Fuel cells and fuel cell stacks

Abstract

To provide a fuel cell that prevents stress and damage to the cell during stack assembly while obtaining high output density.SOLUTION: A fuel cell is equipped with a unit cell including a structure in which an electrolyte layer is sandwiched between an anode electrode layer and a cathode electrode layer. The unit cell is arranged between a first member and a second member. An intermediate substrate is arranged between the first and second members. The unit cell is supported by the intermediate substrate at its peripheral portion. The width of the electrolyte layer is equal to or less than the maximum width of a cavity portion formed between at least one of the first and second members and the unit cell.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a fuel cell using a solid electrolyte.

Background Art

[0002] In recent years, fuel cells have attracted attention as a power generation system that uses fuels such as hydrogen and does not emit carbon dioxide. A fuel cell has a structure in which an electrolyte is sandwiched between two electrodes, an anode and a cathode, and a power generation operation is performed by supplying a fuel gas to the anode side and a gas containing oxygen such as air to the cathode side.

[0003] For the purpose of safely and efficiently extracting the generated power to the outside, a stack is assembled with components such as a current collector, which is a mesh-structured metal that combines electrical connection and gas permeation, a separator that separates the flow paths of the fuel gas and air, and a gasket for preventing gas leakage to the outside. By applying compressive stress from above and below by tightening a screw or the like, improvement in airtightness and reduction in contact electrical resistance are achieved.

[0004] Also, a technique for improving the current collection performance by housing a fuel cell in two support substrates is known (Patent Document 1).

[0005] Also, a battery cell is known that includes an electrode layer at a position covering an opening formed in a support substrate, a solid electrolyte layer having a thickness of 1000 nm or less, and at least a part of a region of the electrode layer covering the opening is porous (Patent Document 2).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] While the output of a fuel cell improves as the electrolyte layer becomes thinner, its mechanical strength decreases, making it more susceptible to cracks and other damage.

[0008] Patent Document 1 describes a structure in which the entire lower surface of the cell is in contact with a support substrate, and another support substrate is also in contact with the outer periphery of the upper surface. Therefore, if a high power density is achieved by using a thin film of, for example, 1 μm or less for the electrolyte layer, there is a risk that the electrolyte will be damaged by compressive stress during stack assembly. Damage to the electrolyte layer directly leads to cell failure, so this must be avoided.

[0009] Patent Document 2 discloses a cell having an electrolyte layer with a thickness of 1000 nm or less, but it did not consider the stress applied to the electrolyte layer via a separator.

[0010] This invention has been made in view of the above-mentioned problems, and aims to provide a fuel cell that achieves high power density while preventing stress application to cells and damage during stack assembly. [Means for solving the problem]

[0011] One aspect of the present invention is a fuel cell equipped with a unit cell having a structure in which an electrolyte layer is sandwiched between an anode electrode layer and a cathode electrode layer, wherein the unit cell is disposed between a first member and a second member, an intermediate substrate is disposed between the first member and the second member, the outer periphery of the unit cell is supported by the intermediate substrate, and the width of the electrolyte layer is less than or equal to the maximum width of the cavity formed between at least one of the first member and the second member and the unit cell.

[0012] Another aspect of the present invention is a fuel cell having a unit cell including a structure in which an electrolyte layer is sandwiched between an anode electrode layer and a cathode electrode layer, wherein the unit cell is disposed between a first member and a second member, and an intermediate substrate is disposed between the first member and the second member. The unit cell is supported by the intermediate substrate at its outer peripheral portion, and the fuel cell is characterized in that the thickness of the electrolyte layer is 1 μm or less.

[0013] Another aspect of the present invention is a fuel cell stack having the above fuel cell, characterized in that a compressive stress is applied from above and below the entire fuel cell.

Advantages of the Invention

[0014] According to the present invention, it is possible to provide a fuel cell that obtains a high output density and prevents stress application and damage to the cell during stack assembly.

Brief Description of the Drawings

[0015] [Figure 1] Cross-sectional view of the fuel cell of Example 1. [Figure 2] Cross-sectional view showing the definition of the width of the cavity in the example. [Figure 3] Perspective view of each component of the fuel cell of Example 1. [Figure 4] Cross-sectional view of the fuel cell stack of Example 1. [Figure 5] Cross-sectional view of the fuel cell stack of Example 2. [Figure 6] Cross-sectional view of the fuel cell of Example 4. [Figure 7] Cross-sectional view of the fuel cell of Example 5. [Figure 8] Cross-sectional view of the fuel cell of Example 6. [Figure 9] Cross-sectional view of the fuel cell of Example 7. [Figure 10] Cross-sectional view of the fuel cell of Example 8. [Figure 11] Cross-sectional view of the fuel cell of Example 10. [Figure 12A] Cross-sectional view of the fuel cell of Example 11. [Figure 12B]Perspective view of the intermediate substrate of Example 11. [Figure 13] Perspective view of each component of the fuel cell of Example 12. [Figure 14] Perspective view of the intermediate substrate of Example 13. [Figure 15] Cross-sectional view of the fuel cell of Example 14. [Figure 16A] Cross-sectional view of the fuel cell of Example 15. [Figure 16B] Perspective view of the intermediate substrate of Example 15. [Figure 17] Cross-sectional view of the fuel cell of Example 16. [Figure 18] Cross-sectional view of the fuel cell of Example 17. [Figure 19A] Cross-sectional view of the fuel cell of Example 18. [Figure 19B] Perspective view of the intermediate substrate of Example 18.

Mode for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described in detail based on the drawings. In the following embodiments, when necessary for convenience, they are divided into a plurality of sections or embodiments for description. However, unless otherwise specified, they are not unrelated to each other, and one is related to a partial or entire modification example, detail, supplementary explanation, etc. of the other. Also, in the drawings used in the following embodiments, even if it is a plan view, hatching may be added to make the drawing easier to view. Further, in all the drawings for explaining the following embodiments, those having the same function are generally denoted by the same reference numerals, and the repeated explanation thereof is omitted. Also, in order to make the drawings easier to view, those having the same function in the cross-sectional views may be given the same shape and the same hatching and the reference numerals may be omitted.

[0017] One fuel cell according to the embodiment is a fuel cell equipped with a unit cell having a structure in which an electrolyte layer is sandwiched between an anode electrode layer and a cathode electrode layer. The unit cell is supported by an intermediate substrate at its outer peripheral portion, and the width of the electrolyte layer is not more than the maximum width of the cavity portion. <00 One of the fuel cells according to the embodiment is a fuel cell equipped with a unit cell having a structure in which an electrolyte layer is sandwiched between an anode electrode layer and a cathode electrode layer, wherein the unit cell is supported on its outer periphery by an intermediate substrate, and the thickness of the electrolyte layer is 1 μm or less. [Examples]

[0019] Figure 1 is a cross-sectional view showing an example of the structure of a fuel cell according to Embodiment 1 of the present invention. The fuel cell 1 of Embodiment 1 has at least one unit cell 3 (hereinafter also simply referred to as a cell) mounted on an intermediate substrate 2. The unit cell 3 consists of a porous support layer 4, an anode electrode layer 5, an electrolyte layer 6, and a cathode electrode layer 7, with the electrolyte layer 6 sandwiched between the anode electrode layer 5 and the cathode electrode layer 7. In some cases, the porous support layer 4 may be omitted.

[0020] The intermediate substrate 2 is an insulator, and it is desirable that it be made of a material that has a certain level of mechanical strength even at high temperatures, such as aluminum oxide, zirconium oxide, or silicon nitride. The intermediate substrate 2 is provided with a first conductive region 8 and a second conductive region 9, which are formed on the intermediate substrate 2 by printing and wiring technology using metal materials such as gold or silver.

[0021] The porous support layer 4 plays a role in supporting the entire cell when the anode electrode layer 5, electrolyte layer 6, and cathode electrode layer 7 are thin films, for example, 1 μm thick, for the purpose of manufacturing a high power density cell. The porous support layer 4 is made of a ceramic material such as aluminum oxide, and its porous structure allows fuel gas to reach the anode electrode layer 5. The anode electrode layer 5 is made of a material such as nickel and stabilized zirconia cermet and is electrically connected to the first conductive region 8 by a conductive paste or the like.

[0022] As shown in Figure 1, by narrowing the range of the electrolyte layer 6 and the cathode electrode layer 7 compared to the anode electrode layer 5, it becomes possible to orient the cathode electrode layer 7 downwards and bring the anode electrode layer 5 into contact with the first conductive region 8, or to prevent the cathode electrode layer 7 from coming into contact with the first conductive region 8, and to house the cell in the recessed portion of the intermediate substrate 2. If the lower surface of the anode electrode layer 5 is exposed, it is desirable to shield it with a glass sealant or the like to prevent it from coming into contact with air.

[0023] The electrolyte layer 6 is made of a material such as stabilized zirconia (yttria-stabilized zirconia) with an yttria composition ratio of 8%. If a thin film of 1 μm or less is formed by a film deposition process such as sputtering, it is possible to obtain high power density power generation. The cathode electrode layer 7 is made of a material such as platinum, a cermet of platinum and GDC (Gadolinium Doped Ceria), or LSC ((La,Sr)CoO3), and is electrically connected to the second conductive region 9 by bonding wires 10, etc.

[0024] Current collectors 11 are positioned in contact with the first conductive region 8 and the second conductive region 9, respectively. These are made of conductive materials such as nickel or silver, but it is desirable that those positioned on the air passage side be made of a material that does not oxidize even at high temperatures. A gasket 12 is positioned on the outside of the current collectors 11. By sandwiching the current collectors 11 and gasket 12, which are positioned vertically on the intermediate substrate 2, between two separators 13 and applying compressive stress, gas leakage to the outside is prevented. If the current collectors 11 have a mesh structure with gaps, when compressed they will be the same thickness as the gasket 12, which is expected to improve sealing performance and also ensure good electrical connection with the conductive regions. The vertical direction refers to the direction in which each layer is stacked, and the upper and lower directions are interchangeable.

[0025] The separator 13 is made of a material such as stainless steel and is electrically connected to the first conductive region 8 and the second conductive region 9 via the current collector 11, thereby enabling the extraction of power generated by the unit cell 3 to the outside. At this time, the overlapping portion of the current collector 11 is limited to the intermediate substrate 2, and the width of the electrolyte layer 6 is kept below the maximum width of the cavity, so that when the fuel cell 1 is pressurized from above or below, stress is not applied to the cells, and consequently, damage to the cells can be prevented.

[0026] Figure 2 shows the definition of the width of the cavity in the fuel cell 1 in the embodiment. No components are placed above or below the unit cell 3, resulting in cavities 201 and 202. In each arbitrary cross-section of the cavity, the maximum width of the cavity within the cross-section is defined as W1. Also, the maximum width of the electrolyte layer 6 in the same cross-section is defined as W2. During stack assembly, compressive stress is applied from the upper and lower separators 13, but if the value of W2 is less than or equal to W1 in any cross-section parallel to the stress application direction, no stress is applied to the electrolyte layer 6, and damage can be prevented.

[0027] For example, in the cross-section shown in Figure 2, the maximum width of the electrolyte layer 6 is smaller than the maximum width of the upper cavity 201, so no force applied from above is applied to the electrolyte layer 6. Also, since the maximum width of the electrolyte layer 6 is smaller than the maximum width of the lower cavity 202, no force applied from below is applied to the electrolyte layer 6.

[0028] Figure 3 is a perspective view showing an example of the structure of a fuel cell according to Embodiment 1 of the present invention. The unit cell 3 has its cathode electrode layer facing downwards, and as shown in Figure 1, the area of ​​the electrolyte layer 6 and the cathode electrode layer 7 is narrower than that of the anode electrode layer 5, so that the anode electrode layer 5 can be brought into contact with the first conductive region 8. In this case, fuel needs to be supplied to the upper side of the unit cell 3 and air to the lower side. In this description, the gasket 12 placed on the intermediate substrate 2 is distinguished as the anode-side gasket 12', and the gasket 12 placed below the intermediate substrate 2 is distinguished as the cathode-side gasket 12''.

[0029] The intermediate substrate 2 has a fuel inlet 2a, a fuel outlet 2b, an air inlet 2c, and an air outlet 2d. Similarly, the gasket 12' has a fuel inlet 12'a, a fuel outlet 12'b, an air inlet 12'c, and an air outlet 12d', the gasket 12'' has a fuel inlet 12''a, a fuel outlet 12''b, an air inlet 12''c, and an air outlet 12''d, and the separator 13 has a fuel inlet 13a, a fuel outlet 13b, an air inlet 13c, and an air outlet 13d.

[0030] When fuel gas is supplied from the fuel inlet 13a of the lower separator 13, the fuel gas moves upward, passing through the fuel inlet 12′′a of the cathode-side gasket 12′′ and the fuel inlet 2a of the intermediate substrate 2. At this time, by providing a notch in the fuel inlet 12′a of the anode-side gasket 12′, it is possible to supply fuel gas to the upper side of the unit cell 3. The fuel gas is then discharged to the outside via the fuel outlet 12b of the gasket 12, the fuel outlet 2b of the intermediate substrate 2, and the fuel outlet 13b of the separator 13. Furthermore, if the same structure is repeated above the upper separator 13, the fuel gas is supplied upward by passing through the fuel inlet 13a of the upper separator 13.

[0031] Similarly, when air is supplied from the air inlet 13c of the lower separator 13, it is possible to supply air to the lower side of the unit cell 3 by providing a notch in the air inlet 12''c of the gasket 12'' on the cathode side. The air is then discharged to the outside from the fuel outlet 13d of the separator 13 via the air outlet 12''d of the cathode-side gasket 12''. Furthermore, if the same structure is repeated above the upper separator 13, air is supplied upwards by passing through the air inlet 2c of the intermediate substrate 2 and the air inlet 12''c of the cathode-side gasket 12''.

[0032] Figure 4 is a cross-sectional view showing an example of the structure of a fuel cell stack according to Embodiment 1 of the present invention. The fuel cell stack 400 consists of a fuel cell 1, a bottom jig 401, two gaskets 402, a top jig 403, a support column 404, and a fastening member 405. At least one of the bottom jig 401 and the top jig 403, and the gasket 402, are required to have a flow path or hole that allows the movement of fuel gas and air between the fuel inlet 13a, air inlet 13c, and air outlet 13d of the separator 13.

[0033] The fuel cell stack 400 can be assembled by stacking the components in the following order from bottom to top: bottom jig 401, gasket 402, fuel cell 1, gasket 402, and top jig 403. The top and bottom surfaces of the support column 404 are provided with holes that match the shape of the fastening member 405.

[0034] To prevent fuel gas and air from leaking to the outside, through holes are made in the outer circumference of the bottom jig 401 and the top jig 403, the support column 404 is passed through them, and the fastening member 405 is tightened to apply compressive stress to the fuel cell 1 from above and below.

[0035] At this time, since the width of the electrolyte layer 6 is less than or equal to the maximum width of the cavity, no compressive stress is applied by the fastening member 405, thus preventing damage. The compressive stress applied by the fastening member 405 acts on the intermediate substrate 2 that holds the unit cell 3, enabling the sealing of the fuel cell 1 while preventing damage to the thin electrolyte layer 6, for example, 1 μm or less in thickness. [Examples]

[0036] Figure 5 is a cross-sectional view showing an example of the structure of a fuel cell stack according to Embodiment 2 of the present invention. The fuel cell stack 500 consists of a fuel cell 501, a bottom jig 401, two gaskets 402, a top jig 403, a support column 404, and a fastening member 405.

[0037] The difference from Example 1 is that the structure of the fuel cell 1 shown in Figure 1 is stacked vertically. This allows two unit cells 3 to be connected in series, increasing the output voltage of the stack. In the case of simply stacking the structure of Figure 1, two separators 13 are placed in the middle layer, but this can be done with just one separator, which acts as a relay member connecting the unit cells 3 in series and also separates the fuel gas flow path from the air flow path. Furthermore, by repeatedly stacking this structure, it is possible to create a series of three or more, and the output voltage of the stack increases in proportion to the number of stacks.

[0038] Even when multiple layers are stacked in this manner, similar to Example 1, by making the width of the electrolyte layer 6 less than or equal to the maximum width of the cavity, stress is not applied when the stack is tightened by the fastening member 405, thereby preventing damage. [Examples]

[0039] In Examples 1 and 2, the porous support layer 4 was made of a ceramic material, but it can also be made of a conductive metal material. For example, an alloy containing 50% or more iron can be used. In this case, while the current path was only in the anode electrode layer 5 when using a ceramic material, the current also flows through the porous support layer 4, reducing parasitic resistance and thus reducing power loss within the stack. In particular, the thinner the film thickness of the electrolyte layer 6, the greater the current, and therefore the greater the effect of reducing power loss. [Examples]

[0040] Figure 6 is a cross-sectional view showing an example of the structure of a fuel cell according to Embodiment 4 of the present invention. The difference from Embodiments 1 to 3 is that the unit cell 3 does not have a porous support layer 4. While Embodiments 1 to 3 used a porous support layer 4 as the base for forming the anode electrode layer 5, electrolyte layer 6, and cathode electrode layer 7 of the cell, it is also possible to form the electrolyte layer 6 and cathode electrode layer 7 with the anode electrode layer 5 as the base. In this case as well, by making the width of the electrolyte layer 6 less than or equal to the maximum width of the cavity, stress is not applied during stack assembly, and damage can be prevented. [Examples]

[0041] Figure 7 is a cross-sectional view showing an example of the structure of a fuel cell according to Embodiment 5 of the present invention. In this embodiment, bonding wires 10 are not used, and the cathode electrode layer 7 is electrically connected to the separator 13 by a current collector 11 with a mesh metal structure containing air gaps.

[0042] In Example 1, since the current is directed towards the bonding wire 10, there is lateral electron movement within the cathode electrode layer 7, and parasitic resistance equivalent to the sheet resistance of the cathode electrode layer 7 is generated. Therefore, in order to reduce power loss, the thickness of the cathode electrode layer 7 must be increased, which leads to increased manufacturing costs and decreased throughput.

[0043] In this embodiment, since the entire cathode electrode layer 7 can be connected, there is no need to consider the sheet resistance of the cathode electrode layer 7, making it possible to maintain throughput and reduce power loss simultaneously. This effect becomes more pronounced as the electrolyte layer 6 is made thinner and the current output is increased.

[0044] In this case as well, by making the width of the electrolyte layer 6 less than or equal to the maximum width of the cavity, stress is not applied during stack assembly, and damage can be prevented. The current collector 11 has a mesh structure with voids, and its elasticity ensures good electrical contact. However, in this embodiment of the present invention, nothing is placed on the upper surface of the unit cell 3, so there is a possibility of delamination occurring between the intermediate substrate 2, which is bonded with conductive paste, and the unit cell 3. For this reason, it is desirable to design the thickness of the current collector 11 to be sufficiently large to prevent delamination. Also, similar to Embodiment 3, it is possible to reduce power loss on the anode side by making the porous support layer 4 a conductive material. [Examples]

[0045] Figure 8 is a cross-sectional view showing an example of the structure of a fuel cell according to Embodiment 6 of the present invention. In this embodiment, the unit cell 3 does not have a porous support layer 4, but a configuration in which the cathode electrode layer 7 is electrically connected to the separator 13 by a current collector 11 with a mesh metal structure having voids is applicable, similar to Embodiment 5. [Examples]

[0046] Figure 9 is a cross-sectional view showing an example of the structure of a fuel cell according to Embodiment 7 of the present invention. The difference from previous embodiments is that the unit cell 3 is installed with the porous support layer 4 at the bottom and the cathode electrode layer 7 at the top. Therefore, the cathode-side gasket 12'' is placed on the intermediate substrate 2 and the anode-side gasket 12'' is placed below the intermediate substrate 2 so that air flows above the unit cell 3 and fuel gas flows below the unit cell 3.

[0047] In this case as well, by making the width of the electrolyte layer 6 less than or equal to the maximum width of the cavity, stress is not applied during stack assembly, and damage can be prevented. [Examples]

[0048] Figure 10 is a cross-sectional view showing an example of the structure of a fuel cell according to Embodiment 8 of the present invention. In this embodiment, the porous support layer 4 is made of a conductive material. Therefore, the lower surface of the unit cell 3 is electrically connected to the anode electrode layer 5, and an electrical connection with the separator 13 can be made by placing a current collector 11 with a mesh metal structure containing air gaps directly below the unit cell 3, for example, as shown in Figure 8.

[0049] In this case as well, by making the width of the electrolyte layer 6 less than or equal to the maximum width of the cavity, stress is not applied during stack assembly, and damage can be prevented. Furthermore, it is desirable to bond the intermediate substrate 2 and the unit cell 3 with a conductive paste or the like to prevent delamination. [Examples]

[0050] In Example 8, the porous support layer was made of a metal material, but even when a ceramic material is used, by forming metal within the gas flow path holes in the porous support layer, electrical connection to the separator 13 via the current collector 11 from the bottom surface of the unit cell 3 is possible, as shown in Figure 10. Metal formation within the gas flow path holes can be done by forming a metal film only on the surface without filling the flow path holes, or by selectively filling the flow path holes with metal and dividing them into areas responsible for electrical connection to the bottom surface and areas responsible for fuel gas supply to the unit cell 3. [Examples]

[0051] Figure 11 is a cross-sectional view showing an example of the structure of a fuel cell according to Embodiment 10 of the present invention. In this embodiment, the porous support layer 4 from Embodiment 8 is absent. Since the anode electrode layer 5 is made of a conductive material, an electrical connection with the separator 13 can be made by placing the current collector 11 directly below the unit cell 3, similar to Embodiment 8. [Examples]

[0052] Figure 12A is a cross-sectional view showing an example of the structure of a fuel cell according to Embodiment 11 of the present invention. In this embodiment, multiple unit cells 3 are mounted on a single intermediate substrate 2. From the viewpoint of power density, it is desirable to mount only one unit cell 3 with a large area, but the larger the area, the greater the risk of damage. In particular, in the case of solid oxide fuel cells (SOFCs), since the operating temperature is 600 degrees Celsius or higher, there is a concern about damage due to thermal stress during heating and cooling. In contrast, in this embodiment, the risk of damage can be reduced by reducing the area of ​​the unit cell 3. Furthermore, the effect of improving manufacturing yield can also be obtained.

[0053] Figure 12B is a perspective view showing an example of the structure of an intermediate substrate according to Embodiment 11 of the present invention. As shown above, by providing multiple through holes and counterbores in the intermediate substrate 2, multiple unit cells 3 can be mounted on a single intermediate substrate 2. [Examples]

[0054] Figure 13 is a perspective view showing an example of the structure of a fuel cell according to Embodiment 12 of the present invention. Similar to Embodiment 11, multiple unit cells 3 are mounted on a single intermediate substrate 2, but this embodiment is characterized by the mounting of unit cells 3 with different characteristics. There are three types of unit cells 3 with different characteristics, which are referred to as the first unit cell 3a, the second unit cell 3b, and the third unit cell 3c, respectively, for distinction. Furthermore, when operated under the same conditions, the first unit cell 3a generates more power than the second unit cell 3b, and the second unit cell 3b generates more power than the third unit cell 3c.

[0055] Assuming the fuel gas and air flow paths are the same as in Example 1, air flows below each unit cell 3 and fuel gas flows above each unit cell 3. The air flow is indicated by arrow 1301, and the fuel gas flow is indicated by arrow 1302.

[0056] When a fuel cell is in operation, hydrogen in the fuel gas and oxygen in the air are consumed through chemical reactions, and their concentrations decrease as you move downstream. Therefore, if all unit cells 3 have the same characteristics, the unit cells 3 located downstream will generate less power. This imbalance can be mitigated by placing units with better characteristics downstream.

[0057] In this embodiment, the hydrogen concentration is lower in the left and upper cells, and the oxygen concentration is lower in the right and upper cells. Therefore, by placing the unit cell 3c, which generates the least power under the same operating conditions, at the bottom, and the unit cell 3a, which generates the most power under the same operating conditions, at the top, variations in power generation between each unit cell during fuel cell operation can be suppressed.

[0058] One way to control the characteristics of the unit cell 3 is to change the thickness of the electrolyte layer 6. When the electrolyte layer 6 is made thicker, the power generated decreases. [Examples]

[0059] Figure 14 is a perspective view showing an example of the structure of an intermediate substrate according to Embodiment 13 of the present invention. When multiple unit cells 3 are mounted on a single intermediate substrate 2, fuel flows to areas where there are no unit cells 3, leading to a decrease in fuel utilization efficiency.

[0060] In this embodiment, by making the through-holes and counterbore portions of the intermediate substrate 2 rectangular to match the fuel gas flow path, the reduction in efficiency when mounting multiple unit cells 3 can be suppressed. The airflow on the back of the intermediate substrate 2 is shown by arrow 1301. The fuel gas flow is shown by arrow 1302.

[0061] The shape of the unit cell 3 is also rectangular to match the recessed portion of the intermediate substrate 2, but by making the width of the electrolyte layer 6 less than or equal to the maximum width of the cavity on both the long and short sides, stress is not applied during stack assembly, thus preventing damage. [Examples]

[0062] Figure 15 is a cross-sectional view showing an example of the structure of a fuel cell according to Embodiment 14 of the present invention. The difference from Embodiment 1 is that the cathode electrode layer 7 is divided, and dividing the cathode electrode layer 7 is also an effective measure for controlling the manufacturing yield of the unit cell 3. Since the dimensions and shape can be easily changed by shielding materials during film formation, there is an advantage of greater flexibility compared to changing the shape of the porous support layer 4. [Examples]

[0063] Figure 16A is a cross-sectional view showing an example of the structure of a fuel cell according to Embodiment 15 of the present invention, and Figure 16B is a perspective view of the intermediate substrate. In this embodiment, there is one unit cell mounted on one intermediate substrate 2, but the anode electrode layer 5, electrolyte layer 6, and cathode electrode layer 7 are separated, and a cell support portion 1601 is provided on the intermediate substrate 2. This increases the support area of ​​the unit cell 3, which prevents deformation when stress occurs that causes it to bend downward due to temperature changes, and reduces the risk of damage.

[0064] The anode electrode layer 5 does not necessarily need to be divided. For example, if there is no porous support layer 4 as in Example 4, this embodiment can be applied by dividing only the electrolyte layer 6 and the cathode electrode layer 7. Also, if the cathode electrode layer 7 is facing upwards as in Example 7, it is not necessary to divide the electrolyte layer 6 and the cathode electrode layer 7.

[0065] In this embodiment, the current path from the cathode electrode layer 7 to the separator 13 is limited to the outer periphery, It is also possible to reduce parasitic resistance by providing a second conductive region 9 in the cell support portion 1601 and a current collector 11 below it. However, it is important to note that the larger the area occupied by the cell support portion 1601, the smaller the power generation area of ​​the unit cell 3 will be. [Examples]

[0066] Figure 17 is a cross-sectional view showing an example of the structure of a fuel cell according to Embodiment 16 of the present invention. In this embodiment, the fuel cell 1 has multiple unit cells 3 mounted on the same intermediate substrate 2, and they are connected in series by providing through electrodes 1701 on the intermediate substrate 2.

[0067] According to this embodiment, the output voltage of the fuel cell 1 can be increased and the output current can be decreased, thereby reducing power loss. Generally, power loss due to parasitic resistance is proportional to the square of the current value, so this effect is particularly pronounced when the electrolyte layer 6 is a thin film of 1 μm or less, as the output current is large.

[0068] If all the unit cells 3 mounted on the same intermediate substrate 2 are connected in series, the wiring becomes more complex, and there is a risk of insulation failure due to the high output voltage of the stack formed by repeatedly stacking the fuel cell 1 structure vertically. However, if the unit cells 3 are arranged regularly in two orthogonal directions as shown in Figure 12B, each row can be connected in parallel, and the rows can be connected in series, preventing the wiring from becoming more complex and also allowing for adjustment of the output voltage and output current of each layer after the stack is assembled. [Examples]

[0069] Figure 18 is a cross-sectional view showing an example of the structure of a fuel cell according to Embodiment 17 of the present invention. In this embodiment, the intermediate substrate 2 is mainly made of a conductor, and it has a three-layer structure in which an insulating layer 1801 prevents short circuits between the anode and cathode. The rest is the same as in Embodiment 1, and the generated power is sent to the separator 13 via the current collector 11 by connecting the anode to the first conductive layer 1802 and the cathode to the second conductive layer 1803. In this case as well, by making the width of the electrolyte layer 6 less than or equal to the maximum width of the cavity, stress is not applied during stack assembly, and damage can be prevented. [Examples]

[0070] Figure 19A is a cross-sectional view showing an example of the structure of a fuel cell according to Embodiment 18 of the present invention, and Figure 19B is a perspective view. Figure 19A is a cross-section of the dashed line AA' in Figure 19B, and in Figure 19B, the angle of the uppermost separator 13 is changed to show the back view. Furthermore, when it is necessary to distinguish between the uppermost separator 13 and the lowermost separator 13, the separator 13 placed in the uppermost position will be described as the anode-side separator 13', and the separator 13 placed in the lowermost position will be described as the cathode-side separator 13''.

[0071] In this embodiment, the separator 13 is provided with a flow channel groove 1901. This allows fuel gas and air to be supplied to the unit cell 3 without the need to provide a notch in the gasket 12, and improves sealing performance as the flow channel of the gasket 12 consists only of a circular hole. Furthermore, it is possible to reduce the risk of the unit cell 3 or bonding wire 10 coming into contact with the separator 13 when the counterbore of the intermediate substrate 2 is shallow relative to the thickness of the unit cell 3, or when the current collector 11 or gasket 12 is thin.

[0072] When air is supplied from the air inlet 13''c of the cathode-side separator 13'', the air is supplied to the unit cell 3 through the flow channel groove 1901 and then discharged to the outside from the air outlet 13''d. Fuel gas passes through the fuel inlet 13''a of the cathode-side separator 13'', the fuel inlet 12a of the gasket 12, and the fuel outlet 2b of the intermediate substrate 2 to the anode-side separator 13'', and is supplied to the unit cell 3 via the flow channel groove 1901. It is then discharged to the outside via the fuel outlet 12b of the gasket 12, the fuel outlet 2b of the intermediate substrate 2, and the fuel outlet 13''b of the cathode-side separator 13''.

[0073] When a similar structure is repeatedly stacked as shown in Figure 4, each separator 13 is provided with a fuel inlet 13a, a fuel outlet 13b, an air inlet 13c, and an air outlet 13d, and further, flow channel grooves 1901 are provided on both sides. In this case, the depth of the flow channel grooves 1901 must be less than half the thickness of the separator 13.

[0074] According to the embodiment described above, the unit cell is mounted on an intermediate substrate separate from the separator, and electrical connection to the separator is made via the intermediate substrate. According to this embodiment, stress application to the cell during stack assembly can be prevented. Consequently, cell failure caused by damage to the electrolyte layer can be prevented. Furthermore, by making the electrolyte layer thinner, it is possible to improve the power density.

[0075] According to the examples, high-performance fuel cells can be realized, reducing carbon emissions, preventing global warming, and contributing to the realization of a sustainable society. [Explanation of Symbols]

[0076] 1 fuel cell 2 Intermediate board 2a Fuel inlet 2b Fuel outlet 2c Air inlet 2d Air outlet 3 unit cells 4. Porous support layer 5. Anode electrode layer 6 Electrolyte layer 7. Cathode electrode layer 8. First conductive region 9. Second conductive region 10 Bonding wires 11 Current collector 12 Gaskets 12′ Anode side gasket 12′′ Cathode side gasket 13 Separator 13′ Anode-side separator 13′′ Cathode-side separator 400 fuel cell stacks 401 Bottom jig 402 Gasket 403 Top surface jig 404 Post 405 Fastening Member 500 fuel cell stacks 501 Fuel Cell 1601 Cell support section 1701 Through electrode 1801 Insulating layer 1802 First conductive layer 1803 Second conductive layer 1901 Flow channel groove

Claims

1. A fuel cell equipped with a unit cell having a structure in which an electrolyte layer is sandwiched between an anode electrode layer and a cathode electrode layer, The unit cell is positioned between the first member and the second member. An intermediate substrate is placed between the first member and the second member. The unit cell is supported by the intermediate substrate at its outer periphery. The width of the electrolyte layer is less than or equal to the maximum width of the cavity formed between at least one of the first member and the second member and the unit cell. The electrolyte layer has a flat plate shape with no bends in its cross-sectional shape, and its end face is open to the cavity. The first surface of the electrolyte layer is in contact with only the anode electrode layer, and the second surface of the electrolyte layer opposite to the first surface is in contact with only the cathode electrode layer. A fuel cell characterized in that the anode electrode layer is in contact with the entire surface of a first surface of the electrolyte layer, and the cathode electrode layer is in contact with the entire surface of a second surface of the electrolyte layer opposite to the first surface.

2. A fuel cell according to claim 1, characterized in that the electrolyte layer is yttria-stabilized zirconia.

3. A fuel cell according to claim 1, characterized in that a cell support portion is provided so as to divide the through-hole of the intermediate substrate.

4. A fuel cell according to claim 1, characterized in that a plurality of the unit cells are mounted on one intermediate substrate.

5. A fuel cell according to claim 1, characterized in that the cavity is formed both between the first member and the unit cell, and between the second member and the unit cell.

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