JPH08130024A - Fuel cell - Google Patents

Abstract

PURPOSE: To quickly exhaust water produced in a flow path of fuel of a fuel cell from the flow path. CONSTITUTION: A fuel cell is constituted by stacking an electrolyte film 20, a gas diffusion electrode 30, and a current collecting electrode 40. A plurality of ribs 42 are formed on a contact surface of the current collecting electrode 40 with the gas diffusion electrode 30, and a gas flow path 44 to let to flow an oxidizing gas or fuel gas is formed between the rib 42 and the surface of the gas diffusion electrode 30. Carbon short fibers 52 having a diameter of 5μm and a length of 100μm, coated with polytetrafluoroethylene having water repellent property are planted on the surface of the gas flow path 44 with a conductive adhesive 50. When the fuel cell is operated, water produced by reaction in the gas flow path 44 on the cathode electrode side is repelled by the carbon short fibers 52, and supported around the tips of the carbon short fibers 52, and converted into a water drop 60. The water drop 60 is kept in almost point contact to decrease contact resistance, and exhausted from the gas flow path by the dead load when the direction of the gas flow path 44 is in the perpendicular direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell, and more specifically, to an electrolyte layer, an electrode sandwiching the electrolyte layer to form a power generation layer, and a fuel flow between the electrode sandwiching the power generation layer. And a flow path forming member that forms a path.

[0002]

2. Description of the Related Art In a fuel cell such as a polymer electrolyte fuel cell, two electrodes (oxygen electrode and fuel electrode) facing each other with an electrolyte membrane sandwiched between a fuel gas containing hydrogen and an oxidizing gas containing oxygen. By supplying and, respectively, the reactions shown in the following equations (1) and (2) are performed, and the chemical energy is directly converted into electric energy.

Cathode reaction (oxygen electrode): 2H ⁺ + 2e ⁻ + (½) O ₂ → H ₂ O (1) Anode reaction (fuel electrode): H ₂ → 2H ⁺ + 2e ⁻ (2)

In order to carry out this reaction continuously and smoothly, it is necessary for the oxygen electrode to rapidly remove the water produced by the reaction and continuously supply the oxidizing gas to the oxygen electrode.
Usually, the supply channel for supplying the oxidizing gas to the oxygen electrode is formed by the rib of the collector electrode on the oxygen electrode side and the surface of the oxygen electrode. This supply flow path also serves as a discharge flow path for water generated by the reaction. Therefore, prompt discharge of the generated water in the oxidizing gas supply channel is required.

In order to carry out the above reaction continuously and smoothly, in the fuel electrode, the fuel gas is continuously supplied to the fuel electrode and the hydrogen ions generated in the fuel electrode are smoothly diffused in the electrolyte membrane. There is also a need. Since hydrogen ions combine with water in the electrolyte membrane to move into a hydrated state in the electrolyte membrane, it is necessary to replenish the electrolyte membrane with water from the outside so that water near the fuel electrode does not become insufficient. Water is usually supplied to the fuel electrode by humidifying the fuel gas to increase the vapor pressure of the fuel gas. If the humidified fuel gas is supplied to the fuel cell that has not reached the temperature in the steady operation state immediately after the start of operation, or if the fuel gas in which steam is supersaturated is supplied to the fuel cell, Water vapor condenses on the surface of the fuel gas supply passage formed by the ribs of the collecting electrode and the surface of the fuel electrode to form a water droplet, which causes the fuel gas to flow smoothly in the fuel gas supply passage. There are cases in which the flow is disturbed. Therefore, when water vapor is condensed on the surface where the fuel gas supply passage is formed, it is required to quickly discharge the condensed water droplets from the fuel gas supply passage.

[0006] Conventionally, as a fuel cell which meets such a demand, there has been proposed a fuel cell in which a fluororesin film having water repellency is formed on a surface where a fuel gas or oxidizing gas supply passage formed by a collector electrode and an electrode is formed. (For example, Japanese Patent Laid-Open No.
-12462 publication). According to this fuel cell, the fluororesin film repels water droplets adhering to the surface on which the fuel gas supply channel is formed and the generated water discharged to the oxidizing gas supply channel to quickly discharge the fuel electrode. It is said that the fuel gas and the oxidizing gas are continuously supplied to the oxygen electrode. Also,
By not forming a fluororesin coating on the contact surface of the collector electrode with the electrode, the contact surface is made a water-absorbing portion rich in hydrophilicity, and water droplets adhering to the formation surface of the fuel gas supply channel from this contact surface It is said that the produced water discharged to the oxidizing gas supply passage is absorbed and quickly discharged from the fuel gas and oxidizing gas supply passage.

[0007]

However, in a fuel cell in which a coating film of fluororesin is formed on the surface where the supply passage is formed, the generated water discharged into the supply passage or water droplets adhering to the formation surface are repelled. There is a problem in that a plurality of such water droplets are collected to form large water droplets, which may hinder the supply of fuel gas or oxidizing gas to the electrodes. Particularly in a narrow or wide supply channel, the surface tension of water may block the supply channel, which may significantly reduce the operating efficiency of the fuel cell.

The fuel cell of the present invention has the following constitution for the purpose of solving these problems and promptly discharging the water generated in the fuel flow passage from the flow passage.

[0009]

A fuel cell of the present invention comprises an electrolyte layer, electrodes for sandwiching the electrolyte layer to form a power generation layer, and a fuel flow channel between the power generation layer and the electrodes. A flow cell forming member to be formed, wherein the flow path forming member is formed by arranging a plurality of short fibers having water repellency on at least the surface on the surface forming the flow path. Is the gist.

Here, in the fuel cell, the short fiber may be a short fiber formed of carbon.

[0011]

The fuel cell of the present invention constructed as described above is
In the flow passage of the fuel, a plurality of short fibers that are water-repellent at least on the surface forming the flow passage of the fuel of the flow passage forming member repel water generated in the flow passage of the fuel. Promote the discharge of water generated in the.

[0012]

Preferred embodiments of the present invention will be described below in order to further clarify the structure and operation of the present invention described above. FIG. 1 is an explanatory view illustrating the configuration of a unit cell 10 that constitutes a fuel cell that is a preferred embodiment of the present invention, and FIG. 2 is an enlarged explanatory view showing an enlarged portion of a broken line circle in FIG. is there. The unit cell 10 is a unit cell that constitutes a laminated body of a polymer electrolyte fuel cell, and as shown in FIG.
And two gas diffusion electrodes 30 that sandwich the electrolyte membrane 20 from both sides to form a sandwich structure, and two collector electrodes 40 that sandwich the sandwich structure from both sides.

The electrolyte membrane 20 is made of a polymer material such as a fluorine resin and has a thickness of 100 μm to 20 μm.
It is a 0 μm ion-exchange membrane and exhibits good electric conductivity in a wet state. The two gas diffusion electrodes 30 are formed of a carbon cloth woven with a yarn having a surface ratio of carbon fibers coated with polytetrafluoroethylene and carbon fibers not treated at all in a ratio of 1: 1. Since the poly (tetrafluoroethylene) of the gas diffusion electrode 30 exhibits water repellency, its surface is not covered with water and does not hinder gas permeation. On the surface of the carbon cloth on the electrolyte membrane 20 side and in the gap, carbon powder carrying platinum or an alloy of platinum and another metal is kneaded to form a catalyst layer 32 (see FIG. 2). The electrolyte membrane 20 and the two gas diffusion electrodes 30 have a sandwich structure in which the two gas diffusion electrodes 30 sandwich the electrolyte membrane 20.
° C. In to 160 ° C. preferably at temperatures of from 110 ° C. 130 ° C., to no 1MPa {10.2kgf / cm ^2} 20MP
a {102 kgf / cm ² } preferably 5 MPa {51 kgf / c
They are joined by a hot pressing method in which a pressure of m ² } to 10 MPa {102 kgf / cm ² } is applied to join.

The collector electrode 40 is made of dense carbon that is made by compressing carbon to make it dense and gas impermeable. A plurality of ribs 42 arranged in parallel with each other are formed on the left and right surfaces (laminating surfaces) of FIG. 1 that are in contact with the gas diffusion electrode 30 of the collecting electrode 40 so as to be orthogonal to each other. On the laminated surface on which the ribs 42 are formed, a conductive adhesive 50, for example, an epoxy adhesive or a carbon paste obtained by mixing carbon powder with a fluorine resin such as polytetrafluoroethylene is used. , Thickness 5μm, length 100
A large number of short carbon fibers 52 having a surface of μm and coated with polytetrafluoroethylene are planted. The ribs 42 on which the short carbon fibers 52 are implanted form a gas flow path 44 that forms a flow path for the oxygen-containing oxidizing gas or the hydrogen-containing fuel gas together with the surface of the gas diffusion electrode 30.
The two collecting electrodes 40 facing each other with the electrolyte membrane 20 and the two gas diffusion electrodes 30 interposed therebetween are arranged such that the ribs 42 facing each other are orthogonal to each other.

Short carbon fibers 52 and gas diffusion electrode 3
The coating of polytetrafluoroethylene on the carbon fibers constituting 0 is performed as follows. First, ordinary carbon fiber is immersed in a dispersion of polytetrafluoroethylene (for example, Polyflon D-1 manufactured by Daikin Industries, Ltd.). Next, after drying in air at room temperature for a while, it is dried in air at a temperature of 100 ° C. for 30 minutes to 1 hour,
Completely evaporate the water content of the dispersion. continue,
By heating in a nitrogen atmosphere at 250 ° C. to 300 ° C. for 2 hours to 3 hours, polytetrafluoroethylene is baked on the surface of the carbon fiber to obtain carbon fiber exhibiting water repellency. The water-repellent carbon fibers thus obtained are cut into short pieces to form short carbon fibers 52 exhibiting water repellency.

Next, how the short carbon fibers 52 are planted on the collecting electrode 40 will be described with reference to the process chart shown in FIG. First, the adhesive 50 is applied to the laminated surface of the base material of the collector electrode 40 on which the ribs 42 are formed (step S100). Then, the collecting electrode 40 is grounded or charged negatively, and the carbon short fiber 52 coated with polytetrafluoroethylene on the surface is charged positively (step S110). Then, positively charged short carbon fibers 52 are sprayed on the laminated surface of the grounded or negatively charged collecting electrode 40 coated with the adhesive 50 (step S120). Then, carbon short fiber 52
Is planted so as to stand on the adhesive 50 on the laminated surface of the collector electrode 40 by electrostatic induction. Subsequently, the adhesive 50 applied to the collecting electrode 40 is dried and cured at a temperature of 150 ° C. for 30 minutes (step S130) to complete the implantation of the short carbon fibers 52 on the collecting electrode 40.

In the fuel cell formed by stacking the unit cells 10 thus constructed, if the oxidizing gas and the fuel gas are caused to flow through the pair of gas flow channels 44 facing each other with the electrolyte membrane 20 and the two gas diffusion electrodes 30 interposed therebetween, The electrochemical energy shown in the above reaction formulas (1) and (2) is performed to directly convert chemical energy into electrical energy.

Next, the state of the inside of the gas flow path 44 when the fuel cell formed by stacking the unit cells 10 is operated will be described. First, the inside of the gas flow path 44 on the cathode side will be described. In the gas flow path 44 on the cathode electrode side, water generated on the surface of the gas diffusion electrode 30 on the cathode electrode side of the electrolyte membrane 20 when the fuel cell is operated (see formula (1)).
Are guided to the surface on the gas flow path 44 side by the untreated carbon fibers forming the gas diffusion electrode 30. Since the carbon short fibers 52 exhibit water repellency due to the polytetrafluoroethylene coated on the surface thereof, the gas flow path 4
As shown in FIG. 2, the water guided to 4 is repelled to support the water droplets 60 near the tips of the short carbon fibers 52. Since the water droplets 60 are in a state close to point contact due to the short carbon fibers 52, the resistance becomes small and the water droplets 60 easily move. Therefore, if the longitudinal direction of the gas flow path 44 is set to be the vertical direction, the water droplet 60 falls vertically downward due to its own weight and is quickly discharged from the gas flow path 44.

On the other hand, in the gas passage 44 on the anode side,
Since the humidified fuel gas is made to flow to near the saturated vapor pressure, it may become oversaturated depending on the operating condition of the unit cell 10, and water vapor may condense on the formation surface of the gas flow path 44. The water generated by such dew condensation is repelled by the short carbon fibers 52 exhibiting water repellency similarly to the cathode side, and becomes water droplets 60 supported by the vicinity of the tips of the short carbon fibers 52. When the water vapor pressure of the fuel gas does not reach the saturated water vapor pressure, the water droplets 60 are vaporized from the surface of the water droplets 60 into the fuel gas, and the water vapor pressure of the fuel gas is set to the saturated water vapor pressure on the anode side of the electrolyte membrane 20. Promote the supply of insufficient water.

Further, in the collecting electrode 40 of the embodiment, the rib 42
The short carbon fibers 52 are also planted on the end surface 46 that contacts the gas diffusion electrode 30 of FIG. Therefore, a layer having a minute gap formed by the short carbon fibers 52 is formed between the contact portion 34 of the gas diffusion electrode 30 that contacts the end face 46 and the end face 46, and the gas flow path is formed through the gap of this layer. The oxidizing gas or fuel gas 44 diffuses into the contact portion 34. Further, the short carbon fibers 52 planted on the end surface 46 are entangled with the carbon fibers forming the gas diffusion electrode 30, so that the contact resistance between the collecting electrode 40 and the gas diffusion electrode 30 becomes small. Further, the short carbon fibers 52 that are planted on the side surfaces of the ribs 42 that form the gas passages 44 disturb the flow of the oxidizing gas or the fuel gas in the gas passages 44, and the gas diffusion electrode 30 of the oxidizing gas or the fuel gas 30. To improve the diffusion.

FIG. 4 illustrates the relationship between the current density and the cell voltage in the unit cell 10 of this embodiment and the unit cell in which the short carbon fibers 52 are not implanted (hereinafter referred to as "conventional unit cell"). It is a graph. In the graph, a curve A shows the relationship between the current density of the unit cell 10 and the cell voltage, and a curve B shows the relationship between the current density of the conventional unit cell and the cell voltage. As shown in the figure, a single cell 1 in which short carbon fibers 52 are implanted.
0 indicates that the performance is remarkably improved as compared with the conventional unit cell in which hair is not transplanted.

According to the fuel cell described above, the collector electrode 4
Immediately discharging the water generated in the gas flow channel 44 from the gas flow channel 44 by implanting short carbon fibers 52 coated with polytetrafluoroethylene on the surface forming the 0 gas flow channel 44. Therefore, it is possible to prevent the generated water from inhibiting the diffusion of the oxidizing gas or the fuel gas into the gas diffusion electrode 30. Therefore, an efficient fuel cell can be obtained.

Further, by implanting short carbon fibers 52 on the end surfaces 46 of the ribs 42, a layer having a minute gap is formed at the contact portion between the contact portion 34 and the end surface 46. Alternatively, the fuel gas can be diffused inside the contact portion 34. In this way, since the oxidizing gas or the fuel gas is diffused to the inside of the contact portion 34,
The utilization rate of the gas diffusion electrode 30 that contributes to the electrochemical reaction can be increased to improve the performance of the unit cell 10 and thus the fuel cell. Furthermore, since the short carbon fibers 52 on the end surface 46 of the rib 42 are entangled with the carbon fibers forming the gas diffusion electrode 30, the contact resistance can be reduced,
The fuel cell can have a small internal resistance. In addition, the short carbon fibers 52 planted on the side surfaces of the ribs 42 forming the gas flow path 44 disturb the flow of the oxidizing gas or the fuel gas in the gas flow path 44 and improve the diffusibility to the gas diffusion electrode 30. be able to.

In the embodiment, the thickness is 5 μm and the length is 10
Although the carbon short fibers 52 of 0 μm were implanted, the thickness and the length are not limited, and the thickness is 0.1 μm to 100 μm, preferably 1 μm to 10 μm, and the length is 10 μm to 1 mm, preferably 50 μm to 30.
It may be 0 μm. The thickness and length are determined by the width and depth of the gas passage 44.

In the embodiment, short carbon fibers 52 are planted on the surface of the collecting electrode 40 on which the gas flow paths 44 are formed, but the material is not limited to carbon as long as the short fibers exhibit water repellency. For example, a short fiber which is made of a conductive metal and whose surface is treated to be water repellent may be used.

In the embodiment, the gas diffusion electrode 30 of the rib 42 is used.
The short carbon fibers 52 were also planted on the end face 46 that contacts the end face 14 that is the contact face of the rib 142 of the collecting electrode 140 with the gas diffusion electrode 30 as in the single cell 110 shown in FIG.
The carbon short fibers 52 may not be planted on the 6's. If the short carbon fibers 52 are not implanted on the end surface 146 like the single cell 110, the carbon short fibers 52 are replaced with a material having no conductivity (for example, resin) and the surface is treated to be water repellent. Short fibers are also acceptable.

The embodiment of the present invention has been described above.
The present invention is not limited to these examples, and it is needless to say that the present invention can be implemented in various modes without departing from the scope of the present invention, such as a configuration applied to a phosphoric acid fuel cell. is there.

[0028]

As described above, according to the fuel cell of the present invention, a plurality of short fibers, at least the surface of which has water repellency, are planted on the surface of the flow path forming member forming the fuel flow path,
The water generated in the fuel flow path can be repelled to quickly discharge the water generated in the fuel flow path. Therefore,
Water generated in the fuel flow channel does not hinder the diffusion of the fuel to the electrodes, and it is possible to maintain high operating efficiency of the fuel cell.

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating the configuration of a unit cell 10 that constitutes a fuel cell that is a preferred embodiment of the present invention.

FIG. 2 is an enlarged explanatory view showing an enlarged part of a broken line circle in FIG.

3A to 3C are process diagrams illustrating the state of forming a collecting electrode 40.

FIG. 4 is a graph exemplifying the relationship between the current density and the cell voltage in the unit cell 10 and a conventional unit cell.

FIG. 5 is a unit cell 11 which is a modification of the unit cell 10 of the embodiment.
It is an expansion explanatory view which expanded and showed a part of 0.

[Explanation of symbols]

 10 ... Single cell 20 ... Electrolyte membrane 30 ... Gas diffusion electrode 32 ... Catalyst layer 34 ... Contact part 40 ... Collection electrode 42 ... Rib 44 ... Gas flow path 46 ... End face 50 ... Adhesive 52 ... Short carbon fiber 60 ... Water drop 110 ... Single cell 140 ... Collection electrode 142 ... Rib 146 ... End surface

Claims (2)

[Claims] 1. An electrolyte layer, an electrode for sandwiching the electrolyte layer to form a power generation layer, and a flow channel forming member for sandwiching the power generation layer and forming a fuel flow channel with the electrode. The fuel cell is a fuel cell, wherein the flow path forming member is formed by arranging a plurality of short fibers having water repellency on at least the surface on the surface forming the flow path. 2. The fuel cell according to claim 1, wherein the short fibers are short fibers formed of carbon.