Repetition unit for a stack and related manufacturing method

Abstract

The present invention relates to a repetition unit for a stack comprising at least one electrochemical cell formed by a cathode, an anode and an electrolyte; a conductive metal interconnector that supports the electrochemical cell, and a sealing element between the interconnector and the electrochemical cell. The invention is characterised in that the interconnector is made of two flat metal plates formed by pressing, hydroforming and / or any other forming process in which pressure is applied on a piece placed in a mould that is used as an upper plate and a lower plate; wherein the upper plate and the lower plate comprise air and fuel inlet and / or outlet holes; wherein at least one of the plates supports the electrochemical cell; and wherein the plates are joined by welding and / or sealing carried out in selected areas of the outer perimeter thereof.

Description

[0001]

[0002] TECHNICAL SECTOR

[0003] The present invention relates to the sector of solid oxide electrochemical cells for use as fuel cells (SOFC), solid oxide electrolyzers (SOEC) of water vapor or electrocatalytic reactors for the conversion of CO2, NH3 or hydrocarbons.

[0004] Specifically, the present invention relates to an arrangement of a repeating unit that forms part of an electrochemical cell stack in a solid oxide carbon stack (SOFC) and / or a high-temperature electrolyzer (SOEC) and / or electrocatalytic reactors. The present invention also relates to the manufacturing process associated with the repeating unit.

[0005] BACKGROUND OF THE INVENTION

[0006] As the demand for efficient and clean energy increases, so do technologies related to the search for new energy sources that offer a real alternative to conventional energy sources.

[0007] This is in addition to the effects of climate change, caused by the increase in CO2 levels in our atmosphere due to the combustion of fossil fuels to generate electricity.

[0008] In this sense, solid oxide fuel cells, SOFC, and solid oxide electircs, SOEC, appear as an alternative that increases the efficiency of energy generation from fossil fuels, without the need to resort to their combustion, thereby reducing emissions of greenhouse gases or other toxic pollutants that pose a danger to life or the integrity of living beings. SOFCs or SOECs belonging to the state of the art are formed by at least one repetitive unit, which comprises at least two different elements, an electrochemical cell and an interconnector or bipolar plate (4).

[0009] Each electrochemical cell (8) is composed of a cathode (1) and an anode (2), separated by an electrolyte (3). Where the cathode (1) and the anode (2) are electrical conductors, made of a porous material. And where the electrolyte (3) is gas-tight, electrically insulating and ion-conducting, in particular, the electrolyte is a conductor of O ions. 2 '

[0010] And where the interconnector (4) serves as a support and electrical connection between the adjacent electrochemical cells (8), generating at least one compartment on the anode side and one compartment on the cathode side.

[0011] Additionally, interconnectors are used as a means to facilitate the circulation of gases in the vicinity of each electrochemical cell (8). In this way, a cathode compartment and an anode compartment are generated in each repetitive unit.

[0012] The inclusion of sealing elements (9) in the repeating units, located between the interconnectors and the electrochemical cells (8), as well as the use of a contact layer or current collector, such as a nickel foam or filter (19), which facilitates electrical contact between the cathode and the adjacent interconnector, belongs to the state of the art.

[0013] In the structure described in the previous points, a dual function can be achieved, on the one hand, operation in SOEC electrolyzer mode is possible, and on the other hand, operation in SOFC fuel cell mode is possible.

[0014] Looking at Figure 1, we find an example of the operation of a solid oxide cell in electrolyzer mode (SOEC).

[0015] A first gas, such as water vapor, is introduced on the cathode side (1); and a second gas containing oxygen, such as air, is introduced on the anode side (2). The assembly is also powered by an electric current, connected to an external power source, preferably a renewable energy source.

[0016] The passage of water vapor through the cathode compartment, in combination with the supply of an electric current, causes the dissociation of the H2O molecules according to the formula:

[0017] In this way, the O ions 2 ' dissociated according to the previous formula, they pass through the electrolyte (3), and are replaced in the cathodic compartment, forming O2 again, according to the following formula:

[0018] In this way, according to the above formulas, it is possible to generate hydrogen and oxygen from water, which can be used directly in subsequent stages of an industrial process, or which can be stored for later use.

[0019] Looking at Figure 2, we find an example of the operation of a solid oxide fuel cell (SOFC) in fuel cell mode.

[0020] Air containing oxygen is introduced through the cathode side (1); and H2 is introduced through the anode side (2). The assembly is also connected by a load that requires electrical consumption from an electric current.

[0021] In the cathodic compartment, oxygen combines with two electrons to generate an oxygen ion according to the following formula:

[0022] In the same way as in the previous case, the oxygen ions pass through the electrolyte (3) and are introduced into the anodic compartment, where they combine with the introduced hydrogen according to the following formula:

[0023] In this way, according to the previous formulas, from the introduction of hydrogen into the anode compartment, it is possible to generate an electric current that supplies an external load.

[0024] The reactions described above, according to current state-of-the-art knowledge, are advantageously carried out at high temperatures to reduce their sensitivity to fuel impurities, reducing the required filtration steps, thereby increasing the efficiency of power generation and reducing the complexity of the entire process.

[0025] As can be seen in Figure 4, a common practice in the state of the art is based on creating a stack (5) of a plurality of repetitive units (5.1, 5.2,...), in which a plurality of anodic and cathodic compartments are generated, where the repetitive units (5.1, 5.2,...) are electrically insulated from each other by using electrolytes (3), and where the plurality of repetitive units (5.1, 5.2,...) are located between two end plates, an upper plate (6) and a lower plate (7), which are the ones that receive the electrical connections, the supply of the gases introduced into the stack and the escape of the gases released after the reactions that take place in the stack.

[0026] In particular, the interconnectors (4) are in electrical contact with one or more electrodes, and perform the function of introducing and collecting the electric current, in addition to delimiting the circulation flows of the gases introduced into each of the compartments.

[0027] Specifically, the interconnectors (4) provide electrical contact through one of their faces with the cathode (1) of an electrochemical cell; and the interconnectors (4) provide electrical contact through the other face with the anode (2) of the adjacent electrochemical cell.

[0028] According to the common knowledge of the state of the art, the interconnectors (4) are made of a metallic alloy. The stacks (5) are intended to increase the flow rates of the introduced gases, increasing the results obtained, whether a greater quantity of hydrogen generated in the SOEC operating mode, or a greater quantity of electrical energy generated in the SOFC operating mode.

[0029] In accordance with common practices in the state of the art, as can be seen in Figure 3, taking into account reasons of ease of manufacture and improvement in operating efficiency in both SOEC and SOFC, the repeating units have a square or substantially square shape, although they may have any other morphology, such that the gas introduced into the cathode compartment is fed through one of the sides of the repeating unit and escapes through the opposite side; and such that the feed and escape of the gas introduced into the anode compartment are carried out through sides that do not coincide with those of the feed and escape of the gas introduced into the cathode compartment.

[0030] One of the problems encountered with solid oxide fuel cells, both in SOEC and SOFC operation, is the difficulty in manufacturing their components.

[0031] In particular, there is a problem in the configuration of the interconnectors, which must fulfill the double function previously mentioned, that is, serve as an electrical contact, and generate a compartment on the cathode side (1) and a compartment on the anode side (2).

[0032] In the state of the art, we can find different configurations that aim to solve the problems described above, and which are based on the use of different parts to configure the interconnector.

[0033] Document US2018202055 describes an interconnector composed of three different pieces: a first flat metal sheet comprising a hollow central portion, and comprising gas inlet / outlet ports on the periphery of the central portion, configured to contact the adjacent cathode; a second flat metal sheet not comprising a hollow central portion, and comprising gas inlet / outlet ports on the periphery of the central portion; and a central metal sheet comprising a raised central portion for defining gas flow channels, and comprising gas inlet / outlet ports on the periphery of the central portion, configured to contact the adjacent anode.

[0034] In particular, the central metal sheet comprises at least six ports, each comprising steel sheet tabs spaced apart from each other, forming a comb, and each comprising slits defined between the edge of one of the ports and one or between two consecutive tabs, with the aim of regulating the passage of gas to each of the anodic or cathodic compartments of the interconnector.

[0035] Using this configuration, US201820202055 uses three different types of repeating units combined in a single stack, such that two of the repeating units allow the passage of air and fuel, while the other repeating unit only allows the passage of air.

[0036] That is, document US2018202055 describes a way to generate an interconnector that requires the use of at least three pieces to distribute the gases to each of the cathode and anode compartments.

[0037] Document US2012107714 describes a repeating unit for stacking a stack comprising an electrochemical cell, an interconnector, and at least a first sealing gasket placed between the lower surface of the electrochemical cell and the interconnector, and a second sealing gasket placed on the upper surface of the electrochemical cell.

[0038] In this way, by regulating the height of the sealing joints, the cathodic and anodic compartments are generated in which the gases flow to carry out the chemical reactions.

[0039] That is, document US2012107714 describes a method of generating the compartments that requires the use of at least two additional sealing gaskets. Document EP4047696 describes an interconnector for gas distribution, comprising a base plate, in contact on a first side with an electrochemical cell, and a structure formed by two plates arranged one above the other to form a gas distribution. Specifically, it describes that the plate structure comprises a first plate and a second plate, with gas inlets and outlets.

[0040] Where the first plate comprises a first hole pattern, with a plurality of holes arranged in rows parallel to the main gas flow direction, without comprising channels. And where the second plate comprises a second hole pattern with a plurality of holes arranged in rows parallel to the main gas flow direction. The invention is characterized in that the first hole pattern is offset relative to the second hole pattern in the main gas flow direction.

[0041] That is, document EP4047696 describes an interconnector that uses at least three parts: the base plate and the two plates that form the gas distribution structure.

[0042] Document US20090117414 describes a particular interconnector configuration, which is made up of two different pieces. A first electrically conductive piece provides electrical conductivity within the fuel cell, with each of the first pieces in contact with the cathode of the previous cell and the anode of the next cell. The second electrically insulating piece mechanically connects the fuel cells and forms the frame for the first piece.

[0043] That is, document US20090117414 describes the realization of an interconnector in two different pieces, where both pieces comprise a volume sufficient to generate the anodic and cathodic compartments, one of the pieces serving solely as a support structure for the electrochemical cell, and as a frame for the other of the pieces, which is the one that has electrical conduction capacity and the one that is in contact with the anode and cathode of the cells. Document US20090325023 describes the realization of a repetition unit comprising an electrochemical cell, with at least a first layer and at least two additional layers. Where the cell, the first layer and the additional layers comprise a flat area at least in the area surrounding the active area of ​​the electrochemical cell, allowing the welding of all the pieces using the flat area.

[0044] That is, document US20090325023 describes the use of flat plates, at least in a certain region, which are configured to be welded together and form the stack interconnector, but which, in order to configure the cathode and anode compartments, require two additional pieces.

[0045] As can be seen from the documents belonging to the state of the art, most of the proposed solutions involve the use of more than two pieces in order to configure the anode and cathode compartments, since it has not been found a way to generate volumes with flat plates, while complying with the remaining requirements of fuel cells, such as, for example, the tightness between the different compartments.

[0046] On the other hand, we find documents that only use two pieces, but these are not made from flat, shaped plates, but rather are elements with volumes configured to allow the generation of the anode and cathode compartments.

[0047] Finally, there are documents in the state of the art that use the welding technique to achieve the union of three or more flat plates, shaped flat plates, or a combination of both; however, as previously mentioned, all require additional plates to generate the compartments.

[0048] This is why the solutions proposed by the state of the art entail a high cost, as they require the independent manufacture of different flat plates and / or shaped flat plates or require more expensive manufacturing methods, such as sintering, machining or chemical machining. This is why an interconnector configuration is necessary that allows reducing costs, both for the independent manufacture of the components that make up each interconnector, and for the joint manufacture of the interconnector itself from the union of the components that make it up.

[0049] EXPLANATION OF THE INVENTION

[0050] The repetitive unit for stack and the associated manufacturing process that the invention proposes is therefore configured as a notable novelty within its field of application, since, according to its implementation and in a taxative manner, the objectives indicated below are achieved, with the characterizing details that make it possible and that distinguish them, conveniently included in the final claims that accompany this description.

[0051] The terms "upper" and "lower" have been used in this description to facilitate understanding of the invention. However, this should not be a limitation when interpreting it.

[0052] Likewise, in this document the word "stack" refers, in a non-limiting manner, to a stacking of repetitive units that allows the series connection of a plurality of electrochemical cells placed consecutively, together with the distribution of gases between the cells.

[0053] To facilitate the understanding of the invention, the present description has been made considering inlet and / or outlet holes of a first gas, considered in basic operating mode as air (12), and inlet and / or outlet holes of a second gas, considered in basic operating mode as fuel (13), each of them having certain characteristics.However, the inventors do not find any obstacle to the exchange of the circulating gas for each of them or to the gases from one chamber and another being composed of any chemical composition that allows the stack to operate in different operating modes, so this definition should not be understood as limiting when interpreting or carrying out possible embodiments of the present invention and the definition of air or fuel side will be used for a better understanding of the invention. The present invention aims to solve the above problems, that is, it manages to reduce manufacturing costs by using a smaller number of parts, which are also manufactured according to lower cost manufacturing processes. The repetitive unit comprises at least one electrochemical cell (8) with a cathode.

[0054] (1 ), an anode (2), and a non-conductive electrolyte (3) located between the cathode (1 ) and the anode

[0055] (2); a conductive metal interconnector (4), which serves as a support for the electrochemical cell (8). It may also comprise a sealing element (9) between the electrochemical cell (8) and the interconnector (4).

[0056] The electrochemical cell (8) comprises, at least in one area of ​​its surface, an active area in which ionic exchange between the gas and fuel flows occurs.

[0057] Specifically, the active area is the one that comes into contact with the air flow on one of its upper or lower sides, and with the fuel flow on the other of its upper or lower sides.

[0058] In particular, the present invention describes the use of an upper plate (6) and a lower plate (7), which are formed from a stamping process.

[0059] The upper plate (6) and the lower plate (7) comprise at least two holes to allow the entry and / or exit of air (12); and at least two holes to allow the entry and / or exit of fuel (13), where the holes corresponding to the entry and / or exit of air (12) are located on opposite sides of the upper and lower plates (6,7); and where the holes corresponding to the entry and / or exit of fuel^ 3) are located on opposite sides of the upper and lower plates (6,7).

[0060] In this way, the circulating flows, both on the air side and on the fuel side, are crossed flows, understood as crossed flows that have directions perpendicular to each other. The upper plate (6) comprises an upper face, a lower face, and a hole or combination of holes or central perforated area (10). Where the upper face serves as a support for the electrochemical cell (8), such that the lower face of the electrochemical cell (8) is exposed to the air chamber on the lower face of the upper plate (6).

[0061] The lower plate (7) comprises an upper face, a lower face and a central area configured as a gas flow distribution element (11).

[0062] One of the main characteristics of the present invention lies in the joining means used between the lower and upper flat plates (6,7).

[0063] In particular, the upper plate (6) and the lower plate (7) will be fixedly joined by a selected area of ​​their outer perimeter, so that the lower face of the upper plate (6) is in permanent contact with the upper face of the lower plate (7).

[0064] Preferably, selected areas of the outer perimeter of the upper plate (6) and the lower plate (7) are flat.

[0065] Furthermore, selected areas of the outer perimeter of the upper plate (6) and the lower plate (7) are coincident, in order to allow a weld to be made between the upper plate (6) and the lower plate (7).

[0066] The fixed connection between both plates is made in such a way that the central hole (10) is aligned with the flow distribution element (11), in this way, the flow that passes through the lower area of ​​the electrochemical cell (8) is directed according to the flow distribution made by the flow distribution element (11).

[0067] Additionally, the present invention proposes the selection of second welding areas, which are also flat and coincident on the upper plate (6) and the lower plate (7), and which surround the air inlet and / or outlet hole (12).

[0068] In this way, a seal is achieved that prevents the loss of fuel flow, which is forced to follow the path towards the active area of ​​the electrochemical cell (8). As explained in the background, there is an unsolved problem in the state of the art, related to the impossibility of generating anodic or cathodic compartments by using only two flat plates. Therefore, an additional plate is commonly used as an element to distance the upper plate from the lower one and generate the anodic and cathodic compartments.

[0069] In the interconnector object of the present invention, the generation of the compartments is achieved by using two perimeter edges, each of them located on each of the upper and lower plates (6,7).

[0070] In particular, the upper plate (6) comprises an upper edge (14) projecting superiorly with respect to the upper plate (6); and the lower plate (7) comprises a lower edge (15) projecting internally with respect to the lower plate (7). Where the upper edge (14) and the lower edge (15) are coincident, and are located on the outside of the area delimited by the weld.

[0071] By superimposing the upper and lower edges (14,15) the separations between the upper plate (6) and the lower plate (7) are generated, which allow the appearance of the volumes that make up the compartments.

[0072] Additionally, as initially indicated, each repetitive unit comprises at least a first sealing element (9), which serves to prevent losses of air or fuel flow, at least between the electrochemical cell (8) and the upper plate (6).

[0073] The present invention also describes a stack configured from the stacking of a plurality of repetitive units as described, in which the upper face of the electrochemical cell (8) comes into contact with the lower face of the lower plate (7) of the immediately superior repetitive unit, optionally an intermediate element can be added as a contact layer or current collector whose function is to improve the electrical contact between the cathode and the lower plate (7) of the immediately superior repetitive unit, allowing electrical conduction between repetitive units and the air inlet and / or outlet holes (12) and the fuel inlet and / or outlet holes (13) between the different repetitive units being coincident.The sealing between the upper and lower plates (6,7) of each repeating unit is carried out, as indicated above, by welding the matching flat areas of the upper plate (6) and the lower plate (7).

[0074] Additionally, the sealing of the perimeter of the inlet and / or outlet holes of one or both gases (12) or (13) can also be carried out by means of welding in the matching flat areas surrounding the aforementioned holes in each of the upper and lower plates (6,7).

[0075] To achieve sealing between the upper and lower plates (6,7) of two adjacent repetitive units, a second sealing element (9) is used to prevent air flow losses that may occur during stacking.

[0076] Specifically, the sealing element (9) will be located between the upper edge (14) of the upper plate (6) and the lower edge (15) of the adjacent lower plate (7); and in the areas surrounding the fuel inlet and / or outlet holes (13), generating a compartment for the air flow, contained internally by the upper plate (6), superiorly by the lower plate (7) of the upper adjacent repeating unit; and delimited by the second sealing element (9) between the previous plates.

[0077] Preferably, the first sealing element (9), between the upper plate (6) and the electrochemical cell (8); and the second sealing element (9), between the upper plate (6) and the lower plate (7) of the upper adjacent repeating unit; are configured from a single sealing element (9).

[0078] According to the previous configuration, the fuel flow compartment is delimited by the weld between the upper plate (6) and the lower plate (7), leaving a single path free for the fuel flow towards the flow distribution element (11) and, therefore, towards the active area of ​​the electrochemical cell (8).

[0079] On the other hand, the air flow compartment is delimited by the sealing element (9), which prevents the air flow from mixing with the fuel flow, while preventing the air flow from escaping through the perimeter between the upper plate (7) and the lower plate (6) of the adjacent upper repetitive unit. In order to avoid the possible diversion of the air flow from the air inlet hole to the air outlet hole, which would cause the loss of at least a part of the flow, which would not pass through the active area of ​​the electrochemical cell (8), the present invention proposes the use of closing elements that prevent communication between the air flow inlet and the air flow outlet.

[0080] Likewise, these closing elements generate two chambers, a first chamber at the air flow inlet (16) and a second chamber at the air flow outlet (17). The chambers achieve an improvement in the supply and exhaust of the air flow, by homogenizing the air flow conditions at the inlet and outlet.

[0081] In preferred embodiments of the present invention, the closing elements are comprised of at least a first recess (18) in the upper plate (6), and at least a second recess (19) in the lower plate (7), which are coincident in their position within the upper plate (6) and the lower plate (7).

[0082] Preferably, there will be two first and second recesses (18,19) in each of the upper and lower plates (6,7), where each pair of recesses will be located on one of the sides where the fuel inlet and / or outlet holes are located (13).

[0083] By means of the recesses (18,19), in combination with the sealing element (9), it is possible to isolate the air inlet orifice from the air outlet orifice, avoiding a possible diversion between the air inlet and / or outlet orifices (12), which would cause the loss of at least a part of the flow, which would not pass through the active area of ​​the electrochemical cell.

[0084] Additionally, through the recesses (18,19), the chambers at the inlet and outlet of the fuel flow (16,17) are generated.

[0085] Preferably, the recesses (18, 19) are in the form of ramps, with a given angle of inclination, which allows their simple and inexpensive manufacture by means of stamping, multiple stamping or hydroforming techniques. Obviously, the sealing element (9) must be able to adapt to the morphology of the recesses (18, 19).

[0086] Preferably, the position of the recesses (18,19) is varied in the adjacent repetitive units so that, if the recesses (18,19) of a repetitive unit are located in a certain area, the recesses (18,19) of the adjacent repetitive units are located in a different area and do not coincide with the previous one.

[0087] Preferably, to facilitate the manufacturing and assembly process, if the recesses (18,19) of a repeating unit are located in an area close to or substantially close to the air inlet orifice; the recesses (18,19) of the adjacent repeating units, both superiorly and internally, must be located in an area close to or substantially close to the air outlet orifice.

[0088] The present invention also describes the method of manufacturing a repeating unit as described above, which can be used in combination with one or more other repeating units to configure a stack, where each repeating unit includes an electrochemical cell (8), an interconnector formed by an upper plate (6) and a lower plate (7), and a sealing element (9).

[0089] Where the upper plate (6) and the lower plate (7) are made from a flat, shapeless plate made of a conductive metallic material, which is subjected to a stamping process.

[0090] In particular, the following operations are carried out by means of the stamping process on the upper plate (6):

[0091] Air inlet and / or outlet holes (12);

[0092] Fuel inlet and / or outlet holes (13);

[0093] Center hole, multiple holes or central micro perforations (10) on top plate (6);

[0094] Top edge (14);

[0095] Rebate (18). And particularly, through the stamping process on the lower plate (7) the following operations are carried out:

[0096] Air inlet and / or outlet holes (12);

[0097] Fuel inlet and / or outlet holes (13);

[0098] Flow distribution element (11 );

[0099] Bottom edge (15);

[0100] Lowering (19).

[0101] Once the upper plate (6) and the lower plate (7) have been formed, they are placed relative to each other in such a way that:

[0102] The air inlet and / or outlet holes (12) and the fuel inlet and / or outlet holes (13) are aligned;

[0103] The central hole (10) of the upper plate (6) is aligned with the flow distribution element (11) of the lower plate (7);

[0104] The upper edge (14) of the upper plate (6) coincides with the lower edge (15) of the lower plate (7);

[0105] The recess (18) of the upper plate (6) is coincident with the recess (19) of the lower plate (7).

[0106] Once both elements are aligned, the welding and / or sealing is carried out to achieve:

[0107] The union of the upper plate (6) and the lower plate (7) by welding the upper and lower plates (6,7) along the selected areas of their perimeters;

[0108] Sealing of the air inlet and / or outlet holes (12).

[0109] Once the upper plate (6) and the lower plate (7) are joined, the sealing element (9) is pre-installed on the upper plate (6), and the electrochemical cell (8) on the sealing element (9), so that it coincides with the central hole (10) of the upper plate (6). By subjecting the previous assembly to a high temperature heating process, with the possibility of also applying pressure, the upper plate (6) is joined to the sealing element (9), and the sealing element (9) to the electrochemical cell (8).

[0110] If the last two operations, pre-installation of the sealing element (9) and the electrochemical cell (8), together with the previous heating, are carried out for a plurality of repetitive units in which the interconnector has been configured from the described operations, a stack of repetitive units is obtained as described above.

[0111] The repeating unit for the stack, the manufacturing process and the set of elements described represent an innovation with previously unknown structural and constitutive characteristics, reasons which, combined with its practical usefulness, provide sufficient grounds for obtaining the exclusive privilege requested.

[0112] BRIEF DESCRIPTION OF THE DRAWINGS

[0113] To complement the description being made and in order to help better understand the characteristics of the invention, a set of drawings is attached as an integral part of said description, in which the following has been represented for illustrative and non-limiting purposes:

[0114] Figure 1. - Schematic of an operating electrochemical cell SOEC Figure 2. - Schematic of an operating electrochemical cell SOFC

[0115] Figure 3. - Schematic of an alternative mode of operation, in which the electrolysis of water and the oxidative reforming of a fuel gas stream are combined, generating two separate gas streams: wet H2 and CO2.

[0116] Figure 4. - Exploded view of a repeating unit according to the invention

[0117] Figure 5. - Example of a stacking of repeating units according to the invention

[0118] Figure 6. - Detail of a top plate

[0119] Figure 7. - Detail of a bottom plate

[0120] Figure 8. - Exploded view of an interconnector according to the invention

[0121] Figure 9. - Detail of two consecutive repetitive units of a stack. List of references and figures:

[0122] 1. Cathode

[0123] 2. Anode

[0124] 3. Electrolyte

[0125] 4. Interconnector

[0126] 5. Stacking

[0127] 6. Top plate

[0128] 7. Bottom plate

[0129] 8. Electrochemical cell

[0130] 9. Sealing element

[0131] 10. Center hole

[0132] 11. Flow distribution element

[0133] 12. Air inlet and / or outlet holes

[0134] 13. Fuel inlet and / or outlet holes

[0135] 14. Upper edge of the top plate

[0136] 15. Lower edge of the bottom plate

[0137] 16. Air flow inlet chamber

[0138] 17. Air flow outlet chamber

[0139] 18. First reduction

[0140] 19. Second lowering

[0141] 20. Nickel foam

[0142] PREFERRED EMBODIMENT OF THE INVENTION

[0143] In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part of this specification, and in which specific preferred embodiments in which the invention may be carried out are shown by way of illustration.

[0144] In this document, the word "comprises" and its variants are to be interpreted as open-ended expressions that are not intended to exclude the possibility of additional technical features or components beyond those explicitly recited. Furthermore, the word "comprise" includes the case "consists of," and is interpreted as a closed-ended expression limited only to the explicitly recited technical features or components. For those skilled in the art, other objects, advantages, and features of the invention will be apparent in part from the description and in part from the practice of the invention. Furthermore, the present invention covers all possible combinations of embodiments indicated herein.

[0145] Specifically, the present invention describes a repetitive unit for a stack, comprising at least one electrochemical cell (8) formed from a cathode (1), an anode (2) and a non-conductive electrolyte (3), located between the cathode (1) and the anode (2); a conductive metallic interconnector (4), which serves as a support for the electrochemical cell (8), and a sealing element (9) between the interconnector (4) and the electrochemical cell (8).

[0146] Where the invention is characterized in that: the interconnector (4) is made from two flat metal plates formed by stamping, hydroforming and / or any other forming process in which pressure is applied to a piece placed in a mold, which serve as an upper plate (6) and a lower plate (7); where the upper plate (6) and the lower plate (7) comprise air inlet and / or outlet holes (12) and fuel inlet and / or outlet holes (13); where at least one of the upper or lower plates (6,7) serves as a support for the electrochemical cell (8); and where the upper plate (6) and the lower plate (7) are joined by welding and / or sealing carried out in selected flat areas of its outer perimeter, where the selected area of ​​the upper plate (6) and the selected area of ​​the lower plate (7) are coincident.

[0147] In this way, a repeating unit is obtained formed from flat plates subjected to a stamping, hydroforming or similar process, which are subsequently welded and / or sealed in areas specifically selected to carry out the welding and / or sealing between the upper plate (6) and the lower plate (7). Preferably, the repeating unit comprises a plurality of electrochemical cells (8) distributed according to a matrix, with n cells per row and m cells per column. For example, in one embodiment, a 2x2 matrix of electrochemical cells could be had.

[0148] Preferably, the repetitive unit is characterized in that the upper plate (6) comprises an upper face configured as a support for at least one electrochemical cell (8), a lower face and at least one central hole (10), responsible for connecting the electrochemical cell (8) of the upper part of the upper plate (6) with the lower part of the upper plate (6).

[0149] Furthermore, the lower plate (7) comprises an upper face, a lower face and at least one central area configured as a flow distribution element (11), which serves as an electrical contact with the electrochemical cell (8).

[0150] According to this preferred embodiment, the upper plate (6) is the one that would serve as support for the electrochemical cell (8), which would be in electrical contact with the flow distribution element (11) of the lower plate (7), through the central hole (10) of the upper plate (6).

[0151] In a preferred embodiment, the repetitive unit comprises at least a second welding and / or sealing area, which surrounds, at least partially, the fuel inlet and / or outlet hole, so as to prevent the air flow from entering the compartment between the upper plate (6) and the lower plate (7), which is intended for the circulation of the fuel flow.

[0152] In a preferred embodiment, the upper plate (6) comprises an upper edge (14), and the lower plate (7) comprises at least one lower edge (15), where the upper edge (14) and the lower edge (15) are coincident and form a separation between the upper plate and the lower plate.

[0153] By superimposing the upper and lower edges (14,15) the separations between the upper plate (6) and the lower plate (7) are generated, which allow the appearance of the volumes that configure the air and fuel compartments. In a preferred embodiment, the upper edge (14) and the lower edge (15) are located in an area outside the area that defines the welding and / or sealing between the upper plate (6) and the lower plate (7), so that they do not interfere with the circulation of the air and fuel flows, but only perform the function of generating the compartments for the circulation of the previous flows.

[0154] In a preferred embodiment, the repeating unit comprises at least one closing element located between the upper plate (6) and the lower plate (7), which prevents the passage of air flow from the air inlet hole to the air outlet hole.

[0155] With this embodiment, the invention aims to avoid a direct diversion of the air flow from the air inlet opening to the air outlet opening, which would cause a decrease in the performance of the assembly, as the air flow does not circulate through the active zone of the electrochemical cell.

[0156] At the same time, this embodiment manages to generate two chambers, one chamber surrounding the air inlet opening, and one chamber surrounding the air outlet opening, so that the conditions of the circulating flow are homogenized, favoring the supply or exhaust of air flow.

[0157] In a preferred embodiment, the closure element is comprised of at least a first recess (18) made in the upper plate (6); and a second recess (19) made in the lower plate. The first recess (18) and the second recess (19) must coincide in the upper (6) and lower (7) plates of the same repeating unit.

[0158] Preferably, the repeating unit comprises a first recess (18) and a second recess (19), coinciding on the side where the fuel inlet orifice is located; and another first recess (18) and another second recess (19), coinciding on the side where the fuel outlet orifice is located.

[0159] That is, according to the previous embodiment, there will be at least two sets of recesses in a single repeating unit: one set on the side where the fuel inlet orifice is located, and one set on the side where the fuel outlet orifice is located. This configuration, which the inventors have found advantageous, allows for the unambiguous generation of the chamber surrounding the air inlet orifice and the chamber surrounding the air outlet orifice.

[0160] Preferably, the recesses (18,19) are ramp-shaped, with an angle that allows the stamping operation of the upper and lower plates (6,7).

[0161] In a preferred embodiment, the repeating unit comprises at least a first pre-chamber at the fuel inlet and / or outlet, and at least a second pre-chamber at the air inlet and / or outlet.

[0162] In particular, the inventors have found it advantageous to include a pre-chamber at the fuel inlet, a pre-chamber at the fuel outlet, a pre-chamber at the air inlet, and a pre-chamber at the air outlet.

[0163] In a preferred embodiment, the air inlet and / or outlet holes (12) are located on opposite sides of the upper and lower plates (6, 7); and the fuel inlet and / or outlet holes (13) are located on opposite sides of the upper and lower plates (6, 7). In addition, the air inlet and / or outlet holes (12) and the fuel inlet and / or outlet holes (13) are not coincident.

[0164] In this way, compared to the common square or rectangular configuration of a repeating unit, two opposite sides would have the air inlet and outlet; and the other two opposite sides would have the fuel inlet and outlet, allowing the gas flow to be crossed, that is, at a 90° angle.

[0165] By means of the above embodiments, a repetitive unit is achieved with an interconnector formed from two flat plates, which are manufactured by a stamping process, and joined by a welding process, with perimeter edges that allow the generation of the compartments for the air side and the fuel side, without the need to use additional parts. The present invention also describes a stack formed from at least two repetitive units as described above, that is, from repetitive units comprising at least one electrochemical cell (8) formed from a cathode (1), an anode (2) and a non-conductive electrolyte (3), located between the cathode (1) and the anode (2); a conductive metallic interconnector (4), which serves as a support for the electrochemical cell (8), and a sealing element (9) between the interconnector (4) and the electrochemical cell (8).

[0166] The stack is characterized in that the interconnector (4) of each repetitive unit is made from two flat metal plates formed by stamping, hydroforming and / or any other forming process in which pressure is applied to a piece placed in a mold, which serve as an upper plate.

[0167] (6) and a lower plate (7); where the upper plate (6) and the lower plate (7) comprise air inlet and / or outlet holes (12) and fuel inlet and / or outlet holes (13); where at least one of the upper or lower plates (6, 7) serves as a support for the electrochemical cell (8); and where the upper plate (6) and the lower plate

[0168] (7) are joined by welding and / or sealing carried out in selected flat areas of their outer perimeter, where the selected area of ​​the upper plate (6) and the selected area of ​​the lower plate (7) are coincident.

[0169] In a preferred embodiment, the upper plate (6) comprises a face configured as a support for at least one electrochemical cell (8), a lower face and at least one central hole, series of holes or microperforated area (10); and the lower plate (7) comprises an upper face, a lower face and at least one central area configured as an element for distributing the flow and supporting the electrochemical cell (11) that serves as an electrical contact with the electrochemical cell.

[0170] In a preferred embodiment, the upper plate (6) and the upper plate (7) comprise a second welding area that surrounds, at least partially, the air inlet and / or outlet hole.

[0171] In a preferred embodiment, the upper plate (6) comprises at least one upper edge (14), and the lower plate (7) comprises at least one lower edge (15), where the upper edge (14) and the lower edge (15) are coincident and configure a separation between the upper plate (6) and the lower plate (7). Preferably, the upper edge (14) and the lower edge (15) are located in an area outside the area that defines the weld between the upper plate (6) and the lower plate (7).

[0172] The particularity of the upper and lower edges (14,15) when stacking is carried out, lies in that the lower edge (15) of the lower plate (7) of a repeating unit rests on the upper edge (14) of the upper plate (6) of the adjacent lower repeating unit.

[0173] In this way, the space generated by the upper edge (14) and the lower edge (15) of the same repetitive unit, configure a compartment for the circulation of fuel.

[0174] While the space generated by the lower edge (15) of a repeating unit and the upper edge (14) of the adjacent lower repeating unit, configure a compartment for air circulation.

[0175] By stacking a plurality of repeating units with the above characteristics, a plurality of fuel compartments and a plurality of air compartments are achieved.

[0176] Preferably, the adjacent repeating units comprise a perimeter sealing element (9) between the upper plate (6) of a repeating unit and the lower plate (7) of the upper adjacent repeating unit.

[0177] Preferably, the previous sealing element (9) is located in the contact area between the upper edge (14) of the upper plate (6) and the lower edge (15) of the lower plate (7).

[0178] As a constructive alternative, it is possible that the sealing element (9) between the electrochemical cell (8) and the upper plate (6); and the sealing element (9) between adjacent repetitive units, is carried out by means of a single sealing structure or sealing element (9). In a preferred embodiment, each repetitive unit comprises at least one closing element located between the upper plate (6) and the lower plate (7), which prevents the passage of air flow from the air inlet hole to the air outlet hole, with the objective of avoiding a direct derivation of the air flow from the air inlet hole to the air outlet hole, which would cause a decrease in the performance of the assembly, since the air flow does not circulate through the active zone of the electrochemical cell.

[0179] In a preferred embodiment, the closure element is comprised of at least a first recess (18) made in the upper plate (6); and a second recess (19) made in the lower plate. The first recess (18) and the second recess (19) must coincide in the upper (6) and lower (7) plates of the same repeating unit.

[0180] Preferably, the repeating unit comprises a first recess (18) and a second recess (19), coinciding on the side where the fuel inlet orifice is located; and another first recess (18) and another second recess (19), coinciding on the side where the fuel outlet orifice is located.

[0181] That is, according to the previous embodiment, there will be at least two sets of recesses in a single repeating unit: one set on the side where the fuel inlet orifice is located, and one set on the side where the fuel outlet orifice is located. This configuration, which the inventors have found advantageous, allows for the unambiguous generation of the chamber surrounding the air inlet orifice and the chamber surrounding the air outlet orifice.

[0182] Preferably, the recesses (18,19) are ramp-shaped, with an angle that allows the stamping operation of the upper and lower plates (6,7).

[0183] The particularity of the recesses (18, 19) in a stack of repeating units lies in the need for the positions of the recesses (18, 19) between adjacent repeating units not to coincide. Therefore, preferably, if the recesses (18, 19) of a repeating unit are located in an area close to or substantially close to the air inlet opening; the recesses (18, 19) of the adjacent repeating units, both above and internally, must be located in an area close to or substantially close to the air outlet opening.

[0184] This prevents the coincidence in the position of the recesses (18,19) in adjacent repetitive units, which would eliminate the function of the recesses themselves (18,19), that is, if the recesses (18,19) of two adjacent repetitive units have a coinciding position, they would not perform the function of delimiting the chambers at the air inlet and outlet, so a possible direct derivation between the air inlet and outlet would not be avoided.

[0185] Therefore, preferably, the recesses (18,19) of two adjacent repeating units are located in alternate positions.

[0186] In a preferred embodiment, the repeating units of the stack comprise at least one pre-chamber at the fuel inlet and / or outlet, and one pre-chamber at the air inlet and / or outlet.

[0187] Specifically, each repeating unit comprises a pre-chamber at the fuel inlet, a pre-chamber at the fuel outlet, a pre-chamber at the air inlet, and a pre-chamber at the air outlet.

[0188] The present invention also describes the manufacturing process of a repetitive unit for a stack, comprising an electrochemical cell (8), an interconnector (4) with an upper plate (6) and a lower plate (7), and a sealing element (9).

[0189] In particular, the manufacturing process is characterized by the manufacturing process of the upper and lower plates (6,7), which are made from a flat, shapeless plate of a conductive metallic material, by applying the following steps: Carrying out a stamping process on the upper plate (6) to perform the operations of:

[0190] • air inlet and / or outlet holes (12);

[0191] • fuel inlet and / or outlet holes (13);

[0192] • central hole (10) in top plate (6);

[0193] • top edge (14);

[0194] • recess (18);

[0195] Carrying out a stamping process on the lower plate, to perform the following operations:

[0196] • air inlet and / or outlet holes (12);

[0197] • fuel inlet and / or outlet holes (13);

[0198] • flow distribution element (11);

[0199] • lower edge (15);

[0200] • recess (19).

[0201] Positioning the upper plate (6) and the lower plate (7), so that:

[0202] • the air inlet and / or outlet holes (12) and the fuel inlet and / or outlet holes (13) are aligned;

[0203] • the central hole (10) of the upper plate (6) is aligned with the flow distribution element (11) of the lower plate (7);

[0204] • the upper edge (14) of the upper plate (6) coincides with the lower edge (15) of the lower plate (7);

[0205] • the recess (18) of the upper plate (6) is aligned with the recess (19) of the lower plate (7). These alignments ensure the correct functioning of the assembly, so that the different elements that form part of the upper plate (6) and the lower plate (7) are correctly aligned.

[0206] Thus, for the correct circulation of air and fuel, it is necessary that, obviously, the air inlet and / or outlet holes (12); and the fuel inlet and / or outlet holes (13) are aligned.

[0207] It is also necessary that the central hole (10) is correctly aligned with the flow distribution element (11), since this area represents the active area of ​​the electrochemical cell (8).

[0208] The alignment of the upper edge (14) with the lower edge (15) is what allows obtaining the volumes in the interconnector (4), since they are the ones that generate the compartments through which the air and fuel circulate.

[0209] Finally, as described above, the recesses (18,19) prevent the direct derivation of air from the inlet orifice to the outlet orifice, creating chambers at the air inlet and outlet, which force the flow to circulate through the active area of ​​the electrochemical cell (8).

[0210] Welding of the upper plate (6) and the lower plate (7) along selected areas of their perimeters.

[0211] Through the previous stages, an interconnector is manufactured that, starting from flat or substantially flat plates, generates sufficient volumes to configure the anodic and cathodic compartments without the need to use additional parts that generate the previous compartments.

[0212] In this way, by stamping and welding the two plates, on the one hand, the compartment through which the air circulates is created, and on the other hand, the compartment through which the fuel circulates is created. The method preferably comprises the steps of pre-installation of the sealing element (9) and the electrochemical cell (8), as well as the subsequent heat treatment of the assembly formed by the two welded plates, together with the pre-installation of the sealing element (9) and the electrochemical cell (8).

[0213] These stages respond to the ordinary procedures for joining an interconnector with its corresponding electrochemical cells.

[0214] Applying the above procedures to the manufacturing of a stack of a stack, we find two particularities: on the one hand, we have the alternation in the position of the recesses (18,19), and on the other hand we find the final heat treatment of a stack of repetitive units as described above.

[0215] Firstly, the alternation in the position of the recesses (18,19) is carried out in a manner that the inventors have considered advantageous in relation to the reduction of manufacturing costs.

[0216] To this end, the interconnectors (4) are manufactured according to the procedure described above, that is, by independent stamping of each of the upper and lower plates (6,7), and the subsequent welding of the upper and lower plates (6,7) along the selected areas of their perimeter.

[0217] However, when assembling the interconnectors (4) thus manufactured, not all of them will be placed in the same orientation, but rather the orientation is modified at a certain angle, depending on the specific application design. In the case shown in Figure 4, the angle of change in orientation is 180° for each of the adjacent repetitive units so that the recesses 18 and 19 do not coincide in position between adjacent repetitive units.

[0218] Therefore, once the first repetitive unit is placed, the other is placed with a certain rotation, which in the case shown in Figure 4 is 180°, such that the recesses (18,19) are placed in a different position from that in which the recesses (18,19) of the second repetitive unit mounted in the stack are located, which in the case shown in Figure 4 is on the opposite side. In other application cases, position variations with different angles between adjacent repetitive units can be opted for, preferably 30°, 60°, 90°, since the comparative design advantage lies in the position of the recesses 18 and 19 differing between adjacent repetitive units.

[0219] This operation is repeated for all the repeating units mounted in the stack, so that the position of the recesses (18,19) alternates between adjacent repeating units.

[0220] Secondly, with respect to the application of heat treatments to a stack of repeating units, the invention allows the heat treatment to be carried out both on repeating units independently and on the entire stack of the plurality of repeating units.

[0221] This means that, according to the manufacturer's preferences, the invention raises the possibility of applying the heat treatment to the repetitive units independently or, alternatively, the stacking of repetitive units can be carried out with their corresponding pre-installations of the sealing elements (9) and the electrochemical cells (8), subjecting all the elements of the stack to a single heat treatment.

[0222] Having sufficiently described the nature of the present invention, as well as the manner of putting it into practice, it is not considered necessary to explain it further so that any expert in the field may understand its scope and the advantages derived from it, stating that, within its essence, it may be put into practice in other embodiments that differ in detail from the one indicated as an example, and to which the protection sought will also be granted, provided that its fundamental principle is not altered, modified or changed.

Claims

CLAIMS 1. A repetitive unit for a stack comprising at least one electrochemical cell (8) formed from a cathode (1), an anode (2), and a non-conductive electrolyte (3) located between the cathode (1) and the anode (2); a conductive metallic interconnector (4) serving as a support for the electrochemical cell (8), and a sealing element (9) between the interconnector (4) and the electrochemical cell (8), characterized in that the interconnector (4) is made from two flat metallic plates formed by stamping, hydroforming, and / or any other forming process in which pressure is applied to a piece placed in a mold that serves as an upper plate (6) and a lower plate (7); where the upper plate (6) and the lower plate (7) comprise air inlet and / or outlet holes (12) and fuel inlet and / or outlet holes (13); where at least one of the upper or lower plates (6,7) serves as support for the electrochemical cell (8);where the upper plate (6) and the lower plate (7) are joined by welding and / or sealing carried out in selected areas of its outer perimeter, where the selected area of ​​the upper plate (6) and the selected area of ​​the lower plate (7) are coincident.; 2. Repetitive unit according to the preceding claim, characterized in that it comprises a plurality of electrochemical cells (8) distributed according to a matrix.

3. Repetitive unit according to any of the preceding claims, characterized in that the upper plate (6) comprises an upper face configured as a support for at least one electrochemical cell (8), a lower face and at least one central hole, central holes, or microperforated central area (10); and the lower plate (7) comprises an upper face, a lower face and at least one central area configured as a flow distribution element (11) that serves as an electrical contact with the electrochemical cell (8).

4. Repetitive unit according to any of the preceding claims, characterized in that it comprises a second welding and / or sealing area that surrounds, at least partially, the air inlet and / or outlet hole (12).

5. Repetitive unit according to any of the preceding claims, characterized in that the upper plate (6) comprises at least one upper edge (14), and the lower plate (7) comprises at least one lower edge (15), where the upper edge (14) and the lower edge (15) coincide and form a separation between the upper plate (6) and the lower plate (7).

6. Repetitive unit according to the previous claim, characterized in that the upper edge (14) and the lower edge (15) are located in an area outside the area that defines the welding and / or sealing between the upper plate (6) and the lower plate (7).

7. Repetitive unit according to any of the preceding claims, characterized in that it comprises at least one closing element between the upper plate (6) and the lower plate (7) between the air inlet orifice and the air outlet orifice.

8. Repetitive unit according to the preceding claim, characterized in that the closing element is comprised of at least a first recess (18) in the upper plate (6), and at least a second recess (19) in the lower plate (7), where the first recess (18) and the second recess (19) are coincident in the upper plate (6) and the lower plate (7).

9. Repetitive unit according to the preceding claim, characterized in that it comprises a first recess (18) and a second recess (19) on the side where the fuel inlet orifice is located; and another first recess (18) and another second recess (19) on the side where the fuel outlet orifice is located.

10. Repetitive unit according to any of claims 6 and 7, characterized in that the recesses (18,19) are ramp-shaped.

11. Repetitive unit according to any of the preceding claims, characterized in that it comprises at least one pre-chamber at the fuel inlet and / or outlet, and comprises at least one pre-chamber at the air inlet and / or outlet.

12. Repetitive unit according to any of the preceding claims, characterized in that the holes corresponding to the air inlet and / or outlet (12) are located on opposite sides of the upper and lower plates (6, 7); and the fuel inlet and / or outlet holes (13) are located on opposite sides of the upper and lower plates (6, 7).

13. Repetitive unit according to the preceding claim, characterized in that the air inlet and / or outlet holes (12) and the fuel inlet and / or outlet holes (13) do not coincide.

14. Stack comprising at least two repetitive units comprising at least one electrochemical cell (8) formed from a cathode (1), an anode (2) and a non-conductive electrolyte (3), located between the cathode (1) and the anode (2); a conductive metallic interconnector (4), which serves as a support for the electrochemical cell (8), and a sealing element (9) between the interconnector (4) and the electrochemical cell (8), characterized in that the interconnector (4) is made from two flat metallic plates formed by stamping, hydroforming and / or any other forming process in which pressure is applied to a piece placed in a mold that serve as an upper plate (6) and a lower plate (7); where the upper plate (6) and the lower plate (7) comprise air inlet and / or outlet holes (12) and fuel inlet and / or outlet holes (13);where at least one of the upper or lower plates (6,7) serves as a support for the electrochemical cell (8); where the upper plate (6) and the lower plate (7) are joined by welding and / or sealing carried out in selected areas of their outer perimeter, where the selected area of ​​the upper plate (6) and the selected area of ​​the lower plate (7) are coincident; 15. Stack according to any of the preceding claims, characterized in that the upper plate (6) comprises an upper face configured as a support for at least one electrochemical cell (8), a lower face and at least one central hole (10); and the lower plate (7) comprises an upper face, a lower face and at least one central area configured as a flow distribution element (11) that serves as an electrical contact with the electrochemical cell (8).

16. Stack according to any of the preceding claims, characterized in that the upper plate (6) and the upper plate (7) comprise a second welding area surrounding, at least partially, the air inlet and / or outlet hole (12).

17. Stack according to any of the preceding claims, characterized in that the upper plate (6) comprises at least one upper edge (14), and the lower plate (7) comprises at least one lower edge (15), where the upper edge (14) and the lower edge (15) coincide and form a separation between the upper plate (6) and the lower plate (7).

18. Stack according to the previous claim, characterized in that the upper edge (14) and the lower edge (15) are located in an area outside the area that defines the weld between the upper plate (6) and the lower plate (7).

19. Stack according to any of the preceding claims, characterized in that it comprises a perimeter sealing element (9) between the upper plate (6) of a repetitive unit and the lower plate (7) of the upper adjacent repetitive unit.

20. Stack according to the previous claim, characterized in that the perimeter sealing element (9) between the upper plate (6) and the lower plate (7) is located in the area coinciding between the upper edge (14) and the lower edge (15).

21. Stack according to any of claims 14 or 15, characterized in that the sealing element (9) between the electrochemical cell (8) and the upper plate (6), and the sealing element (9) between the upper plate (6) of a repetitive unit and the lower plate (7) of the upper adjacent repetitive unit, are made by means of a single sealing element (9).

22. Stack according to any of the preceding claims, characterized in that it comprises at least one closing element between the upper plate (6) and the lower plate (7) between the air inlet hole and the air outlet hole.

23. Stack according to the previous claim, characterized in that the closing element is comprised of at least a first recess (18) in the upper plate (6), and at least a second recess (19) in the lower plate (7), where the first recess (18) and the second recess (19) coincide in the upper plate (6) and the lower plate (7) of the same repetitive unit.

24. Stack according to the preceding claim, characterized in that it comprises a first recess (18) and a second recess (19) on the side where the fuel inlet orifice is located; and another first recess (18) and another second recess (19) on the side where the fuel outlet orifice is located.

25. Stack according to any of claims 6 and 7, characterized in that the recesses (18,19) are ramp-shaped.

26. Stack according to any of claims 18 to 20, characterized in that the recesses (18,19) are located in alternate positions in adjacent repeating units.

27. A stack according to the preceding claim, characterized in that the recesses (18, 19) of a repeating unit are located in an area close to the air inlet opening; and the recesses (18, 19) of adjacent repeating units are located in an area close to the air outlet opening, and vice versa.

28. Stack according to any of the preceding claims, characterized in that the holes corresponding to the air inlet and / or outlet (12) are located on opposite sides of the upper and lower plates (6, 7); and the fuel inlet and / or outlet holes (13) are located on opposite sides of the upper and lower plates (6, 7).

29. Stack according to any of the preceding claims, characterized in that it comprises at least one pre-chamber at the fuel inlet and / or outlet, and comprises at least one pre-chamber at the air inlet and / or outlet.

30. Stack according to the preceding claim, characterized in that the air inlet and / or outlet holes (12) and the fuel inlet and / or outlet holes (13) do not coincide.

31. Manufacturing process of a repetitive unit for a stack comprising an electrochemical cell (8), an interconnector (4) formed from an upper plate (6) and a lower plate (7), and a sealing element (9) characterized in that the upper plate (6) and the lower plate (7) are made from a flat, shapeless plate made of a conductive metallic material, and in that it comprises the steps of: • Stamping process on the upper plate (6) to perform the following operations: • air inlet and / or outlet holes (12); • fuel inlet and / or outlet holes (13); • central hole (10) in top plate (6); • top edge (14); • recess (18); • Stamping process on the lower plate (7) to perform the following operations: • air inlet and / or outlet holes (12); • fuel inlet and / or outlet holes (13); • flow distribution element (11 ); • lower edge (15); • recess (19). • Position the upper plate (6) and the lower plate (7) so that: • the air inlet and / or outlet holes (12) and the fuel inlet and / or outlet holes (13) are aligned; • the central hole (10) of the upper plate (6) is aligned with the flow distribution element (11) of the lower plate (7); • the upper edge (14) of the upper plate (6) coincides with the lower edge (15) of the lower plate (7); • the recess (18) of the upper plate (6) coincides with the recess (19) of the lower plate (7). Welding and / or sealing of the upper plate (6) and the lower plate (7) along selected areas of their perimeters.

32. Manufacturing process of a repetitive unit for a stack according to the previous claim, characterized in that it comprises the following steps: • Pre-installation of the sealing element (9) and the electrochemical cell (8). • High temperature heat treatment of the assembly consisting of the interconnector (4), the sealing element and the electrochemical cell (8).

Images