, said spring component having a progressive spring characteristic curve selected so as to achieve a deformation in a range of a normal contact pressure of 5-25 bars.

16. The electrochemical cell of claim 14 constructed as a PEM electrolysis cell or a galvanic cell.

17. An electrolyzer, comprising a PEM electrolysis cell which includes a bipolar plate, an electrode, and a gas diffusion layer arranged between the bipolar plate and the electrode, said gas diffusion layer including at least two separate layers formed as elements which are separate from each other, with one of the layers being layered on top of another one of the layers, and a spring component forming at least one of the at least two layers, said spring component having a progressive spring characteristic curve selected so as to achieve a deformation in a range of a normal contact pressure of 5-25 bars.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) Exemplary embodiments of the invention can be explained with reference to a drawing, in which:

(2) FIG. 1 shows the basic structure of an electrochemical cell, which is configured by way of example as a PEM electrolysis cell,

(3) FIG. 2 shows progressive spring characteristic curves,

(4) FIG. 3 shows a side view of a first embodiment of a spring component of a gas diffusion layer,

(5) FIG. 4 shows a plan view of the first embodiment of a spring component of a gas diffusion layer,

(6) FIG. 5 shows a side view of a second embodiment of a spring component of a gas diffusion layer,

(7) FIG. 6 shows a plan view of the second embodiment of a spring component of a gas diffusion layer,

(8) FIG. 7 shows a spiral, which is part of the second embodiment as shown in FIG. 5 and FIG. 6,

(9) FIG. 8 shows a side view of a third embodiment of a spring component of a gas diffusion layer, and

(10) FIG. 9 shows a perspective illustration of the third embodiment of a spring component of a gas diffusion layer.

(11) Identical reference signs have the same meaning in the various figures.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(12) FIG. 1 schematically shows the structure of an electrochemical cell 2, which is in the form of a PEM electrolysis cell. The electrochemical cell 2 is part of an electrolyzer (not shown in more detail here) for the cleavage of water by electric current for the production of hydrogen and oxygen.

(13) The electrochemical cell 2 comprises an electrolyte consisting of a proton-conducting membrane 4 (Proton-Exchange-Membrane, PEM), on both sides of which are located the electrodes 6a, 6b. The assembly consisting of membrane and electrodes is referred to as a membrane-electrode-assembly (MEA). 6a in this respect denotes a cathode, and 6b denotes an anode. A gas diffusion layer 8 rests in each case on the electrodes 6a, 6b. The gas diffusion layers 8 are contacted by what are termed bipolar plates 10, which in the assembled state of an electrolysis stack separate a plurality of individual electrolysis cells 2 from one another.

(14) The electrochemical cell 2 is fed with water, which is decomposed at the anode 6b into oxygen gas O.sub.2 and protons H.sup.+. The protons H.sup.+ migrate through the electrolyte membrane 4 in the direction of the cathode 6a. On the cathode side, they recombine to form hydrogen gas H.sub.2.

(15) In another exemplary embodiment, the electrochemical cell 2 is designed as a galvanic cell, or fuel cell, formed for generating electricity. According to the invention, the gas diffusion layers 8 of electrochemical cells 2 formed in this manner are to be modified in a manner analogous to the electrolysis cell shown in FIG. 1. Without limiting generality, reference is therefore made hereinbelow, by way of example, to an electrochemical cell 2 formed as an electrolysis cell.

(16) The gas diffusion layer 8 ensures an optimum distribution of the water and also removal of the product gases. In the case of a galvanic cell, the gas diffusion layers 8 accordingly serve for feeding reactants to the respective electrodes. It is essential in this respect that the gas diffusion layer 8 is permeable to the gaseous products or reactants in any case.

(17) The gas diffusion layer 8 moreover serves as a power distributor, particularly in the case of an electrolysis cell. For these reasons, the gas diffusion layer 8 is formed from an electrically conductive, porous material.

(18) In the exemplary embodiment shown, component tolerances, in particular those of the contiguous bipolar plates 10, are compensated for by the gas diffusion layer 8. Therefore, the gas diffusion layer 8 contains layers layered one on top of another, with an outer layer being in the form of a spring component 12a, 12b, 12c (see FIGS. 3 to 9) having a progressive spring characteristic curve. The gas diffusion layer 8 comprises, in particular, a shown contacting component, a diffusion component and the spring component, which differ from one another in terms of their structure and/or composition.

(19) FIG. 2 shows two exemplary progressive spring characteristic curves K1 and K2. On the x axis, S denotes the spring travel, and on the y axis F denotes the spring force. As is apparent from FIG. 2, the spring characteristic curves are divided into three regions. A maximum elastic deformation V.sub.max, which is at approximately 50 bar in the exemplary embodiment shown, represents the point of transition between the elastic progression and the plastic progression of the spring characteristic curve, or between the elastic behavior and the plastic behavior of the spring. To the right of the maximum elastic deformation V.sub.max (corresponds to 100%), the spring undergoes purely plastic deformation.

(20) In a first region I, the spring component undergoes a relatively high degree of deformation at a relatively low contact pressure of up to 5 bar; in particular, a deformation of the spring characteristic curve K1 lies between 20% and 30% and a deformation of the spring characteristic curve K2 even lies at up to above 60%.

(21) In a second region II, at a contact pressure of between 5 bar and 25 bar, the deformation of the spring component lies between approximately 60% and approximately 90% with respect to the maximum elastic deformation V.sub.max.

(22) The spring component is moreover configured in such a manner that only a small degree of deformation takes place at a contact pressure of above 25 bar, such that the part of the standardized spring travel S is covered between 60% and 100% for K1 and between approximately 85% and 100% for K2.

(23) FIG. 3 and FIG. 4 show a first exemplary embodiment of a gas diffusion layer 8 having a spring component 12a. This comprises a metal sheet 14 with bent triangles 16, which are cut out at the surface and provide the metal sheet 14 with its resilient behavior. The spring behavior of a spring component 12a of this type is progressive, but has to be limited mechanically in order to avoid excessive plastic deformation of the metal sheet 14. In this case, this is done by spacers 18 impressed between the triangles 16. The spacers 18 are considerably more rigid than the upwardly bent triangles 16, and therefore the spring characteristic curve of the spring component 12a rises greatly as soon as the spacers 18 are moved into contact with the adjoining bipolar plate 10. As is apparent from FIG. 3, the gas diffusion layer 8 moreover comprises a contacting component 19, which is formed from a non-woven material and rests in the assembled state on an electrode 6a, 6b.

(24) FIG. 5 and FIG. 6 show a second embodiment of a gas diffusion layer 8 having a further spring component 12b. Here, the spring component 12b comprises a spiral mesh. The spiral mesh comprises cross-bars 20, which are arranged in succession and around which there are wound a plurality of spirals 22. FIG. 7 moreover shows an individual spiral 22, which forms the basis for the spring action of the mesh. The spiral mesh 12b is formed when spirals 22 with the same geometry but with a different winding direction are pushed alternately into one another and connected by the cross-bars 20. The cross-bars 20 are manufactured from plastic, for example. The spirals 22 are made of an electrically conductive material such as, e.g., high-grade steel, titanium, niobium, tantalum or nickel.

(25) FIG. 5 moreover shows a top layer 24, which takes on the function of a contacting component 19 of the gas diffusion layer 8. In this case, the top layer 24 is formed from a layering of expanded metal or of other porous and mechanically stable materials. Also conceivable, for example, are a non-woven material on a woven wire fabric, metal foam or a sintered metal disk.

(26) FIG. 8 and FIG. 9 show a third embodiment of the gas diffusion layer 8 having a third spring component 12c. In this case, the spring component 12c is configured in the manner of a corrugated metal sheet with an alternately opposing corrugation. This shape has the significant advantage that the flow is simultaneously guided in the indicated direction S. The resilience is provided here in three stages progressively rising from a very soft spring to a stop-like behavior (see FIG. 2). In FIG. 8 and FIG. 9, the reference sign 26 denotes locations which are fixed points on an expanded metal. The hatched area 28 in FIG. 9 represents a top layer 24 or contacting component 19 which is directed toward one of the electrodes 6a, 6b.

(27) The embodiment of the spring component 12c which is shown in FIG. 8 and FIG. 9 has a substantially two-dimensional form. A plurality of elastic portions of the spring component 12c are arranged at different intervals with respect to a lateral direction running substantially perpendicular to the two-dimensional extent (FIG. 8), in order to provide the progressive spring characteristic curve. This has the effect that only a few outer portions of the spring component 12c are deformed in the case of small deviations. In the case of relatively large deviations, both the deformation and the number of deformed portions of the spring component 12c increase, resulting in a non-linear rise in the force required for the deformation, and consequently a progressive spring characteristic curve.

(28) All of the above-described spring components 12a, 12b, 12c or gas diffusion layers 8 have the property that they compensate for component tolerances which arise in the electrolyzer, in order to allow for uniform contacting of the membrane-electrode-assembly in every instance of tolerance. On account of the progressive spring characteristic curve of the spring components 12a, 12b, 12c, excessive deformation of the gas diffusion layer 8 on one side is prevented in the case of overloading. In all of the embodiments, it is moreover conceivable to arrange a porous diffusion component (not shown in more detail here) between the spring component 12a, 12b, 12c and the contacting component 19, 24, 28.