Fuel cell stack, fuel cell device

Abstract

The invention relates to a fuel cell stack (12) for a fuel cell device (10) for operation with ammonia (A), comprising a plurality of fuel cells (100) stacked on top of one another and a plurality of interconnectors (96), wherein one interconnector (96) is arranged between every two adjacent fuel cells (100). According to the invention, the interconnectors (96) each have an ammonia cracker (98) for converting the ammonia (A) into nitrogen (N) and hydrogen (H).

Description

[0001] Description

[0002] title

[0003] Fuel cell stack, fuel cell device

[0004] The invention relates to a fuel cell stack for operation with ammonia according to the preamble of the independent claim. The invention further relates to a fuel cell device for operation with ammonia comprising such a fuel cell stack.

[0005] State of the art

[0006] Ammonia as a potential transport medium for hydrogen is discussed in numerous sources. The possibility of using preferably green ammonia to generate electricity in high-temperature fuel cells is the subject of various research projects, for example, for the shipping industry. But the use of ammonia as an energy carrier also appears advantageous for other applications compared to hydrogen or methane; hydrogen is difficult to store and transport, and methane releases CO2 during its conversion.

[0007] High-temperature fuel cells are suitable for the use of ammonia as fuel, as the high temperatures can facilitate the reforming or cracking of the ammonia to hydrogen. However, the use of ammonia is also associated with problems; solid oxide fuel cells, in particular, are destroyed by the reaction of nitrogen with electrode and / or electrolyte material, especially a nickel anode. Therefore, the direct use of ammonia as fuel is only possible in very low concentrations.

[0008] The objective of the present invention is to create a high-temperature fuel cell system, in particular a fuel cell stack for high-temperature fuel cells, which enables the direct conversion of ammonia. Disclosure of the invention

[0009] Advantages

[0010] The present invention describes a fuel cell stack for a fuel cell device for operation with ammonia, comprising a plurality of stacked fuel cells and a plurality of interconnectors, wherein an interconnector is arranged between each pair of adjacent fuel cells, and wherein the interconnectors each comprise an ammonia cracker for converting the ammonia into nitrogen and hydrogen.

[0011] This has the advantage that the ammonia (NH3) can be directly converted into hydrogen (H2) and nitrogen (N2) within the fuel cell stack. This makes it possible to operate a fuel cell stack according to the invention with ammonia in the same way as a conventional fuel cell stack designed for hydrogen. By using the ammonia cracker, a conversion rate of 100% for ammonia can be achieved even at moderate operating temperatures of approximately 600°C. In contrast, the conversion rate of ammonia in fuel cell stacks designed for hydrogen, for example in fuel cells based on yttria-stabilized zirconia (YSZ) with a nickel cermet as the anode, is limited to approximately 80%. Additionally, in such fuel cell stacks, the nickel cermets, for example nickel-YSZ or nickel-CGO, are subjected to nitrification or...The formation of nickel-nitrogen compounds—for example, of the type NiaN or Ni(NX)2, where X can represent H2, N2, or O2, among others—is destroyed. CGO is understood to mean cerium-gadolinium oxide or gadolinium-doped cerium.

[0012] Furthermore, fuel cell stacks designed for hydrogen operation with fuel cells using a metal support have the disadvantage that the active hydrogen and nitrogen compounds produced during the splitting of ammonia lead to nitrification or the formation of nitrogen-metal compounds at the interface between the nickel cermet and the metal support, which accelerates the aging of the metal support, making it brittle, fragile, and ultimately destroyed.

[0013] All the disadvantages mentioned above of fuel cell stacks designed for hydrogen operation are overcome by the fuel cell stack according to the invention.

[0014] Advantageously, the ammonia cracker is arranged on the interconnector in such a way that the ammonia flowing into the fuel cell stack is first contacted by the ammonia cracker before the ammonia can reach the fuel cell, in particular an anode and / or a support of the fuel cell.

[0015] A fuel cell device is understood to be, in particular, a device that forms a component, especially a functional one, particularly a structural and / or functional component, of a fuel cell system, or the entire fuel cell system. In this context, a fuel cell system is understood to be, in particular, a system for the stationary and / or mobile generation of, in particular, electrical and / or thermal energy using at least one fuel cell unit.

[0016] A fuel cell system comprises one or more fuel cell stacks. Typically, a fuel cell system includes components and lines for supplying fuel and air to the fuel cell stack. Furthermore, a fuel cell system includes components and lines for removing exhaust gases from the fuel cell stack. Fuel, air, and exhaust gases are fluids. For the purposes of this invention, the term "fluids" refers to both liquid and gaseous fluids.

[0017] Advantageously, fuel cell systems have a recirculation circuit or anode recirculation circuit, comprising components and lines, designed to return unreacted fuel to the fuel cell stack. In this context, a recirculation circuit or anode recirculation circuit is understood to be, in particular, a fluid connection or fluid path designed to supply fuel- or hydrogen- and water-containing anode exhaust gas from the fuel cell unit to a mixing point – the recirculation inlet point – where the anode exhaust gas is mixed with the at least substantially pure fuel or hydrogen. Specifically, the recirculation circuit is designed to supply unreacted fuel or hydrogen back to the anode side of the fuel cell device. The mixing of the anode exhaust gas and the fuel or hydrogen is particularly important.Hydrogen is intended to be supplied to the fuel cell unit on the anode side.

[0018] Overall, a fuel cell system comprises at least one or more fans designed to convey a fluid, in particular a gaseous fluid. The fluid can be, in particular, a fuel, air, exhaust gas, or a combination thereof. The fans can be, in particular, air supply fans, fuel supply fans, exhaust gas discharge fans, and / or recirculation fans. Advantageously, the fuel cell system comprises one or more heat exchangers, in particular to recover heat from the exhaust gas, or more specifically, the anode and cathode exhaust gases, and to transfer heat to the fluids supplied to the fuel cell unit—in particular, air, fuel, and / or recirculated fluid. For the purposes of this text, the terms heat exchanger and heat transfer unit are used synonymously.

[0019] In this context, a fuel cell stack refers specifically to a unit comprising multiple fuel cells. A fuel cell is an electrochemical cell for converting fuel and oxygen into heat and electrical energy. Typically, the fuel cells in a fuel cell stack are stacked on top of each other. Advantageously, a fuel cell can have a plate-shaped support on which the functional layers, in particular electrolyte layers, are arranged. The plate-shaped support can, for example, be made of metal, especially stainless steel, and designed to be resistant to the high temperatures and humidity prevailing in a fuel cell stack.

[0020] According to the invention, the fuel cell stack has interconnectors between the individual fuel cells. An interconnector is preferably plate-shaped and advantageously has projections, in particular projections designed as fluid-carrying and / or fluid-conducting elements, for example in the form of channels. An interconnector is arranged in the fuel cell stack between each fuel cell and another adjacent fuel cell. In the context of this invention, "adjacent fuel cells" shall be understood to mean two fuel cells directly adjacent to each other, i.e., no further fuel cell is arranged between the two adjacent fuel cells.

[0021] The interconnector advantageously establishes electrical contact between adjacent fuel cells. Furthermore, the interconnector, particularly through its raised sections, creates a gap and thus a flow-through space between each adjacent fuel cell. This enables the supply of fluids to the fuel cell and its functional layers. Advantageously, the fuel cells are electrically connected in series. It is also conceivable that the fuel cells are electrically connected in parallel. The fuel cells in the fuel cell stack can advantageously be arranged on a common chassis or support, or in a common housing.

[0022] The interconnector is thus configured with one side facing the anode of an adjacent fuel cell and the other side facing the cathode of another adjacent fuel cell. Advantageously, the ammonia cracker is arranged on the side of the interconnector facing the anode of a fuel cell and optionally making contact with it. A fuel cell is specifically designed to convert at least the chemical reaction energy of at least one fuel gas, particularly hydrogen, and at least one oxidizing agent, particularly oxygen, into electrical energy. The fuel cell can, for example, be designed as a solid oxide fuel cell (SOFC). It is also conceivable that the fuel cell is designed in the manner of a proton conductor or proton-conducting oxide (PCO).Such fuel cells are also known as protonic ceramic fuel cells (PCFCs).

[0023] An ammonia cracker is understood to be, in particular, a catalytically active material for cracking ammonia. Advantageously, the type of ammonia cracker, as well as its quantity and arrangement in the fuel cell stack, is selected such that, at an operating temperature of the fuel cell stacks, typically between 550°C and 700°C, preferably between 575°C and 650°C, and particularly preferably between 600°C and 625°C, an ammonia conversion rate of at least 95.0%, preferably at least 98.0%, and particularly preferably at least 99.5% is achieved.

[0024] A fuel supply is understood to be a source of fuel that is supplied to the fuel cell device. For example, the fuel supply can be a connection for an external fuel line, such as from a fuel network or a fuel cylinder. In the present invention, the fuel is ammonia or a mixture of ammonia with methanol, natural gas, and / or another hydrocarbon-based fuel with a high ammonia content. Preferably, the fuel is largely pure ammonia, since in this way the fuel cell device has no CO2 emissions.

[0025] Advantageous further developments of the fuel cell device are possible due to the features listed in the dependent claims. A further improvement is possible if the ammonia cracker contains nickel. Nickel has proven to be a particularly efficient ammonia cracker.

[0026] The combination of nickel on aluminum oxide (Al₂O₃) is particularly advantageous. In some variants, the ammonia cracker may contain nickel on cerium oxide (CeO₂) or a cerium oxide doped with ruthenium.

[0027] In principle, it is also conceivable that a material other than ammonia crackers is intended, for example ruthenium, in particular ruthenium on aluminum oxide and / or ruthenium on cerium oxide or a cerium oxide doped with ruthenium.

[0028] The fuel cell stack can be further improved by arranging the ammonia cracker on a fuel guide structure. This ensures that the ammonia flowing into the fuel cell stack first contacts the ammonia cracker before coming into contact with the fuel cells.

[0029] A fuel guide structure is understood to be, in particular, a structure designed to guide the fuel—that is, ammonia and, above all, the hydrogen derived from the ammonia—flow-wise to the fuel cell, to an anode side of the fuel cell, or into an anode compartment. For example, the fuel guide structure can comprise at least one conduit or tube and / or at least one channel; it is also conceivable that the fuel guide structure is formed by a surface suitable for guiding the fuel, for example, through a special surface finish.

[0030] In particular, the fuel guide structure can be a fuel guide structure of the interconnector. For example, it is conceivable that the fuel guide structure is a channel structure and / or a structure of protrusions and / or a structure of depressions in the interconnector. It is particularly conceivable that the fuel guide structure is imprinted in the interconnector. The channel structure can also have a special coating on the interconnector. The object is further improved by the arrangement of a protective layer between the ammonia cracker and the adjacent fuel cell. In this way, a harmful interaction between ammonia and or nitrogen derived from the ammonia and any nitrogen compounds with the fuel cell can be avoided. In particular, damage to an anode layer of the fuel cell and / or damage to a support of the fuel cell can be avoided.In particular, the protective layer should be arranged between the ammonia cracker and the adjacent fuel cell, with its anode side facing the ammonia cracker or the interconnector.

[0031] The protective layer must be permeable at least to the hydrogen produced from the ammonia. In particular, the protective layer can have a porous ceramic, for example a porous aluminum oxide layer.

[0032] A further improvement is possible if the ammonia cracker is arranged in a cracker layer and is graduated along a layer thickness within the cracker layer. This is an advantageous alternative method to prevent harmful interactions between ammonia and nitrogen derived from the ammonia, and potentially nitrogen compounds, and the fuel cell.

[0033] The fact that the ammonia cracker is arranged in a graduated pattern along the thickness of the cracker layer means, in particular, that the concentration of the ammonia cracker changes, preferably continuously, along the thickness of the cracker layer. In preferred embodiments, the cracker layer has a minimum concentration of the ammonia cracker, preferably 0%, on the outer surface facing the fuel cell, whose anode side is oriented towards the cracker layer, and a maximum concentration of the ammonia cracker on the inner surface, which is located opposite the outer surface with respect to the thickness of the layer. Preferably, the cracker layer is arranged in contact with the inner surface on the interconnect. The concentration of the ammonia cracker decreases continuously from the inner surface to the upper surface along the thickness of the layer until the minimum concentration is reached.In this way, the splitting of the ammonia will primarily occur on the inner surface and away from the outer surface, thus keeping it at a distance from the approaching fuel cell. This minimizes or prevents any harmful interaction between the substances resulting from the ammonia and the fuel cell.

[0034] For example, it is conceivable that the cracker layer has a porous aluminum oxide layer which has a different nickel concentration depending on its position along the layer thickness.

[0035] In some variations, it is conceivable that the cracker layer exhibits its maximum concentration at a position midway along the layer thickness, while a minimum concentration exists at the inner and outer surfaces. The concentration of ammonia crackers then decreases continuously along the layer thickness from the midway position towards the inner or outer surface. This has the additional advantage of minimizing or preventing harmful interactions between the substances derived from the ammonia and the interconnector or an interconnector carrier.

[0036] The fuel cell stack can be further improved by installing an ammonia cracker at one of the fuel inlets. This allows the ammonia to be at least partially broken down into hydrogen and nitrogen before it reaches the fuel cells.

[0037] A fuel inlet is understood to be, in particular, an inlet of the fuel cell stack designed for the intake of fuel, specifically ammonia and / or hydrogen. Advantageously, a fuel inlet also includes an internal fuel line or fuel distribution structure of the fuel cell stack, designed to distribute the fuel to the fuel cell stacks. For example, a central fuel chamber or a fuel tube fluidically connected to the fuel cell stacks can be part of the fuel inlet. It is advantageous for the ammonia cracker to be arranged on a body with a high surface area per volume, such as a porous body, particularly a ceramic and / or metallic porous body.

[0038] The invention further relates to a fuel cell device for operation with ammonia, comprising at least one fuel cell stack according to the present invention and a fuel supply for ammonia.

[0039] In this way, a fuel cell device is created that can reliably and easily convert ammonia into fuel. The advantages of such a fuel cell device arise from the benefits of ammonia as a fuel, such as easy storage and transportability, as well as the possibility of conversion in the fuel cell device without CO₂ emissions. In addition, compared to a fuel cell device operating on natural gas, the device has a much simpler design, since no fuel reforming is necessary; the fuel cell stack can simply be supplied with ammonia.

[0040] The fuel cell device can be further improved by including an ammonia cracker in the anode path. This allows the ammonia to be at least partially broken down into hydrogen and nitrogen before it reaches the fuel cells.

[0041] The term "anode path" refers specifically to the fluid path of the fuel cell device, which is intended for supplying the anode compartment and for disposing of the anode exhaust gases, or which is fluidically connected to the anode compartment, and includes both lines and components. In particular, the fuel supply line, the anode exhaust system, the recirculation circuit, and the anode compartment are components of the anode path.

[0042] The phrase "the anode path includes the ammonia cracker" means, in particular, that the ammonia cracker is arranged in the fluid path of the anode path, especially in the components and / or lines of the anode path. It is particularly advantageous for the ammonia cracker to be arranged in a heat exchanger. This has the advantage that the heat required for cracking the ammonia can be supplied in the heat exchanger, for example, by hot exhaust gases.

[0043] It is advantageous to consider that the ammonia cracker is arranged on a body in the anode path with a high surface area per volume, for example a porous body, in particular a ceramic and / or metallic porous body.

[0044] A further improvement is possible if the fuel cell device includes a reactor for converting the ammonia into nitrogen and hydrogen, wherein the reactor includes a catalyst with an ammonia cracker and a hydrogen-conducting membrane.

[0045] This enables a fuel cell device that can convert ammonia as fuel with high efficiency. Furthermore, it advantageously ensures that the fuel cell stack can be supplied with a proportion of hydrogen and therefore has to convert smaller amounts of ammonia directly. This allows for particularly reliable, trouble-free, and low-maintenance operation.

[0046] A reactor is defined as a device designed to split ammonia (NH3) into hydrogen (H2) and nitrogen (L). The reactor is intended to supply the fuel cell stack of the fuel cell device with the hydrogen split from the ammonia as fuel for the electrochemical reaction. This prevents the fuel cell stack from being poisoned or damaged by nitrogen. In this case, the reactor includes a catalyst with an ammonia cracker, which is designed for the catalytic splitting of ammonia into hydrogen and nitrogen. Furthermore, the reactor has a hydrogen-conducting membrane. This membrane allows the separation of the unwanted nitrogen. In this way, a hydrogen-rich fuel can be supplied to the fuel cell stack. Such a reactor is also called a membrane reactor.The membrane offers the advantage that the ammonia conversion in the catalyst can be increased in the reactor, due to the equilibrium of the reaction.

[0047] 2 NH3-> N2+ 3 H2 by separating the product H2, which is continuously shifted to the product side through the membrane.

[0048] An improvement is possible if the reactor catalyst contains ruthenium. This specifically means that the catalyst contains ruthenium as an ammonia cracker. Ruthenium has proven to be a particularly efficient ammonia cracker. For example, the catalyst can contain ruthenium on aluminum oxide (Al₂O₃). This advantageously allows for the almost complete conversion of NH₃ to N₂ and H₂ at temperatures of approximately 550°C.

[0049] In some variations, the catalyst could consist of ruthenium on cerium oxide (CeO2) or a cerium oxide doped with ruthenium. This would allow the complete conversion of NH3 to N2 and H2 at temperatures below 500°C.

[0050] In further embodiments, it is conceivable that the reactor incorporates an amide and / or imide catalyst. This would allow the complete conversion of NH3 to 1 / 12 and H2 at temperatures well below 500°C.

[0051] Further improvement is possible if the reactor is fluidically connected to the fuel cell stack via a hydrogen outlet. Supplying a hydrogen-rich gas produced in this way for conversion in the fuel cell stack offers the advantages of a higher electrical fuel cell voltage and lower volumetric flow rates in the anode path, thus eliminating the need for unnecessary blower power due to a nitrogen flow. Furthermore, a high recirculation rate is possible because no significant nitrogen accumulation occurs in the anode path. Overall, this enables high system efficiency. A hydrogen outlet is defined as a line designed to remove the hydrogen separated by the membrane in the reactor. The hydrogen separated in this way contains only a very small residual ammonia content, typically less than 1% by volume.

[0052] The phrase "a first component is fluidically connected to a second component" means, in particular, that the first component is connected to the second component via appropriate connections and lines in such a way that a fluid flow is possible from the first component to the second component and / or from the second component to the first component. The first and second components can be directly fluidically connected via a line, but it is also conceivable that further fluid-carrying components are arranged in the fluid path between the first and second components.

[0053] In certain configurations, an improvement is possible if the fuel supply is fluidically connected to the fuel cell stack via an ammonia line, allowing for direct ammonia delivery to the fuel cell stack. In this case, a portion of the ammonia can be converted directly within the fuel cell stack using the ammonia cracker. In such configurations, the fuel cell stack is supplied with a proportion of ammonia in addition to the hydrogen produced from the reactor; for example, 60% ammonia and 40% hydrogen by volume. Advantageously, a fuel cell device with an ammonia supply line to the fuel cell stack operates with a reduced recirculation rate compared to a fuel cell device without an ammonia line. This prevents nitrogen accumulation in the anode path.

[0054] This offers the advantage that an endothermic conversion of ammonia within the fuel cell stack can achieve a cooling effect compared to simply supplying hydrogen to the fuel cell stack. This reduces the energy required for air cooling of the fuel cell stack, particularly via the cathode-side air supply, for example, by reducing the fan power for the cathode air compared to operation without an ammonia supply to the fuel cell stack. In this way, the overall efficiency of the fuel cell device can be increased.

[0055] The ammonia line can be directly connected to the fuel cell stack in terms of fluid dynamics. It is also conceivable that the ammonia line is indirectly connected to the fuel cell stack in terms of fluid dynamics; for example, it is conceivable that the ammonia line is fluid-technically connected to a hydrogen outlet, a fuel supply line upstream of the fuel cell stack, and / or a line or component of the anode path, particularly the recirculation circuit.

[0056] A further improvement is possible if the reactor is thermally connected to a burner for heating it. The burner is designed to continuously supply the reactor with heat for the endothermic decomposition of ammonia into hydrogen and nitrogen. Advantageously, the reactor, and especially the catalyst, is designed so that the ammonia decomposition reaction proceeds sufficiently quickly at temperatures significantly below the operating temperature of the fuel cell stack, for example, at 550°C, 500°C, or below 500°C. This has the advantage that waste heat from the stack can be used for ammonia decomposition. The burner is then advantageously only intended to supply the reactor with any additional heat that may be necessary. This might be the case, for example, during start-up operation when the waste heat from the fuel cell stack is not yet sufficient. The burner output is also advantageously adjustable.

[0057] The burner can be operated with hydrogen and / or ammonia. Advantageously, the burner can be operated with anode exhaust gas and / or recirculated fluid from a recirculation loop, so that hydrogen not converted in the fuel cell unit can be converted in the burner. A further improvement is possible if the reactor is fluidically connected to the burner via a nitrogen outlet. In this way, particularly efficient ammonia splitting with a high splitting fraction is possible, ideally resulting in almost complete ammonia splitting.

[0058] A nitrogen drain is defined as a line designed to remove the nitrogen separated from the hydrogen by the membrane in the reactor. The nitrogen thus separated constitutes the main residual fraction of the unreacted ammonia in the reactor, typically up to about 5% by volume.

[0059] The fact that the reactor is fluidically connected to the burner via a nitrogen outlet makes it possible, in particular, for the exhaust gas from the fuel cell device to consist essentially only of nitrogen, oxygen and water vapor.

[0060] Further improvement is possible by integrating the reactor and burner into a single assembly. This minimizes heat transfer losses from the burner to the reactor. While it is conceivable that the burner and reactor could be designed as separate components, direct integration into a single assembly offers the additional advantage of reducing the complexity of the fuel cell device, in addition to minimizing thermal losses. Specifically, no special piping is required for heat transfer from the burner to the reactor. Overall, this results in an efficient and simple fuel cell device that is easy to manufacture, reliable, and easy to maintain.

[0061] The integration of the burner and reactor into a single assembly means, in particular, that the burner and the reactor form a single structural unit. Specifically, it is conceivable that the reactor and burner are mounted on a common support or frame. It is also conceivable that the reactor and burner are integrated into a common housing.

[0062] A further improvement is possible if the fuel cell device incorporates a recirculation circuit to return anode exhaust gas from the fuel cell stack to a fuel supply line for the fuel cell stack. This enables particularly efficient hydrogen utilization.

[0063] In advantageous embodiments, an oxygen sensor, preferably a lambda probe, is arranged on the burner to control the burner. This enables optimal combustion, allowing for the most stoichiometric and thus largely complete combustion possible. Advantageously, the air supply and fuel supply to the burner are controlled according to the signal from the oxygen sensor. For example, the oxygen sensor can be arranged at the burner's exhaust gas outlet.

[0064] The oxygen sensor can, for example, have a broadband lambda probe or a switching lambda probe.

[0065] Further improvement is possible if a condensation heat exchanger is installed in the anode path, particularly in the recirculation circuit, to condense water. This enables high fuel gas utilization at the system level. Additionally, this allows for a reduction in the volumetric or mass flow rate of a recirculation blower or a fuel blower in the anode path, thus reducing the required blower power and increasing system efficiency.

[0066] Drawings

[0067] The drawings illustrate exemplary embodiments of the fuel cell device, which are explained in more detail in the following description. Figure 1 shows a schematic representation of a variant of the fuel cell device according to the present invention.

[0068] Figure 2 shows a schematic representation of a fuel cell stack according to the present invention and

[0069] Figure 3 shows a detailed view of an interconnector between two fuel cells.

[0070] Description

[0071] Figure 1 shows a schematic circuit diagram of an exemplary embodiment of a fuel cell device 10. The fuel cell device 10 comprises, by way of example, a fuel cell stack 12, which has a plurality of fuel cells, in this case solid oxide fuel cells (SOFC), and a plurality of processor units 14.

[0072] The fuel cell stack 12 is electrically connected to a power electronics unit 94. The power electronics unit 94 includes, in particular, an inverter or DC-AC inverter. The power electronics unit 94 is specifically designed to absorb the electrical power generated in the fuel cell stack 12 during fuel conversion and to make it available for use outside the fuel cell device 10.

[0073] The fuel cell device 10 further comprises a control unit (not shown) which is intended for regulating and controlling the fuel cell device 10, in particular for regulating fluid flows and electrical currents. For this purpose, the control unit has a processing unit and a memory and is equipped with appropriate communication interfaces for receiving sensor data and sending control commands. In particular, the control unit is configured to control the controllable components of the fuel cell device 10. Specifically, the control unit is configured to receive and evaluate signals from sensors shown and not shown, in particular temperature sensors, flow sensors, oxygen sensors, and the like.

[0074] In the context of this invention, a processor unit 14 shall be understood to be, in particular, a unit or component of the fuel cell device 10 that is not a fuel cell and / or a fuel cell stack 12. In the present case, the processor units 14 are units for the chemical and / or thermal pre- and / or post-treatment of at least one medium to be converted and / or converted in the fuel cell stack 12, such as, for example, a fuel gas, air and / or exhaust gas.

[0075] One of the processor units 14 is, for example, a heat exchanger 18 arranged in an air supply line 16 for heating the air L supplied to one of the fuel cell stacks 12. In this case, the air L is supplied, for example, during normal operation, to a cathode compartment 20 of the fuel cell stack 12, while the fuel hydrogen H is supplied to an anode compartment 22. In the fuel cell stack 12, the fuel is electrochemically converted to generate electricity and heat.

[0076] Hydrogen (H) is generated by supplying ammonia (A) from a fuel supply 25 or fuel source to the fuel cell device 10 via a fuel supply line 24. In a further processor unit 14, a reactor 50, the ammonia is converted into hydrogen (H) and nitrogen (N). For this purpose, the reactor 50 has a catalyst for splitting the ammonia (A) into hydrogen (H) and nitrogen (N).

[0077] Nitrogen (N) and a membrane permeable to hydrogen (H) are present. The hydrogen (H) is discharged from the reactor 50 via a hydrogen outlet 52. The nitrogen (N) is discharged from the reactor 50 via a nitrogen outlet 54. Unreacted ammonia (A) is primarily discharged from the reactor 50 via the nitrogen outlet 54; only a small amount of ammonia is discharged via the hydrogen outlet 52. The hydrogen outlet 52 is part of the fuel supply line 24. In this embodiment, the reactor 50 is fluidically connected to the fuel cell stack 12 and its anode compartment 22 via the hydrogen outlet 52 and fuel supply line 24, respectively. In this way, the hydrogen (H) generated in the reactor 50 can be supplied to the fuel cell stack 12 via the fuel supply line 24.

[0078] The fuel cell device 10 includes a further processor unit 14 and a burner 56, which is designed to supply the reactor 50 with the heat necessary for the ammonia A splitting process. The fuel cell stack 12 is connected to the burner 56 on the exhaust side. Exhaust gas from the fuel cell stack 12 is supplied to the burner 56, in this case via a cathode exhaust gas duct 30 (cathode exhaust gas KAb) and via an anode exhaust gas duct 32 (a portion of an anode exhaust gas AAb). The cathode exhaust gas KAb contains predominantly unused air L, while the anode exhaust gas AAb contains, among other things, unreacted fuel, in particular hydrogen H. Furthermore, the anode exhaust gas AA typically contains water vapor.

[0079] The exhaust gas Ab produced during combustion in the burner 56 is discharged from the burner 56 via an exhaust gas duct 34 and the heat exchanger 18. In this way, the heat of the hot exhaust gas Ab can be transferred to the supplied air L in the air supply line 16. Similarly, the heat of the hot exhaust gas A can be used to preheat the supplied air L in the air supply line 16.

[0080] As an example, the cathode exhaust system 30 has an adjustable three-way valve 74, which is designed to direct a portion or partial flow of the cathode exhaust gas KAa flowing through the cathode exhaust system 30 past the burner 56 via a burner bypass line 76. The three-way valve 74 divides the cathode exhaust gas flow from the cathode chamber 20 through the cathode exhaust system 30 into two partial flows, one of which continues through the cathode exhaust system 30 to the burner 56, and the other partial flow via the burner bypass line 76 to a mixing point 78 of the exhaust system 34. The three-way valve 74 is fluidically arranged on the cathode exhaust system 30 between the fuel cell stack 12 and the burner 56. The three-way valve 74 is fluidically connected to the mixing point 78 via the burner bypass line 76.As an example, the mixing point 78 is arranged in the exhaust gas duct 34 between the burner 56 and the heat exchanger 18. The burner output of the burner 56 can be adjusted by means of the controllable three-way valve 74, thus allowing the cathode exhaust gas flow into the burner 56 to be regulated.

[0081] In the illustrated embodiment, the reactor 50 and the burner 56 are integrated into a common assembly 80. For example, the reactor 50 and the burner 56 are mounted on a common mounting frame and enclosed by a housing. The common mounting on the mounting frame and the common housing, together with the reactor 50 and burner 56, form the assembly 80.

[0082] As an example, the cathode exhaust gas duct 30 has a mixing point 82, which is designed to mix the nitrogen (N) and ammonia (A) separated in the reactor 50. The mixing point 82 is, for illustrative purposes, located between the three-way valve 74 and the burner 56. The reactor 50 is fluidically connected to the mixing point 82 via the nitrogen outlet 54. In this way, the nitrogen (N) and any remaining unreacted ammonia (A) from the reactor 50 can be routed to the burner 56 via the mixing point 82. In particular, the ammonia (A) can be reacted in the burner 56 and thus contribute to heating the reactor 50.

[0083] Downstream of the heat exchanger 18 with respect to the exhaust gas Ab, another processor unit 14, in this case the heat exchanger 36, is located in the exhaust gas duct 34. The heat exchanger 36 is fluidically connected to the fuel supply 25 and the burner 50 via the fuel supply line 24; in particular, the heat exchanger 36 is fluidically arranged between the fuel supply 25 and the burner 50. In this way, the remaining heat from the exhaust gas Ab can be transferred to the ammonia supplied to the burner 50. Similarly, the remaining heat from the exhaust gas Ab can be used to generate the heat required in the burner 50 for the splitting of the ammonia A into hydrogen H and nitrogen N. Downstream of the heat exchanger 36, the exhaust gases A are discharged from the fuel cell device 10, for example, via a chimney 46.

[0084] Advantageously, the heat exchanger 36 is provided for the evaporation of the ammonia A from the fuel supply 25. In variants where the fuel supply 25 already provides gaseous ammonia, the heat exchanger 36 can be omitted. In such variants, the heat exchanger 18 is directly connected to the chimney 46 via the exhaust gas duct 34.

[0085] Furthermore, the fuel cell device 10 has a return line 38 by means of which the anode exhaust gas AAb from the anode exhaust line 32 can be fed to the fuel supply line 24. The return line 38, together with the fuel supply line 24, forms an anode recirculation circuit 40 by means of which anode exhaust gas AAb can be returned to the anode chamber 22 of the fuel cell stack 12, so that any unreacted fuel, in particular hydrogen H in the anode exhaust gas AAb, can subsequently be converted, thereby further increasing the efficiency of the fuel cell device 10.

[0086] The anode recirculation circuit 40 has a mixing point 48 to which the fuel supply line 24, the return line 38, and the fuel cell stack 12 or its anode compartment 22 are connected, so that a recirculated anode or anode exhaust gas AAb flowing through the return line 38 can be mixed with hydrogen H flowing through the fuel supply line 24 or hydrogen outlet 52 at the mixing point 48, and the mixture can be supplied to the fuel cell stack 12 or its anode compartment 22. In an alternative formulation of the same circuit topology, the fuel supply line 24 or

[0087] The hydrogen outlet 52 is fluidically directly connected to the fuel cell stack 12 or its anode compartment 22, and the fuel supply line has a mixing point 48, which is fluidically connected to the return line 38 and is fluidically located upstream of the fuel cell stack 12. The anode recirculation circuit 40 has a compressor 42. The compressor 42 is fluidically connected to the return line 38, so that the recirculation rate of the anode exhaust gas AAb can be controlled via the compressor 42. The compressor 42 is a recirculation blower. The mixing point 48 is fluidically connected between the reactor 50 and the fuel cell stack 12 or its anode compartment 22. The mixing point 48 is fluidically connected between the compressor 42 and the fuel cell stack 12 or its anode compartment 22.

[0088] In the exemplary embodiment, a heat exchanger 44 is arranged on the anode recirculation circuit 40 downstream of the compressor 42 in the flow direction of the recirculated fluid or anode exhaust gas AAb. This heat exchanger transfers the heat from the anode exhaust gas AAb flowing from the anode chamber 22 via the anode exhaust gas duct 32 or the return line 38 to the hydrogen H or the returning anode exhaust gas AAb flowing into the anode chamber 22 via the fuel supply line 24 or from the anode recirculation circuit 40. Downstream of the reactor 50 in the hydrogen H flow direction, the heat exchanger 44 is arranged. For example, the heat exchanger 44 is fluidically positioned between the mixing point 48 and the fuel cell stack 12.

[0089] In the direction of flow of the hot anode exhaust gas AAb flowing from the fuel cell stack 12, the heat exchanger 44 follows directly after the fuel cell stack 12. The heat exchanger 44 is directly connected to the fuel cell stack 12 via the anode exhaust gas guide 32.

[0090] As an example, a heat exchanger 58 follows the flow direction of the anode exhaust gas AAb flowing from heat exchanger 44. Heat exchanger 44 is fluidically connected to heat exchanger 58 via the return line 38. Heat exchanger 58 is located at the fuel supply line 24 and is designed to transfer the heat of the anode exhaust gas AAb to the ammonia A flowing into reactor 50. Alternatively, heat exchanger 58 is fluidically located between fuel supply 25 and reactor 50. Alternatively, heat exchanger 58 is fluidically located between heat exchanger 36 and reactor.

[0091] As an example, a branch point 62 is arranged in the recirculation circuit 40 on the return line 38 between the fuel cell stack 12 and the compressor 42. The branch point 62 is a flow divider and is designed to separate a portion of the anode exhaust gas AAb flowing through the return line 38 and direct it into a branch line 64. The branch point 62 is connected to the burner 56 via the branch line 64. In this way, a portion of the anode exhaust gas flow from the recirculation circuit 40 can be directed into the burner 56, where unreacted hydrogen from the anode exhaust gas AAb can be used to heat the reactor 50. Alternatively, the branch point 62 can be arranged between the heat exchanger 58 and the compressor 42. In some variations, it is conceivable that branch point 62 has an adjustable three-way valve, which allows the setting of the proportion orThe current of the anode exhaust gas AAb, branched off from the return line 38, is enabled.

[0092] In the exemplary embodiment, a heat exchanger 60, which is a condensing heat exchanger 60, is arranged in the recirculation circuit 40. The heat exchanger 60 is designed to condense any water or water vapor present in the anode exhaust gas AAb and to discharge it from the recirculation circuit 40, preferably from the fuel cell device 10. Advantageously, the heat exchanger 60 is arranged upstream of the compressor 42 in the return line 38 with respect to the flow direction of the anode exhaust gas AAb. This has the advantage that, during operation, a dehumidified anode exhaust gas AAb flows through the compressor 42, which advantageously reduces the load and power requirement of the compressor 42.By way of example, the heat exchanger 60 is arranged fluidically between the heat exchanger 44 and the compressor 42 on the return line 38, specifically between the heat exchanger 58 and the compressor 42, and particularly between the branch point 62 and the compressor 42. In this embodiment, the condensing heat exchanger 60 condenses the vapor from the anode exhaust gas AAb by transferring the heat from the anode exhaust gas to the air L supplied to the fuel cell stack 12. By way of example, the air supply line 16 has an adjustable three-way valve 66, which is designed to divert an adjustable proportion or flow of air L from the air supply line 16. The three-way valve 66 is connected to the heat exchanger 60 via an air branch line. As an example, the three-way valve 66 is arranged in terms of flow technology between an air source 68 and the heat exchanger 18.The air supply line 16 has a mixing point 70, which is designed to mix the heated air flowing from the heat exchanger 60 into the airflow of the air supply line 16. The mixing point 70 is fluidically connected to the heat exchanger 60 via an air return line. Advantageously, the mixing point 70 is arranged on the air supply line 16 in the direction of air flow L downstream of the three-way valve 66. By way of example, the mixing point 70 is fluidically arranged between the three-way valve 66 and the heat exchanger 18.

[0093] The condensation heat exchanger 60 has a condensate drain 84, which is designed to drain the water condensed from the anode exhaust gas AAb, in particular from the fuel cell device 10.

[0094] An air blower 72 is arranged on the air supply line 16 as an example. The air blower 72 is designed to convey the air L from the air source 68 into the fuel cell stack 12 or its cathode chamber 20. Advantageously, the air blower 72 is arranged between the air source 68 and the fuel cell stack 12 from a fluid dynamics perspective. In the exemplary embodiment, the air blower is arranged between the three-way valve 66 and the heat exchanger 18 from a fluid dynamics perspective, in particular between the mixing point 70 and the heat exchanger 18.

[0095] Furthermore, the fuel cell device 10 includes, by way of example, an ammonia line 86, which is intended for supplying the fuel cell stack 12 or its anode compartment 22 with ammonia A. For this purpose, the fuel supply line 24, in the direction of flow of the ammonia A upstream of the reactor 50, has, by way of example, an adjustable three-way valve 88, which is fluidically connected to the ammonia line 86 and is intended to direct a portion of the ammonia flow through the ammonia line 86 to a mixing point 92 in the return line 38 of the recirculation circuit 50. In this way, ammonia A from the fuel supply 25 can bypass the reactor 50 and be directed directly into the fuel cell stack 12 or its anode compartment 22. The three-way valve 88 is fluidically connected to the mixing point 92 via the ammonia line 86.

[0096] Because the three-way valve 88 is adjustable, the proportion of ammonia supplied to the fuel cell stack 12 can be set. The ammonia concentration required for safe and reliable operation of the fuel cell stack 12 depends on the details of the fuel cells installed in the stack, particularly their cell chemistry and geometry. In the present embodiment, the fuel cell stack 12 is configured for ammonia conversion, such that, by way of example, an ammonia concentration of 50% by volume is added.

[0097] In the illustrated embodiment, the burner 56 has an oxygen sensor 90. For example, the oxygen sensor 90 is arranged on the exhaust gas duct 34 directly adjacent to the burner 56. In this embodiment, the oxygen sensor 90 is a lambda probe. The oxygen sensor 90 makes it possible to control the burner 56 in such a way as to achieve optimal combustion. For example, the airflow supplied to the burner 56 can be controlled via the adjustable three-way valve 74 by adjusting the cathode exhaust gas KAa. It is also conceivable that the airflow is controlled according to the signal from the oxygen sensor 90 in such a way that the oxygen sensor 90 detects stoichiometric combustion.

[0098] Figure 2 shows a section through the fuel cell stack 12. The fuel cell stack 12 comprises a plurality of fuel cells 100 stacked one above the other. For clarity, only 8 fuel cells 100 are shown as an example. In typical high-temperature fuel cells, the fuel cell stacks 12 comprise approximately 100 to 500 fuel cells 100. An interconnector 96 is arranged between each directly adjacent fuel cell 100. The interconnectors 96 each have an ammonia cracker 98. The fuel cells 100 are fluidically connected to a fuel chamber 102, which in turn is fluidly connected to a fuel inlet 104.

[0099] It is planned that ammonia A and hydrogen H will be introduced into the fuel inlet 104 of the fuel cell stack 12 via the fuel supply line 24. The ammonia A and hydrogen H supplied in this way will be distributed to the fuel cells 100 via the fuel chamber 102 and reacted electrochemically there.

[0100] Figure 3 shows a detail from a sectional view of a fuel cell stack 12, depicting a partial view of a section of two adjacent fuel cells 100 stacked directly on top of each other. In the figure above, a first fuel cell 100a is arranged, and a second fuel cell 100b is arranged below it. An interconnector 96 is arranged between the two fuel cells 100.

[0101] The fuel cells 100 each have a metal support 106. For example, the metal support 106 is made of stainless steel. An anode layer 108 is arranged on the metal support 106. This anode layer, for example, comprises a nickel cermet. The anode layer 108 is completely covered by an electrolyte layer 110. A cathode layer 112 is arranged on the electrolyte layer 110. For example, the cathode layer 112 comprises a cobalt-doped lanthanum-nickel oxide, e.g., LaNio.sCoo.ziOa-s or LCN60. The metal supports 106 have a multitude of perforations or holes, which are designed to conduct hydrogen H to the anode layer 108.

[0102] The interconnector 96 has a base plate 114, which is exemplarily made of stainless steel. By way of example, a first protective layer 116 is arranged on the base plate 114 on the side of the first fuel cell 100a, i.e., the fuel cell 100 with its anode side or anode layer 108 facing the interconnector 96. A cracker layer 118 is arranged on the first protective layer 116. The cracker layer 118 has the ammonia- - TI -

[0103] Cracker 98. Cracker layer 118 is an example.

[0104] Aluminium oxide layer, which contains 98 nickel as an ammonia cracker.

[0105] The first protective layer 116 between the cracker layer 118, or between the ammonia cracker 98 and the base plate 114, serves to protect the base plate 114 from nitrification or from a reaction of the base plate with the nitrogen N produced during the cracking of the ammonia, or with the resulting nitrogen compounds. For example, the first protective layer 116 comprises aluminum.

[0106] As an example, a second protective layer 120 is arranged on the base plate 114 of the second fuel cell 100b, i.e., the fuel cell 100 with the cathode side or cathode layer 112 facing the interconnector 96. The second protective layer 120 is intended to protect the base plate 114 from oxidation. For example, the second protective layer 120 contains cobalt and cerium. The second protective layer 120 can advantageously be deposited on the base plate 114 by physical vapor deposition (PVD).

[0107] The interconnector 96 has protrusions 122 extending towards the first fuel cell 100a or towards the second fuel cell 100b. The protrusions 122 constitute a fuel conduction structure 122. The protrusions 112 can be produced, for example, by hydroforming and / or stamping the base plate 114, and the layers 116, 118, 120 can then be applied to the thus formed base plate 114. In this way, the protrusions 122, or the fuel conduction structure 122, feature the ammonia cracker 98.

[0108] The interconnector 96, with its projections 122 extending towards the first fuel cell 100a, contacts the first fuel cell 100a on the anode side and thereby contacts the metal support 106. The interconnector 96, with its projections extending towards the second fuel cell 100b, contacts the second fuel cell 100b on the cathode side and is in contact with the cathode layer 112. By way of example, the interconnector 96 has a local coating of a cathode contact layer 124 on the projections 122 extending towards the first fuel cell 100a. The cathode contact layer 124 is designed to prevent a chemical reaction between the cathode layer 112 and the second protective layer 120.

[0109] By structuring the interconnector 96 with the protrusions 112, two fluidically separated fluid spaces are created. A first fluid space exists between the first fuel cell 100a and the interconnector plate 96 and is located on the anode side of the first fuel cell 100a; this first fluid space is part of the anode space 22 of the fuel cell stack 12, or the anode space 22 of the first fuel cell 100a. A second fluid space exists between the second fuel cell 100b and the interconnector plate 96 and is located on the cathode side of the second fuel cell 100b; this second fluid space is part of the cathode space 20 of the fuel cell stack 12, or the cathode space 20 of the second fuel cell 100b.

[0110] During operation of the fuel cell device 10, the anode compartment 22 of the fuel cell stack 12 is supplied with a mixture of hydrogen (H) and ammonia (A). The ammonia (A) travels along the raised sections 122 and comes into contact with the ammonia cracker 98 contained in the cracker layer 188, where it is almost completely converted into hydrogen (H) and nitrogen (N). The hydrogen (H) produced from the ammonia (A) and the hydrogen originally supplied to the fuel cell stack 12 then pass through the holes in the metal support 106 to the anode layer 108, where it undergoes an electrochemical reaction. In alternative configurations, it is conceivable that the fuel cell stack 12 and the anode compartment 22 are supplied only with ammonia (A), which is almost completely converted into hydrogen (H) by the ammonia cracker 98.

Claims

Claims 1. Fuel cell stack (12) for a fuel cell device (10) for operation with ammonia (A), comprising a plurality of stacked fuel cells (100) and a plurality of interconnectors (96), wherein an interconnector (96) is arranged between each of two adjacent fuel cells (100), characterized in that the interconnectors (96) each comprise an ammonia cracker (98) for converting the ammonia (A) into nitrogen (N) and hydrogen (H).

2. Fuel cell stack (12) according to claim 1 , characterized in that the ammonia cracker (98) comprises nickel.

3. Fuel cell stack (12) according to one of the preceding claims, characterized in that the ammonia cracker (98) is arranged on a fuel guide structure (122).

4. Fuel cell stack (12) according to one of the preceding claims, characterized in that a protective layer is arranged between the ammonia cracker (98) and the adjacent fuel cell (100).

5. Fuel cell stack (12) according to one of the preceding claims, characterized in that the ammonia cracker (98) is arranged in a cracker layer (118) and the ammonia cracker (98) is arranged in a graduated manner within the cracker layer (118) along a layer thickness.

6. Fuel cell stack (12) according to one of the preceding claims, characterized in that an ammonia cracker (98) is arranged at a fuel inlet (104).

7. Fuel cell device (10) for operation with ammonia (A), comprising at least one fuel cell stack (12) according to one of the preceding Claims as well as a fuel supply (25) for ammonia (A).

8. Fuel cell device (10) according to claim 7, characterized in that an anode path (24, 32, 40) has an ammonia cracker (98), in particular a heat exchanger (36, 58, 44) of the anode path (24, 32, 40).

9. Fuel cell device (10) according to claim 7 or 8, characterized in that the fuel cell device (10) comprises a reactor (50) for converting the ammonia (A) into nitrogen (N) and hydrogen (H), characterized in that the reactor (50) comprises a catalyst with an ammonia cracker and a It has a hydrogen (H) conducting membrane.

10. Fuel cell device (10) according to one of the preceding claims, characterized in that the fuel supply (25) is fluidically connected to the fuel cell stack (12) via an ammonia line (86) for the direct supply of the fuel cell stack (12) with ammonia (A).

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