Fuel cell

Abstract

The purpose of the present invention is to provide a fuel cell stack which has high output and high reliability by excluding divided cells that adversely affect the power generation output in cases where divided cells are constituted by dividing a fuel cell on a substrate. A fuel cell according to the present invention comprises a porous substrate, a first electrode layer, a solid electrolyte layer, and a second electrode layer. At least one of the first electrode layer and the second electrode layer is divided so as to form divided cells, and at least some of the divided cells each have an insulating buffer part that insulates the electrode layer from a collector (see Fig. 6).

Description

fuel cell

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

[0002] A solid oxide fuel cell (SOFC) has a structure in which an electrolyte layer is sandwiched between an anode electrode layer and a cathode electrode layer. For example, a fuel gas such as hydrogen is supplied to the anode side, and an oxygen-containing gas such as air is supplied to the cathode side, thereby generating electricity.

[0003] The following Patent Document 1 aims to "suppress variations in the amount of electrochemical reaction in the in-plane direction of a unit cell," and describes a technology in which "an electrochemical reaction unit includes a unit cell and an air electrode-side current collecting member disposed on the air electrode side of the unit cell and electrically connected to the surface of the air electrode, the air electrode having a rectangular shape as viewed in a first direction, with a first side of the rectangle positioned closest to a supply port for gas supplied to the air electrode and a second side positioned closest to a supply port for gas supplied to the fuel electrode. As viewed in the first direction, the surface of the air electrode is divided into four equal parts, and a specific connection area where the air electrode and the air electrode-side current collecting member are electrically connected in a specific division including a first corner is smaller than the average of three other connection areas where the air electrode and the air electrode-side current collecting member are electrically connected in each of three other divisions" (see Abstract).

[0004] The fuel cell disclosed in Patent Document 1 has a laminated structure of a fuel electrode, an electrolyte membrane, and an air electrode, and a divided current collecting member is in contact with the surface on the air electrode side. The fuel cell in this document uses this structure to change the area average of the air electrode-side current collecting member, which also means that the distribution of the electrochemical reaction rate in the fuel cell can be changed. In this document, the area average of the air electrode-side current collecting member closest to both the fuel gas and the oxidant gas (hereinafter collectively referred to as the medium gas) is reduced to suppress variation in the electrochemical reaction rate in the in-plane direction of the fuel cell.

[0005] Patent Document 2 describes a technology that includes "a first fuel cell having a first anode electrode and a second cathode electrode on both sides of a first electrolyte, each of which constitutes a plurality of electrode regions divided by dividing grooves, with a plurality of unit cells being formed by a stack structure including one electrode region on one side of each of the two sides and another electrode region on the other side opposite the one electrode region, and a first electrolyte, and these unit cells are connected in series to form a plurality of first fuel cells; a second fuel cell having a second anode electrode and a second cathode electrode on both sides of a second electrolyte, and a second conductive portion that penetrates the second electrolyte to short-circuit between the second anode electrode and the second cathode electrode; and non-conductive separators that separate the plurality of first fuel cells and the plurality of second fuel cells" (see abstract). In this document, the first fuel cell is heated by the heat of an electrochemical reaction in the second fuel cell and Joule heat due to electric current, thereby mitigating the temperature distribution within the stack.

[0006] Patent Document 3 describes the following technology (see Abstract): "The present invention aims to provide a fuel cell system with improved reliability by accurately detecting a leak of anode gas or cathode gas. The fuel cell according to the present invention has a first electrode, an electrolyte membrane, and a second electrode stacked on a support substrate, and at least one of the first electrode, the electrolyte membrane, and the second electrode is electrically separated by an insulating member to form a first region and a second region, and the insulating member is positioned so as not to overlap with an opening in the support substrate (see Figure 3)."

[0007] JP 2019-003793 A, WO 2021 / 095340, WO 2020 / 217467

[0008] To further miniaturize and increase the power output of fuel cell stacks, it is necessary to improve the power density per stack layer. Thinner electrolytes are a promising approach to this end. However, thinning the electrolyte can lead to localized, extremely thin areas (defects) due to the roughness of the anode and the unevenness of the electrolyte film thickness. These defects can easily cause short circuits between the anode and cathode when a voltage is applied between them.

[0009] In the method described in Patent Document 1, neither the fuel electrode nor the air electrode of the fuel cell is separated, and short cells have to be discarded, which raises concerns about increased manufacturing costs and hinders efforts to increase the output of fuel cell stacks.

[0010] In the method described in Patent Document 2, both the fuel electrode and the air electrode are separated, and multiple unit cells exist within a single fuel cell. However, the unit cells are connected via conductive parts inherent in the electrolyte membrane. This document does not mention what to do if a short cell occurs due to a defect in the manufacturing process, and therefore, if a short cell occurs, the entire fuel cell must be discarded. This raises concerns about increased manufacturing costs and hinders the development of higher-output fuel cell stacks.

[0011] The method described in Patent Document 3 detects the gas pressure inside a fuel cell stack during power generation, and if the gas pressure becomes high, bypasses the gas to protect the fuel cell cells. This document does not describe initial short cells, and therefore, the occurrence of short cells will hinder the fuel cell stack from achieving high output.

[0012] The present invention has been made in view of the above-mentioned problems, and aims to provide a fuel cell stack that has high output and high reliability by excluding divided cells that have a negative effect on power generation output when divided cells are constructed by dividing a fuel cell unit on a substrate.

[0013] A fuel cell according to the present invention comprises a porous substrate, a first electrode layer, a solid electrolyte layer, and a second electrode layer, wherein at least one of the first electrode layer and the second electrode layer is divided to form divided cells, and at least some of the divided cells have insulating buffer portions that insulate the electrode layer from current collectors.

[0014] According to the fuel cell of the present invention, when divided cells are constructed by dividing fuel cells on a substrate, by eliminating divided cells that have a negative effect on power output, it is possible to provide a fuel cell stack with high output and high reliability. Problems, configurations, and effects other than those described above will become clear from the description of the embodiments below.

[0015] 1 is a side cross-sectional view showing a general structure of a fuel cell 1 having a solid electrolyte layer. FIG. 1 is a plan view of the fuel cell 1. FIG. 2 is a plan view showing the effect of electrode division. FIG. 3 is a graph showing a method for determining the film thickness of the electrolyte layer 4 of the fuel cell 1 and the length of one side of a divided cell. FIG. 4 is a graph showing the maximum value of the occupancy rate of non-defective parts of the fuel cell 1 and the length of one side of the divided cell at that time. FIG. 5 is a schematic diagram showing an example of the configuration of a fuel cell stack 300 according to embodiment 1. FIG. 6 is a cross-sectional view taken along the fuel flow path 318. FIG. 7 is a cross-sectional view taken along line A-A in FIGS. 6 to 7. FIG. 8 is an equivalent circuit diagram of the fuel cell stack 300 shown in FIGS. 6 to 8. FIG. 9 is a diagram showing a procedure for determining non-defective cells 6a and short cells 6b. FIG. 10 is a side cross-sectional view showing the configuration of a fuel cell stack 300 according to embodiment 2. FIG. 11 is a cross-sectional view taken along line D-D in FIG. 11. FIG. 12 is a cross-sectional view showing an example of the configuration of a fuel cell stack 300 according to embodiment 3. FIG. 13 is a cross-sectional view taken along line E-E in FIG. 13. FIG. 14 is a cross-sectional view showing an example of the configuration of a fuel cell stack 300 according to embodiment 4. FIG. 15 is a cross-sectional view taken along line F-F in FIG. 15. FIG. 16 is a cross-sectional view showing an example of the configuration of a fuel cell stack 300 according to embodiment 5. 19 shows an equivalent circuit diagram of the fuel cell stack 300 shown in FIG. 17. FIG. 19 is a side cross-sectional view showing an example of the configuration of the fuel cell stack 300 according to embodiment 6. FIG. 19 is a cross-sectional view taken along line G-G in FIG. 19. FIG. 19 is a side cross-sectional view showing an example of the configuration of the fuel cell stack 300 according to embodiment 7. FIG. 19 is a cross-sectional view taken along line H-H. FIG. 19 is a plan view showing a fuel cell 1 used in the fuel cell stack 300. FIG. 19 is a side cross-sectional view showing an example of the configuration of the fuel cell stack 300 according to embodiment 8. FIG. 19 is a schematic view showing an example of the configuration of the fuel cell stack 300 according to embodiment 9.

[0016] First Embodiment FIG. 1 is a side cross-sectional view showing a typical structure of a fuel cell 1 equipped with a solid electrolyte layer. FIG. 2 is a plan view of the fuel cell 1. A first electrode layer 3, an electrolyte layer 4, and a second electrode layer 5 are formed on a porous substrate 2 that is permeable to a carrier gas. The second electrode layer 5 is divided into multiple parts, thereby forming multiple divided cells within the fuel cell 1. For example, in a probe test, a voltage is applied between the first electrode layer 3 and the second electrode layer 5 of a divided cell, and the leakage current is measured. If a defect 11 is present in a divided cell, the leakage current increases, resulting in a short cell 6b that adversely affects power generation output. This process allows divided cells (good cells 6a) with leakage currents smaller than a threshold (defective cells 6a) to be selected and mounted. In FIGS. 1 and 2, the defects 11 are enlarged for emphasis; however, in reality, they are minute and many are indistinguishable by visual inspection.

[0017] The porous substrate 2 has through-holes that allow a carrier gas to pass through, and serves to increase the strength of the fuel cell membrane electrode assembly. Examples of the porous substrate 2 include a metal substrate with through-holes or an anodized alumina (hereinafter referred to as AAO (anodic aluminum oxide)) substrate. The AAO substrate can be made conductive by forming a film of platinum (Pt) or the like on the wall surfaces of the through-holes by chemical vapor deposition (CVD) or atomic layer deposition (ALD).

[0018] The first electrode layer 3 is formed by a film formation process such as sputtering, and is preferably porous to allow diffusion of the carrier gas that has permeated the porous substrate 2, but a dense thin film may also be used to reduce in-plane resistance. Materials for supplying fuel gas to the first electrode layer 3 to function as an anode layer include Pt, a cermet of Pt and gadolinium-doped ceria (GDC), nickel (Ni), and a cermet of Ni and GDC. To prevent the diffused fuel gas and oxidant gas from mixing, the outer periphery of the porous substrate 2 may be sealed with an electrolyte layer 4 without forming the first electrode layer 3.

[0019] The electrolyte layer 4 functions to conduct oxygen ions supplied from the air electrode during the reduction reaction of the oxidant gas to the fuel electrode. Typical materials include YSZ (yttria-stabilized zirconia), ScSZ (scandia-stabilized zirconia), and CaSZ (calcia-stabilized zirconia). The electrolyte layer 4 is formed, for example, by sputtering or ALD, and its thickness is thinner than that of conventional sintered cells, e.g., 1 μm or less. The thinner the electrolyte layer 4, the greater its ionic conductivity and the higher the cell's output power density. However, it also increases the likelihood of short-circuiting, where the first electrode layer 3 and the second electrode layer 5 come into contact through minute defects 11. Furthermore, if the electrolyte layer 4 is too thin compared to the pore size of the porous substrate 2, the pores cannot be blocked, resulting in short-circuiting. If a short-circuiting occurs, the potential cannot be extracted externally, resulting in power generation failure and a decrease in output power density. Therefore, the electrode area and thickness are determined based on the defect density of the electrolyte, etc. The determination method will be described later. The probability of the defects 11 causing the short circuit failure described above occurring increases when the electrolyte resistance is thinned to the minimum allowable value for the pore diameter of the substrate and the surface irregularities of the layer below the electrolyte layer 4 .

[0020] Dividing the second electrode layer 5 and insulating the divided cells from each other on the fuel cell 1 makes it possible to reduce the electrode area that becomes unable to generate electricity due to defects 11. The divided cells configured in the fuel cell 1 are formed into good cells 6a that have not experienced a short circuit defect and short cells 6b that have experienced a short circuit defect. Although the second electrode layer 5 is divided in FIGS. 1 and 2, it is also possible to divide the first electrode layer 3. In this case, for example, one method is to leave the electrolyte layer 4 uncoated on part of the divided electrode, leaving the current collection area exposed.

[0021] 3 is a plan view showing the effect of dividing the electrode. When the electrolyte layer 4 is sufficiently thick compared to the porous substrate 2, the probability of a short circuit occurring is low. However, when the electrolyte layer 4 is thinned, localized extremely thin areas (defects) occur due to the roughness of the anode and the distribution of the electrolyte film thickness, making it more likely that a short circuit will occur when a voltage is generated between the anode and cathode. By dividing the electrode, the area in which power generation is disabled due to a single defect 11 can be reduced.

[0022] 4 and 5 are graphs showing a method for determining the length of one side of a divided cell of the fuel cell 1. As mentioned above, the thinner the electrolyte layer 4, the more likely it is that a short circuit will occur, and the larger the area of ​​the electrode, the larger the area that will become unable to generate electricity due to a single defect 11. FIG. 4 shows the length of one side of a divided cell that has the highest occupancy rate of non-defective parts of the fuel cell 1 for each defect density. It is assumed that one side of the fuel cell 1 is 10 cm, and the defect density is 0 / cm. ２ The case where the length of one side of the divided cell (square) is 10 cm represents the fuel cell 1 in an undivided state. Since gaps are provided between the divided cells to ensure insulation, the proportion of non-defective products decreases as the length of one side of the divided cells decreases. However, when the cells are not divided, the defect density is 0.01 / cm. ２ Even if the defect density is 0.1 cm, the occupancy rate of non-defective parts is 40% or less, whereas if the cell is divided into 0.1 cm sides, the occupancy rate is 90% or more. Therefore, dividing the cell and using only non-defective cells is advantageous for increasing output. Note that the gap here is assumed to be 0.01 cm to ensure insulation between the divided electrodes. The graph in Figure 5 shows this relationship, and for each defect density, there is an optimal value for the length of one side of the divided cell at which the occupancy rate of non-defective parts is at its maximum. For example, if the defect density of fuel cell 1 is 0.1 defects / cm, ２ In this case, if the cells are not divided, the non-defective part occupancy rate will be 5% or less, but by setting the length of one side of the divided cells to 0.4 cm, it is possible to obtain a non-defective part occupancy rate of 95% or more.

[0023] Fig. 6 is a schematic diagram showing an example of the configuration of a fuel cell stack 300 according to embodiment 1. Fig. 7 shows a cross-sectional view taken along a fuel flow channel 318.

[0024] The fuel cell stack 300 is used at temperatures of, for example, about 400 to 600° C. Therefore, the materials used in the fuel cell stack 300 must be heat resistant within the operating temperature range.

[0025] Each layer constituting the stack is constituted by a fuel cell 1, for example, as shown in FIG. 2. Of the divided electrodes of the second electrode layer 5 of the fuel cell 1, only the good cells 6a are coated with a conductive film 7. This conductive film 7 is made of a metal material such as silver (Ag) that has high electronic conductivity and does not oxidize in the air environment at the operating temperature (for example, about 400-600°C), or LSC ((La,Sr)CoO ３ By not forming the conductive film 7 on the short cells 6b, a gap 12 is formed between the cell upper current collector 305 and the short cells 6b, thereby providing electrical insulation between them.

[0026] The defects 11 in the electrolyte layer 4 are caused by the roughness of the fuel electrode and the film thickness distribution of the electrolyte, and occur in different locations for each fuel cell 1. Figure 6 shows that the locations of the defects 11 are different between the first and second layers, and indicates that even in such cases, it is possible to eliminate short cells 6b according to this embodiment.

[0027] The fuel cell 1 is bonded to a conductive substrate 301 having through-holes for the transmission of carrier gases by a substrate adhesive layer 302. The conductive substrate 301 can be formed of, for example, SUS (Steel Use Stainless Steel). The substrate adhesive layer 302 preferably has high electronic conductivity and is porous to allow gases to pass through, in order to electrically connect the porous substrate 2 and the conductive substrate 301. The substrate sealing layer 303 serves to prevent direct reaction between the fuel gas (FUEL) and air (oxidizer gas) (Air) in the substrate adhesive layer 302. For example, a metal paste with gas sealing properties, or a paste made of an alumina-based, silica-based, or zirconia-based material can be applied as the substrate adhesive layer 302.

[0028] In addition to the above-mentioned upper cell current collector 305, conductive film 7, fuel cell 1, substrate adhesive layer 302, substrate sealing layer 303, and conductive substrate 301, a cell gasket 308 that prevents leakage of the carrier gas and a lower cell current collector 304 that contacts the conductive substrate 301 form a unit stack 322. During power generation, a carrier gas is introduced into the cell fuel flow path 306 and the cell air flow path 307, and oxygen in the air (oxidant gas) is reduced to oxygen ions in the second electrode layer 5. These oxygen ions are then supplied to the first electrode layer 3 through the electrolyte layer 4. An electrochemical reaction occurs between the supplied oxygen ions and hydrogen in the fuel gas (FUEL), supplying electrons to the stack circuit and simultaneously generating water vapor. A mixture of fuel gas (FUEL) and water vapor is discharged from the cell fuel flow path 306.

[0029] 6 is formed by stacking any number of unit stacks 322, sandwiching them between a lower jig 323 consisting of a bottom jig 314, a lower gasket 310, and a lower separator 312, and an upper jig 324 consisting of a top jig 315, an upper gasket 311, and an upper separator 313, and compressing them with supports 316 and a clamping jig 317. To prevent mixing of fuel gas (FUEL) and air (oxidant gas) (Air), cell separators 309 are inserted between adjacent unit stacks 322. When the fuel cell stack 300 generates power, the fuel gas (FUEL) is supplied from the supply side of the fuel port 320, and the air (oxidant gas) (Air) is supplied from the supply side of the air port 321 to the fuel cell 1 through a fuel flow path 318 and an air flow path 319, respectively. The water vapor produced by the electrochemical reaction and the unconsumed fuel gas (FUEL) are discharged from the discharge side of the fuel port 320, and the air (oxidant gas) (Air) is discharged from the discharge side of the air port 321 (shown in FIG. 7).

[0030] Wiring can be connected to the lower jig 323 and upper jig 324 of the fuel cell stack 300, allowing the output of the stack to be taken out to the outside. When the fuel cell stack 300 generates power, current flows from the upper jig 324 through any number of unit stacks 322, and then from the lowest unit stack 322 to the lower jig 323.

[0031] 6, the cell fuel flow path 306 and the cell air flow path 307 are perpendicular to each other, but it is also possible to make them parallel by, for example, arranging the fuel flow path 318 and the air flow path 319 adjacent to each other. This results in a more complicated structure than a cross-flow configuration, but it makes it easier to exhaust the heat generated by the oxidation-reduction reaction, and it is possible to reduce the temperature distribution within the stack.

[0032] The cell part gasket 308, lower gasket 310, and upper gasket 311 (hereinafter, simply referred to as gaskets will be a general term for all of these) that make up the fuel cell stack 300 in Figure 6 need to be insulators so that they can be easily processed to form the fuel flow paths 318 and air flow paths 319, and so that the first electrode layer 3 and second electrode layer 5 of the same unit stack are not electrically connected. Materials that meet the above requirements include, for example, glass materials, ceramic materials, and vermiculite-based materials.

[0033] In Figure 6, the cell separator 309, lower separator 312, and upper separator 313 (hereinafter, simply referred to as separators) that make up the fuel cell stack 300 have a flat structure, but they can also be grooved to uniformly diffuse the carrier gas. The separators also have holes to allow the carrier gas to pass through. The fuel flow path 318 and the air flow path 319 are formed by gaskets and holes in the separators. The separators can be made of, for example, SUS (Steel Use Stainless Steel) or an insulator with a metal-plated surface.

[0034] Fig. 7 is a schematic diagram showing an example of the configuration of the fuel cell stack 300. Fig. 7 shows a cross-sectional view along the air flow path 319. While Fig. 6 is a cross-sectional view taken along the XZ plane, Fig. 7 is a cross-sectional view taken along the YZ plane.

[0035] 8 is a cross-sectional view taken along line A-A in FIGS. 6 and 7. Of the divided electrodes of the second electrode layer 5, a conductive film 7 is formed only on the surface of the good cells 6a. The conductive film 7 formed on the good cells 6a is in contact with the upper cell current collector 305. The cross-sectional view taken along line B-B in FIG. 8 is FIG. 6, and the cross-sectional view taken along line C-C is FIG. 7.

[0036] A fuel flow path 318 and an air flow path 319 are formed on the outer periphery of the cell portion gasket 308 and the conductive substrate 301, and during power generation, a medium gas is supplied to the fuel cell 1 via these flow paths. Since Fig. 8 shows the air electrode side, notches connecting the air flow path 319 and the cell portion air flow path 307 (rectangular portions with arrows located on the top and bottom sides of the conductive substrate 301 in Fig. 8) are formed in the cell portion gasket 308. The notches connecting the fuel flow path 318 and the cell portion fuel flow path 306 are formed on the fuel electrode side and are indicated by dashed lines in the figure (rectangular portions with arrows located on the left and right sides of the conductive substrate 301 in Fig. 8).

[0037] Figure 9 shows an equivalent circuit diagram of the fuel cell stack 300 shown in Figures 6 to 8. The fuel cell 1 is connected to the cell lower current collector 304 via the conductive substrate 301, and to the cell upper current collector 305 via the conductive film 7. The divided electrodes of the unit stack 322 are connected in parallel, and if a short cell 6b is connected, all divided cells of the unit stack 322 will be unable to generate electricity. Therefore, as shown in Figure 8, the short cell 6b is electrically insulated. The unit stacks 322 are connected in series.

[0038] Figure 10 shows the procedure for determining whether a cell 6a is a good cell or a short cell 6b. A first electrode layer 3, an electrolyte layer 4, and a second electrode layer 5 are formed on a porous substrate 2. The second electrode layer 5 is formed in segments as shown in Figure 1. For each segmented electrode, the leakage current between the first electrode layer 3 and the second electrode layer 5 is measured. If the measured leakage current exceeds the determination threshold, a gap is provided between that segmented electrode and the upper cell current collector 305 to insulate them. If the leakage current is below the determination threshold, the segmented electrode and the upper cell current collector 305 are connected by a conductive film 7.

[0039] <Embodiment 2> Figure 11 is a side view showing the configuration of a fuel cell stack 300 according to Embodiment 2 of the present invention. Figure 11 is a cross-sectional view taken along the fuel flow path 318. Figure 12 is a cross-sectional view taken along line D-D in Figure 11. In Embodiment 1, the conductive film 7 is formed only on the second electrode layer 5 of the good cells 6a. Alternatively, as shown in Figures 11 and 12, the conductive film 7 can be formed on the edge of the good cells 6a, so that the conductive film 7 is in contact with both the second electrode layer and the electrolyte layer 4. The remaining configuration is the same as in Embodiment 1.

[0040] The conductive film 7 is formed so as to connect the sides of adjacent divided electrodes, which are the closest to each other, among the divided electrodes formed by the second electrode layer 5, and is also in contact with the upper cell current collector 305. On the other hand, if one of the adjacent divided electrodes is a short cell 6b, the conductive film 7 is not formed, thereby introducing a gap 12 and providing insulation. In this embodiment, when the impact of output loss due to oxygen reduction activity is greater than the impact of output loss due to in-plane resistance, the contact area between the second electrode layer 5 and the cell portion air flow path 307 can be increased, thereby improving the output power density.

[0041] <Embodiment 3> In Embodiments 1 and 2, in order to insulate the short cells 6b, it is possible to avoid forming the conductive film 7 between the short cells 6b and the upper cell current collector 305. However, even if the short cells 6b are insulated during packaging, deterioration due to continuous operation can weaken the adhesion to the separator, and there is a risk that the second electrode layer 5 of the short cells 6b may come into contact with the upper cell current collector 305. Therefore, in Embodiment 3 of the present invention, a configuration example that achieves selective insulation will be described.

[0042] Fig. 13 is a side cross-sectional view showing an example of the configuration of a fuel cell stack 300 according to embodiment 3. Fig. 13 is a cross-sectional view taken along the fuel flow path 318. Fig. 14 is a cross-sectional view taken along line E-E in Fig. 13. The fuel cell 1 and the medium gas flow path structure are basically the same as those described in embodiment 1. The differences will be explained below.

[0043] In the third embodiment, the upper cell current collector 305 is cut out at a location above the short cells 6b, thereby introducing a void 12 and selectively insulating the short cells 6b. Methods for cutting out the current collector include die punching and laser processing. To address random short circuit defects, the upper cell current collector 305 must be individually processed to fit the substrate. However, since the processing involves removing the current collector above the short cells 6b, more reliable insulation is achieved compared to a configuration in which a conductive buffer layer is added. Additionally, the fewer the short cells 6b, the fewer areas that need to be processed, which has the advantage of improving manufacturing costs and throughput.

[0044] <Embodiment 4> In embodiment 3, by removing a portion of the upper cell current collector 305, more reliable insulation is provided than in embodiments 1 and 2. Embodiment 4 of the present invention achieves the same requirements with a different configuration.

[0045] Fig. 15 is a side cross-sectional view showing an example of the configuration of a fuel cell stack 300 according to embodiment 4. Fig. 15 is a cross-sectional view taken along the fuel flow path 318. Fig. 16 is a cross-sectional view taken along line F-F in Fig. 15. The fuel cell 1 and the medium gas flow path structure are basically the same as those described in embodiment 1. The differences will be described below.

[0046] In the fourth embodiment, in addition to the conductive film 7, an insulating film 8 is introduced as a buffer layer that contacts both the second electrode layer 5 and the upper current collector 305. The insulating film 8 can be formed by applying a paste of an alumina-based, silica-based, or zirconia-based material, or by applying a gasket paste whose main component is graphite or mica.

[0047] Because the insulating film 8 has the same thickness as the conductive film 7, pressure in the Z direction is applied evenly to the good cells 6a and the short cells 6b. This prevents pressure from being concentrated on specific cells on the substrate. This is particularly useful when the porous substrate of the fuel cell 1 is prone to cracking or when short cells 6b are concentrated in a localized area, as in the upper right part of Figure 16.

[0048] The porous substrate 2 may be smoothed by CMP (Chemical Mechanical Polishing) or the like to reduce surface irregularities, but depending on the processing conditions, there is a possibility that short cells 6b may be concentrated in a local area. In this case, if the short cells 6b are insulated by voids as in embodiment 1, there is a risk that good cells 6a adjacent to the short cells 6b will not be able to withstand the pressure and will be damaged. The insulating film 8 not only insulates the short cells 6b but also plays a role in evenly distributing the pressure applied to the fuel cell 1 and increasing durability.

[0049] The following effect can be expected when gasket paste is used as the insulating film 8. Although the short cells 6b cannot extract electromotive force to the outside, they consume the carrier gas through electrochemical reactions, which reduces the carrier gas supplied to the other divided cells and reduces the power generation performance of the stack. By covering the second electrode layer 5 of the short cells 6b with the insulating film 8, which has high insulating and gas-tight properties, the consumption of the carrier gas by the short cells 6b can be prevented, thereby improving fuel utilization efficiency and output power density.

[0050] The insulator film 8 and the upper cell current collector 305 may or may not be mechanically connected. In either case, the insulator film 8 acts to reduce the possibility of current flow between a defective cell and the upper cell current collector 305.

[0051] <Fifth Embodiment> Fig. 17 is a side cross-sectional view showing an example of the configuration of a fuel cell stack 300 according to a fifth embodiment of the present invention. Fig. 17 is a cross-sectional view taken along a fuel flow path 318. The configuration of the fuel cell 1 is basically the same as that described in the first embodiment. The selective current collection method is the formation of an insulating film 8, as in the fourth embodiment, but the format of the other embodiments can also be used. The differences will be described below.

[0052] In embodiment 5, a structure in which two fuel cells 1 are arranged with their second electrode layers 5 facing each other is called a unit stack 322. The opposing fuel cells 1 of a unit stack 322 share a cell section air flow path 307, and the cell section fuel flow path 306 is shared by unit stacks 322 adjacent in the Z direction. Both of the two fuel cells 1 included in a unit stack 322 are in contact with a current collector or interconnector 327 via the second electrode layer 5, meaning that all of the divided cells in the stack are connected in parallel. The lower conductive substrate 301 of the unit stack 322 is bonded to the lower separator 312 or the cell section separator 309 via an insulator layer 325, and the upper conductive substrate 301 is in contact with the cell section gasket 308 and the lower cell current collector 304 formed inside it. The unit stacks 322 are electrically connected in series via an inter-stack current collector 326. In other words, when the fuel cell stack 300 generates electricity, the current path flows through the top jig 315, the conductive substrate 301, the substrate adhesive layer 302, the fuel cell 1, the upper cell current collector 305, and then to the adjacent cell separator 309 or the bottom jig 314.

[0053] In the first embodiment, 2N medium gas flow channels must be formed to stack N unit stacks, but in the fifth embodiment, the number of medium gas flow channels required to stack the same number of unit stacks 322 can be reduced to N+1. Furthermore, since the unit stack 322 of the fifth embodiment includes two fuel cell cells 1, the number of unit stacks required to achieve the same power generation area can be reduced to N / 2. Due to these effects, the present embodiment achieves an improved output power density per volume compared to the first embodiment.

[0054] AAO, which can be used as a porous substrate for fuel cell 1, is known to undergo a phase transition when annealed at around 600°C, the operating temperature range of a fuel cell, causing the surface with large through-hole diameters to warp. This warping can cause cell damage when pressure is applied to the stack in the Z direction. Therefore, a unit stack 322 is formed so that one of the opposing fuel cell cells 1 contacts the back surface of the AAO and the other contacts the front surface of the AAO, and a current collector or interconnector 327 (conductive connecting member) is provided between the fuel cell cells 1. This prevents pressure from concentrating on the warped parts, improving mechanical strength.

[0055] Figure 18 shows an equivalent circuit diagram of the fuel cell stack 300 shown in Figure 17. The fuel cell cells 1 in a unit stack 322 are connected so that their second electrode layers 5 face each other across the upper cell current collector 305, and the conductive substrates 301 of the two fuel cell cells 1 are connected by the lower cell current collector 304. Therefore, the divided electrode layers of the two fuel cell cells 1 in a unit stack 322 are all connected in parallel. Each unit stack 322 is connected in series.

[0056] Sixth Embodiment Fig. 19 is a side cross-sectional view showing an example of the configuration of a fuel cell stack 300 according to a sixth embodiment of the present invention. Fig. 19 is a cross-sectional view taken along the fuel flow path 318. Fig. 20 is a cross-sectional view taken along line G-G in Fig. 19. The fuel cell 1 and the medium gas flow path structure are basically the same as those described in the first embodiment. The differences will be described below.

[0057] In the sixth embodiment, four fuel cell units 1 are used in one unit stack 322. It is also possible to use a greater or lesser number of fuel cell units 1 in the unit stack 322. Configuring the unit stack 322 from a plurality of fuel cell units 1 means that the area of ​​the porous substrate per cell can be reduced.

[0058] As mentioned above, some porous substrates warp within the operating temperature range. As the area of ​​the substrate decreases, the flatness decreases and the resistance to pressure increases, so using multiple fuel cells in a unit stack 322 helps prevent cell damage. Furthermore, in this embodiment, even if short cells 6b are densely packed in a local area of ​​a fuel cell 1, it is possible to arrange the fuel cells 1 so that the pressure is dispersed within the unit stack 322, as shown in Figure 20.

[0059] 19 and 20, the conductive film 7 and the gap 12 are used as a selective current collection method, but other embodiments may also be used. Also, the lower cell current collector 304 and the upper cell current collector 305 may be separated so that they are present only at the top of each fuel cell 1.

[0060] Seventh Embodiment In the above embodiments, the conductive film 7 is used exclusively as the current collection method on the air electrode side. However, this method inevitably results in pressure being applied to the fuel cell 1 in the Z direction to prevent gas leakage. The pressure distribution in the fuel cell 1 can be alleviated by forming an insulating film 8 on the surface of the short cell 6b as well. However, this method cannot address the case where, for example, the porous substrate 2 is made thinner to increase the permeability of the fuel gas (FUEL), resulting in the porous substrate 2 being deformed by the pressure required for gas sealing. Therefore, in a seventh embodiment of the present invention, a current collection method other than the conductive film 7 will be described.

[0061] Fig. 21 is a side cross-sectional view showing an example of the configuration of a fuel cell stack 300 according to embodiment 7. Fig. 21 is a cross-sectional view taken along the fuel flow path 318. Fig. 22 is a cross-sectional view taken along line H-H. The fuel cell 1 and the medium gas flow path structure are basically the same as those described in embodiment 1. The differences will be explained below.

[0062] In the seventh embodiment, the fuel cell 1 is mounted so that the conductive substrate 301 and the electrolyte layer 4 are in contact with each other, and a gas seal layer 9 is used for adhesion. The first electrode layer 3 is connected to the separator via the porous substrate 2 and the lower cell current collector 304, and the second electrode layer 5 is connected to the conductive substrate 301 via a conductive wire 10. The conductive wire 10 may be, for example, a gold (Au) conductor. While one conductive wire 10 is connected to each good cell 6a in FIGS. 21 and 22, multiple conductive wires can also be connected to reduce parasitic resistance. By connecting the conductive wire 10 only to the good cells 6a and leaving the short cells 6b without a conductive wire 10, forming a gap 12, a selective current collection method is possible. The conductive substrate 301 is connected to the separator via the upper cell current collector 305.

[0063] In embodiment 7, the upper cell current collector 305, which is the electrical contact between the unit stack 322 and the upper separator 313, is not in contact with the fuel cell 1, so pressure is not applied to the cell from above. Furthermore, while the porous substrate 2 and the lower cell current collector 304 are in contact in FIG. 21 , for example, by using an insulating substrate with conductive patterns formed on both the front and back sides as the conductive substrate 301, it is possible to electrically connect the second electrode layer 5 to the front surface of the conductive substrate 301, and also to electrically connect the first electrode layer 3 to the back surface of the conductive substrate 301. In this case, pressure is not applied to the fuel cell 1, so damage to the fuel cell 1 due to stack clamping does not occur. Additionally, increasing the stack clamping pressure enhances gas sealing and improves fuel utilization efficiency.

[0064] In this embodiment, the conductive wire 10 is used for electrical connection between the second electrode layer 5 and the conductive substrate 301, but other conductive leads may be used instead of or in combination with the conductive wire 10. For example, a conductive ribbon may be used.

[0065] Eighth Embodiment Because short cells 6b occur with a certain probability, there is a certain degree of variation in the effective power generation area of ​​the fuel cell 1. In this case, if there is a large difference in the total effective power generation area of ​​each unit stack 322 that makes up the fuel cell stack 300, the current density flowing through the good cells 6a will also vary. However, since the current density required for the fuel cell 1 to achieve the highest output power density is predetermined by its internal resistance, the greater the variation in current density, the fewer the number of fuel cell cells 1 that generate power under optimal conditions, resulting in a decrease in the output of the fuel cell stack 300. Therefore, in an eighth embodiment of the present invention, a method is provided for reducing the difference in output power density between each unit stack 322 and suppressing the decrease in output of the fuel cell stack 300.

[0066] 23 is a plan view showing a fuel cell 1 used in a fuel cell stack 300. In the ninth embodiment, four fuel cell cells 1, each with an effective power generation area of ​​85% to 99%, are used in one fuel cell stack 300, but the number of fuel cell cells 1 and the effective power generation area are not limited to these values. The selective current collection method uses a conductive film 7 and an insulating film 8, but other insulation methods can also be used.

[0067] Fig. 24 is a side cross-sectional view showing an example of the configuration of a fuel cell stack 300 according to embodiment 8. Fig. 24 is a cross-sectional view taken along a fuel flow path 318. The carrier gas flow path structure is basically the same as that described in embodiment 1. Differences will be described below.

[0068] In embodiment 8, the fuel cells 1 are mounted so that the total effective power generation area of ​​each unit stack 322 constituting the fuel cell stack 300 is the same. When the output power density of each fuel cell 1 is the same, the total output power density of the unit stacks 322 is proportional to the effective power generation area. Therefore, by making the effective power generation area of ​​each unit stack 322 the same, the influence of differences in output power density between the fuel cell cells 1 is reduced, and each fuel cell 1 can generate power at its maximum output power density. In addition, suppressing variations in output power density also leads to suppressing differences in the rate of deterioration between the unit stacks 322 due to power generation, and therefore it is also possible to improve the long-term stability of the fuel cell stack 300.

[0069] In embodiment 8, an example in which the effective power generation areas of the unit stacks 322 can be considered to be uniform is when the difference between the effective power generation areas of the unit stacks 322 and the average value is less than ±19.5%. For example, if two randomly selected fuel cell units 1 each having an average effective power generation area of ​​80% are used to form a unit stack 322, the variation in the effective power generation area that includes 99.7% of the unit stacks 322 will be ±19.5%. Therefore, if the difference between the effective power generation areas of the unit stacks 322 and the average value is less than ±19.5%, it can be said that the effective power generation areas of these unit stacks 322 are uniform. Similarly, if the proportion of defective cells (i.e., insulating buffer portions) between the unit stacks 322 is less than ±19.5%, the effective power generation areas of the unit stacks 322 can be considered to be uniform.

[0070] In the eighth embodiment, another example of how to arrange the fuel cells 1 used in the fuel cell stack 300 is to arrange the fuel cells 1 in descending or ascending order of effective power generation area, and after a finite number of rearrangements, assemble them into the unit stack 322 in that order. The finite number of rearrangements is performed so as to minimize the difference in effective power generation area between the unit stacks 322. For example, when attempting to form the fuel cell stack 300 by stacking two unit stacks 322 each using two fuel cells 1, assume that the effective power generation areas of the fuel cells 1 are 80%, 70%, 90%, and 60%. In this case, by first arranging the fuel cells 1 in the order of 60%, 70%, 80%, and 90%, and then rearranging them in the order of 60%, 90%, 80%, and 70%, the difference in effective power generation area between the layers can be reduced. The number of rearrangements does not necessarily have to be the number required to minimize the difference in effective power generation area; it is determined based on the number of fuel cells 1 to be assembled into the fuel cell stack 300 and the allowable output reduction. By using this method, the difference in power density between the unit stacks 322 can be reduced more easily than by calculating the variation in the difference in effective power generating area.

[0071] Ninth Embodiment In the above embodiments, a method for improving the output power density when the fuel cell stack 300 is only performing power generation has been provided. On the other hand, the fuel cell 1 can generate hydrogen by supplying water vapor instead of hydrogen to the fuel electrode side and applying voltage. Therefore, a ninth embodiment of the present invention provides a method for suppressing a decrease in output when the fuel cell stack 300 is used as a device with both power generation and hydrogen generation functions, or a decrease in the amount of hydrogen generated when the fuel cell stack 300 is used as a hydrogen generation device with only a hydrogen generation function.

[0072] 25 is a schematic diagram showing an example of the configuration of a fuel cell stack 300 according to embodiment 9, and is a cross-sectional view taken along a fuel flow path 318. The fuel cell 1 and the medium gas flow path structure are basically the same as those described in embodiment 1. Differences will be described below.

[0073] In this embodiment, water vapor is supplied to the fuel flow channel 318 instead of hydrogen. It is desirable that the temperature of the water vapor is raised to near the operating temperature. The water vapor is supplied from the fuel flow channel 318 to the cell fuel flow channel 306, passes through the conductive substrate 301 and the porous substrate 2, and reaches the first electrode layer 3. Electrons are supplied to the first electrode layer 3 from an external voltage, and the water vapor is reduced to hydrogen and O. ２－ The hydrogen and unreduced water vapor flow downstream of the cell fuel flow path 306 and are discharged from the other fuel flow path 318. ２－ passes through the electrolyte layer 4 and becomes oxygen in the second electrode layer 5. Note that, unlike during power generation, oxygen is not consumed in the second electrode layer during hydrogen generation, so the air flow path 319 is open to the atmosphere.

[0074] If the short cell 6b is electrically connected during hydrogen generation, the electrons supplied by the applied voltage will not be used to reduce hydrogen and will instead flow to the second electrode layer 5, so a selective insulating structure is necessary, just as during power generation.

[0075] In the ninth embodiment, a conductive film 7 is used as a selective current collection method, and an insulating film 8 is used as a buffer portion. While other selective current collection methods are possible, an insulating film 8 with gas sealing properties is suitable for insulating the short cells 6b. The occurrence of short cells 6b occurs when the electrolyte layer 4 is not sufficiently dense, causing contact between the two electrodes, and there is a high possibility that the gas sealing properties are also reduced. However, if atmospheric oxygen and generated hydrogen react at defective portions of the electrolyte layer 4 at the operating temperature range, this could lead to damage to the fuel cell 1. A similar phenomenon can occur during power generation, but the hydrogen concentration is higher during generation than during power generation, when hydrogen is consumed by the first electrode layer 3, making such damage more likely. Therefore, using an insulating film 8 for insulation improves the reliability of the fuel cell stack 300 when used as a reversible device for power generation and hydrogen production.

[0076] <Regarding Modifications of the Present Invention> The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0077] In the drawings used to explain the present invention, when similar elements are present in multiple locations in the same drawing, only some of the elements may be indicated by numerals. This does not mean that elements with and without numerals are different, but rather that elements that are depicted in the same way refer to similar elements.

[0078] REFERENCE SIGNS LIST 1 fuel cell, 2 porous substrate, 3 first electrode layer, 4 electrolyte layer, 5 second electrode layer, 6a good cell, 6b short cell, 7 conductive film, 8 insulator film, 10 conductive wire, 11 defect, 12 void, 300 fuel cell stack, 301 conductive substrate, 302 substrate adhesive layer, 303 substrate seal layer, 304 lower cell current collector, 305 upper cell current collector, 306 cell fuel flow path, 307 cell air flow path, 308 cell gasket, 309 cell separator, 310 lower gasket, 311 upper gasket, 312 lower separator, 313 upper separator, 314 bottom jig, 315 top jig, 316 support, 317 tightening jig, 318 fuel flow path, 319 air flow path, 320 Fuel port, 321 air port, 322 unit stack, 323 lower jig, 324 upper jig, 325 insulator layer, 326 inter-stack current collector, 327 current collector or interconnector

Claims

1. A fuel cell comprising: a fuel cell; and a current collector that collects output power from the fuel cell, wherein the fuel cell comprises: a porous substrate that is permeable to a carrier gas; a first electrode layer adjacent to the porous substrate; a solid electrolyte layer adjacent to the first electrode layer; and a second electrode layer adjacent to the solid electrolyte layer, wherein at least one of the first electrode layer and the second electrode layer is divided into a plurality of pieces, thereby dividing the fuel cell into a plurality of divided cells, and at least some of the divided cells have an insulating buffer section that electrically insulates the current collector from the divided first electrode layer or the second electrode layer.

2. The fuel cell according to claim 1, wherein the thickness of said solid electrolyte layer is 1 μm or less.

3. The fuel cell according to claim 1, characterized in that, of the divided cells, the conducting divided cells that are not insulated from the current collector by the insulating buffer portion are electrically connected to the current collector by a conductive film.

4. The fuel cell according to claim 3, wherein the insulating buffer portion is constituted by a gap formed by not disposing the conductive film between the current collector and the divided cell.

5. The fuel cell according to claim 1, further comprising a conductive substrate in contact with the porous substrate, and the first electrode layer and the conductive substrate are electrically connected via the porous substrate.

6. The fuel cell according to claim 3, wherein the conductive film is arranged so as to electrically connect the solid electrolyte layer of the conductive dividing cell and the current collector.

7. The fuel cell according to claim 6, wherein the insulating division cells insulated from the current collector by the insulating buffer portion and the conductive division cells are arranged adjacent to each other on the first electrode layer or the second electrode layer, and the conductive film is arranged around those of the conductive division cells that are not adjacent to the insulating division cells, but is not arranged on those of the conductive division cells that are adjacent to the insulating division cells.

8. The fuel cell according to claim 1, characterized in that the divided cells include insulating divided cells that are insulated from the current collectors by the insulating buffer portions, and the insulating buffer portions are configured by having gaps that prevent the current collectors from contacting the insulating divided cells.

9. The fuel cell according to claim 1, wherein the insulating buffer portion is formed of an insulating film disposed between the current collector and the divided cell.

10. The fuel cell according to claim 9, wherein said insulating film has gas sealing properties.

11. The fuel cell according to claim 1, characterized in that the fuel cell comprises a unit stack made up of one or more of the fuel cell cells.

12. The fuel cell according to claim 11, characterized in that the unit stack includes a first cell and a second cell as the fuel cell cells, the unit stack is configured by arranging the first cell and the second cell so that the second electrode layers face each other, the fuel cell has a first flow path and a second flow path for transporting gas, the fuel cell has a first stack and a second stack as the unit stack, the first flow path is shared between the first cell and the second cell within the single unit stack, and the second flow path is shared between the first stack and the second stack.

13. The fuel cell according to claim 11, characterized in that the unit stack includes a first cell and a second cell as the fuel cell cells, and the unit stack has a connecting member disposed between the first cell and the second cell, electrically connecting the first cell and the second cell.

14. The fuel cell according to claim 1, characterized in that, of the divided cells, conductive divided cells that are not insulated from the current collector by the insulating buffer portion are electrically connected to the current collector by conductive leads.

15. The fuel cell according to claim 14, further comprising a conductive substrate in contact with the current collector, the current collector not being in mechanical contact with the fuel cell unit, and the conductive dividing cell being electrically connected to the conductive substrate via the conductive lead, thereby being electrically connected to the current collector.

16. The fuel cell according to claim 11, characterized in that the fuel cell has a plurality of the unit stacks, and the fuel cell cells in each unit stack are arranged in order from the fuel cell with the smallest effective power generation area to form each unit stack, and then the stack is formed by swapping the fuel cell cells between each unit stack.

17. The fuel cell according to claim 11, characterized in that the fuel cell has a plurality of the unit stacks, and the variation of the effective power generation area of ​​the fuel cell cells in each of the unit stacks from the average value is less than ±19.5%.

18. The fuel cell according to claim 11, characterized in that the fuel cell has a plurality of the unit stacks, and 99.7% or more of the effective power generation area of ​​the fuel cell cells in each of the unit stacks has a variation of less than ±19.5% from the average value of the effective power generation area.

19. The fuel cell according to claim 16, wherein the variation in the number of insulating buffer portions from the average value of each of the unit stacks is within ±19.5%.

20. The fuel cell according to claim 1, characterized in that the fuel cell is configured to generate hydrogen when water vapor is supplied to one of the first electrode layer or the second electrode layer and a voltage is applied to the other electrode layer so that the other electrode layer has a higher potential than the first electrode layer.

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