JP2008277211A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize both flooding prevention at the exit part and drying prevention at the entrance part in both of a fuel gas passage and an oxidizer gas passage in a fuel battery cell. <P>SOLUTION: In a unit cell C of a fuel cell stack S, the flowing direction of an oxidizer gas passage 21 installed on the oxidizer gas side separator 2 and a fuel gas passage 31 installed on a fuel gas side separator 3 is made to be opposed. On the exit part 23 side of the oxidizer gas passage 21, a heat insulating coating layer 5A is arranged between the oxidizer gas side separator 2 and a cooling medium passage 4 and an heat insulating region 24 where the temperature on the oxidizer gas side is higher than the fuel gas side is formed and moisture is permeated to the entrance part 32 side of the fuel gas passage 31. On the exit part 33 side of the fuel gas passage 31, a heat insulating coating layer 5B is arranged between the fuel gas side separator 3 and the cooling medium passage 4, and an heat insulating region 34 where the temperature on the fuel gas side is higher than the oxidizer gas side is formed and moisture is permeated to the entrance part 22 side of the oxidizer gas passage 21. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell that generates power using a chemical reaction between an oxidizing gas and a fuel gas, and more particularly to a cell configuration for preventing flooding and dry-up in a cell plane.

  In a polymer electrolyte fuel cell, electric energy is generated by supplying a chemical reaction by supplying an oxidizing gas such as air and a fuel gas such as hydrogen to a fuel cell stack in which a plurality of cells are stacked. A cell serving as a basic unit generally includes a membrane electrode assembly called MEA (Membrane Electrode Assembly) in which a catalyst layer is formed on both sides of a solid polymer electrolyte membrane and is further integrated by sandwiching both sides with a diffusion layer. It has a structure in which an oxidizing gas side separator and a fuel gas side separator are disposed on both sides of the MEA. The oxidizing gas side separator and the fuel gas side separator that sandwich the MEA form an oxidizing gas channel and a fuel gas channel between the MEA diffusion layers.

  In the fuel electrode (anode) of the fuel cell, the supplied hydrogen is ionized by catalytic action, passes through the electrolyte membrane, and moves to the air electrode (cathode) side. Oxygen supplied to the air electrode reacts with the moving hydrogen to produce water. An electromotive force is generated by this power generation reaction, and the generated water passes through the diffusion layer together with surplus gas and is discharged to the oxidizing gas flow path. A part of the generated water passes through the electrolyte membrane, moves to the fuel electrode side, and is discharged to the fuel gas flow path. For this reason, the moisture distribution in the gas flow path is changed, and there is a possibility that the moisture is condensed to cause flooding that inhibits gas diffusion.

  Therefore, the inventors previously described in Patent Document 1 by providing a cooling water flow path only on the back surface of the oxidant gas side separator of the fuel cell in order to prevent flooding in the fuel gas flow path of the fuel cell. A configuration has been proposed in which the temperature in the cell surface on the fuel gas side is higher than that on the oxidizing gas side. This increases the saturated water vapor pressure on the fuel gas side and increases the amount of moisture that permeates the electrolyte membrane from the fuel gas side to the oxidant gas side. Flooding can be prevented.

Further, as a conventional technique, Patent Document 2 discloses a thermal resistance such as an air layer between the downstream portion of the oxidizing gas flow channel and the cooling water flow channel in order to uniformize the moisture distribution in the oxidizing gas flow channel of the fuel cell. A fuel cell is disclosed that prevents flooding in the oxidant gas flow path by increasing the temperature on the downstream side of the oxidant gas flow path, which tends to cause excessive water, by promoting the discharge of moisture.
JP 2005-203313 A JP 2005-158610 A

  By the way, in fuel cells, prevention of flooding as well as prevention of drying are important issues. In general, it is desirable that the solid polymer electrolyte membrane is substantially saturated with water in order to maintain its function. For example, the moisture of the reaction gas supplied is adjusted to maintain moisture. For this reason, when trying to prevent flooding, the membrane tends to dry up on the inlet side of the gas flow path with a relatively small amount of water, and there is a problem in that the specific resistance of the membrane increases and the output decreases. It was.

  Moreover, although the structure of patent document 1 can prevent the flooding in a fuel gas flow path, the flooding in the oxidizing gas flow path side is not considered. In general, a fuel cell stack has a temperature distribution in the stacking direction, and a temperature difference is likely to occur in the cell at both ends. For this reason, for example, in a cell in which the oxidizing gas channel is located on the stack end face side, moisture permeation from the fuel gas channel side to the oxidizing gas channel side is promoted, and flooding is likely to occur on the oxidizing gas channel side.

  Similarly, in the configuration of Patent Document 2, flooding on the oxidizing gas channel side can be prevented, but flooding on the fuel gas channel side is not taken into consideration. For this reason, in the cell in which the fuel gas flow path is located on the stack end face side, the temperature of the latter half of the oxidizing gas flow path is higher than the temperature on the fuel gas flow path side, and the oxidation gas flow path side to the fuel gas flow path side. There was a problem that the water permeation of the water increased and flooding occurred on the fuel gas flow path side.

  The present invention has been made in view of the above problems, and an object of the present invention is to prevent the occurrence of flooding in both the fuel gas channel and the oxidant gas channel in the cell of the fuel cell, and It is to realize a high-performance fuel cell capable of preventing flooding and drying prevention in any cell constituting the fuel cell stack.

The invention of claim 1 is a fuel cell comprising a fuel cell stack in which a large number of unit cells that generate power by a chemical reaction between an oxidizing gas and a fuel gas are stacked, and a cooling medium flow path is provided between the unit cells.
In the unit cell, an oxidizing gas side separator that forms an oxidizing gas channel is formed on one surface side of a membrane electrode assembly in which electrodes are disposed on both surfaces of the electrolyte membrane, and a fuel gas channel is formed on the other surface side. A fuel gas side separator is provided, and an inlet portion of the oxidizing gas passage and an outlet portion of the fuel gas passage, an outlet portion of the oxidizing gas passage and an inlet portion of the fuel gas passage are respectively connected to the membrane electrode. It is made to oppose on both sides of a joined body, and it is set as the channel composition where the direction of the flow of oxidation gas and fuel gas is opposed,
While the oxidizing gas channel and the cooling medium channel are adjacent to each other through the oxidizing gas side separator, the fuel gas channel and the cooling medium channel are adjacent to each other via the fuel gas side separator,
On the outlet side of the oxidizing gas flow path, a heat insulating layer is disposed between the oxidizing gas side separator and the cooling medium flow path to form a heat insulating region in which the temperature on the oxidizing gas side is higher than that on the fuel gas side. And
On the outlet side of the fuel gas flow path, a heat insulating layer is disposed between the fuel gas side separator and the cooling medium flow path to form a heat insulating region in which the temperature on the fuel gas side is higher than that on the oxidizing gas side. It is a thing.

  In the structure of Claim 1, it arrange | positions so that the inlet_port | entrance part and exit part of an oxidizing gas flow path and a fuel gas flow path may oppose, and it heat-insulates between cooling medium flow paths in the downstream area of each gas flow path. Since the layer is disposed, the temperature on the outlet side increases. Here, in the oxidizing gas flow path, the amount of water rises toward the outlet side due to the generated water accompanying power generation, but in the heat insulating region, the temperature on the oxidizing gas side is maintained higher than that on the fuel gas side. Due to the partial pressure difference, the amount of moisture that permeates the electrolyte membrane and moves to the fuel gas side increases. For this reason, it suppresses that water vapor partial pressure reaches saturation and liquid water arises. Moreover, drying is prevented by the moving water | moisture content at the entrance part side of a fuel gas flow path.

  Similarly, in the fuel gas flow path, in the heat insulating region on the outlet side, the temperature on the fuel gas side is maintained higher than that on the oxidant gas side. The amount of water to increase increases and the liquid water decreases. On the other hand, drying at the inlet side of the oxidizing gas flow path through which moisture moves is also prevented.

  Therefore, in both the oxidizing gas channel and the fuel gas channel, flooding can be prevented and drying can be prevented, and a fuel cell with high power generation performance can be realized.

  In the invention of claim 2, the size or thickness of the heat insulating layer is changed depending on the position of the fuel cell stack in the stacking direction.

  In general, the temperature of the fuel cell stack tends to decrease toward the end in the stacking direction. For example, in a cell close to the end, the heat insulation layer disposed at the gas flow path outlet is enlarged or thickened to achieve the required temperature rise and efficiently generate power throughout the fuel cell stack. be able to.

  In the invention of claim 3, the temperature difference between the fuel gas side and the oxidizing gas side at the outlet part of the fuel gas channel or the outlet part of the oxidizing gas channel is set in advance for the size or thickness of the heat insulating layer. The fuel cell stack is changed according to the position in the stacking direction and the position in the flow path direction so as to be in the range.

  More specifically, the necessary moisture permeation amount is secured by setting the size or thickness of the heat insulation layer so that the temperature difference between the two flow paths becomes a predetermined value for each cell position. In addition, flooding and drying prevention can be realized at an arbitrary position of the fuel cell stack.

  Specifically, as in the invention of claim 4, specifically, on the outlet portion side of the fuel gas side separator or the oxidizing gas side separator, the separator surface on the cooling medium flow path side is covered with a heat insulating coating material, thereby A heat insulation layer can be formed.

  As in the fifth aspect of the present invention, for example, a silicon-based polymer material or a conductive material can be used as the heat insulating coating material.

  FIG. 1 shows a fuel cell configuration according to the first embodiment of the present invention. FIG. 1A is a schematic diagram showing a main part configuration of the fuel cell stack S, and FIG. 1B is a schematic configuration diagram of the entire fuel cell system including the fuel cell stack S. As shown in FIG. 1B, the fuel cell stack S is formed by stacking a large number of cells C, which are basic units, and electrically connecting them in series, and oxidizing gas (for example, air) or fuel gas (for example, hydrogen). ) Supply / discharge flow path, cooling water supply / discharge flow path as a cooling medium, various control devices, etc. are connected to form a fuel cell system. The fuel cell stack S generates electric power by an electrochemical reaction between an oxidizing gas and a fuel gas, and is used for driving a load after voltage adjustment by a DC / DC converter. The load is, for example, a motor for driving a fuel cell vehicle or various auxiliary machines, and the controller controls the entire system including the control means for the reaction gas and the cooling water according to the required power.

  As shown in FIG. 1 (a), each cell C of the fuel cell stack S has MEA (Membrane Electrode Assembly: membrane electrodes) in which a catalyst layer and a diffusion layer are arranged on both surfaces of an electrolyte membrane 11 to form electrodes 12 and 13, respectively. (Jointed body) 1, and a configuration in which the oxidizing gas side separator 2 is disposed on one side (right side in the figure) and the fuel gas side separator 3 is disposed on the other side (left side in the figure) with the MEA 1 interposed therebetween. It has become. A groove that becomes the oxidizing gas flow path 21 is formed on the surface facing the MEA 1 of the oxidizing gas side separator 2, and a groove that becomes the fuel gas flow path 31 is formed on the surface facing the MEA 1 of the fuel gas side separator 3. Is formed. Grooves formed on the surfaces of the oxidizing gas side separator 2 and the fuel gas side separator 3 on the side opposite to the MEA 1 serve as a cooling water flow path 4 as a cooling medium flow path. Thereby, the cooling water flow path 4 is interposed between the adjacent cells C of the fuel cell stack S.

  The electrolyte membrane 11 is a hydrogen ion conductive solid polymer electrolyte membrane having a known structure, specifically, a perfluorosulfone-based polymer such as Nafion (manufactured by DuPont: registered trademark) or the like formed into a membrane shape. Are preferably used. A catalyst layer and a diffusion layer constituting the air electrode (cathode) 12 are laminated in this order on one surface in the thickness direction of the electrolyte membrane 11, and a fuel electrode (anode) 13 is formed on the other surface. The catalyst layer and the diffusion layer are formed and integrated in this order, and are in contact with the oxidizing gas passage 21 and the fuel gas passage 31, respectively. The catalyst layer is configured by supporting a catalyst such as a platinum catalyst on a material having good conductivity, such as a carbon material. The diffusion layer is made of a material having good electrical conductivity and gas diffusibility, such as a carbon material, and can impart properties such as water repellency as necessary.

  The oxidizing gas side separator 2 and the fuel gas side separator 3 are made of a conductive plate member made of, for example, a carbon material or a metal. The oxidant gas flow path 21 formed between the oxidant gas side separator 2 and the MEA 1 has an oxidant gas inlet part 22 on the upper end side and an oxidant gas outlet part 23 on the lower end side of the figure. Connected to the channel and the discharge channel. On the other hand, the fuel gas side separator 3 has a lower end side in the figure as a fuel gas inlet portion 32 and an upper end side as a fuel gas outlet portion 33, and is connected to a fuel gas supply passage and a discharge passage (not shown), respectively. . Thus, the oxidizing gas inlet 22 and the fuel gas outlet 33, and the oxidizing gas outlet 23 and the fuel gas inlet 32 are opposed to each other so that the MEA 1 is sandwiched therebetween.

  FIG. 1A schematically shows a flow path configuration in which the flow directions of the oxidizing gas and the fuel gas are opposed to each other. The shape of the oxidizing gas side separator 2 or the fuel gas side separator 3 for constituting the flow path is such that the inlet and outlet portions of the oxidizing gas flow path 21 and the fuel gas flow path 31 face each other and the flow directions face each other. Can be arbitrarily set. Usually, for example, a plurality of grooves provided on the plate surface of the oxidizing gas side separator 2 or the fuel gas side separator 3 are connected to form a continuous flow path, and both ends are used as an inlet portion or an outlet portion. The cooling water flow path 4 is the same, and a flow path can be formed between the opposing surfaces by providing a groove on at least one surface of the oxidizing gas side separator 2 and the fuel gas side separator 3 and abutting each other.

  Here, in order to advance the power generation reaction efficiently, the electrolyte membrane 11 needs to be sufficiently hydrated. Usually, the oxidizing gas is humidified and supplied to the gas flow path inlet 22. However, in the fuel cell, water is generated by the reaction of the oxidizing gas and the fuel gas. Therefore, when the humidification of the supply gas is high, the amount of water in the gas flow path increases, and the liquid flow is increased at the gas flow path outlets 23 and 33 side. It is easy to cause flooding that generates water. If this liquid water causes water clogging inside and outside the MEA 1, diffusion of the reaction gas may be hindered. If the humidification of the supply gas is lowered so as to avoid this, dry-up of the electrolyte membrane 11 is likely to occur on the gas flow path inlet portions 22 and 32 side. Both of these are factors that reduce the output.

  For this reason, in this embodiment, as shown in FIG. 1A, a heat insulating layer is formed on the surface of the oxidizing gas side separator 2 on the cooling medium flow path 4 side in the downstream area near the outlet 23 of the oxidizing gas flow path 21. The heat insulating coating layer 5A is formed as a heat insulating region 24. In the heat insulating region 24, heat radiation from the oxidizing gas passage 21 to the cooling medium passage 4 is suppressed, and the temperature on the oxidizing gas side becomes higher than that on the fuel gas side. Similarly, in the downstream region near the outlet 33 side of the fuel gas channel 31, a heat insulating coating layer 5B, which is a heat insulating layer, is formed on the surface of the fuel gas side separator 3 on the cooling medium channel 4 side to form a heat insulating region 34. And In the heat insulating region 34, heat radiation from the fuel gas flow path 31 to the cooling medium flow path 4 is suppressed, and the temperature on the fuel gas side becomes higher than that on the oxidizing gas side. By these heat insulating regions 24 and 34, the amount of moisture and the partial pressure of water vapor in the oxidizing gas passage 21 and the fuel gas passage 31 and the amount of moisture permeating between the gas passages are adjusted to suppress flooding and dry-up.

  The heat insulating coating layers 5A and 5B are formed by applying a heat insulating coating material having a thermal conductivity lower than that of carbon or metal material constituting the separators 2 and 3 and having a heat insulating effect with a thin film. Specifically, in addition to a silicon-based polymer material and a fluorine-based polymer material, a conductive material such as a metal material having a low thermal conductivity, a conductive resin, or the like can be used. The formation range of the heat insulating coating layers 5A and 5B, that is, the size of the heat insulating regions 24 and 34, is the temperature of the gas channel outlet and the temperature between the channels on the oxidizing gas channel 21 side and the fuel gas channel 31 side, respectively. It can be arbitrarily set so that the difference becomes a desired value. Usually, on the outlet portions 23 and 33 side of the oxidant gas passage 21 and the fuel gas passage 31, they may be appropriately selected within a range of about 30 to 70% of the gas passage length from the downstream end.

Next, the operation of the fuel cell having the above configuration will be described. In FIG. 1, when hydrogen is supplied as fuel gas and air is supplied as oxidizing gas to each cell C of the fuel cell stack S, hydrogen and air are respectively supplied to the oxidizing gas passage 21 and the fuel gas passage 31 of the cell C. When introduced, the following electrochemical reactions (1) and (2) occur at both electrodes 12 and 13 of the MEA 1. That is, hydrogen that has reached the catalyst layer through the diffusion layer in the fuel electrode 13 passes through the electrolyte membrane 11 as hydrogen ions, and reacts with oxygen that has reached the catalyst layer through the diffusion layer at the air electrode 12 to react with water. Is generated. The generated water moves in the air electrode 12 together with the unreacted gas and is discharged to the oxidizing gas flow channel 21, and part of the generated water passes through the electrolyte membrane 11 and moves toward the fuel electrode 13, and enters the fuel gas flow channel 31. Discharged.
Anode electrode reaction (fuel electrode 13) H ₂ → 2H ⁺ + 2e ⁻ (1)
Cathode electrode reaction (air electrode 12) 2H ⁺ + 1 / 2O ₂ ⁺ + 2e ⁻ → H ₂ O (2)

  At this time, in the oxidizing gas channel 21, the oxidizing gas (oxygen) is consumed by the power generation, so that the gas flow rate decreases from the inlet portion 22 side where the oxidizing gas is introduced toward the outlet portion 23 side. However, when air is used as the oxidizing gas, the amount of decrease is generally small. Moreover, in the oxidizing gas flow path 21, since the water produced | generated with an electric power generation is discharged | emitted, the moisture content in the distribute | circulating gas rises toward the exit part 23 side. When the water vapor partial pressure reaches the saturated water vapor pressure at that temperature, liquid water appears in the oxidizing gas channel 21. On the other hand, in the fuel gas flow path 31, as with the oxidizing gas side, fuel gas (hydrogen) is consumed by power generation, so the gas flow rate decreases from the inlet portion 32 side where the fuel gas is introduced toward the outlet portion 33 side. To do. In the fuel gas flow path 31, there is no generation of water due to power generation unlike the oxidizing gas side, but moisture moves from the oxidizing gas side through the electrolyte membrane 11. The amount of moisture fluctuates due to the influence of this moisture, and similarly tends to rise toward the outlet 23 side.

  Here, in this embodiment, the downstream area close to the outlet 23 of the oxidizing gas channel 21 is used as the heat insulating region 24, and the heat insulating coating layer 5 </ b> A is interposed between the cooling water channel 4 and the oxidizing gas side separator 2. . For this reason, the temperature drop due to the heat radiation to the cooling water is suppressed, and the temperature in the vicinity of the outlet portion 23 of the oxidizing gas passage 21 is higher than the temperature in the vicinity of the inlet portion 32 of the fuel gas passage 31 opposed across the MEA 1. The water vapor partial pressure on the oxidizing gas channel 21 side becomes higher than that on the fuel gas channel 31 side. This difference in water vapor partial pressure increases the amount of water that permeates from the oxidant gas side to the fuel gas side. As a result, the amount of water near the oxidant gas outlet 23 decreases, so that liquid water accumulates and flooding occurs. Can be prevented.

  On the other hand, in the vicinity of the inlet 32 of the fuel gas channel 31, the amount of water and the partial pressure of water vapor in the fuel gas rise due to the permeated water. For this reason, since the appropriate water | moisture content is normally replenished in the vicinity of the inlet part 32 of the fuel gas flow path 31 to which dry hydrogen is directly supplied, the drying of the electrolyte membrane 11 can be prevented.

  Similarly, on the fuel gas flow path 31 side, a heat insulating coating layer 5 </ b> B is interposed between the cooling water flow path 4 and the fuel gas side separator 3 with the downstream area close to the outlet portion 33 as a heat insulating area 34. For this reason, the temperature drop due to the heat radiation to the cooling water is suppressed, and the temperature in the vicinity of the outlet portion 33 of the fuel gas passage 31 is higher than the temperature in the vicinity of the inlet portion 22 of the oxidizing gas passage 21 opposed across the MEA 1. The water vapor partial pressure on the fuel gas channel 31 side becomes higher than that on the oxidizing gas channel 21 side. Due to the difference in the partial pressure of water vapor, the amount of water that permeates from the fuel gas side to the oxidizing gas side increases, and as a result, the liquid water near the fuel gas outlet portion 33 is reduced, and the effect of preventing flooding is obtained. .

  Further, in the vicinity of the inlet portion 22 of the oxidizing gas channel 21, the amount of moisture in the oxidizing gas and the water vapor partial pressure rise due to the permeated moisture. For this reason, in order to prevent flooding on the outlet 23 side, even when humidification of the air supplied to the inlet 22 is insufficient, appropriate moisture is supplied to the vicinity of the inlet 22 of the oxidizing gas channel 21. The drying of the electrolyte membrane 11 can be prevented.

  2 and 3 show a second embodiment of the present invention. In this embodiment, formation of the heat insulating coating layers 5A and 5B formed on the oxidizing gas side separator 2 or the fuel gas side separator 3 of the cell C according to the position in the stacking direction of the fuel cell stack S shown in FIG. The range, that is, the size of the heat insulating regions 24 and 34 is changed. FIG. 2B shows how the temperature in the vicinity of the center portion of the cell C of the fuel cell stack S (the temperature at the site where the line AA ′ in FIG. 2A passes) changes depending on the position in the stacking direction. It is a thing.

  As shown in the figure, the temperature of each cell is substantially constant at the central portion (region C) in the stacking direction, but the cell temperature tends to be lower at both ends (regions B and D) than at the central portion (region C). In this case, the temperature drops greatly as it approaches the end face. For this reason, also in each cell C, a temperature difference tends to occur in the stacking direction, and the temperature closer to the end face becomes lower. For example, in the region B where the fuel gas side separator 3 is located on the end surface side, the fuel gas channel 31 side is at a lower temperature than the oxidizing gas channel 21 side, and in the region D where the oxidizing gas side separator 2 is located on the end surface side, the fuel gas The temperature of the oxidizing gas channel 21 becomes lower than that of the channel 31 and liquid water is likely to be generated.

  In this case, if the heat insulating regions 24 and 34 are uniformly set in the fuel cell stack S, depending on the position in the stacking direction, the temperature rise due to the heat insulating coating layers 5A and 5B becomes insufficient, and the desired effect due to the above-described moisture movement. May not be obtained. Therefore, as shown in FIG. 3, different heat insulating regions 24 and 34 are set in the regions B to D in the stacking direction, and the temperature of the gas flow channel outlet located at the end face side at both ends (regions B and D) is set. In order to make it higher, the heat insulation area is enlarged.

  For example, as shown in FIG. 3A, in the region B where the temperature of the fuel gas channel 31 tends to be low, the heat insulating coating layer 5B between the fuel gas separator 3 and the cooling water channel 4 is moved from the channel middle region to the downstream region. The heat insulation area 34 on the fuel gas flow path 31 outlet 33 side is made larger than the area C in FIG. Further, as shown in FIG. 3C, in the region D where the temperature of the oxidizing gas channel 21 tends to be low, the heat insulating coating layer 5A between the oxidizing gas side separator 2 and the cooling water channel 4 is moved from the channel middle region to the downstream region. The heat insulation region 24 on the side of the outlet 23 of the oxidizing gas channel 21 is made larger than the region C in FIG. Specifically, the heat insulating regions 24 and 34 in the region C are set to about 30% of the channel length, and the heat insulating region 34 in the region B and the heat insulating region 24 in the region D are set to 30% to 70%, for example, 60% of the channel length. %.

  Thus, flooding and drying can be effectively prevented in the entire fuel cell stack S by changing the size of the heat insulating regions 24 and 34 depending on the cell position in the stacking direction. The regions B and D are each about 20% of the length in the stacking direction of the fuel cell stack S, and the region C is about 60%, for example. The method of dividing these regions B to D and the setting of the heat insulating regions 24 and 34 are examples, and can be changed as appropriate.

  Alternatively, as shown in FIG. 4 as the third embodiment, the same effect can be obtained by changing the formation thickness of the heat insulating coating layers 5A and 5B instead of changing the size of the heat insulating regions 24 and 34. You can also. That is, the sizes of the heat insulating regions 24 and 34 in the regions B to D in the stacking direction are set to be equal, and in both end portions (regions B and D), the temperature of the gas flow path outlet portion located on the end face side is increased. Further, the heat insulating coating layers 5A and 5B are applied thicker.

  For example, as shown in FIG. 4A, in the region B where the temperature of the fuel gas channel 31 tends to be low, the heat insulating coating layer 5B between the fuel gas side separator 3 and the cooling water channel 4 is changed to the region C of FIG. The heat insulating region 34 is formed in the downstream area of the flow path on the fuel gas flow path 31 outlet 33 side. Further, as shown in FIG. 4C, in the region D where the temperature of the oxidizing gas flow channel 21 tends to be low, the heat insulating coating layer 5A between the oxidizing gas side separator 2 and the cooling water flow channel 4 is replaced with the region C of FIG. A heat insulating region 24 is formed in the downstream region of the flow channel on the side of the outlet 23 of the oxidizing gas flow channel 21 so as to be thicker. The heat insulating regions 24 and 34 in these regions B to D are both about 30%, for example.

  Thus, the same effect is acquired also by changing the thickness of 5 A of thermal insulation coating layers used as the thermal insulation area | regions 24 and 34 by the cell position of a lamination direction. Of course, even if both the size of the heat insulating regions 24 and 34 and the thickness of the heat insulating coating layers 5A and 5B are changed, the temperature on the outlet side of the gas flow path to prevent flooding is the gas to prevent the opposite drying. By forming the heat insulating region so as to be higher than the temperature on the inlet side of the flow path, both prevention of flooding and prevention of drying can be achieved.

  As shown in FIG. 5 as a fourth embodiment, the oxidizing gas side separator 2 and the fuel gas side separator 3 may be formed of a thin conductive plate material and may be formed into a corrugated plate to constitute a flow path. At this time, as shown in FIG. 5A, the oxidizing gas flow path 21 is provided between the corrugated oxidizing gas side separator 2 and the MEA 1, and the fuel gas flow is provided between the corrugated fuel gas side separator 3 and the MEA 1. The configuration in which the channel 31 is formed and the cooling water channel 4 is formed between the separators 2 and 3 is the same as in the above embodiment. With such a configuration, the separators 2 and 3 can be made thin, and the fuel cell stack S can be made compact with respect to the number of stacked cells C.

  Here, since it is necessary to ensure conductivity at the abutting position of the separators 2 and 3 excluding the portion where the cooling water flow path 4 is formed, the heat insulating coating layer 5A made of a resin material or the like in FIG. It is formed only on the inner surface of the cooling water flow path 4 of the gas side separator 2. The same applies when the heat insulating coating layer 5B is formed on the fuel gas side separator 3. However, when the heat insulating coating layers 5A and 5B are conductive materials, the heat insulating coating layer 5A is formed on the entire surface of the oxidizing gas side separator 2 on the cooling water flow path 4 side as shown in FIG. This is easy to manufacture and is advantageous in terms of cost.

  FIG. 6 shows an example of the flow path configuration in which the flow directions of the oxidizing gas flow path 21 and the fuel gas flow path 31 are opposed to each other. FIG. 6 (a) shows the first embodiment of FIG. This is a case where a flow path from one side of the cell surface to the other side is formed. Here, the oxidizing gas flows from the left to the right in the figure, and the fuel gas flows from the right to the left in the figure. FIG. 6B shows a case where a plurality of flow paths formed in parallel to the cell surface are connected to form a continuous flow path as in the fourth embodiment of FIG. The fuel gas flows from the upper left to the lower right so that the fuel gas flows from the lower right to the upper left in the figure.

  As described above, the present invention is based on the premise that the gas flow is basically a counter flow, and is particularly effective. In any of the flow path configurations, the above-described effect can be obtained by forming a heat insulating coding layer between the oxidizing gas side and the fuel gas side at the downstream end portion between the cooling water flow path.

A simulation result for confirming the effect of the present invention will be described with reference to FIG. In FIG. 7A, heat insulating coating layers 5 </ b> A and 5 </ b> B are formed on the outlet portions 23 and 33 side of the oxidizing gas passage 21 and the fuel gas passage 31, respectively. Here, assuming that the outlet 33 side of the oxidizing gas flow channel 21 is thermally insulated with a silicon film having a thickness of 0.1 mm as the heat insulating coating layer 5A, the temperature rise is calculated as follows.
Thermal conductivity: 0.15 W / m · K
If the power generation area is 10 × 10 = 100 cm ² ,
Thermal resistance = 0.0001 / (0.15 × 0.1 × 0.1) = 0.067
If the power generation amount is 0.8 A / cm ² and 0.6 V,
Calorific value = 0.8 × 100 × (1.23−0.6) = 50.4 W
Temperature rise = 0.067 × 50.4 = 3.4 ° C.
Therefore, the temperature of the air electrode (cathode) 12 side rises by about 3.4 ° C. due to heat insulation.

Due to this temperature rise, moisture permeates from the air electrode (cathode) 12 side to the fuel electrode (anode) 13 side. The amount of water movement on the hydrogen side from saturation to no saturation is
Since the saturated water vapor partial pressure is 47.6 kPa at 80 ° C,
When the hydrogen flow rate at this time is 1.0 L / min and the back pressure is 100 kPaG, 1 × 47.6 / (200−47.6) /22.4×18=0.25 g / min
Since the saturated water vapor partial pressure is 42.2 kPa at 77 ° C,
1 × 42.2 / (200-42.2) /22.4×18=0.21 g / min
Therefore, the amount of water movement when the temperature rises by 3 ° C. increases by 0.04 g / min.

Furthermore, as an effect when the amount of water movement increases by 0.04 g, when the amount of liquid water at the outlet 23 side of the oxidizing gas channel 21 is estimated,
When both the anode and cathode are humidified at 60 ° C and the air flow rate is 2.5 L / min, the cell temperature is 76 ° C and 0.426 g / min.
0.393 g / min at a cell temperature of 78 ° C.
At a cell temperature of 79 ° C., 0.376 g / min
Thus, when the amount of liquid water is reduced by 0.05 g / day, a difference in current-voltage characteristics occurs as shown in FIG.

  In the above calculation, the temperature difference between the electrodes is not taken into consideration, but when the cooling water temperature is 76 ° C. and the temperature difference between the electrodes is 3 ° C., the liquid water is increased due to the temperature rise on the outlet 23 side of the oxidizing gas passage 21. It is reduced by 0.05 g, and further reduced by about 0.04 g due to moisture permeation. In this case, it can be predicted that the power generation performance is improved to a cooling water temperature of 79 ° C. or higher shown in FIG.

  The preferred embodiment of the present invention has been described above. However, the fuel cell to which the present invention is applied is not limited to the above-described configuration, and various fuel cell configurations that are used in commonly known fuel cell systems. It is possible to apply.

BRIEF DESCRIPTION OF THE DRAWINGS It is 1st Embodiment of this invention, (a) is a principal part schematic block diagram of the fuel cell stack in the fuel cell of 1st Embodiment, (b) is the schematic which shows the whole structure of a fuel cell system. FIG. 2A is a schematic configuration diagram of a fuel cell stack according to a second embodiment, and FIG. 2B is a diagram illustrating a relationship between a position in the stack stacking direction and a cell temperature. (A)-(c) is a figure which respectively shows the structural example of the heat insulation layer in area | region BD of a fuel cell stack in 2nd Embodiment of this invention. (A)-(c) is a figure which respectively shows the structural example of the heat insulation coating layer in area | region BD of a fuel cell stack in 3rd Embodiment of this invention. (A), (b) is a figure which respectively shows the structural example of the heat insulation coating layer in the oxidizing gas side separator of a fuel cell stack, or a fuel gas side separator in 4th Embodiment of this invention. (A), (b) is a figure which respectively shows the structural example of the oxidizing gas flow path in the cell surface of a fuel cell stack, and a fuel gas flow path. 2A and 2B are diagrams for explaining the effects of the present invention, in which FIG. 1A is a schematic configuration diagram of a main part of a fuel cell stack, and FIG.

Explanation of symbols

S Fuel cell stack C cell (unit cell)
1 MEA (membrane electrode assembly)
DESCRIPTION OF SYMBOLS 11 Electrolyte membrane 2 Oxidizing gas side separator 21 Oxidizing gas flow path 22 Inlet part 23 Outlet part 24 Heat insulation area 3 Fuel gas side separator 31 Fuel gas flow path 32 Inlet part 33 Outlet part 34 Heat insulation area 4 Cooling water flow path (cooling medium flow path )
5A, 5B Thermal insulation coating layer (thermal insulation layer)

Claims (5)

In a fuel cell including a fuel cell stack in which a large number of unit cells that generate power by a chemical reaction between an oxidizing gas and a fuel gas are stacked and a cooling medium flow path is provided between the unit cells.
In the unit cell, an oxidizing gas side separator that forms an oxidizing gas channel is formed on one surface side of a membrane electrode assembly in which electrodes are disposed on both surfaces of the electrolyte membrane, and a fuel gas channel is formed on the other surface side. A fuel gas side separator is provided, and an inlet portion of the oxidizing gas passage and an outlet portion of the fuel gas passage, an outlet portion of the oxidizing gas passage and an inlet portion of the fuel gas passage are respectively connected to the membrane electrode. It is made to oppose on both sides of a joined body, and it is set as the channel composition where the direction of the flow of oxidation gas and fuel gas is opposed,
While the oxidizing gas channel and the cooling medium channel are adjacent to each other through the oxidizing gas side separator, the fuel gas channel and the cooling medium channel are adjacent to each other via the fuel gas side separator,
On the outlet side of the oxidizing gas flow path, a heat insulating layer is disposed between the oxidizing gas side separator and the cooling medium flow path to form a heat insulating region in which the temperature on the oxidizing gas side is higher than that on the fuel gas side. And
On the outlet side of the fuel gas flow path, a heat insulating layer is disposed between the fuel gas side separator and the cooling medium flow path to form a heat insulating region in which the temperature on the fuel gas side is higher than that on the oxidizing gas side. A fuel cell characterized by that.   The fuel cell according to claim 1, wherein the size or thickness of the heat insulating layer is changed depending on a position in the stacking direction of the fuel cell stack.   The size or thickness of the heat insulating layer is set such that the temperature difference between the fuel gas side and the oxidizing gas side at the outlet of the fuel gas channel or the outlet of the oxidizing gas channel is within a preset range. The fuel cell according to claim 1, wherein the fuel cell stack is changed according to a position in a stacking direction and a position in a flow path direction of the fuel cell stack.   The fuel according to any one of claims 1 to 3, wherein the heat insulating layer is formed by coating the surface of the separator on the cooling medium flow path side with a heat insulating coating material on the outlet side of the fuel gas side separator or the oxidizing gas side separator. battery.   The fuel cell according to claim 4, wherein the heat insulating coating material is a silicon-based polymer material or a conductive material.