JP2011070980A - Polymer electrolyte of solid polymer fuel cell, method for manufacturing the same, membrane-electrode assembly containing polymer electrolyte, and method for manufacturing the same membrane-electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a polymer electrolyte which has high proton conductivity and high gas permeability without changing a structure of the polymer electrolyte, and a solid polymer fuel cell having a membrane-electrode assembly including the polymer electrolyte. <P>SOLUTION: In the manufacturing method for a polymer electrolyte, a polymer electrolyte ink including a polymer electrolyte dispersion solution, a solvent, and an organic object wherein dipole moment is 2.0 D or more is produced, a coated film is formed by applying the polymer electrolyte ink to a base material, and the organic object in the film attained by drying the coated film is removed with acid treatment. Thus, the polymer electrolyte having high proton conductivity and high gas permeability can be attained. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a polymer electrolyte and a solid polymer fuel cell comprising a membrane electrode assembly containing the polymer electrolyte.

  A fuel cell is a power generation system that generates electricity simultaneously with heat by causing a reverse reaction of electrolysis of water between a fuel gas containing hydrogen and an oxidant gas containing oxygen at an electrode containing a catalyst. This power generation system has features such as high efficiency, low environmental load, and low noise as compared with conventional power generation methods, and is attracting attention as a clean energy source in the future. There are several types depending on the type of ion conductor used, and those using an ion conductive polymer membrane are called solid polymer fuel cells.

  Among fuel cells, polymer electrolyte fuel cells can be used at room temperature, so they are expected to be used for on-vehicle sources and household stationary power sources. In recent years, various research and development have been conducted. Yes. A polymer electrolyte fuel cell is a membrane / electrode assembly (MEA) called a membrane electrode assembly, in which a pair of electrocatalyst layers are arranged on both sides of a polymer electrolyte, and one of the electrodes contains hydrogen. It is a battery that is sandwiched between a pair of separator plates that are provided with a gas flow path for supplying a fuel gas and supplying an oxidant gas containing oxygen to the other electrode. Here, the electrode for supplying the fuel gas is called a fuel electrode, and the electrode for supplying the oxidant gas is called an air electrode. These electrodes are composed of an electrode catalyst layer formed by laminating carbon particles carrying a catalyst substance such as a platinum-based noble metal and a polymer electrolyte, and a gas diffusion layer having both gas permeability and electron conductivity.

  Proton conductivity of 0.1 S / cm at 120 ° C. and 20% RH is required to use the polymer electrolyte of the solid polymer fuel cell as a vehicle-mounted source. Therefore, the polymer electrolyte contained in the catalyst electrode layer is required to have gas permeability.

JP 2006-24389 A

Electrochimica Acta 54 4328-4333 2009

  In order to solve the above problem, in Patent Document 1, the fluorinated polymer electrolyte membrane and the fluorinated polymer electrolyte have a small EW (Equivalent Weight) equivalent to the average molecular weight per ion-exchange group. And attempts to increase the sulfonic acid group density. However, by increasing the sulfonic acid group density, the fluorine-based polymer electrolyte easily swells and cannot stably generate power.

  Further, in Non-Patent Document 1, the specific activity (mass activity) of an electrode catalyst is determined using a hydrocarbon-based polymer electrolyte. However, since the hydrocarbon polymer electrolyte has poor gas permeability compared to the fluorine polymer electrolyte, there is a problem that high specific activity cannot be obtained.

  The present invention is intended to solve such conventional problems, and provides a method for producing a polymer electrolyte with improved proton conductivity and gas permeability without changing the molecular structure. An object of the present invention is to provide a polymer electrolyte fuel cell having high power generation performance under various conditions by using a molecular electrolyte as a polymer electrolyte in an electrolyte membrane or a catalyst electrode layer.

  In order to achieve the above object, the invention according to claim 1 of the present invention is to produce a polymer electrolyte ink comprising a polymer electrolyte dispersion solution, a solvent, and an organic substance having a dipole moment of 2.0D or more, A method for producing a polymer electrolyte, comprising: applying a polymer electrolyte ink on a substrate to form a coating film; and drying the coating film to remove organic substances in the film by acid treatment. Is.

  The invention according to claim 2 of the present invention is the method for producing a polymer electrolyte according to claim 1, wherein the organic substance is monoethylene glycol or urea.

  The invention according to claim 3 of the present invention is characterized in that the polymer electrolyte ink contains a sulfonic acid, and the organic substance is at least twice the sulfonic acid group equivalent of the polymer electrolyte ink. The method for producing a polymer electrolyte described in 2 is used.

  According to a fourth aspect of the present invention, there is provided a polymer electrolyte produced by the production method according to any one of the first to third aspects.

  The invention according to claim 5 of the present invention is a membrane electrode assembly comprising a polymer electrolyte membrane and an electrode catalyst layer sandwiching the polymer electrolyte membrane, wherein the polymer electrolyte according to claim 4 comprises: The membrane / electrode assembly is used as a polymer electrolyte membrane or an electrode catalyst layer.

  According to a sixth aspect of the present invention, there is provided a polymer electrolyte ink comprising a polymer electrolyte dispersion solution, a solvent, and an organic substance having a dipole moment of 2.0 D or more, and the polymer electrolyte ink is formed on a substrate. A film is formed by coating the film, and the film obtained by drying the film is sandwiched between the electrode catalyst layers, and organic substances in the film are removed by acid treatment to form a polymer electrolyte membrane. The method for producing a membrane electrode assembly is as follows.

  The invention according to claim 7 of the present invention is the process for producing a membrane electrode assembly according to claim 6, wherein the organic substance is monoethylene glycol or urea.

  The invention according to claim 8 of the present invention is characterized in that the polymer electrolyte ink contains a sulfonic acid, and the organic substance is at least twice the sulfonic acid group equivalent of the polymer electrolyte ink. 7. The method for producing a membrane / electrode assembly according to claim 7 is used.

  According to the method for producing a polymer electrolyte according to the present invention, a polymer electrolyte produced by mixing and acid-treating an organic substance can increase the cluster size formed by an assembly of sulfonic acid groups. It is possible to provide a polymer electrolyte having high proton conductivity and high gas permeability in a high humidity environment. Moreover, a polymer electrolyte fuel cell provided with the membrane electrode assembly using the polymer electrolyte concerning this invention can be provided.

It is explanatory drawing of the manufacturing method of the polymer electrolyte which concerns on this invention. 1 is an exploded schematic view of a polymer electrolyte fuel cell according to the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 and 2. Note that the present invention is not limited to the embodiments described below, and modifications such as design changes can be made based on the knowledge of those skilled in the art, and such modifications are added. The embodiments may be included in the scope of the present invention.

(Polymer electrolyte production method)
A method for producing a polymer electrolyte according to the present invention will be described with reference to FIG. In the method for producing a polymer electrolyte of the present invention, a polymer electrolyte dispersion solution and monoethylene glycol (MEG) or urea (Urea) are mixed and mixed for 1 hour to form a sulfonic acid group aggregate. Since monoethylene glycol or urea is taken into the cluster to be formed, the cluster size can be increased. (Step 1 in Fig. 1)

Next, a PTFE sheet is placed on the glass substrate, the polymer electrolyte ink prepared in Step 1 is applied on PTFE, and applied with an applicator (Step 2 in FIG. 1). Further, the coated polymer electrolyte is dried, the residual solvent is removed (step 3 in FIG. 1), and the polymer electrolyte is peeled off (step 4 in FIG. 1). Finally, the obtained polymer electrolyte is hot-pressed to fix the enlarged cluster (step 5 in FIG. 1).

Next, the polymer electrolyte obtained in step 5 is washed with pure water at 70 ° C., a 3% hydrogen peroxide aqueous solution, a 1M sulfuric acid aqueous solution, and pure water again (steps 6 to 9 in FIG. 1). Finally, a polymer electrolyte having an expanded cluster size can be obtained by drying.

In the polymer electrolyte of the present invention, the organic substance to be mixed preferably has a large dipole interaction. Specifically, monoethylene glycol, urea or the like having a hydrogen bonding group and a dipole moment of 2.0 D (Debye) or more is preferable. This is because if the organic substance has a dipole moment of less than 2.0D, it is difficult to hydrogen bond with the sulfonic acid group in the polymer electrolyte, and the cluster size is difficult to increase.

In the polymer electrolyte of the present invention, the amount of the organic substance to be mixed is preferably twice or more with respect to the sulfonic acid group equivalent of the polymer electrolyte. The reason is that if it is less than 2 times, the amount of organic substances is small, and the probability of hydrogen bonding with the sulfonic acid group decreases, so that the cluster size is difficult to increase.

Next, the membrane electrode assembly (MEA) using the polymer electrolyte of the present invention, a method for producing the same, and the polymer electrolyte fuel cell of the present invention will be described in more detail.

(Electrocatalyst ink)
The solvent used as a dispersion medium for the electrode catalyst ink of the present invention is a fluidity of the polymer electrolyte without eroding the polymer electrolyte obtained by mixing and acid-treating catalyst particles, polymer electrolyte or organic matter. There is no particular limitation as long as it can be dissolved or dispersed as a fine gel in a high state. However, it is desirable to include at least a volatile liquid organic solvent, and is not particularly limited, but is not limited to methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol. Alcohols such as alcohol, isobutyl alcohol, tert-butyl alcohol, pentanole, ketone solvents such as acetone, methyl ethyl ketone, pentanone, methyl isobutyl ketone, heptanone, cyclohexanone, methylcyclohexanone, acetonyl acetone, diisobutyl ketone, tetrahydrofuran , Dioxane, diethylene glycol dimethyl ether, anisole, methoxytoluene, dibutyl ether and other ether solvents, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol Le, diethylene glycol, diacetone alcohol, polar solvents such as 1-methoxy-2-propanol may be used. Moreover, you may use what mixed 2 or more types among these solvents.

In addition, those using lower alcohol as the solvent have a high risk of ignition, and when using such a solvent, it is preferable to use a mixed solvent with water. Water that is compatible with the polymer electrolyte may be contained. The amount of water added is not particularly limited as long as the polymer electrolyte is not separated to cause white turbidity or gelation.

If the solid content in the electrode catalyst ink is more than 50% by mass, the viscosity of the electrode catalyst ink becomes high, so that the surface of the electrode catalyst layer tends to crack, and conversely if it is less than 1% by mass, the film formation rate is increased. However, since productivity will fall very slowly, it is preferable that they are 1 mass% or more and 50 mass% or less.

(Electrode catalyst layer)
In the method for producing a membrane / electrode assembly produced using the polymer electrolyte according to the present invention, the polymer electrolyte of the present invention in which organic substances are mixed and removed by acid treatment, or catalyst-supported carbon particles embedded with the polymer electrolyte are: Alternatively, the catalyst-supporting carbon particles and the electrode catalyst ink in which the polymer electrolyte is dispersed in a solvent may be applied to a transfer sheet and dried.

At this time, as a coating method, a doctor blade method, a dipping method, a screen printing method, a roll coating method, a spray method, or the like may be used.

As a substrate in the method for producing an electrode catalyst layer of the present invention, a gas diffusion layer, a transfer sheet, a polymer electrolyte membrane obtained by mixing and removing the organic matter of the present invention by acid treatment, or a polymer electrolyte membrane may be used. . As the gas diffusion layer, a material having gas diffusibility and conductivity may be used. The transfer sheet may be any material that has good transferability.

When a transfer sheet is used as the substrate, the transfer sheet is peeled after the electrode catalyst layer is bonded to the polymer electrolyte membrane, and a membrane electrode assembly having electrode catalyst layers on both sides of the polymer electrolyte membrane can be obtained. .

  The removal of the organic substance by acid treatment cleaning may be performed after producing a polymer electrolyte membrane and an electrode catalyst layer produced using a polymer electrolyte containing the organic substance and producing a membrane electrode assembly.

As the gas diffusion layer and the separator, those used in ordinary fuel cells may be used. Specifically, a porous carbon material such as carbon cloth, carbon paper, and nonwoven fabric may be used as the gas diffusion layer. As the separator, a carbon type or a metal type may be used. The fuel cell is manufactured by assembling other accompanying devices such as a gas supply device and a cooling device.

  FIG. 2 shows an exploded schematic view of the polymer electrolyte fuel cell according to the embodiment of the present invention. In the polymer electrolyte fuel cell of the present invention, the gas diffusion layer 4 on the air electrode side and the gas diffusion layer on the fuel electrode side are opposed to the electrode catalyst layer 2 and the electrode catalyst layer 3 of the membrane electrode assembly 12. 5 is arranged. As a result, an air electrode (cathode) 6 and a fuel electrode (anode) 7 are formed. A pair of separators 10 made of a conductive and impermeable material is disposed, which includes a gas flow path 8 for gas flow and a cooling water flow path 9 for cooling water flow on the opposing main surface. For example, hydrogen gas is supplied as a fuel gas from the gas flow path 8 of the separator 10 on the fuel electrode 7 side. On the other hand, a gas containing oxygen, for example, is supplied as an oxidant gas from the gas flow path 8 of the separator 10 on the air electrode 6 side. An electromotive force can be generated between the fuel electrode and the air electrode by causing electrode reaction between hydrogen and oxygen gas of the fuel gas in the presence of the catalyst.

  In the solid polymer fuel cell shown in FIG. 2, the solid polymer electrolyte membrane 1, the electrode catalyst layers 2, 3, and the gas diffusion layers 4, 5 are sandwiched between a pair of separators. Although it is a so-called single cell polymer electrolyte fuel cell, in the present invention, a plurality of cells may be stacked via a separator 10 to form a fuel cell.

  Examples and comparative examples will be described below.

(Polymer electrolyte dispersion)
A 20% by mass polymer electrolyte dispersion solution (Nafion: Nafion (registered trademark), manufactured by Dupont) was used as the polymer electrolyte dispersion solution.

Example 1
(Production of polymer electrolyte)
In a 10 ml glass container, 6.6 times as much monoethylene glycol as the sulfonic acid group equivalent of the 20% by mass polymer electrolyte dispersion and polymer electrolyte was mixed and stirred for 1 hour. Next, a polymer electrolyte ink was applied onto a polymer film (PTFE) bonded to glass via an adhesive, and was applied with a doctor blade so that the film thickness was about 25 μm. Then, it was made to dry for 5 minutes at 60 degreeC, and it peeled from the polymer film. Thereafter, the polymer electrolyte was hot pressed at 130 ° C. for 30 minutes.

(Removal of monoethylene glycol from polymer electrolyte)
The polymer electrolyte was immersed in pure water at 70 ° C., 3 wt% hydrogen peroxide aqueous solution, 1 M sulfuric acid aqueous solution and pure water for 1 hour to remove monoethylene glycol. Then, the polymer electrolyte was produced by making it vacuum-dry at 80 degreeC for 1 hour.

(Example 2)
(Production of polymer electrolyte)
In a 10 ml glass container, 20% by mass of the polymer electrolyte dispersion solution and 2.2 times of urea with respect to the sulfonic acid group equivalent of the polymer electrolyte were mixed and stirred for 1 hour. Next, a polymer electrolyte ink was applied onto a polymer film (PTFE) bonded to glass via an adhesive, and was applied with a doctor blade so that the film thickness was about 25 μm. Then, it was made to dry for 5 minutes at 60 degreeC, and it peeled from the polymer film. Thereafter, the polymer electrolyte was hot pressed at 130 ° C. for 30 minutes.

(Removal of urea from polymer electrolyte)
Each of the polymer electrolytes was immersed in 70 ° C. pure water, 3 wt% aqueous hydrogen peroxide solution, 1M sulfuric acid aqueous solution and pure water for 1 hour to remove urea. Then, the polymer electrolyte was produced by making it vacuum-dry at 80 degreeC for 1 hour.

(Comparative example)
(Production of polymer electrolyte)
A 20% by mass polymer dispersion solution was applied on a polymer film (PTFE) bonded to glass via an adhesive, and was coated with a doctor blade so that the film thickness was about 25 μm. Then, it was made to dry for 5 minutes at 60 degreeC, and it peeled from the polymer film. Thereafter, the polymer electrolyte was hot pressed at 130 ° C. for 30 minutes.

(Polymer electrolyte cleaning)
The polymer electrolytes were immersed in pure water at 70 ° C., 3 wt% aqueous hydrogen peroxide, 1 M sulfuric acid, and pure water for 1 hour, respectively. Then, the polymer electrolyte was produced by making it vacuum-dry at 80 degreeC for 1 hour.

(Adjustment of electrode catalyst ink)
A platinum-supported carbon catalyst (trade name: TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with a platinum-supported amount of 50% by mass and a 20% by mass polymer electrolyte dispersion (Nafion: Nafion (registered trademark), manufactured by Dupont) in a solvent. And dispersion treatment was performed using a planetary ball mill (trade name: Pulverisette 7, manufactured by Fritsch). Ball mill pots and balls made of zirconia were used. The electrode catalyst ink was prepared by setting the composition ratio of the starting material to 2: 1 by mass ratio of platinum-supporting carbon particles and Nafion (Nafion (registered trademark), manufactured by Dupont).

(Production of electrode catalyst layer)
The electrode catalyst layer ink was applied onto a PTFE base material and applied with a doctor blade. The coated electrode catalyst layer was produced by drying at 60 ° C. for 5 minutes. The thickness of the electrode catalyst layer was adjusted so that the amount of platinum supported was about 0.3 mg / cm ^2, and the electrode area of the electrode catalyst layer was cut so as to be a square of 5 cm ² .

(Production of membrane electrode assembly)
A transfer sheet was placed so that the electrode catalyst layer cut into a 5 cm ² square faced both surfaces of the polymer electrolyte membrane, and hot-pressed at 130 ° C. for 15 minutes to prepare a membrane electrode assembly.

(Measurement of hydrogen gas leak current)
The membrane electrode assembly was bonded so as to sandwich a carbon cloth as a gas diffusion layer, and installed in a power generation evaluation cell (manufactured by NF Circuit Design Block). Using a fuel cell measurement device (trade name: GFI-SG1, manufactured by Toyo Technica Co., Ltd.), the cell temperature was 80 ° C., and the humidifier was adjusted to 100% RH for both the anode and the cathode.

  As fuel gas, 200 ml / min of hydrogen or nitrogen was flowed on the anode side, and 200 ml / min of nitrogen was flowed on the cathode side.

  The hydrogen gas leakage current was calculated by LSV (linear sweep voltammetry) measurement with a counter electrode and a reference electrode arranged on the anode and a working electrode arranged on the cathode. LSV is a measurement in which the potential of the working electrode is scanned only in the forward direction from the initial potential to the end potential. At the time of measurement, 0 to 0.8 mV vs. 1 at a scanning speed of 1 mV / sec. Performed in the RHE range. When calculating the hydrogen gas leakage current, LSV measurement is performed when nitrogen is supplied to both the anode and cathode, and LSV measurement is performed when hydrogen is supplied to the anode and nitrogen is supplied to the cathode, and the background current is subtracted to obtain hydrogen Gas leakage current was used.

In Table 1 below, 0.5 mV vs. The hydrogen gas leak current value in the case of RHE is shown.

  From Table 1, when Examples and Comparative Examples are compared, according to Examples 1 and 2, hydrogen gas leakage current is increased by mixing and acid-treating urea (Urea) or monoethylene glycol (MEG). I was able to confirm.

(Proton conductivity measurement)
The conductivity of the film is calculated from the film resistance and the film size as in the following equation.
σ = (1 / R) · (L / S)
σ: conductivity, R: electrical resistance, L: distance between electrodes, S: cross-sectional area film resistance were measured by an AC impedance method. As the measuring device, FRA 5080 manufactured by NF circuit design block was used. The measurement frequency was 10 Hz to 2 MHz. The AC applied voltage was 100 mV, and the DC applied voltage was 0 V. Moreover, the measurement environment at that time was measured under the conditions of 80, 50 ° C., 30, 50, 70, and 95% RH.

Table 2 shows Nafion (Nafion (registered trademark), manufactured by Dupont), Nafion mixed with urea and removed by acid treatment (Nafion (registered trademark), manufactured by Dupont), and Nafion (Nafion mixed with acid and treated with monoethylene glycol). (Registered trademark) manufactured by Dupont) shows the relationship between the relative humidity and proton conductivity.

  From Table 2, when Examples and Comparative Examples are compared, according to Examples 1 and 2, the polymer electrolyte to which monoethylene glycol or urea is added is proton conductive even under low or high humidification. Was confirmed to be high.

As described above, according to the comparison between the example and the comparative example, according to the present invention, the polymer electrolyte added with monoethylene glycol or urea having a dipole moment of 2.0 D (Debye) or higher has a low humidification or high It was confirmed that both proton conductivity and gas permeability were high even under humidification. From this, it was confirmed that the polymer electrolyte according to the present invention is more useful not only as a polymer electrolyte membrane but also as a polymer electrolyte of an electrode catalyst layer.

  INDUSTRIAL APPLICABILITY The present invention can be used for a polymer electrolyte fuel cell used for an electric vehicle, a mobile phone, a vending machine, an underwater robot, a submarine, a spacecraft, an underwater vehicle, a power source for an underwater base, and the like.

DESCRIPTION OF SYMBOLS 1 Solid polymer electrolyte membrane 2 Electrode catalyst layer 3 Electrode catalyst layer 12 Membrane electrode assembly 4 Gas diffusion layer 5 Gas diffusion layer 6 Air electrode (cathode)
7 Fuel electrode (anode)
8 Gas flow path 9 Cooling water flow path 10 Separator

Claims (8)

Producing a polymer electrolyte ink comprising a polymer electrolyte dispersion solution, a solvent, and an organic substance having a dipole moment of 2.0D or more;
The polymer electrolyte is formed by applying the polymer electrolyte ink on a substrate to form a coating film, and drying the coating film to remove the organic matter in the film obtained by acid treatment. Method.   The method for producing a polymer electrolyte according to claim 1, wherein the organic substance is monoethylene glycol or urea.   3. The polymer electrolyte according to claim 1, wherein the polyelectrolyte ink contains sulfonic acid, and the organic substance is at least twice the sulfonic acid group equivalent of the polyelectrolyte ink. Production method.   A polymer electrolyte produced by the production method according to claim 1. A membrane electrode assembly comprising a polymer electrolyte membrane and an electrode catalyst layer sandwiching the polymer electrolyte membrane,
5. The membrane / electrode assembly, wherein the polymer electrolyte according to claim 4 is used as the polymer electrolyte membrane or the electrode catalyst layer. Producing a polymer electrolyte ink comprising a polymer electrolyte dispersion solution, a solvent, and an organic substance having a dipole moment of 2.0D or more;
Applying the polymer electrolyte ink on a substrate to form a coating film, and sandwiching a film obtained by drying the coating film with an electrode catalyst layer,
A method for producing a membrane / electrode assembly, wherein the organic substance in the membrane is removed by acid treatment to form a polymer electrolyte membrane.   The method for producing a membrane / electrode assembly according to claim 6, wherein the organic substance is monoethylene glycol or urea.   The membrane electrode assembly according to claim 6 or 7, wherein the polymer electrolyte ink contains sulfonic acid, and the organic substance is at least twice as much as a sulfonic acid group equivalent of the polymer electrolyte ink. Manufacturing method.