WO2004093211A2

WO2004093211A2 - Fuel cell and/or electrolyser and method for the production thereof

Info

Publication number: WO2004093211A2
Application number: PCT/EP2004/003893
Authority: WO
Inventors: Robert Ruckdäschel; Erich Bittner; Olav Finkenwirth; Carola Schneider
Original assignee: Bayerische Motoren Werke; Deutsches Zentrum Für Luft-Und Raumfahrt Dlr
Priority date: 2003-04-15
Filing date: 2004-04-13
Publication date: 2004-10-28
Also published as: DE10317359A1; WO2004093211A3

Abstract

The invention relates to a fuel cell and/or an electrolyser comprising an electrolyte layer, one face of which is in contact with a cathode layer and the other face is in contact with an anode layer, the latter being connected electrically and/or mechanically to a first interconnector. According to the invention, a contact device is located in the vicinity of a free face of the cathode layer, said device being connected to both a second interconnector and the cathode layer in an electrically conductive and mechanical manner by means of a material union and/or a positive fit.

Description

Fuel cell and / or electrolyser and process for their production

The invention relates to a fuel cell and / or an electrolyser according to the preamble of claim 1 and a method for their production according to the preamble of claim 23.

It is known from the prior art that, because of the low voltage that a single fuel cell is able to deliver, several cells have to be connected in series to form a fuel cell stack for technical applications. The electrical connection is made via so-called interconnectors or bipolar plates. In the case of a planar stack structure, in addition to the electrical connection of the individual cells, the bipolar plates also take on the task of supplying fuel and oxide gas to the electrodes of the fuel cells and separating the fuel and oxide gases from neighboring cells.

The bipolar plates are bonded to a metallic substrate of vacuum plasma-sprayed solid electrolyte fuel cells (so-called SOFC), for example by brazing, capacitor discharge welding, laser soldering, etc.). This ensures a low-resistance connection between a bipolar plate and the ceramic anode of the solid electrolyte fuel cell, which is arranged adjacent to the metallic substrate. The ceramic cathode of the solid electrolyte fuel cell is usually connected to the bipolar plate by a non-positive connection. This type of connection has a significantly higher contact resistance than the anode-side, material connection. In addition, due to the low flexibility of the bipolar plate and the solid electrolyte fuel cell, uneven surfaces due to manufacturing tolerances can only be compensated for by very high contact forces, which in turn can lead to mechanical damage to the sensitive ceramic layers of the solid electrolyte fuel cells.

In order to improve the electrical contacting of the cathode and at the same time manufacturing tolerances such. B. to compensate for surface roughness and surface ripples, a deformable ceramic suspension is applied before the assembly of the solid electrolyte fuel cell stack between the cathode and the adjacent bipolar plate - z. B. using screen printing or wet powder spraying. This suspension dries and solidifies during the initial start-up of the fuel cell stack and forms a porous functional layer. A complete sintering of the functional layer and cathode does not take place, however, since the usual operating temperatures of the solid electrolyte fuel cell, which are in the range between 750 ° C. and 900 ° C., are below the sintering temperature of the materials used, which is approximately 1400 ° C.

The frictional connection of a bipolar plate and a solid electrolyte fuel cell cathode has the following disadvantages: 1. There is a conflict of objectives when optimizing the thickness of the functional layer. On the one hand, the functional layer must be made relatively thick in order to allow the highest possible manufacturing tolerances of the solid electrolyte fuel cells and the bipolar plates. In addition, despite its porosity, a thicker functional layer represents a high oxygen transport resistance to the cathode and thereby reduces the electrical performance of the cell.

2. Since the ceramic functional layer is not able to sinter onto a metallic surface (eg a bipolar plate), the connection between the bipolar plate and the cathode has only a low adhesive strength and is not able to absorb tensile stresses. In addition, the functional layer shows little mechanical flexibility. Especially in cyclical use with many and rapid temperature changes, such as occur particularly in the mobile use of a solid electrolyte fuel cell as an auxiliary power supply unit in a motor vehicle, this can lead to failure of the functional layer in the form of high electrical contact resistances at the connecting surfaces between the metallic bipolar plate and the ceramic Lead functional layer.

DE 19836351 A1 discloses a high-temperature fuel cell in which a nickel mesh is arranged between the anode and the bipolar plate closest to the anode, the nickel mesh being attached to the bipolar plate in an electrically conductive manner by means of metallic soldering. A fuel cell according to DE 19836351 AI also has the disadvantages mentioned above, since the connection of the interconnector plate is only non-positively connected to the anode.

DE 4237602 AI describes a high-temperature fuel cell or a high-temperature fuel cell stack and a method. Ren known for their / its manufacture, wherein a functional layer is provided between the electrodes and the respectively adjacent bipolar plates and wherein the functional layer is electronically conductive and easily deformable at the operating temperature of the stack. A high-temperature fuel cell described in DE 4237602 A1 essentially corresponds to the prior art described at the outset.

DE 4340153 Cl discloses a device for contacting electrodes of high-temperature fuel cells. This device is essentially designed as an electrically conductive, elastic and gas-permeable contact pad with a deformable surface structure. During operation of the fuel cell, this device only lies non-positively on the adjacent separator plate and on the electrode to be contacted, so that this device, too, cannot prevent the disadvantages mentioned above.

From DE 19841919 AI a fuel cell module and a method for its production is known, in which the anode is attached to its associated interconnector plate with the aid of a solder and the cathode is electrically connected to its associated interconnector plate by means of a ceramic functional layer. Such a fuel cell also has the disadvantage of a lack of mechanical tensile strength between the cathode and its facing interconnector plate, since the ceramic functional layer does not bond to the cathode and thus tensile forces can only be insufficiently transmitted.

DE 19932194 A1 discloses a method for producing a contact layer on the cathode side of a fuel cell, the contact layer between the cathode and an interconnector plate or an intermediate protective layer layer is provided and the method essentially comprises the following steps:

1.Application of at least one type of individual carbonate of the end product lanthanum-perovskite to the interconnector plate or the cathode in the form of powder, soldering of the individual components of the fuel cell under load and heat development, the individual carbonates of the contact layer being first calcined and at the same time those from the individual carbonates Resulting oxide phase of the lanthanum perovskite sintered to the contact layer. The fuel cell is then cooled. Thus, the contact layer to be produced according to this document is sintered on one side with an adjacent layer. This in turn creates the poorly resilient bond to the bipolar plate in the pulling direction, so that a fuel cell produced in this way disadvantageously has an increased contact resistance between the cathode and the associated interconnector plate after some operating time. A mixture of individual oxides and individual carbonates (starting material) is specified as the connecting medium, which is incorrectly referred to as solder in DE 19932194 A1, which react by heating and pressing to form a lanthanum perovskite. A ceramic layer of the same material as is used for the production of a cathode is thus formed as the connecting layer. When joining a fuel cell stack, a chemical calcination or a sintering process creates a connection layer between the cathode and a protective layer, intermediate products being formed during the chemical reaction which have a different volume compared to end products. This process is referred to in DE 19932194 AI as soldering. However, this does not agree with the generally accepted definition of a solder joint. A soldered connection is according to Dubbel, 16th edition, page G20; 1.2.1 through the bind heated metals that remain in the solid state defined by melting metallic fillers. There is no chemical reaction of the solder. In this respect, "soldering" according to DE 19932194 AI only has the heating of the components to be connected in common with the definition of soldering.

In a fuel cell according to DE 19932194 AI, it is also disadvantageous that the resulting contact layer is a ceramic contact layer which is sensitive to mechanical stresses. The mechanical stresses can arise in a solid electrolyte fuel cell, which works as a high-temperature fuel cell, for example as a result of different thermal expansions of the layers present in the fuel cell stack. The ceramic contact layer according to DE 19932194 is characterized by sensitivity to brittle fracture, so that even with only slight mechanical deformation, damage to the contact layer and thus deterioration in the electrical contact resistance between a cathode and an associated interconnector plate can occur.

The object of the invention is to provide a fuel cell and / or an electrolyzer which is resistant to high mechanical and thermal alternating loads and also has a high electrical power density. In addition, a method for producing a fuel cell and / or an electrolyser is to be specified, which is simple and inexpensive to carry out. In particular, the method should be suitable for large-scale production.

This object is achieved with a fuel cell and / or an electrolyzer with the features of claim 1 and a method for their production with the features of Claim 23 solved. Advantageous embodiments are specified in the claims, each of which is dependent on the independent main claims.

According to the invention for the first time an air-permeable metallic contact element is cohesively applied to the side of the bipolar plate which establishes the electrical connection to the cathode of the adjacent solid electrolyte fuel cell, e.g. B. by means of brazing, laser soldering or resistance welding. In the metallic contact element, it can, for. B. a knitted fabric, knitted fabric, braid, fabric or a perforated metal foil. The task of the metallic contact element is to make electrical contact with the cathode, possibly in conjunction with a functional layer which is applied with a wet ceramic material for additional contact area enlargement.

The contact element should still have a certain elasticity even at the operating temperature of the solid electrolyte fuel cell. H. have a certain spring effect in order to maintain the necessary contact pressure over the entire contact surface even after many temperature cycles. The contact element can therefore be designed especially constructively, for. B. with a wave or channel structure. In addition, defined material properties, such as. B. the spring hardness can be used. By varying the mesh size, looping and wrap angle as well as wire diameter of the contact element, both lateral and vertical density gradients can be incorporated into the contact element to the fuel cell, which enable an optimization of the oxygen transport.

Further improvements in the metallic contact element can be achieved by introducing a second metallic phase. This second material can be advantageous Characterize properties that the first phase does not have or only insufficiently, such as. B. high electrical conductivity, catalytic activity and / or high spring stiffness. It can either be in the form of wires, fibers and / or surface coatings of the first phase.

Since the metallic contact element is exposed to a highly reactive oxidant at high temperature, it is important that the metal used forms a stable, passivating surface. To prevent the oxide skin from reducing the electrical current flow at the points of contact of the wires with one another, the oxide skin of the material used must have sufficient electrical conductivity at operating temperature, e.g. B. be designed as an electrical high-temperature semiconductor.

Furthermore, the coefficient of thermal expansion of the metal used is preferably matched to that of the cathode and the bipolar plate.

The requirements mentioned z. B. ferritic steels with high chromium and low aluminum and silicon content. A small proportion of rare earth elements, such as. B. yttrium or lanthanum improves the adhesive strength of the passivating oxide skin on the surface of the wires.

In addition to the metallic contact element, a ceramic functional layer is still arranged between the metallic contact element and the cathode, because otherwise the electrical contact resistance between the metallic contact element and the ceramic cathode would be high due to the low coupling of the two materials, and because of this the performance of the solid electrolyte Fuel cell would be reduced. This applies in particular if the fuel cell is thermally is exposed to mixing cycles, which cause the mechanical contact forces to swell and then swell and, as a result, break off the material-to-material connections. Therefore, above all, a firm connection between the metallic and the ceramic component is desired, which under the given operating conditions of a solid electrolyte fuel cell auxiliary power supply unit is also able to absorb mechanical stresses.

A particularly firm connection between the metallic and the ceramic component can be achieved by applying the ceramic functional layer to the surfaces of the metallic contact element that contact the cathode by means of thermal coating processes, e.g. the vacuum plasma spraying process can be achieved. All thermal coating processes, e.g. B. vacuum plasma spraying, which are suitable for applying high-melting ceramics to a wide variety of substrates.

Ceramics from the group of perovskites come into consideration as functional layer materials, which are similar to cathode ceramics and therefore allow good electrical contact due to the affinity of the materials. When selecting the contact layer materials, it must be ensured that no undesired chemical reactions with the material and the oxide skins of the metallic contact element can occur. In addition, the functional layer should be able to prevent any chemical reactions between the metallic contact element and the cathode.

Further desirable properties of the functional layer are a coefficient of thermal expansion matched to the cathode and the metallic contact element and an oxidation ons-inhibiting effect on the wire surface at the interface between the contact element and functional layer.

To form and strengthen the adhesive forces between the functional layer and the cathode, it is necessary for the two ceramics to sinter together. For this purpose, it is either necessary to expose the joined fuel cell stack to a temperature significantly above the usual operating temperature or to insert a second ceramic functional layer which, due to its structure and / or the addition of so-called "sintering aids", causes the required sintering temperature to drop. For the application of the second functional layer, various wet ceramic coating methods are available, such as. B. screen printing technology, wet powder spraying or dispensers with one travel unit.

The combination "bipolar plate with material-tightly connected, air-permeable, metallic contact element - ceramic functional layer - cathode" has the following advantages over the previously used combination "bipolar plate - functional layer - cathode":

1. Manufacturing tolerances of the bipolar plate and the solid electrolyte fuel cell are compensated for during the joining of the stack by the elastic properties of the metallic contact element on the cathode side.

2. Even if the spring stiffness decreases after a long operating time or many thermal operating cycles (e.g. due to time, temperature and load-dependent creeping processes) of the metallic contact element and the associated decrease in the contact forces up to the transition into the area of the flat tensile load the electrical contact between a bipolar plate and a cathode is maintained since both the sintered ceramics of the functional layer (s) and the cathode as well as the thermally coated connection of the functional layer and the metallic contact element are still able to absorb mechanical stresses at operating temperature.

3. The thermal functional coating is only at the points of contact between the metallic contact element and the cathode; it is not applied over the entire surface or is reduced to a minimum thickness when using a second wet ceramic applied functional layer. This means a significant reduction in the oxygen diffusion resistance through the functional layer and thus a low oxygen activation potential at the cathode, which in turn leads to increased cell performance. Due to its high porosity, the metallic contact element itself represents almost no transport resistance for the oxygen.

4. Optimization of the air distribution over the cell surface of the solid electrolyte fuel cell is easy to achieve by means of an embossed channel structure and a graded structure of the contact element.

5. In principle, thermal coating processes are better suited for coating uneven surfaces (e.g. due to manufacturing tolerances), in contrast to e.g. B. the screen printing process, which places high demands on the surface flatness of the substrate to be printed.

The invention is explained in more detail below by way of example with reference to the drawing. Show it: 1 schematically shows a cross section through a fuel cell stack with individual fuel cells according to the invention;

FIG. 2 shows an enlarged detailed view X from FIG. 1 of a contacting of a cathode according to the invention with an adjacent bipolar plate;

3 shows an enlarged detailed view X of a second embodiment of the invention in a partial exploded view.

The invention is explained below on the basis of the description of a fuel cell. All information naturally applies accordingly to the operation of the fuel cell according to the invention as an electrolyzer.

A fuel cell stack 1 (FIG. 1) has a plurality of individual fuel cells 2. The individual fuel cells 2 have an electrolyte layer 3, an anode layer 4 and a cathode layer 5, which are designed in a known manner in the manner of a solid electrolyte fuel cell (SOFC). The anode layer 4 is constructed as a ceramic-metal composite (English: cermet = ceramic and metal) and consists, for. B. from nickel and zirconia. The electrolyte layer 3 usually consists of yttrium-stabilized zirconium oxide. The cathode layer 5 usually consists, for. B. from ceramic lanthanum strontium-manganese oxide (LSM), which is often additionally mixed with yttrium-stabilized zirconium oxide (YSZ). The anode layer 4 is shown thicker in the figures than the electrolyte layer 3 and the cathode layer 5. The anode layer 4 may be arranged on a mechanically load-bearing substrate layer (not shown). With a free side 6 opposite the electrolyte layer 3 the anode layer 4 or the substrate layer is connected to a first interconnector 7. The first interconnector 7 is constructed essentially in the form of a plate from a metal and has a first flat side 8 and a second flat side 9. Both flat sides 8, 9 optionally have gas channels 10 and 11 in the area of the electrically active layers 3, 4, 5, the gas channels 10, which are arranged in the area of the first flat side 8, being fuel gas channels facing the anode layer 4. The gas channels 11, which face a cathode layer 5 in the region of the second flat side 9, lead during the operation of the fuel cell to an oxidation gas required for the oxidation of the fuel gas, e.g. B. atmospheric oxygen. The gas channels 10 are each separated by webs 12, the gas channels 11 by webs 13. The free side 6 of the anode layer 4 is electrically conductive and preferably mechanically integrally connected to free ends of the webs 12 of the first interconnector 7. The anode layer 4 or the substrate layer is connected to the first interconnector 7, for example, by hard soldering, by a capacitor discharge welding or by laser soldering or roller seam welding or the like.

A contacting device 21 is arranged on a free side 20 of the cathode layer 5 opposite the electrolyte layer 3. The contacting device 21 is essentially layer-shaped and is, for example, a knitted fabric, knitted fabric, net or a perforated sheet. The contacting device 21 is also formed from an electrically conductive material, which is also designed to be elastic in a direction 22 perpendicular to the layer planes of the electrolyte layer 3, the anode layer 4, the cathode layer 5 and the contacting device 21. The contacting device 21 is thus preferably used in particular their resiliently compressible metal wire mesh, metal wire mesh, metal wire mesh, metal wire bulge or perforated metal foil.

According to a preferred embodiment, the channels 10, 11 in the interconnector 7 can be omitted. In this case, the gas-permeable contacting device 21 takes over the gas supply or the reaction product discharge.

The contacting device 21 is an air-permeable, porous, flexible, metallic structure. It is formed from a metal, which forms a stable, passivating surface, so that the oxide skin does not reduce the electrical current flow at the points of contact of the metallic contacting device 21 with the cathode layer 5 and a second interconnector 30. For this purpose, the oxide skin of the metal used must have sufficient electrical conductivity at the operating temperature of the solid electrolyte fuel cell, which is usually in the range above 700 ° C., ie it must be a so-called high-temperature semiconductor. These requirements meet e.g. B. ferritic, steels with high chromium and low aluminum content. A small proportion of rare earth elements, such as. B. yttrium or lanthanum improves the adhesive strength of the passivating oxide skin on the surface of the material forming the contacting device 21.

The contacting device 21, which is designed as a layer, is connected with a free flat side to the second interconnector 30 of an adjacent individual fuel cell 2 in an electrically conductive and mechanically cohesive manner. A mechanically integral connection 31 between the contacting device 21 and the second interconnector 30 is designed, for example, as a suitable type of brazing, capacitor discharge welding or laser soldering or the like.

In the following, a first embodiment of the integral and positive connection between the cathode layer 5 and the second interconnector 30 is explained in more detail by way of example via the contacting device 21 using the detail X from FIG. 1, which is shown in FIG. 2.

For example, in FIG. 2 the contacting device 21 is designed as a wire bulge made of a thin metal wire 32, with metal wire arch sections 33 facing the second interconnector 30 and metal wire arch sections 34 facing the contacting device 21 of the cathode layer 5. The metal wire arc sections 33 are connected by means of the integral connection 31 to the second interconnector 30, z. B. the metal wire arc sections 33 are embedded in a layer of the integral connection 31 and are thus firmly, in particular tensile, connected to the second interconnector 30 in a direction 22.

The metal wire arc sections 34, which face the cathode layer 5, are connected by means of a connecting layer 40, which is on the one hand cohesively connected to the cathode layer 5 and on the other hand cohesively and / or positively connected to the contacting device 21. According to the invention, the connection layer 40 is designed as a ceramic functional layer applied to the free side of the contacting device 21 by means of a thermal application process, for example the vacuum plasma spraying process. The connecting layer 40 is preferably formed from ceramics from the group of the Perovskite, which are similar to the material of the cathode layer 5 and thus due to their affinity ensure good electrical contact and a good mechanical connection. The connection layer 40 is preferably not formed over the entire surface, but only in the areas on a free surface 70 of the cathode layer 5 in which the metal wire arc sections 34 run in the vicinity of the cathode layer 5. The connecting layer 40 is preferably arranged in partial areas on the free surface of the contacting device 21 in such a way that partial areas' of the metal wire arc sections 34 are embedded in the connecting layer 40 in a form-fitting manner, the embedding preferably taking place in the areas of the metal wire arc sections 34 which correspond to a free surface 70 of the cathode layer 5 are arranged closest. This creates a small-area, in particular point-to-point material and / or positive connection between the contacting device 21 and the cathode 5, in which it is particularly advantageous that partial areas of the free surface 70 of the cathode layer 5 remain uncovered by the connecting layer 40, so that in these areas a Unhindered oxygen exchange can take place, which contributes to an increased performance of a fuel cell 2. Because of the affinity between the ceramic connection layer 40 and the cathode material with regard to the material, a tensile-strength material connection between the connection layer 40 and the cathode 5 is ensured by sintering the materials of the connection layer 40 and the cathode 5. The metal wire arc sections are embedded in the connecting layer 40 in a material and / or form-fitting manner, so that the contacting device 21 is connected to the cathode 5 in a direction 22 that is resistant to tensile force and electrically conductive.

On the other hand, the contacting device 21 is cohesive with an interconnector plate 30, as described above connected so that the connection between a cathode 5 and an interconnector plate 30 as a whole is highly resistant to tensile forces in one direction 22, without the electrical contacting properties between the interconnector plate 30 and the cathode 5 being adversely affected.

According to a second embodiment of the integral bond between the cathode layer 5 and the second interconnector 30 via the contacting device 21, a second functional layer 90 is additionally present. This embodiment is explained in more detail below using the detail X from FIG. 1, which is shown in FIG. 3, as an example.

The second embodiment of the invention according to FIG. 3 is constructed essentially identically to the embodiment of FIG. 2, to which reference is made in full. In contrast to the first embodiment, however, the second embodiment has a second functional layer 90, which is applied as a very thin layer to the free surface 70 of the cathode layer 5. This second functional layer 90 is formed from a ceramic material which is very similar to the ceramic material of the connecting layer 40 and the cathode material, so that good sintering between these materials and thus a good material connection can be achieved when the fuel cell stack is joined. The functional layer 90 is preferably by means of wet application techniques, such as. B. screen printing, spraying, brushing, applied as a pasty mass or suspension on the free surface 70 of the cathode 5. When the fuel cell stacks are joined, the sections of the connecting layer 40 applied to the contacting device 21 by means of thermal coating processes reach the still pasty or deformable second functional layer 90 and dip into it, so that the connecting layer 40 or its sections are at least partially surrounded by pasty ceramic mass. The materials of the second functional layer 90 are preferably provided with sintering aids, so that a reduction in the sintering temperature required for connecting the functional layer 90 to the connecting layer 40 can be achieved. When a fuel cell stack assembled in this way is put into operation for the first time, the thermally applied ceramic materials of the connecting layer 40 sinter reliably and with high strength with the wet-applied ceramic functional layer 90, so that a cohesive ceramic connection between the layers 40 and 90 that is highly resilient in one direction 22 is created. Together with the material and / or positive connection of the connection layer 40 to the metal wire arches 34 of the contacting device 21, a highly tensile connection is created between the contacting device 21 and the cathode 5. As already described with reference to the embodiment according to FIG. 2, the contacting device 21 is cohesive connected to the interconnector 30, so that in the synopsis a high tensile load-resistant connection is formed between the interconnector 30 and the cathode 5. Compared to the embodiment according to FIG. 2, the embodiment according to FIG. 3 is characterized by a somewhat higher tensile load-resistant connection between the contacting device 21 and the cathode 5, in return a slightly higher oxygen diffusion resistance due to the full coverage of the cathode 5 with the functional layer 90 compared to the embodiment according to FIG. 2 must be accepted. However, this oxygen diffusion resistance is significantly lower than in the prior art, since the combination of the connecting layers 40 and 90 was able to significantly reduce the thickness of the functional layer 90, so that the oxygen diffusion resistance is significantly reduced compared to the known prior art could be, which results in an increase in performance of the fuel cell.

The method according to the invention for producing a fuel cell is explained in more detail below: The sequence of the method steps selected below is not binding for the chronological sequence of the production method. It only serves to illustrate the method and represents a possible, particularly preferred sequence of the production steps.

First, the electrochemically active layer structure, consisting of anode layer 4, electrolyte layer 3 and cathode layer 5, for a high-temperature solid electrolyte fuel cell is produced in a substantially known manner. This can usually be done by means of the vacuum plasma spray manufacturing process or by means of a sintered ceramic manufacturing process by mixing a metallic-ceramic suspension and a subsequent sintering process for the respective layer. In the vacuum plasma spray production process, the layer structure of the individual layers 3, 4, 5 is produced by blowing the materials that form the layers in each case into a plasma jet of a plasma torch, the plasma torch being guided, for example, in a meandering manner over a substrate layer, so that the change-like process of the plasma torch is achieved in layers.

The composite of anode layer 4, electrolyte layer 3 and cathode layer 5 is connected on the anode side to a free flat side 8 of a first interconnector 7, the connection being electrically conductive and / or preferably mechanically cohesive. The types of fastening of brazing, capacitor discharge welding or laser soldering are particularly suitable for this. The contacting device 21 is fastened to the second flat side 9 of a second interconnector 30 in the same way as the anode layer 14 is fastened on the first interconnector 7, so that an electrically conductive, mechanically tensile connection between the contacting device 21 and the associated one second interconnector 30 is produced.

On a free side of the contacting device 21 opposite the second interconnector 30, according to the invention, a thermal application method, for. B. the vacuum plasma spraying, a ceramic connection layer 40 is applied, wherein a high material strength can be achieved between the connection layer 40 and the contacting device 21 by using a thermal application method. In addition, a porous contacting device, for example in the form of a wire crust, is also partially positively connected to the connecting layer 40 applied by the thermal application process, because, for example, metal wire arches 34 are surrounded by the ceramic connecting layer 40 during application and thus form-fitting after the ceramic of the connecting layer 40 has hardened are embedded in the ceramic connection layer 40. The connecting layer 40 applied by means of thermal coating processes is already hardened when the fuel cell stack is joined, but due to its material similarity to the cathode material 5 it has a high affinity and a high tendency to sinter with the material of the cathode 5. In this respect, according to the invention it is possible, by means of a hard connection layer 40 applied with thermal coating methods, to achieve a good material connection and thus tensile strength-resistant bond between the ceramic connection layer 40 and the cathode manufacture ceramics. This material bond is formed by a sintering process when the fuel cell stack is started up for the first time, the fuel cell stack preferably being heated once to a temperature above the later operating temperature of the fuel cell stack in order to ensure the sintering to a sufficient extent.

In a particularly preferred manner, a punctiform or partial area arrangement of the connecting layer 40 can take place such that the starting materials for the connecting layer 40 are only partially applied to the side of the contacting device 21 facing the cathode layer 5, wherein it is ensured that the materials forming the connecting layer 40 merely be attached to the areas of the contacting device 21 which are to come into contact with the cathode layer 5 later.

According to a second embodiment of the invention, a second ceramic functional layer 90 is additionally applied to the free surface 70 of the cathode layer 5. The second ceramic functional layer 90 is in the form of a suspension and / or a paste by means of so-called wet application techniques, e.g. B. screen printing, wet powder spraying and the like, applied to the cathode 5 before the joining process of the fuel cell stack 1. In the joining process of the fuel cell stack 1, the second interconnector 30 with the connected contacting device 21 and the thermally applied first functional layer 40 is then placed on the free side 20 of the cathode layer 5, so that the first functional layer 40 is immersed in the wet second functional layer 90. Thus, between the metal wire arc sections 34 of the contacting device 21 and the cathode layer 5 are the previously applied layers 40, 90, which are special sinter well together and thus form a material connection.

After the joining of the fuel cell stack 1, the ceramics of the cathode 5 and the layers 40, 90 are sintered together, so that a mechanical tensile force-resistant composite is formed. For this purpose, the fuel cell stack 1 is exposed to a temperature significantly above the usual operating temperature of the fuel cell stack 1, so that these materials are well sintered.

The second ceramic functional layer 90 is a ceramic which, through its structure and / or the addition of so-called sintering aids, brings about a reduction in the required sintering temperature. The second functional layer 90 can by means of wet ceramic coating methods, such as. B. screen printing, wet powder spraying or dispensers can be applied with one travel unit.

It is particularly advantageous in the case of the fuel cell according to the invention or the electrolyzer according to the invention and the method according to the invention for the production thereof, that each individual fuel cell forms a bond with an adjacent individual fuel cell which can absorb tensile forces in a direction opposite to the joining direction of the fuel cell stack. This ensures long-term high-quality electrical contact between the cathode and the adjacent interconnector. In addition, the method according to the invention specifies a manufacturing method which can be carried out in a simple manner and can be used in particular in the field of large series production. At the same time, a fuel cell according to the invention has an increased electrical power density, since the inventive design of the integral connection between the contacts Clocking device 21 and the cathode layer 5 free surface sections 70a of the free surface 70 are formed, which are not covered by the functional layer and thus in no way hinder the diffusion of the oxygen ions through the cathode.

Claims

claims

Fuel cell and / or electrolyzer with an electrolyte layer (3) which is connected on one side to a cathode layer (5) and on the other side to an anode layer (4), and the anode layer (4) is electrically and / or mechanically connected to a first interconnector (7 ) is connected, characterized in that a contacting device (21) is arranged in the region of a free side (20) of the cathode layer (5) and is electrically conductive both with a second interconnector (30) and with the cathode layer (5) and is mechanically cohesively and / or positively connected.

Fuel cell and / or electrolyser according to Claim 1, characterized in that the mechanically integral and / or positive connection between the cathode layer (5) and the contacting device (21) is a ceramic connecting layer (40) which is connected to the contacting device (by means of a thermal application process). 21) is connected.

Fuel cell and / or electrolyzer according to claim 1, characterized in that the mechanically integral and / or positive connection between the cathode layer (5) and the contacting device (21) has a further ceramic connection layer (90) which is designed as a functional layer (90) and by means of wet application techniques, e.g. B. a screen printing process, a spray process, is applied to the cathode 5.

4. The fuel cell and / or the electrolyzer according to one or more of the preceding claims, characterized in that the second functional layer (90) consists of a ceramic material which is optionally mixed with sintering aids.

5. Fuel cell and / or electrolyzer according to one or more of the preceding claims, characterized in that the mechanical connection (31) between the contacting device (21) and the second interconnector (30) integrally, z. B. is designed as capacitor discharge welding or roller seam welding or brazing.

6. Fuel cell and / or electrolyser according to one or more of the preceding claims, characterized in that the ceramic connecting layer (40) is formed from ceramics, in particular from the group of perovskites, which are similar to the cathode ceramic.

7. Fuel cell and / or electrolyzer according to one or more of the preceding claims, characterized in that the anode layer (4) is made of a ceramic-metal composite and z. B. consists of nickel and zirconia.

8. Fuel cell and / or electrolyzer according to one or more of the preceding claims, characterized in that the electrolyte layer (3) consists of a ceramic material, for. B. from yttria-stabilized zirconia.

9. Fuel cell and / or electrolyzer according to one or more of the preceding claims, characterized in net that the cathode layer (5) consists of ceramic lanthanum-strontium-manganese oxide (LSM), which may also be mixed with yttrium-stabilized zirconium oxide (YSZ).

10. Fuel cell and / or electrolyzer according to one or more of the preceding claims, characterized in that the anode layer (4) is applied to a mechanically load-bearing metallic or ceramic substrate layer.

11. Fuel cell and / or electrolyzer according to one or more of the preceding claims, characterized in that the anode layer (4) with a free side (6) opposite the electrolyte layer (3) is connected to a first interconnector (7).

12. The fuel cell and / or electrolyzer according to one or more of the preceding claims, characterized in that the interconnector (7) is designed without a gas channel.

13. Fuel cell and / or electrolyzer according to one or more of the preceding claims, characterized in that the contacting device (21) is gas-permeable.

14. The fuel cell and / or electrolyser according to one or more of the preceding claims, characterized in that the anode layer (4) is connected to the first interconnector (7) by means of hard soldering, capacitor discharge welding or by laser soldering or roller seam welding.

5. Fuel cell and / or electrolyzer according to one or more of the preceding claims, characterized in that the contacting device (21) is arranged on the free side (20) of the cathode layer (5) opposite the electrolyte layer (3), the contacting device (21 ) is essentially layered and is, for example, a knitted fabric, knitted fabric, net or a perforated sheet.

16. The fuel cell and / or electrolyzer according to one or more of the preceding claims, characterized in that the contacting device (21) is formed from an electrically conductive material, the contacting device (21) in a direction (22) perpendicular to the layer planes the electrolyte layer (3), the anode layer (4), the cathode layer (5) and the contacting device (21) is elastic.

17. The fuel cell and / or electrolyzer according to one or more of the preceding claims, characterized in that the contacting device (21) is designed as a resiliently compressible knitted metal wire, knitted metal wire, metal wire mesh or metal wire bulge.

18. Fuel cell and / or electrolyzer according to one or more of the preceding claims, characterized in that the contacting device (21) is formed from a metal which forms a stable passivating surface.

19. Fuel cell and / or electrolyzer according to one or more of the preceding claims, characterized in that the oxide skin of the metal is a high-temperature semiconductor.

20. Fuel cell and / or electrolyzer according to one or more of the preceding claims, characterized in that the contacting device (21) made of a ferritic steel with a high chromium and low aluminum content and possibly with a small proportion of rare earth elements, such as. B. yttrium or lanthanum.

21. Fuel cell and / or electrolyser according to one or more of the preceding claims, characterized in that the contacting device (21) is formed from a thin metal wire (32), wherein metal wire arc sections (33) and metal wire arc sections (34) cohesively and / or positively and tensile in one direction (22) with the adjacent layers (30,

5) are connected.

22. The fuel cell and / or electrolyzer according to one or more of the preceding claims, characterized in that the contacting device (21) is connected only in regions to the cathode layer (5).

23. A method for producing a fuel cell and / or an electrolyzer with an electrolyte layer (3), an anode layer (4) and a cathode layer (5), the anode layer (4) having a first interconnector (7) being electrically conductive and / or is mechanically connected, characterized in that a contacting device

(21) is connected both to the cathode layer (5) and to a second interconnector (30) in an electrically conductive and mechanically integral and / or positive manner.

24. The method according to claim 23, characterized in that for electrically conductive and mechanically integral and / or positive connection of the contacting device (21) to the cathode layer (5), at least one ceramic connecting layer (40) is used, which is connected to the contacting device (21) by means of a thermal application method.

25. The method according to claim 23 and / or 24, characterized in that a composite of the anode layer (4), the electrolyte layer (3) and the cathode layer (5) on the anode side is connected to a free flat side of a first interconnector (7) , wherein the connection is electrically conductive and preferably mechanically integrally formed.

26. The method according to one or more of claims 23 to 25, characterized in that the connection between the anode layer (4) and the first interconnector (7) is produced by means of brazing and / or by means of capacitor discharge welding and / or by means of laser soldering.

27. The method according to one or more of claims 23 to 26, characterized in that the contacting device (21) with a second interconnector (30) is produced by means of brazing and / or capacitor discharge welding and / or laser soldering.

28. The method according to one or more of claims 23 to 27, characterized in that a second functional layer

(90) is used, which as a paste and / or ceramic suspension on a free surface (70) of the cathode layer (5) by means of a wet application method, for. B. spraying, screen printing, brushing is applied.

9. The method according to one or more of claims 23 to 28, characterized in that a material bond between the connecting layer (40) and the functional layer (90) is produced by sintering.