Solid oxide fuel cell stack

Abstract

A fuel cell stack (1) comprising a plurality of modular units (2), including at least a first modular unit (21) and a second modular unit (22), wherein both the first and second modular units (21, 22) comprise a fuel cell (3), two contact layers (4), an interconnector (5), a clamping gasket (6), and wherein the fuel cell stack (1) comprises a removable junction (9) interposed between the first modular unit (21) and the second modular unit (22), wherein the removable junction (9) comprises an electrically conductive metal layer (10), optionally a metal plate or a metal paste, and a second compression gasket (8), at least partially interposed between the metal layer (10) and the interconnector (5) of the second modular unit (22), and wherein the metal layer (10) is positioned interposed in contact with the second contact layer (12) of the first modular unit (21) and with the interconnector (5) of the second modular unit (22), so as to electrically connect the first modular unit (21) and the second modular unit (22).

Description

“Solid Oxide Fuel Cell Stack”

[0001] Field of the Invention

[0002] The present invention relates to a fuel cell stack, in particular a modular solid oxide fuel cell stack, also known as Solid Oxide Cells (SOCs), generally used for an electrolyzer and / or an energy and heat co-generator.

[0003] Background of the Invention

[0004] In the 21st century, one of the most urgent challenges facing humanity is that of sustainable energy supply. This issue is made even more pressing by the increase in the world population and the consequent rise in energy consumption. The energy revolution is underway, with a progressive abandonment of fossil fuels in favor of renewable resources, which are redefining old energy paradigms. It is therefore essential to develop non-polluting technological solutions capable of integrating into a new energy system that uses efficient energy carriers, produced and used within a closed cycle of carbon dioxide emission and reuse.

[0005] Solid oxide fuel cells (Solid Oxide Cells, SOCs) are electrochemical devices capable of converting chemical energy into electricity and heat, or of reversibly storing excess electrical energy and heat by producing chemical fuels.

[0006] By using electricity from renewable sources, SOCs produce energy with high efficiency and generate clean chemical products such as green hydrogen, ammonia or syngas. Hydrogen can be used as fuel for hydrogen vehicles or in steel production, ammonia in fertilizer production, and syngas for energy generation.

[0007] Furthermore, the chemical reaction for the production of syngas uses CO2, contributing to carbon dioxide absorption. Alternatively, by feeding the cell with methane or hydrogen, electrical energy is obtained. When hydrogen is used as fuel, the only byproduct is water, while using methane carbon dioxide is produced, but still avoids the formation of NOx and SOx.

[0008] This technology offers various advantages, including reversibility, high efficiency, low cost and fuel flexibility. SOCs are made with widely available ceramic oxide materials, such as zirconium oxide and nickel oxide.

[0009] However, systems powered with SOCs still present several critical issues that have hindered their large-scale diffusion, production cost representing one of the main obstacles to overcome, together with the durability of the stack system, which contains several components interfacing with one another.

[0010] The stack is composed of a series of steel interconnectors connected to each other. Each interconnector houses the cell and also performs several functions, includingdiffusing and keeping separate the gases that must reach the cell electrodes, conducting current, conducting heat and providing a mechanical structure for the stack.

[0011] The combination of the cell, the interconnector and the individual sealing elements is generally called a Repeat Element (RE). Each Repeat Element consists of an interconnector, a cell, a glass-ceramic gasket, a compression gasket, a cathode contact layer and an anode contact layer (Figure 1).

[0012] In the prior art known to the inventors, REs are stacked and connected in series, in a number necessary to deliver a total power suitable for the required application (Figure 2). For a 5 kW electrolyzer, between 60 and 70 REs are required. On each of them, the cell is glued and sealed by means of gaskets that may be composed of a glassceramic paste, a metal paste or a composite material paste, and compression gaskets, or a combination thereof. Finally, the REs are connected to each other in series to ensure current conduction and sealed by means of gaskets composed of glass-ceramic pastes, metal pastes or composite material pastes, or a combination thereof.

[0013] The gaskets are applied to the cell and the interconnector at room temperature and subsequently dried. The stack is then assembled by stacking all the REs one on top of another and tightening them through a pneumatic or hydraulic compression kit. To harden and seal the gaskets, the stack is subjected to a thermal cycle at temperatures between 600 and 1000 °C, keeping it under a pressure of about 50-150 bar. During the gasket firing step, the stack shrinks under the effect of the applied pressure and the gasket further densifies until the final sealing is achieved. The stack can then be kept under compression, as a preventive measure, throughout its entire life cycle by means of a mechanical tightening system. Alternatively, it may not be kept under compression during its life cycle. Compression of the stack during the firing of the sealing material is performed using an appropriate compression kit during the stack production and assembly step.

[0014] At this point, the stack is ready to operate. During its operation, it reaches temperatures between 600 and 900 °C.

[0015] In the event of a malfunction, it is necessary to cool the stack before intervention can be performed. The causes of stack failure may include the breakage of a cell, gasket leakage, inadequate RE assembly or a defective interconnector. Often, the causes of stack failure are irreversible and require replacement. At present, the replacement of a single RE is impossible. It is also impossible to exclude a single malfunctioning RE from the stack while keeping the rest of the stack operational.

[0016] Therefore, in the event of malfunctioning of even a single RE and / or cell, it isalways necessary to replace the entire stack, significantly increasing investment and operational costs and producing a large quantity of waste.

[0017] Gaskets made of glass-ceramic pastes, which represent the most widely used solution for sealing the stack, especially for operations above 700 °C, once densified through firing, are difficult to remove without irreversibly damaging the interconnector. The interconnector is coated with a protective layer that serves to reduce chromium evaporation, which would otherwise contaminate the cell and reduce its performance. Once the glass-ceramic paste densifies, it is no longer possible to remove it from the interconnector without also removing its protective layer.

[0018] Moreover, if one still wished to proceed with the replacement of an RE, it would be necessary to deposit a new gasket and densify it through a firing cycle, placing the stack back under compression. These steps cannot be performed at the maintenance site. Therefore, in the case of malfunction of individual stack elements, it is necessary to replace the entire stack with a new one and, possibly, return the broken stack to the facility for disposal. Both the new stack and the damaged one must therefore be shipped individually in suitable crates, resulting in a costly expenditure of time and resources.

[0019] The inability to replace a single malfunctioning RE represents a major limitation to the widespread adoption of SOC-based stacks. This limitation implies the need to replace the entire stack in case of malfunction, significantly increasing investment costs and negatively affecting overall durability, creating a competitive disadvantage with respect to other technologies.

[0020] There is therefore a need for an alternative stack design that allows the replacement of a minimum unit of REs in order to ensure operational continuity of the remaining functioning stack.

[0021] There is also a need for an alternative stack design capable of allowing the bypass of an RE that presents operational anomalies, enabling the stack to continue operating even in the presence of a cell degrading faster than the others.

[0022] Solution

[0023] The purpose of the present invention is to provide a new configuration of a solid oxide fuel cell stack that allows the replacement of malfunctioning sections of the stack.

[0024] A further particular purpose of the present invention is to provide a new configuration of a solid oxide fuel cell stack that is scalable, economical, and increases the durability of the device on which the stack will operate.

[0025] A further particular purpose of the present invention is to provide a new configuration of a solid oxide fuel cell stack that allows maintenance intervention to becarried out at the location where the stack is already operating, in an agile and rapid manner.

[0026] A further particular purpose of the present invention is to provide a new configuration of a solid oxide fuel cell stack that allows the bypassing of certain malfunctioning interconnectors without having to shut the stack down, enabling it to continue functioning without excessive degradation, at a slightly lower potential, prior to any maintenance intervention.

[0027] A further particular purpose of the present invention is to provide a new configuration of a solid oxide fuel cell stack that enables the stack to continue operating even in the presence of a malfunction, thereby ensuring improved economic efficiency and reliability of the application.

[0028] A further particular purpose of the present invention is to provide a new configuration of a solid oxide fuel cell stack that improves system safety by isolating faults that may sometimes lead to localized overheating, introducing a bypass mechanism that reduces the risk of more severe damage to the stack or surrounding equipment.

[0029] A further particular purpose of the present invention is to make available a new configuration of a solid oxide fuel cell stack that facilitates the identification and isolation of faults within the stack through the presence of a bypass circuit, thereby simplifying diagnostic and maintenance procedures. As a matter of fact, fuel cells may degrade over time, and degradation may begin unevenly among the cells. Detailed monitoring would allow detection of anomalies or issues in individual cells before they can affect the entire stack, preventing sudden failures and reducing maintenance costs. This would simplify repairs and reduce the time and costs associated with system maintenance.

[0030] These and other purposes are achieved through a new design of a solid oxide fuel cell stack, according to the independent claims.

[0031] The dependent claims relate to preferred and advantageous embodiments of the present invention.

[0032] Figures

[0033] To better understand the invention and appreciate its advantages, several exemplary and non-limiting embodiments will be described below, with reference to the attached figures, in which:

[0034] - Figure 1 is a schematic cross-sectional view of a modular unit of a fuel cell stack, in particular transverse to the extension plane of the modular unit, according to one embodiment of the invention;

[0035] - Figure 2 is a schematic cross-sectional view of a plurality of modular unitsstacked on top of one another in a fuel cell stack, according to one embodiment of the invention;

[0036] - Figure 3 is a schematic cross-sectional view of a fuel cell stack, according to one embodiment of the invention;

[0037] - Figure 4 is a schematic top view of a removable gasket of a fuel cell stack, according to one embodiment of the invention;

[0038] - Figure 5 is a schematic exploded perspective view of a removable gasket of a fuel cell stack, according to one embodiment of the invention;

[0039] - Figure 6 is a schematic cross-sectional view of a fuel cell stack, according to one embodiment of the invention, in a first operating condition;

[0040] - Figure 7 is a further schematic cross-sectional view of the fuel cell stack schematically depicted in Figure 6, in a second operating condition.

[0041] Description of Some Preferred Embodiments

[0042] In the following description, a fuel cell stack, in particular a modular solid oxide fuel cell stack, is generally denoted by reference number 1.

[0043] By “fuel cell, in particular solid oxide fuel cell” is meant in particular “Solid Oxide Electrolysis Cells (SOEC)”, but also “Solid Oxide Fuel Cells (SOFC)”.

[0044] The fuel cell stack 1 comprises a plurality of modular units 2, including at least a first modular unit 21 and a second modular unit 22.

[0045] Both the first and the second modular units 21 , 22 comprise:

[0046] - a fuel cell 3, formed by two electrodes and an electrolyte interposed between the two electrodes;

[0047] - two contact layers 4 made of an electrically conductive material, sandwiching the fuel cell 3, wherein a first contact layer 11 is positioned in contact with one of the two electrodes and a second contact layer 12 is positioned in contact with the other of the two electrodes;

[0048] - an interconnector 5 made of an electrically conductive material, optionally made of steel;

[0049] - a clamping gasket 6, comprising a first compression gasket 8 and a glassceramic gasket 7 and / or a metal or composite material paste.

[0050] The interconnector 5 defines a blind interconnector seat 13 open towards the clamping gasket 6.

[0051] The first contact layer 11 and the fuel cell 3 are accommodated in the blind interconnector seat 13.

[0052] The fuel cell 3 and the interconnector 5 sandwich the first contact layer 11.

[0053] The clamping gasket 6 is positioned superimposed on the interconnector 5, preferably at least partially in contact with the interconnector 5.

[0054] Furthermore, the clamping gasket 6 defines an extended gasket seat 14 passing through the clamping gasket 6.

[0055] The second contact layer 12 is accommodated in the gasket seat 14.

[0056] The fuel cell stack 1 comprises a removable junction 9 interposed between the first modular unit 21 and the second modular unit 22.

[0057] The removable junction 9 comprises:

[0058] - an electrically conductive metal layer 10, optionally a metal plate or a metal paste, and

[0059] - a second compression gasket 8, at least partially interposed between the metal layer 10 and the interconnector 5 of the second modular unit 22.

[0060] The metal layer 10 is positioned interposed in contact with the second contact layer 12 of the first modular unit 21 and with the interconnector 5 of the second modular unit 22, so as to electrically connect the first modular unit 21 and the second modular unit 22.

[0061] Advantageously, a fuel cell stack 1 configured in this manner is more scalable and economical with respect to the prior art, and allows increasing the durability of the device on which the fuel cell stack 1 will operate.

[0062] With further advantage, the fuel cell stack 1 configured in this manner, by means of the removable junction 9, allows disconnecting the at least two modular units 2 and performing the replacement of at least one of the two modular units 2, and furthermore allows performing a maintenance intervention at the location where the fuel cell stack 1 is already operating.

[0063] Specifically, the compression gasket 8 of the removable junction 9 is configured to become sealing and to shrink in thickness when compressed and at high temperatures, namely the normal operating temperatures of the fuel cell stack 1. At the same time, the compression gasket 8 of the removable junction 9 is configured to return to its initial thickness when decompressed at room temperature. Furthermore, the compression gasket 8 does not adhesively adhere to any of the components forming the fuel cell stack 1 previously described; therefore, it is easily removable without causing damage to the modular units 2, thus allowing removal and replacement of the latter, avoiding replacement of the entire fuel cell stack 1 . Specifically, the removable junction9 is easily removable when the stack 1 is cooled and decompressed.

[0064] The metal layer 10 is positioned in contact with the underlying modular unit 2, thus creating an electrical connection between the two opposite modular units 2 between which the metal layer 10 is interposed.

[0065] With further advantage, the metal layer 10 is gas-impermeable, at the same time providing gas sealing of the fuel cell stack 1 .

[0066] According to one embodiment, the first and second modular units 21 , 22 comprise a barrier layer interposed between the electrolyte and one of the two electrodes. Advantageously, the barrier layer prevents migration of ions from the electrode, which would otherwise mix with the electrolyte to form a non-conductive material.

[0067] According to one embodiment, the fuel cell stack 1 comprises a plurality of first modular units 21 and second modular units 22, alternately stacked on one another so as to form a stacking sequence repeated at least once, preferably a plurality of times, consisting of:

[0068] - a first modular unit 21 superimposed on a removable junction 9,

[0069] - a further removable junction 9 superimposed on the first modular unit 21 ,

[0070] - a second modular unit 22 superimposed on the further removable junction 9.

[0071] Advantageously, a fuel cell stack 1 configured in this manner enables replacement of any malfunctioning modular unit 2, since all modular units 2 are selectively separated from one another by means of a removable junction 9.

[0072] According to one embodiment, the fuel cell stack 1 comprises at least one additional modular unit 23, optionally up to six or up to thirteen or up to twenty additional modular units 23.

[0073] Each additional modular unit 23 comprises:

[0074] - a fuel cell 3, formed by two electrodes and an electrolyte interposed between the two electrodes;

[0075] - two contact layers 4 made of an electrically conductive material, sandwiching the fuel cell 3, wherein a first contact layer 11 is positioned in contact with one of the two electrodes and a second contact layer 12 is positioned in contact with the other of the two electrodes;

[0076] - an interconnector 5 made of an electrically conductive material, optionally made of steel;

[0077] - a clamping gasket 6, comprising a glass-ceramic gasket 7 and / or acompression gasket 8 and / or a metal or composite material paste.

[0078] The interconnector 5 defines a blind interconnector seat 13 open towards the clamping gasket 6.

[0079] The first contact layer 11 and the fuel cell 3 are accommodated in the blind interconnector seat 13.

[0080] The fuel cell 3 and the interconnector 5 sandwich the first contact layer 11.

[0081] The clamping gasket 6 is positioned superimposed on the interconnector 5, preferably at least partially in contact with the interconnector 5.

[0082] Furthermore, the clamping gasket 6 defines an extended gasket seat 14 passing through the clamping gasket 6.

[0083] The second contact layer 12 is accommodated in the gasket seat 14.

[0084] The fuel cell stack 1 further comprises a plurality of first modular units 21 and second modular units 22.

[0085] The first modular units 21 , the second modular units 22 and the additional modular units 23 are stacked so as to form a stacking sequence repeated at least once (Fig. 3), preferably a plurality of times, consisting of:

[0086] - a second modular unit 22 superimposed on a removable junction 9;

[0087] - an additional modular unit 23 superimposed on the second modular unit 22, or a stack of up to six or up to thirteen or up to twenty additional modular units 23 superimposed on one another, wherein the stack of additional modular units 23 is superimposed on the second modular unit 22;

[0088] - a first modular unit 21 superimposed on the additional modular unit 23, or superimposed on the stack of up to six or up to thirteen or up to twenty additional modular units 23.

[0089] A further removable junction 9 can be superimposed on the first modular unit 21 , to repeat the stacking sequence.

[0090] Advantageously, a fuel cell stack 1 configured in this manner optimizes the ratio between overall costs and modular units 2 replaceable through the removable junctions 9.

[0091] According to one embodiment, the fuel cell stack is configured such that:

[0092] - the at least one additional modular unit 23 is superimposed on the second modular unit 22 so that the interconnector 5 of the at least one additional modular unit 23 is superimposed in contact with the second contact layer 12 of the second modular unit 22;

[0093] - the first modular unit 21 is superimposed on the at least one additional modular unit 23 so that the interconnector 5 of the first modular unit 21 is superimposed in contact with the second contact layer 12 of the at least one additional modular unit 23,

[0094] and, optionally, an additional modular unit 23 is superimposed on another additional modular unit 23 so that the interconnector 5 of the additional modular unit 23 is superimposed in contact with the second contact layer 12 of the other additional modular unit 23.

[0095] According to one embodiment (Fig. 4-5), the second compression gasket 8 of the removable junction 9 defines a junction opening 15 extending through the second compression gasket 8.

[0096] The metal layer 10 comprises a base portion 16 and a projecting portion 17, wherein the projecting portion 17 extends projecting from the base portion 16, optionally defining an angle of substantially 90° with the base portion 16.

[0097] Optionally, the base portion 16 and the projecting portion 17 have structural continuity.

[0098] The second compression gasket 8 of the removable junction 9 is positioned superimposed on the base portion 16, and the projecting portion 17 is positioned inserted through the junction opening 15.

[0099] The base portion 16 of the metal layer 10 is positioned in contact with the first modular unit 21 , in particular creating an electrical connection with the first modular unit 21.

[0100] The projecting portion 17 is positioned in contact with the second modular unit 22, in particular creating an electrical connection with the second modular unit 22.

[0101] According to one embodiment, the fuel cell stack 1 comprises an auxiliary external electrical circuit or external electrical bypass circuit 18.

[0102] The external electrical bypass circuit 18 forms an electrical in-series connection of a plurality of modular units 2.

[0103] Preferably, the external electrical bypass circuit 18 is configured to form an electrical in-series connection of all modular units 2.

[0104] Advantageously, a fuel cell stack 1 configured in this manner ensures that the stack can operate even in the presence of a malfunction, thereby ensuring improved economic efficiency and application reliability. Indeed, the stack configured in this manner enables isolation of faults which may sometimes lead to localized overheating, introducing a bypass mechanism that reduces the risk of more serious damage to thestack or surrounding equipment.

[0105] The external electrical bypass circuit 18 is open under normal operating conditions of the fuel cell stack 1 , while it is locally closed, in particular at the one or more malfunctioning modular units 2, under malfunction conditions of the fuel cell stack 1.

[0106] Advantageously, such a configuration allows the current flow generated by the stack 1 to bypass, through the circuit 18, the one or more malfunctioning modular units 2, ensuring continuation of the operations of the stack 1.

[0107] As schematically shown in Fig. 6, under normal operating conditions the stack 1 generates a current flow that passes through the stack of modular units 2 without passing through the external electrical bypass circuit 18, which is configured to be open under normal operating conditions. Conversely, in the event of malfunction of one or more modular units, the current flow generated by the stack 1 , which would be blocked by the malfunctioning modular unit 2, is instead directed into the external electrical bypass circuit 18, which locally closes at the malfunctioning modular unit 2 as schematically represented in Fig. 7, and is then redirected back into the stack 1 , thereby allowing the obstacle represented by the malfunctioning modular unit 2 to be overcome.

[0108] Therefore, the external bypass circuit 18 is configured to be open under normal operating conditions of the fuel cell stack 1 (Fig. 6). Furthermore, the external bypass circuit 18 is configured to close locally at one or more malfunctioning modular units 2, forming an electrical connection between at least one correctly functioning modular unit 2 upstream of the one or more malfunctioning modular units 2 and at least one correctly functioning modular unit 2 downstream of the one or more malfunctioning modular units 2 (Fig. 7).

[0109] According to one embodiment, the external bypass circuit 18 is configured to form an electrical in-series connection between the respective interconnectors 5 of a plurality of modular units 2.

[0110] Therefore, the external bypass circuit 18 is configured to be open under normal operating conditions of the fuel cell stack 1 (Fig. 6). Furthermore, the external bypass circuit 18 is configured to close locally at one or more malfunctioning modular units 2, forming an electrical connection between the interconnector 5 of at least one correctly functioning modular unit 2 upstream of the one or more malfunctioning modular units 2 and the interconnector 5 of at least one correctly functioning modular unit 2 downstream of the one or more malfunctioning modular units 2 (Fig. 7).

[0111] Preferably, the external electrical bypass circuit 18 forms an electrical inseries connection between the interconnectors 5 of all modular units 2.

[0112] According to one embodiment, the fuel cell stack 1 comprises a first group of modular units 21 , 22, 23 stacked on top of one another without the interposition of a removable junction 9, and a second group of modular units 21 , 22, 23 stacked on top of one another without the interposition of a removable junction 9.

[0113] The first group of modular units 21 , 22, 23 is separated from the second group of modular units 21 , 22, 23 by the interposition of a removable junction 9.

[0114] The external bypass circuit 18 is configured to form an electrical in-series connection between at least only one interconnector 5 of the first group of modular units 21 , 22, 23 and only one interconnector 5 of the second group of modular units 21 , 22, 23.

[0115] According to one embodiment, the fuel cell stack 1 comprises at least one detection device configured to detect at least one electrical parameter relating to the external electrical bypass circuit 18.

[0116] Optionally, the at least one detection device comprises a voltmeter or an ammeter configured to detect the voltage of the external bypass circuit 18 at least one interconnector 5 or the current intensity of the external bypass circuit 18 at least one interconnector 5.

[0117] Advantageously, such a configuration facilitates identification and isolation of faults within the stack, simplifying diagnostic and maintenance procedures. Fuel cells may degrade over time, and degradation may begin unevenly among the cells. Detailed monitoring makes it possible to detect anomalies or problems in individual cells before they can affect the entire stack, preventing sudden failures and reducing maintenance costs. This simplifies repairs and reduces the time and costs associated with system maintenance.

[0118] Furthermore, variation in performance among cells may cause imbalances that could compromise the stability and efficiency of the system. By monitoring each cell, it is possible to implement balancing strategies to ensure coordinated operation of all cells, avoiding excessive stress on some cells compared to others. By monitoring each individual cell, it is possible to identify those operating below their optimal capacity and make corrections, thereby improving the overall efficiency of the system. Continuous monitoring allows maintaining fuel cells within ideal operating parameters, reducing accelerated degradation that may occur under suboptimal operating conditions. This helps extend the service life of the stack.

[0119] According to one embodiment, the clamping gasket 6 consists of a first compression gasket 8 superimposed on a glass-ceramic gasket 7.

[0120] Furthermore, in at least one modular unit 2, preferably in each modular unit 2, the glass-ceramic gasket 7 of the modular unit 2 is interposed between the first compression gasket 8 and the interconnector 5 of the same modular unit 2.

[0121] According to one embodiment, the metal layer 10 consists of a metal plate.

[0122] According to one embodiment, the thickness of the metal layer 10 is between 0.1 mm and 5.0 mm.

[0123] According to one embodiment, the clamping gasket 6, the interconnector 5 and the removable junction 9 substantially have the same transverse overall dimension with respect to a stacking direction of the modular units 2.

[0124] According to one embodiment, the metal layer 10 is coated with a protective layer configured to prevent chromium evaporation, in particular during normal operation of the stack 1.

[0125] According to an embodiment, the removable junction 9, in particular the second compression gasket 8, is formed of non-metallic and / or deformable and / or electrically insulating and / or refractory materials up to temperatures of 1000 °C. In particular, these materials are suitable for working in oxidizing environments.

[0126] According to an embodiment, the removable junction 9, in particular the second compression gasket 8, is formed of non-metallic and deformable and electrically insulating and refractory materials up to temperatures of 1000 °C.

[0127] According to an embodiment, the second compression gasket 8 is made of:

[0128] - mica and / or mica compounds, and / or

[0129] - vermiculite and / or vermiculite derivatives, and / or

[0130] - flexible ceramic materials, and / or

[0131] - ceramic fibres, and / or

[0132] - mineral fibres, and / or

[0133] - deformable refractory materials in the form of a sheet, felt, paper, or multilayer composite, and / or

[0134] - shaped as a sheet made of one or a combination of the preceding materials, optionally as a mica sheet.

[0135] Advantageously, a compression gasket 8 made in this manner, when in a compressed configuration, acts as an insulator, while when in a decompressed configuration, it neither insulates nor adheres to the surfaces against which it is incontact, thus being easily removable without requiring the destruction of the stack 1.

[0136] According to an embodiment, the first compression gasket 8 is also formed of non-metallic and / or deformable and / or electrically insulating and / or refractory materials up to temperatures of 1000 °C. In particular, these materials are suitable for working in oxidizing environments.

[0137] According to an embodiment, the first compression gasket 8 is also formed of non-metallic and deformable and electrically insulating and refractory materials up to temperatures of 1000 °C.

[0138] According to an embodiment, the first compression gasket 8 is also made of:

[0139] - mica and / or mica compounds, and / or

[0140] - vermiculite and / or vermiculite derivatives, and / or

[0141] - flexible ceramic materials, and / or

[0142] - ceramic fibres, and / or

[0143] - mineral fibres, and / or

[0144] - deformable refractory materials in the form of a sheet, felt, paper, or multilayer composite, and / or

[0145] - shaped as a sheet made of one or a combination of the preceding materials, optionally as a mica sheet.

[0146] According to a further aspect of the invention, a method of assembling a fuel cell stack 1 as previously described comprises:

[0147] - a step of stacking a plurality of modular units 2 so as to form the previously described fuel cell stack 1 ;

[0148] - a step of clamping the fuel cell stack 1 , carried out with a pressure between 10 bar and 50 bar.

[0149] Naturally, a person skilled in the art will be able to make modifications or adaptations to the present invention without, however, departing from the scope of the claims set out below.REFERENCES1. Fuel cell stack2. Modular unit3. Fuel cell4. Contact layer5. Interconnector6. Clamping gasket7. Glass-ceramic gasket8. Compression gasket9. Removable junction10. Metal layer11. First contact layer12. Second contact layer13. Blind interconnector seat14. Gasket seat15. Junction opening16. Base portion17. Projecting portion18. External electrical bypass circuit21. First modular unit22. Second modular unit23. Additional modular unit

Claims

Claims1. A fuel cell stack (1), comprising a plurality of modular units (2), of which at least a first modular unit (21) and a second modular unit (22), wherein both the first and second modular units (21 , 22) comprise:- a fuel cell (3), formed by two electrodes and an electrolyte interposed between the two electrodes;- two contact layers (4) made of an electrically conductive material, sandwiching the fuel cell (3), wherein a first contact layer (11) is positioned in contact with one of the two electrodes and wherein a second contact layer (12) is positioned in contact with the other of the two electrodes;- an interconnector (5) made of an electrically conductive material, optionally made of steel;- a clamping gasket (6), comprising a first compression gasket (8) and a glass-ceramic gasket (7) and / or a metal or composite material paste, wherein the interconnector (5) defines a blind interconnector seat (13) open towards the clamping gasket (6), wherein the first contact layer (11) and the fuel cell (3) are accommodated in the blind interconnector seat (13), wherein the fuel cell (3) and the interconnector (5) sandwich the first contact layer (11), wherein the clamping gasket (6) is positioned superimposed on the interconnector (5), preferably at least partially in contact with the interconnector (5), and wherein the clamping gasket (6) defines an extended gasket seat (14) passing through the clamping gasket (6), wherein the second contact layer (12) is accommodated in the gasket seat (14), and wherein the fuel stack (1) comprises a removable junction (9) interposed between the first modular unit (21) and the second modular unit (22), wherein the removable junction (9) comprises:- an electrically conductive metal layer (10), optionally a metal plate or a metal paste, and- a second compression gasket (8), at least partially interposed between the metal layer (10) and the interconnector (5) of the second modular unit (22), and wherein the metal layer (10) is positioned interposed in contact with the second contact layer (12) of the first modular unit (21) and with the interconnector (5) of the second modular unit (22), so as to electrically connect the first modular unit (21) and the second modular unit (22).

2. A fuel cell stack (1) according to claim 1 , comprising a plurality of first modular units (21) and second modular units (22), alternately stacked on top of one another so as to form a stacking sequence repeated at least once, preferably a plurality of times, formed by:- a first modular unit (21) superimposed on a removable junction (9),- a further removable junction (9) superimposed on the first modular unit (21),- a second modular unit (22) superimposed on the further removable junction (9).

3. A fuel cell stack (1) according to claim 1 , comprising at least one additional modular unit (23), optionally up to six or up to thirteen or up to twenty additional modular units (23), wherein each additional modular unit (22) comprises:- a fuel cell (3), formed by two electrodes and an electrolyte interposed between the two electrodes;- two contact layers (4) made of an electrically conductive material, sandwiching the fuel cell (3), wherein a first contact layer (11) is positioned in contact with one of the two electrodes and wherein a second contact layer (12) is positioned in contact with the other of the two electrodes;- an interconnector (5) made of an electrically conductive material, optionally made of steel;- a clamping gasket (6), comprising a glass-ceramic gasket (7) and / or a compression gasket (8) and / or a metal or composite material paste, wherein the interconnector (5) defines a blind interconnector seat (13) open towards the clamping gasket (6), wherein the first contact layer (11) and the fuel cell (3) are accommodated in the blind interconnector seat (13), wherein the fuel cell (3) and the interconnector (5) sandwich the first contact layer (11), wherein the clamping gasket (6) is positioned superimposed on the interconnector (5), preferably at least partially in contact with the interconnector (5), and wherein the clamping gasket (6) defines an extended gasket seat (14) passing through the clamping gasket (6), wherein the second contact layer (12) is accommodated in the gasket seat (14), wherein the fuel stack (1) further comprises a plurality of first modular units (21) and second modular units (22),and wherein the first modular units (21), the second modular units (22), and the additional modular units (23) are stacked so as to form a stacking sequence repeated at least once, preferably a plurality of times, formed by:- a second modular unit (22) superimposed on a removable junction (9);- an additional modular unit (23) superimposed on the second modular unit (22), or a stack of up to six or up to thirteen or up to twenty additional modular units (23) superimposed on one another, wherein the stack of additional modular units (23) is superimposed on the second modular unit (22);- a first modular unit (21) superimposed on the additional modular unit (23), or superimposed on the stack of up to six or up to thirteen or up to twenty additional modular units (23).

4. A fuel cell stack (1) according to claim 3, wherein:- the at least one additional modular unit (23) is superimposed on the second modular unit (22) so that the interconnector (5) of the at least one additional modular unit (23) is superimposed in contact with the second contact layer (12) of the second modular unit(22);- the first modular unit (21) is superimposed on the at least one additional modular unit(23) so that the interconnector (5) of the first modular unit (21) is superimposed in contact with the second contact layer (12) of the at least one additional modular unit (23), and, optionally, an additional modular unit (23) is superimposed on another additional modular unit (23) so that the interconnector (5) of the additional modular unit (23) is superimposed in contact with the second contact layer (12) of the other additional modular unit (23).

5. A fuel cell stack (1) according to any one of the preceding claims, wherein the second compression gasket (8) of the removable junction (9) defines an extended junction opening (15) passing through the second compression gasket (8), wherein the metal layer (10) comprises a base portion (16) and a projecting portion (17), wherein the projecting portion (17) extends to project from the base portion (16), wherein the second compression gasket (8) of the removable junction (9) is positioned superimposed on the base portion (16), and wherein the projecting portion (17) is positioned inserted through the junction opening (15), and wherein the base portion (16) of the metal layer (10) is positioned in contact with the first modular unit (21), and wherein the projecting portion (17) is positioned in contactwith the second modular unit (22).

6. A fuel cell stack (1) according to any one of the preceding claims, comprising an external electrical bypass circuit (18), wherein the external electrical bypass circuit (18) forms an electrical in-series connection of a plurality of modular units (2), preferably wherein the external electrical bypass circuit (18) forms an electrical in-series connection of all modular units (2).

7. A fuel cell stack (1) according to claim 6, wherein the external by-pass circuit (18) forms an electrical in-series connection between the respective interconnectors (5) of a plurality of modular units (2), preferably wherein the external electrical bypass circuit (18) forms an electrical in-series connection between the interconnectors (5) of all modular units (2).

8. A fuel cell stack (1) according to claim 7, comprising a first group of modular units (21, 22, 23) stacked on top of one another without the interposition of a removable junction (9), and a second group of modular units (21 , 22, 23) stacked on top of one another without the interposition of a removable junction (9), wherein the first group of modular units (21 , 22, 23) is separated from the second group of modular units (21 , 22, 23) by the interposition of a removable junction (9), and wherein the external by-pass circuit (18) forms an electrical in-series connection between at least only one interconnector (5) of the first group of modular units (21 , 22, 23) and only one interconnector (5) of the second group of modular units (21 , 22, 23).

9. A fuel cell stack (1) according to any one of claims 6 to 8, comprising at least one detection device configured to detect at least one electrical parameter relating to the external electrical bypass circuit (18), and wherein, optionally, the at least one detection device comprises a voltmeter or ammeter configured to detect the voltage of the external by-pass circuit (18) at least one interconnector (5) or the current intensity of the external by-pass circuit (18) at least one interconnector (5).

10. A fuel cell stack (1) according to any one of the preceding claims, wherein the clamping gasket (6) consists of a first compression gasket (8) superimposed on a glass-ceramic gasket (7),and wherein, in at least one modular unit (2), preferably in each modular unit (2), the glass-ceramic gasket (7) of the modular unit (2) is interposed between the first compression gasket (8) and the interconnector (5) of the same modular unit (2), and / or wherein the metal layer (10) consists of a metal plate, and / or wherein the thickness of the metal layer (10) is between 0.1 mm and 5.0 mm, and / or wherein the clamping gasket (6), the interconnector (5), and the removable junction (9) substantially have the same transverse dimension with respect to a stacking direction as the modular units (2), and / or wherein the metal layer (10) is coated with a protective layer configured to prevent the evaporation of chromium.11 . A fuel cell stack (1 ) according to any one of the preceding claims, wherein the second compression gasket (8) is formed of non-metallic and deformable and electrically insulating and refractory materials up to temperatures of 1000 °C.

12. A fuel cell stack (1) according to any one of the preceding claims, wherein the second compression gasket (8) is made of:- mica and / or mica compounds, and / or- vermiculite and / or vermiculite derivatives, and / or- flexible ceramic materials, and / or- ceramic fibres, and / or- mineral fibres, and / or- deformable refractory materials in the form of a sheet, felt, paper, or multilayer composite, and / or- shaped as a sheet made of one or a combination of the preceding materials.

13. A method of assembling a fuel cell stack (1) according to any one of the preceding claims, comprising:- a step of stacking the plurality of modular units (2), so as to form the fuel cell stack (1);- a step of clamping the fuel cell stack (1), carried out with a pressure between 10 bar and 50 bar.

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