JP2013131300A - Fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of suppressing the drying in the neighborhood of a reaction gas supply port.SOLUTION: The fuel cell includes a stack of a plurality of cells laminated in the horizontal direction, a reaction gas supply port provided at a lower part of the stack and receiving reaction gas supply, a reaction gas exhaust port provided at an upper part of the stack and communicating with the reaction gas supply port so as to exhaust the reaction gas, a fuel gas supply port provided in the side surface of the stack and receiving fuel gas supply, a fuel gas exhaust port provided in the side surface of the stack lower than the fuel gas supply port so as to exhaust the fuel gas, and a fuel gas flow path connecting the fuel gas supply port and fuel gas exhaust port and switching back horizontally in the stack. The swelling rate of ionomer of a catalyst layer in the neighborhood of the fuel gas flow path on downstream side is set higher than the swelling rate of ionomer of a catalyst layer in the neighborhood of the fuel gas flow path on upstream side.

Description

  The present invention relates to a fuel cell.

  In recent years, fuel cells mounted on automobiles have attracted attention. In a fuel cell using an electrolyte membrane, the vicinity of the cathode gas (air) supply port is easy to dry because there is little water produced by the electrochemical reaction. For this reason, the fuel cell is provided with a humidifier for humidifying the cathode gas. However, there has been a request to eliminate the humidifier in order to reduce the cost of the fuel cell, and to improve the performance at high temperatures such as when climbing a car.

  Such a problem is not limited to fuel cells mounted on automobiles, but is a problem common to all fuel cells including stationary fuel cells.

JP 2010-061865 A

  The present invention has been made to solve at least a part of the above-described conventional problems, and an object of the present invention is to provide a technique capable of suppressing drying in the vicinity of a reaction gas supply port.

  In order to solve at least a part of the problems described above, the present invention can take the following forms or application examples.

[Application Example 1]
A fuel cell,
A stack in which a plurality of cells are stacked horizontally;
A reaction gas supply port provided at a lower portion of the stack for receiving supply of a reaction gas;
A reaction gas outlet provided at an upper part of the stack, communicated with the reaction gas supply port, and for discharging the reaction gas;
A fuel gas supply port provided on a side surface of the stack for receiving the supply of the fuel gas;
A fuel gas discharge port that is provided on a side surface of the stack and below the fuel gas supply port, and discharges the fuel gas;
A fuel gas flow path that connects the fuel gas supply port and the fuel gas discharge port and is a flow path that folds back horizontally in the stack;
Each of the cells has an electrolyte membrane, and a catalyst layer containing an ionomer is formed on the surface of the electrolyte membrane.
The swelling rate of the ionomer of the catalyst layer in the vicinity of the downstream side of the fuel gas channel is set to a value higher than the swelling rate of the ionomer of the catalyst layer in the vicinity of the upstream side of the fuel gas channel.
Fuel cell.
According to this configuration, since the ionomer swelling rate is appropriately set, drying in the vicinity of the reaction gas supply port can be suppressed. The swelling ratio of the aoinomer is a volume ratio of water that the ionomer can contain.

  Note that the present invention can be realized in various modes. For example, it is realizable with forms, such as a manufacturing method of a fuel cell, a manufacturing apparatus, and a method of controlling dryness of a fuel cell.

It is explanatory drawing which shows schematic structure of the fuel cell as one Example of this invention, the cell environment of a fuel cell, etc. FIG. It is explanatory drawing which shows schematic structure of the fuel cell in 2nd Example, the cell environment of a fuel cell, etc. FIG.

A. First embodiment:
FIG. 1 is an explanatory diagram showing a schematic configuration of a fuel cell 100 as one embodiment of the present invention, a cell environment of the fuel cell 100, and the like. In this embodiment, the X direction shown in FIG. 1 is the horizontal direction, the Y direction is the vertical direction, and the Z direction is the depth direction. The fuel cell 100 has a stack 10 in which a plurality of cells are stacked in the horizontal direction. In FIG. 1, the stacking direction of the cells is the depth direction. An air supply port 20 for receiving supply of air as a reaction gas is provided at the lower portion of the stack 10 (in this embodiment, the bottom surface of the stack 10). Is provided with an air discharge port 30 for communicating with the air supply port 20 and for discharging air.

  A hydrogen supply port 40 that receives supply of hydrogen gas as a fuel gas is provided on a side surface of the stack 10, and hydrogen that discharges hydrogen gas is provided on the side surface of the stack 10 and below the hydrogen supply port 40. A discharge port 50 is provided. Inside the stack 10, a hydrogen gas flow path 60 that connects the hydrogen supply port 40 and the hydrogen discharge port 50 is provided. The hydrogen gas flow path 60 has a “serpentine shape” that is a shape that folds in the horizontal direction (X direction) in the middle of the stack 10 from upstream to downstream, that is, a meandering shape like a snake.

  In addition, although illustration is abbreviate | omitted, the electrolyte membrane is arrange | positioned in each cell, and the electrode catalyst layer is formed on both surfaces of the electrolyte membrane. In this embodiment, the electrode catalyst layer is formed of supported carbon (carbon black), a catalyst, and an ionomer. A gas diffusion layer is disposed outside the electrode catalyst layer.

  In the fuel cell 100 having such a configuration, air flows from the lower side to the upper side of the stack 10, and hydrogen gas flows in a direction opposite to the air, that is, from the upper side to the lower side of the stack 10 (so-called “so-called”). Counter flow). With such a configuration, the generated water generated in the vicinity of the upstream side of the hydrogen gas flow path 60 (that is, the upper side of the stack 10) easily moves downward, so that drying in the vicinity of the air supply port 20 is suppressed. Can do. However, in the present embodiment, since the hydrogen gas flow path 60 has a serpentine shape, the wet and dry environment in the cell differs in the vicinity of the upstream, the middle, and the downstream of the hydrogen gas flow path 60.

  Therefore, in this embodiment, the swelling rate of the ionomer in the electrode catalyst layer is set according to the structure of the hydrogen gas channel 60. The aoinomer swelling ratio is a volume ratio of water that can be contained in the ionomer. The higher the swelling ratio, the more water can be contained, and it becomes difficult to dry in a high temperature, non-humidified environment.

  Specifically, on the upstream side of the hydrogen gas flow channel 60 (in this embodiment, on the upper side of the stack 10), since the environment in the cell tends to become wet, the ionomer swelling rate is low (this embodiment). In the example, it is set to 140%). On the other hand, on the downstream side of the hydrogen gas flow channel 60 (the lower side of the stack 10 in this embodiment), the environment in the cell tends to be in a dry state, so that the ionomer swelling rate is high (300 in this embodiment). %). In the vicinity of the middle stream of the hydrogen gas flow channel 60, the environment in the cell is in the middle state between the upstream side and the downstream side, so the swelling rate of the ionomer is set to a medium value (220% in this embodiment). Has been.

Control of the swelling rate of the ionomer can be realized by adjusting at least one of the conditions of I / C, heat treatment temperature, and heat treatment time within the following range.
・ I / C 0.85-0.65
・ Heat treatment temperature 135 ℃ ～ 165 ℃
Heat treatment time 15 minutes to 60 minutes If the above conditions are adjusted, the ionomer swelling ratio can be controlled in the following range.
・ Ionomer swelling rate: 300% to 140%
That is, the swelling ratio of the ionomer may be controlled by combining the above conditions. For example, the swelling ratio of the ionomer may be controlled by adjusting only the I / C value and keeping the same heat treatment conditions.

  Here, I / C is a ratio of the mass I of ionomer and the mass C of carbon black in the catalyst ink applied to the electrolyte membrane. The heat treatment is carried out by hot pressing after applying a catalyst ink prepared by mixing supported carbon, catalyst, and ionomer to the electrolyte membrane. According to hot pressing, different heat treatment temperatures and heat treatment times can be applied to the areas of the applied catalyst ink.

  In the present example, as shown in the table on the right side of FIG. 1, on the upstream side of the hydrogen gas channel 60, the I / C is 0.65 and the heat treatment temperature is 165 in order to set the ionomer swelling ratio to 140%. The heat treatment time was set to 60 ° C. for 60 minutes. In the vicinity of the middle flow of the hydrogen gas flow path 60, in order to set the ionomer swelling ratio to 220%, the I / C was set to 0.75, the heat treatment temperature was set to 135 ° C., and the heat treatment time was set to 30 minutes. On the downstream side of the hydrogen gas flow channel 60, in order to set the ionomer swelling ratio to 300%, the I / C was 0.85, the heat treatment temperature was 145 ° C., and the heat treatment time was 15 minutes.

  As described above, in the first embodiment, since the ionomer swelling rate is set according to the structure of the hydrogen gas flow channel 60, flooding is performed upstream of the hydrogen gas flow channel 60, that is, in the vicinity of the air outlet 30. While being able to suppress, it is possible to suppress the drying in the downstream of the hydrogen gas flow path 60, ie, in the vicinity of the air supply port 20.

B. Second embodiment:
FIG. 2 is an explanatory diagram showing a schematic configuration of the fuel cell 100b and a cell environment of the fuel cell 100b in the second embodiment. The difference from the first embodiment shown in FIG. 1 is that the hydraulic pressure of MPL (Micro Porous Layer) is set according to the structure of the hydrogen gas flow channel 60 instead of the swelling rate of ionomer. Other configurations are the same as those of the first embodiment.

  MPL is a water-repellent layer formed on the surface of the gas diffusion layer on the catalyst layer side, and has finer pores than the gas diffusion layer. The MPL can be formed by applying a water repellent paste to the surface of the gas diffusion layer and baking it. Since the generated water is less likely to permeate as the MPL hydraulic pressure is higher, in this embodiment, the MPL hydraulic pressure at a position that tends to be in a dry state is set high, and the MPL hydraulic pressure at a position that tends to be in a wet state is set. It is set low.

  Specifically, in the present embodiment, the water pressure in the MPL is set to a low value because the inside of the cell is likely to be wet on the upstream side of the hydrogen gas flow path 60 (the upper side of the stack in this embodiment). Has been. On the other hand, on the downstream side of the hydrogen gas flow path 60 (the lower side of the stack in the present embodiment), the inside of the cell tends to be in a dry state, and therefore the MPL hydraulic pressure is set to a high value. In the vicinity of the middle stream of the hydrogen gas flow path 60, the environment in the cell is in the middle state between the upstream side and the downstream side, so the hydraulic pressure of the MPL is set to a medium value.

  Control of the hydraulic pressure of MPL can be realized by adjusting the carbon particle size of MPL or adjusting the water repellency and hydrophilicity of MPL. Specifically, in order to increase the hydraulic pressure of MPL, the carbon particle size of MPL may be reduced or the water repellency of MPL may be increased. On the other hand, in order to lower the hydraulic pressure of MPL, the carbon particle size of MPL may be increased or the water repellency of MPL may be reduced.

  As described above, in this embodiment as well, the MPL hydraulic pressure is set according to the structure of the hydrogen gas flow channel 60, so that flooding is performed upstream of the hydrogen gas flow channel 60, that is, in the vicinity of the air outlet 30. While being able to suppress, it is possible to suppress the drying in the downstream of the hydrogen gas flow path 60, ie, in the vicinity of the air supply port 20.

C. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

C1. Modification 1:
In the above embodiment, the hydrogen gas flow path 60 is folded twice in the horizontal direction, but the number of times of folding may be one or three or more.

C2. Modification 2:
In the first embodiment, the ionomer swelling rate is set for three regions, but the ionomer swelling rate may be set for two regions or four or more regions. Further, the ionomer swelling rate may be set to change continuously and continuously from the upstream side to the downstream side of the hydrogen supply port 40. The same applies to the setting of the MPL hydraulic pressure in the second embodiment.

DESCRIPTION OF SYMBOLS 10 ... Stack 20 ... Air supply port 30 ... Air discharge port 40 ... Hydrogen supply port 50 ... Hydrogen discharge port 60 ... Hydrogen gas flow path 100 ... Fuel cell 100b ... Fuel cell

Claims (1)

A fuel cell,
A stack in which a plurality of cells are stacked horizontally;
A reaction gas supply port provided at a lower portion of the stack for receiving supply of a reaction gas;
A reaction gas outlet provided at an upper part of the stack, communicated with the reaction gas supply port, and for discharging the reaction gas;
A fuel gas supply port provided on a side surface of the stack for receiving the supply of the fuel gas;
A fuel gas discharge port that is provided on a side surface of the stack and below the fuel gas supply port, and discharges the fuel gas;
A fuel gas flow path that connects the fuel gas supply port and the fuel gas discharge port and is a flow path that folds back horizontally in the stack;
Each of the cells has an electrolyte membrane, and a catalyst layer containing an ionomer is formed on the surface of the electrolyte membrane.
The swelling rate of the ionomer of the catalyst layer in the vicinity of the downstream side of the fuel gas channel is set to a value higher than the swelling rate of the ionomer of the catalyst layer in the vicinity of the upstream side of the fuel gas channel.
Fuel cell.

Images