Cathode wire mesh support for molten carbonate fuel cell

Abstract

Molten carbonate fuel cell structures are provided that include a structured grid support layer at an interface between a cathode surface and a cathode current collector. The structured mesh layer may have a mesh open area of 25% to 45%. In addition to providing structural support, the structural grid layer may reduce or minimize ohmic resistance at the interface between the cathode and the cathode current collector.

Description

Technical Field

[0001] The present invention provides cathode screen supports for improving the interface between the cathode and cathode current collector in a molten carbonate fuel cell, and methods of operating such a fuel cell. Background Art

[0002] Molten carbonate fuel cells utilize hydrogen and / or other fuels to generate electricity. Hydrogen can be provided by reforming methane or other reformable fuels in a steam reformer, such as a steam reformer located upstream of the fuel cell or integrated in the fuel cell. Fuel can also be reformed in the anode cell in the molten carbonate fuel cell, which can be operated to create conditions suitable for reforming the fuel in the anode. Another option can be to carry out some reforming outside and inside the fuel cell. Reformable fuels can include hydrocarbon substances that can react with steam and / or oxygen to produce gaseous products containing hydrogen at high temperature and / or high pressure.

[0003] The basic structure of a molten carbonate fuel cell includes a cathode, an anode, and a matrix located between the cathode and the anode, the matrix including one or more molten carbonates serving as an electrolyte. During normal operation of a molten carbonate fuel cell, the molten carbonate partially diffuses into the pores of the cathode. This diffusion of the molten carbonate into the pores of the cathode provides an interfacial area where CO 2 Can be converted into CO 3 2- to be transported through the electrolyte to the anode.

[0004] In addition to these basic structures, volumes adjacent to the anode and cathode are typically included in a fuel cell. This allows the anode gas flow and the cathode gas flow to be delivered to the anode and cathode, respectively. In order to provide volume for the cathode gas flow while still providing electrical contact between the cathode and the separator defining the outer boundary of the fuel cell, a cathode current collector structure can be used. An anode collector can be used to similarly provide volume for the anode gas flow.

[0005] US Patents 6,492,045 and 8,802,332 describe examples of current collectors for molten carbonate fuel cells. The current collectors correspond to a corrugated structure.

[0006] U.S. Patent Application Publication No. 2020 / 0176783 describes a cathode current collector structure that provides an increased open area for the cathode surface adjacent to the cathode current collector. A mesh layer with a large open area that does not provide structural support is also described.

[0007] U.S. Patent Application Publication No. 2021 / 0159523 describes examples of how flow to a fuel cell can be managed when operating in co-current or counter-current mode. Summary of the invention

[0008] In one aspect, a molten carbonate fuel cell is provided. The fuel cell includes an anode. The fuel cell also includes a first separator. The fuel cell also includes an anode collector, the anode collector is in contact with the anode and the first separator to define an anode gas collection area between the anode and the first separator. The fuel cell also includes a cathode having a cathode surface. The fuel cell also includes a second separator. The fuel cell also includes a cathode current collector, the cathode current collector is in contact with the second separator and is adjacent to the cathode surface to define a cathode gas collection area between the cathode and the second separator. The battery also includes a structural grid layer disposed between the cathode surface and the cathode current collector, the structural grid layer including 50 openings / cm 2 or more, and having a mesh contact area of ​​55% to 75%. In addition, the fuel cell includes an electrolyte matrix containing an electrolyte between the anode and the cathode. Optionally, the contact area of ​​the cathode current collector can be less than 55%.

[0009] Optionally, the fuel cell can be used in a method of using a fuel cell. In such a method, the method can include adding a 2 , a reformable fuel, or a combination thereof, into the anode gas collection region. The method may also include introducing an anode gas input stream comprising O 2 and CO 2 The method may include introducing a cathode input stream of 60 mA / cm 2 The molten carbonate fuel cell is operated at an average current density of 100 Å or higher to produce electricity, an anode exhaust, and a cathode exhaust. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 An example of a cathode current collector configuration having a grid layer at the interface between the cathode current collector and the cathode surface is shown.

[0011] Figure 2 An example of a molten carbonate fuel cell is shown.

[0012] Figure 3 An example of a cathode current collector structure is shown.

[0013] Figure 4 It is shown that it can be used to represent Figure 3 An example of a repeating pattern unit of a cathode current collector structure is shown.

[0014] Figure 5Shows Figure 4 Another example of a repeating pattern unit.

[0015] Figure 6 An example flow pattern for a molten carbonate fuel cell is shown, where the anode flow direction is oriented approximately perpendicular to the cathode flow direction.

[0016] Figure 7 The change in ohmic resistance over time during operation of a molten carbonate fuel cell including and not including a structural grid layer is shown.

[0017] Figure 8 The operating voltage and ohmic resistance of a molten carbonate fuel cell with and without a structured grid layer are shown as a function of time.

[0018] Fig. 9 Shows Figure 8 The ohmic resistance of a fuel cell is shown as a function of time.

[0019] Fig.10 Ohmic resistance versus CO for fuel cells including various types of mesh layers disposed between the cathode current collector and the cathode surface is shown. 2 The relationship between utilization.

[0020] Fig.11 The operating voltage and CO of a fuel cell including various types of mesh layers disposed between the cathode current collector and the cathode surface are shown. 2 The relationship between utilization.

[0021] Fig.12 Ohmic resistance versus CO for fuel cells including various types of mesh layers disposed between the cathode current collector and the cathode surface is shown. 2 The relationship between utilization.

[0022] Fig.13 The operating voltage and CO of a fuel cell including various types of mesh layers disposed between the cathode current collector and the cathode surface are shown. 2 The relationship between utilization.

[0023] Fig.14 It shows that in various CO 2 Using CO2 from fuel cells operating at horizontal 2 Capture selectivity. DETAILED DESCRIPTION

[0024] Overview

[0025] In various aspects, a molten carbonate fuel cell structure is provided that includes a structural grid support layer at the interface between the cathode surface and the cathode current collector. The structural grid layer can have a contact area of ​​55% to 75%, which corresponds to a grid open area of ​​25% to 45%. In addition to providing structural support, the structural grid layer can reduce or minimize the ohmic resistance at the interface between the cathode and the cathode current collector while also maintaining a high resistance for transferring CO to the cathode. 2 Favorable open area for gas flow from the cathode to the electrolyte.

[0026] Molten carbonate fuel cells offer an unusual and advantageous opportunity for carbon capture from power generation and industrial flue gases: because CO 2 Molten carbonate fuel cells can provide CO 2 The capture and transfer of carbon from a lower concentration cathode gas stream to a higher concentration anode gas stream also produces electricity. Therefore, carbon capture processes using molten carbonate fuel cells can be net energy exporters, unlike processes that rely on CO2 that require energy input. 2 Conventional carbon capture processes of absorption or adsorption work in reverse.

[0027] CO removed from the cathode stream of molten carbonate fuel cells 2 From CO-rich 2 However, using molten carbonate fuel cells, 80 vol% or more of the CO is captured from the cathode feed stream. 2 There is a difficulty because the CO in the cathode gas 2 depletion. At such high levels of CO 2 At low utilization rates, it may be more difficult to maintain efficient operation of the fuel cell. 2 Depletion may also reduce the life of the fuel cell. For example, at high levels of CO 2 Utilization and / or low levels of CO in the cathode inlet gas 2 Under these conditions, a portion of the charge transferred across the electrolyte can potentially be transported in the form of alternate ions (such as hydroxyl ions). This "parasitic" charge transport consumes the fuel supplied to the anode without contributing to CO 2 Due to various factors, this high CO 2 Utilization can also lead to degradation of fuel cell performance.

[0028] For mitigating high CO 2 Utilization and / or low CO in the cathode 2One option for operating at high CO concentrations is to use a cathode current collector structure that results in an increase in the open area of ​​the cathode surface (as defined by the cathode current collector). For example, such a cathode current collector structure that provides an increased open area of ​​the cathode surface is described in U.S. Patent Application Publication No. 2020 / 0176783. As described in U.S. Patent Application Publication No. 2020 / 0176783, when the cathode current collector is operated at high CO concentrations, the cathode current collector structure is increased. 2 When operating a molten carbonate fuel cell at a utilization rate of 55%, using a cathode current collector structure having a contact area of ​​55% or less (i.e., providing an open area of ​​45% or more of the cathode surface when in contact with the cathode surface) can provide various advantages. It is believed that these advantages are due in part to the fact that the CO 2 The resistance from the cathode gas flow to the cathode pores is low, where CO 2 The cathode current collector structure provides 45% or more of the cathode surface open area / 55% or less of the contact area in contrast to conventional cathode current collector structures, which typically provide about 33% or less of the cathode surface open area / 67% or more of the contact area.

[0029] Although at high CO 2 Utilization and / or low CO in the cathode inlet gas 2 When operating at a concentration of 1.5 Å, it may be beneficial to use a cathode current collector structure that provides an increased open area of ​​the cathode surface, but it has now been found that such a cathode current collector structure may lead to an increase in the ohmic resistance within the fuel cell. Over time, this may cause the battery operating voltage to decrease. Without being bound by any particular theory, the increase in the open area of ​​the cathode current collector leads to a corresponding decrease in the contact area between the cathode current collector and the cathode, which itself will increase the ohmic resistance due to the reduction in the total contact area between the cathode current collector and the cathode. In addition, it is believed that the reduction in this contact area also leads to an increase in the deformation of the cathode and the electrolyte matrix, as well as a potential increase in the formation of scale at the contact point between the cathode and the cathode current collector.

[0030] It has now been found that by using a properly designed structural grid layer between the cathode surface and the cathode current collector, these difficulties of using a cathode current collector that provides an increased open area of ​​the cathode surface can be reduced, minimized or mitigated. In these new molten carbonate fuel cells, the structural grid layer can provide improved electrical contact between the cathode and the cathode current collector, rather than having the cathode current collector directly contact the cathode surface. In addition, the structural grid can advantageously improve the mechanical stability of the battery and the gas transport within the battery. It has been found that a structural grid layer having a grid open area smaller than the open area of ​​the cathode surface (as defined by the cathode current collector) can improve battery operation by reducing or minimizing the loss of battery voltage over time. In some aspects, a structural grid layer having a contact area of ​​55% to 75% (i.e., a grid open area of ​​25% to 45%) can provide an improved battery operating voltage while maintaining a high selectivity for the transmission of carbonate ions through the electrolyte. Such a structural grid layer having a grid open area of ​​25% to 45% can also have a high density of openings per unit area. Therefore, even though the mesh contact area is higher than the contact area of ​​the cathode current collector, it is believed that the large number of openings per unit area allows the benefit of increased gas transport from the cathode current collector volume to the cathode to be maintained. By combining a relatively low mesh open area (high contact area) with a relatively high density of openings in the mesh, the mesh can also provide sufficient structural stability to improve fuel cell performance.

[0031] In various aspects, the presence of the structured grid layer allows the contact force of the cathode current collector to be distributed over a larger area while keeping the size of the components in contact with the cathode surface small. This is important for improving CO 2 The goal of transporting gas from the cathode chamber to the cathode pores where the electrochemical process occurs is beneficial. The small features of the structural grid layer allow for a large amount of contact area while reducing or minimizing the average diffusion path required for the gas to travel around the contact features and reach the cathode surface. At the same time, the larger contact area of ​​the structural grid layer distributes the weight of the cathode current collector over a larger percentage of the cathode surface. Thus, the many small contact features of the structural grid layer create contact / support while keeping the average diffusion path short under the cathode current collector-cathode surface contact, which is a feature that reduces transfer resistance.

[0032] In various aspects, the structural mesh layer can have one or more (e.g., up to all) of the following features. The structural mesh layer can have a mesh contact area of ​​55% to 75% or 55% to 70%, which corresponds to a mesh open area of ​​25% to 45% or 30% to 45%. Additionally or alternatively, the structural mesh layer can have 50 openings / cm 2 or more, or 75 openings / cm 2 or more, or 100 openings / cm 2 or more, or 125 openings / cm 2or more, such as up to 1000 openings / cm 2 Or possibly a higher cell density or opening density.Further additionally or alternatively, the structural grid layer may have a thickness or height of at least 0.25 mm or at least 0.30 mm, such as up to 0.80 mm or possibly higher.

[0033] It should be noted that during operation, even with a structural grid layer between the cathode surface and the cathode current collector, sufficient deformation of the cathode surface may occur to bring the cathode current collector into direct contact with the cathode, i.e., the cathode grid below the current collector legs may be fully pressed into the porous cathode surface so that the current collector legs may be in direct contact with the cathode. However, even if such deformation does occur, it is believed that the presence of the grid structural layer may reduce or minimize the rate of such deformation, and the current collector-cathode interface may still be enhanced, thereby increasing the mechanical stability of the battery. It is further believed that such a reduction in the rate of deformation may provide a corresponding reduction in the rate of increase of the ohmic resistance over time and / or a corresponding reduction in the rate of loss of the operating voltage over time. In this discussion, reference to improvements in mechanical structural stability is understood to be based on improved operation of the fuel cell over an extended period of time (e.g., reduced loss of operating voltage) due to the presence of a structural grid layer as described herein.

[0034] definition

[0035] Contact area: The contact area of ​​the structural grid layer or cathode current collector is defined herein as the percentage of a flat or horizontal surface in contact with the structural grid layer or cathode current collector when the structural grid layer / cathode current collector is placed on the surface. Note that this definition represents an idealized amount of contact, because changes in the surface (such as the cathode surface) may result in an increase or decrease in the actual contact area. However, when the structural grid layer / cathode current collector is placed on the cathode surface, this idealized value is useful for comparing how the structural grid layer or cathode current collector will interact with the cathode. Because the contact area is defined based on the interaction of the structural grid layer / cathode current collector with an idealized flat or horizontal surface, the contact area is a characteristic of the structural grid layer / cathode current collector, and even if the structural grid layer or cathode current collector is not actually in contact with the horizontal surface, the contact area is well defined. When describing the structural grid layer, the contact area may be referred to as the grid contact area. When describing the cathode current collector, the contact area may be referred to as the cathode current collector contact area. The contact area of ​​the structural grid layer / cathode current collector may be expressed as an absolute area, or as a percentage of the total area of ​​the structural grid layer / cathode current collector that will be in contact with the horizontal surface. In this discussion, contact area is usually expressed as a percentage of the total area in contact with the horizontal surface.

[0036] Grid open area or cathode collector open area: This value is the complement of the contact area. When the contact area of ​​the structure is expressed as a percentage, the open area can be calculated as 100% - <contact area>. Alternatively, if it is easier to characterize the area of ​​the horizontal surface that is not in contact with the structure grid layer or the cathode current collector, the open area can be determined first, and then the contact area can be calculated based on 100% - <open area>.

[0037] Calculation of contact area / open area : Figure 4 An example of a repeating unit (i.e., a unit cell) that can be used to represent the contact area of ​​the cathode surface and the open area of ​​the cathode surface adjacent to the cathode current collector is shown. Such a cathode surface can be in contact with the cathode current collector (unstructured grid layer), or can be in contact with a structured grid layer disposed between the cathode surface and the cathode current collector. Figure 4 The exemplary repeating units in correspond to those that can be used to represent, for example, Figure 3 The cathode current collector structure of the structure shown has a repeating pattern (unit cell). Figure 4 In the figure, the patterned area corresponds to the area where the collector is in contact with the cathode surface, while the open area corresponds to the area where gas can pass between the cathode and the collector. In the following calculations, the open area is calculated and then the contact area can be determined as 100% - <open area>. It is understood that for convenience, the contact area can be calculated first and then the open area can be determined as 100% - <contact area>.

[0038] for Figure 4 Based on the repeating pattern shown, a calculation can be performed to calculate the open area of ​​the center region 510, which is open in this example. Figure 4 , distance 424 can be set to 8.0, distance 544 can be set to 1.0, distance 426 can be set to 8.0, and distance 566 can be set to 1.0. This results in an open area of ​​64 / 100 or 64%. This can be determined, for example, by noting that the area of ​​the open area is 8.0*8.0=64, while the area of ​​the total repeating unit is (1.0+8.0+1.0)*(1.0+8.0+1.0)=10. Note that Figure 4 The distances in are normalized and therefore are arbitrary length units. It should also be noted that the selection of different relative values ​​of distances 424, 426, 544, and 566 may allow for corresponding selection of patterns with various amounts of open area. It should also be noted that similar calculations may be performed for patterns where the central region 510 corresponds to a blocked area and the area surrounding the central region 510 corresponds to an open area. For example, if using Figure 3 For the cathode current collector structure shown, such that the ring structure is in contact with the cathode surface, an open area calculation can be performed by using the central region 510 as the blocking area (the area where the ring is in contact with the cathode) and the surrounding area as the open area.

[0039] The contact area of ​​the cathode surface corresponds to the remainder of the cathode surface that does not correspond to the open area of ​​the cathode surface. Therefore, one option for calculating the contact area of ​​the cathode surface is to subtract the open area of ​​the cathode surface from 100%. For the above example, this would correspond to a contact area of ​​100%-64%=36%.

[0040] Note that the open area of ​​the cathode surface is defined independently of the presence or absence of the structural grid layer. The presence of the structural grid layer does not change the calculated value of the open area of ​​the cathode surface. In various aspects, when the structural grid layer is disposed between the cathode surface and the cathode current collector, the mesh open area of ​​the structural grid layer can be less than the open area of ​​the cathode surface, as defined by the cathode current collector.

[0041] Average cathode gas lateral diffusion length : The average cathode gas lateral diffusion length is defined as the average lateral distance from an open area position on the cathode surface to each point on the cathode surface. For the purpose of this definition, the lateral diffusion length of any point corresponding to an open area position is defined as zero.

[0042] For a repeating pattern such as Figure 4 The average cathode gas lateral diffusion length can also be calculated using the cathode surface of the repeating pattern shown in Figure 1. Figure 4 The same normalized distances are shown, where the final result is multiplied by the appropriate scaling factor to represent the given configuration.

[0043] One option for determining the average cathode gas lateral diffusion length may be to calculate this value directly based on the repeating pattern elements, for example by using a commercially available software package. Furthermore, a relatively good approximation may be determined in a straightforward manner. Figure 5 Shows Figure 4 Another example of a repeating pattern element is shown. Figure 5 No shading is used to indicate open and contact areas. Figure 5 , the area around the center area 510 can be divided into several parts. For the lateral areas 672 and 674, the average distance from the open area is only half of the length of the lateral area, or 0.5. Similarly, for the vertical areas 682 and 684, the average distance from the open area is half of the width of the vertical area, or 0.5. For the corner areas 692, 694, 696 and 698, the upper limit of the average distance can be determined based on the maximum distance or the distance from the open area to the top corner of the square. Half of the maximum distance is approximately 0.7, which provides a boundary upper limit for the average distance within the corner areas 692, 694, 696 and 696.

[0044] The above average distances can then be used to determine the average cathode gas lateral diffusion length by multiplying the average distance by the percentage of the total area corresponding to each distance. Regions 672, 674, 682, and 684 correspond to Figure 5 32% of the total area of ​​the repeating pattern unit shown. The corner area corresponds to 4% of the total area. The remaining 64% of the area corresponds to the open central area 510, which has a zero distance by definition. These values ​​can be used to determine that the upper limit of the average cathode gas lateral diffusion length is (0.64*0+0.32*0.5+0.04*0.7)=0.188. Then, the 0.188 value can be multiplied by the scaling factor representing the real system. As an example, a scaling factor of 0.635mm can be used. Multiplying 0.188 by the scaling factor of 0.635mm results in an average cathode gas lateral diffusion length of 0.12mm. Note that based on the assumptions used when calculating the average distance values ​​of the corner areas 692, 694, 696 and 698, the value of 0.12mm represents the upper limit of the actual average cathode gas lateral diffusion length.

[0045] Average contact area diffusion length : The average contact area diffusion length is defined as the average lateral distance from the contact area location on the cathode surface to each point on the cathode surface. For the purposes of this definition, the contact area diffusion length of any point corresponding to the contact area location is defined as zero. An example of such a calculation is further described below.

[0046] Fuel cell and fuel cell stack definition: In this discussion, a fuel cell may correspond to a single cell, whose anode and cathode are separated by an electrolyte. The anode and cathode may receive an input gas flow to promote respective anode and cathode reactions, thereby transporting charge through the electrolyte and generating electricity. A fuel cell stack may represent multiple cells in an integrated unit. Although a fuel cell stack may include multiple fuel cells, the fuel cells may generally be connected in parallel and may (approximately) function as if they collectively represent a single fuel cell of larger size. When an input stream is delivered to the anode or cathode of a fuel cell stack, the fuel cell stack may include flow channels for distributing the input stream between each cell in the stack and flow channels for combining output streams from each cell. In this discussion, a fuel cell array may be used to refer to multiple fuel cells (such as multiple fuel cell stacks) arranged in series, in parallel, or in any other convenient manner (e.g., a combination of series and parallel). A fuel cell array may include one or more stages of fuel cells and / or fuel cell stacks, wherein the anode / cathode output from the first stage may be used as the anode / cathode input of the second stage. Note that the anodes in a fuel cell array do not have to be connected in the same manner as the cathodes in the array. For convenience, the input to the first stage anode of the fuel cell array may be referred to as the anode input of the array, and the input to the first stage cathode of the fuel cell array may be referred to as the cathode input of the array. Similarly, the output from the final stage anode / cathode may be referred to as the anode / cathode output from the array.

[0047] It should be understood that the use of fuel cells mentioned herein generally refers to a "fuel cell stack" consisting of a single fuel cell, and more generally refers to the use of one or more fuel cell stacks that are fluidly connected. Individual fuel cell elements (plates) can generally be "stacked" together in a rectangular array called a "fuel cell stack". The fuel cell stack can generally obtain a feed stream and distribute reactants between all individual fuel cell elements, and then products can be collected from each of these elements. When regarded as a unit, the fuel cell stack in operation can be regarded as a whole, even if it is composed of many (usually dozens or hundreds) of individual fuel cell elements. These individual fuel cell elements can generally have similar voltages (because the reactant and product concentrations are similar), and when the elements are electrically connected in series, the total power output can be generated by the sum of all currents in all battery elements. The stack can also be arranged in a series arrangement to produce a high voltage. The parallel arrangement can increase the current. If a sufficiently large fuel cell stack can be used to process a given exhaust stream, the system and method described herein can be used with a single molten carbonate fuel cell stack. In other aspects of the present invention, multiple fuel cell stacks may be desired or required for various reasons.

[0048] For the purposes of the present invention, unless otherwise specified, the term "fuel cell" shall be understood to also refer to and / or be defined as including a fuel cell stack consisting of one or more individual fuel cell element groups, which has a single input and output, which is the way fuel cells are usually used in practice. Similarly, unless otherwise specified, the term fuel cell (plural) shall be understood to also refer to and / or be defined as including multiple individual fuel cell stacks. In other words, unless otherwise specified, all references herein can refer to the operation of the fuel cell stack interchangeably as "fuel cell". For example, the volume of exhaust gas produced by a commercial-scale combustion generator may be too large for being processed by a conventionally sized fuel cell (i.e., a single stack). In order to process all exhaust gas, multiple fuel cells (i.e., two or more individual fuel cells or fuel cell stacks) can be arranged in parallel so that each fuel cell can process (roughly) an equal portion of the combustion exhaust gas. Although multiple fuel cells can be used, each fuel cell can generally be operated in a roughly similar manner, given its (roughly) equal portion of the combustion exhaust gas.

[0049] Fuel cell structure including a structural grid layer

[0050] In various aspects, a structural grid layer may be included in a molten carbonate fuel cell structure that also includes a cathode current collector that provides a reduced contact area / increased amount of open area. For example, in some aspects, the fuel cell may have a cathode current collector that has a contact area (when in contact with an idealized horizontal or flat surface) of 55% or less, or 50% or less, or 40% or less, or 30% or less (such as as low as 5% or possibly lower). This corresponds to an open area of ​​45% or greater, or 50% or greater, or 60% or greater, or 70% or greater, such as up to 95% or possibly higher. In such a fuel cell structure, a structural grid layer having one or more of the following features may be used. In some aspects, the structural grid layer may have a contact area of ​​55% to 75% or 55% to 70%, which corresponds to a grid open area of ​​25% to 45% or 30% to 45%. Additionally or alternatively, the structural grid layer may have 50 openings / cm 2 or more, or 75 openings / cm 2 or more, or 100 openings / cm 2 or more, or 125 openings / cm 2 or more, such as up to 1000 openings / cm 2 Or possibly a higher cell density or opening density. Although the mesh open area of ​​the structural mesh layer is lower than the open area of ​​the cathode surface (as defined by the cathode current collector), it is believed that the large number of openings in the mesh structure allows the fuel cell to maintain a high selectivity for carbonate ion transport through the electrolyte matrix.

[0051] The structural grid layer can be formed in any convenient manner. In some aspects, the structural grid layer can correspond to a conventional grid in which wires define a square grid of openings having a target opening density and providing a target open grid area. In other aspects, the structural grid layer can be formed as a perforated plate containing a substantially regular set of openings to provide a target opening density and provide a target open grid area. More generally, a method for forming a perforated plate having 50 openings / cm 2 The structured mesh layer may be formed by any convenient method of structure having an opening density of 25% to 45% mesh open area (55% to 75% contact area) or greater.

[0052] Note that the mesh has a relatively low open area (25% to 45%) while also having a high opening density (50 openings / cm 2 The combination of 50% or more (or more) allows the mesh to be used as a structural support. This is in contrast to a mesh layer having a mesh open area of ​​50% or more, where a large amount of mesh open area reduces or minimizes the ability of the mesh to also provide structural support. In contrast, it is believed that having a mesh open area of ​​50% or more provides insufficient structural stability, such that even with the presence of the mesh, difficulties with cathode deformation, matrix deformation, and / or increased scaling accumulation still occur.

[0053] The structural grid layer can be described relative to the typical structure of a molten carbonate fuel cell. Figure 2 A general example of a portion of a molten carbonate fuel cell stack is shown, which essentially corresponds to a single fuel cell. Figure 2 The portion of the stack shown in corresponds to fuel cell 301. In order to isolate the fuel cell from adjacent fuel cells in the stack and / or other elements in the stack, the fuel cell includes separators 310 and 311. Figure 2 In the embodiment, fuel cell 301 includes an anode 330 and a cathode 350, which are separated by an electrolyte matrix 340 containing an electrolyte 342. In various aspects, cathode 350 may correspond to a double layer (or multilayer) cathode. Anode collector 320 provides electrical contact between anode 330 and other anodes in the stack, while cathode current collector 360 provides similar electrical contact between cathode 350 (through a structural grid layer) and other cathodes in the fuel cell stack. In addition, anode collector 320 allows gas to be introduced and exhausted from anode 330, while cathode current collector 360 allows gas to be introduced and exhausted from cathode 350. In various aspects, structural grid layers (such as Figure 1 The layer 750 in the cathode 350 may be disposed between the cathode current collector 360. It is worth noting that Figure 3 An example of the configuration of the cathode current collector 360 is shown.

[0054] During operation, CO 2 With O 2 Together they enter the cathode current collector 360. CO 2 The electrolyte 342 and O2 diffuse into the porous cathode 350 and travel to the cathode interface region near the boundary of the cathode 350 and the electrolyte matrix 340. In the cathode interface region, a portion of the electrolyte 342 may be present in the pores of the cathode 350. 2 and O 2 can be converted into carbonate ions (CO 3 2- ), which can then be transported through electrolyte 342 (and thus through electrolyte matrix 340) to facilitate the generation of electrical current. After being transported through electrolyte 342, the carbonate ions can reach the anode interface region near the boundary of electrolyte matrix 340 and anode 330. 2 In the presence of 2 and H 2 O, releasing electrons that are used to form the current generated by the fuel cell. H 2 and / or suitable for forming H 2 The hydrocarbons are introduced into the anode 330 through the anode collector 320.

[0055] Typically, the cathode current collector structure, such as Figure 1 The structure 110 shown is oriented so that the plate-like surface is in contact with the cathode surface. In various aspects, instead of using conventional configurations, a cathode current collector (such as Figure 1 ) can be oriented so that the bottom edge 122 of the ring structure 120 is in contact with the cathode surface, while the plate surface is in contact with the separator.

[0056] Figure 1 Shows how to modify Figure 2 A portion of a fuel cell / fuel cell stack is shown including an example of a structural grid component or layer. Figure 1In the example shown, the bottom edge 122 of the ring structure 120 is where the cathode current collector 110 is intended to provide electrical contact with the cathode surface 730. In a fuel cell in which the structural grid layer 750 is not present, having the bottom edge 122 of the ring structure 120 as a point of contact with the cathode surface 730 can reduce the blocked area of ​​the cathode surface 730 / increase the open area of ​​the cathode surface 730 based on a cathode current collector having a contact area of ​​55% or less, or 50% or less, or 40% or less, or 30% or less, such as as low as 5% or possibly lower. (This would correspond to an open area of ​​the cathode surface 730 of 45% or greater, or 50% or greater, or 60% or greater, or 70% or greater, such as up to 95% or possibly higher.) Unfortunately, placing a cathode current collector 110 having such a low contact area in direct contact with the cathode surface 730 can result in a decrease in cell voltage over time and / or an increase in ohmic resistance over time.

[0057] Instead of having the cathode current collector in direct contact with the cathode surface 730, a structural grid layer 750 may be disposed between the cathode current collector 110 and the cathode surface 730. Figure 1 In the illustrated configuration, the cathode current collector 110 may be located on / in contact with the structural grid layer 750. The structural grid layer 750 then provides electrical contact between the cathode current collector 110 and the cathode surface 730. By placing the structural grid layer 750 between the cathode current collector 110 and the cathode surface 730, it is believed that the pressure exerted by the cathode current collector on the cathode surface 730 is more evenly distributed on the cathode surface 730, thereby reducing or minimizing any deformation of the cathode surface. For example, for Figure 1 In the illustrated configuration, the bottom edge 122 of the ring structure 120 can be in contact with the structural grid layer 750. This reduces or minimizes deformation of the cathode surface 730 due to direct contact with the ring structure 120. Instead, the pressure applied by the ring structure 120 of the cathode current collector 110 is distributed across the cathode surface 730. Due to the high density of openings in the structural grid layer, it has been found that the advantageous gas transport properties of using a cathode current collector that provides increased open area at the cathode surface can also be maintained.

[0058] It should be noted that the average contact area diffusion length can also be greatly reduced based on the small mesh size of the structured mesh layer 750. For example, for a mesh size of 1.0 mm or less (approximately 100 openings / cm 2 or larger), the corresponding average contact area diffusion length can be reduced to 0.3 mm or less.

[0059] According to this aspect, the structural grid layer can have a thickness (height) of about 0.25 mm to 0.80 mm (-0.01 in to -0.03 in). The structural grid layer can be made of any suitable material that is relatively chemically inert under the conditions present at the cathode / cathode current collector interface. Various types of stainless steel are examples of suitable materials.

[0060] Example of molten carbonate fuel cell operation: cross-flow orientation of cathode and anode

[0061] The flow direction in the anode of a molten carbonate fuel cell can have any convenient orientation relative to the flow direction in the cathode. One option may be to use a co-current or counter-current flow configuration. Using co-current flow or counter-current flow can help provide higher gas concentration uniformity in the fuel cell. However, using co-current or counter-current flow increases the complexity of gas flow management. U.S. Patent Application Publication No. 2021 / 0159523 describes an example of how to manage flow to a fuel cell when operating in co-current or counter-current mode.

[0062] Another option may be to use a cross-flow configuration so that the flow direction in the anode is at approximately a 90° angle relative to the flow direction in the cathode. This type of flow configuration may have practical benefits because using a cross-flow configuration may allow the manifold and / or conduits for the anode inlet / outlet to be located on a different side of the fuel cell stack than the manifold and / or conduits for the cathode inlet / outlet.

[0063] Figure 6 An example of a top view of a fuel cell cathode is schematically shown, along with arrows indicating the direction of flow within the fuel cell cathode and corresponding fuel cell anode. Figure 6 4, arrow 405 indicates the direction of flow within cathode 450, while arrow 425 indicates the direction of flow at an anode (not shown).

[0064] Because the anode and cathode flows are oriented at approximately 90° relative to each other, the anode and cathode flow patterns can contribute to different reaction conditions in different portions of the cathode. Corner 482 corresponds to a portion of the fuel cell that is close to the entry point of both the cathode input flow and the anode input flow. As a result, depending on the fuel utilization and CO 2 Utilization, at corner 482 CO 2 (in the cathode) and H 2 The concentration of H (in the anode) can be relatively high. Corner 484 corresponds to a portion of the fuel cell near the entry point of the cathode input stream and near the exit point of the anode output stream. At a location near corner 484, under some conditions, the concentration of H (in the anode) can be relatively high. 2 The concentration of CO can be reduced, while 2The concentration of H can be relatively high. Corner 486 corresponds to a portion of the fuel cell near the exit point of the anode output stream and near the exit point of the cathode output stream. At a location near corner 486, depending on the operating conditions of the fuel cell, H 2 (in the anode) and CO 2 The concentration of H (in the cathode) may be lower. Corner 488 corresponds to a portion of the fuel cell near the entry point of the anode input stream and near the exit point of the cathode output stream. At a location near corner 484, under some conditions, the concentration of H (in the anode) may be lower. 2 The concentration of CO can be increased, while 2 The concentration can be relatively low.

[0065] Anode input and output

[0066] In various aspects, the anode input stream of the MCFC may include hydrogen, hydrocarbons such as methane, hydrocarbon-containing or hydrocarbon-like compounds that may contain heteroatoms other than C and H, or combinations thereof. The source of hydrogen / hydrocarbon / hydrocarbon-like compounds may be referred to as a fuel source. In some aspects, most of the methane (or other hydrocarbons, hydrocarbon-containing or hydrocarbon-like compounds) supplied to the anode may typically be fresh methane. In this specification, a fresh fuel such as fresh methane refers to a fuel that is not recycled from another fuel cell process. For example, methane recycled from the anode outlet stream back to the anode inlet may not be considered "fresh" methane, but may be described as recovered methane.

[0067] The fuel source used can be shared with other components, for example using a portion of the fuel source to provide a CO-containing gas for cathode input. 2 The fuel source input may include water in a ratio to the fuel suitable for reforming hydrocarbon (or hydrocarbon-like) compounds in the reforming section to produce hydrogen. For example, if methane is reformed to produce H 2 If the fuel input is 1:1, the molar ratio of water to fuel may be from about one to one to about ten to one, such as at least about two to one. For external reforming, a ratio of four to one or greater is typical, but for internal reforming, lower values ​​may be typical. 2 As part of the fuel source, in some optional aspects, additional water may not be required in the fuel because H 2 Oxidation at the anode may tend to produce H that can be used to reform the fuel. 2 O. The fuel source may also optionally contain components incidental to the fuel source (e.g., a natural gas feed may contain some amount of CO 2 As an additional component). For example, a natural gas feed may contain CO 2 、N 2and / or other inert (rare) gases as additional components. Optionally, in some aspects, the fuel source may also contain CO, such as CO from a recycled portion of the anode exhaust. An additional or alternative potential source of CO in the fuel entering the fuel cell assembly may be CO produced by steam reforming of a hydrocarbon fuel prior to entering the fuel cell assembly.

[0068] More generally, various types of fuel streams may be suitable for use as anode input streams for the anodes of molten carbonate fuel cells. Some fuel streams may correspond to streams containing hydrocarbons and / or hydrocarbon-like compounds, which may also include heteroatoms other than C and H. In this discussion, unless otherwise stated, references to hydrocarbon-containing fuel streams for MCFC anodes are defined as including fuel streams containing such hydrocarbon-like compounds. Examples of hydrocarbon (including hydrocarbon-like) fuel streams include natural gas, streams containing C1-C4 carbon compounds (such as methane or ethane), and streams containing heavier C5+ hydrocarbons (including hydrocarbon-like compounds), and combinations thereof. Other additional or alternative examples of potential fuel streams for anode input may include biogas-type streams, such as methane produced by the natural (biological) decomposition of organic materials.

[0069] In some aspects, molten carbonate fuel cells can be used to process input fuel streams that have low energy content due to the presence of diluent compounds, such as natural gas and / or hydrocarbon streams. For example, some sources of methane and / or natural gas are CO 2-rich fuel cells that can contain large amounts of CO 2-rich fuel cells. 2 or other inert molecules such as nitrogen, argon or helium. 2 and / or inert materials, the energy content of the fuel stream based on that source can be reduced. Using fuels with low energy content for combustion reactions (e.g., to power an internal combustion turbine) can cause difficulties. However, molten carbonate fuel cells can generate electricity based on low energy content fuel sources with a reduced or minimal impact on the efficiency of the fuel cell. The presence of additional gas volume may require additional heat to raise the temperature of the fuel to the temperature for reforming and / or anode reactions. In addition, due to the equilibrium nature of the water-gas shift reaction within the fuel cell anode, the additional CO 2 The presence of H in the anode output 2 However, otherwise inert compounds have only minimal direct effects on the reforming and anode reactions. If present, CO in the fuel stream of a molten carbonate fuel cell 2The amount of the inert compound may be at least about 1% by volume, such as at least about 2% by volume, or at least about 5% by volume, or at least about 10% by volume, or at least about 15% by volume, or at least about 20% by volume, or at least about 25% by volume, or at least about 30% by volume, or at least about 35% by volume, or at least about 40% by volume, or at least about 45% by volume, or at least about 50% by volume, or at least about 75% by volume. Additionally or alternatively, the CO in the fuel stream of the molten carbonate fuel cell may be at least about 1% by volume, such as at least about 2% by volume, or at least about 5% by volume, or at least about 10% by volume, or at least about 20% by volume, or at least about 25% by volume, or at least about 30% by volume, or at least about 35% by volume, or at least about 40% by volume, or at least about 45% by volume, or at least about 50% by volume, or at least about 75% by volume. 2 The amount of and / or inert compounds may be about 90 vol % or less, such as about 75 vol % or less, or about 60 vol % or less, or about 50 vol % or less, or about 40 vol % or less, or about 35 vol % or less.

[0070] Other examples of potential sources of anode input streams may correspond to refinery and / or other industrial process output streams. For example, coking is a common process used in many refineries to convert heavier compounds to lower boiling ranges. Coking typically produces an exhaust gas containing a variety of compounds that are gases at room temperature, including CO and various C 1 –C 4 hydrocarbon compounds. This waste gas may be used as at least a portion of the anode input stream. Other refinery waste gas streams may additionally or alternatively be suitable for inclusion in the anode input stream, such as light fractions (C 1 -C 4 Other suitable refinery streams may additionally or alternatively include those containing CO or CO 2 A refinery stream containing H 2 and / or reformable fuel compounds.

[0071] Other potential sources for anode input may additionally or alternatively include streams with increased water content. For example, an ethanol output stream from an ethanol plant (or another type of fermentation process) may contain a significant portion of H prior to final distillation. 2 O. This H 2 O generally has only minimal impact on the operation of the fuel cell. Thus, a fermentation mixture of alcohol (or other fermentation product) and water can be used as at least a portion of the anode input stream.

[0072] Biogas or digester gas is another additional or alternative potential source of anode input. Biogas may consist primarily of methane and CO. 2 , and is typically produced by decomposing or digesting organic matter. Anaerobic bacteria can be used to digest organic matter and produce biogas. Impurities, such as sulfur compounds, can be removed from the biogas before being used as an anode input.

[0073] The output flow from the MCFC anode may include H2 O、CO 2 , CO and H 2 Optionally, the anode output stream may also have unreacted fuel (such as H 2 or CH 4 ) or inert compounds as additional output components. Instead of using this output stream as a fuel source to provide heat for the reforming reaction or as a combustion fuel for heating the cell, one or more separations may be performed on the anode output stream to separate the CO 2 with components that have potential value as input to another process (such as H 2 or CO) separation. 2 And / or the CO can be used as syngas for chemical synthesis, as a source of hydrogen for chemical reactions, and / or as a fuel with reduced greenhouse gas emissions.

[0074] Cathode input and output

[0075] In general, a molten carbonate fuel cell can be operated based on drawing a desired load while consuming a portion of the fuel in the fuel stream delivered to the anode. The voltage of the fuel cell can then be determined by the load, the fuel input to the anode, the air supplied to the cathode, and the CO 2 The cathode can be provided with CO in part by using the anode exhaust as at least a portion of the cathode input stream. 2 In contrast, the present invention can use separate / different sources for the anode input and cathode input. By removing any direct connection between the components of the anode input stream and the cathode input stream, additional options are provided for the operation of the fuel cell, such as to produce excess syngas, to improve carbon dioxide capture, and / or to improve the overall efficiency of the fuel cell (electrical power plus chemical power), etc.

[0076] An example of a CO-containing stream suitable for use as a cathode input stream may be an output stream or exhaust stream of a combustion source. Examples of combustion sources include, but are not limited to, sources based on the combustion of natural gas, the combustion of coal, and / or the combustion of other hydrocarbon fuels, including bio-derived fuels.

[0077] Additional or alternative sources may include other types of boilers, fired heaters, furnaces, and / or other types of devices that burn carbon-containing fuels to heat another substance (such as water or air). According to this aspect, the CO in the fuel cell 2 The utilization rate can be 50% or more, or 70% or more, or 80% or more, or 90% or more, such as up to 98% or possibly higher. Note that molten carbonate fuel cells used in conventional configurations for power generation typically operate at less than 70% CO 2Conversely, when the fuel cell is used to perform other applications, such as using the fuel cell to achieve a target level of carbon capture, the benefits of including the structural grid layer can also be realized. In these aspects, CO 2 The utilization rate can be 70% to 98%, or 75% to 98%, or 80% to 98%. In some aspects, the CO of the cathode input stream 2 The content can be 3.0 vol% to 20 vol%, or 3.0 vol% to 15 vol%, or 5.0 vol% to 20 vol%, or 5.0 vol% to 15 vol%, or 10 vol% to 20 vol%. In other aspects, such as some aspects where the cathode input stream is based on flue gas from a power plant burning natural gas, the CO content of the cathode input stream is 2 The content may be 5.0 vol% or less or 4.0 vol% or less, such as 1.5 vol% to 5.0 vol%, or 1.5 vol% to 4.0 vol%, or 2.0 vol% to 5.0 vol%, or 2.0 vol% to 4.0 vol%. In some aspects, the CO of the cathode output stream is 2 The content may be 1.5 volume % or less, or 1.0 volume % or less, such as as low as 0.1 volume % or possibly less.

[0078] Other potential sources of cathode input streams may additionally or alternatively include biologically produced CO 2 This can include, for example, CO generated during the processing of bio-derived compounds. 2 , such as CO produced during ethanol production 2 Additional or alternative examples may include CO produced by the combustion of biogenic fuels, such as the combustion of lignocellulosic 2 Other potential additional or alternative CO 2 The source may correspond to an output stream or exhaust stream from various industrial processes, such as a CO-containing gas generated by a plant for manufacturing steel, cement, and / or paper. 2 flow.

[0079] CO 2 Another additional or alternative potential source could be CO from fuel cells. 2 The CO2-containing stream from the fuel cell 2 The streams may correspond to cathode output streams from different fuel cells, anode output streams from different fuel cells, recycle streams from cathode output of a fuel cell to cathode input, and / or recycle streams from anode output to cathode input of a fuel cell. For example, an MCFC operating in stand-alone mode under conventional conditions may produce a CO having at least about 5 vol. % 2 The cathode exhaust contains CO 2The cathode exhaust gas may be used as a cathode input to an MCFC operated according to one aspect of the present invention. More generally, CO may be generated from the cathode exhaust gas in addition or alternatively. 2 Other types of fuel cells that output CO, and other types of CO2 that are not produced by "combustion" reactions and / or internal combustion generators 2 Optionally but preferably, a CO-containing stream from another fuel cell 2 The stream can come from another molten carbonate fuel cell. For example, for molten carbonate fuel cells connected in series with respect to the cathode, the output from the cathode of the first molten carbonate fuel cell can be used as the input of the cathode of the second molten carbonate fuel cell.

[0080] In addition to CO 2 In addition, the cathode input stream may include O 2 To provide the components necessary for the cathode reaction. Some cathode input streams can be based on air as a component. For example, a combustion exhaust stream can be formed by burning a hydrocarbon fuel in the presence of air. This combustion exhaust stream or another type of cathode input stream having an oxygen content based on air may have an oxygen content of about 20 volume % or less, such as about 15 volume % or less, or about 10 volume % or less. Additionally or alternatively, the oxygen content of the cathode input stream can be at least about 4 volume %, such as at least about 6 volume %, or at least about 8 volume %. More generally, the cathode input stream may have an oxygen content suitable for conducting the cathode reaction. In some aspects, this may correspond to an oxygen content of about 5 volume % to about 15 volume %, such as about 7 volume % to about 9 volume %. For many types of cathode input streams, CO 2 and O 2 The combined amount of can correspond to less than about 21% by volume of the input stream, such as less than about 15% by volume of the input stream or less than about 10% by volume of the input stream. The oxygen-containing air stream can be combined with the CO having a low oxygen content. 2 Source Combinations. For example, an exhaust stream generated by burning coal may include a low oxygen content that may be mixed with air to form the cathode inlet stream.

[0081] In addition to CO 2 and O 2 In addition, the cathode input stream can also consist of inert / non-reactive substances such as N 2 , H 2 O and other typical oxidant (air) components. For example, for a cathode input derived from an exhaust gas of a combustion reaction, if air is used as part of the oxidant source for the combustion reaction, the exhaust gas may include typical components of air, such as N 2 , H 2 O and other compounds present in small amounts in air. Depending on the nature of the fuel source used for the combustion reaction, additional substances present after combustion based on the fuel source may include H2 O, oxides of nitrogen (NOx) and / or oxides of sulfur (SOx), and one or more of other compounds present in the fuel and / or as a product of partial or complete combustion of compounds present in the fuel (such as CO). These substances may be present in amounts that do not poison the cathode catalyst surface, although they may reduce overall cathode activity. This reduction in performance is acceptable, or substances that interact with the cathode catalyst can be reduced to acceptable levels by known contaminant removal techniques.

[0082] O present in a cathode input stream (such as an input cathode stream based on combustion exhaust gas) 2 The amount of O may advantageously be sufficient to provide the oxygen required for the cathode reaction in the fuel cell. 2 The volume percentage of CO in the exhaust gas can be advantageously 2 Optionally, additional air may be added to the cathode input as needed to provide sufficient oxidant for the cathode reaction. When some form of air is used as the oxidant, the N 2 The amount of can be at least about 78 volume %, such as at least about 88 volume %, and / or about 95 volume % or less. In some aspects, the cathode input stream may additionally or alternatively contain compounds that are generally considered contaminants, such as H 2 S or NH 3 In other aspects, the cathode input stream can be cleaned to reduce or minimize the amount of such contaminants.

[0083] Suitable temperatures for MCFC operation can be between about 450°C and about 750°C, such as at least about 500°C, for example, an inlet temperature of about 550°C and an outlet temperature of about 625°C. Before entering the cathode, if necessary, for example, heat can be added to or removed from the cathode input stream to provide heat for other processes, such as reforming the fuel input for the anode. For example, if the source of the cathode input stream is a combustion exhaust stream, the temperature of the combustion exhaust stream may be greater than the desired temperature of the cathode inlet. In such an aspect, heat can be removed from the combustion exhaust before being used as a cathode input stream. Alternatively, the combustion exhaust can be at a very low temperature, such as after a wet gas scrubber on a coal-fired boiler, in which case the combustion exhaust can be below about 100°C. Alternatively, the combustion exhaust can be from the exhaust of a gas turbine operating in a combined cycle mode, where the gas can be cooled by generating steam to operate a steam turbine for additional power generation. In this case, the gas can be below about 50°C. Heat can be added to the combustion exhaust at a lower temperature than required.

[0084] Example

[0085] A series of laboratory-scale single fuel cells were tested, which included various types of configurations at the interface between the cathode surface and the cathode current collector. The laboratory-scale fuel cells each had a 250 cm 2 The cathode current collector in the fuel cell has a structure corresponding to 10% contact area / 90% open area at the cathode surface. Some fuel cells do not have a mesh layer between the cathode current collector and the cathode surface. Other fuel cells have a structured mesh layer that has openings of varying densities in the mesh and provides varying amounts of mesh open area. Generally in these embodiments, the fuel cell is operated under various conditions: CO in the cathode inlet gas 2 In the range of 4.0 vol% to 10 vol%; 140 mA / cm 2 Up to 180mA / cm 2 The current density of CO 2 Utilization rates range between 65% and 98%.

[0086] In a first set of test runs, the operation of a fuel cell without a mesh layer was compared to the operation of a fuel cell including a structured mesh layer having 100 openings / cm 2 or greater opening density and 25% to 45% mesh open area (55% to 75% contact area). Multiple cells were run using both types of configurations. Figure 7 The operation shown, the cell is at about 90% CO 2 Run at utilization. Figure 7 The ohmic resistance of the cell over an extended run length is shown. Figure 7 Each line in corresponds to data from the operation of a single fuel cell. Figure 7 As shown, the cell without the mesh layer initially has an ohmic resistance similar to that of the cell including the mesh layer. However, during operation of the fuel cell without the mesh layer, the ohmic resistance increases rapidly over time. In contrast, the cell including the structural mesh layer unexpectedly maintains substantially the same ohmic resistance value throughout operation.

[0087] Figure 8 and Fig. 9 The effect of increased ohmic resistance on fuel cell performance is shown. Fig. 9 Corresponding to Figure 7 Same type of diagram, but for a CO 2 For clarity, only one fuel cell without a mesh layer is shown (line 890), and only two fuel cells including a mesh layer are shown (lines 810 and 820). Figure 8 shows how changes in ohmic resistance change the operating voltage of a fuel cell. Figure 8 As shown, for a fuel cell without a mesh wire, the increased ohmic resistance over time results in a significant drop in operating voltage. In contrast, a fuel cell including a mesh layer unexpectedly maintains substantially the same operating voltage over time under selected operating conditions.

[0088] Figure 7 , Figure 8 and Fig. 9 The operation of a fuel cell without a mesh was compared to a fuel cell including a structured mesh layer having a high density of openings and a low mesh open area. Additional test runs were performed to determine whether a Figure 7 , Figure 8 and Fig. 9 Additional test runs were performed under two different types of operating conditions. For both types of operating conditions, the CO 2 utilization to determine how the operating voltage and ohmic resistance vary with CO 2 Varies with utilization.

[0089] Table 1 shows six different types of mesh layers tested in various runs. Table 1 shows the mesh open area, opening density and thickness of each mesh layer. In Table 1, mesh layers 3-6 correspond to comparative mesh layers with insufficient mesh open area and / or insufficient opening density to provide unexpected benefits.

[0090] Table 1 - Grid layer characteristics

[0091]

[0092] A fuel cell including a grid layer based on grid 1, grid 2, and grid 3 is subjected to various CO 2 Utilization level operation. Fig.10 shows how the ohmic resistance varies with CO 2 Utilization changes, while Fig.11 shows the operating voltage vs. CO 2 The relationship between utilization. Fig.10 and Fig.11 The values ​​shown in the table represent the values ​​at a specific CO 2 The average value obtained by maintaining multiple fuel cells running for a period of time at the same utilization level.

[0093] like Fig.10 As shown, both the cell including Grid 1 (line 1010) and the cell including Grid 2 (line 1020) show a significant reduction in ohmic resistance relative to the cell not including the grid layer (line 1090). For comparison purposes, error bars are also provided for line 1090 (the cell without the grid layer) to demonstrate Fig.10The difference in ohmic resistance of Mesh 1 and Mesh 2 shown in FIG. 1 is not simply due to the expected level of variation in fuel cell behavior. Instead, the cell including Comparative Mesh 3 (line 1030) has an ohmic resistance comparable to that of a cell not including a mesh layer (line 1090). Note that Comparative Mesh 3 has a relatively high density of openings. However, the mesh open area of ​​Comparative Mesh 3 is too high.

[0094] Fig.11 shows the operating voltage with respect to CO 2 Similar trends in utilization. Fig.11 As shown, the cells including Grid 1 and Grid 2 have higher operating voltages than the cell without the grid layer. The cell including comparative Grid 3 has a similar operating voltage as the cell without the grid layer.

[0095] Additional testing was conducted using a second set of operating conditions for cells including Comparative Grid 4, Comparative Grid 5, and Comparative Grid 6. Fig.12 shows the ohmic resistance vs. CO 2 The relationship between utilization and Fig.13 shows the operating voltage vs. CO 2 Similarly, Fig.12 and Fig.13 The data in represent average values ​​based on operation of multiple batteries with the same configuration.

[0096] like Fig.12 As shown, the cells including comparative mesh 5 (line 1250) and comparative mesh 6 (line 1260) actually show a reduction in ohmic resistance relative to the cell without a mesh layer (line 1290). The cell including comparative mesh 4 (line 1240) has an ohmic resistance similar to the cell without a mesh layer (line 1290).

[0097] Although the cells including Comparative Grid 5 and Comparative Grid 6 have reduced ohmic resistance, these cells do not gain a corresponding benefit in operating voltage. Fig.13 As shown, the cells including Comparative Grid 5 and Comparative Grid 6 appear to have similar or possibly even lower operating voltages relative to the cells without the grid layer. Without being bound by any particular theory, it is believed that even though the grid open area is relatively high, the low density of openings can lead to shadowing and CO 2 Poor transport from cathode current collector to cathode.

[0098] based on Figure 7-13 As a result, the use of a structural mesh layer with a relatively low mesh open area and a relatively high opening density can allow for improved fuel cell operation over time. As further confirmation, Fig.14Results from additional runs performed using cells containing Grid 1, Grid 2, and no grid layer are shown. In the additional runs, the transfer of the cell was measured as a function of CO 2 The migration is the function of the utilization rate of carbonate ions (CO 2 The fraction of ions that migrate through the electrolyte matrix, as opposed to other types of ions such as hydroxide ions. Fig.14 As shown, adding Grid 1 (1410) or Grid 2 (1420) to the battery results in substantially the same or possibly higher migration levels than the battery without the grid (1490).

[0099] Additional embodiments

[0100] Embodiment 1. A molten carbonate fuel cell, comprising: an anode; a first separator; an anode collector, the anode collector being in contact with the anode and the first separator to define an anode gas collection area between the anode and the first separator; a cathode having a cathode surface; a second separator; a cathode current collector, the cathode current collector being in contact with the second separator and adjacent to the cathode surface to define a cathode gas collection area between the cathode and the second separator, the cathode current collector having a contact area of ​​less than 55%; a structural grid layer disposed between the cathode surface and the cathode current collector, the structural grid layer comprising 50 openings / cm 2 or more, and having a mesh contact area of ​​55% to 75%; and an electrolyte matrix comprising an electrolyte located between the anode and the cathode.

[0101] Embodiment 2. A molten carbonate fuel cell according to embodiment 1, wherein the structural grid layer comprises 75 openings / cm 2 or more.

[0102] Embodiment 3. A molten carbonate fuel cell according to any one of the above embodiments, wherein the structural grid layer comprises 125 openings / cm 2 or more.

[0103] Embodiment 4. A molten carbonate fuel cell according to any one of the above embodiments, wherein the contact area of ​​the cathode current collector is 50% or more.

[0104] Embodiment 5. A molten carbonate fuel cell according to any of the above embodiments, wherein the structural grid layer provides electrical contact between the cathode current collector and the cathode surface.

[0105] Embodiment 6. A molten carbonate fuel cell according to any one of the above embodiments, wherein the average contact area diffusion length is 1.0 mm or less, or wherein the average cathode gas lateral diffusion length is 0.35 mm or less, or a combination thereof.

[0106] Embodiment 7. A molten carbonate fuel cell according to any of the above embodiments, wherein the structural grid layer comprises a thickness of 0.25 mm to 0.80 mm.

[0107] Embodiment 8. A molten carbonate fuel cell according to any of the above embodiments, wherein the structural grid layer is composed of stainless steel.

[0108] Embodiment 9. A method for generating electricity in a molten carbonate fuel cell according to any one of Embodiments 1-8, comprising: 2 , a reformable fuel or a combination thereof, into the anode gas collection region; 2 and CO 2 The cathode input flow is introduced into the cathode gas collection zone; and at 60mA / cm 2 The molten carbonate fuel cell is operated at an average current density of 1000 Å or higher to produce electricity, an anode exhaust, and a cathode exhaust.

[0109] Embodiment 10. A method according to embodiment 9, wherein the fuel cell operates at 80% or more CO 2 Utilization runs.

[0110] Embodiment 11. A method according to Embodiment 9 or 10, wherein the cathode input stream comprises 5.0 vol% or less CO 2 , or wherein the cathode exhaust contains 1.0 vol% or less CO 2 , or a combination thereof.

[0111] Embodiment 12. The method according to any one of Embodiments 9 to 11, wherein the cathode input stream comprises 4.0 vol% to 10 vol% CO 2 .

[0112] All numerical values ​​in the detailed description and claims herein are modified by the value indicated as "about" or "approximately", and take into account experimental errors and variations that would be expected by a person of ordinary skill in the art.

[0113] Although the present invention has been described in terms of specific embodiments, the present invention is not necessarily limited thereto. Suitable changes / modifications for operation under specific conditions should be apparent to those skilled in the art. Therefore, the following claims are intended to be interpreted as covering all such changes / modifications that fall within the true spirit / scope of the present invention.

Claims

1. A molten carbonate fuel cell comprising: anode; First bulkhead; an anode collector in contact with the anode and the first separator to define an anode gas collection region between the anode and the first separator; a cathode having a cathode surface; a second separator; a cathode current collector in contact with the second separator and adjacent to a surface of the cathode to define a cathode gas collection region between the cathode and the second separator, the cathode current collector having a contact area of ​​less than 55%; A structural grid layer is provided between the cathode surface and the cathode current collector, wherein the structural grid layer comprises 50 openings / cm 2 or more, and having a mesh contact area of ​​55% to 75%; and an electrolyte matrix comprising an electrolyte located between the anode and the cathode.

2. The molten carbonate fuel cell according to claim 1, wherein the structural grid layer comprises 75 openings / cm 2 or more.

3. The molten carbonate fuel cell of claim 1, wherein the structural grid layer comprises 125 openings / cm 2 or more.

4. The molten carbonate fuel cell according to claim 1, wherein the contact area of ​​the cathode current collector is 50% or less.

5. The molten carbonate fuel cell of claim 1, wherein the structural grid layer provides electrical contact between the cathode current collector and the cathode surface.

6. The molten carbonate fuel cell of claim 1, wherein the average contact area diffusion length is 1.0 mm or less.

7. The molten carbonate fuel cell according to claim 1, wherein the average cathode gas lateral diffusion length is 0.35 mm or less.

8. The molten carbonate fuel cell of claim 1, wherein the structural grid layer comprises a thickness of 0.25 mm to 0.80 mm.

9. The molten carbonate fuel cell of claim 1, wherein the structural grid layer is composed of stainless steel.

10. A method of generating electricity in a molten carbonate fuel cell, the method comprising: An anode input stream containing H2, a reformable fuel or a combination thereof is introduced into an anode gas collection region, wherein the anode gas collection region is defined by an anode surface, a first separator and an anode collector providing support between the anode surface and the separator; a cathode input stream containing O2 and CO2 is introduced into a cathode gas collection region, wherein the cathode gas collection region is defined by a cathode surface, a second separator and a cathode current collector adjacent to the cathode surface and in contact with the second separator, wherein a structural grid layer is provided between the cathode surface and the cathode current collector, wherein the structural grid layer includes 50 openings / cm 2 or more, and having a grid contact area of ​​55% to 75%, the cathode current collector having a contact area of ​​less than 55%; and at 60mA / cm 2 The molten carbonate fuel cell is operated at an average current density of 1000 Å or higher to produce electricity, an anode exhaust, and a cathode exhaust.

11. The method of claim 10, wherein the average contact area diffusion length is 1.0 mm or less.

12. The method according to claim 10, wherein: The cathode current collector has a contact area of ​​50% or more.

13. The method of claim 10, wherein the average cathode gas lateral diffusion length is 0.35 mm or less.

14. The method of claim 10, wherein the structural grid layer comprises 75 openings / cm 2 or more.

15. The method of claim 10, wherein the structural grid layer comprises 125 openings / cm 2 or more.

16. The method of claim 10, wherein the fuel cell operates at a CO2 utilization of 80% or more.

17. The method of claim 10, wherein the cathode input stream comprises 5.0 vol% or less CO2, or wherein the cathode exhaust comprises 1.0 vol% or less CO2, or a combination thereof.

18. The method of claim 10, wherein the cathode input stream comprises 4.0 vol% to 10 vol% CO2.

19. The method of claim 10, wherein the structural grid layer comprises a thickness of 0.25 mm to 0.80 mm.

20. The method of claim 1, wherein the structural grid layer provides electrical contact between the cathode current collector and the cathode surface.

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