JP4672165B2 - Polymer electrolyte fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polymer electrolyte fuel cell including a polymer electrolyte membrane.
[0002]
[Prior art]
While petroleum resources are depleted, environmental problems such as global warming due to the consumption of fossil fuels are becoming serious, and fuel cells are attracting attention as a clean power source for motors that does not generate carbon dioxide, and have been widely developed. And some have begun to be put into practical use. When the fuel cell is mounted on an automobile or the like, a solid polymer fuel cell using a polymer electrolyte membrane is preferably used because a high voltage and a large current can be easily obtained.
[0003]
The polymer electrolyte fuel cell has a structure in which a polymer electrolyte membrane capable of conducting ions is sandwiched between a pair of electrodes of a fuel electrode and an oxygen electrode, and the fuel electrode and the oxygen electrode are each diffused. A catalyst layer, and the catalyst layer is in contact with the polymer electrolyte membrane. The catalyst layer includes catalyst particles in which a catalyst such as Pt is supported on a catalyst carrier, and is formed by integrating the catalyst particles with an ion conductive polymer binder.
[0004]
In the polymer electrolyte fuel cell, when a reducing gas such as hydrogen or methanol is introduced into the fuel electrode, the reducing gas reaches the catalyst layer through the diffusion layer and generates protons by the action of the catalyst. To do. The protons move from the catalyst layer to the catalyst layer on the oxygen electrode side through the polymer electrolyte membrane.
[0005]
On the other hand, when the reducing gas is introduced into the fuel electrode and an oxidizing gas such as air or oxygen is introduced into the oxygen electrode, the protons are oxidized in the catalyst layer on the oxygen electrode side by the action of the catalyst. Reacts with sex gases to produce water. Therefore, a current can be taken out by connecting the fuel electrode and the oxygen electrode with a conducting wire.
[0006]
Conventionally, in the polymer electrolyte fuel cell, a perfluoroalkylenesulfonic acid polymer compound (for example, Nafion (trade name) manufactured by DuPont) is used as an ion conductive polymer binder for the polymer electrolyte membrane and the catalyst layer. Widely used. The perfluoroalkylenesulfonic acid polymer compound has excellent proton conductivity due to being sulfonated and also has chemical resistance as a fluororesin, but is very expensive. There's a problem.
[0007]
Therefore, as an inexpensive polymer electrolyte membrane, an aromatic ion conductive material having a molecular structure that does not contain fluorine or has a reduced fluorine content has been proposed in recent years. As the aromatic ion-conducting material, for example, in US Pat. No. 5,403,675, a polymer obtained by polymerizing an aromatic compound having a phenylene chain is reacted with a sulfonating agent. Sulfonated rigid polyphenylenes with sulfonic acid groups introduced have been proposed. Also known as the aromatic ion conductive material is a sulfonated polyether ether ketone polymer in which a polyether ether ketone polymer is reacted with a sulfonating agent to introduce a sulfonic acid group into the polymer. Yes.
[0008]
However, the ion conductivity of the aromatic ion conductive material cannot be obtained unless it contains a certain amount of moisture, and the ion conductivity is 50% relative humidity with respect to the ion conductivity. Humidity dependency is high, as compared with the ionic conductivity at a relative humidity of 90%. For this reason, the polymer electrolyte fuel cell including the polymer electrolyte membrane made of the sulfonated polyarylene polymer has a disadvantage that a desired power generation performance may not be obtained when the relative humidity is low.
[0009]
[Problems to be solved by the invention]
An object of the present invention is to provide an inexpensive solid polymer fuel cell having a polymer electrolyte membrane that eliminates such inconvenience and has low humidity dependency of ion conductivity.
[0010]
In order to achieve this object, the polymer electrolyte fuel cell of the present invention is a polymer electrolyte membrane comprising a pair of electrodes and a polymer electrolyte membrane sandwiched between both electrodes. the state, and are not the maximum amount of water that can be held in a state of untreated subjected to hot water treatment aromatic ion conducting material in the range of 80 to 300 wt% relative to the total material, the aromatic The group-based ion conductive material is a copolymer composed of 30 to 95 mol% of the aromatic compound unit represented by the formula (1) and 70 to 5 mol% of the aromatic compound unit represented by the formula (2). It consists of a sulfonated polyarylene polymer having a sulfonic acid group in the side chain .
[0011]
In the present specification, the “maximum water content that can be held in an untreated state” may be abbreviated as “initial water content”.
[0012]
In the aromatic ion conductive material, if the initial water content is less than 80% by weight based on the whole material, ion conductivity cannot be obtained, and if it exceeds 300% by weight, the expansion / contraction rate due to heat increases. The desired durability cannot be obtained. The initial water content is the maximum amount of water that the aromatic ion conductive material can hold in an untreated state as described above, and the aromatic ion conductive material actually contains. It does not mean moisture.
[0013]
The aromatic ion conductive material exhibits ion conductivity by containing predetermined moisture, but the ion conductivity is highly dependent on humidity, and when the humidity is low, the ion conductivity is small. When the humidity is high, the ionic conductivity is very large as compared to when the humidity is low.
[0014]
Therefore, the aromatic ion conductive material is then subjected to hot water treatment. The hot water treatment may be performed, for example, by immersing the aromatic ion conductive material itself in hot water having a temperature in the range of 80 to 95 ° C. for 0.5 to 5 hours, or the aromatic system. You may carry out by immersing an electrode structure provided with the polymer electrolyte membrane which consists of an ion conductive material in the hot water of the temperature of the range of 80-95 degreeC for 0.5 to 5 hours.
[0015]
The aromatic ion conductive material can reduce the humidity dependency on the ion conductivity by performing the hot water treatment. This is because the hydrothermal treatment increases the ability of the aromatic ion conductive material to retain moisture under low humidity conditions, thereby increasing the ion conductivity under the low humidity conditions. Conceivable.
[0016]
When the temperature of the hot water is less than 80 ° C. and the immersion time is less than 0.5 hours, the hot water treatment has an effect of reducing the humidity dependency on the ion conductivity of the aromatic ion conductive material. I can't. Moreover, when the temperature of the hot water exceeds 95 ° C. and the immersion time exceeds 5 hours, the mechanical strength of the polymer electrolyte membrane made of the aromatic ion conductive material is lowered.
[0017]
In addition, the hydrothermal treatment is performed in a solid polymer fuel cell including a polymer electrolyte membrane made of the aromatic ion conductive material in a high temperature and high humidity environment of 80 to 95 ° C. and a relative humidity of 90%. You may make it carry out by operating for 5 to 5 hours and aging.
[0021]
The sulfonated polyarylene polymer is inexpensive because it contains no fluorine in the molecular structure or only contains fluorine as the electron-withdrawing group, and can reduce the cost of the polymer electrolyte fuel cell. it can.
[0022]
Here, the sulfonic acid group is not introduced into the aromatic ring adjacent to the electron withdrawing group, but is introduced only into the aromatic ring not adjacent to the electron withdrawing group. Therefore, in the sulfonated polyarylene polymer, the sulfonic acid group is introduced only into the aromatic ring represented by Ar of the aromatic compound unit represented by the formula (1). By changing the molar ratio between the aromatic compound unit shown and the aromatic compound unit shown by the formula (2), the amount of the sulfonic acid group introduced, in other words, the ion exchange capacity can be adjusted.
[0023]
Therefore, when the aromatic compound unit represented by the formula (1) is less than 30 mol% and the aromatic compound unit represented by the formula (2) is more than 70 mol%, the sulfonated polyarylene polymer has The ion exchange capacity required for the molecular electrolyte membrane cannot be obtained. Further, when the aromatic compound unit represented by the formula (1) exceeds 95 mol% and the aromatic compound unit represented by the formula (2) is less than 5 mol%, the amount of the sulfonic acid group to be introduced increases. The molecular structure becomes weak.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is an explanatory cross-sectional view showing the configuration of the polymer electrolyte fuel cell of the present embodiment.
[0026]
In the polymer electrolyte fuel cell of this embodiment, as shown in FIG. 1, a polymer electrolyte membrane 1 is sandwiched between an oxygen electrode 2 and a fuel electrode 3, and the oxygen electrode 2 and the fuel electrode 3 are Each includes a diffusion layer 4 and a catalyst layer 5 formed on the diffusion layer 4.
[0027]
Each diffusion layer 4 includes a separator 6 that is in close contact with the outer surface. The separator 6 includes an oxygen passage 2a through which an oxygen-containing gas such as air flows in the oxygen electrode 2, and a fuel passage 3a through which a fuel gas such as hydrogen flows in the fuel electrode 3 on the diffusion layer 4 side. Yes.
[0028]
In the present embodiment, an aromatic ion conductive material such as a sulfonated polyarylene polymer or a sulfonated polyetheretherketone is used as the polymer electrolyte membrane 1 of the solid polymer fuel cell. The aromatic ion conductive material has an initial water content of 80 to 300% by weight based on the whole material.
[0029]
Examples of the sulfonated polyarylene polymer include polyarylene polymer comprising 30 to 95 mol% of the aromatic compound unit represented by the formula (1) and 70 to 5 mol% of the aromatic compound unit represented by the formula (2). It is possible to use a product obtained by sulfonating a coalescence with concentrated sulfuric acid and introducing a sulfonic acid group into a side chain.
[0030]
[Chemical formula 5]
[0031]
[Chemical 6]
[0032]
Examples of the monomer corresponding to the formula (1) include 2,5-dichloro-4′-phenoxybenzophenone. Examples of the monomer corresponding to the formula (2) include 4,4′-dichlorobenzophenone and 4,4′-bis (4-chlorobenzoyl) diphenyl ether.
[0033]
The aromatic ion conductive material is dissolved in a solvent such as N-methylpyrrolidone, and formed into a desired dry film thickness by a casting method, whereby the polymer electrolyte membrane 1 is obtained.
[0034]
In the polymer electrolyte fuel cell, the diffusion layer 4 of the oxygen electrode 2 and the fuel electrode 3 is composed of carbon paper and an underlayer. For example, carbon black and polytetrafluoroethylene (PTFE) are mixed at a predetermined weight ratio. A slurry uniformly dispersed in an organic solvent such as ethylene glycol is applied to one side of the carbon paper and dried to form the underlayer.
[0035]
The catalyst layer 5 is made of a perfluoroalkylene sulfonic acid polymer compound (for example, Nafion (trade name) manufactured by DuPont) in which catalyst particles in which platinum is supported on carbon black (furnace black) at a predetermined weight ratio. A catalyst paste obtained by uniformly mixing a solution obtained by dissolving an ion conductive binder in a solvent such as isopropanol or n-propanol at a predetermined weight ratio is screen-printed on the underlayer 7 so as to have a predetermined platinum amount. It is formed by drying. The drying is performed, for example, by drying at 60 ° C. for 10 minutes and then drying at 120 ° C. under reduced pressure.
[0036]
The polymer electrolyte membrane 1 is hot-pressed while being sandwiched between the oxygen electrode 2 and the catalyst layer 5 of the fuel electrode 3 to form the solid polymer fuel cell. The hot pressing can be performed, for example, by applying a secondary press at 160 ° C. and 4 MPa for 1 minute after the primary press at 80 ° C. and 5 MPa for 2 minutes.
[0037]
In the solid polymer fuel cell of this embodiment, the polymer electrolyte membrane 1 is hydrothermally treated by immersing it in hot water having a temperature in the range of 80 to 95 ° C. for 0.5 to 5 hours. In the hot water treatment, the polymer electrolyte membrane 1 may be immersed in the hot water alone, or may be immersed in the hot water when the electrode structure (MEA) is formed. The hydrothermal treatment may be performed by aging the polymer electrolyte fuel cell by operating it at a high temperature and high humidity of 80 to 95 ° C. and a relative humidity of 90% for 0.5 to 5 hours. .
[0038]
Next, an example is shown.
[0039]
[Example 1]
In this example, first, an aromatic ion conductive material composed of a sulfonated polyarylene polymer represented by the formula (3) and having an ion exchange capacity of 2.3 meq / g was dissolved in N-methylpyrrolidone, and cast. Thus, a polymer electrolyte membrane 1 having a dry film thickness of 50 μm was prepared.
[0040]
[Chemical 7]
[0041]
Next, carbon black and polytetrafluoroethylene (PTFE) are mixed at a weight ratio of carbon black: PTFE = 4: 6 to prepare a slurry uniformly dispersed in ethylene glycol. The base layer 7 was formed by coating and drying, and the diffusion layer 4 composed of the carbon paper 6 and the base layer 7 was formed.
[0042]
Next, the ion conductivity of catalyst particles in which platinum is supported on furnace black in a weight ratio of furnace: platinum = 1: 1 is made of a perfluoroalkylenesulfonic acid polymer compound (Nafion (trade name) manufactured by DuPont). A catalyst paste was prepared by uniformly mixing the binder in an isopropanol / n-propanol solution at a weight ratio of catalyst particles: binder = 8: 5. Next, the catalyst paste 4 was screen-printed on the underlayer 7 so as to have a platinum amount of 0.5 mg / cm ² and dried to form the catalyst layer 4. The drying was performed at 60 ° C. for 10 minutes and then dried at 120 ° C. under reduced pressure.
[0043]
Next, the polymer electrolyte membrane 1 is subjected to primary pressing at 80 ° C. and 5 MPa for 2 minutes while being sandwiched between the catalyst layer 5 of the oxygen electrode 2 and the fuel electrode 3, and further at 160 ° C. and 4 MPa. By applying a second press for 1 minute, the polymer electrolyte fuel cell shown in FIG. 1 was formed.
[0044]
The aromatic ion conductive material made of the sulfonated polyarylene polymer has an initial water content of 114% by weight based on the whole material. Therefore, in this example, after the polymer electrolyte membrane 1 made of the aromatic ion conductive material was immersed in hot water at 95 ° C. for 1 hour for hot water treatment, used.
[0045]
Next, the ionic conductivity of the polymer electrolyte membrane 1 before the hydrothermal treatment and the ionic conductivity after the hydrothermal treatment were measured.
[0046]
For the ion conductivity, the resistance value of the polymer electrolyte membrane 1 at 85 ° C. was measured by the AC two-terminal method under the conditions of an applied voltage of 1 V and a frequency of 10 kHz, and the resistance value was converted to ion conductivity. In the measurement, the polymer electrolyte membrane 1 before the hydrothermal treatment and the polymer electrolyte membrane 1 before the hydrothermal treatment were measured at a relative humidity of 50% and a relative humidity of 90%, respectively.
[0047]
The result was expressed as a value of B / A, where A is the ion conductivity when the relative humidity is 50% and B is the ion conductivity when the relative humidity is 90%. Further, the value of D / C when the value of B / A of the polymer electrolyte membrane 1 before the hydrothermal treatment is C and the value of B / A of the polymer electrolyte membrane 1 after the hydrothermal treatment is D Was used as an index for reducing humidity dependency.
[0048]
Table 1 shows the initial moisture content of the polymer electrolyte membrane 1 of this example, the B / A values before and after the hydrothermal treatment, and the D / C values.
[0049]
[Example 2]
In this example, the polymer electrolyte membrane 1 was prepared using an aromatic ion conductive material made of a sulfonated polyarylene polymer represented by the formula (4) and having an ion exchange capacity of 1.7 meq / g. A polymer electrolyte fuel cell was formed in exactly the same manner as in Example 1.
[0050]
[Chemical 8]
[0051]
The aromatic ion conductive material made of the sulfonated polyarylene polymer has an initial water content of 94% by weight based on the whole material. Next, the ion conductivity before the hydrothermal treatment and the ion conductivity after the hydrothermal treatment of the polymer electrolyte membrane 1 made of the aromatic ion conductive material were measured.
[0052]
Table 1 shows the initial moisture content of the polymer electrolyte membrane 1 of this example, the B / A values before and after the hydrothermal treatment, and the D / C values.
[0053]
[Example 3]
In this example, the polymer electrolyte membrane 1 was prepared using an aromatic ion conductive material made of a sulfonated polyarylene polymer represented by the formula (3) and having an ion exchange capacity of 2.5 meq / g. Were exactly the same as in Example 1 to form a polymer electrolyte fuel cell.
[0054]
The aromatic ion conductive material made of the sulfonated polyarylene polymer has an initial water content of 276% by weight based on the whole material. Next, the ion conductivity before the hydrothermal treatment and the ion conductivity after the hydrothermal treatment of the polymer electrolyte membrane 1 made of the aromatic ion conductive material were measured.
[0055]
Table 1 shows the initial moisture content of the polymer electrolyte membrane 1 of this example, the B / A values before and after the hydrothermal treatment, and the D / C values.
[0056]
[Reference example]
In this reference example , a polymer electrolyte membrane 1 was prepared using an aromatic ion conductive material made of a sulfonated polyetheretherketone polymer represented by the formula (5) and having an ion exchange capacity of 1.5 meq / g. Except for the above, a polymer electrolyte fuel cell was formed in exactly the same manner as in Example 1.
[0057]
[Chemical 9]
[0058]
The aromatic ion conductive material made of the sulfonated polyetheretherketone polymer has an initial water content of 300% by weight based on the whole material. Next, the ion conductivity before the hydrothermal treatment and the ion conductivity after the hydrothermal treatment of the polymer electrolyte membrane 1 made of the aromatic ion conductive material were measured.
[0059]
Table 1 shows the initial moisture content of the polymer electrolyte membrane 1 of the present example, the B / A values before and after the hydrothermal treatment, and the D / C values.
[0060]
[Table 1]
[0061]
From Table 1, each of the polymer electrolyte membranes 1 made of the aromatic ion conductive material having an initial water content of 94 to 300% by weight is ion-conductive at a relative humidity of 50% before the hydrothermal treatment. The ratio (B / A) of the ionic conductivity B at 90% relative humidity with respect to the rate A is large, and it is clear that the ionic conductivity is highly dependent on humidity. However, each of the polymer electrolyte membranes 1 has a small B / A value after the hydrothermal treatment, and the hydrothermal treatment reduces the humidity dependence of the ion conductivity. it is obvious.
[0062]
As apparent from the D / C values in Table 1, the reduction in humidity dependence is in the range of 0.26 to 0.45 times for each polymer electrolyte membrane 1, and is considered to be effective in this range.
[0063]
According to the polymer electrolyte fuel cell of the present embodiment, as described above, the humidity dependency on the ionic conductivity of each polymer electrolyte membrane 1 is reduced, and as a result, the desired power generation performance is obtained regardless of humidity conditions. It is expected to produce an effect that it can be obtained.
[Brief description of the drawings]
FIG. 1 is an explanatory cross-sectional view showing a configuration of a polymer electrolyte fuel cell according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Polymer electrolyte membrane, 2, 3 ... Electrode.

Claims (2)

In a polymer electrolyte fuel cell comprising a pair of electrodes and a polymer electrolyte membrane sandwiched between both electrodes,
The polymer electrolyte membrane is obtained by hydrothermally treating an aromatic ion conductive material in which the maximum water content that can be retained in an untreated state is in the range of 80 to 300% by weight with respect to the entire material. Oh it is,
The aromatic ion conductive material is composed of 30 to 95 mol% of an aromatic compound unit represented by the formula (1) and 70 to 5 mol% of an aromatic compound unit represented by the formula (2). A polymer electrolyte fuel cell comprising a sulfonated polyarylene polymer having a sulfonic acid group in the side chain of the coalescence .
  The hot water treatment is performed by immersing the polymer electrolyte membrane or an electrode structure provided with the polymer electrolyte membrane in hot water in a temperature range of 80 to 95 ° C. for 0.5 to 5 hours. The polymer electrolyte fuel cell according to claim 1.