JP5233183B2 - Fuel cell and fuel cell system. - Google Patents

Description

  The present invention relates to 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 a decrease in the output of the fuel cell. 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 the 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 a polymer electrolyte fuel cell, it has also been proposed to provide a conductive water-repellent layer on the side of the diffusion layer that contacts the reaction layer or on both sides of the diffusion layer. (Patent Document 1). In the fuel cell using the diffusion layer with the conductive water-repellent layer, the water present in the reaction layer is repelled by the conductive water-repellent layer, making it difficult to pass through. It is said that the power generation efficiency does not decrease so much even if it is not humidified.
Japanese Patent Laid-Open No. 9-245800

The fuel cell described in Patent Document 1 is not required to have 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. For this reason, there has been a demand for a diffusion layer that can be driven without a humidifier, a cooling device, or a methanol reformer and can highly prevent drying of the membrane-electrode assembly.

  This invention is made | formed in view of the said conventional situation, Comprising: It is set as the problem which should be solved to provide the fuel cell and fuel cell system which can prevent the drying of a membrane-electrode assembly highly.

  A fuel cell according to a 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, and the diffusion of the oxygen electrode and / or the fuel electrode. The layer is composed of a member that sucks out the water present on the reaction layer side into the diffusion layer and holds it as liquid water in the diffusion layer.

  In the fuel cell according to the first aspect of the present invention, the oxygen electrode and / or the diffusion layer of the fuel electrode sucks out the water present on the reaction layer side into the diffusion layer and holds the liquid water in the diffusion layer. Consists of. For this reason, the water on the reaction layer side is held in the diffusion layer, and it is suppressed that the water in the diffusion layer is taken away by the gas flowing through the gas flow path. For this reason, the drying of the membrane-electrode assembly can be highly prevented.

In the fuel cell according to the second aspect of the present invention, the diffusion layer of the oxygen electrode sucks out the water generated in the reaction layer into the diffusion layer and holds it as liquid water in the diffusion layer, and the diffusion layer. A first microporous layer formed on the reaction layer side of the layer base material and having a pore size smaller than that of the diffusion layer base material; And a second microporous layer having a pore diameter that does not substantially pass.
If it is like this, the diffusion layer of the oxygen electrode sucks out the water produced in the reaction layer into the diffusion layer, and is retained 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.

In the fuel cell according to the third aspect of the present invention, the diffusion layer of the fuel electrode can hold the water generated in the reaction layer of the oxygen electrode through the back diffusion of the solid polymer electrolyte layer and moved to the fuel electrode side. A diffusion layer substrate, a first microporous layer formed on the reaction layer side of the diffusion layer substrate and having a smaller pore diameter than the diffusion layer substrate, and opposite to the reaction layer of the diffusion layer substrate And a second microporous layer having a pore diameter that is formed on the side and does not substantially allow liquid to pass through the gas.
In this case, since the water that has moved through the solid polymer electrolyte layer by back diffusion is retained in the diffusion layer, the amount that is evaporated and carried away into the hydrogen gas is reduced. For this reason, the drying of the membrane-electrode assembly can also be prevented to a high degree.

  In a fuel cell not provided with a reforming device for supplying fuel gas or a fuel cell not provided with a humidifier, the fuel gas contains almost no water vapor, so that the diffusion layer on the fuel electrode side is also easily dried. In such a case, the fuel cell according to the third aspect of the present invention is particularly useful.

  In the fuel cell according to the fourth aspect of the present invention, the diffusion layer is formed on the diffusion layer base material holding water and the reaction layer side of the diffusion layer base material, and has a pore size smaller than that of the diffusion layer base material. And a second microporous layer formed on the side opposite to the reaction layer of the diffusion layer base material and having a pore diameter that does not substantially allow liquid to pass through the gas.

一方、反応ガスは極めて小さな径の通路であっても水よりも容易に通過することができる。本発明の第２の局面の燃料電池及び第３の局面の燃料電池では、拡散層において、反応層側に形成されている第１マイクロポーラス層は、拡散層基材よりも細孔径が小さくされている。このため、水蒸気は透過しやすく、水は透過し難くなることから、反応層及び固体高分子電解質層の乾燥を防ぐことができる。また、反応層と反対側に形成されている、第2ポーラス層は、ガスを通して液体を通さない細孔径を有するため、水蒸気の状態でしか流路側へ移動することはできない。このため、水は拡散層基材に保持され、空気中や水素ガス中へ蒸発して持ち去られる量が少なくなる。このため、膜−電極接合体の乾燥を高度に防ぐことができる。 It is known that the water pressure ΔP required when water passes through the communicating pores is represented by the following equation (1).

On the other hand, the reaction gas can pass through even a very small diameter passage more easily than water. In the fuel cell of the second aspect and the fuel cell of the third aspect of the present invention, in the diffusion layer, the first microporous layer formed on the reaction layer side has a pore diameter smaller than that of the diffusion layer substrate. ing. For this reason, since water vapor | steam is easy to permeate | transmit and water becomes difficult to permeate | transmit, drying of a reaction layer and a solid polymer electrolyte layer can be prevented. In addition, the second porous layer formed on the side opposite to the reaction layer has a pore diameter that does not allow liquid to pass through the gas, and therefore can move to the channel side only in the state of water vapor. For this reason, water is held by the diffusion layer base material, and the amount that is evaporated away into the air or hydrogen gas is reduced. For this reason, the drying of the membrane-electrode assembly can be highly prevented.

  In the fuel cell according to the fifth aspect of the present invention, the first and second microporous layers have a pore diameter of 0.15 μm or less. According to the above formula (1), the smaller the pore size of the microporous layer, the greater the water pressure ΔP required when water passes through the microporous layer, making it difficult for water to pass. According to the inventor's test results, if the microporous layer has a pore size of 0.15 μm or less, even if it is used as a diffusion layer of an air-cooled fuel cell without humidifying the reaction gas, the voltage drop is small. As a result, the power generation efficiency is improved. Here, the pore diameter means a pore diameter communicating with the outside among the pores existing in the microporous layer. Such a pore diameter can be measured with a porosimeter.

  In the fuel cell according to the sixth aspect of the present invention, the first and second microporous layers have a large number of carbon particles, and the pore diameter is controlled by gaps generated between the carbon particles. Carbon particles usually have fine particles agglomerated to form secondary particles, and the secondary particles have pores communicating with the outside (that is, gaps formed in the carbon particles). The smaller the pore diameter is, 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. Therefore, the pore diameter of the microporous layer can be controlled by setting the pore diameter in the gap generated in the carbon particles.

  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 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, it is possible to prevent the diffusion layer from being deformed or broken due to the pressing. 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-Celmet, and stainless steel sintered bodies.

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 is
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 diffusion layer of the oxygen electrode is composed of a member that sucks out water generated in the reaction layer into the diffusion layer and holds it as liquid water in the diffusion layer,
The control means controls the stoichiometric ratio of the supply air to be in the range of 10 to 200.

  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. For this reason, as described above, drying of the membrane-electrode assembly can be highly prevented. For this reason, 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 drying, 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.

  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 the first embodiment configured as described above, the reaction layer 12d side of the diffusion layer substrate 12a on the oxygen electrode side has a pore diameter much smaller than that of the diffusion layer substrate 12a. Since one microporous layer 12b is provided, water vapor is easily permeable and liquid water is difficult to permeate. Therefore, excess water that prevents the diffusion of the oxidizing gas can be discharged to the diffusion layer substrate 12a, and the reaction Drying of the layer 12d and the solid polymer electrolyte layer 11 can be prevented. 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.

(Embodiment 2)
As shown in FIG. 2, the fuel cell single-layer cell 20 of Embodiment 2 includes a porous microporous layer containing carbon powder and a water-repellent resin on both sides of the hydrogen-side diffusion layer 16 and the diffusion layer substrate 16a. 16b and 16c are formed, and a reaction layer 16d containing a carbon carrying a platinum catalyst and Nafion is formed on the polymer electrolyte membrane 11 side. Other configurations are the same as those in the first embodiment, and the same components are denoted by the same reference numerals and description thereof is omitted.

  In the fuel cell single layer cell 20 of the second embodiment configured as described above, the first microporous layer 16b and the second microporous layer similar to the diffusion layer 12 on the oxygen electrode side are also formed on the diffusion layer 16 on the hydrogen electrode side. A layer 16c is formed. For this reason, not only the oxygen electrode side but also the amount that is evaporated and held in the fuel gas is reduced, and the drying of the polymer solid electrolyte membrane 11 can be further prevented.

Example 1
A fine powder of polytetrafluoroethylene is mixed with the carbon black powder (primary particle diameter 16 nm) to 35% by weight, and then a plain weave carbon cloth is prepared. They are integrated by thermocompression bonding at 345 ° C.
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-supporting 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.

(Example 2)
In Example 2, carbon black having a primary particle diameter of 35 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.

(Example 3)
In Example 3, 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.

(Comparative Example 1)
In Comparative Example 1, the microporous layer was formed only on the reaction layer side, and the microporous layer was not formed on the flow path side. Others are the same as the fuel cell single layer cell of Example 3, and description is abbreviate | omitted.

  In Examples 1 to 3 and Comparative Example 1, the pore distribution of the microporous layer is shown in FIG.

<Evaluation>
As shown in FIG. 4, in the gas flow path of the separator on the air electrode side of the fuel cell single layer cells of Examples 1 to 3 and Comparative Example 1 produced in this way, the air pump 31, the temperature of the air, the humidity of the air, A control device 32 for adjusting the control 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 dew points was measured.

  As a result, as shown in FIGS. 5 and 6, Examples 1 to 3 show a high cell voltage even at a low dew point temperature, and in particular, Examples using the finest carbon whose primary particle diameter is 16 nm for the microporous layer. 1 showed the highest value. On the other hand, in the fuel cell single-layer cell of Comparative Example 1, the cell voltage was low, and particularly when the current was as large as 6 A, the cell voltage was 0 and power generation was impossible. In Examples 1 to 3, since a microporous layer in which water vapor easily permeates and water hardly permeates is formed in the diffusion layer base on the air electrode side, the air is supplied to the gas flow path. This is because the amount held by evaporation is reduced. From the above results, in the fuel cell single-layer cells of Examples 1 to 3, the membrane-electrode assembly can be highly prevented from drying, the supply air is not humidified, and dry hydrogen is used as the fuel gas. As a result, it was found that excellent power generation performance can be achieved as an air-cooled solid polymer electrolyte fuel cell.

Example 4
In Example 4, carbon black having a primary particle diameter of 48 nm was used as a material for forming the microporous layer on the hydrogen electrode side and the microporous layer on the air electrode side. Other conditions are the same as those of the fuel cell single-layer cell of Example 1, and the description thereof is omitted.

(Example 5)
In Example 5, carbon black having a primary particle size of 48 nm is used as a material for forming a microporous layer on the hydrogen electrode side, and carbon black having a primary particle size of 16 nm is used as a material for forming a microporous layer on the air electrode side. Was used. Other conditions are the same as those of the fuel cell single-layer cell of Example 1, and the description thereof is omitted.

(Example 6)
In Example 6, carbon black having a primary particle diameter of 16 nm was used as a material for forming the microporous layer on the hydrogen electrode side and the microporous layer on the air electrode side. Other conditions are the same as those of the fuel cell single-layer cell of Example 1, and the description thereof is omitted.

<Evaluation>
About the fuel cell single layer cell of Examples 4-6 produced as mentioned above, the cell voltage in 15 degreeC was measured. The hydrogen gas was measured using a dry gas in a sealed state with a flow. Hydrogen gas was exhausted as off-gas every predetermined time. The dew points of the introduced air were controlled to be 15 ° C. and 25 ° C., and the temperature of the fuel cell single layer cell was maintained at 60 ° C. by circulating temperature-controlled water.

As a result, as shown in Table 1 below, in Example 4 using a microporous layer having a pore size of 0.15 μm for both the hydrogen electrode and the air electrode, the pore size of the hydrogen electrode was 0, compared to 0.32 V. In Example 5 where the pore diameter of the air electrode was 0.015 μm, it was 0.50 V, and in Example 6 where the pore diameter of both the hydrogen electrode and the air electrode was 0.015 μm, it was 0.57 V.
From the above results, it was found that the cell voltage was higher when both the hydrogen electrode and the air electrode were formed with a microporous layer having a fine pore diameter. The reason for this is explained as follows. That is, the smaller the pore size of the microporous layer, the greater the water pressure ΔP required when water passes through the microporous layer, making it difficult for water to pass. For this reason, water is held in the diffusion layer, the drying of the solid polymer electrolyte layer and the reaction layer can be prevented, the voltage drop is reduced, and the power generation efficiency is also improved.

Moreover, about the fuel cell single layer cell of Examples 4-6, the cell voltage was measured by changing the dew point of the air introduce | transduced into the air electrode side. As measurement conditions, the cell temperature was 60 ° C or 65 ° C, and the dew point of the introduced air was 14 ° C or 24 ° C. Hydrogen introduced to the hydrogen electrode side was circulated in an enclosed state, and the circulated hydrogen was exhausted as off-gas every predetermined time. The cell voltage was measured at a constant current of 2A. In addition, the relationship between the passage of time and the cell voltage, and the relationship between the passage of time and the internal resistance were also measured.
The measurement result of the cell voltage is shown in FIG. From this figure, the cell voltage under the same conditions is Example 4 <Example 5 <Example 6, and in particular, in the measurement at 65 ° C. in Example 4, the cell voltage becomes 0 and power generation is impossible. I understood. Here, Example 4 uses a microporous layer having a pore diameter of 0.15 μm for both the hydrogen electrode and the air electrode. In Example 5, the pore diameter of the hydrogen electrode is 0.15 μm and the pore diameter of the air electrode is A microporous layer of 0.015 μm is used, and since the microporous layer having a pore diameter of 0.015 μm is used for both the hydrogen electrode and the air electrode in Example 6, both the hydrogen electrode and the oxygen electrode have fine pore diameters. It was found that the cell voltage increased as the microporous layer was formed. The reason for this is also understood by the fact that the smaller the pore size of the microporous layer, the more difficult it is for water to pass through, and the water is retained in the diffusion layer and the solid polymer electrolyte layer and reaction layer can be prevented from drying.

  FIG. 9 shows the relationship between time and cell voltage, and time and internal resistance. It can be seen that the periodical change of each graph is due to the effect of offgas exhaust since it is synchronized with the offgas exhaust cycle. In Example 4 using a microporous layer of 0.15 μm for both the hydrogen electrode and the air electrode, it can be seen that the cell voltage greatly drops and the internal resistance jumps greatly during off-gas exhaust. And at the same time when the dew point of the introduced air was changed from 24 ° C. to 14 ° C., the cell voltage became 0 and the internal resistance jumped greatly. This is a result of the fact that water is exhausted together with hydrogen by off-gas exhaust, and the solid polymer electrolyte layer and the reaction layer are in a dry state, resulting in difficulty in electrochemical reaction and proton transfer in the solid polymer electrolyte. It is understood. On the other hand, in Example 5, the drop in cell voltage and the increase in internal resistance during off-gas exhaust are small, and in Example 6, it is even smaller. This is understood by the fact that the smaller the pore size of the microporous layer, the more difficult it is for water to pass through, and the water is retained in the diffusion layer, thereby preventing the solid polymer electrolyte layer and reaction layer from drying.

(Example 7)
In Example 7, a titanium sintered plate (a material obtained by sintering a fiber cutting powder having a thickness of 300 μm, a porosity of 45%, and a titanium of 20 μmΦ) was used as the base material of the diffusion layer. The other configuration is the same as that of Example 6 (that is, the microporous layer having a pore diameter of 0.015 μm is used for both the hydrogen electrode and the air electrode), and the description thereof is omitted.

(Example 8)
In Example 8, carbon paper was used as the base material of the diffusion layer. Other configurations are the same as those of the sixth embodiment, and the description thereof is omitted.

  About the fuel cell unit cell of Examples 6 to 8, a dry gas of hydrogen was introduced into the hydrogen electrode side, and air having a predetermined dew point was introduced into the air electrode, and the cell voltage was measured. The cell current during measurement was a constant current of 2A and 6A. The results are shown in FIGS. From these figures, it was found that the operation was normally performed in a non-humidified state regardless of the type of the gas diffusion layer.

<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.

  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. 6 is a schematic cross-sectional view of a single-layer cell for a fuel cell according to Embodiment 2. FIG. In Examples 1-3 and the comparative example 1, it is the pore diameter distribution curve of the carbon used for the microporous layer. It is a block diagram of a fuel cell system. It is a graph which shows the relationship between the dew point of introductory air when a current is 2A, and a cell voltage. It is a graph which shows the relationship between the dew point of the introduction air at the time of setting an electric current to 6 A, and a cell voltage. It is a graph which shows the relationship between the dew point of introduction air, and a cell voltage. It is a graph which shows the relationship between time passage, cell voltage, time passage, and internal resistance. It is a graph which shows the relationship between the dew point of introduction air, and a cell voltage in 2A constant current. It is a graph which shows the relationship between the dew point of introduction air, and a cell voltage in 6 A constant current. 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, 16a ... Diffusion layer base material 12b, 16b ... 1st microporous layer 12c, 16c ... 2nd microporous Layers 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 (5)

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 and / or the fuel electrode includes a diffusion layer base material that sucks out water generated in the reaction layer into the diffusion layer and holds it as liquid water in the diffusion layer, and a reaction layer of the diffusion layer base material A first microporous layer having a smaller pore diameter than the diffusion layer substrate and a fine layer that is formed on the opposite side of the reaction layer of the diffusion layer substrate and substantially does not allow liquid to pass through the gas. A fuel cell comprising a second microporous layer having a pore size . 2. The fuel cell according to claim 1 , wherein the first and second microporous layers have a pore diameter of 0.15 μm or less. The fuel cell according to claim 1 or 2 , 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 3 , wherein the diffusion layer is made of a metal porous body. 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; a fuel gas supply means for supplying a fuel gas to the fuel electrode; and an oxidizing gas on the oxygen electrode And a fuel cell system comprising: air supply means for supplying air as refrigerant gas; and control means for controlling the temperature of the fuel cell by controlling the air supply amount;
The diffusion layer of at least the oxygen electrode is formed on a diffusion layer base material that sucks out water generated in the reaction layer into the diffusion layer and holds it as liquid water in the diffusion layer, and on the reaction layer side of the diffusion layer base material. A first microporous layer having a pore size smaller than that of the diffusion layer substrate, and a first microporous layer formed on the opposite side of the reaction layer of the diffusion layer substrate and having a pore size that does not substantially allow liquid to pass through the gas. Two microporous layers,
The fuel cell system, wherein the control means controls the stoichiometric ratio of supply air to be in a range of 10 to 200.

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