JP7235408B2 - Membrane electrode assembly for fuel cell - Google Patents

Description

Article 30, Paragraph 2 of the Patent Act applies. Proceedings of the Society of Polymer Science, Vol. 68, No. 2 [2019] Publisher: The Society of Polymer Science, Japan Publication date: September 11, 2019 Molecular Symposium Date: September 26, 2019

The present disclosure relates to membrane electrode assemblies for fuel cells.

Fuel cells are known that generate electricity by chemically reacting an anode gas, such as hydrogen, and a cathode gas, such as oxygen.

Traditionally, ionomers have been used to conduct protons inside fuel cells, eg, in the catalytic electrode layer. However, since ionomer conducts protons through water, the proton conductivity in the catalyst electrode layer may decrease under low-humidity conditions, for example, in a high-temperature environment of 100° C. or higher, and the power generation characteristics of the fuel cell may decrease. There is

Therefore, the conventional fuel cell requires a system for humidifying and cooling the inside of the cell, and such a system increases the cost of the fuel cell.

In order to solve such a problem, application of an ionic liquid capable of conducting protons without passing through water, for example, to a catalyst electrode layer has been studied.

Techniques related to the application of ionic liquids to fuel cells include, for example, the techniques described in Patent Documents 1 to 3.

Patent Document 1 discloses a fuel cell having a catalytic electrode layer containing a catalyst and an ionic liquid as an anode electrode.

In addition, Patent Document 2 discloses a proton conductor composed of a compatible solution of an ionic liquid and a polymer having a substituent having an active hydrogen such as a hydroxyl group, and a polymer electrolyte fuel cell using the proton conductor as an electrolyte. are doing.

Further, Patent Literature 3 discloses a configuration in which a gas flow path is provided in a fuel cell catalyst electrode layer containing a catalyst, a catalyst carrier, an ionic liquid, and an immobilizing agent.

Japanese Patent Application Laid-Open No. 2008-218098 JP 2012-041474 A JP 2008-177134 A

In applying ionic liquids to fuel cells, in order to achieve high power generation characteristics, it is necessary to improve the proton conduction path, electron conduction path, gas diffusion, and suppress the outflow of the ionic liquid due to the generated water. A configuration corresponding to the following is required.

An object of the present disclosure is to provide a membrane electrode assembly for a fuel cell that has high power generation characteristics even in a low humidity environment and can suppress outflow of ionic liquid due to humidified water or generated water. .

The present discloser has found that the above objects can be achieved by the following means:
It has a gas diffusion catalyst electrode layer and an electrolyte membrane,
The gas diffusion catalyst electrode layer has a fibrous carbon gas diffusion layer containing a catalyst metal, a carbon carrier supporting the catalyst metal, and an ionic liquid,
The mass ratio of the ionic liquid to the carbon support is 0.40 to 0.60, and the ionic liquid is diethylmethylammonium trifluoromethanesulfonate, diethylmethylammonium nonafluorobutanesulfonate, or diethylmethylammonium heptadecafluoro is octane sulfonate,
Membrane electrode assembly for fuel cells.

Advantageous Effects of Invention According to the present disclosure, it is possible to provide a membrane electrode assembly for a fuel cell that has high power generation properties even in a low-humidity environment and is capable of suppressing outflow of ionic liquid due to humidified water or generated water. .

FIG. 1A is a graph showing the IV curves of the fuel cells of Examples 1 and 2 and Comparative Example 1 when the cathode relative humidity is 80% RH. FIG. 1B is a graph showing the IV curves of the fuel cells of Examples 1 and 2 and Comparative Example 1 when the cathode relative humidity is 30% RH. FIG. 1C is a graph showing the IV curves of the fuel cells of Examples 1 and 2 and Comparative Example 1 when the cathode relative humidity is non-humidified (0% RH). FIG. 2A is a graph showing the IV curves of the fuel cells of Examples 1-3 when the cathode relative humidity is 80% RH. FIG. 2B is a graph showing the IV curves of the fuel cells of Examples 1-3 when the cathode relative humidity is 30% RH. FIG. 2C is a graph showing the IV curves of the fuel cells of Examples 1-3 when the cathode relative humidity is non-humidified (0% RH). FIG. 3A is a graph showing the IV curves of the fuel cells of Examples 3 and 6 when the cathode relative humidity is 80% RH. FIG. 3B is a graph showing the IV curves of the fuel cells of Examples 3 and 6 when the cathode relative humidity is 30% RH. FIG. 3C is a graph showing the IV curves of the fuel cells of Examples 3 and 6 when the cathode relative humidity is non-humidified (0% RH). FIG. 4A is a graph showing Nyquist plots of fuel cells of Examples 1 and 2 and Comparative Example 1 when the cathode relative humidity is 80% RH. FIG. 4B is a graph showing Nyquist plots of the fuel cells of Examples 1 and 2 and Comparative Example 1 when the cathode relative humidity is 30% RH. FIG. 4C is a graph showing Nyquist plots of the fuel cells of Examples 1 and 2 and Comparative Example 1 when the relative humidity of the cathode is non-humidified (0% RH). FIG. 5A is a graph showing Nyquist plots of the fuel cells of Examples 1-3 when the cathode relative humidity is 80% RH. FIG. 5B is a graph showing Nyquist plots of the fuel cells of Examples 1-3 when the cathode relative humidity is 30% RH. FIG. 5C is a graph showing Nyquist plots of the fuel cells of Examples 1-3 when the cathode relative humidity is non-humidified (0% RH). 6 is a graph showing the relationship between the relative humidity and OCV of the fuel cells of Examples 1, 2, 4 and 5 and Comparative Examples 1 and 2. FIG. 7 is a graph showing measurement results of ECA of the fuel cells of Examples 1, 2, 4 and 5 and Comparative Examples 1 and 2. FIG. FIG. 8 is a graph showing IV curves of the fuel cells of Example 7 and Reference Examples 1 to 4 when the relative humidity of the cathode is 80% RH. FIG. 9 is a graph showing Nyquist plots of fuel cells of Example 7 and Reference Examples 1 to 4 when the relative humidity of the cathode is 80% RH. 10A is a graph showing CV measurement results after each cycle of the fuel cell of Example 8. FIG. 10B is a graph showing CV measurement results after each cycle of the fuel cell of Comparative Example 3. FIG. FIG. 11A is a graph showing changes in ECA value calculated based on CV measurement for the fuel cell of Example 8 according to NEDO's "Cell Evaluation Analysis Protocol", with the horizontal axis being the logarithmic axis. FIG. 11B is a graph showing changes in the ECA value calculated based on the CV measurement for the fuel cell of Comparative Example 3 according to the "cell evaluation analysis protocol" by NEDO, with the horizontal axis being the logarithmic axis.

Hereinafter, embodiments of the present disclosure will be described in detail. It should be noted that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the disclosure.

The fuel cell membrane electrode assembly of the present disclosure has a gas diffusion catalyst electrode layer and an electrolyte membrane, and the gas diffusion catalyst electrode layer contains a catalyst metal, a carbon carrier supporting the catalyst metal, and an ionic liquid. containing a fibrous carbon gas diffusion layer, the mass ratio of the ionic liquid to the carbon support is 0.40-0.60, and the ionic liquid is diethylmethylammonium trifluoromethanesulfonate (dema[ TFO]), diethylmethylammonium nonafluorobutanesulfonate (dema[NFO]), or diethylmethylammonium heptadecafluorooctane sulfonate (dema[HFO]).

In a conventional membrane electrode assembly using an ionomer, the proton conductivity decreases under low humidity conditions, for example, at a relative humidity of 30% RH to 0% RH. was there. This is due to ionomer proton conduction through water.

In the membrane electrode assembly of the present disclosure, as a proton conductor, dema[TFO], dema[NFO], or dema[HFO], which is an ionic liquid capable of conducting proton conduction without water, is used as a catalyst metal. By impregnating the carbon support, which is the catalyst support to be supported, at a mass ratio of 0.40 to 0.60, it is possible to improve the power generation characteristics higher than when using the conventional Nafion (registered trademark) ionomer, particularly low. It has high power generation characteristics in a humid environment, and can suppress outflow of ionic liquid due to humidification water and generated water.

Furthermore, in the membrane electrode assembly of the present disclosure, the carbon support is impregnated with the ionic liquid at a mass ratio of 0.4 to 0.6. An ionic liquid can be immobilized on a fibrous carbon gas diffusion layer.

Moreover, the membrane electrode assembly of the present disclosure has higher durability than a membrane electrode assembly using an ionomer.

《Gas diffusion catalyst electrode layer》
In the present disclosure, the gas diffusion catalyst electrode layer has a fibrous carbon gas diffusion layer containing a catalyst metal, a carbon support supporting the catalyst metal, and an ionic liquid. The gas diffusion catalyst electrode layer may be the gas diffusion catalyst electrode layer on either the fuel electrode side or the air electrode side. is preferred.

The fibrous carbon gas diffusion layer is impregnated with the catalyst metal, the carbon carrier supporting the catalyst metal, and the catalyst ink containing the ionic liquid. It can contain a carrier and an ionic liquid.

The gas diffusion catalyst electrode layer has a catalyst metal, a carbon support supporting the catalyst metal, and a fibrous carbon gas diffusion layer containing an ionic liquid, and the mass ratio of the ionic liquid to the carbon support is 0.40 to 0.60.

The mass ratio of the ionic liquid to the carbon support may be 0.40 or more, 0.45 or more, 0.50 or more, or 0.52 or more, 0.60 or less, 0.58 or less, 0.55 or less, Or it may be 0.53 or less.

The method for producing the catalyst metal, the carbon support supporting the catalyst metal, and the gas diffusion catalyst electrode layer containing the ionic liquid is not particularly limited. Impregnation into the catalyst electrode layer, more specifically coating with catalyst ink, more specifically hand coating or the like can be used.

<Catalyst metal>
Catalyst metals include, for example, Pt, Pt alloys, or combinations thereof. A catalyst metal is supported on a carbon carrier.

<Carbon carrier>
The carbon support may be any carbon-based support that can be used for fuel cell catalysts, and examples thereof include carbon black.

<Ionic liquid>
The ionic liquid is diethylmethylammonium trifluoromethanesulfonate (dema[TFO]), diethylmethylammonium nonafluorobutanesulfonate (dema[NFO]), or diethylmethylammonium heptadecafluorooctane sulfonate (dema[HFO]). The ionic liquid may be a mixture of these.

In addition to high proton conductivity, these ionic liquids have fluoro chain lengths (TfO:CF ₃ ⁻ , NfO: C ₄ F ₉ ⁻ ) has an appropriate length, so the gas diffusibility is easily maintained due to the drainage effect (flooding suppression) of generated water due to hydrophobicity, and when mixed with catalyst particles, dispersibility A good catalyst ink can be prepared, and a uniform proton-conducting thin film layer can be formed with an appropriate coverage.

<Fibrous carbon gas diffusion layer>
The fibrous carbon gas diffusion layer can be either an anode gas diffusion layer or a cathode gas diffusion layer.

The material of the fibrous carbon gas diffusion layer may be any fibrous carbon material that can be used for the anode gas diffusion layer and cathode gas diffusion layer of fuel cell catalysts. Examples of such materials include porous carbon materials such as carbon paper, carbon cloth, and vitreous carbon.

《Electrolyte membrane》
As the material for the electrolyte membrane, any material that can be used for the electrolyte membrane of the fuel cell unit cell can be used. Examples of such materials include fluorine-based ion-conducting polymer membranes, more specifically, proton-conducting ion-exchange membranes comprising perfluorosulfonic acid. The electrolyte membrane may be a Nafion® membrane.

<<Examples 1 to 6, and Comparative Examples 1 and 2>>
Fuel cells of Examples 1 to 6 and Comparative Examples 1 and 2 were produced as follows.

<Example 1>
A mixed solution of diethylmethylammonium trifluoromethanesulfonate (dema[TfO]) as an ionic liquid and ethanol was prepared in a 9 mL sample bottle. The amount of dema[TfO] was 2% by mass with respect to the entire mixture. The mixed liquid was added to Pt-supported carbon to which a small amount of purified water was added, and stirred at 40° C. for 3 hours to prepare a catalyst ink. A gas diffusion electrode catalyst layer on the side of the air electrode was produced by uniformly applying the catalyst ink to a carbon fiber nonwoven fabric as a gas diffusion layer by hand coating and drying under reduced pressure at 60° C. for 30 minutes.

In addition, in the gas diffusion electrode catalyst layer on the air electrode side, the mass ratio of dema[TfO] to the carbon support was 0.52. Also, the coating amount of Pt was 1.05 mg/cm ² .

Next, a mixed solution of Nafion (registered trademark) as an ionomer and ethanol was prepared. The amount of Nafion® was 2% by weight based on the total mixture. The mixed liquid was added to Pt-supported carbon to which a small amount of purified water was added, and stirred at 40° C. for 3 hours to prepare a catalyst ink. A gas diffusion electrode catalyst layer on the fuel electrode side was prepared by uniformly applying the catalyst ink to a carbon fiber nonwoven fabric as a gas diffusion layer by hand coating and drying under reduced pressure at 60° C. for 30 minutes.

In addition, in the gas diffusion electrode catalyst layer on the fuel electrode side, the mass ratio of Nafion (registered trademark) to the carbon support was 0.89. Also, the coating amount of Pt was 1.07 mg/cm ² .

A Nafion (registered trademark) 112 membrane is sandwiched between the prepared gas diffusion electrode catalyst layers on the air electrode side and the fuel electrode side to form a membrane electrode assembly without hot pressing, and a fuel cell is produced at a confining pressure of 1.8 N/m. bottom.

The surface area of the active region of the fuel cell was 5.06 cm ² .

For the prepared fuel cell, the conditions were as follows: cell temperature 80° C., both poles 80% RH, anode flow rate 0.5 L/min, cathode flow rate 1.0 L/min, both poles 1 ata until a steady IV curve was obtained. I did a run-in with Hydrogen was used as the anode gas, and air was used as the cathode gas.

<Example 2>
Example 1 was repeated except that diethylmethylammonium nonafluorobutanesulfonate (dema[NfO]) was used as the ionic liquid instead of dema[TfO] in the preparation of the gas diffusion electrode catalyst layer on the air electrode side. A fuel cell was produced by using the same method, and a break-in operation was performed.

<Example 3>
The gas diffusion electrode catalyst layer on the air electrode side was prepared in the same manner as in Example 1, except that diethylmethylammonium heptadecafluorooctane sulfonate (dema[HFO]) was used instead of dema[TfO]. A fuel cell of Example 3 was produced and run-in was performed.

<Comparative Example 1>
A fuel cell was produced in the same manner as in Example 1, except that Nafion (registered trademark) was used as an ionomer in place of the ionic liquid in the production of the gas diffusion electrode catalyst layer on the air electrode side, and run-in was performed. did

<Examples 4 to 6, and Comparative Example 2>
A fuel cell of Example 4 was produced in the same manner as in Example 1, except that the Nafion (registered trademark) 112 membrane in Example 1 was replaced with a Nafion (registered trademark) 115 membrane, and a break-in operation was performed. rice field.

Similarly, Examples 2 and 3, and Comparative Example 1, respectively, except that the Nafion (registered trademark) 112 membrane in Examples 2 and 3, and Comparative Example 1 was replaced with a Nafion (registered trademark) 115 membrane. Fuel cells of Examples 5 and 6 and Comparative Example 2 were produced in the same manner and preliminarily run.

〈Ｉ－Ｖ特性の評価〉
実施例１～３、及び比較例１の燃料電池セルそれぞれについて、セル温度８０℃、アノード８０％ＲＨ、アノード流速０．５Ｌ／ｍｉｎ、カソード流速１．０Ｌ／ｍｉｎ、２ａｔａの条件下にてカソードの相対湿度を８０％ＲＨ、３０％ＲＨ、及び無加湿（０％ＲＨ）に変化させ、それぞれの相対湿度におけるＩ－Ｖ曲線を測定した。なお、アノードガスには水素を、カソードガスには空気を、それぞれ用いた。

<Evaluation of IV characteristics>
For each of the fuel cells of Examples 1 to 3 and Comparative Example 1, the cathode was heated under the conditions of a cell temperature of 80° C., an anode of 80% RH, an anode flow rate of 0.5 L/min, a cathode flow rate of 1.0 L/min, and 2 ata. The relative humidity was changed to 80% RH, 30% RH, and no humidity (0% RH), and the IV curve was measured at each relative humidity. Hydrogen was used as the anode gas, and air was used as the cathode gas.

<Electrochemical impedance measurement>
Each of the fuel cells of Examples 1 to 3 and Comparative Example 1 was connected to an external AC power supply, and the impedance was measured by changing the frequency of the AC signal input by this AC power supply. The real part of the impedance (Z') and the imaginary part of the impedance (Z'') were calculated.

In the measurement, the relative humidity of the cathode was changed to 80% RH and 30% RH under the conditions of a cell temperature of 80°C, an anode of 80% RH, an anode flow rate of 0.5 L/min, a cathode flow rate of 1.0 L/min, and 2 ata. , and non-humidified (0% RH), and the impedance was measured at each relative humidity. Hydrogen was used as the anode gas, and air was used as the cathode gas.

<Measurement of electrochemically effective surface area>
For the fuel cells of Examples 1, 2, 4, and 5 and Comparative Examples 1 and 2, respectively, hydrogen was sent to the fuel electrode side of the membrane electrode assembly, nitrogen was sent to the air electrode side, and hydrogen absorption was performed by a potentiostat. The electrochemical effective surface area was measured by cyclic voltammetry with repeated desorption and Pt redox. Specifically, the electrochemical effective surface area (ECA) was calculated from the amount of hydrogen adsorption electricity, the Pt coating amount of the air electrode, and the surface area of the active region of the fuel cell when cyclic voltammetry was performed.

In the measurement of ECA, the relative humidity of the cathode was 80% RH, 30 % RH and non-humidified (0% RH), and the impedance was measured at each relative humidity. Hydrogen was used as the anode gas, and air was used as the cathode gas.

<result>
The measurement results of IV characteristics are shown in FIGS. 1A-C, 2A-C, and 3A-C.

1A to 1C show the fuel cells of Examples 1 and 2 and Comparative Example 1 when the relative humidity of the cathode is changed to 80% RH, 30% RH, and no humidity (0% RH), respectively. 1 is a graph showing an IV curve;

As shown in FIGS. 1A to 1C, the fuel cell of Example 1 using dema[TfO] as the proton conductor of the gas diffusion catalyst electrode layer on the air electrode side, and the fuel of Example 2 using dema[NfO] The power generation characteristics of both the battery cell and the fuel cell of Comparative Example 1 using Nafion (registered trademark) were measured. It exhibited high power generation characteristics, and this tendency did not change even when the humidity decreased.

2A-C show IV curves of the fuel cells of Examples 1-3 when the relative humidity of the cathode is changed to 80% RH, 30% RH, and no humidity (0% RH), respectively. It is a graph showing.

As shown in FIGS. 2A to 2C, the fuel cell of Example 3 using dema [HfO] as the proton conductor of the gas diffusion catalyst electrode layer on the air electrode side also has high power generation as in Examples 1 and 2. showed characteristics.

3A-C show the IV curves of the fuel cells of Examples 3 and 6 when the relative humidity of the cathode is changed to 80% RH, 30% RH, and no humidity (0% RH), respectively. It is a graph showing.

As shown in FIGS. 3A to 3C, in Examples 3 and 6 in which dema [HfO] was used as the proton conductor of the gas diffusion catalyst electrode layer on the air electrode side, both exhibited high power generation characteristics. , Example 3, which used a Nafion® 112 membrane as the electrolyte layer, was higher than Example 6, which used a Nafion® 115 membrane.

Electrochemical impedance measurement results are shown in FIGS. 4A-C and 5A-C.
4A to 4C show the fuel cells of Examples 1 and 2 and Comparative Example 1 when the relative humidity of the cathode is changed to 80% RH, 30% RH, and no humidity (0% RH), respectively. 4 is a graph showing a Nyquist plot;

As shown in FIGS. 4A to 4C, the fuel cell of Example 1 using dema[TfO] as the proton conductor of the gas diffusion catalyst electrode layer on the air electrode side, and the fuel cell of Example 2 using dema[NfO] The charge transfer resistance in each fuel cell is lower than that of the fuel cell in Comparative Example 1 in which Nafion (registered trademark) is used as the proton conductor of the gas diffusion catalyst electrode layer on the air electrode side, and this tendency is due to the decrease in humidity. It grew as it did. This indicates that the ionic liquids used in the fuel cells of Examples 1 and 2 have more favorable proton conductivity and gas permeability for the cathode reaction than Nafion (registered trademark). there is

Further, as shown in FIGS. 5A to 5C, the fuel cell of Example 3 using dema [HfO] as the proton conductor of the gas diffusion catalyst electrode layer on the air electrode side was also treated in the same manner as in Examples 1 and 2. result was obtained.

FIG. 6 shows the open circuit voltage (OCV) obtained by measuring IV characteristics, and FIG. 7 shows the ECA measurement results.

As shown in FIG. 6, no clear difference was observed between the fuel cells of Examples 1 and 2 and Comparative Example 1 in terms of OCV. However, in Examples 2 and 5 using dema[NfO] as the ionic liquid, the OCV tended to increase at low humidity. Since the comparison range is 1.02 V to 0.94 V and the Nafion (registered trademark) 112 membrane or Nafion (registered trademark) 115 membrane is used as the electrolyte membrane, it is rate-limiting for OCV to some extent. It is also possible.

Further, as shown in FIGS. 1A to 1C, when comparing the Kinetic region (low current region) of the IV curve, the fuel cells of Examples 1 and 2 have higher output than the fuel cell of Comparative Example 1. Since the voltage is shown, it can be seen that it contributes to the improvement of the output of the entire membrane electrode assembly.

As shown in FIG. 7, ECA showed a clearer difference than OCV. The fuel cells of Examples 1 and 4 using dema[TfO] as the proton conductor of the gas diffusion catalyst electrode layer on the air electrode side, and the fuel cells of Examples 2 and 5 using dema[NfO] showed a higher ECA than the fuel cells of Comparative Examples 1 and 2 using Nafion® 112. Since there is no significant difference in ionic conductivity between the materials, it is conceivable that there is a difference in the state of adsorption to the catalyst.

<<Example 7 and Reference Examples 1 to 4>>
Fuel cells of Example 7 and Reference Examples 1 to 4 were produced as follows.

<Example 7>
A mixture of dema[TfO] as an ionic liquid and ethanol was prepared in a 9 mL sample bottle. The amount of dema[TfO] was 2% by mass with respect to the entire mixture. The mixed liquid was added to Pt-supported carbon to which a small amount of purified water was added, and stirred at 40° C. for 3 hours to prepare a catalyst ink. A gas diffusion electrode catalyst layer on the side of the air electrode was produced by uniformly applying the catalyst ink to the carbon fiber nonwoven fabric as the gas diffusion layer by hand coating and drying under reduced pressure at 50° C. for 30 minutes.

In addition, in the gas diffusion electrode catalyst layer on the air electrode side, the mass ratio of dema[TfO] to the carbon support was 0.52. Also, the coating amount of Pt was 1.05 mg/cm ² .

Next, a mixed solution of Nafion (registered trademark) as an ionomer and ethanol was prepared. The amount of Nafion® was 2% by weight based on the total mixture. The mixed liquid was added to Pt-supported carbon to which a small amount of purified water was added, and stirred at 40° C. for 3 hours to prepare a catalyst ink. A catalyst ink was uniformly applied to a carbon fiber nonwoven fabric as a gas diffusion layer by a spray method, and dried under reduced pressure at 50° C. for 30 minutes to prepare a gas diffusion electrode catalyst layer on the fuel electrode side.

In addition, in the gas diffusion electrode catalyst layer on the air electrode side, the mass ratio of Nafion (registered trademark) to the carbon support was 1.00. Also, the coating amount of Pt was 0.153 mg/cm ² .

The Nafion® 211 membrane was then gently stirred in 2% hydrogen peroxide at 80° C. for 1 hour. The membrane was taken out and gently stirred in boiling purified water for 1 hour. To remove metal impurities, 0.5 M sulfuric acid was used and stirred at 80° C. for 1 hour. In order to remove sulfuric acid, it was washed with purified water three times at 80° C. for 1 hour. This activated the Nafion (registered trademark) 211 membrane as the electrolyte membrane.

A Nafion (registered trademark) 211 membrane is sandwiched between the prepared gas diffusion electrode catalyst layers on the air electrode side and the fuel electrode side to form a membrane electrode assembly without hot pressing, and a fuel cell is produced at a confining pressure of 2.8 N/m. bottom.

The surface area of the active region of the fuel cell was 5.06 cm ² .

For the prepared fuel cell, the conditions were as follows: cell temperature 80° C., both poles 80% RH, anode flow rate 0.5 L/min, cathode flow rate 1.0 L/min, both poles 1 ata until a steady IV curve was obtained. I did a run-in with Hydrogen was used as the anode gas, and air was used as the cathode gas.

<Reference example 1>
The amount of dema[TfO] in the mixture of dema[TfO] as the ionic liquid and ethanol is set to 1% by mass, and the mass ratio of dema[TfO] to the carbon support in the gas diffusion electrode catalyst layer on the air electrode side. A fuel cell of Reference Example 1 was produced in the same manner as in Example 7, except that the was set to 0.16, and a break-in operation was performed. The coating amount of Pt was 1.08 mg/cm ² for the gas diffusion electrode catalyst layer on the air electrode side and 0.164 mg/cm ² for the gas diffusion electrode catalyst layer on the fuel electrode side.

<Reference example 2>
A fuel cell of Reference Example 2 was produced in the same manner as in Example 7, except that the mass ratio of dema [TfO] to the carbon support in the gas diffusion electrode catalyst layer on the air electrode side was set to 0.27. did the driving. The coating amount of Pt was 1.07 mg/cm ² for the gas diffusion electrode catalyst layer on the air electrode side and 0.163 mg/cm ² for the gas diffusion electrode catalyst layer on the fuel electrode side.

<Reference example 3>
A fuel cell of Reference Example 3 was produced in the same manner as in Example 7, except that the mass ratio of dema [TfO] to the carbon support in the gas diffusion electrode catalyst layer on the air electrode side was set to 0.77. did the driving. The coating amount of Pt was 0.98 mg/cm ² for the gas diffusion electrode catalyst layer on the air electrode side and 0.159 mg/cm ² for the gas diffusion electrode catalyst layer on the fuel electrode side.

<Reference example 4>
A fuel cell of Reference Example 4 was produced in the same manner as in Example 7, except that the mass ratio of dema [TfO] to the carbon support in the gas diffusion electrode catalyst layer on the air electrode side was set to 1.04. did the driving. The coating amount of Pt was 1.03 mg/cm ² for the gas diffusion electrode catalyst layer on the air electrode side and 0.170 mg/cm ² for the gas diffusion electrode catalyst layer on the fuel electrode side.

<Evaluation of IV characteristics>
Example 7 and Reference Example in the same manner as <Evaluation of IV characteristics> in <Examples 1 to 6 and Comparative Examples 1 and 2> above, except that the relative humidity was only 80% RH. 1 to 4 were evaluated for IV characteristics.

<Electrochemical impedance measurement>
Except that the relative humidity was only 80% RH, Example 7 and Reference Examples 1- 4 was evaluated for IV characteristics.

<result>
The configurations of the fuel cells of Example 7 and Reference Examples 1 to 4, evaluation results of IV characteristics, and electrochemical impedance measurement results are summarized in Table 2 below.

FIG. 8 shows the measurement results of IV characteristics. FIG. 8 is a graph showing IV curves of the fuel cells of Example 7 and Reference Examples 1-4. As shown in FIG. 8, the IV characteristics were the best in Example 7 where the mass ratio of dema[TfO] to carbon support was 0.52.

Further, no correlation was found between the mass ratio of dema[TfO] to the carbon support and the OCV and limiting current density in each fuel cell shown in Table 2.

FIG. 9 shows the electrochemical impedance measurement results. FIG. 9 is a graph showing Nyquist plots of the fuel cells of Example 7 and Reference Examples 1-4.

Both the film resistance and the charge transfer resistance in FIG. 9 and Table 2 were the best in Example 7 in which the mass ratio of dema[TfO] to the carbon support was 0.52.

<<Example 8 and Comparative Example 3>>
<Example 8>
A mixture of dema[TfO] as an ionic liquid and ethanol was prepared in a 9 mL sample bottle. The amount of dema[TfO] was 2% by mass with respect to the entire mixture. The mixed liquid was added to Pt-supported carbon to which a small amount of purified water was added, and stirred at 40° C. for 3 hours to prepare a catalyst ink. A gas diffusion electrode catalyst layer on the side of the air electrode was produced by uniformly applying the catalyst ink to the carbon fiber nonwoven fabric as the gas diffusion layer by hand coating and drying under reduced pressure at 50° C. for 30 minutes.

In addition, in the gas diffusion electrode catalyst layer on the air electrode side, the mass ratio of dema[TfO] to the carbon support was 0.53. Also, the coating amount of Pt was 1.07 mg/cm ² .

Next, a mixed solution of Nafion (registered trademark) as an ionomer and ethanol was prepared. The amount of Nafion® was 2% by weight based on the total mixture. The mixed liquid was added to Pt-supported carbon to which a small amount of purified water was added, and stirred at 40° C. for 3 hours to prepare a catalyst ink. A catalyst ink was uniformly applied to a carbon fiber nonwoven fabric as a gas diffusion layer by a spray method, and dried under reduced pressure at 50° C. for 30 minutes to prepare a gas diffusion electrode catalyst layer on the fuel electrode side.

In addition, in the gas diffusion electrode catalyst layer on the air electrode side, the mass ratio of Nafion (registered trademark) to the carbon support was 0.89. Also, the coating amount of Pt was 1.09 mg/cm ² .

A Nafion (registered trademark) 112 membrane is sandwiched between the prepared gas diffusion electrode catalyst layers on the air electrode side and the fuel electrode side to form a membrane electrode assembly without hot pressing, and a fuel cell is produced at a confining pressure of 1.8 N/m. bottom.

The surface area of the active region of the fuel cell was 5.06 cm ² .

For the prepared fuel cell, the conditions were as follows: cell temperature 80° C., both poles 80% RH, anode flow rate 0.5 L/min, cathode flow rate 1.0 L/min, both poles 1 ata until a steady IV curve was obtained. I did a run-in with Hydrogen was used as the anode gas, and air was used as the cathode gas.

<Comparative Example 3>
A fuel cell was produced in the same manner as in Example 8, except that Nafion (registered trademark) as an ionomer was used instead of the ionic liquid in the production of the gas diffusion electrode catalyst layer on the air electrode side, and the running-in was performed. did

In the gas diffusion electrode catalyst layer on the air electrode side, the mass ratio of Nafion (registered trademark) to the carbon support was 1.00, and the coating amount of Pt was 0.345 mg/cm ² . In the gas diffusion electrode catalyst layer on the fuel electrode side, the mass ratio of Nafion (registered trademark) to the carbon fiber nonwoven fabric was 1.00, and the coating amount of Pt was 0.158 mg/cm ² .

<Evaluation of fuel cell performance>
As evaluation of the performance of the fuel cells of Example 8 and Comparative Example 3, cyclic voltammetry (CV) measurement, IV characteristic measurement, and electrochemical impedance measurement were performed in this order. After that, a load response test of a predetermined cycle was performed multiple times, and immediately after the load response test, CV measurement, IV characteristic measurement, and electrochemical impedance measurement were performed in this order. Then, the electric quantity was obtained from the lower limit current of about 0.05 to 0.47 V of CV, and the load response test was terminated when the ECA calculated based on this became half of the initial state.

<result>
The CV measurement result after each cycle of the fuel cell of Example 8 is shown in FIG. 10A, and the CV measurement result of the fuel cell of Comparative Example 3 after each cycle is shown in FIG. 10B. In FIGS. 10A and 10B, the redox current due to Pt decreases as the number of cycles increases.

Change in ECA value calculated based on CV measurement, National Research and Development Agency New Energy and Industrial Technology Development Organization (New Energy and Industrial Technology Development Organization: NEDO) according to the "cell evaluation analysis protocol", logarithm on the horizontal axis 11A for the fuel cell of Example 8 and FIG. 11B for the fuel cell of Comparative Example 3, respectively.

After 2400 cycles, after 3000 cycles, after 3600 cycles, after 4800 cycles, and after 6600 cycles in this graph, the number of cycles at which the ECA is half of the initial state calculated from the approximate expression of the ECA residual rate is The fuel cell of Comparative Example 3 had about 6850 cycles, and the fuel cell of Comparative Example 3 had about 4600 cycles.

Claims (1)

It has a gas diffusion catalyst electrode layer and an electrolyte membrane,
The gas diffusion catalyst electrode layer has a fibrous carbon gas diffusion layer containing a catalyst metal, a carbon carrier supporting the catalyst metal, and an ionic liquid,
The mass ratio of the ionic liquid to the carbon support is 0.40 to 0.60, and the ionic liquid is diethylmethylammonium trifluoromethanesulfonate, diethylmethylammonium nonafluorobutanesulfonate , or diethylmethylammonium heptadecafluoro is octane sulfonate,
Membrane electrode assembly for fuel cells.

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