JP2009205803A - Method of manufacturing membrane-electrode assembly for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a membrane-electrode assembly for a fuel cell, which can exhibit the same effect quickly as when carrying out running-in operation or the like. <P>SOLUTION: This invention relates to the method of manufacturing the membrane-electrode assembly for the fuel cell having: an electrolyte membrane composed of a solid polymer; a pair of catalyst layers arranged and installed on both face sides of the electrolyte membrane; and a pair of gas diffusion layers each arranged and installed outside the respective catalyst layers. The method includes: a gas diffusion layer treatment step of permeating pressurized water to at least one of the pair of the gas diffusion layers in the thickness direction of the gas diffusion layers; and a gas diffusion layer treatment step of immersing at least one of the pair of gas diffusion layers into boiled water. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a membrane electrode assembly for a fuel cell that can shorten the time required for aging.

  In a fuel cell, in order to stably bring out the inherent performance, processing called running-in operation, conditioning, aging treatment, and pre-operation (hereinafter referred to as “run-in operation”) is performed.

  For example, before putting a fuel cell into a power generation state, the fuel cell is connected to an external circuit, and the output current density per predetermined effective electrode area required based on an external load requirement at the time of power generation is connected to the fuel cell and the external circuit. A method of conditioning is disclosed by flowing a current in advance that gives a current density value per effective electrode area higher than a set value (Patent Document 1).

  In addition, a method for improving the utilization rate of consumed gas is disclosed (Patent Document 2) so that flooding occurs in the fuel cell during preliminary operation of the fuel cell.

  Then, after raising the fuel cell stack to the normal operating temperature, the humidified air is supplied to the oxidant gas inlet via the humidifier, and the humidified hydrogen gas is supplied to the fuel gas inlet via the humidifier. The fuel cell stack is generated for a predetermined time. After the power generation is stopped, water drops are removed by dry purging with dry air and hydrogen without using a humidifier. After the dry purge, the temperature of the fuel cell stack is lowered to zero, the moisture in the stack is condensed, and the solid polymer is hydrated. A method of repeating such temperature increase, power generation, power generation stop, dry purge, and temperature decrease is disclosed (Patent Document 3).

Also, an anode medium such as aqueous methanol solution is supplied to the anode electrode of the direct methanol fuel cell, and a cathode medium such as air is supplied to the cathode electrode, and the force is applied in the same direction as the energization during fuel cell power generation between these electrodes. A method of conducting electricity is disclosed (Patent Document 4).
JP 2002-319421 A JP 2003-217622 A JP 2005-259526 A JP 2006-40869 A

In Patent Documents 1 to 3, the amount of water supplied to the ion exchange resin of the electrolyte membrane and the catalyst layer is restricted by the amount of power generated by the fuel cell. For example, even when the maximum current value shown in Patent Document 1 is 2.0 A / cm ² , only 11 mg / (cm ² · min) of water is supplied. Furthermore, in reality, at the initial stage of the break-in operation, the amount of power generation is very small, so the amount of water generated by power generation is very small.

  On the other hand, as in Patent Document 4, the method of forcibly flowing current from the outside causes the entire or local potential reversal to occur inside the fuel cell when the current is forced to exceed the power generation capacity of the fuel cell. Then, electrolysis of water occurs, and oxygen is generated from the anode side and hydrogen is generated from the cathode side.

  In addition, as in Patent Document 3, a method that uses a procedure for lowering the temperature of a cell and dewing water after power generation requires a separate device for cooling the cell or stack, and cooling the cell or stack. It is expected that considerable time will be required.

  The present invention has been made in view of the above circumstances, and it is an object to be solved to provide a method of manufacturing a membrane electrode assembly for a fuel cell that can quickly exhibit the same effect as when performing a break-in operation or the like. .

  In these conventional techniques, the break-in operation in the fuel cell is necessary because the ion exchange resin contained in the electrolyte membrane and the catalyst layer is sufficiently moistened with moisture so as to be formed from the electrolyte membrane, the catalyst layer and the gas. It is mentioned that the phase interface can be sufficiently formed. In other words, it has been considered necessary to perform a break-in operation or the like in order to sufficiently form a so-called three-phase interface composed of an electrolyte, a catalyst, and a gas layer.

  However, after the inventors performed a break-in operation based on the prior art and put the cell of the fuel cell in which high output performance is stably obtained in a vacuum dryer and completely removed the water, When the case of starting the fuel cell was examined again, it was observed that the start-up time was significantly shortened as compared with the cell not running in. From this, as previously thought, it was thought that as a result of the running-in operation, a phenomenon accompanied by some irreversible phenomenon occurred rather than sufficiently moistening the ion exchange resin of the electrolyte membrane and the catalyst layer with water. It was speculated that this was more appropriate.

  The main factor that requires the break-in operation is that the structure of the pores formed in the gas diffusion layer immediately after the production generates water generated by the power generation of the fuel cell as a membrane electrode assembly (hereinafter referred to as “membrane electrode assembly”). It was presumed that this was not an appropriate structure for discharging out of the system of “MEA” as appropriate. In general, a gas diffusion layer in a fuel cell is often manufactured by impregnating and coating a carbon fiber sheet such as carbon paper or carbon cloth with carbon black and a water-repellent material. The gas diffusion layer has a pore structure formed between carbon fiber, carbon black, and a water-repellent material, and water (product water) generated by supplying fuel / oxidizing gas or generating power through the pores. ) Is drained.

  However, the pores of the gas diffusion layer immediately after production (as produced) are not penetrated from the front surface to the back surface, or even if the pores penetrate, It is considered that a part (necking state) or all of the pore diameter is small or the pore is bent.

  Therefore, in the prior art (for example, Document 1), the fuel cell is operated at a current value equal to or higher than the operating current value that is always used (that is, set as the fuel cell specification), and is generated at the current value set in the specification. It is considered that more water is generated than this, and the pores of the gas diffusion layer are penetrated, the narrow portions of the pores are expanded, or an irreversible phenomenon that eliminates bending is generated. As a result, it is considered that the output performance can be improved and stabilized when operating at the current value set in the specification.

  In order to verify the above hypothesis, a test was conducted using the evaluation apparatus shown in FIG. The evaluation apparatus includes a holder 10 that holds the gas diffusion layer S, a cylinder 20, and a connection pipe 30 that connects between the holder 10 and the cylinder 20. The holder 10 holds one side of the gas diffusion layer S with a mesh or porous member so that no local force is applied to the gas diffusion layer S. A space is provided on the side of the holder 10 that contacts the other surface side of the gas diffusion layer S, and a pressure gauge 11 that measures the pressure in the space is connected. A piston 21 that can move at a constant speed is disposed in the cylinder 20. The gas diffusion layer S is held in the holder 10 so that the treatment liquid is permeated from the catalyst layer side. Water as a processing liquid is put into the cylinder 20 and the piston 21 is moved at a constant speed, so that water is forcibly permeated from the catalyst layer surface side of the gas diffusion layer S to the separator surface side at a constant flow rate. Was recorded and evaluated. FIG. 2 shows a typical measurement result.

  Region I shows the time until water contacts the gas diffusion layer S. Initially, the gas diffusion layer S and water are not in contact with each other (there is an air layer), and the region where residual air is discharged until the water contacts is shown. Region II indicates a region where water contacts the surface of the gas diffusion layer S on the catalyst layer side and water enters the pores of the gas diffusion layer S. The pores of the gas diffusion layer S are water repellent by a water repellent material, and a large water pressure is required when water is inserted into the pores. Between the region II and the region III, the generation of water droplets can be visually confirmed from the surface opposite to the catalyst layer side of the gas diffusion layer S, and the water pressure decreases beyond the peak. The occurrence of water droplets is initially recognized only from one or two fixed pores, but in region III, the number of pores where water droplets are generated gradually increases, and the discharge of water droplets also stabilizes, Along with this, a drop in water pressure is observed. Thereafter, little change in water pressure is shown in region IV, and water droplets are discharged stably from the pores. The peak height of the water pressure when going from the region II to the region III, the time until the stable drainage is shown through the region III, and the magnitude of the water pressure when the water pressure is stabilized are the manufacturing conditions of the gas diffusion layer S, for example, It varies greatly depending on the composition, loading amount and loading method of carbon black and water repellent material.

  When the gas diffusion layer S that has reached the region IV is taken out of the holder 10 and dried, and then the pore distribution of the gas diffusion layer is measured by mercury porosimetry, an increase in the pore volume of 10 μm or more can be confirmed ( FIG. 3). That is, as is clear from FIG. 3, it can be seen that the volume of pores having a pore diameter larger than that is about 10 μm. And in the area | region of a pore diameter of 100 micrometers or more, the big increase (about 2 times or more) is recognized.

  When the MEA is manufactured and the discharge evaluation is performed using the gas diffusion layer S that has reached the region IV, a sufficiently high and stable battery output can be obtained even in a state where the conventional break-in operation immediately after the manufacture is not performed. .

  Based on the above experimental facts, investigations have been repeated and the following inventions have been made to shorten the time required for running-in of the fuel cell.

That is, the feature of the method for producing a membrane electrode assembly for a fuel cell according to claim 1 that solves the above-described problem is that an electrolyte membrane made of a solid polymer and a pair of catalyst layers disposed on both sides of the electrolyte membrane And a method of manufacturing a membrane electrode assembly for a fuel cell having a pair of gas diffusion layers respectively disposed outside the catalyst layers,
The present invention has a gas diffusion layer treatment step in which at least one of the pair of gas diffusion layers transmits a pressurized treatment liquid in the thickness direction of the gas diffusion layer.

  A feature of the method for producing a membrane electrode assembly for a fuel cell according to claim 2 that solves the above-described problem is that, in claim 1, the gas diffusion layer treatment step includes superposing a plurality of the gas diffusion layers, and superposing them. Further, it is a step of allowing the treatment liquid to permeate the gas diffusion layer.

The feature of the method for producing a membrane electrode assembly for a fuel cell according to claim 3 for solving the above-mentioned problem is that an electrolyte membrane made of a solid polymer, a pair of catalyst layers disposed on both sides of the electrolyte membrane, A method for producing a membrane electrode assembly for a fuel cell having a pair of gas diffusion layers disposed on the outside of each catalyst layer,
The present invention has a gas diffusion layer treatment step in which at least one of the pair of gas diffusion layers is immersed in a boiled treatment liquid.

  The characteristic of the manufacturing method of the membrane electrode assembly for fuel cells which concerns on Claim 4 which solves the said subject is that the said process liquid is water in any one of Claims 1-3.

  The characteristic of the manufacturing method of the membrane electrode assembly for fuel cells which concerns on Claim 5 which solves the said subject is the gas diffusion layer before and after the said gas diffusion layer process process in any one of Claims 1-4. The number of pores having a pore diameter of 10 μm or more is increased.

  In the manufacturing method of the fuel cell membrane electrode assembly according to claim 1 configured as described above, the pore structure formed in the gas diffusion layer by allowing the treatment liquid to permeate the gas diffusion layer. When the fuel cell is operated as a fuel cell, water generated in the membrane electrode assembly can be quickly discharged out of the system. As a result, it is possible to reduce or eliminate the need for break-in operation when applied to a fuel cell.

  By forcibly permeating the treatment liquid to which pressure has been applied in the thickness direction of the gas diffusion layer, it is possible to increase the volume of the pores of the gas diffusion layer and reduce the tortuosity. In this case, it is possible to permeate a large amount of the processing liquid (water) over the entire surface of the gas diffusion layer rather than performing power generation as in the prior art, and the gas diffusion layer that has been subjected to such treatment is used. The MEA that has been used can significantly reduce the time required for the break-in operation. In addition, the process liquid can be forced to permeate through the gas diffusion layer, and the judgment of whether the increase in the volume of the pores and the bending degree can be reduced can be easily confirmed by monitoring the pressure of the treatment liquid as described above. can do.

  In the method of manufacturing a fuel cell membrane electrode assembly according to claim 2 configured as described above, the treatment liquid is allowed to pass in a state where a plurality of gas diffusion layers are overlapped. The time required can be shortened.

  In the method of manufacturing a fuel cell membrane electrode assembly according to claim 3 configured as described above, the fuel cell membrane electrode assembly is formed in the gas diffusion layer by a simple method such as immersing the gas diffusion layer in a boiled processing liquid. The pore structure can be optimized, and water generated in the membrane electrode assembly when operating as a fuel cell can be quickly discharged out of the system. As a result, it is possible to reduce or eliminate the need for break-in operation when applied to a fuel cell.

  Usually, since the gas diffusion layer has been subjected to water repellency treatment, it is difficult to permeate water into the pores only by immersing the gas diffusion layer in water (treatment liquid). ) And water vapor (gas) are immersed in boiling water, the water enters the pores of the gas diffusion layer in the state of water vapor (gas), and water (liquid ) Will occur. Since the water that has entered the pores also boils and vaporizes in the pores, the pores of the gas diffusion layer are affected by the volume expansion of the water itself when vaporized and the effect of extruding the aggregated water in the pores. This has the effect of increasing the volume and lowering the bending degree, and can reduce the break-in operation time without requiring a special device or jig. However, since the agglomeration and re-evaporation of steam at the time of boiling are used, speed control as in the invention according to claim 1 may not be sufficiently performed.

  In the method for manufacturing a membrane electrode assembly for a fuel cell according to claim 4 configured as described above, the cost can be reduced by employing water as the treatment liquid, and the water is used for the reaction in the fuel cell. There is an advantage that it is difficult to adversely affect.

  In the method of manufacturing a membrane electrode assembly for a fuel cell according to claim 5 configured as described above, water generated in the fuel cell is effectively generated by increasing pores having a pore diameter of 10 μm or more. Can be discharged.

  Hereinafter, the method for producing a membrane electrode assembly for a fuel cell according to the present invention will be described in detail based on specific embodiments. The fuel cell membrane electrode assembly produced by this production method has an electrolyte membrane, a pair of catalyst layers, and a pair of gas diffusion layers. The catalyst layer is disposed so as to be sandwiched from both sides of the electrolyte membrane, and the gas diffusion layer is disposed so as to be sandwiched from the outside of the catalyst layer.

  The electrolyte membrane is formed from a solid polymer that is a material having ion conductivity. The electrolyte membrane is preferably made of a material that exhibits good ionic conductivity, particularly in a wet state. The electrolyte membrane functions as a cation exchange membrane that moves protons between the anode-side and cathode-side catalyst layers in the fuel cell. The electrolyte membrane can be formed of a solid polymer material such as a fluorine-containing polymer. For example, a perfluorocarbon polymer having a sulfonic acid type perfluorocarbon polymer, a polysulfone resin, a phosphonic acid group, or a carboxylic acid group. Etc. can be used. Examples of the sulfonic acid type perfluorocarbon polymer include Nafion (“Nafion”, a registered trademark of DuPont).

  The catalyst layer is a porous film, and can be composed of, for example, ion-exchange resin particles and a conductive carrier carrying a catalytically active substance. The catalyst layer is formed by applying and forming a paste formed by dispersing ion exchange resin particles and a conductive carrier in an appropriate dispersion medium on the surface of the electrolyte membrane or the gas diffusion layer described later, A general method such as a method of coating and forming a film on a simple substrate can be employed. The ion exchange resin particles are preferably formed from the same polymer material as the electrolyte membrane. Examples of the catalytically active substance include noble metal particles such as platinum, ruthenium and rhodium. Examples of the conductive carrier that supports the catalyst include carbon material particles such as carbon black, acetylene black, and carbon nanotubes.

  The gas diffusion layer has a function of supplying the gas supplied to the gas flow path to the catalyst layer. In addition, it has a function of moving electrons generated by a power generation reaction to an external circuit and a function of releasing water, unreacted gas, and the like generated by a battery reaction to the outside. The gas diffusion layer is preferably composed of a porous body having electron conductivity as a base material, and can be composed of a carbon base material such as carbon paper or carbon cloth made of carbon fibers, for example. In this gas diffusion layer, if necessary, it is impregnated with polytetrafluoroethylene (PTFE) or the like to impart water repellency, or a carbon paste such as carbon black or the like kneaded with PTFE is applied. May be.

  The method for producing a membrane electrode assembly for a fuel cell according to this embodiment includes a gas diffusion layer treatment step for treating a gas diffusion layer included in the membrane electrode assembly for a fuel cell. The gas diffusion layer treatment step is a step applied to at least one of a pair of gas diffusion layers included in the fuel cell membrane electrode assembly to be manufactured. The gas diffusion layer treatment step may be performed before or after combining the fuel cell membrane electrode assembly from the electrolyte membrane, the catalyst layer, and the gas diffusion layer, or may be performed before or after any of the combination steps. The gas diffusion layer processing step will be described in detail below.

(First form)
The gas diffusion layer treatment step of this embodiment is a step of allowing the treatment liquid pressurized against the gas diffusion layer to permeate in the thickness direction of the gas diffusion layer. This step is a method of making the pores in the gas diffusion layer appropriate by allowing the pressurized treatment liquid to permeate. The gas diffusion layer and other members (electrolyte membrane, catalyst layer) are presumed to have different proper pore size distributions, but the method of this embodiment exerts an effect of expanding the pore size without distinction to them. Therefore, it is desirable that the gas diffusion layer processing step of this embodiment be performed on the gas diffusion layer alone. In other words, it is desirable to apply this step after forming the gas diffusion layer and before forming the membrane electrode assembly for a fuel cell.

  In addition, when processing the gas diffusion layer before forming the MEA, it is possible to perform the processing separately one by one, as well as stacking a plurality of gas diffusion layers and superimposing them. A plurality of gas diffusion layers may be processed simultaneously.

  Although it does not specifically limit as a processing liquid, It is desirable to employ | adopt the liquid with a little bad influence with respect to the material which comprises a gas diffusion layer. For example, the adverse effect is that the material constituting the gas diffusion layer is eluted, or a chemical reaction occurs to cause alteration. A particularly desirable treatment liquid is water. In addition to a pure substance, a solution in which some solute is dissolved may be employed as the treatment liquid. For example, a substance that adjusts pH, osmotic pressure, etc., or a substance that causes some reaction to the gas diffusion layer and performs post-treatment can be dissolved.

  The pressure for pressurizing the treatment liquid is not particularly limited. By using a high pressure, the gas diffusion layer treatment process can be carried out more rapidly, but if a too high pressure is employed, there is a risk of physical damage to the gas diffusion layer. Therefore, it is desirable to employ a pressure as high as the strength of the gas diffusion layer allows.

  It does not specifically limit as time to continue a gas diffusion layer processing process. For example, it is desirable to adopt a condition in which the amount of pores having a pore diameter of 10 μm or more (more desirably 100 μm or more) is increased when the pore diameter distribution in the gas diffusion layer before and after the gas diffusion layer treatment step is measured. Further, as described above, when the processing liquid is allowed to permeate through the gas diffusion layer at a predetermined pressure, the pressure gradually decreases after reaching the maximum value once (the boundary between the region II and the region III in FIG. 2). (Region (III)) and become steady (Region (IV)) may be the end of the gas diffusion layer treatment process with the steady state (or after a while after steadying). it can. When this method is employed, it is desirable to employ a control method in which the treatment liquid is sent to the gas diffusion layer in a certain amount instead of performing the control to keep the pressure constant. In that case, control is performed so that the pressure is smaller than the maximum pressure (value derived from the strength of the gas diffusion layer) that can be applied by the treatment liquid.

(Second form)
The gas diffusion layer processing step of this embodiment is a step of immersing the gas diffusion layer in a boiled processing liquid. This step is a method of making the pores in the gas diffusion layer appropriate by boiling the gas diffusion layer in the treatment liquid. The gas diffusion layer and other members (electrolyte membrane, catalyst layer) are presumed to have different proper pore size distributions, so the gas diffusion layer processing step of this embodiment performs processing on the gas diffusion layer alone. It is desirable. In other words, it is desirable to apply this step after forming the gas diffusion layer and before forming the membrane electrode assembly for a fuel cell. In the method of this embodiment, it is possible to adjust the operation of each of the gas diffusion layer, the electrolyte membrane, and the catalyst layer by adjusting the composition of the treatment liquid, and the gas diffusion layer is used as the main subject of the treatment. Since it is conceivable that processing can be performed, it may be desirable to perform processing after forming the MEA.

  It does not specifically limit as time to continue a gas diffusion layer processing process. For example, it is desirable to adopt a condition in which the amount of pores having a pore diameter of 10 μm or more (more desirably 100 μm or more) is increased when the pore diameter distribution in the gas diffusion layer before and after the gas diffusion layer treatment step is measured.

-Gas diffusion layer production procedure (1) First, carbon black (Cabot: Valcan XC-72R) and PTFE dispersion (Daikin: D1) are mixed, and the mass ratio of carbon black and PTFE is 1: 1. A water repellent paste was prepared.
(2) The water-repellent paste was dipped in a commercially available carbon paper (manufactured by Toray: TGP-H60) by a dipping method to impregnate the water-repellent paste in the carbon paper.
(3) After drying at room temperature, heat treatment was performed in the air at 380 ° C. for 1 hour to fix the water-repellent paste to the carbon paper to form a gas diffusion layer (GDL).
-Production procedure of MEA (membrane electrode assembly) (1) Platinum catalyst (manufactured by Johnson Matthey: HiSPEC4000) and polymer electrolyte solution (manufactured by Asahi Kasei: 5 mass% Aciplex solution) in a mass ratio of 1:15 The catalyst paste thus mixed was cast on a PTFE film using an applicator and dried at room temperature to prepare a catalyst layer sheet.
(2) Using a transfer method (decal method), a catalyst layer is transferred onto both sides of a polymer electrolyte membrane (DuPont: Nafion 112) using a hot press to produce a catalyst coated electrolyte membrane (CCM).
(3) The gas diffusion layer was cut out to φ36 (S = 10 cm ² ) and joined to the catalyst coated electrolyte membrane (CCM) by a hot press method to form MEA.
-Evaluation method of startability of fuel cell (1) The produced MEA was incorporated into an evaluation cell of the fuel cell, the cell was purged with nitrogen gas, and the residual air was replaced. As shown in FIG. 4, the evaluation cell has an electrolyte membrane 41, catalyst layers 42A and 42B disposed on both sides of the electrolyte membrane 41, and gas diffusion layers 43A and 43B disposed further outside. A fuel cell membrane electrode assembly 4 and a pair of separators 5 that sandwich the fuel cell membrane electrode assembly 4 from both sides and form a gas flow path together with the fuel cell membrane electrode assembly 4 are provided. Note that FIG. 4 is a schematic diagram, and the size of the component may not reflect the exact size for convenience of illustration.
(2) After holding the cell temperature at 75 ° C., humidification of 0.1 MPa on the anode side (dew point temperature of 70 ° C.) 100 CCM of pure hydrogen and humidification of 0.1 MPa on the cathode side (dew point temperature of 70 ° C.) Holding was performed for 15 minutes in an open circuit state (OCV) while flowing 300 CCM of air.
(3) While maintaining the cell temperature and the gas flow rates of the anode and cathode, using a load power supply device, the current density is changed from 0 A / cm ² (OCV) to (1 A / cm ² ) / min at a constant rate of 0. 4 after increasing the current density to a / cm ^2, and held at 0.4 a / cm ^2, and record the output voltage of 0.4 a / cm ² definitive fuel cell every 5 minutes.
-Preparation method of evaluation sample [Example 1]
(1) The gas diffusion layer produced by the above gas diffusion layer production procedure is placed in the holder 10 of the apparatus shown in FIG. 1, and water at room temperature is supplied at a rate of about 1 g / (cm ² · min) (about 179 A / cm ² And corresponding to the amount of water produced when the fuel cell was operated in).
(2) The diffusion layer produced by the above-described procedure for producing the diffusion layer sample shows a change in water pressure as shown in FIG. 2, exceeds the water pressure peak, and enters the region III in about 1.5 minutes. Entered the steady state (region IV). After entering Region IV, water penetration was continued for another 2 minutes, then the water supply was stopped and the diffusion layer sample was removed.
(3) The gas diffusion layer subjected to the water penetration treatment was converted to MEA according to the above-described MEA production procedure, and the test sample of Example 1 was obtained.

[Example 2]
(1) The MEA was produced according to the procedure for producing the MEA without any special pretreatment of the gas diffusion layer produced by the procedure for producing the gas diffusion layer.
(2) The MEA was immersed in boiling water, and a sample immersed and held for 30 minutes while keeping the boiling state was used as a test sample of Example 2.

[Comparative Example 1: No leveling]
(1) The MEA was produced according to the MEA production procedure without using any special pretreatment for the gas diffusion layer produced by the gas diffusion layer production procedure, and used as a test sample of a comparative example.

[Comparison practices 2 to 4: There is leveling]
In order to compare the effect with the running-in operation by the power generation of the fuel cell of the prior art, confirmation was performed in the following procedure.
(1) The MEA used was prepared in the same procedure as in Comparative Example 1.
(2) The produced MEA was subjected to operation in accordance with the procedures (1) and (2) of the fuel cell start-up evaluation method.
(3) While maintaining the cell temperature and the gas flow rate of the anode and cathode, using a load power supply device, a current density of 0 A / cm ² (OCV) to (1 A / cm ² ) / min at a constant rate of 0.7 A after increasing the current density up / cm ^2, 0.7 a / cm ² for 15 minutes (Comparative example 2), 60 minutes (Comparative example 3) and 120 minutes (Comparative example 4) after maintaining each respective open circuit Returned to the state.
(4) The time change of the output voltage at 0.4 A / cm ² was recorded according to the procedure (3) of the fuel cell start-up evaluation method.

[result]
The above Examples 1 and 2, Comparative Example 1 (without running-in operation) and Comparative Examples 2 to 4 (with running-in operation) were evaluated according to the procedure of the fuel cell start-up evaluation method, and the results are shown in FIG. Indicated.

As is clear from FIG. 5, the test sample of Comparative Example 1 (without running-in) has very low performance at the start of the fuel cell, and output performance with the lapse of holding time at a current density of 0.4 A / cm ^2. After a while (after holding for about 20 minutes), it settled to a certain value.

  On the other hand, it was revealed that the test samples of other comparative examples and examples showed stable and high output characteristics immediately after operation. And the output performance in the order of Comparative Example 2 (15-minute break-in operation), Comparative Example 3 (60-minute break-in operation), Comparative Example 4 (120-minute break-in operation), Example 2, and the test sample of Example 1 Was found to have improved.

The first improvement in output performance in the test sample of Comparative Example 1 is that the pore structure of the gas diffusion layer is changed by water generated by power generation, and the generated water can be discharged out of the MEA system. Conceivable. However, if it becomes possible to stably operate at a current corresponding to 0.4 A / cm ² (in other words, if a pore structure capable of treating generated water corresponding to 0.4 A / cm ² can be formed), Since it is not necessary to generate electricity on the entire surface of the electrode, the pore change of the gas diffusion layer further spreads and does not spread to the entire surface of the electrode, but only proceeds locally in the plane of the MEA, and the pore diameter in the local region only expands. As a result, the output is considered to settle to a low constant value.

This is evident from the fact that the test samples of Comparative Examples 2-4, which were subjected to comparative break-in operation at a higher current density before steady operation at 0.4 A / cm ² according to the prior art, showed higher output characteristics. It is. That is, the pores of the gas diffusion layer operated at a higher current density break-in condition (0.7 A / cm ² ) have a history of discharging more product water, and lower than that. It is considered that a high output is stably obtained at the current density.

  In Comparative Example 2 in which the break-in operation was performed for 15 minutes, it was considered that the optimization of the pore structure of the gas diffusion layer was insufficient in terms of time, but in Comparative Example 3 in which the break-in operation was performed for 60 minutes and 120 minutes, The test sample No. 4 has almost the same output characteristics, and it is estimated that the effect of the running-in operation is saturated in this operation range.

  On the other hand, Examples 1 and 2 stably show high output characteristics immediately after the start-up of the fuel cell without performing a special pre-running operation. This can be presumed to be because the pore structure could be optimized over the entire surface of the gas diffusion layer. In particular, in the test samples of Examples 1 and 2, a larger volume of pores can be obtained by allowing a large amount of water to permeate through the gas diffusion layer, which cannot be realized by a method using its own power generation such as a break-in operation. The increase and the further decrease in the degree of bending of the pores occur, and it is considered that the optimization of the pore structure of the gas diffusion layer is further progressing. In particular, it can be seen that the test sample of Example 1 in which water is allowed to permeate through the gas diffusion layer by applying pressure from the outside is further improved in performance as compared with the test sample of Example 2.

It is a schematic block diagram of the apparatus used for the test which permeate | transmits water to a gas diffusion layer. It is a graph which shows the pressure change at the time of making water permeate | transmit a gas diffusion layer with the apparatus of FIG. It is a graph which shows the pore diameter distribution of the pore in the gas diffusion layer before and behind processing with the apparatus of FIG. It is a schematic sectional drawing of the cell for fuel cell evaluation used in the Example. It is a graph which shows the operating time dependence of the output voltage of the fuel cell which employ | adopted each test sample in an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Holder 11 ... Pressure gauge 20 ... Cylinder 21 ... Piston 30 ... Connecting pipe 4 ... Fuel cell membrane electrode assembly 41 ... Electrolyte membrane 42A ... Catalyst layer (anode side) 42B ... Catalyst layer (cathode side) 43A ... Gas diffusion Layer (anode side) 43B ... Gas diffusion layer (cathode side)
5 ... Separator

Claims (5)

A fuel cell membrane having an electrolyte membrane made of a solid polymer, a pair of catalyst layers disposed on both sides of the electrolyte membrane, and a pair of gas diffusion layers respectively disposed outside the catalyst layers A method for producing an electrode assembly,
A fuel cell membrane electrode assembly comprising a gas diffusion layer treatment step of allowing a pressurized treatment liquid to permeate in a thickness direction of the gas diffusion layer with respect to at least one of the pair of gas diffusion layers. Manufacturing method.   2. The fuel cell membrane electrode bonding according to claim 1, wherein the gas diffusion layer treatment step is a step of superposing a plurality of the gas diffusion layers, and allowing the treatment liquid to permeate the superposed gas diffusion layers. Body manufacturing method. A fuel cell membrane electrode comprising an electrolyte membrane made of a solid polymer, a pair of catalyst layers disposed on both sides of the electrolyte membrane, and a pair of gas diffusion layers respectively disposed on the outside of the catalyst layers A method for manufacturing a joined body, comprising:
A method for producing a membrane electrode assembly for a fuel cell, comprising a gas diffusion layer treatment step in which at least one of the pair of gas diffusion layers is immersed in a boiled treatment liquid.   The method for producing a membrane electrode assembly for a fuel cell according to any one of claims 1 to 3, wherein the treatment liquid is water.   The method for producing a membrane electrode assembly for a fuel cell according to any one of claims 1 to 4, wherein pores having a pore diameter of 10 µm or more included in the gas diffusion layer increase before and after the gas diffusion layer treatment step.

Images