JP2009301938A - Evaluation method of catalyst ink for manufacturing electrode for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaluation method of mixed state of catalyst carrying conductive particles and a polymer electrolyte in a catalyst ink for manufacturing a fuel cell electrode. <P>SOLUTION: This is an evaluation method of a mixed state of the catalyst carrying conductive particles and polymer electrolyte in the catalyst ink in which the catalyst carrying conductive particles and the polymer electrolyte are mixed for manufacturing a fuel cell electrode. With the catalyst ink as an object, measurement is carried out by a pulse NMR method, and by analyzing the measurement result, the polymer electrolyte is separated into a hard component which has a comparatively short horizontal (spin-spin) relaxation time (T<SB>2</SB>) and a soft component which has a comparatively long relaxation time (T<SB>2</SB>), evaluation is carried out based on the abundance ratio of the hard component. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for evaluating a mixed state of catalyst-carrying conductive particles and a polymer electrolyte in a catalyst ink for producing a fuel cell electrode.

  One method for improving the performance of a fuel cell is to improve the electrode. In order to improve the electrode, it is necessary to evaluate the electrode. As one of such electrode evaluation methods, a method for evaluating the performance of a catalyst constituting the electrode is known. Specifically, a method has been proposed in which oxygen atom adsorption energy on the catalyst metal surface obtained from molecular simulation analysis is used as an index for performance evaluation (see, for example, Patent Document 1).

JP2007-273099A JP-A-7-333178 JP 2003-254907 A

  However, since the fuel cell electrode is composed of a mixture of conductive particles carrying a catalyst and a polymer electrolyte, in order to evaluate the performance as an electrode, a state in which the conductive particles and the polymer electrolyte are mixed is used. It is desirable to evaluate with. Among the properties representing the state where such conductive particles and polymer electrolyte are mixed, the mixed state of the catalyst-carrying conductive particles and the polymer electrolyte has a large effect on the output of the fuel cell and the durability of the electrode. It can be said that this is an influencing property. Therefore, a method for evaluating the mixed state of the catalyst-supporting conductive particles and the polymer electrolyte in the fuel cell electrode has been desired.

  The present invention has been made to solve the above-described conventional problems, and evaluates a mixed state of catalyst-supporting conductive particles and a polymer electrolyte in a catalyst ink for manufacturing an electrode for a fuel cell. With the goal.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
A method for evaluating a mixed state of the catalyst-carrying conductive particles and the polymer electrolyte in a catalyst ink comprising a mixture of catalyst-carrying conductive particles and a polymer electrolyte for producing a fuel cell electrode. The catalyst ink was measured by a pulsed NMR method, and the analysis of the measurement results showed that the polymer electrolyte was separated from the hard component having a relatively short transverse (spin-spin) relaxation time (T ₂ ) and the relaxation time. An evaluation method in which (T ₂ ) is separated into soft components having a relatively long length, and the mixed state of the catalyst-supporting conductive particles and the polymer electrolyte is evaluated based on the abundance ratio of the hard components.

In the evaluation method described in Application Example 1, the catalyst-supporting conductive particles and the catalyst-supporting conductive particles are obtained on the basis of the abundance ratio of the hard component having a relatively short relaxation time (T ₂ ), which is obtained by measuring the catalyst ink by the pulse NMR method. The mixed state with the polymer electrolyte is evaluated. Therefore, the abundance ratio of the hard component is a value reflecting the adsorption state of the polymer electrolyte with respect to the catalyst-carrying conductive particles, so that the mixed state of the catalyst-carrying conductive particles and the polymer electrolyte in the catalyst ink, particularly the catalyst It can be evaluated from the viewpoint of the degree of adsorption of the polymer electrolyte to the supported conductive particles.

[Application Example 2]
The method for evaluating a mixed state of the catalyst-carrying conductive particles and the polymer electrolyte according to Application Example 1, wherein the polymer electrolyte is contained in the same concentration as the catalyst ink without containing the catalyst-carrying conductive particles. Evaluation method for evaluating the mixed state by an increase rate of the abundance ratio of the hard component in the catalyst ink with respect to the abundance ratio of the hard component obtained by measurement by a pulse NMR method for a polymer electrolyte solution containing . According to the evaluation method of Application Example 2, the abundance ratio of the hard component in the polymer electrolyte solution is a value that is not related to the adsorption of the polymer electrolyte to the catalyst-carrying conductive particles. By using the increase rate of the abundance ratio, it becomes possible to more clearly evaluate the influence of adsorption of the polymer electrolyte on the catalyst-carrying conductive particles.

[Application Example 3]
The method for evaluating a mixed state of the catalyst-carrying conductive particles and the polymer electrolyte according to Application Example 1 or 2, wherein the measurement by the pulse NMR method is performed under a temperature condition corresponding to an operating temperature of the fuel cell. Evaluation method performed. According to the evaluation method of Application Example 3, the mixed state can be evaluated based on a state closer to the adsorption state of the catalyst-carrying conductive particles and the polymer electrolyte in the electrode of the fuel cell during power generation.

[Application Example 4]
The method for evaluating a mixed state of the catalyst-supporting conductive particles and the polymer electrolyte according to any one of Application Examples 1 to 3, wherein the polymer electrolyte is a fluorine-based polymer electrolyte, and the catalyst-supporting conductivity The evaluation method wherein the particles are particles substantially not containing fluorine, and the relaxation time (T ₂ ) is ¹⁹ F nuclear magnetic transverse (spin-spin) relaxation time (T ₂ ). According to the evaluation method of Application Example 4, by paying attention to the mobility of the polymer electrolyte by selecting the measurement nucleus corresponding to the fluorine contained only in the polymer electrolyte and determining the abundance ratio of the hard component, the polymer electrolyte And the mixed state of the catalyst-carrying conductive particles can be evaluated.

[Application Example 5]
The method for evaluating a mixed state of the catalyst-carrying conductive particles and the polymer electrolyte according to Application Example 4, wherein the pulse NMR method is a solid echo method. According to the evaluation method of Application Example 5, when the polymer electrolyte is a fluorine-based polymer electrolyte with relatively low mobility, the polymer electrolyte and the catalyst-carrying conductive particles are based on the mobility of the polymer electrolyte. The mixed state can be evaluated well.

[Application Example 6]
The method for evaluating a mixed state of the catalyst-carrying conductive particles according to any one of Application Examples 1 to 3 and the polymer electrolyte, wherein the polymer electrolyte is a hydrocarbon polymer electrolyte, and the catalyst-carrying conductivity sex particles are particles containing substantially no hydrogen, the relaxation time (T ₂₎ is ¹ H nuclear magnetic transverse (spin - spin) evaluation method is the relaxation time (T _2). According to the evaluation method of Application Example 6, by paying attention to the mobility of the polymer electrolyte by selecting the measurement nucleus corresponding to hydrogen contained only in the polymer electrolyte and determining the abundance ratio of the hard component, the polymer electrolyte And the mixed state of the catalyst-carrying conductive particles can be evaluated.

[Application Example 7]
A method for evaluating a mixed state of the catalyst-carrying conductive particles and the polymer electrolyte in a catalyst ink comprising a mixture of catalyst-carrying conductive particles and a polymer electrolyte for producing a fuel cell electrode. Evaluation method for evaluating that the mixed state is better as the amount of adsorption and / or degree of adsorption is larger based on the adsorption state of the polymer electrolyte adsorbed on the catalyst-supporting conductive particles in the catalyst ink .

  In the evaluation method described in Application Example 7, based on the adsorption state of the polymer electrolyte adsorbed on the catalyst-carrying conductive particles in the catalyst ink, the larger the amount of adsorption and / or the degree of adsorption, the better the mixed state. It is evaluated. Since the adsorption state of the polymer electrolyte to the catalyst-supporting conductive particles described above directly affects the electrode performance when the battery reaction proceeds, the mixed state of the catalyst ink should be evaluated using such a method. Thus, it becomes possible to predict or evaluate the performance of the electrode made from the catalyst ink.

[Application Example 8]
A method for evaluating a mixed state of the catalyst-supporting conductive particles and the polymer electrolyte according to Application Example 7, wherein the catalyst ink is subjected to measurement by a pulsed NMR method, and analysis of the measurement result is performed, The polymer electrolyte is separated into a hard component having a relatively short transverse (spin-spin) relaxation time (T ₂ ) and a soft component having a relatively long relaxation time (T ₂ ). The evaluation method for determining that the amount and / or the degree of adsorption of the polymer electrolyte to the catalyst-carrying conductive particles is large. According to the evaluation method described in Application Example 8, since the catalyst ink can be used as a measurement target as it is, based on the actual adsorption state in the catalyst ink, the catalyst-carrying conductive particles and the polymer electrolyte The mixed state can be evaluated.

  The present invention can be realized in various forms other than the above, and is manufactured using, for example, a fuel cell electrode design method using the evaluation method of the present application or a catalyst ink evaluated by the evaluation method of the present application. It can be realized in the form of a fuel cell electrode or a fuel cell including such a fuel cell electrode.

A. Electrode configuration:
FIG. 1 is an explanatory view schematically showing a schematic configuration of an electrode 10 as an example of an electrode of a fuel cell. The fuel cell including the electrode 10 shown in FIG. 1 is a solid polymer fuel cell, and includes an electrolyte membrane 20 made of a polymer electrolyte. In the fuel cell, a pair of electrodes is formed on both surfaces of the electrolyte membrane 20 as an anode or a cathode. In FIG. 1, only the state of one electrode 10 is shown enlarged, but the other electrode also has the same structure.

  The electrode 10 includes a plurality of conductive particles (for example, carbon particles) 14 carrying a catalyst 12 that is a catalyst metal (for example, platinum or a platinum alloy), and a polymer electrolyte 16, and a space in which gas flows is inside. It is a porous layer formed. The polymer electrolyte 16 is a resin containing fluorine, and can be, for example, a fluorine-based resin including perfluorocarbon sulfonic acid. The polymer electrolyte 16 is interposed between the plurality of catalyst-carrying conductive particles 14 and covers at least a part of the surface of each catalyst-carrying conductive particle 14. FIG. 1 shows a state in which a gas diffusion layer 22 made of a conductive material having gas permeability is further disposed on the electrode 10.

  FIG. 2 is an explanatory diagram showing a manufacturing process of the electrode 10. When producing the electrode 10, first, carbon particles (carbon powder) are prepared (step S100). Here, various carbon particles can be selected, and for example, carbon black or graphite can be used.

  Next, a catalyst metal (here, platinum (Pt)) is supported in the liquid on the carbon particles prepared in step S100 (step S110). In order to support Pt, the carbon particles may be dispersed in a solution of a Pt compound and an impregnation method, a coprecipitation method, or an ion exchange method may be performed. As the Pt compound solution, for example, a tetraammine platinum salt solution, a dinitrodiammine platinum solution, a platinum nitrate solution, or a chloroplatinic acid solution can be used. At this time, the ratio of the weight of the supported catalyst metal to the total weight of the platinum-supported carbon particles, that is, the catalyst support ratio can be set to, for example, 10 to 80 wt%.

  In step S110, when carbon particles are dispersed in the Pt compound solution and Pt is supported on the carbon particles, the carbon particles are then dried and fired (step S120). As a result, carbon particles carrying and supporting Pt fine particles are obtained. For example, in the case of the impregnation method, after the carbon particles are dispersed in a solution containing the above amount of Pt, the solvent is evaporated and dried, and reduction treatment (firing in a reducing atmosphere) is performed. Good.

  Thereafter, the Pt-supported carbon particles obtained in step S120 are dispersed in an appropriate water and an organic solvent, and an electrolyte solution containing an electrolyte having the above-described proton conductivity (for example, DuPont, Nafion PFSA Polymer Dispersions). Are further mixed to prepare a catalyst ink (step S130). Then, the catalyst ink is applied on the electrolyte membrane 20 (step S140).

  Application of the catalyst ink onto the electrolyte membrane 20 can be performed by, for example, a doctor blade method. Moreover, it is good also as performing by screen printing on the electrolyte membrane 20 using a catalyst ink. Alternatively, it can be performed by a spray printing method or an ink jet method. Further, as another method for applying the catalyst ink, the catalyst ink is applied on another substrate (for example, a substrate made of polyethylene terephthalate (PET) or polytetrafluoroethylene (PTFE)), and then the applied catalyst is applied. A method is also possible in which the ink is hot-pressure transferred to the electrolyte membrane 20 and then the substrate is peeled off and removed. Further, after applying the catalyst ink on the gas diffusion layer 22, the gas diffusion layer 22 and the electrolyte membrane 20 may be hot-pressure bonded.

  Thereafter, the catalyst ink applied on the electrolyte membrane 20 is dried (step S150), thereby completing the porous electrode 10 having fine pores therein.

  Here, when power generation is performed in the fuel cell, the reactions shown in the following equations (1) and (2) proceed. Equation (1) represents the reaction at the anode, and equation (2) represents the reaction at the cathode.

H ₂ → 2H ⁺ + 2e ⁻ (1)
2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O (2)

  At the anode where the reaction shown in the above formula (1) proceeds by supplying hydrogen, protons and electrons are generated from the supplied hydrogen on the catalyst 12. Protons generated on the catalyst 12 move to the electrolyte membrane 20 through the polymer electrolyte 16 provided in the anode. Further, the electrons generated on the catalyst 12 move to the gas diffusion layer 22 side via the plurality of catalyst-supporting conductive particles 14. On the other hand, in the cathode where the reaction shown in the above formula (2) proceeds by supplying oxygen, protons move from the electrolyte membrane 20 to the catalyst 12 through the polymer electrolyte 16 provided in the cathode. Further, electrons move from the gas diffusion layer 22 side to the catalyst 12 through the plurality of catalyst-carrying conductive particles 14. On the catalyst 12, protons moved from the electrolyte membrane 20 and electrons moved from the gas diffusion layer 22 side react with the supplied oxygen to generate water.

  In order for the reaction as described above to proceed, in any electrode, it is necessary to efficiently supply a gas to the catalyst 12, transfer of protons between the catalyst 12 and the electrolyte membrane 20, and The movement of electrons between the catalyst 12 and the gas diffusion layer 22 side needs to be performed smoothly. Here, if the position where the polymer electrolyte 16 exists in the electrode is biased, in the catalyst 12 that is thickly covered with the polymer electrolyte 16, there is a possibility that the supply of gas to the catalyst 12 may be hindered, In the catalyst-supporting conductive particles 14 with a small amount of the polymer electrolyte 16 to be covered, there is a possibility that protons are not sufficiently transferred between the catalyst 12 and the polymer electrolyte 16. If the plurality of catalyst-carrying conductive particles 14 are not biased and sufficiently close to each other, the efficiency of electron movement in the electrode may be suppressed. Therefore, in the electrode 10 of the fuel cell, the plurality of conductive particles 14 carrying the catalyst 12 and the polymer electrolyte 16 are sufficiently well mixed. Specifically, the catalyst-carrying conductive particles 14, It can be said that it is important for ensuring the performance of the electrode that the catalyst 12 and the polymer electrolyte 16 are sufficiently in contact with each other and are well dispersed as a whole.

B. Summary of evaluation method:
The evaluation method of this example is a method for evaluating the mixed state of the plurality of catalyst-supporting conductive particles 14 and the polymer electrolyte 16. The good mixing state means that the dispersion state of the catalyst-carrying conductive particles 14 and the polymer electrolyte 16 is good. If the dispersion state of both is good, the catalyst-carrying conductivity is good. It is considered that the adsorption state of the polymer electrolyte 16 on the surface of the particle 14 is improved. The evaluation method of the present embodiment is based on the measurement result of pulse NMR (Nuclear Magnetic Resonance, Nuclear Magnetic Resonance) method, by indirectly evaluating the adsorption state, and based on such adsorption state, the catalyst-supporting conductivity The mixed state of the particles 14 and the polymer electrolyte 16 is evaluated.

In the evaluation method of this example, ¹⁹ F nuclear magnetic transverse (spin-spin) relaxation time (T ₂ ) is measured using the pulse NMR method for the catalyst ink described above for producing a fuel cell electrode. is doing. As the pulse NMR method, for example, a solid echo method can be used. When measuring the catalyst ink, the relaxation time (T ₂ ) is measured under a temperature condition of 80 ° C. corresponding to the operating temperature of the fuel cell. According to the pulse NMR method, if there are a plurality of components having a difference in mobility, the decay speed (transverse relaxation time T ₂ ) differs for each component, and therefore the difference in relaxation time (T ₂ ) is used. Thus, the amount of each component having different motility can be obtained. The evaluation method of this example uses ¹⁹ F constituting the polymer electrolyte 16 as a measurement nucleus. Since the mobility of the polymer electrolyte 16 is reduced by adsorbing to the catalyst-carrying conductive particles 14, the polymer electrolyte 16 is well mixed with the catalyst-carrying conductive particles 14, so As the amount of adsorption of the molecular electrolyte 16 increases, components corresponding to such a decrease in mobility increase.

FIG. 3 shows an example of a signal obtained by the solid echo method for the catalyst ink having the above-described configuration. When the measurement by the solid echo method is performed on the catalyst ink, as shown in FIG. 3, a hard component having a relatively short relaxation time (T ₂ ) (relative mobility is relatively low, and it is not completely swollen even in an aqueous solution). Two components are obtained: a component corresponding to a resin close to a solid state) and a soft component (a component having a relatively high mobility) having a relatively long relaxation time (T ₂ ). The measurement results are analyzed by multi-component curve fitting shown in the following equation (3).

M (t) = A ・ exp (-1/2 ・ (t / T _2A ) ² ) + B ・ (-1/2 ・ (t / T _2B ) ² ) + ... (3)
A and B are abundance ratios, T _2A and T _2B are transverse relaxation times, M is an NMR signal (magnetization), and t is a measurement time.

  In this example, measurement by the pulse NMR method is performed on the catalyst ink under various conditions, and by analyzing the measurement results, the polymer electrolyte 16 is separated into a hard component and a soft component. The adsorption state of the polymer electrolyte 16 is evaluated. That is, as the degree of adsorption of the polymer electrolyte 16 on the catalyst-carrying conductive particles 14 is improved, or as the amount of the polymer electrolyte 16 adsorbed on the catalyst-carrying conductive particles 14 increases, the movement in the polymer electrolyte 16 increases. Since hard components having low properties increase, the adsorption state of the polymer electrolyte 16 is evaluated based on the ratio of such hard components. In this embodiment, when the adsorption state of the polymer electrolyte 16 with respect to the catalyst-carrying conductive particles 14 is improved, the hard component having low mobility is increased. Therefore, the adsorption based on the abundance ratio of the hard component and the rate of increase thereof. Although the state, that is, the mixed state in the catalyst ink is evaluated, a different configuration may be used. For example, the same evaluation may be performed based on the abundance ratio of the soft component and the reduction rate thereof.

C. ¹⁹ F Nuclear magnetic relaxation time (T ₂ ) analysis results:
(C-1) Preparation of catalyst ink and the like:
Various inks having different conditions such as catalyst ink were prepared, and the ¹⁹ F nuclear magnetic relaxation time (T ₂ ) was measured using a pulse NMR method. As catalyst inks, three types of catalyst inks were prepared in which the types of carbon particles constituting the catalyst-carrying conductive particles 14 were different. Furthermore, in place of the catalyst-carrying conductive particles 14, a carbon ink including carbon particles that do not carry a catalyst was prepared, and a resin ink containing only the polymer electrolyte 16 without containing carbon particles was prepared. The production conditions for each ink will be described below.

  FIG. 4 is an explanatory diagram showing the manufacturing process of the catalyst ink. To manufacture the catalyst ink, first, the catalyst-carrying conductive particles 14 were prepared in a dry state (step S200). In this example, Pt-supported carbon particles as the catalyst-supporting conductive particles 14 were produced using three different types of carbon particles. The amount of Pt supported in each Pt-supported carbon particle was 50 wt%. Here, Ketjen black (hereinafter referred to as carbon K) was used as one of the three types of carbon particles prepared. The other two types of carbon particles are hereinafter referred to as carbon G1 and G2. In addition, it is confirmed from the R value by Raman analysis that carbon K has significantly lower crystallinity than carbons G1 and G2 (data not shown).

Next, water was added to the carbon particles prepared in Step S200 and stirred (Step S210), and defoamed with a vacuum desiccator (Step S220). Thereafter, the polymer electrolyte solution was further added and stirred (step S230), and defoamed with a vacuum desiccator (step S240). Here, Nafion (registered trademark) DE1020 manufactured by DuPont was used as the polymer electrolyte. Further, in this embodiment, when producing a catalyst ink using carbon K among the carbon particles, four types of catalyst inks having different polymer electrolyte ratios are obtained by changing the polymer electrolysis mass mixed in step S230. Was made. At this time, by adjusting the amount of water added in step S210, the concentration of the polymer electrolyte is made the same in all finally obtained catalyst inks. In steps S210 and S230, stirring was performed using a centrifugal defoamer. Thereafter, using a zirconia (ZrO ₂ ) ball having a diameter of 1 mm, the mixture was stirred with a planetary bead mill (step S250) and defoamed with a vacuum desiccator (step S260) to complete a catalyst ink.

  When producing the carbon ink, carbon particles not supporting Pt were prepared in a dry state in place of the Pt-supporting carbon particles in Step S200 of FIG. And the process after step S210 was performed similarly and the carbon ink was produced. At this time, when producing the carbon ink, similarly to the catalyst ink, three types of carbon particles K, G1, and G2 were prepared, and the carbon ink was produced for each. In any carbon ink, the concentration of the polymer electrolyte in the ink was the same as that of the catalyst ink.

  Further, when producing the resin ink, the steps S200 to S220 are not performed, and in step S230, the concentration of the polymer electrolyte is the same as that of the other inks with respect to the electrolyte solution described above. Water was added to the. That is, also in the resin ink, the concentration of the polymer electrolyte in the ink is the same as that in the catalyst ink. And the process after step S240 was performed similarly and the resin ink was produced.

  FIG. 5 is an explanatory diagram showing the ratio of the polymer electrolyte and the carbon particles in the catalyst ink, carbon ink, and resin ink produced as described above. FIG. 5 shows the concentration of the polymer electrolyte (resin concentration) and the concentration of carbon particles containing the catalyst (particle concentration) for each ink. Samples (1) to (3) are carbon inks having different carbon types, and samples (4) to (6) are catalyst inks having different carbon types. Samples (7) to (9) are the same carbon K as the samples (1) and (4), and the weight of the polymer electrolyte is based on the carbon particle weight (carbon weight not including the catalyst). The catalyst inks have different ratios (hereinafter referred to as resin / carbon ratios). Sample (10) is resin ink. Here, the number attached to the sample name represents the resin / carbon ratio. In the samples (1) to (3), which are carbon inks, the resin / carbon ratio is 0.75. Samples (4) to (6), which are catalyst inks, also have a resin / carbon ratio of 0.75, but since the carbon particles carry Pt, the carbon particle concentration (wt%) is from samples (1) to (1). It is higher than (3). Samples (7) to (9) have resin / carbon ratios of 0.5, 1.0, and 1.5, respectively.

(C-2) Measurement result of relaxation time (T ₂ ) by pulse NMR:
Using the samples (1) to (10) described above, ¹⁹ F nuclear magnetic transverse (spin-spin) relaxation time (at a temperature of 80 ° C. by pulse NMR method, more specifically, solid echo method) T ₂ ) was measured. Detailed measurement conditions are shown in FIG.

For each of the samples (1) to (10), the measurement by the solid echo method was performed as described above, and the abundance ratio and relaxation time (T ₂ ) of each of the hard component and the soft component were calculated. Shown in As shown in FIG. 7, in the sample (samples (4) to (9)) in which the catalyst-carrying carbon particles are present, or in the sample (samples (1) to (3)) in which the carbon particles are present, only the polymer electrolyte is used. The abundance ratio of the hard component was increased compared to the resin ink contained (sample (10)).

  Here, since the sample (10) is a resin ink containing no carbon particles, the abundance ratio of the hard component in the sample (10) is a value that is not related to the adsorption of the polymer electrolyte to the carbon particles. Therefore, in the samples (1) to (9) containing carbon particles, the increase in the abundance ratio of the hard component in each sample relative to the abundance ratio of the hard component in the sample (10) is the carbon particle of the polymer electrolyte. It can be said that it is a value reflecting the adsorption to the surface. In this example, in order to clarify the influence of the adsorption of the polymer electrolyte on the carbon particles, based on the increasing rate of the hard component abundance ratio in each sample with respect to the abundance ratio of the hard component in the sample (10). Thus, the adsorption state of the polymer electrolyte is evaluated. For samples (1) to (9), the calculation result of the increase rate of the hard component ratio of each sample with respect to the hard component ratio of sample (10) is shown in FIG. 8 as the hard component increase rate. The hard component increase rate can be expressed by the following equation (4).

Hard component increase rate = (hard component ratio of each sample−hard component ratio of sample (10)) /
(Hard component ratio of sample (10)) × 100 (4)

  As shown in FIG. 8 as a result of the samples (4) and (7) to (9), in the catalyst ink using the catalyst-supported carbon having the same type of carbon particles, the hard component increases as the resin / carbon ratio increases. The ratio approached the value of the resin ink, and the hard component increase rate decreased. Here, a large resin / carbon ratio means that there are relatively few carbon particles to be adsorbed by the polymer electrolyte, and that the polymer electrolysis mass adsorbed to the carbon particles is relatively small. That is. As shown in FIG. 8, by comparing the hard component increase rate, in the catalyst ink using the catalyst-supported carbon having the same type of carbon particles, the lower the resin / carbon ratio, the greater the hard component increase rate. It was actually confirmed that the adsorption state of the polymer electrolyte was good.

  Further, as shown in FIG. 8 as a result of the samples (1) to (3), in the carbon ink using the carbon particles that do not carry the catalyst, when the resin / carbon ratio is aligned and compared, There was a difference in the component increase rate. Specifically, in the sample (1) provided with carbon particles composed of carbon K having remarkably low crystallinity, the samples (2) and (3) including carbon particles composed of other carbon G1 or G2 having high crystallinity are used. In comparison, the hard component increase rate was very high. Here, it can be said that the surface area of carbon is larger as the crystallinity is lower. The large surface area of the carbon particles means that the area on which the polymer electrolyte is adsorbed is large, and the polymer electrolyte is more easily adsorbed onto the carbon particles. In addition, due to the difference in crystallinity of carbon, the interaction force between the surface of the carbon particle and the polymer electrolyte differs, and the amount of polymer electrolyte adsorbed on the carbon particle and the polymer electrolyte adsorbed on the carbon particle. It is thought that the degree (adsorption force) is different. As shown in FIG. 8, by comparing the hard component increase rates, the carbon ink having different types of carbon particles increases the hard component increase rate as the ink has carbon particles with lower crystallinity. It was actually confirmed that the adsorption state of was good.

  On the other hand, as shown in FIG. 8 as the results of samples (4) to (6), in the catalyst ink using the catalyst-supported carbon particles, the carbon / carbon ratio was compared with the same value. The difference in the rate of increase in the hard component due to the difference in the type of the ink showed a tendency different from that in the case of the carbon ink without the catalyst. Specifically, in the carbon K having low crystallinity, the difference in the hard component increase rate was small between the sample (1) that is the carbon ink and the sample (4) that is the catalyst ink. On the other hand, in the case of carbon G1 or G2 having high crystallinity, the hard component increase rate is greatly increased in samples (5) and (6) that are catalyst inks compared to samples (2) and (3) that are carbon inks. It was. Such a difference in the hard component increase rate between the carbon ink and the catalyst ink is considered to be due to the influence of the catalyst (Pt) supported by the catalyst-supported carbon. That is, it is considered that the increase amount of the hard component increase rate in the catalyst ink with respect to the hard component increase rate in the carbon ink reflects the polymer electrolysis mass adsorbed on the catalyst. The catalyst-carrying carbon included in any catalyst ink has the same amount of catalyst supported on the carbon, but the surface state of the catalyst on the carbon differs depending on the type of carbon, and as a result, the catalyst and polymer electrolyte It is considered that the polymer electrolysis mass adsorbed on the catalyst changes due to the difference in the state of interaction between them. Since Pt has magnetism, the magnetic relaxation of the polymer electrolyte is promoted if the polymer electrolyte is sufficiently close to Pt. In samples (5) and (6), which are catalyst inks containing carbon with high crystallinity, it is considered that the rate of increase in the hard component was further increased by the adsorption of the polymer electrolyte sufficiently close to Pt. Samples (4) to (6), which are catalyst inks with different types of carbon, have the same rate of increase in the hard component, but increase in the hard component of samples (1) to (3) that are the corresponding carbon inks. When carbon G1 and G2 having high crystallinity are used, the amount of polymer electrolysis adsorbed close to Pt is larger than that of carbon K, and the adsorbed state is evaluated to be better. can do.

According to the evaluation method of the present example configured as described above, the ¹⁹ F nuclear magnetic relaxation time (T ₂ ) obtained from the measurement by the pulse NMR method is used, so that the catalyst-supporting conductive particles in the catalyst ink and the high The mixed state with the molecular electrolyte can be evaluated particularly from the viewpoint of the degree of adsorption of the polymer electrolyte to the catalyst-carrying conductive particles. That is, the catalyst-carrying conductive particles and the polymer electrolyte are well mixed, and if the dispersion state is good, the catalyst-carrying conductive particles and the polymer electrolyte are in sufficient contact and adsorbed on the catalyst-carrying conductive particles. The polymer electrolysis mass increases. Therefore, by comparing the amount of hard components, the ratio of hard components, or the rate of increase in hard components, which is a value reflecting the polymer electrolyte mass adsorbed on the catalyst-carrying conductive particles, the catalyst-carrying conductive particles and the polymer electrolyte are compared. The mixed state can be evaluated.

  In particular, the evaluation method of this example is excellent in that the measurement can be performed using the catalyst ink for forming the fuel cell electrode as it is. As another method for evaluating the dispersion state in the catalyst ink, for example, a method of measuring the particle size distribution of the catalyst ink is also conceivable. However, when the particle size distribution of the catalyst ink is measured using, for example, a laser diffraction / scattering type particle size distribution measuring apparatus, it is necessary to disperse the catalyst ink in an appropriate solvent such as water before the measurement. It may be difficult to say that it is a measurement of the dispersion state. On the other hand, since the evaluation method of this example uses the catalyst ink as it is, the mixed state can be evaluated as a state closer to the mixed state of the catalyst-supporting conductive particles and the polymer electrolyte in the electrode. become. At this time, the temperature condition at the time of measurement by the pulse NMR method is set to a temperature corresponding to the operating temperature of the fuel cell as described above, so that the evaluation is performed as a state closer to the state of the electrode of the fuel cell at the time of power generation. be able to.

  Further, according to the evaluation method of this example, since the mixed state / dispersion state is evaluated based on the degree to which the polymer electrolyte is adsorbed on the catalyst-carrying conductive particles and the mobility is lowered, the electrode performance The evaluation result can be used as an index that directly affects the process. That is, the catalyst ink does not evaluate the degree to which the polymer electrolyte and the catalyst-carrying conductive particles are simply mixed finely, but the catalyst-carrying conductive particles and the polymer electrolyte are actually used. It can be evaluated that the battery is in a state that can contribute to battery performance. For example, when the particle size distribution of the catalyst ink is measured for the samples (4) and (7) to (9) using the laser diffraction / scattering type particle size distribution measuring device described above, the catalyst ink having a larger resin / carbon ratio, The result was small particle size, ie high dispersion (data not shown). On the other hand, according to the evaluation method of this example, as shown in FIG. 8, the catalyst component having a smaller resin / carbon ratio has a higher hard component increase rate, and the catalyst-carrying conductive particles and the polymer electrolyte are separated. Focusing on the state of adsorption so as to function in the electrode, it becomes possible to evaluate that the mixed state is better as the resin / carbon ratio is smaller.

  Further, according to the evaluation method of the catalyst ink of this example, when the performance of the electrode formed using the catalyst ink to be evaluated is evaluated, the polymer electrolyte and the catalyst are directly affected by the battery performance. The adsorption state with the supported conductive particles can be independently evaluated. Therefore, when examining the conditions of the catalyst ink in order to improve the performance of the electrode as a whole, it is possible to examine the effects caused by other conditions based on the influence of the adsorption state. To directly compare the performance of electrodes formed using catalyst inks under different conditions, assemble fuel cells using each catalyst ink under other conditions, and improve power generation performance (current-voltage characteristics, etc.). Compare. For example, as shown as samples (4) and (7) to (9) in FIG. 8, catalyst inks with the same carbon type and different resin / carbon ratios are prepared, and fuel is used using each. When a battery is assembled and power is generated, the performance of each electrode can be compared. As described above, in such an electrode, the lower the resin / carbon ratio, the higher the hard component increase rate, and it is evaluated that the mixed state of the polymer electrolyte and the catalyst-carrying conductive particles is good. However, if the resin / carbon ratio is reduced to reduce the ratio of the polymer electrolyte too much, the efficiency of proton transfer between the catalyst and the polymer electrolyte is reduced in the electrode, which reduces the battery performance. Connected. Using the evaluation method of this example, while independently evaluating the mixed state of the polymer electrolyte and the catalyst-supporting conductive particles, and examining the evaluation results of the entire electrode, other factors other than the mixed state, That is, it becomes possible to evaluate the influence of other factors including a decrease in the proton delivery efficiency described above.

  The ability to evaluate the mixed state of the polymer electrolyte and the catalyst-carrying conductive particles in this way enables, for example, the development of a fuel cell, the type of carbon used to prepare the catalyst ink, the type of polymer electrolyte, and the catalyst The comparison may be made with different types, catalyst loadings, or catalyst mixing methods. For the catalyst ink with different conditions as described above, the mixed state of the catalyst-supporting conductive particles and the polymer electrolyte was evaluated by comparing the hard component amount, the hard component ratio, or the hard component increase rate, Conditions that make the mixed state better can be set. Alternatively, when the fuel ink is actually manufactured by preparing the catalyst ink under the set conditions, measurement is performed on the catalyst ink in the manufacturing process, and the hard component ratio is obtained to determine the mixed state in the catalyst ink in the manufacturing process. It is also possible to check.

D. Variations:
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, the following modifications are possible.

D1. Modification 1:
In the embodiment, the solid echo method is used when obtaining the ¹⁹ F nuclear magnetic relaxation time (T ₂ ) by the pulsed NMR method for the catalyst ink, but a different configuration may be used. For example, when different types of polymer electrolytes are used or when different types of catalyst-supporting conductive particles are used, the CPMG method, the CP method, or the spin echo method may be used instead of the solid echo method. . It is sufficient that the state of the polymer electrolyte adsorbed on the catalyst-carrying conductive particles can be evaluated based on the amount of the hard component and the soft component, and the time corresponding to the target catalyst-carrying conductive particles and the type of polymer electrolyte What is necessary is just to select the kind of pulse NMR method to be used suitably according to a range.

D2. Modification 2:
In the examples, the catalyst ink for producing an electrode in a polymer electrolyte fuel cell provided with an electrolyte membrane made of a fluorine-based polymer electrolyte was evaluated, but a different configuration may be used. For example, a catalyst ink for producing an electrode in a polymer electrolyte fuel cell including an electrolyte membrane made of a hydrocarbon polymer electrolyte may be evaluated. At this time, when a fluorine-based solid polymer is used as the polymer electrolyte included in the catalyst ink, the ¹⁹ F nuclear magnetic relaxation time (T ₂ ) is obtained by the pulse NMR method and evaluated in the same manner as in the examples. Good. On the other hand, when the same hydrocarbon polymer electrolyte as the electrolyte membrane is used as the polymer electrolyte included in the catalyst ink, the ¹ H nuclear magnetic transverse (spin-spin) relaxation time (T ₂ ) is measured by pulse NMR. ) For evaluation. In this way, by selecting the measurement nucleus corresponding to hydrogen contained only in the polymer electrolyte in the catalyst ink and determining the abundance ratio of the hard component, the mixed state of the polymer electrolyte in the catalyst ink and the catalyst-carrying conductive particles is changed. Can be evaluated.

2 is an explanatory diagram schematically showing a schematic configuration of an electrode 10. FIG. 3 is an explanatory diagram illustrating a manufacturing process of an electrode 10. FIG. It is explanatory drawing which shows an example of the signal obtained by the solid echo method. It is explanatory drawing showing the manufacturing process of catalyst ink. It is explanatory drawing showing the composition of sample (1)-(10). It is explanatory drawing which shows the measurement conditions by a solid echo method. It is an explanatory view showing a result of calculating the hard component and a soft component abundance ratio and relaxation time (T _2). It is explanatory drawing which shows the result of having calculated | required the hard component increase rate about each sample.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electrode 12 ... Catalyst 14 ... Catalyst carrying | support conductive particle 16 ... Polymer electrolyte 20 ... Electrolyte membrane 22 ... Gas diffusion layer

Claims (8)

A method for evaluating a mixed state of the catalyst-carrying conductive particles and the polymer electrolyte in a catalyst ink comprising a mixture of catalyst-carrying conductive particles and a polymer electrolyte for producing a fuel cell electrode. ,
Measurement by the pulsed NMR method is performed on the catalyst ink, and analysis of the measurement results shows that the polymer electrolyte is separated from a hard component having a relatively short lateral (spin-spin) relaxation time (T ₂ ) and a relaxation time ( An evaluation method in which T ₂ ) is separated into soft components having a relatively long length, and the mixed state of the catalyst-carrying conductive particles and the polymer electrolyte is evaluated based on the abundance ratio of the hard components. A method for evaluating a mixed state of the catalyst-supporting conductive particles according to claim 1 and the polymer electrolyte,
With respect to the abundance ratio of the hard component obtained by measurement by a pulse NMR method for a polymer electrolyte solution containing the polymer electrolyte at a concentration equivalent to the catalyst ink without containing the catalyst-supporting conductive particles, An evaluation method for evaluating the mixed state based on an increase rate of the abundance ratio of the hard component in the catalyst ink. A method for evaluating a mixed state of the catalyst-carrying conductive particles according to claim 1 or 2 and the polymer electrolyte,
The measurement by the pulse NMR method is performed under a temperature condition corresponding to the operating temperature of the fuel cell. A method for evaluating a mixed state of the catalyst-carrying conductive particles according to any one of claims 1 to 3 and the polymer electrolyte,
The polymer electrolyte is a fluorine-based polymer electrolyte,
The catalyst-carrying conductive particles are particles that do not substantially contain fluorine,
The relaxation time (T ₂ ) is a ¹⁹ F nuclear magnetic transverse (spin-spin) relaxation time (T ₂ ). Evaluation method. A method for evaluating a mixed state of the catalyst-supporting conductive particles according to claim 4 and the polymer electrolyte,
The pulse NMR method is a solid echo method. A method for evaluating a mixed state of the catalyst-carrying conductive particles according to any one of claims 1 to 3 and the polymer electrolyte,
The polymer electrolyte is a hydrocarbon polymer electrolyte,
The catalyst-carrying conductive particles are particles that do not substantially contain hydrogen,
The relaxation time T ₂ is a ¹ H nuclear magnetic transverse (spin-spin) relaxation time (T ₂ ). A method for evaluating a mixed state of the catalyst-carrying conductive particles and the polymer electrolyte in a catalyst ink comprising a mixture of catalyst-carrying conductive particles and a polymer electrolyte for producing a fuel cell electrode. ,
An evaluation method in which, based on the adsorption state of the polymer electrolyte adsorbed on the catalyst-carrying conductive particles in the catalyst ink, the higher the amount of adsorption and / or the degree of adsorption, the better the mixed state. A method for evaluating a mixed state of the catalyst-supporting conductive particles according to claim 7 and the polymer electrolyte,
Measurement by the pulsed NMR method is performed on the catalyst ink, and analysis of the measurement results shows that the polymer electrolyte is separated from a hard component having a relatively short lateral (spin-spin) relaxation time (T ₂ ) and a relaxation time ( T ₂ ) is separated into a relatively long soft component, and the higher the abundance ratio of the hard component, the greater the amount and / or the degree of adsorption of the polymer electrolyte adsorbed on the catalyst-carrying conductive particles. Evaluation methods.

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