JP2008021533A - Fuel cell stack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the transfer of water from one electrode to the other electrode caused by temperature difference even if the temperature difference is produced between both electrodes in one fuel cell depending on stacking portions in a fuel cell stack formed by stacking fuel cells each having an electrolyte membrane and a membrane electrode assembly formed by arranging electrodes on both sides of the electrolyte membrane. <P>SOLUTION: The fuel cell stacks 1, 2 contain the fuel cell equipped with the membrane-electrode assembly having an electrolyte membrane having a certain thickness for making the permeation of water difficult, or a fuel cell in which the concentration difference of water between both electrodes is reduced by making water retention between the both electrodes of the membrane-electrode assembly different. These fuel cells are used in the positions of fuel cells 10A-10D. These fuel cells can suppress the transfer of water even if the temperature of electrodes at ends of the stacks 1, 2 become higher than that of electrode in the central part. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell stack in which fuel cells having a membrane-electrode assembly in which electrodes are formed on both surfaces of an electrolyte membrane are stacked.

  A fuel cell having a membrane-electrode assembly in which electrodes are formed on both surfaces of an electrolyte membrane is known. Some fuel cells of this type include a water retention layer between one electrode and an electrolyte membrane (see, for example, Patent Document 1). This fuel cell can store moisture by the water retention layer. Drying of the electrolyte membrane is prevented by providing moisture stored in the water retention layer to the electrolyte membrane.

JP 2005-19285 A

  By the way, a fuel cell stack in which fuel cells (cells) are stacked may have different temperature conditions depending on the stacking location. For example, the end part of the fuel cell stack is arranged with a good heat conductive member such as a metal current collector plate, end plate, etc., so it is easier to dissipate heat than the center part of the fuel cell stack and the temperature is lower. easy. Also, even in one fuel cell, the temperature of the fuel cell at the end of the stack is likely to be lower than that of the fuel cell at the center of the stack for the same reason, and the temperature between both electrodes Differences may occur. When a temperature difference occurs in one fuel cell (cell), a difference occurs in the saturated water vapor pressure at both electrodes, and water easily moves from one electrode side having a high saturated water vapor pressure to the other electrode side having a low saturated water pressure. Water may easily collect on the electrode side. If water is biased and accumulates on one electrode side, supply of gas necessary for power generation is hindered, causing problems such as a decrease in the output of the fuel cell.

  By the way, if all the cells in the fuel cell stack have the same ease of water movement from one electrode side to the other electrode side, a temperature difference occurs in the fuel cell due to the stacking location. In this case, since the membrane-electrode assembly of the fuel cell does not particularly support the movement of water based on the temperature difference, the water moves through the electrolyte membrane, and the one electrode side to the other electrode side. May be discharged in a biased manner.

  Further, as in Patent Document 1, in a fuel cell including a water retention layer on one electrode of a membrane-electrode assembly, the temperature on the electrode side including the water retention layer is lower than the temperature on the other electrode side. The water may move from the other electrode side through the electrolyte membrane to the electrode side having the water retention layer. In that case, by holding the water that has been moved by the water retaining layer, it is possible to suppress the water from being biased to the outside of the electrode to some extent. However, since all the cells in the fuel cell stack have the same ease of water movement from one electrode side to the other electrode side, for example, the fuel cell unit depends on the cell stacking location. If there is a large temperature difference in the cell, the cell does not support the movement of water based on the large temperature difference, so that the water moves through the electrolyte membrane, and from one electrode side to the other electrode side. May be discharged in a biased manner.

  The fuel cell stack according to the present embodiment is a fuel cell stack in which a fuel cell having an electrolyte membrane and a membrane-electrode assembly in which electrodes are formed on both surfaces of the electrolyte membrane is stacked, from one electrode to the other electrode. It is characterized by including the fuel battery cell from which the ease of movement of water differs.

  In the fuel cell stack, the fuel cells have different water retention between the electrodes of the membrane-electrode assembly.

  In the fuel cell stack, the electrode of the fuel cell includes a catalyst and an electrolyte, and one electrode has a larger electrolytic mass per unit volume than the other electrode.

  In the fuel cell stack, the electrode of the fuel cell includes a catalyst and an electrolyte, and one of the electrodes has a higher hydrophilicity than the other electrode.

  In the fuel cell stack, the electrode of the fuel cell includes a catalyst and an electrolyte, and one electrode has a higher water retention capacity of the electrolyte than the other electrode.

  In the fuel cell stack, the fuel cell arranged on the end side of the fuel cell stack has a membrane-electrode assembly including an electrolyte membrane that is less permeable to water than the fuel cell arranged on the center side. It is characterized by.

  In addition, the fuel cell according to the present embodiment is disposed on one surface of the electrolyte membrane, the electrolyte membrane, and is disposed on the other surface of the electrolyte membrane, the anode electrode to which hydrogen gas is supplied, and supplied with oxygen gas. The anode electrode is disposed between the anode diffusion layer having gas permeability and water permeability, the anode diffusion layer and the electrolyte membrane, and is supplied. An anode-side catalyst layer containing a catalyst for catalyzing an electrochemical reaction of hydrogen and an electrolyte, and the cathode electrode includes a cathode-side diffusion layer having gas permeability and water permeability, a cathode-side diffusion layer, In a fuel cell having a cathode-side catalyst layer that is disposed between an electrolyte membrane and that catalyzes an electrochemical reaction of supplied oxygen and an electrolyte, and generates water by the electrochemical reaction, an anode-side catalyst layer Included in A catalyst, by introducing a hydroxyl group, and wherein the increasing the water retention of the anode catalyst layer.

  The fuel cell is characterized in that the electrolytic mass per unit volume of the anode side catalyst layer is made larger than that of the cathode side catalyst layer to increase the water retention of the anode side catalyst layer.

  The fuel cell stack according to the present invention suppresses water from moving from one electrode side to the other electrode side based on the temperature difference even when a temperature difference occurs between the electrodes of each fuel cell due to the stacking portion. I can do it.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of the fuel cell stacks 1 and 2. The fuel cell stacks 1 and 2 are used, for example, to supply driving power for the vehicle. It can also be used for stationary use. Each fuel cell stack 1, 2 is a stack of a plurality of fuel cells 10. In the fuel cell stacks 1 and 2, each fuel cell 10 is electrically connected in series. The output of each fuel cell 10 is taken out collectively from the ends of the fuel cell stacks 1 and 2. The negative electrode as the whole fuel cell stack 1 is arranged in the fuel cell 10A at one end of the fuel cell stack 1, and the positive electrode as the whole fuel cell stack 1 is arranged in the fuel cell 10B at the other end. . A negative electrode side current collector plate 50A is adjacent to the fuel cell 10A, and a positive electrode side current collector plate 50B is adjacent to the fuel cell 10B. On the other hand, the negative electrode as the whole fuel cell stack 2 is arranged in the fuel cell 10C at one end of the fuel cell stack 2, and the whole fuel cell stack 2 is arranged at the fuel cell 10D at the other end. A positive electrode is arranged. A negative current collector plate 50C is adjacent to the fuel cell 10C, and a positive current collector plate 50D is adjacent to the fuel cell 10D.

  The ends of the fuel cell stacks 1 and 2 are fixed to end plates 60A and 60B. The end on the negative electrode side of the fuel cell stack 1 and the end on the positive electrode side of the fuel cell stack 2 are both fixed to the same end plate 60A, and the end on the positive electrode side of the fuel cell stack 1 and the fuel cell stack Both ends of the negative electrode 2 are fixed to the same end plate 60B. The fuel cell stacks 1 and 2 are connected to the distributor 70. Hydrogen gas, oxidizing gas (air), and refrigerant are passed through the distributor 70, and hydrogen gas and the like are supplied into the fuel cell stacks 1 and 2 using the distributor 70. In addition, off gas such as unconsumed hydrogen gas, warmed refrigerant after circulating through the fuel cell stacks 1 and 2, and the like are also discharged to the outside of the fuel cell stacks 1 and 2 through the distributor 70.

  FIG. 2 is a cross-sectional view showing the configuration of the fuel battery cell 10. The fuel cell 10 includes a membrane-electrode assembly 20 and a pair of separators 30 that sandwich the membrane-electrode assembly 20. The fuel battery cell 10 generates electricity by causing an electrochemical reaction between hydrogen and oxygen in the membrane-electrode assembly 20. The membrane-electrode assembly 20 is also referred to as a membrane-electrode assembly (MEA). The membrane-electrode assembly 20 includes an ion conductive electrolyte membrane 21 and a pair of electrodes 22 formed on the front and back surfaces of the electrolyte membrane 21. The electrolyte membrane 21 is made of, for example, a fluorine-based polymer material having an electrolyte group such as a sulfonic acid group in the side chain. The electrode 22 is provided on one surface of the electrolyte membrane 21, and is provided on the other surface of the electrolyte membrane 21 with an anode electrode 22A that reacts with a fuel gas such as hydrogen gas, and an oxidizing gas such as oxygen gas reacts. Cathode electrode 22B. The anode electrode 22A has an anode side catalyst layer 23A disposed on the electrolyte membrane 21, and an anode side diffusion layer 24A disposed on the catalyst layer 23A. On the other hand, the cathode electrode 22B has a cathode side catalyst layer 23B disposed on the electrolyte membrane 21, and a cathode side diffusion layer 24B disposed on the catalyst layer 23B. The catalyst layers 23 </ b> A and 23 </ b> B include a catalyst-supporting carbon in which a noble metal catalyst such as platinum, gold, palladium, ruthenium, and iridium is supported by carbon, and a resin that adheres the catalyst-supporting carbon to the electrolyte membrane 21. This resin is made of an electrolyte, for example, an ion conductive cation exchange resin. This electrolyte may be the same material as the electrolyte membrane 21. The diffusion layers 24A and 24B are made of a conductive porous material and have conductivity, gas permeability, and water permeability. The separator 30 includes an anode separator 30A disposed on the anode electrode 22A side of the membrane-electrode assembly 20 and a cathode separator 30B disposed on the cathode electrode 22B side. Separator 30 (30A, 30B) consists of metal materials, such as aluminum, titanium, and slenless, and has electroconductivity. The separator 30 (30A, 30B) has a function of separating adjacent fuel cells 10 and a function of collecting electricity generated in the membrane-electrode assembly 20. Furthermore, the anode side separator 30A has a hydrogen gas flow path 31A for supplying hydrogen gas to the anode electrode 22A and a refrigerant flow path 32A for allowing the refrigerant to pass therethrough, and the cathode side separator 30B has oxygen to the cathode electrode 22B. It has an oxidizing gas channel 31B for supplying gas and a refrigerant channel 32B for passing the refrigerant.

  Here, the power generation principle of the fuel cell 10 will be described. The fuel cell 10 is supplied with hydrogen gas and air necessary for power generation from the outside. As shown in FIG. 1, hydrogen gas and air are supplied from the outside to each fuel cell 10 through a distributor 70 connected to the fuel cell stacks 1 and 2. The hydrogen gas supplied to the fuel cell 10 passes through the hydrogen gas flow path 31A of the anode separator 30A and flows along the surface of the anode electrode 22A. At this time, the hydrogen gas enters the diffusion layer 24A of the anode electrode 22A and reaches the catalyst layer 23A while diffusing inside. The hydrogen gas is subjected to a chemical reaction represented by the following formula (1) in the catalyst layer 23A. In this reaction, protons and electrons are generated from hydrogen.

H ₂ → 2H ⁺ + 2e ⁻ (1)

  Protons generated in the catalyst layer 23A of the anode electrode 22A move from the catalyst layer 23A to the electrolyte membrane 21, and further move in the electrolyte membrane 21 toward the cathode electrode 22B. At this time, protons move with water molecules. Protons that have moved through the electrolyte membrane 21 reach the cathode electrode 22B. On the other hand, the generated electrons move from the catalyst layer 23A of the anode electrode 22A to the diffusion layer 24A, further move to the anode side separator 30A, and are collected. The collected electrons move to the cathode separator of the adjacent fuel cell 10.

  On the other hand, the air supplied into the fuel cell 10 passes through the oxidizing gas flow path 31B of the cathode separator 30B and flows along the surface of the cathode electrode 22B of the membrane-electrode assembly 20. At this time, oxygen gas contained in the air enters the diffusion layer 24B of the cathode electrode 22B and reaches the catalyst layer 23B while diffusing inside. Oxygen is subjected to a chemical reaction represented by the following formula (2) in the catalyst layer 23B. In this reaction, oxygen and protons moving from the anode electrode 22A react to generate water. The electrons used in this reaction are those that have been supplied to the catalyst layer 23B of the cathode electrode 22B from the anode separator of another adjacent fuel cell through the cathode separator.

^{_{(1/2) O 2 + 2H +}} + 2e - → H 2 O ··· (2)

  In each fuel cell 10 of the fuel cell stacks 1 and 2, the chemical reaction of the above formulas (1) and (2) continuously proceeds in the membrane-electrode assembly 20, whereby an electron flow is generated and electricity is generated. appear. During power generation, water generated in the catalyst layer 23B of the cathode electrode 22B of the membrane-electrode assembly 20 mainly passes through the diffusion layer 24B and oozes out from the surface of the cathode electrode 22B, and reaches the cathode side separator 30B. It enters the oxidizing gas flow path 31B. The water that has entered the oxidizing gas channel 31B is pushed by the flow of air (off-gas) as a liquid and is discharged from the oxidizing gas channel 31B to the outside of the fuel cell 10 or gas (water vapor). Then, it is taken into the off-gas and is discharged to the outside of the fuel cell 10 through the oxidizing gas flow path 31B together with the off-gas.

  By the way, the fuel cell 10 generates heat during power generation. Therefore, the fuel cell stacks 1 and 2 during power generation are warmer than when power generation is stopped. The fuel cell stacks 1 and 2 shown in FIG. 1 may have different temperatures depending on the fuel cell 10 due to the influence of the external environment during power generation.

  In FIG. 1, the fuel cell stack 1 has fuel cell cells 10A and 10B at the ends thereof in contact with current collector plates 50A and 50B, respectively. Furthermore, the current collector plates 50A and 50B are in contact with the end plates 60A and 60B, respectively. These current collecting plates 50A and 50B and end plates 60A and 60B are made of a material that easily radiates heat, such as metal. Therefore, the fuel cells 10 at the ends of the fuel cells 10A, 10B, etc. that are in contact with these are more likely to lose heat and lower in temperature than the fuel cells 10 at the center. Similarly, the fuel cells at the ends of the fuel cell stack 2 such as the fuel cells 10C and 10D are also easily deprived of heat, and the temperature is likely to decrease.

  Further, even in one fuel battery cell 10, the temperature may vary depending on the location. For example, in the fuel battery cells 10A, 10B, 10C, and 10D, the temperature at the side in contact with the current collecting plates 50A, 50B, 50C, and 50D that easily dissipates heat is likely to be lower than the opposite side. That is, the temperature of the electrode 22 disposed on the end side of the fuel cell stacks 1 and 2 tends to be lower than the temperature of the electrode 22 disposed on the center side.

  FIG. 3 is a graph showing the temperature of each fuel cell 10 during power generation of the fuel cell stack 2 shown in FIG. As shown in this graph, it can be seen that the temperature of the fuel battery cells 10C and 10D on both ends is lower than that of the center part of the fuel battery stack 2 during power generation. Further, also in the temperature difference between the anode electrode 22A and the cathode electrode 22B of each fuel battery cell 10, the temperature difference between the anode electrode 22A and the cathode electrode 22B tends to increase in the fuel cell 10 on the end side. There is. In FIG. 3, the anode electrode side of each fuel cell 10 is indicated by symbol a, and the cathode electrode side is indicated by symbol c. Further, there is almost no temperature difference between the anode electrode side and the cathode electrode side in the fuel cell 10 at the center of the fuel cell stack 2 and there is almost no temperature difference between the fuel cells 10. The display of the data (temperature) of the fuel cell 10 in the center is omitted.

  As described above, when a temperature difference is generated between the anode electrode 22A and the cathode electrode 22B during power generation, water moves from the electrode having the higher temperature toward the electrode having the lower temperature. For example, in the fuel cell 10C located at the end of the fuel cell stack 2, the temperature (Ta) on the anode electrode 22A side is lower than the temperature (Tc) on the cathode electrode 22B side during power generation, and the anode electrode 22A The saturated water vapor pressure (Pa) on the side becomes lower than the saturated water vapor pressure (Pc) on the cathode electrode 22B side. In this case, a phenomenon occurs in which part of the water generated in the catalyst layer 23B of the cathode electrode 22B moves in the electrolyte membrane 21 toward the anode electrode 22A based on the saturated water vapor pressure difference. The water that has moved through the electrolyte membrane 21 and has reached the anode electrode 22A passes through the catalyst layer 23A and the diffusion layer 24A and exudes from the surface of the anode electrode 22A. The water exuded from the surface of the anode electrode 22A is discharged out of the fuel cell 10 through the hydrogen gas passage 31A of the anode separator 30A as a liquid or water vapor. The flow rate of hydrogen gas (off gas) flowing through the hydrogen gas flow path 31A of the anode side separator 30A is generally smaller than the flow rate of air (off gas) flowing through the oxidation gas flow path 31B of the cathode side separator 30B. . Therefore, the anode electrode 22A side has a weaker force (drainage performance) for pushing water than the cathode electrode 22B side. This is because most of the supplied hydrogen gas is consumed at the anode electrode 22A, so that the amount of hydrogen gas discharged as off-gas decreases and the gas pressure decreases. On the other hand, since the cathode electrode 22B is supplied with air containing nitrogen gas in addition to oxygen gas, the off-gas on the cathode electrode 22B side contains nitrogen gas and the like in addition to unconsumed oxygen gas. A certain level of gas pressure is maintained.

  Hereinafter, the fuel cells 100, 102, 103, 104, and 105 used in the fuel cell stacks 1 and 2 according to the present embodiment will be described in detail. These fuel cells 100 and the like are generated between the anode electrode 22A and the cathode electrode 22B based on the temperature difference when a temperature difference occurs between the anode electrode 22A and the cathode electrode 22B during power generation. It suppresses undesirable movement of water. In addition, depending on the degree of temperature difference between the electrodes of each fuel cell stack generated at the stacking location of the fuel cell stacks 1 and 2, the water retention capacity (water retention) of the membrane-electrode assembly 20 and the water of the electrolyte membrane 21 Ease of passing (water permeability) is appropriately set. When the temperature on the anode electrode 22A side is lower than the temperature on the cathode electrode 22B side, the fuel cells 100, 102, 103, and 104 are directed from the cathode electrode 22B side having a higher temperature toward the anode electrode 22A side having a lower temperature. In this way, water is prevented from moving. On the other hand, when the temperature on the cathode electrode 22B side is lower than the temperature on the anode electrode 22B side, the fuel cell 105 has a water flow from the anode electrode 22A side having a higher temperature toward the cathode electrode 22B side having a lower temperature. Is to suppress the movement.

  FIG. 4 is a cross-sectional view showing the configuration of the fuel battery cell 100. The basic configuration of the fuel cell 100 is the same as that of the fuel cell 10 shown in FIG. 2, but the water retention capability of the catalyst layer 123A of the anode electrode 22A is water retention of the catalyst layer 23B of the cathode electrode 22B. It is different in that it is set higher than ability. As a method of increasing the water retention capacity of the catalyst layer 123A, for example, there is a method of introducing a hydrophilic functional group such as a hydroxyl group into a noble metal catalyst such as platinum, gold, palladium, ruthenium, or iridium. As another method, there is a method of increasing the hydrophilicity of the electrolyte contained in the catalyst layer 123A. For example, when the electrolyte is made of a fluorine-based polymer material (resin) having an electrolyte group such as a sulfonic acid group in the side chain, the electrolyte group introduction rate is increased to increase the hydrophilicity of the electrolyte. Furthermore, as another method, there is a method in which the electrolysis mass per unit volume in the catalyst layer 123A is made larger than that of the catalyst layer 23B to increase the hydrophilicity.

  This fuel cell 100 is preferably used, for example, at the position of the fuel cell 10A of the fuel cell stack 1 and the position of the fuel cell 10C of the fuel cell stack 2 shown in FIG. At these positions, during power generation, the temperature on the anode electrode 22A side of the fuel cell 100 may be lower than the temperature on the cathode electrode 22B side, and water generated at the cathode electrode 22B may move to the anode electrode 22A side. However, since the fuel cell 100 has a high water holding capacity of the catalyst layer 123A of the anode electrode 22A, the water that has moved from the cathode electrode 22B through the electrolyte membrane 21 is retained in the catalyst layer 123A of the anode electrode 22A. be able to. Then, the difference (concentration gradient) in the concentration of water between the cathode electrode 22B and the anode electrode 22A is reduced. When the concentration gradient of water between both electrodes becomes small, the movement of water from the cathode electrode 22B to the anode electrode 22A is suppressed. As a result, it can suppress that water accumulates in the hydrogen gas flow path 31A of the anode side separator 30A.

  The fuel cell 100 has the highly hydrophilic anode side catalyst layer 123A. However, in other embodiments, by increasing the hydrophilicity of the anode side diffusion layer 24A, the water retention of the anode electrode 22A is improved. May be raised.

  FIG. 5 is a cross-sectional view showing the configuration of the fuel battery cell 102. The basic configuration of the fuel cell 102 is the same as that of the fuel cell 10 shown in FIG. 2, but the thickness of the electrolyte membrane 221 of the membrane-electrode assembly 20 is the same as that of the electrolyte membrane 21 shown in FIG. It differs in that it is set larger than the thickness. Since the electrolyte membrane 221 is thicker than the electrolyte membrane 21, the amount of water vapor that permeates from one electrode side to the other electrode side can be reduced.

  This fuel cell 102 is preferably used, for example, at the position of the fuel cell 10A of the fuel cell stack 1 and the position of the fuel cell 10C of the fuel cell stack 2 shown in FIG. At these positions, during power generation, the temperature on the anode electrode 22A side of the fuel cell may be lower than the temperature on the cathode electrode 22B side, and water generated at the cathode electrode 22B may move to the anode electrode 22A side. However, since the fuel cell 102 includes the thick electrolyte membrane 221, it is possible to suppress the movement of water (water vapor) from the cathode electrode 22B toward the anode electrode 22A. As a result, it can suppress that water accumulates in the hydrogen gas flow path 31A of the anode side separator 30A.

  FIG. 6 is a cross-sectional view showing the configuration of the fuel battery cell 103. The basic configuration of the fuel cell 103 is the same as that of the fuel cell 10 shown in FIG. The fuel cell 103 has a water retention layer 25A for retaining water between the diffusion layer 24A and the catalyst layer 23A in the anode electrode 22A. The water retaining layer 25A can be formed by adding a pore former to an ion conductive polymer, for example. As the ion conductive polymer, for example, a polymer such as polyfluoroethylene (the same material as the electrolyte membrane 21) can be used. As the pore former, a mixture of carbon black powder and crystalline carbon fiber can be used. The water retention layer 25A has conductivity (electronic conductivity). The configuration of the water retaining layer 25A is not limited to this.

  The fuel cell 103 is preferably used, for example, at the position of the fuel cell 10A of the fuel cell stack 1 and the position of the fuel cell 10C of the fuel cell stack 2 shown in FIG. At these positions, during power generation, the temperature on the anode electrode 22A side of the fuel cell may be lower than the temperature on the cathode electrode 22B side, and water generated at the cathode electrode 22B may move to the anode electrode 22A side. However, since the fuel cell 103 includes the water retention layer 25A on the anode electrode 22A, water that has moved through the electrolyte membrane 21 from the cathode electrode 22B can be mainly retained in the water retention layer 25A of the anode electrode 22A. it can. Then, the difference (concentration gradient) in the concentration of water between the cathode electrode 22B and the anode electrode 22A is reduced. When the concentration gradient of water between both electrodes becomes small, the movement of water from the cathode electrode 22B to the anode electrode 22A is suppressed. As a result, it can suppress that water accumulates in the hydrogen gas flow path 31A of the anode side separator 30A. As a modification, the fuel cell 103 may form a water retention layer between the catalyst layer 23B and the diffusion layer 24B of the cathode electrode 22B when it is desired to increase the water retention property on the cathode electrode 22B side.

  FIG. 7 is a cross-sectional view showing the configuration of the fuel battery cell 104. The basic configuration of the fuel cell 104 is the same as that of the fuel cell 10 shown in FIG. 2, but the water permeability of the electrolyte membrane 321 of the membrane-electrode assembly 20 is the electrolyte membrane shown in FIG. It is different in that it is set lower than 21. The electrolyte membrane 321 is made of, for example, a hydrocarbon ion conductive membrane, and the water permeation amount per unit volume is smaller than the water permeation amount per unit volume of the electrolyte membrane 21 of the fuel cell 10.

  The fuel cell 104 is preferably used, for example, at the position of the fuel cell 10A of the fuel cell stack 1 and the position of the fuel cell 10C of the fuel cell stack 2 shown in FIG. At these positions, during power generation, the temperature on the anode electrode 22A side of the fuel cell may be lower than the temperature on the cathode electrode 22B side, and water generated at the cathode electrode 22B may move to the anode electrode 22A side. However, since the fuel cell 104 has low water permeability of the electrolyte membrane 321, water (water vapor) hardly moves from the cathode electrode 22B toward the anode electrode 22A. When water becomes difficult to move, as a result, it is suppressed that water oozes from the surface of the anode electrode 22A.

  FIG. 8 is a cross-sectional view showing the configuration of the fuel battery cell 105. The basic configuration of the fuel cell 105 is the same as that of the fuel cell 10 shown in FIG. 2, but the water retention capability of the catalyst layer 123B of the cathode electrode 22B is the same as that of the catalyst layer 23A of the anode electrode 22A. It is different in that it is set higher than ability. As a method for increasing the water retention capacity of the catalyst layer 123B, for example, there is a method of introducing a hydrophilic functional group such as a hydroxyl group into a noble metal catalyst such as platinum, gold, palladium, ruthenium, or iridium.

  The fuel cell 105 is preferably used, for example, at the position of the fuel cell 10B of the fuel cell stack 1 and the position of the fuel cell 10D of the fuel cell stack 2 shown in FIG. At these positions, the temperature on the cathode electrode 22B side of the fuel cell may be lower than the temperature on the anode electrode 22A side during power generation. In this case, for example, even if there is a large amount of water on the anode electrode 22A side with a high temperature and water (water vapor) tries to move from the anode electrode 22A side toward the cathode electrode 22B side with a low temperature, Since the concentration gradient of water is small, the movement of water from the anode electrode 22A to the cathode electrode 22B is suppressed.

  FIG. 9 is a schematic configuration diagram of the fuel cell stack 3. In the fuel cell stack 3, the fuel cell 105 is disposed at one end, and the fuel cell 100 is disposed at the other end. Others consist of the fuel cell 10 shown in FIG. The fuel cell 10 is adjacent to the current collector plate 50 on the negative electrode side, and the fuel cell 105 is adjacent to the current collector plate 50 on the positive electrode side. In the fuel cell 100 at one end of the fuel cell stack 3, the anode electrode 22A has higher water retention than the cathode electrode 22B. On the other hand, in the fuel cell 105 at the other end, the cathode electrode 22B has higher water retention than the anode electrode 22A. According to this configuration, even if a temperature difference occurs between both electrodes in the fuel cells 100 and 105 at the end, water movement based on the temperature difference is suppressed from the electrode having the higher temperature to the electrode having the lower temperature. be able to.

  The fuel cell stack according to this embodiment includes a fuel cell 10 and a fuel cell (for example, fuel cell 100, 103, 105) having different water retention between electrodes, and water from one electrode to the other electrode. Ease of movement (water permeability) is provided with fuel cells (for example, fuel cells 102 and 104) lower than the fuel cells 10. The selection and combination of these fuel cells are appropriately performed in consideration of the degree of temperature difference generated in one fuel cell by the stacking position of the stack.

  In fuel cells having different water retention between electrodes (for example, fuel cells 100, 103, and 105), fuel cells having different degrees of water retention between electrodes may be included in one fuel cell stack. . For example, the difference in the degree of water retention between the electrodes of the fuel cell located at the end is set to be the largest, and the difference in the degree of water retention between the electrodes of the fuel cell on the center side is gradually increased. You may set small. Similarly, in the fuel cell (for example, the fuel cells 102 and 104), the ease of movement of water from one electrode to the other electrode (water permeability) is lower than that in the fuel cell 10. The ease of water movement (water permeability) from one electrode of the fuel cell located at the end to the other electrode is the lowest, and in the fuel cell at the center, water gradually flows. You may set so that it may move easily.

FIG. 2 is a schematic configuration diagram of fuel cell stacks 1 and 2. 1 is a cross-sectional view showing a configuration of a fuel battery cell 10. It is a graph which shows the temperature of each fuel cell at the time of the electric power generation of a fuel cell stack. 2 is a cross-sectional view showing a configuration of a fuel cell 100. FIG. 2 is a cross-sectional view showing a configuration of a fuel cell 102. FIG. 3 is a cross-sectional view showing a configuration of a fuel battery cell 103. FIG. 2 is a cross-sectional view showing a configuration of a fuel cell 104. FIG. 2 is a cross-sectional view showing a configuration of a fuel battery cell 105. FIG. 2 is a schematic configuration diagram of a fuel cell stack 3. FIG.

Explanation of symbols

  1, 2, 3 Fuel cell stack 10, 100, 102, 103, 104, 105 Fuel cell, 20 membrane-electrode assembly, 21 electrolyte membrane, 22 electrode, 22A anode electrode, 22B cathode electrode, 23A anode side catalyst Layer, 23B cathode side catalyst layer, 24A anode side diffusion layer, 24B cathode side diffusion layer, 25A water retention layer, 30 separator, 30A anode side separator, 30B cathode side separator, 31A hydrogen gas flow path, 31B oxidizing gas flow path, 32A Refrigerant channel, 32B Refrigerant channel, 50A, 50B, 50C, 50D Current collector plate, 60A, 60B End plate, 70 Distributor, 123A Anode side catalyst layer, 123B Cathode side catalyst layer, 221 Electrolyte membrane, 321 Electrolyte membrane.

Claims (6)

In a fuel cell stack in which an electrolyte membrane and a fuel cell having a membrane-electrode assembly in which electrodes are formed on both surfaces of the electrolyte membrane are laminated,
A fuel cell stack comprising fuel cells having different easiness of movement of water from one electrode to the other electrode. The fuel cell stack according to claim 1, wherein
The fuel cell stack is characterized in that the water retention between the electrodes of the membrane-electrode assembly is different. The fuel cell stack according to claim 1 or 2,
The electrode of the fuel cell includes a catalyst and an electrolyte,
A fuel cell stack, wherein one electrode has a larger electrolytic mass per unit volume than the other electrode. The fuel cell stack according to claim 1 or 2,
The electrode of the fuel cell includes a catalyst and an electrolyte,
A fuel cell stack, wherein one of the electrodes has a higher hydrophilicity than the other electrode. The fuel cell stack according to claim 1 or 2,
The electrode of the fuel cell includes a catalyst and an electrolyte,
A fuel cell stack, wherein one electrode has a higher water retention capacity of the electrolyte than the other electrode. In the fuel cell stack according to any one of claims 1 to 5,
The fuel cell arranged on the end side of the fuel cell stack has a membrane-electrode assembly including an electrolyte membrane that is less permeable to water than the fuel cell arranged on the center side. stack.

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