Fuel cell and fuel cell system for an aircraft

Abstract

The invention relates to a fuel cell and a fuel cell system for an aircraft. In order to improve the availability of hybrid-electric or all-electric aircraft, a fuel cell (10) is presented which has an increased efficiency and an increased, volume-specific or weight-specific energy density. The fuel cell (10) has a self-supporting membrane structure (12) which is designed as a triple periodic smooth surface, which gas-tightly separates a first cavity (14) to which fuel (40) is applied from a second cavity (16) to which oxidizing agent (42) is applied, whereas the two cavities (14, 16) are connected to one another in an ion-conducting manner.

Description

TECHNICAL FIELD

[0001] The present invention relates to a fuel cell. The present invention further relates to a fuel cell system for an aircraft and to an aircraft. BACKGROUND

[0002] Energy storage systems with high energy density are considered as a pioneer for electrically powered aircraft. Alternative drive concepts and energy sources are becoming increasingly important not only in private transportation but also in aviation. One concept is an electrical drive or the production of electrical energy in general in an aircraft. Hybrid electric aircraft and all-electric aircraft as well as other systems and devices (in the field of motor vehicles, industry and leisure) sometimes require energy storage with less weight or volume. From an aviation perspective, high power density, simple maintainability and high scalability are important. A candidate for providing the required energy is a fuel cell, in particular a solid oxide fuel cell.

[0003] Currently, in particular batteries and hydrogen-based systems are used. A solid oxide fuel cell (SOFC) is a high-temperature fuel cell which converts fuel (e.g. hydrogen) and oxidant (e.g. air) into electricity, heat and other by-products such as water.

[0004] SOFCs usually have an electrolyte, an anode and a cathode as well as connectors (so-called interconnectors). Interconnectors are able to better conduct the generated electrical current, since at the usual operating temperatures the electrical conductivity of the anode and cathode can be too low to effectively conduct the current. Today's architectures are based on flat or tubular cells, since these cells are easier to manufacture and the ratio of effective area to volume (also called: A / V) is relatively advantageous. SUMMARY

[0005] It is an object of the present invention to improve a fuel cell for use in aviation.

[0006] The present invention provides a fuel cell, preferably a solid oxide fuel cell, for use in a fuel cell system, preferably a fuel cell system of an aircraft, wherein the fuel cell comprises a self-supporting membrane structure, wherein the membrane structure interconnects a first open cavity with a second open cavity in an ion-conducting manner and separates them from each other in a gas-tight manner, wherein the first cavity and the second cavity penetrate each other.

[0007] It is preferred that each cavity is designed to accommodate at least one elongated, straight interconnector body.

[0008] Preferably, each cavity comprises at least one gas channel which is designed to be elongated and straight such that the interconnector body can be accommodated in the at least one gas channel.

[0009] Preferably, the membrane structure region accordingly interconnects two adjacent gas channels in an ion-conducting manner and separates them from one another in a gas-tight manner.

[0010] Preferably, a straight first gas channel contained in the first cavity and a straight second gas channel contained in the second cavity are arranged twisted relative to one another.

[0011] Preferably, the membrane structure comprises a solid electrolyte.

[0012] Preferably, an electrically conductive anode layer and an electrically conductive cathode layer are applied on the membrane structure, wherein the anode layer is arranged in one of the cavities and the cathode layer is arranged in the other one of the cavities.

[0013] Preferably, the fuel cell comprises a plurality of elongated interconnector elements which are designed to be inserted into each of the cavities and to contact the membrane structure and / or the anode / cathode layers.

[0014] Preferably, the interconnector elements have an interconnector body with a cylindrical outer circumference. Preferably, the interconnector body is designed as a solid round bar or as a tube.

[0015] Preferably, at least one of the interconnector elements is designed to form a line contact, preferably a helical line contact, with the membrane structure and / or the anode / cathode layers when the interconnector element is inserted into one of the cavities.

[0016] Preferably, the interconnector elements are designed to define a vent region together with the membrane structure and / or the anode / cathode layers when the interconnector element is inserted into one of the cavities, the vent region allowing a gas flow in a longitudinal direction and / or a circumferential direction and / or a helical gas flow along the interconnector element.

[0017] Preferably, the fuel cell comprises at least one gas distributor arranged at the inlet side and / or at the outlet side of the membrane structure, wherein the gas distributor arranged preferably at the inlet side is designed such that one of the cavities can be applied with gaseous fuel and the other one of the cavities can be applied with gaseous oxidant; and / or wherein the gas distributor arranged preferably at the outlet side is designed such that reaction products and / or residual gas can be discharged from the respective cavity.

[0018] Preferably, the membrane structure is designed in the form of a triply periodic smooth surface.

[0019] Preferably, the surface shape of the membrane structure is selected from the group comprising a gyroid shape, a gyroid-like shape, a diamond shape, a diamond-like shape, an iWP shape, an iWP-like shape, a black-P shape, and a black-P-like shape.

[0020] The black-P-like surface shape follows the equation:

[0021] cos kx cos ly cos mz = 0.

[0022] The diamond-like surface shape follows the equation:

[0023] sin kx sin ly sin mz + cos kx cos ly cos mz + cos kx sin ly cos mz + cos kx cos ly sin mz = 0.

[0024] sin kx cos ly cos mz + cos kx sin ly cos mz + cos kx cos ly sin mz = 0.

[0025] cos kx sin ly cos mz + sin kx cos ly cos mz + sin kx sin ly sin mz = 0.

[0026] cos kx cos ly sin mz = 0.

[0027] The gyroid-like surface shape follows the equation:

[0028] cos kx sin ly + sin kx cos ly + cos ly sin mz + sin kx cos mz = 0.

[0029] cos ly sin mz + sin kx cos mz = 0.

[0030] sin kx cos mz = 0.

[0031] The iWP-like surface shape follows the equation:

[0032] cos kx cos ly + cos ly cos mz + sin kx sin ly = 0.

[0033] cos ly cos mz + sin kx sin ly = 0.

[0034] cos kx cos ly cos mz = 0.

[0035] cos kx cos ly cos mz = 0.

[0036] It holds here that: where L is the length of the unit cell, and

[0037] It preferably holds that: where L is the length of the unit cell, and In this case, the surface shape is referred to as a helical icosahedron shape, a diamond shape, an iWP shape, and a black-P shape.

[0038] The invention also comprises surface shapes which differ from the above-mentioned surface shapes by less than 10%. It is preferred to use the mean square deviation or the standard deviation from the ideal shape defined by the following equation as a measure of the deviation:

[0039] The invention provides a fuel cell system for an aircraft, comprising a plurality of preferred fuel cells, wherein the fuel cells are electrically connected to each other in series and / or in parallel.

[0040] The invention provides an aircraft, comprising a preferred fuel cell and / or a preferred fuel cell system.

[0041] The invention comprises the use of a minimal surface with triple periodicity as a membrane structure of a fuel cell, wherein the membrane structure interconnects volumes which are able to be applied with fuel and volumes which are able to be applied with oxidizer in an ion-conducting manner and separates them from each other in a gas-tight manner.

[0042] The smooth surface of the three-dimensionally shaped can increase the A / V ratio and thus the energy density of the system. Furthermore, modern manufacturing techniques such as additive manufacturing or 3D printing can also be used.

[0043] One idea is to produce volumes with two cavities by means of separator membranes with the smallest wall thickness. The separators have a three-dimensionally curved and self-supporting geometry (continuous and tangential). Due to the complexity of the design, 3D printing is considered to be the basis for the manufacture of the separators.

[0044] Here, the electrolyte can be manufactured by means of 3D printing. An anode and a cathode can then be applied, for example, by coating the printed electrolyte. It is likewise conceivable to carry out the manufacturing procedure by means of 3D printing of the anode, the cathode and the support structure and subsequent coating of the other layers. It is also conceivable to carry out indirect manufacturing by means of a tool which does not have to be removed from the mold or a mold which does not have to be removed. Here, the casting model or the tool can be 3D printed.

[0045] Small film thicknesses can advantageously reduce electrical losses. Likewise, the pressure difference distribution between the cavities is more advantageously distributed over the curved film surface. Furthermore, the geometry allows easy access to the electrical contacts without obstructing the gas flow.

[0046] A further idea is to use 2-volume triply periodic level surfaces (TPLS) as the basic structure of the electrolyte of a SOFC, e.g. Yttria Stabilized Zirconia (YSZ). Examples of TPLS are especially the gyroid, the diamond, the iWP, the Primitive,...

[0047] The electrical contacts can be realized by means of rods / sticks or wires that are inserted through the cavities that extend orthogonally or diagonally straight.

[0048] Due to the electrolyte or film that can be designed with a small wall thickness of less than 100 pm, the efficiency can be increased. This can be realized by a slurry-based debinding method or a sintering method in 3D printing, for example, since the green body (unsintered state, the particles can be bonded by means of a polymer binder) of the self-supporting surface has a relatively high stiffness.

[0049] TPLS have the intrinsic property of being able to separate gas flows.

[0050] TPLS can have a particularly high functional surface per volume, so that the energy density per volume / weight can be increased.

[0051] Connecting rods or connecting tubes (rigid, hollow and / or porous) can be inserted into the straight regions of the cavities. In the gyroid, a particularly advantageous helical line-shaped contact can be formed between the rod and the gyroid surface.

[0052] The electrical contacts can run through the volume. The fastening and sealing of the connectors with respect to the electrolyte geometry can be realized by the shrinkage of the green body during sintering (volume shrinkage of about 10 to 20% YSZ realizes a tight fit).

[0053] The service life of the SOFC can be increased due to the isotropic thermal stress in combination with the mechanical properties of the structure of the TPLS. Furthermore, the load between the interconnector or connector and the electrolyte or film structure can be reduced.

[0054] As even in conventional fuel cells, hydrogen and oxygen are introduced into two cavities that are separated by a thin film structure. The chemical reaction that takes place over the thickness of the film generates an electric current.

[0055] In contrast to conventional planar membranes, which usually require additional mechanical stabilization, the membranes with TPLS surfaces are self-stabilizing. This means that the pressure differences in the TPLS no longer lead to large deformations that significantly affect the efficiency of the SOFC. The entire system will be self-supporting.

[0056] The TPLS is difficult or impossible to manufacture by means of conventional machine tools. It is therefore proposed to shape the high-temperature-resistant ceramic into a membrane structure by means of 3D printing.

[0057] For a SOFC based on a gyroidal icosahedron, a typical manufacturing method can look as follows.

[0058] Design the functional SOFC part. The cell length and the wall thickness can be minimized to increase the functional area per volume. Thus, with a cell length of 2 mm and a wall thickness of 100 pm, a functional area of 3200 m 3 per volume can be achieved. 2

[0059] 3D print the TPLS-based membrane structure or electrolyte by means of a photolithography paste-based material with 3 to 8 mol% YSZ and subsequent debindering / sintering to produce a ceramic state.

[0060] Produce the anode and cathode layers by means of a coating method, such as paste-based or other methods.

[0061] Insert interconnectors in the shape of rods or tubes into some or all of the straightly extending cavities or gas channels, depending on the SOFC power and the interconnector resistance.

[0062] Seal the outer side of the interconnector elements by means of a glass solder.

[0063] Arrange gas distributors on the upper and lower side of the fuel cell to enable vertical gas flow in the respective cavities in the vertical direction. BRIEF DESCRIPTION OF DRAWINGS

[0064] Embodiments are explained in more detail by means of the schematic drawings. In the drawings:

[0065] Figure 1 An embodiment of a fuel cell is shown;

[0066] Figure 2 A series of diagonal cross sections of a membrane structure is shown;

[0067] Figure 3 A series of orthogonal cross sections of a membrane structure of Figure 2 is shown;

[0068] Figure 4 ​Left: view showing the inserted interconnector element, right: detail view showing the contact area of the interconnector element with the membrane structure;

[0069] Figure 5 Embodiment of an interconnector element is shown;

[0070] Figure 6 Embodiment of a gas distributor is shown; and

[0071] Figure 7 View showing a membrane structure with different triply periodic smooth surface shapes. DETAILED DESCRIPTION

[0072] Reference is first made to a drawing showing an embodiment of a fuel cell 10. Figures 1 to 3 The fuel cell 10 is designed as a solid oxide fuel cell. The fuel cell 10 is designed such that it can be used in a fuel cell system of an aircraft.

[0073] The fuel cell 10 comprises a self-supporting membrane structure 12. The membrane structure 12 creates an open first cavity 14 and an open second cavity 16. The membrane structure 12 separates the first cavity 14 and the second cavity 16 from each other in a gas-tight manner. The membrane structure 12 interconnects the first cavity 14 and the second cavity 16 in an ion-conducting manner.

[0074] The membrane structure 12 preferably comprises a solid electrolyte 15 capable of realizing ion conduction.

[0075] The membrane structure 12 is designed such that the first cavity 14 and the second cavity 16 are through each other.

[0076] The membrane structure 12 forms a triply periodic smooth surface, for example a gyroid 17. Other such surfaces are also conceivable.

[0077] Each cavity 14, 16 contains at least one gas channel 18. The gas channel 18 is designed as an elongated, essentially straight region, such that a corresponding elongated, straight body can be inserted into the region.

[0078] Adjacent gas channels 18 are separated from each other in a gas-tight manner by a membrane structure region of the membrane structure 12, while being interconnected in an ion-conducting manner.

[0079] The membrane structure 12 has a contact layer 22 which is electrically conductive. Depending on the arrangement of the contact layer 22, the contact layer 22 in one cavity, for example the first cavity 14, is referred to as an anode layer 24, while the contact layer 22 in the other cavity, for example the second cavity 16, is referred to as a cathode layer 26.

[0080] The contact layer 22 serves for this to conduct the electrical energy generated in the fuel cell 10 to consumers, for example electrically driven propulsion devices of an aircraft.

[0081] The fuel cell 10 further comprises a plurality of interconnector elements 28 which are inserted into one of the gas channels 18. The interconnector elements 28 are designed, for example, in the shape of a round rod or a tube.

[0082] Reference is made below in particular to Figure 4 and Figure 5 . The interconnector elements 28 preferably form a line contact 30 with the membrane structure 12. The line contact 30 is designed in the shape of a spiral. In other words, the line contact 30 spirally winds around the interconnector element 28 in the longitudinal direction thereof.

[0083] The interconnector element 28 can have an interconnector body 32 which can be formed from an electrically conductive or an insulating material. Furthermore, the interconnector element 28 can also have an electrically conductive strip 34 which spirally winds around the interconnector body 32. Figure 5 ).

[0084] The interconnector element 28 together with the membrane structure 12 preferably defines a vent area 36 which can enable a gas flow along the outside of the interconnector element 28. Alternatively or additionally, a gas flow can flow through the tube-shaped interconnector element 28.

[0085] Reference is made below to Figure 6 . The fuel cell 10 can have a gas distributor 38. The gas distributor 38 is arranged, for example, at the inlet side 40 of the membrane structure 12. A further gas distributor (in particular at the outlet side of the membrane structure 12) can likewise be provided.

[0086] The gas distributor 38 is designed in such a way that fuel 40 (for example hydrogen) can be guided into the first cavities 14 and oxidizing agent 42 (for example air) can be guided into the second cavities 16.

[0087] The (not shown in detail) gas distributor at the outlet side enables the discharge of reaction products and residual gases. The gas distributor at the outlet side is preferably designed identically to the gas distributor 38 at the inlet side.

[0088] Figure 7 In addition to the icosahedron 17, further triply periodic smooth surface shapes are shown which are referred to as diamond, gyroid and iWP. Furthermore, it is shown in Figure 7 how the interconnector elements 28 are inserted into the gas channels 18.

[0089] Due to the inherent properties of the triple periodic smooth surface shape, the anodes 44 and the cathodes 46 are preferably arranged alternately. As will be further explained below, the anodes 44 and the cathodes 46 are preferably arranged in a pattern of a spiral icosahedron 17. Figure 7 It can be seen that not all gas channels 18 have to be equipped with interconnector elements 28.

[0090] In order to improve the availability of a hybrid-electric or all-electric aircraft, a fuel cell 10 is presented having an improved efficiency and an increased, volume-specific or weight-specific energy density. The fuel cell 10 has a self-supporting membrane structure 12 designed as a triple periodic smooth surface, which gas-tightly separates a first cavity 14 to which a fuel 40 is applied from a second cavity 16 to which an oxidizing agent 42 is applied, whereas both cavities 14, 16 are ionically conductively connected to each other.

[0091] List of reference signs:

[0092] 10 fuel cell

[0093] 12 self-supporting membrane structure

[0094] 14 first cavity with openings

[0095] 15 solid electrolyte

[0096] 16 second cavity with openings

[0097] 17 spiral icosahedron

[0098] 18 gas channel

[0099] 22 electrically conductive contact layer

[0100] 24 anode layer

[0101] 26 cathode layer

[0102] 28 interconnector element

[0103] 30 wire contact

[0104] 32 interconnector body

[0105] 34 electrically conductive strip

[0106] 36 vent

[0107] 38 gas distributor

[0108] 40 fuel

[0109] 42 oxidizing agent

[0110] 44 anode

[0111] 46 cathode

Claims

1. A fuel cell for use in a fuel cell system, the fuel cell comprising: A first cavity, the first cavity being open and including one or more first gas channels; The second cavity is open and includes one or more second gas channels; A membrane structure that is self-supporting; and A plurality of interconnect elements, wherein the plurality of interconnect elements are elongated and straight, and one or more of the plurality of interconnect elements include: Interconnector body; and A conductive strip, which is spirally wound around the interconnect body; The membrane structure connects the first cavity and the second cavity to each other in a conductive manner and separates them in an airtight manner. The first cavity and the second cavity are interconnected; The one or more first gas channels are designed to accommodate one or more of the plurality of interconnect elements; The one or more second gas channels are designed to accommodate one or more of the plurality of interconnect elements; Each of the one or more first interconnect elements is inserted into one of the one or more first gas channels and contacts the membrane structure; and Each of the one or more second interconnect elements is inserted into one of the one or more second gas channels and contacts the membrane structure.

2. The fuel cell of claim 1, wherein the membrane structure and the one or more interconnect elements define an vent region, the vent region being designed to allow airflow along the outside of the one or more interconnect elements.

3. The fuel cell according to claim 1, wherein the membrane structure includes a membrane structure region, the membrane structure region being... Two adjacent first gas channels, two adjacent second gas channels, or one of the first gas channels and one of the adjacent second gas channels are interconnected in a manner that conducts ions and are separated from each other in an airtight manner.

4. The fuel cell of claim 1, wherein at least one of the one or more first gas channels is arranged to be twisted relative to at least one of the one or more second gas channels.

5. The fuel cell of claim 1, wherein the membrane structure comprises a solid electrolyte.

6. The fuel cell according to claim 1, wherein the fuel cell comprises: A conductive anode layer; and A conductive cathode layer; The anode layer and the cathode layer are arranged on the membrane structure; The anode layer is disposed in one of the first cavity and the second cavity, and the cathode layer is disposed in the other cavity of the first cavity and the second cavity.

7. The fuel cell according to claim 6, wherein, The plurality of interconnect elements includes a first interconnect element designed to contact the anode layer and a second interconnect element designed to contact the cathode layer.

8. The fuel cell of claim 7, wherein the first interconnect element is designed to: When the first interconnect element is inserted into one of the first and second cavities, it forms a helical line contact with the anode layer or with the film structure and the anode layer; and / or When the first interconnect element is inserted into one of the first cavity and the second cavity, it defines a vent region together with the anode layer or the membrane structure and the anode layer, the vent region allowing airflow in the longitudinal and / or circumferential directions and / or in a spiral pattern along the first interconnect element.

9. The fuel cell of claim 7, wherein the second interconnect element is designed to: When the second interconnect element is inserted into one of the first and second cavities, it forms a helical line contact with the cathode layer or with the film structure and the cathode layer; and / or When the second interconnect element is inserted into one of the first cavity and the second cavity, it defines a vent region together with the cathode layer or the membrane structure and the cathode layer, the vent region allowing airflow in the longitudinal and / or circumferential directions and / or helical airflow along the second interconnect element.

10. The fuel cell according to claim 1, wherein the fuel cell comprises: At least one gas distributor is arranged at the inlet side and / or outlet side of the membrane structure; in: When the at least one gas distributor is arranged at the inlet side, the at least one gas distributor is designed such that one of the first cavity and the second cavity can be supplied with gaseous fuel and the other of the first cavity and the second cavity can be supplied with gaseous oxidant; and / or When the at least one gas distributor is arranged at the outlet side, the at least one gas distributor is designed such that reaction products and / or residual gases can be discharged from the corresponding cavities in the first cavity and the second cavity.

11. The fuel cell of claim 1, wherein the membrane structure is designed in the form of a triple-periodic smooth surface.

12. The fuel cell of claim 11, wherein the shape of the triple-periodic smooth surface is selected from the group consisting of: The shapes include spiral icosahedral, diamond, iWP, and black-P, as well as surface shapes that differ from the above shapes by less than 10%. The mean square deviation or standard deviation of the shape described above is used as the deviation measure.

13. The fuel cell of claim 11, wherein the shape of the triple-periodic smooth surface is selected from the group consisting of: Shapes resembling a spiral icosahedron, a diamond-like shape, an iWP-like shape, and a black-P-like shape, as well as surface shapes that differ from the above shapes by less than 10%. in, The surface shape of the black-like P follows the following equation: ， The surface shape of diamond-like materials follows the following equation: The surface shape of the helical icosahedron follows the equation: The surface shape of an iWP-like device follows the following equation: The following is established here: ,in L It is the length of the cell, and And it does not exist. , The mean square deviation or standard deviation of the shape described above is used as the deviation measure.

14. The fuel cell according to claim 1, wherein the fuel cell is a solid oxide fuel cell.

15. A fuel cell system for an aircraft, the fuel cell system comprising a plurality of fuel cells according to claim 1, the fuel cells being electrically connected in series, in parallel, or in both series and parallel.

16. An aircraft comprising a fuel cell according to claim 1.

17. An aircraft comprising the fuel cell system according to claim 15.

18. A method of using a triple-periodic smooth surface shape as the membrane structure of a fuel cell, the fuel cell comprising: A first cavity, the first cavity being open and including one or more first gas channels; The second cavity is open and includes one or more second gas channels; A membrane structure that is self-supporting; A plurality of interconnect elements, wherein the plurality of interconnect elements are elongated and straight, and one or more of the plurality of interconnect elements include: Interconnector body; and A conductive strip, which is spirally wound around the interconnect body; The membrane structure connects the first cavity and the second cavity to each other in a conductive manner and separates them in an airtight manner. The first cavity and the second cavity are interconnected; The one or more first gas channels are designed to accommodate one or more of the plurality of interconnect elements; The one or more second gas channels are designed to accommodate one or more of the plurality of interconnect elements; Each of the one or more first interconnect elements is inserted into one of the one or more first gas channels and contacts the membrane structure; and Each of the one or more second interconnect elements is inserted into one of the one or more second gas channels and contacts the membrane structure. The method includes: Apply fuel to the first cavity; and An oxidant is applied to the second cavity.

19. The method of claim 18, wherein the membrane structure and the one or more interconnect elements define an vent region, the vent region being designed to allow airflow along the outside of the one or more interconnect elements.

20. The method of claim 19, further comprising at least one gas distributor disposed at the inlet side and / or outlet side of the membrane structure, wherein the interconnect body of each of the one or more interconnect elements is in the form of a rod having a circular cross-section.

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