JP2010251185A - Method of testing membrane electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of testing a membrane electrode assembly in which reliability of a fuel cell ability test can be enhanced. <P>SOLUTION: When an MEA ability test is carried out, humidification condition of a supply gas is arranged at a low humidification condition of relative humidity ≤40%. In the fuel cell integrated with the MEA that is determined as a non-defective article through the ability test under this kind of low humidification condition, power generation capacity can be guaranteed in the low humidificatiion condition. At power generation operation of the fuel cell, the gas humidification condition in the MEA can become the gas humidification condition raised up to a desirable humidification extent for promoting a progress of an electrochemical reaction in an electrolyte, for example, the gas humidification condition of ≥40% of relative humidity. When the supply gas humidification condition is raised, gas diffusion resistance becomes lower, thereby the fuel cell exhibits high power generation ability. Accordingly, in the fuel cell integrated with the MEA determined as the non-defective article through the ability test under the low humidification condition, the power generation ability can be guaranteed even under the high humidification condition wherein the gas diffusion resistance becomes lower than that under the gas humidification condition of the relative humidity of ≤40%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for inspecting a membrane electrode assembly including an electrolyte membrane and a catalyst electrode bonded to both sides of the membrane.

  The fuel cell generates electricity by advancing an electrochemical reaction between a fuel, for example hydrogen, in the fuel gas supplied to the anode and oxygen in the oxygen-containing gas supplied to the cathode. This electrochemical reaction proceeds in a membrane electrode assembly (MEA) including an electrolyte membrane and a catalyst electrode bonded to both sides of the membrane, and when the gas supply becomes uneven on the electrode surface of the MEA, It is well known that the progress of the chemical reaction is different on the electrode surface and the battery performance decreases. For this reason, various techniques have been proposed for reducing the diffusion resistance after the gas supply to the MEA is a gas diffusion supply that provides a uniform supply of gas (for example, Patent Document 1).

JP 2004-273366 A

  According to the above-mentioned patent document, the gas resistance to the electrode surface of the MEA is made uniform by reducing the diffusion resistance of the gas diffusion layer, and the battery cell as a power generation unit having the MEA is formed as a stacked body of the cells. It is possible to improve the power generation capacity of fuel cells. Usually, in the manufacturing process of the fuel cell, the capability test of the MEA to be used or the capability test in the form of the battery cell or the fuel cell is performed, and this capability test is desirable from the viewpoint of promoting the electrochemical reaction in the electrolyte membrane. A gas with a degree of humidification is supplied to the anode and cathode to confirm the power generation capacity.

  In the environment surrounding the fuel cell, for example, in the case of a fuel cell mounted on the vehicle, the humidification state of the gas supplied to the fuel cell is not uniform because the environment changes variously depending on the traveling region and the traveling state. For this reason, even if the power generation capacity guarantee is confirmed in the inspection, if the humidification state of the gas supplied to the fuel cell is lower than the desirable gas humidification degree in order to promote the electrochemical reaction in the electrolyte membrane, the electrochemical reaction This is expected to slow down and reduce power generation capacity.

  In view of the above-described problems, an object of the present invention is to improve the reliability of the fuel cell capability test.

  In order to achieve at least a part of the above object, the present invention adopts the following configuration.

[Application: Inspection method for membrane electrode assembly]
A method for inspecting a membrane electrode assembly comprising an electrolyte membrane and a catalyst electrode bonded to both sides of the membrane,
When supplying a fuel gas and an oxygen-containing gas to the anode and cathode of the membrane electrode assembly and performing a capacity test, the fuel gas and the oxygen-containing gas are supplied after being humidified to a relative humidity of 40% or less. Is the gist.

  In the method for inspecting a membrane electrode assembly having the above-described configuration, the capacity test is performed under the condition that fuel gas and oxygen-containing gas adjusted to a relative humidity of 40% or less are supplied to the anode and cathode of the membrane electrode assembly. Do. Gas humidification with a relative humidity of 40% or less is a humidification situation that is lower than the degree of humidification desirable for the purpose of promoting the electrochemical reaction in the electrolyte membrane. A battery cell incorporating the non-defective membrane electrode assembly, and thus a fuel cell in which the cells are stacked, can ensure power generation capacity under low humidification conditions.

  In the membrane electrode assembly, gas is diffused and supplied to the electrolyte through the catalyst electrode, the gas flow path at the catalyst electrode is formed when the catalyst electrode is formed by the ionomer constituting the catalyst electrode, and the surface of the flow path is the ionomer It becomes the surface of. In other words, the gas diffusion resistance at the catalyst electrode is based on the surface of the ionomer due to the moisture contained in the supplied gas because of the nature of the catalyst electrode that comprises a gas flow path in addition to the catalyst and its support. Under the influence of the degree of wetting and the charge exchange with the ionomer, the gas humidification degree decreases in a situation where the relative humidity exceeds 40%. For this reason, in the situation where the degree of gas humidification exceeds 40% relative humidity, the gas diffusion resistance to the electrolyte membrane is increased due to the lower gas diffusion resistance than in the gas humidification situation where the relative humidity is 40% or less. Proceed smoothly. Therefore, a fuel cell in which a battery cell incorporating a membrane electrode assembly that has been determined to be non-defective by a capacity test in a low humidification state with a relative humidity of 40% or less is lower than in a gas humidification state with a relative humidity of 40% or less. The power generation capacity can be ensured even under highly humidified conditions that cause gas diffusion resistance. As a result, according to the method for inspecting a membrane electrode assembly having the above configuration, the reliability of the capability inspection can be improved.

It is a flowchart which shows the MEA manufacturing procedure containing the MEA test | inspection procedure as an Example of this invention. It is a graph which shows the relationship between the relative humidity of supply gas, and the gas diffusion resistance in a catalyst electrode. It is explanatory drawing which shows the difference in the electric power generation capability about MEA which performed the capability quality determination by step S140. FIG. 2 is a view corresponding to FIG. 1 and showing a procedure for manufacturing an inspection-specific MEA including an inspection procedure. It is explanatory drawing which shows the content of the manufacturing procedure of FIG. 4 typically.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart showing an MEA manufacturing procedure including an MEA inspection procedure as an embodiment of the present invention.

  As shown in the drawing, a catalyst ink for forming anode and cathode catalyst electrodes is prepared (step S100). In this embodiment, since the MEA used for the polymer electrolyte fuel cell is manufactured, the electrolyte membrane is a proton conductive ion exchange membrane formed of a solid polymer material, for example, a fluororesin having perfluorocarbon sulfonic acid. And exhibits good electrical conductivity in a wet state. The catalyst ink for forming a catalyst electrode which is bonded to the membrane surface of the electrolyte membrane and serves as an anode or cathode contains carbon particles carrying platinum and a fluorine-based polymer electrolyte similar to the electrolyte membrane constituting the MEA. ing. For example, the carbon particles carrying platinum are dispersed in a platinum compound solution (for example, a tetraammine platinum salt solution, a dinitrodiammine platinum solution, a platinum nitrate solution, or a chloroplatinic acid solution). It is produced by an impregnation method, a coprecipitation method or an ion exchange method. The platinum-supported carbon particles thus prepared are dispersed in a suitable solvent composed of water and an organic solvent, and an electrolyte solution containing the above-described fluorine-based polymer electrolyte (for example, Nafion solution, manufactured by Aldrich: The catalyst ink is obtained by further mixing Nafion with a trade name). The electrolyte solution in the catalyst ink becomes an ionomer in the catalyst electrode.

  In the present embodiment, the capacity test is performed under a low humidification condition as will be described later, which leads to a reduction in gas diffusion resistance in the catalyst electrode under the low humidification condition. FIG. 2 is a graph showing the relationship between relative humidity and gas diffusion resistance at the catalyst electrode. The gas diffusion resistance in the catalyst electrode has the following relationship with the current density I when power is generated by supplying hydrogen gas / air to the MEA in which both the anode and cathode catalyst electrodes are formed on the electrolyte membrane surface.

Gas diffusion resistance of catalyst electrode = (4F × Po ₂ ) / (10RT × I) Equation 1

In this equation 1, F is the Faraday constant, Po ₂ is the oxygen partial pressure, R is the gas constant, T is the temperature, and the current density I is measured via the gas diffusion layer provided with a porous channel in the MEA. This is the current value when hydrogen gas / air is supplied to the cathode to obtain a voltage of 0.15V.

  As can be seen from FIG. 2, the gas diffusion resistance of the catalyst electrode is large when the relative humidity of the gas is low in both the MEA indicated by black dots and the MEA indicated by white dots in the figure. On the other hand, if the relative humidity of the gas exceeds 40%, both the gas diffusion resistances of both MEAs are lowered and the difference in gas diffusion resistance is reduced. That is, in the humidification situation where the relative humidity of the gas exceeds 40%, the difference in the current density I that determines the gas diffusion resistance of the catalyst electrode is small, and the difference in the current density I (difference in gas diffusion resistance) is 40% or less. This becomes conspicuous when gas is supplied at humidity. If the gas diffusion resistance is small, the current density I is large and synonymous with ensuring high power generation capability. Therefore, as shown in FIG. 2, the catalyst ink is used to reduce the gas diffusion resistance in the catalyst electrode under low humidification conditions. It is desirable to produce. From the viewpoint of increasing the current density I, the reduction of the gas diffusion resistance of the catalyst electrode is caused by the suppression of the aggregation of the catalyst (platinum) involved in the electrochemical reaction in the catalyst electrode and the aggregation of the carbon particles themselves (primary aggregation). Suppression and suppression of the growth of the aggregated carbon particles (secondary aggregation) are beneficial. In addition, since the gas flow path in the catalyst electrode is formed on the surface of the ionomer after the solvent is removed and dried, the dispersibility of the ionomer (Nafion) in the solvent is improved from the viewpoint of suppressing physical blockage by the ionomer in the gas flow path. Is beneficial. For this reason, when the catalyst ink is prepared in step S100, the solution temperature is controlled at the time of ink preparation to suppress catalyst aggregation, or the stirring is promoted to improve the dispersibility of the ionomer, for example, the dispersion is promoted by centrifugation or shearing force. It was decided to do.

  Next, the catalyst ink is applied to a predetermined substrate, and a catalyst electrode (catalyst layer) serving as an anode or a cathode is formed on the substrate (step S110). As a base material to which the catalyst ink is applied, it is sufficient that the substrate has heat resistance at the temperature at the time of heating press described later and has good peelability from the catalyst layer. For example, polyethylene terephthalate (PET) or polytetrafluoro A substrate made of ethylene (PTFE) can be used. The application of the catalyst ink onto the base material can be performed by, for example, a spray method, screen printing, a doctor blade method, or an ink jet method. By using these methods, the catalyst ink can be applied to a desired thickness to form a catalyst layer having a desired thickness.

  After applying the catalyst ink as described above, the applied catalyst ink is dried (step S120). Since the solvent contained in the catalyst ink is vaporized by this drying, the dried catalyst layer becomes a porous catalyst electrode having gas passages as fine pores therein. When the catalyst layer is dried, the suppression of the clogging of the porous gas flow path after the solvent vaporization contributes to the reduction of the gas diffusion resistance of the catalyst electrode. Therefore, in step S120, the gas diffusion resistance of the catalyst electrode is reduced by determining the drying temperature according to the nature of the organic solvent used in the catalyst ink, adjusting the temperature increase rate for drying, or employing vacuum drying. We decided to plan.

  Thereafter, the catalyst layer (catalyst electrode) formed on the base material in step S120 and the already prepared electrolyte membrane are laminated and laminated, and heated and pressed in a laminated state, so that both surfaces of the electrolyte membrane An MEA in which the catalyst electrode is bonded to the substrate is manufactured (step S130). In this MEA conversion, the catalyst electrode is transferred to the membrane surface of the electrolyte membrane by heat and pressure, and the substrate is peeled off after pressing. In the MEA conversion in step S130, the press pressure is adjusted to, for example, about 3 MPa so that the porous gas flow path formed in the catalyst layer after the catalyst layer is dried is not inadvertently blocked by the press pressure, or the ionomer is not used. The press temperature is adjusted to, for example, about 120 ° C. so as not to cause a ready glass transition. If it carries out like this, it can contribute to reduction of the gas diffusion resistance of a catalyst electrode also in MEA conversion.

Following the MEA production, a capability inspection is performed (step S140). This capability inspection need not be performed for all of the produced MEAs, but may be performed by extracting the inspection target MEAs periodically or irregularly. And about the extracted MEA, the current density I as the capability is measured as follows. First, the inspection MEA is attached to the evaluation jig. The evaluation jig joins the gas diffusion layer and the gas supply flow path member on both sides of the inspection area of 1 cm ² of the inspection MEA, and supplies hydrogen gas and air-containing gas to the MEA in the inspection area. Hydrogen gas was humidified and adjusted to a predetermined relative humidity and then supplied to the anode at a flow rate of 500 ml / min. For the cathode, a mixed gas of oxygen and nitrogen (oxygen-containing gas) was adjusted to an oxygen concentration of 2%. Humidification is adjusted in the same manner as hydrogen gas above, and supplied at a flow rate of 500 ml / min. The evaluation jig measures the current density I when the inspection MEA is generated at a voltage of 0.15V while the gas temperature is 80 ° C. and the anode / cathode back pressure is 50 KPaG and the above gas supply is performed. .

  As described above, the measured current density I is converted into the gas diffusion resistance of the catalyst electrode by the equation (1). As shown in FIG. 2, the converted gas diffusion resistance and the relative humidity at the time of gas supply are calculated. The relationship is obtained. That is, with the above-described evaluation jig, hydrogen gas / air-containing gas is supplied under the above conditions such as the flow rate so that the relative humidity (25%, 40%, 65%, 80% and 100%) shown in FIG. When the current density I is measured and the gas diffusion resistance converted from the measured current density I is plotted against the relative humidity adjusted for humidification, FIG. 2 is obtained.

  As described above, the meaning shown in FIG. 2 is that the gas diffusion resistance of the catalyst electrode decreases with an increase in the relative humidity, and in a relative humidity of 40% or less, which is a low humidification state, for each MEA to be inspected. The difference in gas diffusion resistance becomes significant. On the other hand, in gas supply under high humidification conditions with a relative humidity exceeding 40%, the ionomer is wetted by moisture contained in the supplied gas, and is affected by the acceleration of charge transfer in the ionomer, and the current density I is improved. As a result, the gas diffusion resistance is lowered. For this reason, the gas diffusion resistance for each MEA to be inspected is reduced, and the difference is also reduced. For this reason, in the capacity test in step S140 of the present embodiment, the capacity test (current density I measurement) of the test MEA is performed with the humidification status of the gas supplied to the anode / cathode as a low humidification status with a relative humidity of 40% or less. It was decided. By this capability test, the MEA indicated by the black dots in the figure has a high gas diffusion resistance (that is, the current density I is small) in a low humidification state where the relative humidity is 40% or less, and is thus determined to be a low capability MEA. An MEA represented by white dots has a low gas diffusion resistance (ie, a high current density I) in a low humidification state with a relative humidity of 40% or less, and is therefore determined to be an MEA with good performance. The determination of pass / fail of this capability is based on the gas diffusion resistance value of 200 to 220 s / m when the gas humidification state is 40% relative humidity, and from 300 to 220 when the relative humidity is 25%. A gas diffusion resistance value of 320 s / m is set as a criterion.

Here, the validity of the capability test under the low humidification condition where the relative humidity is 40% or less will be described. FIG. 3 is an explanatory diagram showing the difference in power generation capacity for the MEAs that have been judged to be good or bad in step S140. In FIG. 3, each of the low-capacity determination MEA and the high-capacity determination MEA is configured as a battery cell, and power generation is performed over the entire electrode surface, and the generated voltage as the power generation capacity is measured. That is, a gas diffusion layer made of carbon paper, carbon cloth, or the like is bonded to both electrode surfaces of the anode and cathode of both MEAs, a gas flow path member is bonded to the gas diffusion layer, and the gas flow path is connected to the anode and cathode. Hydrogen gas / air-containing gas is supplied from the member through the gas diffusion layer. When measuring the power generation voltage, gas supply to the anode and cathode is performed at a gas temperature of 80 ° C., a back pressure of 100 KPaG, and a flow rate of 500 ml / min. The gas was supplied in a slightly dry state. Then, while gas is supplied under the above-described conditions, the voltage at which a current density of 1.0 A / cm ² is obtained is measured for both the low ability MEA and the good ability MEA. The measurement results are shown in FIG.

  As is clear from FIG. 3, the MEA that is determined to have good capability by the capability determination under the low humidification condition in step S140 has a higher power generation capability than the MEA of low capability determination. This power generation capacity is a measure of gas supply in a dry state. However, if the gas supply is in a humidified condition required from the viewpoint of wetting of the MEA electrolyte membrane during the power generation operation of the power generation cell, the power generation capacity at that time is reduced by reducing the gas diffusion resistance of the catalyst electrode (see FIG. 2), equivalent to or better than the power generation capacity when dry gas is supplied.

  In the present embodiment, the MEA of the good ability determination is shipped through the ability inspection in the low humidification state performed in step S140 of FIG. 1 (step S150). The shipped MEA is incorporated into a battery cell to constitute a fuel cell.

  As described above, according to the present embodiment, the manufactured MEA is subjected to a capability test under a low humidification condition in which the relative humidity is 40% or less (step S140). The gas humidification at the time of this capability test is a humidification situation lower than a desirable humidification degree in order to promote the electrochemical reaction in the electrolyte membrane. If the non-defective product is determined by the capability test in such a low humidification situation, as shown in FIG. 3, in the battery cell incorporating the good MEA, and in the fuel cell in which the cells are stacked, In this way, the power generation capacity can be secured.

  On the other hand, during the power generation operation of the fuel cell, gas is supplied to the anode / cathode in a gas humidification state that is increased to a desirable degree of humidification in order to promote the electrochemical reaction in the MEA electrolyte. That is, during the power generation operation of the fuel cell, gas is supplied in a humidified state exceeding about 40% relative humidity shown in FIG. 2 or higher, so that the surface of the ionomer due to moisture contained in the supplied gas The gas diffusion resistance becomes lower due to the degree of wetting and the effect of charge transfer by the ionomer. Since the gas supply is performed under a low gas diffusion resistance, the fuel cell exhibits a high power generation capability in combination with a humidification situation that is desirable for promoting the electrochemical reaction in the MEA electrolyte. This is because a fuel cell in which a battery cell incorporating a MEA that has been determined to be non-defective by a capacity test in a low humidification state with a relative humidity of 40% or less is lower than a gas humidification state with a relative humidity of 40% or less. It means that the power generation capacity can be secured even under highly humidified conditions that cause diffusion resistance. As a result, according to the capability test of the present embodiment, the reliability of the capability test that guarantees the power generation capability guarantee can be improved.

  As shown in FIG. 2, in the MEA whose performance is good by the capability test of this example, the difference between the gas diffusion resistance when the relative humidity is 40% or less and the gas diffusion resistance when the relative humidity exceeds 40% is It is smaller than the MEA determined to have a low capacity. Therefore, it can be said that an MEA having a small difference between the gas diffusion resistance in the case of performing gas supply under a low humidification condition and the gas supply in a high humidification condition is a desirable MEA in terms of ensuring power generation capacity.

  Further, in this example, in the preparation of the catalyst ink for forming the catalyst electrode in the MEA preparation process, the solution temperature control during the ink preparation and the stirring are promoted to suppress the aggregation of the catalyst (platinum) and the carbon. Suppression of agglomeration (primary agglomeration) of particles itself, suppression of growth of agglomerated carbon particles (secondary agglomeration), and suppression of clogging of gas flow paths in the catalyst electrode after dry formation were performed. For this reason, the gas diffusion resistance in the catalyst electrode under the low humidification condition can be reduced as indicated by the white arrow in FIG. 2, and the power generation capacity under the low humidification condition can be secured.

  In addition, even when the catalyst ink is dried, the gas diffusion resistance of the catalyst electrode under low humidification conditions can be achieved by controlling the drying temperature according to the nature of the organic solvent used in the catalyst ink, adjusting the heating rate, and adopting vacuum drying. It is possible to secure a power generation capacity under low humidification conditions. In addition, when the catalyst electrode is heated and pressed on both membrane surfaces of the electrolyte membrane, the gas flow path inside the catalyst layer (catalyst electrode) is inadvertently blocked by pressure and temperature control during the heating press. In order to reduce the gas diffusion resistance of the catalyst electrode under low humidification conditions, the press pressure is adjusted to, for example, about 3 MPa, or an inadvertent glass transition of the ionomer does not occur. Power generation capacity can be secured.

  Next, the MEA manufacturing procedure shown in FIG. 1 is performed except for the capability inspection in step S140, and the point that the MEA specialized for inspection is manufactured and the capability inspection is performed by following this manufacturing procedure will be described. . FIG. 4 is a diagram corresponding to FIG. 1 and is a procedure diagram showing the manufacturing procedure of the MEA for inspection specialization including the inspection procedure, and FIG. 5 is an explanatory diagram schematically showing the contents of the manufacturing procedure of FIG.

  In the manufacturing procedure of FIG. 4, following steps S100 to 130 of FIG. 1, catalyst ink preparation, catalyst ink application, catalyst layer drying, and MEA preparation are performed (steps S200 to 230). In this case, the catalyst ink application in step S210 is reduced to about 20% of the ink application amount at the time of applying the catalyst ink in FIG. 1 to obtain a catalyst layer specialized for inspection by applying a small amount of ink. In this way, if the amount of catalyst ink for forming the catalyst layer is small, the catalyst layer also has a small amount of catalyst constituting the catalyst layer, the amount of carbon as the carrier, and the amount of ionomer, and naturally the thickness of the catalyst layer is also reduced. . Therefore, in the inspection-specific catalyst layer that has undergone the catalyst ink application in step S210, the gas diffusion resistance decreases as shown in FIG.

  The preparation of the catalyst ink in step S200 and the drying of the catalyst layer in step S220 are performed under the same conditions as the preparation of the catalyst ink in step S100 and the drying of the catalyst layer in step S120 when manufacturing the MEA used in the fuel cell. Then, the solution temperature control and the degree of dispersion during catalyst ink production and the temperature control during catalyst layer drying contribute to the reduction of gas diffusion resistance in the catalyst electrode under low humidification conditions as described above. Moreover, since the gas diffusion resistance is originally small due to the reduction in the amount of ink applied, the solution temperature control and the degree of dispersion during catalyst ink preparation and the temperature control during catalyst layer drying greatly influence the reduction of the gas diffusion resistance.

  For this reason, when it is determined that the capability is low (high gas diffusion resistance) in the capability test in step S230 performed under the low humidification condition in the same manner as in step S130, the solution temperature control and dispersion degree at the time of catalyst ink preparation, and the catalyst layer The temperature control during drying is reflected so as to reduce the gas diffusion resistance (step S250). Therefore, as shown in FIG. 4, if an inspection MEA with a reduced amount of catalyst ink applied is manufactured, and the capability inspection is performed on the inspection MEA in a low humidified state, the reliability of the inspection is improved. In addition to increasing, it is preferable from the viewpoint of securing the power generation capability of MEA as a product.

  The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, in the MEA manufacturing procedure shown in FIG. 2, the catalyst layer is formed on the substrate through the application and drying of the catalyst ink. However, the catalyst ink is directly applied to the membrane surface of the electrolyte membrane and then dried. A layer can also be formed. In this case, for example, if the catalyst ink is sprayed in a temperature-enhanced environment, the solvent evaporation of the catalyst ink proceeds in parallel with the spray coating. This is useful for reducing the gas diffusion resistance of the catalyst electrode.

Claims (1)

A method for inspecting a membrane electrode assembly comprising an electrolyte membrane and a catalyst electrode bonded to both sides of the membrane,
When supplying a fuel gas and an oxygen-containing gas to the anode and cathode of the membrane electrode assembly and performing a capacity test, the fuel gas and the oxygen-containing gas are supplied after being humidified to a relative humidity of 40% or less. Inspection method of electrode assembly.

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