JP2009070637A - Fuel cell, diffusion layer for fuel cell and fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of supplying stable voltage in a wide range from a low load region to a high load region and having an electrode diffusion layer substrate preventing the dryness of a membrane-electrode assembly to a high degree. <P>SOLUTION: A polymer electrolyte membrane 11 is interposed between an oxygen side diffusion layer 12 and a hydrogen side diffusion layer 13, and separators 14, 15 each having a groove-like gas passage are pressed against the outside of the gas diffusion layers 12, 13. The oxygen side diffusion layer 12 has a first microporous layer 12b and a second microporous layer 12c containing carbon powder and water repellent resin on both surfaces of a diffusion layer substrate 12a, and a reaction layer 12d containing carbon carrying a platinum catalyst and Nafion is formed on the first microporous layer 12 side. The first microporous layer 12b has two peaks of pore size distributions of 0.015 and 0.15 μm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell, a diffusion layer for a fuel cell, and a fuel cell system, and can be suitably used for an air-cooled solid polymer fuel cell system.

  A polymer electrolyte fuel cell includes a membrane-electrode assembly in which a membrane made of a polymer electrolyte is sandwiched between catalyst layers, and the outside of the catalyst layer is sandwiched between diffusion layers that play a role of current collection and gas diffusion. ing. In the catalyst layer, carbon particles carrying a catalyst such as platinum and a solid polymer electrolyte such as Nafion (registered trademark, Nafion (manufactured by Dupont)) are mixed. The both surfaces of the membrane-electrode assembly are sandwiched by separators having air or hydrogen gas flow paths to form unit cells, and a stack in which a plurality of unit cells are stacked is formed.

In this polymer electrolyte fuel cell, the following electrochemical reaction is performed.
Anode side: H ₂ → 2H ⁺ + 2e ⁻
Cathode side: 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O
Total reaction: H ₂ + 1 / 2O ₂ → H ₂ O
That is, hydrogen is supplied to the gas flow path of the separator on the anode side, and supplied to the catalyst layer through the diffusion layer. Then, hydrogen is oxidized by the electrochemical reaction in the catalyst layer to generate protons and electrons. The protons thus generated move in the catalyst layer and the polymer solid electrolyte while drawing water in the form of oxonium ions, and reach the cathode side. On the other hand, oxygen supplied to the cathode side combines with oxonium ions to generate water.

  As described above, in the polymer electrolyte fuel cell, since water moves from the anode side toward the cathode side, the membrane-electrode assembly is easily dried on the anode side, and the internal resistance of the fuel cell increases. This will cause the output of the fuel cell to decrease. On the other hand, water is supplied from the anode side on the cathode side, but the vapor pressure of water is increased by the heat generated by the fuel cell itself, and a large amount of water evaporated by the air flowing through the gas flow path of the separator is taken away. Even on the cathode side, the membrane-electrode assembly may be in a dry state.

  When the solid polymer electrolyte membrane constituting the membrane-electrode assembly is dried, proton conductivity is lowered, the internal resistance of the fuel cell is increased, and it is difficult to generate power. For this reason, the membrane-electrode assembly is cooled to reduce the vapor pressure of water, or the air supplied to the cathode is humidified to prevent drying of the membrane-electrode assembly. . However, this requires a cooling device and a humidifying device, which has the problem that the structure becomes complicated and large, and the manufacturing cost increases. In addition, since the cooling device and the humidifying device are operated by a part of the electric power generated by the fuel cell, there is a problem that energy efficiency is deteriorated.

  In this regard, a cooling device is not required for an air-cooled solid polymer fuel cell. However, in an air-cooled solid polymer fuel cell, the membrane-electrode assembly is increased by increasing the stoichiometric ratio (that is, the ratio of the amount of air supplied to the amount of air required for reaction with the supplied hydrogen gas). Therefore, the amount of water carried away by the air supplied to the cathode side increases, and the membrane-electrode assembly tends to be in a dry state.

In addition, as a method for preventing the membrane-electrode assembly from drying in the polymer electrolyte fuel cell, a microporous layer having conductivity and water repellency may be provided on the side of the diffusion layer in contact with the reaction layer or on both sides of the diffusion layer. It has been proposed (Patent Document 1). In a fuel cell using such a microporous layer, the water present in the reaction layer is repelled by the microporous layer, making it difficult for the water to pass through. Therefore, it is difficult to dry and the air supplied to the cathode side does not need to be humidified. However, it is said that the power generation efficiency does not decrease so much.
Japanese Patent Laid-Open No. 9-245800

  However, in the conventional air-cooled polymer electrolyte fuel cell, it is possible to prevent the membrane-electrode assembly from drying in the low load region, but the generated water generated in a large amount in the high load region is transferred to the oxidizing gas reaction layer. Since the supply is hindered, it is difficult to supply a stable voltage in a wide operation range.

  In addition, the fuel cell described in Patent Document 1 does not require a humidifier, but is required to have a methanol reformer. Since hydrogen obtained from the methanol reformer contains a large amount of water vapor, even if the reaction gas is not humidified by the humidifier, water is supplied to the membrane-electrode assembly by the water vapor supplied together with hydrogen. Is supplied.

  However, in order to provide a methanol reformer, the apparatus becomes complicated and large, and the manufacturing cost increases. Therefore, there is a need for a fuel cell, a fuel cell diffusion layer, and a fuel cell system that can be driven without a humidifier, a cooling device, or a methanol reformer, and that can highly prevent the membrane-electrode assembly from drying. It was.

  The present invention has been made in view of the above-described conventional situation, and can supply a stable voltage with a small voltage drop from a low load region to a high load region, and can dry a membrane-electrode assembly. It is an object to be solved to provide a fuel cell, a diffusion layer for a fuel cell, and a fuel cell system that can be highly prevented.

  In order to solve the above-mentioned conventional problems, the inventors examined the relationship between the pore diameter and the power generation characteristics of the water-repellent microporous layer formed on the reaction layer side of the diffusion layer substrate of the oxygen electrode. did. As a result, when the pore size of the microporous layer is small, it becomes difficult to move the liquid water in the microporous layer, so that it is difficult to dry. It was clarified that in a high-load region where there is a lot of water, flooding occurs due to water immersion and gas diffusion into the reaction layer becomes difficult, and the voltage drops rapidly. On the other hand, when the pore size of the microporous layer is large, the voltage is slightly low in the low load region, but liquid water easily moves in the high load region, and flooding phenomenon is prevented. Clarified that there are few. As a result of further research, the pore size distribution of the microporous layer formed on the reaction layer side of the diffusion layer base material has a low load by making the pore size distribution have two or more maximum peaks. It has been found that the fuel cell can prevent the drying in the region and the flooding phenomenon in the high load region, and can supply a stable voltage in a wide range from the low load region to the high load region, thereby completing the present invention. It was.

That is, the fuel cell of the first aspect of the present invention is a fuel cell in which both sides of a solid polymer electrolyte layer are sandwiched between a fuel electrode and an oxygen electrode composed of a reaction layer and a diffusion layer.
The diffusion layer of the oxygen electrode sucks out the water generated in the reaction layer and holds it as liquid water,
Formed on the reaction layer side of the diffusion layer base material, the pore size distribution has two or more maximum peaks, and at least one of the maximum peaks is a pore size that does not substantially allow liquid to pass through the gas; A first microporous layer having a pore size through which a liquid passes at least one of the maximum peaks;
And a second microporous layer that is formed on the opposite side of the diffusion layer substrate from the reaction layer and has a pore diameter that does not substantially allow liquid to pass through the gas.

  In the fuel cell according to the first aspect of the present invention, the diffusion layer of the oxygen electrode includes a diffusion layer base material that sucks out water generated in the reaction layer and holds it as liquid water. The first microporous layer has a pore size distribution having two or more maximum peaks, and at least one of the maximum peaks has a pore size through which a liquid can pass. For this reason, the water generated in the reaction layer passes through the pores through which the liquid in the first microporous layer passes and is held by the diffusion layer base material. Then, due to the presence of the second microporous layer having a pore diameter that does not substantially allow liquid to pass through the gas, water held in the diffusion base material is suppressed from being carried away by the gas flowing through the gas flow path. Therefore, it is possible to highly prevent the membrane-electrode assembly from being dried while preventing the flooding phenomenon in the high load region.

一方、反応ガスは極めて小さな径の通路であっても、液体水よりも容易に通過することができる。反応層側に形成されている第１マイクロポーラス層は、細孔径分布が２つ以上の極大ピークを有し、該極大ピークの少なくとも1つはガスを通して液体を実質的に通さない細孔径とされている。このため、液体水を通さない細孔を持つマイクロポーラス層により、反応層及び固体高分子電解質層の水を保持することができ、乾燥を防ぐことができる。また、第１のマイクロポーラス層には該極大ピークの少なくとも1つは液体を通す細孔径を有するため、燃料電池が高負荷領域で稼動され、反応層で多量の水が生成しても、液体を通す細孔を通って液体水が拡散層基材側に運ばれる。このため、フラッディング現象が防止され、電圧降下が防止されるのである。 Further, the first microporous layer has a pore size distribution having two or more maximum peaks, and at least one of the maximum peaks has a pore size that does not substantially allow liquid to pass through the gas. Drying in a low load region with little water can be prevented. The reason is as follows. That is, it is known that the water pressure ΔP required when water passes through the communicating pores is expressed by the following equation (1).

On the other hand, even if the reaction gas has a very small diameter, it can pass through more easily than liquid water. The first microporous layer formed on the reaction layer side has a pore size distribution having two or more maximum peaks, and at least one of the maximum peaks has a pore size that does not substantially allow liquid to pass through the gas. ing. For this reason, the water of the reaction layer and the solid polymer electrolyte layer can be retained by the microporous layer having pores that do not allow liquid water to pass through, and drying can be prevented. Further, since at least one of the maximum peaks in the first microporous layer has a pore diameter that allows liquid to pass therethrough, even if the fuel cell is operated in a high load region and a large amount of water is generated in the reaction layer, the liquid Liquid water is conveyed to the diffusion layer substrate side through the pores through which the liquid passes. For this reason, the flooding phenomenon is prevented and the voltage drop is prevented.

  Therefore, according to the fuel cell of the first aspect of the present invention, water retention and drainage (gas diffusion) can be balanced from a low load region with a small amount of generated water to a high load region with a large amount of generated water. Drying of the electrode assembly can be highly prevented. For this reason, stable power generation characteristics can be obtained from a low load region to a high load region.

  In the fuel cell of the second aspect of the present invention, the first microporous layer has a pore size distribution having two or more maximum peaks by containing a plurality of types of carbon powders having different particle sizes. It was decided that

  According to the test results of the inventors, when carbon particles are contained in the first microporous layer, the pore size distribution varies depending on the particle size of the carbon powder. That is, the carbon particles are usually formed by agglomerating fine particles to form secondary particles, and the secondary particles have pores communicating with the outside (that is, gaps generated in the carbon particles), The smaller the diameter of the communicating pore, the more difficult it is for water to pass through the microporous layer. For this reason, the pore diameter of the carbon used as the raw material for the microporous layer substantially matches the pore diameter of the microporous layer. For this reason, if a plurality of types of carbon powders having different particle diameters are contained, a microporous layer having a pore size distribution having two or more maximum peaks can be easily obtained. Thus, a fuel cell with a small voltage drop can be supplied easily and at low cost.

  In the fuel cell of the third aspect of the present invention, the first microporous layer has a substantially uniform pore size distribution in the surface direction and the thickness direction. Such a first microporous layer is easy to form, and as a result, a fuel cell with a low manufacturing cost.

  In the fuel cell according to the fourth aspect of the present invention, the first microporous layer has different pore size distributions in the thickness direction. With such a first microporous layer, for example, the reaction layer side in the first microporous layer has a small pore size distribution, preventing water movement and preventing drying, while the first microporous layer has a first pore on the diffusion layer side. By making the microporous layer have a large pore diameter, the water retention of the diffusion layer can be increased.

  In the fuel cell according to the fifth aspect of the present invention, the first microporous layer has different pore size distributions in the plane direction. In this case, the first microporous layer showing a fine pore size distribution is used in a place that is easy to dry, and the first microporous layer showing a coarse pore size distribution is used in a place that is difficult to dry. Can prevent dryness and flooding.

  In the fuel cell according to the sixth aspect of the present invention, the first microporous layer has a hole having a diameter of 1 μm or more penetrating in the thickness direction. In this case, the first microporous layer can easily pass liquid water in the thickness direction, and the flooding phenomenon can be more reliably prevented.

  In the fuel cell according to the seventh aspect of the present invention, the first and second microporous layers are added with a water-repellent resin. In this case, the water wettability of the microporous layer is reduced, and water permeation can be prevented without hindering gas permeability. For this reason, drying of the membrane-electrode assembly can be prevented without hindering the supply of oxygen gas to the reaction layer.

  In the fuel cell according to the eighth aspect of the present invention, the diffusion layer base material is made of a metal porous body. If the porous metal body is used, the mechanical strength of the diffusion layer can be increased. Therefore, the diffusion layer can be thinned to reduce the size and weight of the fuel cell. Further, when the gas channel is formed by pressing the separator against the diffusion layer, the diffusion layer due to the pressing can be prevented from being deformed or broken. Any metal that can withstand the corrosive environment in the fuel cell can be used. Examples of such metals include titanium sintered bodies, stainless steel sintered bodies, Ni-cermets, stainless steel sintered bodies, etc., and those having a structure in which fibers made of the above metals are formed in a three-dimensional network. Is mentioned.

  The fuel cell diffusion layer of the present invention can be used in the fuel cell of the present invention. That is, the diffusion layer for a fuel cell of the present invention is formed on the one side of the diffusion layer base material that sucks out the water generated in the reaction layer and holds it as liquid water, and has two pore size distributions. A first microporous having the above-mentioned maximum peak, wherein at least one of the maximum peaks is a pore diameter that does not substantially allow liquid to pass through the gas, and at least one of the maximum peaks has a pore diameter that allows the liquid to pass through. And a second microporous layer that is formed on the other surface side of the diffusion layer base material and has a pore diameter that does not allow liquid to substantially pass through the gas.

In addition, a fuel cell system can be manufactured using the fuel cell of the present invention. That is, the fuel cell system of the present invention includes a fuel cell in which both sides of a solid polymer electrolyte layer are sandwiched by a fuel electrode and an oxygen electrode composed of a reaction layer and a diffusion layer, and a fuel gas that supplies fuel gas to the fuel electrode In a fuel cell system, comprising: a manual supply, an air supply means for supplying air as an oxidizing gas and a refrigerant gas to the oxygen electrode, and a control means for controlling the temperature of the fuel cell by controlling an air supply amount ,
At least the oxygen electrode diffusion layer is formed on the reaction layer side of the diffusion layer substrate that sucks out the water generated in the reaction layer and holds it as liquid water, and has a maximum pore size distribution of two or more. A first microporous layer having a peak, wherein at least one of the maximum peaks is a pore size that does not substantially allow liquid to pass through the gas, and at least one of the maximum peaks has a pore size that allows the liquid to pass;
A second microporous layer that is formed on the opposite side of the reaction layer of the diffusion layer substrate and has a pore diameter that does not substantially allow liquid to pass through the gas,
The control means controls the stoichiometric ratio of the supply air to be in the range of 10 to 200.
Here, the stoichiometric ratio of the supply air refers to the ratio of the supply amount to the air consumption required for the generated current.

  In the fuel cell system of the present invention, the diffusion layer of the oxygen electrode comprises a member that sucks out the water produced in the reaction layer into the diffusion layer and holds it as liquid water in the diffusion layer. And formed on the reaction layer side of the diffusion layer substrate, the pore size distribution has two or more maximum peaks, and at least one of the maximum peaks is a pore size that does not substantially allow liquid to pass through the gas. And at least one of the maximum peaks is formed on the opposite side of the reaction layer of the diffusion layer base material with a first microporous layer having a pore size through which the liquid passes, and the pore size through which the liquid does not substantially pass through the gas And a second microporous layer. For this reason, as described above, a stable voltage with a small voltage drop can be supplied from the low load region to the high load region, and drying of the membrane-electrode assembly can be highly prevented. Even in a region where the stoichiometric ratio of the supply air is as high as 10 to 200, the membrane-electrode assembly can be prevented from being dried, and the output of the fuel cell can be maintained. Therefore, it can be suitably used for a polymer electrolyte fuel cell having a large stoichiometric ratio of supply air, such as an air-cooled polymer electrolyte fuel cell. Furthermore, the air-cooled solid polymer fuel cell can be driven without a methanol reformer. Various air blowers such as a sirocco fan and a turbo fan can be used as the air supply means.

Hereinafter, embodiments embodying a fuel cell according to the present invention will be described.
(Embodiment 1)
The fuel cell of Embodiment 1 is configured by stacking a plurality of fuel cell single-layer cells 10 shown in FIG. In this fuel cell single-layer cell 10, a polymer electrolyte membrane 11 made of Nafion (registered trademark) is sandwiched between an oxygen side diffusion layer 12 and a hydrogen side diffusion layer 13, and a groove-like gas channel is formed outside thereof. The formed separators 14 and 15 are press-contacted by a mounting jig (not shown).

  The oxygen side diffusion layer 12 is a porous first microporous layer containing carbon powder and a water-repellent resin on both sides of a diffusion layer substrate 12a made of carbon woven fabric, carbon paper or the like capable of gas diffusion. 12b and a second microporous layer 12c are formed, and a reaction layer 12d containing PTFE supported carbon and a platinum catalyst is formed on the first microporous layer 12b side. The pore size distribution of the first microporous layer 12b has two maximum peaks. Among the maximum peaks, the peak with the smaller pore diameter is 0.1 μm or less, and water is not substantially passed through the gas. On the other hand, the peak having the larger pore diameter is 1 μm or more, and water can be passed therethrough.

  In the hydrogen-side diffusion layer 13, a reaction layer 13b containing carbon carrying a platinum catalyst and PTFE is formed on the polymer electrolyte membrane 11 side of the diffusion layer base material 13a.

  As the diffusion layer base materials 12a and 13a, for example, carbon cloth, carbon paper, a nonwoven fabric made of carbon fiber, or the like can be used. The first and second microporous layers 12b and 12c can be used by mixing water-repellent resin powder and carbon powder. Specific examples of the water-repellent resin powder include fluorocarbon polymers (for example, polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA)). ), Polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), ethylene / tetrafluoroethylene copolymer (ETFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), etc. ). Examples of the carbon powder include carbon black, graphite powder, carbon nanofiber, furnace black, and acetylene black.

  In the fuel cell single-layer cell 10 of Embodiment 1 configured as described above, the pore size distribution has two or more maximum peaks on the reaction layer 12d side of the diffusion layer base material 12a on the oxygen electrode side, and the maximum At least one of the peaks is provided with a first microporous layer 12b having a small pore diameter of 0.1 μm or less that does not allow water to substantially pass through the gas. For this reason, since water vapor easily permeates and liquid water hardly permeates, excess water that hinders diffusion of the oxidizing gas can be discharged to the diffusion layer substrate 12a, and the reaction layer 12d and the solid polymer electrolyte layer 11 can be discharged. Can prevent drying. In addition, since the second microporous layer 12c also has a pore diameter that does not allow liquid to pass through the gas, it can move to the flow path side of the oxygen-side separator 14 only in the state of water vapor. For this reason, it can hold | maintain as a liquid with the diffusion layer base material 12a, and when the reaction layer 12d dries, the water currently hold | maintained can be supplied. For this reason, drying of the polymer solid electrolyte membrane 11 can be prevented to a high degree. Furthermore, since the pore size distribution of the first microporous layer 12b has two or more maximum peaks, and at least one of the maximum peaks has a pore size through which the liquid passes, a flooding phenomenon in a high load region. Can be prevented. For this reason, in the fuel cell of embodiment, it becomes a fuel cell with a small voltage drop in a wide load range.

Hereinafter, examples in which the fuel cell of the present invention is more specific will be described in detail in comparison with comparative examples.
Example 1
Carbon black powder having a primary particle diameter of 16 nm and carbon black powder having a primary particle diameter of 48 nm are mixed at a weight ratio of 1: 1. Then, 35 parts by weight of a fine powder of polytetrafluoroethylene (PTFE) is added to 100 parts by weight of the mixture, mixed and molded to obtain a carbon-PTFE self-supporting film. Then, a plain weave carbon cloth is prepared, and is sandwiched between the two welded carbon-PTFE self-supporting films and thermocompression bonded at 345 ° C. to be integrated.

Next, 2 g to 200 g of Nafion (registered trademark) solution (5 wt% water / isopropanol solution) is added to 1 g of commercially available platinum-supported carbon (platinum content 60 wt%), and stirred with a hybrid mixer to obtain a catalyst paste. The surface of the film integrated by the method was printed so that the amount of Pt supported was 0.01 to ² mg / cm ² and dried to obtain a diffusion layer with a reaction layer.
Instead of printing on the diffusion layer to form the reaction layer, the catalyst paste is printed on a polytetrafluoroethylene sheet, dried, and peeled to produce a self-supporting reaction layer film. The reaction layer may be formed by thermocompression bonding with a diffusion layer.

  A polymer electrolyte membrane made of Nafion (registered trademark) is prepared by preparing a diffusion layer with an oxygen electrode side reaction layer produced as described above and a diffusion layer with a hydrogen electrode side reaction layer obtained by pressure-bonding the membrane only on the reaction layer side. The reaction layer was sandwiched from both sides and pressed by hot pressing. Further, oxygen and hydrogen gas supply passages were formed on the outside thereof to produce a fuel cell single layer cell.

(Comparative Example 1)
In Comparative Example 1, only carbon black having a primary particle diameter of 16 nm was used as carbon for forming the microporous layer. Others are the same as those of the fuel cell single-layer cell of Example 1, and the description is omitted.

(Comparative Example 2)
In Comparative Example 2, only carbon black having a primary particle diameter of 48 nm was used as carbon for forming the microporous layer. Others are the same as those of the fuel cell single-layer cell of Example 1, and the description is omitted.

<Evaluation>
(Measurement of pore size distribution)
The pore size distribution of the carbon-PTFE self-supporting films according to Example 1 and Comparative Examples 1 and 2 prepared above was measured. As a result, as shown in FIG. 2, the peak of the pore size distribution is 0.015 μm in Comparative Example 1, and the peak of the pore size distribution is 0.15 μm in Comparative Example 2, each having a single pore size distribution peak. On the other hand, in Example 1, the peak of the pore size distribution showed two peaks of 0.015 μm and 0.15 μm.

(Measurement of power generation characteristics)
Further, the power generation characteristics of the fuel cell single layer cells of Example 1 and Comparative Examples 1 and 2 manufactured as described above were measured. That is, in the gas flow path of the separator on the air electrode side of the fuel cell single layer cell of Example 1 and Comparative Examples 1 and 2, as shown in FIG. 3, the air pump 31, the temperature of the air, and the humidity of the air A control device 32 for adjusting is connected. Further, a hydrogen gas supply device 33 is connected to the gas flow path of the separator on the fuel electrode side. Then, the control unit is configured to introduce the dry hydrogen gas from the hydrogen gas supply device 33 into the gas flow path of the fuel electrode side separator and to supply the stoichiometric ratio of supply air to the gas flow path of the oxygen side separator. The cell voltage was controlled at 32, the cell temperature was 60 ° C., and the cell voltage at various current values was measured.

  As a result, as shown in FIG. 4, in Comparative Example 1 having pores with small pore diameter distribution peaks of 0.015 μm, the voltage dropped rapidly in the high load region, although the voltage was high in the low load region. Further, in Comparative Example 2 having large pores having a pore size distribution peak of 0.15 μm, the voltage in the low load region was low, although there was no rapid voltage drop in the high load region. In contrast, in Example 1 in which the maximum peak of the pore size distribution has two peaks of 0.015 μm and 0.15 μm, it can be seen that a stable voltage can be obtained in a wide load range from a low load region to a high load region. It was.

<Fuel cell system>
An embodiment of the fuel cell system of the present invention is shown in FIG. This fuel cell system is air-cooled, and a fuel cell stack 40, a hydrogen gas supply system 50 for supplying hydrogen gas as a fuel gas to the fuel cell stack 40, and air as an oxidizing gas to the fuel cell stack 40. The air supply system 60 for supplying and the control apparatus 70 for controlling the air blower 61 provided in the air supply system 60 are provided.

  The fuel cell stack 40 has a structure in which the single-layer cells for fuel cells of the above-described embodiments are stacked, and in order to introduce air into the air flow path of the fuel cell stack 40 upstream of an air flow path (not shown). The air manifold 41 is provided, and an air duct 42 for exhausting air is provided downstream of the air flow path. The air duct 42 is provided with a temperature sensor 43 for measuring the temperature of the exhaust gas. The temperature sensor 43 is connected to the control device 70, receives a signal related to the temperature from the temperature sensor 43, and controls the blower 61. It can be controlled.

  The air supply system 60 is provided with a blower 61 for taking in outside air, and is connected to the air manifold 41 through a supply pipe 62. The blower 61 has a capacity of a total pressure of 30 kPa. Note that the air supply system 30 is not provided with a humidifier.

  In the hydrogen supply system 50, a hydrogen cylinder 51 serving as a hydrogen source is connected to a hydrogen pump 58 via adjustment valves 52 to 57, and further connected to a hydrogen gas flow path (not shown) of the fuel cell stack 40 from the hydrogen pump 58. Has been.

When driving the fuel cell system configured as described above, the adjustment valves 52 to 57 of the hydrogen supply system 50 are adjusted to a predetermined pressure, supplied to the hydrogen pump 58, and further driven by driving the hydrogen pump 58. Then, hydrogen gas is supplied to the hydrogen gas flow path of the fuel cell stack 40 at a predetermined flow rate.
Further, the blower 61 of the air supply system 60 is driven to supply air from the air manifold 41 to the air flow path of the fuel cell stack 40. Thereby, an electrochemical oxidation reaction of hydrogen gas and an electrochemical reduction reaction of oxygen are performed in the fuel cell stack 40, and a current flows to the load 80.
Excess air supplied to the air flow path is exhausted from the air duct 42, and the temperature sensor 43 senses the temperature of the exhausted air and transmits a temperature-related signal to the control device 70. Further, the control device 70 compares the temperature sensed by the temperature sensor 43 with the set temperature. If the sensed temperature is higher than the set temperature, the output of the blower 61 is increased to send more air, and the fuel cell stack 40 Air-cool. Further, when the sensed temperature is lower than the set temperature, the output of the blower 61 is lowered to lower the air flow rate. As a result, the temperature of the fuel cell stack 40 increases. Thus, the stoichiometric ratio can be adjusted by the control device 70.

In the fuel cell system of the embodiment, the diffusion layer of the oxygen electrode in the fuel cell stack 40 sucks out water generated in the reaction layer into the diffusion layer, and is held as liquid water in the diffusion layer.
For this reason, even if air is supplied to the oxygen electrode, water is retained in the diffusion layer, and the amount that is evaporated and taken away into the air is reduced. For this reason, the drying of the membrane-electrode assembly can be highly prevented. For this reason, although the air-cooled fuel cell is driven with a large stoichiometric ratio, the membrane-electrode assembly of the fuel cell stack 40 is prevented from being dried and the output of the fuel cell system is prevented from being lowered. Furthermore, since the pore size distribution of the first microporous layer has two or more maximum peaks, drying in a low load region and flooding in a high load region can be prevented, and a voltage drop over a wide load range. It becomes a small fuel cell system.

(Example 2)
Example 2 is a diffusion layer in which the first microporous layer has a different pore size distribution in the thickness direction, and is produced as follows.
35 parts by weight of a fine powder of polytetrafluoroethylene (PTFE) is added to and mixed with 100 parts by weight of carbon black powder having a primary particle size of 16 nm, and this carbon-PTFE mixture is welded to form a self-supporting film. Furthermore, 35 parts by weight of a fine powder of polytetrafluoroethylene (PTFE) is added to and mixed with 100 parts by weight of carbon black powder having a primary particle diameter of 48 nm, and this carbon-PTFE mixture is welded to form a self-supporting film. By sticking the two carbon-PTFE self-supporting films having different pore diameter distributions obtained in this way by hot pressing, a first microporous layer having different pore diameter distributions in the thickness direction can be produced. Furthermore, using the first microporous layer thus obtained, the diffusion layer of Example 2 is obtained by the same method as in Example 1.

(Example 3)
Example 3 is a diffusion layer in which the first microporous layer has a different pore size distribution in the plane direction, and is produced as follows.
Two types of carbon-PTFE self-supporting membranes having different pore size distributions are prepared by the same method as in Example 2. The two types of carbon-PTFE self-supporting membranes thus prepared were used as diffusion layers with an oxygen electrode side reaction layer, and were arranged according to the location (for example, carbon with a small pore diameter in a location that tends to be dried due to high temperature) A PTFE self-supporting membrane) and a polymer electrolyte membrane made of Nafion (registered trademark). Thus, the first microporous layer having different pore size distributions in the plane direction can be produced. Furthermore, the diffusion layer of Example 3 is obtained by the same method as in Example 1 using the first microporous layer thus obtained.

Example 4
Example 4 is a diffusion layer provided with a first microporous layer having pores penetrating in the thickness direction, and is produced as follows.
35 parts by weight of a fine powder of polytetrafluoroethylene (PTFE) is added to and mixed with 100 parts by weight of carbon black powder having a primary particle size of 16 nm, and this carbon-PTFE mixture is welded to form a self-supporting film. A pore penetrating in the thickness direction is formed in the self-supporting film using a laser beam or a needle. Using the thus obtained self-supporting membrane with through-holes, a diffusion layer is produced by the same method as in Example 1.

  The present invention is not limited to the description of the embodiments and examples of the invention described above. Various modifications are also included in the present invention as long as those skilled in the art can easily conceive without departing from the scope of the claims.

1 is a schematic cross-sectional view of a single-layer cell for a fuel cell according to Embodiment 1. FIG. 2 is a pore size distribution curve of a first microporous layer in Example 1 and Comparative Examples 1 and 2. FIG. It is a block diagram of a fuel cell system. 5 is a graph showing power generation characteristics of fuel cell single-layer cells according to Example 1 and Comparative Examples 1 and 2. FIG. It is a systematic diagram of a fuel cell system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Solid polymer electrolyte layer 12d, 13b, 16d ... Reaction layer 12, 13, 16 ... Diffusion layer 12a, 13a ... Diffusion layer base material 12b ... 1st microporous layer 12c ... 2nd microporous layer 31, 61, 62 ... Air supply means (61 ... Air pump, 62 ... Supply pipe)
33, 51-58 ... hydrogen gas supply device (51 ... hydrogen cylinder, 52-57 ... regulating valve, 58 ... hydrogen pump)
32, 70 ... Control device (control means)

Claims (11)

In a fuel cell in which both sides of a solid polymer electrolyte layer are sandwiched between a fuel electrode and an oxygen electrode composed of a reaction layer and a diffusion layer,
The diffusion layer of the oxygen electrode sucks out the water generated in the reaction layer and holds it as liquid water,
Formed on the reaction layer side of the diffusion layer base material, the pore size distribution has two or more maximum peaks, and at least one of the maximum peaks is a pore size that does not substantially allow liquid to pass through the gas; A first microporous layer having a pore size through which a liquid passes at least one of the maximum peaks;
A fuel cell comprising: a second microporous layer that is formed on a side opposite to the reaction layer of the diffusion layer base material and has a pore diameter that does not substantially allow liquid to pass through the gas.   The first microporous layer has a pore size distribution having two or more maximum peaks by containing a plurality of types of carbon powders having different particle sizes. Fuel cell.   3. The fuel cell according to claim 1, wherein the first microporous layer has a substantially uniform pore size distribution in a surface direction and a thickness direction.   3. The fuel cell according to claim 1, wherein the first microporous layer has different pore size distributions in a thickness direction.   3. The fuel cell according to claim 1, wherein the first microporous layer has different pore size distributions in a plane direction. 4.   3. The fuel cell according to claim 1, wherein the first microporous layer has a hole having a diameter of 1 μm or more penetrating in the thickness direction. 4.   The fuel cell according to any one of claims 1 to 6, wherein a water-repellent resin is added to the first and second microporous layers.   The fuel cell according to any one of claims 1 to 7, wherein the diffusion layer substrate is made of a metal porous body. A diffusion layer base material that sucks out water generated in the reaction layer and holds it as liquid water;
Formed on one side of the diffusion layer substrate, the pore size distribution has two or more maximum peaks, and at least one of the maximum peaks is a pore size that does not substantially allow liquid to pass through the gas, and the maximum At least one of the peaks has a first microporous layer having a pore size through which liquid passes;
A fuel cell diffusion layer, comprising: a second microporous layer formed on the other surface side of the diffusion layer base material and having a pore diameter that does not allow liquid to substantially pass through the gas. A fuel cell in which both sides of a solid polymer electrolyte layer are sandwiched by a fuel electrode and an oxygen electrode composed of a reaction layer and a diffusion layer, a fuel gas supply hand-pump for supplying fuel gas to the fuel electrode, and an oxidation to the oxygen electrode In a fuel cell system comprising air supply means for supplying air as gas and refrigerant gas, and control means for controlling the temperature of the fuel cell by controlling the air supply amount,
At least the oxygen electrode diffusion layer is formed on the reaction layer side of the diffusion layer substrate that sucks out the water generated in the reaction layer and holds it as liquid water, and has a maximum pore size distribution of two or more. A first microporous layer having a peak, wherein at least one of the maximum peaks is a pore size that does not substantially allow liquid to pass through the gas, and at least one of the maximum peaks has a pore size that allows the liquid to pass;
A second microporous layer that is formed on the opposite side of the reaction layer of the diffusion layer substrate and has a pore diameter that does not substantially allow liquid to pass through the gas,
The fuel cell system, wherein the control means controls the stoichiometric ratio of supply air to be in a range of 10 to 200.   9. The fuel cell system according to claim 8, wherein the air supply means uses a blower.

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