JPH07320753A - Solid polymer electrolyte membrane type fuel cell - Google Patents

Abstract

PURPOSE:To uniformly supply water and uniformly exhaust reaction water by forming a gas separator having small diameter pores and large diameter pores with a hydrophilic porous body. CONSTITUTION:When hydrogen serving as fuel and water (gaseous or liquid state) for humidification are supplied from the upper part of a gas separator 1B, since the separator 1B made of a hydrophilic porous body has an average pore diameter of about 10-100mum but actually has smaller diameter pores and larger diameter pores than the average pore diameter as pore diameter distribution, the supplied water is filled in the small diameter pores as liquid water by capillary condensation, and distributed all over the surface of a hydrogen electrode side electrode diffusion layer 3A of a cell 7 to humidify a hydrogen electrode. Since the larger diameter pores in the separator 1B have no condensed water and are left as continuous pores, hydrogen-containing wet gases freely move and diffuse inside the pores, and hydrogen serving as fuel is distributed all over the surface of the hydrogen electrode side electrode diffusion layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a solid polymer electrolyte membrane fuel which requires humidification of fuel hydrogen to moisten an electrolyte membrane, and must discharge moisture generated by an internal reaction to the outside. The present invention relates to a battery (hereinafter, simply referred to as a fuel cell).

[0002]

2. Description of the Related Art It is known that a solid polymer electrolyte membrane used in a fuel cell is a cation exchange membrane and exhibits maximum proton conductivity when it is saturated with water. That is, as such an electrolyte membrane, a polystyrene cation exchange membrane having a sulfonic acid group, a membrane in which fluorocarbon sulfonic acid and polyvinylidene fluoride are mixed,
Perfluorocarbon sulfonic acid membranes, etc. are known, but these electrolyte membranes have a proton exchange group in their molecular structure and have good proton conductivity (specific resistance at room temperature) by wetting water to saturation. Is about 2
0 Ω · cm or less) and acts as an electrolyte membrane.

The following various methods have been conventionally proposed as a moisturizing method for wetting the electrolyte membrane with water and a water managing method in a fuel cell. is there.

(Type I) Direct Water Addition Method This method, as shown in US Pat. No. 3,061,658, directly reacts with air (oxygen) and fuel hydrogen gas to be reacted in a fuel cell, respectively. Liquid water is added.

However, in the humidifying method of this system, water is added directly to both the hydrogen electrode and the air electrode (oxygen electrode).
There is a problem in that the water supply becomes excessive and a water film is formed between the air phase (or oxygen gas phase) and the air electrode, and this water film interferes with the diffusion of oxygen and deteriorates the power generation performance. Also,
In the worst case, there is a problem that liquid water blocks the gas flow path and a large gas drift occurs, and it is difficult to control an appropriate amount of water.

(Type II) External Humidifier Installation Method This method is based on EA Ticianelli et al; J. Electroche
m. Soc., Vol.135. p. As shown in 2209 (1988), a humidifier is provided in each supply line to humidify each gas before supplying air and fuel hydrogen to the fuel cell.

In the humidifying method according to this method, a humidifier is separately required outside the fuel cell, and the steam-state humidifying water that humidifies each gas is prevented from condensing in the pipe leading to the fuel cell. In addition, since it is necessary to keep the temperature of the pipes and humidify each gas in the form of steam, the thermal load required for this is large, and the thermal efficiency of the system deteriorates.

(Type III) Water Repellent Porous Utilization Method In this method, as shown in JP-A-4-95357, a groove is formed in a water repellent porous body in a concave shape, and the inner space of the concave portion is used as a running water channel. The openings above the recesses are designed to directly contact the cells that make up the fuel cell and supply water to the cells.

In the humidifying method by this method, there is a problem that the separator on the hydrogen electrode side has a two-stage structure for water supply and hydrogen supply and becomes complicated. Also, the air electrode side has not been specially devised, and the discharge of reaction water is supplied to the air electrode side.
Since the air is not consumed but is simply entrained in the air discharged from the cell and discharged, there is a problem that the water discharge performance becomes insufficient.

(Type IV) Hydrophilic Porous Utilization Method Two humidification methods based on this method are considered. (1) One is to form a plate in which the cross section of a hydrophilic porous body is uneven as shown in JP-A-1-309263, and the tip of the convex part of the plate is brought into contact with a hydrogen electrode,
Further, the space of the recess is used as a hydrogen flow path, and water is supplied to the plate to maintain the wet state of the electrolyte membrane. On the other hand, also in the air electrode, similarly, a plate having an uneven cross-section of the hydrophilic porous body is formed, and the uneven surface and the air electrode surface are brought into contact with each other, and the space of the concave portion serves as an air flow path, and the tip of the convex portion, The reaction water generated in the air electrode is removed from the air electrode by a capillary action, and is transported to the inner surface of the central portion of the recess, and further evaporated from the inner surface into the air and discharged to the outside of the cell. is there.

In the humidifying method based on this method, the water supply on the hydrogen electrode side is controlled by adjusting the water pressure of the pump. However, the water supply amount is controlled by following the load without excess or deficiency. Is difficult, and the discharge of water at the cathode side is carried out by entraining it in the air.
Similar to III, there is a problem that water discharge performance is insufficient especially under high load.

(2) Another one is JP-A-4-12462.
As shown in No. 3, a water supply pot and a water discharge trap are respectively installed outside the cell, and a hydrophilic porous plate is used to supply water from the water supply pot to the hydrogen electrode, and The reaction product water is discharged from the air electrode to the water trap.

In the humidifying method according to this method, since the distance from the supply pot to the hydrogen electrode of the cell is long, the amount of water supplied is distributed, and the distance from the air electrode to the water trap is long. There is also a problem that the emission amount of is distributed.

So far, the wetness of the electrolyte membrane and the control of water in the conventional fuel cell have been described. The problems associated with these are summarized below.

In the process of supplying water to the hydrogen electrode side for wetting the electrolyte membrane, (1) the amount of water supplied is not uniform in the cell. (2) It is difficult to control the optimum amount of water supply according to the cell load. (3) When supplying water in the form of steam, the thermo-economic efficiency is poor, and the equipment cost is high due to the sophisticated control equipment for the water supply.

In addition, in the process of discharging the reaction water from the air electrode side, (4) the discharging speed of water decreases in the order of the vicinity of the air inlet, the center of the cell and the vicinity of the air outlet, so that the electrolyte membrane is close to the air inlet. It will tend to be dry and submerged near the air outlet, and the entire surface of the cell cannot effectively contribute to power generation. (5) Even in the vicinity of the air inlet, it is necessary to increase the air flow rate in order to obtain the discharge speed of water corresponding to the predetermined power generation density. Increasing costs. (6) There is a limit to the scale-up of the cell, because the drainage capacity of the reaction water becomes more and more distributed as the cell becomes larger.

[0017]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of the prior art, has a self-controllability capable of appropriately supplying and discharging water by following the power generation density of the cell, and directly Water can be supplied uniformly and reaction water can be discharged uniformly.
An object is to provide a solid polymer electrolyte membrane fuel cell.

[0018]

Therefore, the solid polymer electrolyte membrane fuel cell of the present invention has the following means to solve the drawbacks of the conventional method.

Water is supplied to the hydrogen electrode by utilizing the capillary action (wick action) of a hydrophilic porous body having excellent conductivity (for example, hydrophilic porous carbon),
Further, the reaction water is discharged from the air electrode by utilizing the condensation action of water vapor on the cooling surface. That is, when the pores distributed in the porous body are wet with water and fill the pores, the relationship between the pore radius r _c and the partial pressure P _H20 of water vapor in the gas phase is given by the formula 1. .

[0020]

[Equation 1]

As an example, the porous plate is made of a material whose surface is well wetted (cos θ≈1.0), and the pore diameter r _c is 10 μm.
When the partial pressure P _H20 of water vapor at 80 ° C. when m is calculated, it becomes 0.11 atm. Therefore, conversely, when the partial pressure of water vapor in the gas phase is 0.11 atm, in the pores with a pore radius of 10 μm or less in the hydrophilic porous body, capillary condensation of water vapor occurs and Since the liquid water is filled with water and these pores communicate with each other, the liquid water has a pore radius of 10 μm.
It moves in the porous body through the following pores. On the other hand, in the pores having a pore radius of 10 μm or more, capillary condensation of water vapor does not occur, water is absent and communicates with each other. The flow and diffusion of gas (hydrogen, air) can be freely performed in the porous plate without being subject to the above.

[0022]

The operation of the solid polymer electrolyte membrane fuel cell of the present invention will be described with reference to FIGS. 1 and 2 showing an embodiment of the present invention.

FIG. 1 is a diagram showing a first embodiment of the present invention. In the figure, 2 in the central portion is a solid polymer electrolyte membrane described in detail, and on the left side of the electrolyte membrane 2 is a catalyst reaction layer 4
A layer comprising a hydrogen electrode composed of A, the electrode diffusion layer 3A and the gas separator 1B is laminated and joined, and an air electrode composed of the catalytic reaction layer 4B, the electrode diffusion layer 3B and the gas separator 1A is similarly formed on the right side of the electrolyte membrane 2. The layers forming the (oxygen electrode) are laminated and joined.

The gas separator 1 is an air electrode side gas separator 1A made of a conductive and hydrophilic porous material.
Similarly, a pair of cells 7 is configured by combining both sides of the hydrogen electrode side gas separator 1B, which is also made of a conductive hydrophilic porous material, with conductive and gas impermeable partition walls 5 interposed therebetween. To be done. In addition, a plurality of sets of cells 7 are stacked to form an integral fuel cell.

Here, considering the case where hydrogen as fuel is supplied from the upper part of the gas separator 1B together with humidifying water (gaseous or liquid), the gas separator 1B of hydrophilic porous body has an average value. The pore size is 10 to 1
Although it is a porous body having a size of about 00 μm, it has pores with a smaller pore size distribution (small pore size pores) and larger pore size distribution (large pore size pores). The water, which is liquid water obtained by capillary condensation, fills the small pores and is distributed throughout the entire surface of the electrode diffusion layer 3A on the hydrogen electrode side of the cell 7 to humidify the hydrogen electrode. On the other hand, since the large pores of the hydrophilic porous body in the gas separator 1B have no condensed water and are the continuous pores, the wet gas containing hydrogen has the large pores. Since it can freely flow and diffuse inside, hydrogen as fuel can also be distributed over the entire surface of the electrode diffusion layer 3A on the hydrogen electrode side of the cell 7.

In this way, when the mixture of fuel hydrogen and humidifying water is supplied from the upper part of the gas separator 1B, it is transported to the right in the porous body by the capillary action of the small pores of the gas separator 1B. After reaching the right outer surface of the separator 1B, a part of which evaporates in a hydrogen gas stream flowing in the large-pores during that time to humidify the flowing hydrogen, and the remaining part directly It flows and diffuses through the diffusion layer 3A and then the catalytic reaction layer 4A, reaches the left surface of the solid polymer electrolyte membrane 2, and keeps the electrolyte membrane 2 in a wet state. When the cell 7 is in a power generation state, hydrogen dissociates by the catalytic action of the catalytic reaction layer 4A, and then moves in the proton state (H ⁺ ) in the electrolyte membrane 2 by coordinating the water described above. The electrons (e ⁻ ) that reach the catalyst reaction layer 4B on the air electrode side on the right side and flow therein through an external electric circuit, and diffuse through the flow path of air (or oxygen) in the large pores of the gas separator 1A. Reacts with inflowing oxygen (O ₂ ) to produce water.

That is, the reactions at the above electrode part are summarized as follows. -In the catalytic reaction layer 4A on the hydrogen electrode side,

[0028]

[Equation 2]

In the catalytic reaction layer 4B on the air electrode side,

[0030]

[Equation 3]

The water generated in the above process and a part of the permeated water that has moved with the protons in the electrolyte membrane 2 are taken into the catalytic reaction layer 4B on the air electrode side, but the power is continuously generated. In order to continue the state, it is necessary to discharge the reaction product water and the permeated water from the catalytic reaction layer 4B.

Referring again to FIG. 1, the water existing inside the catalytic reaction layer 4B diffuses to the right, and then passes through the electrode diffusion layer 3B on the air electrode side to form a conductive hydrophilic porous layer. The left side surface of the gas separator (air electrode side) 1A of the quality plate is reached. Here, the gas separator 1A is also
As with the gas separator 1B, the average pore diameter is 10
It is a porous body having a size of about 100 μm, and the pore size distribution is made up of small pores smaller than this and large pores larger than this. Therefore, the water moves as liquid water due to capillary condensation through the small pores,
Water vapor flows through large pores with air (or oxygen)
It diffuses and is carried to the downstream side of the gas separator 1A,
It is discharged outside the cell 7. With such a water movement mechanism, water can be continuously supplied and discharged in a self-controlled manner, so that a stable power generation state of the cell can be obtained.

Thus, in the embodiment shown in FIG.
In this case, in order to remove heat generated during power generation in the cell 7, cooling is performed by evaporation of humidifying water supplied in a liquid state, cooling effect that the supplied air carries away as sensible heat rise, and heat dissipation effect to the outside. . However, if the cell area increases, the number of layers increases, and the cell power generation density per unit area increases, the cooling capacity of the cell may be insufficient.

Therefore, even in such a case, the second applicable
An embodiment of is shown in FIG. In the present embodiment, a gas-permeable conductive partition wall 5 is interposed between the gas separators 1A and 1B, and a water channel 6 for circulating cooling water is provided inside the partition wall 5. The same as in the first embodiment. The water flow path 6 is provided in contact with the gas separator 1A, and the water flowing / diffusing in the gas separator 1A and flowing into the cooling water passage 6 is discharged to the outside of the cell 7.

[0035]

EXAMPLE An example based on the first embodiment of the present invention shown in FIG. 1 is shown in Table 1. In this example, the electrode diffusion layer was made of the same material as the gas separator because it was lightweight, electrically conductive, and corrosion resistant. However, this material does not necessarily have to be exactly the same as the material of the gas separator.

Further, the pore diameter formed in the porous body constituting the gas separator is generally such that predetermined values of the average pore diameter and the pore diameter distribution are obtained in the manufacturing process. For example, it can be obtained by appropriately selecting various conditions such as distribution of powder particle diameter before sintering, press load at the time of sintering, sintering temperature, and sintering time. In the present example, the average particle size was adjusted to a predetermined value, but the pore size distribution is not a manufacturing method targeted for adjustment.

Further, the humidifying water permeates the electrolyte membrane from the hydrogen electrode side to the air electrode side, and the amount of water commensurate with the flow rate of water escaping into the air is supplied to the hydrogen electrode side inlet. To be supplied to the department.

In this embodiment, the hydrogen utilization rate is almost 80%.
%, The power utilization performance of the cell was measured by setting the respective supply amounts so that the air utilization rate was approximately 25%. Hydrogen reaction amount = 2.25 × 0.8 (hydrogen utilization ratio) = 1.
8 mol / h-Amount of oxygen reaction in air = 17.1 x 0.21 x 0.25
(Air utilization rate) = 0.898 mol / h, and in the general reaction formula in the fuel cell, H ₂ +1/2 O ₂ → H ₂ O, 1/2 mol of oxygen reacts with 1 mol of hydrogen.
It was confirmed that the reaction amount ratio was almost in line with the theory, and that almost the desired power generation performance was achieved. This proves that the supply and discharge of water proposed by the present invention is effective.

The heat of combustion of hydrogen is 57.
Since it is 8 kcal, combustion heat of reaction hydrogen (HHV base) = 1.8 × 57.
8 = 104 kcal / h ・ Power generation amount = 0.75 V × 0.2 A / cm ² × 400 cm ² =
60 W = 51.6 kcal / h Therefore, the power generation efficiency η was: η = 51.6 / 104 × 100 = 49.6%.

Further, based on the second embodiment of the present invention shown in FIG. 2, 1.02 l / min of cooling water (80 ° C., supplied at normal pressure) is caused to flow through the channel 6, and other conditions are shown in Table 1. When power generation was performed with the same setting as above, results similar to the power generation performance in Table 1 were obtained. Table 1 Specific Examples (1) Structural conditions of cell-Effective power generation area of cell: 20 cm x 20 cm x 1 cell-Electrolyte membrane (material): Perfluorosulfonic acid type ion exchange membrane (film thickness): 125 μm (ion exchange) capacity): 1.1meq / g-resin · catalysis layer (material): P _t carrying carbon particle layer (bipolar side both) (reaction layer thickness): 0.12 mm (P _t supported amount): 1 mg / cm ²・ Electrode diffusion layer (material): Porous carbon sheet (thickness): 0.4 mm ・ Hydrogen electrode side gas separator (material): Porous carbon material (average pore diameter): Average diameter 55 μm (porosity): 65%・ Air electrode side gas separator: Porous carbon material (same as hydrogen electrode side) (2) Operating conditions ・ Cell temperature: 85 ° C ・ Hydrogen electrode side (pressure): 1.5 atg (hydrogen flow rate): 2.25 mol / h Oxygen electrode side (pressure): 1.45 atg (air flow rate): 17. mol / h (3) power generation performance, voltage: 0.75 V, current density: 0.2 A / cm ²

[0041]

As described above in detail, according to the solid polymer electrolyte membrane fuel cell of the present invention, the following effects can be obtained with the structure shown in claim 1. (1) Since the drain (water) is not mixed in the hydrogen flow path during the humidification process on the hydrogen electrode side, a gas-liquid mixed phase does not occur and hydrogen gas and humidification water can be uniformly distributed. That is,
In the hydrophilic communicating porous body, the moving flow paths of the liquid water and the gas mixture are automatically divided. (2) On the air electrode side, in order to remove water that has permeated from the hydrogen electrode side and water that is generated by the reaction on the air electrode side, movement of liquid water and movement of gaseous water contained in the air are performed. Since they are carried out individually, blockage of the gas flow path does not occur, and it becomes possible to uniformly distribute air and quickly remove water. (3) Furthermore, since the atmosphere on both sides of the electrodes is close to saturation and filled with water vapor, the electrolyte membrane is always kept in a wet state, and the power generation capacity of the cell can be sufficiently exhibited.

Further, the following effects can be obtained by the structure according to claim 2.

Since the reaction water is drained by the cooling water passage due to the increase in size of the cell, the cell can be easily scaled up and the cell size is not limited.

[Brief description of drawings]

FIG. 1 is a first solid polymer electrolyte membrane fuel cell of the present invention.
Is a partial view showing a configuration of a fuel cell as an embodiment of

FIG. 2 is a partial view showing a configuration of a fuel cell as a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas separator 1A Gas separator (air electrode side) 1B Gas separator (hydrogen electrode side) 2 Electrolyte membrane 3A (hydrogen electrode side) electrode diffusion layer 3B (air electrode side) electrode diffusion layer 4A (hydrogen electrode side) catalytic reaction layer 4B (Air electrode side) Catalytic reaction layer 5 Partition wall 6 Cooling water passage 7 Fuel cell

Claims (2)

[Claims] 1. A hydrogen electrode and an air electrode are formed by laminating a catalytic reaction layer, an electrode diffusion layer, and a gas separator on both sides of a solid polymer electrolyte membrane, and are supplied to the hydrogen electrode and the air electrode. In a solid polymer electrolyte membrane fuel cell adapted to generate oxygen by reacting oxygen in the air, the gas separator has a small pore size and a gas flow having a water transport characteristic by a capillary condensation action in which the gas separators communicate with each other. A solid polymer electrolyte membrane fuel cell characterized by having a pore size distribution composed of large pores having characteristics and being formed of a conductive and hydrophilic porous body. 2. The solid polymer electrolyte membrane fuel cell according to claim 1, wherein a cooling water passage is formed in contact with the inside of the porous body or the side surface of the porous body.