JP2010138325A - Proton conductive composite electrolyte membrane, and membrane electrode assembly and fuel cell using the same - Google Patents

Abstract

The present invention provides a proton conductive composite electrolyte membrane having both excellent proton conductivity and low fuel permeability.
A proton conductive composite electrolyte membrane according to the present invention includes a metal compound particle having proton conductivity, an organic polymer material having proton conductivity, and a dispersant having a sulfonic acid group, and the metal compound. The average primary particle size of the particles is 0.5 nm or more and 5 nm or less, the average secondary particle size is 50 nm or less, the average dispersed particle size is 30 nm or less, and the content of the metal compound particles is the total weight of the electrolyte membrane In contrast, the weight ratio is 30% by weight or more and 60% by weight or less, and the weight ratio of the dispersant to the metal compound particles is 0.1: 100 to 5: 100.
[Selection] Figure 1

Description

  The present invention relates to a proton conductive composite electrolyte membrane that achieves both high proton conductivity and low fuel permeability, a membrane electrode assembly using the same, and a fuel cell.

  In recent years, as a power source for portable devices replacing lithium ion secondary batteries, fuel cells using methanol or hydrogen as fuel (direct methanol fuel cells (DMFC) and polymer electrolyte fuel cells (PEFC)) are used. Fuel Cell) is expected, and development is actively conducted for practical use.

  A fuel cell electrode is a membrane electrode assembly (MEA) in which a cathode (oxygen electrode) catalyst layer and an anode (fuel electrode) catalyst layer are respectively arranged on the front and back of a proton-conducting solid polymer electrolyte membrane. It is composed of The catalyst layer is formed as a matrix in which the catalyst-supporting carbon and the solid polymer electrolyte are appropriately mixed, and an electrode reaction takes place at the three-phase interface where the catalyst on the carbon, the solid polymer electrolyte, and the reactant are in contact. Is called. In addition, the carbon connection serves as an electron path, and the solid polymer electrolyte connection serves as a proton path.

  For example, in DMFC, the reactions shown in the following formulas (1) and (2) occur in the catalyst layer of the fuel electrode and the catalyst layer of the oxygen electrode, respectively, and electricity can be taken out.

_{CH 3 OH + H 2 O →} CO 2 + 6H + + 6e - (1)
O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O (2)
The DMFC is theoretically said to have an energy density about 10 times that of a lithium ion secondary battery. However, at present, the output of MEA to be used is lower than that of a lithium ion secondary battery, and it has not been put into practical use.

  In order to improve the output of MEA, there are approaches such as improvement of constituent materials such as catalyst and electrolyte membrane, and optimization of MEA structure. Above all, improvement of the electrolyte membrane is an important key for improving the output of MEA. The performance required for the electrolyte membrane includes two points: (1) high proton conductivity and (2) low fuel (methanol or hydrogen) permeability. The reason why the proton conductivity of (1) is required to be high is that when the proton conductivity is low, the resistance of the electrolyte membrane is high, and the increase in membrane resistance directly leads to a decrease in output. In addition, the low fuel permeability in (2) is required because the fuel on the fuel electrode side passes through the electrolyte membrane and reaches the oxygen electrode when the fuel permeability is high. For it to happen. The fuel that has reached the oxygen electrode generates heat by chemically reacting with oxygen on the catalyst of the oxygen electrode. This crossover not only causes deterioration of the electrolyte membrane itself, but also causes an increase in the overvoltage of the oxygen electrode, which causes a decrease in the output of the MEA.

  At present, the most commonly used electrolyte membrane is a perfluorosulfonic acid electrolyte membrane called “Nafion” (registered trademark) manufactured by DuPont. Nafion has a hydrophobic polytetrafluoroethylene (PTFE) skeleton with a side chain to which a hydrophilic sulfonic acid group is fixed at the terminal, and the sulfonic acid group, proton, and water molecule are associated with each other in a hydrous state. , Forming ion clusters. In this cluster, the concentration of sulfonic acid groups is high, so that it becomes a passage for protons, and Nafion exhibits high proton conductivity. However, although Nafion has high proton conductivity, it has a problem of high fuel permeability.

  As electrolyte membranes other than Nafion, there are hydrocarbon electrolyte membranes, aromatic hydrocarbon electrolyte membranes, etc., all of which have proton donors such as sulfonic acid groups, phosphonic acid groups or carboxyl groups. Similar to Nafion, even in these electrolyte membranes, protons dissociate and exhibit proton conductivity when placed in a water-containing state. Here, it is possible to increase the proton conductivity by increasing the concentration of the proton donor such as a sulfonic acid group. However, these conventional proton-conducting electrolyte membranes, when the concentration of a proton donor such as a sulfonic acid group is increased, the water content increases, so that the membrane itself swells and a gap is formed in the membrane accordingly. In addition, the fuel permeability increases.

  Thus, in a single electrolyte membrane using only an organic polymer material, there is a trade-off relationship between proton conductivity and fuel permeability, and high proton conductivity / low fuel permeability (low crossover). It is difficult to obtain an electrolyte membrane that satisfies both of the above.

In recent years, an inorganic-organic composite electrolyte membrane in which an inorganic material and an organic material are combined has attracted attention as an electrolyte membrane that achieves both high proton conductivity and low fuel permeability. For example, Non-Patent Document 1 discloses a composite electrolyte membrane in which a heteropolyacid (12 tungstophosphoric acid) that is an inorganic substance is dispersed in polyvinyl alcohol that is an organic substance. Non-Patent Document 2 discloses a composite electrolyte membrane in which a kind of inorganic zeolite (mordenite) is dispersed in polyvinyl alcohol, which is an organic substance. Non-Patent Document 3 discloses a composite electrolyte membrane in which SiO ₂ , TiO ₂ , and ZrO ₂ that are inorganic substances are dispersed in a sulfonated polyether ketone or sulfonated polyether ether ketone that is an organic substance.

  Furthermore, Patent Document 1 discloses an electrolyte membrane in which a metal oxide hydrate is dispersed in an organic polymer material. Further, although not an inorganic / organic composite electrolyte membrane, Patent Document 2 discloses an electrolyte membrane in which pores of a porous substrate that does not substantially swell with methanol and water are filled with a polymer having proton conductivity. Is disclosed.

  Thus, a composite electrolyte membrane of an inorganic material and an organic material has attracted attention as an electrolyte membrane that achieves both high proton conductivity and low fuel permeability. Above all, in a composite electrolyte membrane made of a proton-conductive metal compound and a proton-conductive organic polymer material, the metal compound itself has proton conductivity, so that the conductivity of the membrane is not hindered and improved. In addition, it is possible to form a membrane skeleton by containing inorganic particles and prevent swelling of the membrane when it contains water, so that an electrolyte that has both high proton conductivity and low fuel permeability It is considered promising as a membrane.

However, various conditions are necessary in order to sufficiently bring out the characteristics considered to be inherent to the composite electrolyte membrane. In particular, it is necessary to optimize not only the characteristics and particle size of the metal compound to be dispersed, but also the arrangement in the film, the dispersed state, and the like.
Materials Letters, 57, p. 1406, 2003 AIChE Journal, Vol. 49, p. 991, 2003 J. et al. Membrane Science, Volume 203, p.215, 2002 JP 2003-331869 A International Publication No. 00/54351 Pamphlet

  Currently, it is known that among metal compounds, electrolyte membranes in which metal oxide hydrate particles are combined tend to improve characteristics such as proton conductivity and fuel permeability. Since the dispersion state of the hydrate particles is not optimized, sufficient performance cannot be exhibited yet in terms of high proton conductivity and low fuel permeability.

FIG. 3 is a schematic cross-sectional view of a composite electrolyte membrane composed of conventional metal oxide hydrate particles having proton conductivity and an organic polymer material. 3, 31 is an organic polymer material having a proton donor such as a sulfonic acid group, 32 is a metal oxide hydrate particle having proton conductivity, and FIG. 3 shows a metal oxide hydrate. As a specific example of the particles 32, an example using zirconium oxide hydrate particles (ZrO ₂ · nH ₂ O) is shown. The organic polymer material exhibits proton conductivity in a water-containing state. This is because protons dissociate and conduct from proton donors such as sulfonic acid groups in a water-containing state. When this organic polymer material is used alone as an electrolyte membrane, the membrane swells due to an increase in water content, and fuel such as methanol or hydrogen permeates through the organic polymer material accordingly. On the other hand, in the metal oxide hydrate particles, protons are conducted through hydrated water adsorbed in the crystal and on the surface. Furthermore, since these inorganic particles are present at a high content rate, the organic polymer material that forms a skeleton of the inorganic particles and serves to connect these inorganic particles also has a suppressed movement. Swelling of the membrane due to water content is suppressed, and fuel crossover is also suppressed at the same time. Metal oxide hydrate has a relatively high proton conductivity as an inorganic substance. For example, the proton conductivity at 25 ° C., the zirconium oxide hydrate (ZrO ₂ · nH ₂ O) in 2.8 × 10 ^-3 S / cm, tin oxide hydrate _{(SnO 2 · nH 2 O)} 4 0.7 × 10 ⁻³ S / cm. Furthermore, because of the properties of metal oxide hydrate, it has the ability to adsorb and retain hydrated water, so that the proton conductivity of the membrane itself is maintained by the water content of these particles even in relatively low humidity environments. There is a possibility that you can.

  As described above, it is considered that the composite electrolyte membrane combining the organic polymer material and the metal compound particles makes it possible to obtain an electrolyte membrane that allows protons to pass through while blocking the permeation of fuel. That is, it is expected that the trade-off relationship between proton conductivity and fuel crossover seen in a single electrolyte membrane of an organic polymer material can be improved. However, the actual characteristics of the composite electrolyte membrane vary greatly depending on the dispersion state of the metal compound particles. For this reason, at present, sufficient performance cannot be exhibited in terms of high proton conductivity and low fuel permeability.

  The present invention solves the above problem, and in a composite electrolyte membrane composed of metal compound particles and an organic polymer material, by adding a dispersant to the metal compound particles and the organic polymer material, the fineness of the metal compound particles can be improved. Dispersion is realized, and a composite electrolyte membrane having high proton conductivity and low fuel permeability is provided. The present invention also provides a high-power MEA for fuel cells using the composite electrolyte membrane and a fuel cell using the MEA.

  The proton conductive composite electrolyte membrane of the present invention is a proton conductive composite electrolyte membrane comprising metal compound particles having proton conductivity, an organic polymer material having proton conductivity, and a dispersant having a sulfonic acid group. The average primary particle size of the metal compound particles is 0.5 nm or more and 5 nm or less, the average secondary particle size of the metal compound particles is 50 nm or less, and the average dispersed particle size of the metal compound particles is 30 nm or less, the content of the metal compound particles is 30 wt% or more and 60 wt% or less with respect to the total weight of the electrolyte membrane, and the weight ratio of the dispersant to the metal compound particles is 0 .1: 100 to 5: 100.

  The membrane electrode assembly of the present invention is an oxygen electrode including a catalyst layer for reducing oxygen, a fuel electrode including a catalyst layer for oxidizing fuel, and the oxygen electrode and the fuel electrode. It includes the proton conductive composite electrolyte membrane of the present invention.

  Furthermore, the fuel cell of the present invention includes the membrane electrode assembly of the present invention.

  According to the present invention, it is possible to provide a proton conductive composite electrolyte membrane that has both excellent proton conductivity and low fuel permeability. Further, by using the proton conductive composite electrolyte membrane of the present invention, a higher output membrane electrode assembly and a fuel cell using the same can be provided.

  A state where the primary particle diameter of the metal compound particles is large and the gaps between the metal compound particles cannot be finely filled, and even if the primary particle diameter of the metal compound particles is small, the secondary particle diameter is increased due to aggregation, In a state where the number of particles distributed in the state of primary particles is small and the gaps between the metal compound particles cannot be filled, the ratio of the portion composed only of the organic polymer material without the metal compound particles in the film increases. Further, since the fuel permeates through the gaps between the metal compounds, or the water-containing swelling of the portion composed only of the organic polymer material is likely to occur, the crossover cannot be sufficiently suppressed. Furthermore, when these metal compound particles have coarse aggregates or a particle size of a submicron size or more, if worsened, the metal compound particles may be dispersed to increase crossover. Therefore, the primary particle size and the secondary particle size of the metal compound particles to be dispersed must be below a certain level, and these particles are uniformly distributed throughout the film in order to form a film skeleton and prevent swelling. It is considered necessary to be.

  An ideal dispersion state in this case is schematically shown in FIG. FIG. 1 is a schematic view showing an ideal dispersion state of the metal compound particles of the present invention. In FIG. 1, 11 is an organic polymer material, and 12 is a metal compound aggregate.

  Further, by dispersing the metal compound particles having proton conductivity, the fuel permeability can be reduced without inhibiting the proton conductivity of the entire membrane. In this case, the organic polymer is used because (1) the content of the metal compound particles is low, (2) the dispersion of the metal compound particles is non-uniform, and (3) the aggregation diameter of the metal compound particles is large. If there are many parts composed of only materials and the connection of conduction between metal compound particles becomes discontinuous, the so-called DC circuit, metal compound particles → hydrophilic clusters of organic polymer materials → metal compound particles Thus, protons are conducted through the organic polymer material, and the high proton conductivity of the original metal compound particles cannot be effectively exhibited. In this case, if the aggregate (secondary particles) is focused on only the metal compound particles (primary particles) contained therein, the metal compound particles are arranged in the closest position in the sense of “direct contact”. However, as shown in FIG. 2, the distance between the aggregates in the film of the metal compound particles is increased, and the path of proton conduction is cut off. FIG. 2 is a schematic diagram showing a dispersion state when the aggregate of metal compound particles is coarsened. In FIG. 2, 21 indicates an organic polymer material, and 22 indicates a metal compound aggregate. For the above reasons, when improving the proton conductivity, it is possible to bring out better characteristics by increasing the content of the inorganic particles with respect to the organic polymer material, and uniformly including the entire membrane. Be expected.

  The present invention has been made in view of the above points, and embodiments of the present invention will be described below.

(Embodiment 1)
First, the proton conductive composite electrolyte membrane of the present invention will be described. The proton conductive composite electrolyte membrane of the present invention includes metal compound particles having proton conductivity, an organic polymer material having proton conductivity, and a dispersant having a sulfonic acid group.

  The average primary particle diameter of the metal compound particles is 0.5 nm or more and 5 nm or less. Moreover, the said metal compound particle | grain aggregates the primary particle, forms a secondary particle, The average secondary particle diameter is 50 nm or less. Furthermore, the average dispersed particle diameter of the primary particles and the secondary particles of the metal compound particles is 30 nm or less. This is because if the particle diameter of the metal compound particles is within these ranges, the gap between the metal compound particles does not increase, and the fuel permeability can be lowered. The lower limits of the average secondary particle size and the average dispersed particle size are about the value of the average primary particle size.

  In the present invention, the average particle diameter of the particles in the electrolyte membrane can be determined by small angle scattering measurement described later.

  Further, the content of the metal compound particles is 30% by weight or more and 60% by weight or less with respect to the total weight of the proton conductive composite electrolyte membrane of the present invention. If the amount is less than 30% by weight, the effect of adding metal compound particles does not appear. If the amount exceeds 60% by weight, the strength of the film decreases and it becomes difficult to form a self-supporting film.

  The reason why the dispersant having a sulfonic acid group is used is that the compatibility with the organic polymer material is good. The weight ratio of the dispersant to the metal compound particles is 0.1: 100 to 5: 100. By adding a dispersant within this range, it becomes possible to cover the surface of the metal compound particles with the dispersant to such an extent that a dispersion effect can be exerted, and an excess that cannot be adsorbed on the surface of the metal compound particles This is because it is possible to prevent the dispersant from being mixed in the organic polymer material. As a result, the metal compound particles having high proton conductivity can be uniformly contained at a high content in the organic polymer material, and the proton conductivity that achieves both excellent proton conductivity and low fuel permeability. A composite electrolyte membrane can be provided. If the weight ratio of the dispersant is less than 0.1, the effect of the dispersant is not exhibited, and if it exceeds 5, the proton conductivity may be hindered.

  Examples of the metal compound having proton conductivity include zirconium oxide hydrate, tungsten oxide hydrate, tin oxide hydrate, niobium-doped tungsten oxide hydrate, silicon oxide hydrate, and phosphoric acid hydrate. Further, metal oxide hydrates such as zirconium oxide-doped silicon oxide hydrate, tungstophosphoric acid hydrate, and molybdophosphoric acid hydrate can be used. A mixture of these metal oxide hydrates can be used. In particular, as the metal compound to be dispersed in the electrolyte membrane for high-temperature operation type PEFC, zirconium oxide hydrate or tin oxide hydrate that is likely to cause proton conduction by crystal water is desirable.

  These metal oxide hydrate particles can be produced by using an aqueous production method in which fine particles with a high amount of hydrated water can be obtained, and well-known production methods such as coprecipitation methods and hydrothermal methods can be applied. Among them, it is particularly preferable to use a hydrothermal method in order to obtain a high amount of hydrated water. In using the hydrothermal method, it is preferable to perform the treatment in a low temperature range of 70 to 150 ° C., which is not used in the normal hydrothermal method. When hydrothermal treatment is carried out at a high temperature exceeding 150 ° C., a regular crystal structure is formed and water of crystallization is reduced. By producing metal oxide hydrate particles using the hydrothermal method under the above conditions, a metal having an average primary particle diameter of 0.5 nm or more and 5 nm or less and a hydrated water amount of 2.7 or more Oxide hydrate particles can be obtained.

In particular, the metal oxide hydrate particles are preferably zirconium oxide hydrate particles represented by the general formula ZrO ₂ · nH ₂ O (n ≧ 2.7). This is because the zirconium oxide hydrate particles have high proton conductivity. The amount n of hydrated water per molecule of the metal oxide hydrate particles is preferably 2.7 or more, more preferably 4 or more. Thereby, the proton conductivity of the metal compound particles themselves can be further increased. The upper limit of the amount of hydration water is not particularly limited, but is usually about 10.

  N in the above general formula is obtained by dispersing zirconium oxide hydrate particles in water, followed by filtration, and then drying in air at 60 ° C. for 6 hours, followed by simultaneous differential thermothermal gravimetric analysis (TG / DTA). It is the numerical value measured by. This is because the amount of hydrated water of the zirconium oxide hydrate particles, especially the amount of adsorbed water, varies depending on the drying conditions, and the amount of hydrated water as the sum of the crystal water and adsorbed water of the zirconium oxide hydrate particles is mutually determined. This is to clarify the standard for comparison. In simultaneous differential thermothermal gravimetric analysis, the change in the amount of hydrated water in zirconium oxide hydrate is continuous, including adsorbed water and crystal water. Exothermic peaks are observed in the range of about 400 to 500 ° C. due to the remarkable change in crystal structure. The amount of hydrated water in the present invention is determined from the change in the amount of water up to the point where this exothermic peak is observed in the differential thermothermal gravimetric simultaneous analysis.

  Examples of the organic polymer material having proton conductivity include perfluorocarbon sulfonic acid, polystyrene, polyether ketone, polyether ether ketone, polysulfone, polyether sulfone, other engineering plastic materials, sulfonic acid groups, phosphonic acid groups, A proton donor such as a carboxyl group doped or chemically bonded and immobilized can be used. It is also desirable to improve the material stability by forming a cross-linked structure or partial fluorination in the above material.

  The dispersant having a sulfonic acid group preferably has a number average molecular weight of 150 to 1,000. If the number average molecular weight of the dispersant is within this range, it is easy to penetrate between the metal compound particles, and the metal compound particles are easily dispersed. Specifically, for example, at least one selected from lauryl benzene sulfonate, benzene sulfonate, toluene sulfonate, styrene sulfonate, octyl benzene sulfonate, diisooctyl sulfosuccinate and the like may be used. it can. That is, in general, organic polymer materials having high proton conductivity and capable of forming a self-supporting membrane often have a long chain structure and a plurality of sulfonic acid groups per molecule. A metal compound that is considered to be adsorbed and bound to is difficult to adsorb due to the complex three-dimensional structure of the organic polymer material. On the other hand, the dispersant has a relatively small number of sulfonic acid groups per molecule and a small molecular weight. Therefore, the three-dimensional size of the dispersant molecule is small, and it easily enters the aggregate of the metal compound. Further, since the number of sulfonic acid groups of each dispersant is small, all the sulfonic acid groups of the dispersant and the metal compound can be easily adsorbed and bonded. Therefore, when this dispersing agent is adsorbed on the surface of the metal compound, the metal compound can be more finely dispersed.

  Further, in the case of a membrane composed only of a conventional proton conductive organic polymer material and a metal compound, the sulfonic acid group of the organic polymer material is adsorbed to the metal compound while maintaining a complicated shape. Therefore, in order to maintain the state, there is a drawback that the film becomes hard, but by using a dispersant having a small molecular weight as described above, it is possible to increase flexibility as a bridge between the organic polymer material and the metal compound. It becomes possible.

  The number average molecular weight of the dispersant in the present invention can be determined by a GPC (Gel Permeation Chromatography) method.

  The dispersant is preferably an organic material having a benzene ring. Since the dispersing agent has a benzene ring, the binding property between the dispersing agent and the organic polymer material is increased, and as a result, the metal compound particles and the organic polymer material can be more firmly bonded via the dispersing agent. is there. Moreover, the function as a bridge | bridging of an organic polymer material and a metal compound can be exhibited more by this.

  In addition to the polymer material having proton conductivity and the dispersant having a sulfonic acid group, other materials such as polyallylamine compounds and divinyl compounds are used for the proton conductive composite electrolyte membrane of the present invention for crosslinking. It may be added. However, it is necessary to select a material that does not inhibit proton conductivity as the other material, and it is necessary that the amount of addition be in a range that does not adversely affect proton conductivity.

  Next, a method for producing the proton conductive composite electrolyte membrane of the present invention will be described. In the method for producing a proton conductive composite electrolyte membrane of the present invention, first, the metal compound particles, the organic polymer material, the dispersant, and if necessary, other organic materials and an organic solvent are mixed to form an organic solvent. The organic polymer material and the dispersant are dissolved, and the metal compound particles are dispersed to prepare a dispersion.

  The organic solvent is not particularly limited as long as it dissolves the organic polymer material, the dispersant and the like, and can be removed by transpiration thereafter. N, N-dimethylformamide, N, N-dimethylacetamide, Aprotic polar solvents such as N-methyl-2-pyrrolidone and dimethyl sulfoxide; alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether and propylene glycol monoethyl ether; dichloromethane and trichloroethane Halogenous solvents such as i-propyl alcohol, t-butyl alcohol and the like can be used. The organic solvent is appropriately selected according to the organic polymer material and the like to be used, and the solubility is preferably 10% by weight or more. The solubility at this time affects the solid content of the dispersion to be produced. However, if the solid content is too small, it is not preferable because it is difficult to obtain a film having a sufficient thickness when forming a film. There are also means such as multi-layer coating to obtain a sufficient thickness, and even an organic solvent having a solubility of less than 10% by weight is not necessarily available, but in order to obtain a uniform film, a high coating technique and a complicated Since a process is required, it is not preferable.

  Content of the said metal compound particle shall be 30 to 60 weight% with respect to the total weight of the solid content of the said dispersion. When the content of the metal compound particles is less than 30% by weight, it is effective in reducing the fuel permeability, but the effect of improving the proton conductivity is hardly obtained. That is, when the content of the metal compound particles is low, the distance between the metal compound particles is inevitably increased, and the proton conductivity as a membrane rapidly decreases. In addition, when the content exceeds 60% by weight, a metal that is necessarily an adsorbed material is obtained if an attempt is made to obtain a connection between organic polymer materials for forming a self-supporting film at such a high content. The specific surface area of the compound particles must be reduced. This means that the metal compound particles have a larger particle size or a coarse secondary particle size due to aggregation, and the fuel permeability cannot be lowered in the finally obtained electrolyte membrane. Therefore, the content of the metal compound needs to be 30% by weight or more and 60% by weight or less, and particularly 40% by weight or more and 55% by weight in the sense of improving both the properties of proton conductivity and low fuel permeability. % Or less is more preferable.

  The method for producing the dispersion is not particularly limited. For example, the metal compound particles can be prepared by mixing in a solution in which an organic polymer material and a dispersant are dissolved and dispersing using a disperser. As the dispersion method, a stirrer method, a ball mill method, a jet mill method, a nanomill method, an ultrasonic method, or the like can be used.

  Next, an inorganic-organic composite electrolyte membrane can be obtained by applying the dispersion to a substrate and evaporating the organic solvent. Then, the proton-conducting composite electrolyte membrane of the present invention is obtained by immersing in water to peel off the composite electrolyte membrane from the substrate. A method for applying the dispersion to the substrate is not particularly limited, and a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, a screen printing method, and the like can be used. The substrate is not particularly limited as long as the film can be peeled off after the dispersion is applied, and a glass plate, a fluororesin sheet, a polyimide sheet, or the like can be used.

  The thickness of the proton conductive composite electrolyte membrane of the present invention is not particularly limited, but is preferably 10 μm or more and 200 μm or less. A thickness of more than 10 μm is preferable to obtain a membrane strength that can withstand practical use, and a thickness of less than 200 μm is preferable to reduce membrane resistance, that is, to improve power generation performance. In particular, 20 μm or more and 100 μm or less is preferable. When the film is formed by the solution casting method, the film thickness can be controlled by the solution concentration or the coating thickness on the substrate. Moreover, when forming into a film using a molten material, a film thickness can be controlled by extending | stretching the film of the predetermined thickness obtained by the melt press method or the melt extrusion method to a predetermined magnification.

  As described above, a composite electrolyte membrane having an average primary particle diameter of 0.5 nm or more and 5 nm or more and in which ultrafine metal compound particles having high proton conductivity are dispersed can be obtained.

  As a method for evaluating the dispersion state of the proton conductive composite electrolyte membrane of the present invention thus obtained, for example, the following indicators are used.

(1) Transmission electron microscope (TEM) observation About the obtained electrolyte membrane, the cross-sectional TEM photograph can be image | photographed and an aggregated particle diameter (secondary particle diameter) and an inorganic particle filling rate can be calculated | required visually. The smaller the aggregate particle size, the higher the filling rate of the inorganic particles, and the smaller the space of only the organic material (in the TEM photograph, the portion that appears white like the background carbon) is determined to be more finely dispersed. be able to.

(2) Optical measurement When the primary particle diameter of inorganic particles other than black is sufficiently small and about 200 nm or less, generally visible light is transmitted if finely dispersed. In the present invention, since the average primary particle diameter of the metal compound particles is a particle having a size of several nanometers, a film that transmits visible light at a certain ratio is always obtained if it is dispersed. At this time, the aggregated particle diameter inside the film is reduced, and if the variation in the aggregated particle diameter is reduced when viewed as a whole, the number of coarse particles that obstruct visible light transmission is reduced, so the visible light transmittance is high. Thus, the haze value (surface scattered light) decreases as the non-uniformity due to variations decreases. Therefore, it can be determined that the same inorganic particle content and the same film thickness are more finely dispersed when the visible light transmittance is higher and the haze value is smaller. Here, the haze value is a haze value defined in Japanese Industrial Standard (JIS) K7105. In such a determination based on optical characteristics, it is possible to evaluate the “uniformity” as a whole, which is difficult to determine with a TEM photograph. Is a useful method together with photographic observation.

(3) Small-angle scattering measurement The transmission-type small-angle scattering spectrum of the obtained electrolyte membrane is measured, and the average particle size and distribution of the particles in the membrane can be obtained from the result. When the true density of each material is clear, it can be uniquely measured without depending on the film thickness, the content rate, or the like. However, the average particle size that can be precisely measured using small angle scattering measurement is up to about 100 nm, and the particle size cannot be determined accurately unless the distribution state is somewhat sharp. Therefore, when a coarser aggregate is included, this measurement method cannot be used.

  In the present invention, since the aggregated particle diameter is fine, any of the above methods may be used as an analysis method, but it is unambiguous regardless of the aggregated particle diameter, inorganic particle content, film thickness, etc. In addition, small-angle scattering measurement that can determine the dispersion state of particles in the film is used.

(Embodiment 2)
Next, the membrane electrode assembly of the present invention and a fuel cell using the same will be described. Embodiment 1 The membrane electrode assembly of the present invention is disposed between an oxygen electrode including a catalyst layer for reducing oxygen, a fuel electrode including a catalyst layer for oxidizing fuel, and the oxygen electrode and the fuel electrode. And the proton-conducting composite electrolyte membrane of the present invention described above. The fuel cell of the present invention includes the membrane electrode assembly of the present invention. By using the proton conductive composite electrolyte membrane of the present invention, a higher output membrane electrode assembly and a fuel cell using the same can be provided.

  Hereinafter, an example of a membrane electrode assembly of the present invention and a fuel cell using the same will be described with reference to the drawings.

  FIG. 4 is a schematic cross-sectional view showing an example of the membrane electrode assembly of the present invention and a fuel cell using the same. In FIG. 4, the fuel cell 40 includes a membrane electrode assembly 41, and the membrane electrode assembly 41 includes an oxygen electrode 1, a fuel electrode 2, and a proton conductive composite electrolyte membrane 3.

  The oxygen electrode 1 and the fuel electrode 2 include catalyst layers 1b and 2b and gas diffusion layers 1a and 2a, respectively. However, the oxygen electrode 1 and the fuel electrode 2 are configured only by the catalyst layers 1b and 2b, respectively. May be. Further, the gas diffusion layer 1a of the oxygen electrode 1 and the gas diffusion layer 2a of the fuel electrode 2 can be made of a porous electron conductive material or the like, for example, a porous carbon sheet subjected to water repellent treatment or the like. Can be used. The proton conductive composite electrolyte membrane 3 is the proton conductive composite electrolyte membrane of the present invention described in the first embodiment.

  The fuel cell 40 includes current collecting plates 5 and 6 outside the gas diffusion layer 1a of the oxygen electrode 1 and the gas diffusion layer 2a of the fuel electrode 2, respectively. The current collector plate 5 on the oxygen electrode 1 side is provided with a hole 9 for taking in oxygen (air), and is further connected to a lead body 5a. Further, the current collector plate 6 on the fuel electrode 2 side is provided with a hole 7 for taking in fuel (hydrogen or the like) from the fuel path 8, and further connected to a lead body 6a. The membrane electrode assembly 41 is sandwiched between the current collector plates 5 and 6 and sealed with the sealing material 4 to constitute the fuel cell 40.

  The current collecting plates 4 and 5 can be made of, for example, a noble metal such as platinum or gold, a corrosion-resistant metal such as stainless steel, or a carbon material. Further, the surface may be plated or painted to improve the corrosion resistance.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to a following example.

Example 1
<Preparation of metal compound particles>
As a metal compound used in this example, zirconium oxide hydrate particles were prepared as follows.

  First, 15.12 g of 28% aqueous ammonia solution was dissolved in 300 mL of water to prepare an aqueous ammonia solution. Separately from this aqueous ammonia solution, 8 g of zirconium chloride oxide was dissolved in 100 mL of water to prepare a zirconium salt aqueous solution.

  Next, the aqueous zirconium solution was stirred while dropping the aqueous zirconium salt solution to produce a precipitate containing zirconium oxide hydrate particles. All the aqueous zirconium salt solutions were used dropwise. The pH of the suspension containing this precipitate was 11.8. This precipitate was aged at 25 ° C. for 15 hours in the form of a suspension. The pH of the suspension after 15 hours was 11.3.

  Subsequently, the suspension containing the precipitate was charged into an autoclave and subjected to hydrothermal treatment at 100 ° C. for 7 hours.

  Finally, in order to remove unreacted substances and impurities from the hydrothermally treated precipitate, it is washed with water using an ultrasonic cleaner, filtered, and at 60 ° C. in accordance with the above-mentioned hydration water content measurement standard. Drying was performed in air for 6 hours. Thereafter, the mixture was lightly crushed with a mortar to obtain zirconium oxide hydrate particles.

  The obtained zirconium oxide hydrate particles were observed using a transmission electron microscope (TEM), and the arithmetic average of the diameter or major axis length of 300 zirconium oxide hydrate particles was measured using the TEM photograph. The average primary particle diameter of the obtained zirconium oxide hydrate particles was 2 nm.

Subsequently, for the zirconium oxide hydrate particles that have passed for 1 hour after the completion of drying, simultaneous differential thermothermogravimetric analysis (TG / DTA) using a differential thermobalance (equipment model number: TG-DTA-2000S) manufactured by Rigaku Corporation. And the amount of hydrated water n of the zirconium oxide hydrate particles represented by the general formula ZrO ₂ · nH ₂ O was determined to be 5.5.

<Preparation of proton conductive composite electrolyte membrane>
Using the zirconium oxide hydrate particles (ZrO ₂ .5.5H ₂ O) as metal compound particles, and an organic polymer material having proton conductivity, SM-PES (sulfonated) in which sulfonic acid groups are introduced into polyethersulfone. Methyl-Poly Ether Sulfone) was used. The ion exchange capacity per dry weight of SM-PES was 1.25 meq / g. Further, sodium laurylbenzene sulfonate (number of sulfonic acid groups per molecule = 1) was used as a dispersant having a sulfonic acid group.

First, SM-PES and sodium laurylbenzenesulfonate were dissolved in dimethyl sulfoxide as an organic solvent to prepare a solution having an SM-PES concentration of 25% by weight and a sodium laurylbenzenesulfonate concentration of 10% by weight. Next, dimethyl sulfoxide and zirconium oxide hydrate particles were added to this solution at the following weight ratio, and mixed for 30 hours using a ball mill method to prepare a dispersion in which zirconium oxide was dispersed.
(1) Zirconium oxide hydrate particles 100 parts by weight (2) SM-PES solution (concentration: 25% by weight) 400 parts by weight (3) Sodium laurylbenzenesulfonate (concentration: 10% by weight) 10 parts by weight (4) 300 parts by weight of dimethyl sulfoxide

  Next, this dispersion was applied onto a glass plate with an applicator and dried at 60 ° C. for 3 hours with a vacuum dryer to evaporate dimethyl sulfoxide to form a film. Then, it peeled off from the glass plate by immersing the obtained film | membrane in water. Subsequently, the membrane was protonated by immersing it in a 1 M aqueous sulfuric acid solution to obtain a proton conductive composite electrolyte membrane in which zirconium oxide hydrate particles were dispersed. The obtained composite electrolyte membrane was a uniform white transparent membrane as a whole, the content of zirconium oxide hydrate particles during drying was 50% by weight, sodium laurylbenzenesulfonate, zirconium oxide hydrate particles, The weight ratio was 1: 100, and the thickness was 25 μm.

  With respect to the electrolyte membrane thus obtained, the particle size distribution was determined from small angle scattering measurement. As a result, two kinds of particle distributions of about 3 nm due to the primary particles of zirconium oxide and particle distributions of about 40 nm due to secondary particles composed of aggregates of the primary particles of zirconium oxide were observed. From these results, the average primary particle size and average secondary particle size of the zirconium oxide hydrate particles were determined, and the average particle size of these particles was taken as the average dispersed particle size. Further, the cross section of the electrolyte membrane was observed with a TEM, and the maximum secondary particle size was measured after visually confirming that these distribution measurement results were appropriate. A small angle scattering measurement spectrum of the electrolyte membrane of this example is shown in FIG. 5, and a TEM photograph of a cross section of the electrolyte membrane is shown in FIG. The average dispersed particle size, average secondary particle size, maximum secondary particle size of the above zirconium oxide hydrate particles, type of dispersant, weight ratio of metal compound, and zirconium oxide hydrate particles (metal compound particles) Table 1 together with the weight percent of

(Example 2)
A dispersion was produced in the same manner as in Example 1 except that the zirconium oxide hydrate particles were dispersed in the following weight ratio.
(1) Zirconium oxide hydrate particles 100 parts by weight (2) SM-PES solution (concentration: 25% by weight) 933 parts by weight (3) Sodium laurylbenzenesulfonate (concentration: 10% by weight) 10 parts by weight (4) 300 parts by weight of dimethyl sulfoxide

  Thereafter, using this dispersion, the content of zirconium oxide hydrate particles during drying was 30% by weight, and the weight ratio of sodium laurylbenzenesulfonate to zirconium oxide hydrate particles was the same as in Example 1. A white transparent proton-conducting composite electrolyte membrane having an overall uniformity of 1: 100 and a thickness of 25 μm was produced.

  The proton conductive composite electrolyte membrane thus obtained was measured for the average dispersed particle size, average secondary particle size, and maximum secondary particle size of the zirconium oxide hydrate particles in the same manner as in Example 1. The results are shown in Table 1 together with the type of dispersant, the weight ratio of the metal compound, and the weight percent of the zirconium oxide hydrate particles (metal compound particles).

(Example 3)
A dispersion was produced in the same manner as in Example 1 except that the zirconium oxide hydrate particles were dispersed in the following weight ratio.
(1) Zirconium oxide hydrate particles 100 parts by weight (2) SM-PES solution (concentration: 25% by weight) 290 parts by weight (3) Sodium laurylbenzenesulfonate (concentration: 10% by weight) 10 parts by weight (4) 300 parts by weight of dimethyl sulfoxide

  Thereafter, using this dispersion, the content of zirconium oxide hydrate particles during drying was 58% by weight in the same manner as in Example 1, and the weight ratio of sodium laurylbenzenesulfonate to zirconium oxide hydrate particles was A white transparent proton-conducting composite electrolyte membrane having an overall uniformity of 1: 100 and a thickness of 25 μm was produced.

  The proton conductive composite electrolyte membrane thus obtained was measured for the average dispersed particle size, average secondary particle size, and maximum secondary particle size of the zirconium oxide hydrate particles in the same manner as in Example 1. The results are shown in Table 1 together with the type of dispersant, the weight ratio of the metal compound, and the weight percent of the zirconium oxide hydrate particles (metal compound particles).

Example 4
Instead of sodium laurylbenzenesulfonate, diisooctyl sulfosuccinate (“Aerosol OT”, number of sulfonic acid groups per molecule = 1) was used, and zirconium oxide hydrate particles were dispersed at the following weight ratios: Produced a dispersion in the same manner as in Example 1.
(1) Zirconium oxide hydrate particles 100 parts by weight (2) SM-PES solution (concentration: 25% by weight) 400 parts by weight (3) diisooctyl sulfosuccinate (concentration: 10% by weight) 10 parts by weight (4) dimethyl 300 parts by weight of sulfoxide

  Thereafter, using this dispersion, the content of zirconium oxide hydrate particles during drying was 50% by weight in the same manner as in Example 1, and the weight ratio of diisooctyl sulfosuccinate to zirconium oxide hydrate particles was 1. : 100, a thickness of 25 μm, and an overall uniform white transparent proton conductive composite electrolyte membrane was produced.

  The proton conductive composite electrolyte membrane thus obtained was measured for the average dispersed particle size, average secondary particle size, and maximum secondary particle size of the zirconium oxide hydrate particles in the same manner as in Example 1. The results are shown in Table 1 together with the type of dispersant, the weight ratio of the metal compound, and the weight percent of the zirconium oxide hydrate particles (metal compound particles).

(Example 5)
A dispersion was produced in the same manner as in Example 1 except that the zirconium oxide hydrate particles were dispersed in the following weight ratio.
(1) Zirconium oxide hydrate particles 100 parts by weight (2) SM-PES solution (concentration: 25% by weight) 400 parts by weight (3) Sodium laurylbenzenesulfonate (concentration: 10% by weight) 40 parts by weight (4) 300 parts by weight of dimethyl sulfoxide

  Thereafter, using this dispersion, the content of zirconium oxide hydrate particles during drying was 50% by weight in the same manner as in Example 1, and the weight ratio of sodium laurylbenzenesulfonate to zirconium oxide hydrate particles was 4: 100, a thickness of 25 μm, and an entirely uniform white transparent proton conductive composite electrolyte membrane was produced.

  The proton conductive composite electrolyte membrane thus obtained was measured for the average dispersed particle size, average secondary particle size, and maximum secondary particle size of the zirconium oxide hydrate particles in the same manner as in Example 1. The results are shown in Table 1 together with the type of dispersant, the weight ratio of the metal compound, and the weight percent of the zirconium oxide hydrate particles (metal compound particles).

(Comparative Example 1)
A dispersion was prepared in the same manner as in Example 1 except that sodium laurylbenzenesulfonate was not used and the zirconium oxide hydrate particles were dispersed at the following weight ratio.
(1) Zirconium oxide hydrate particles 100 parts by weight (2) SM-PES solution (concentration: 25% by weight) 400 parts by weight (3) dimethyl sulfoxide 300 parts by weight

  Thereafter, using this dispersion, the content of zirconium oxide hydrate particles during drying was 50% by weight and the thickness was 25 μm in the same manner as in Example 1. A conductive composite electrolyte membrane was prepared.

  The proton conductive composite electrolyte membrane thus obtained was measured for the average dispersed particle size, average secondary particle size, and maximum secondary particle size of the zirconium oxide hydrate particles in the same manner as in Example 1. The results are shown in Table 1 together with the weight percent of zirconium oxide hydrate particles (metal compound particles).

(Comparative Example 2)
A dispersion was produced in the same manner as in Example 1 except that the zirconium oxide hydrate particles were dispersed in the following weight ratio.
(1) Zirconium oxide hydrate particles 1000 parts by weight (2) SM-PES solution (concentration: 25% by weight) 4000 parts by weight (3) Sodium laurylbenzenesulfonate (concentration: 10% by weight) 3 parts by weight (4) 3000 parts by weight of dimethyl sulfoxide

  Thereafter, using this dispersion, the content of zirconium oxide hydrate particles during drying was 50% by weight in the same manner as in Example 1, and the weight ratio of sodium laurylbenzenesulfonate to zirconium oxide hydrate particles was A uniform white transparent proton conductive composite electrolyte membrane having a thickness of 0.03: 100 and a thickness of 25 μm was produced.

  The proton conductive composite electrolyte membrane thus obtained was measured for the average dispersed particle size, average secondary particle size, and maximum secondary particle size of the zirconium oxide hydrate particles in the same manner as in Example 1. The results are shown in Table 1 together with the type of dispersant, the weight ratio of the metal compound, and the weight percent of the zirconium oxide hydrate particles (metal compound particles). Moreover, the TEM photograph of the cross section of the electrolyte membrane of this comparative example is shown in FIG.

(Comparative Example 3)
A dispersion was produced in the same manner as in Example 1 except that the zirconium oxide hydrate particles were dispersed in the following weight ratio.
(1) Zirconium oxide hydrate particles 100 parts by weight (2) SM-PES solution (concentration: 25% by weight) 171 parts by weight (3) Sodium laurylbenzenesulfonate (concentration: 10% by weight) 10 parts by weight (4) 300 parts by weight of dimethyl sulfoxide

  Thereafter, using this dispersion, the content of zirconium oxide hydrate particles during drying was 70% by weight, and the weight ratio of sodium laurylbenzenesulfonate to zirconium oxide hydrate particles was the same as in Example 1. 1: 100, 25 μm in thickness, and a uniform white transparent proton-conducting composite electrolyte membrane was obtained, but the mechanical strength was very weak and many cracks were generated when the solvent was dried. It was difficult to maintain the shape. For this reason, measurement of the average dispersed particle size, average secondary particle size, and maximum secondary particle size of the zirconium oxide hydrate particles was not performed on the obtained proton conductive composite electrolyte membrane.

  As shown in Table 1, in the electrolyte membranes of Examples 1 to 5, all of the average dispersed particle size, average secondary particle size, and maximum secondary particle size of the metal compound particles were compared to Comparative Examples 1 and 2. I understand that it is small. With efficient proton conduction in mind, even if the average dispersed particle size is fine, if there are coarse secondary particles in it, it will be a factor that inhibits proton conduction. In addition, it is preferable that both the average secondary particle size and the maximum secondary particle size are fine, and the results of Examples 1 to 5 are commensurate with this. This is because when the metal compound particles are dispersed in the proton conductive organic polymer material, the metal compound particles are considered to be adsorbed and dispersed on the hydrophilic group of the organic polymer material. By using a dispersant that has a lower molecular weight than the molecular material and a smaller number of sulfonic acid groups in the molecule, the collision probability between the sulfonic acid groups in the dispersion and the metal compound particles is increased, resulting in more efficient dispersion. It is thought that was able to be done.

  On the other hand, in Comparative Example 1, since no dispersant was added, it is considered that the dispersibility of the metal compound particles was lowered and the particle diameter of the metal compound particles was increased. Moreover, in Comparative Example 2, although the dispersant was added, the amount of the dispersant was small, so it seems that the effect of the dispersant was not expressed. Furthermore, in Comparative Example 3, since the content of the metal compound particles was too large, it is considered that the amount of the organic polymer material was relatively insufficient and a self-supporting film could not be formed.

  As described above, since the proton conductive composite electrolyte membrane of the present invention has excellent proton conductivity and low fuel permeability, by using this, a higher output membrane electrode assembly and a fuel using the same Battery can be provided.

It is a schematic diagram which shows the ideal dispersion state of the metal compound particle | grains of this invention. It is a schematic diagram which shows a dispersion state when the aggregate of metal compound particles is coarsened. It is a schematic cross section of a composite electrolyte membrane composed of conventional metal oxide hydrate particles having proton conductivity and an organic polymer material. It is a schematic cross section which shows an example of the membrane electrode assembly of this invention, and a fuel cell using the same. 3 is a diagram showing a small angle scattering measurement spectrum of the electrolyte membrane of Example 1. FIG. 3 is a diagram showing a TEM photograph of a cross section of the electrolyte membrane of Example 1. FIG. 6 is a diagram showing a TEM photograph of a cross section of an electrolyte membrane of Comparative Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Oxygen electrode 2 Fuel electrode 3 Proton conductive composite electrolyte membrane 11, 21, 31 Organic polymer material 12, 22 Metal compound aggregate 32 Metal oxide hydrate particle 40 Fuel cell 41 Membrane electrode assembly

Claims (6)

A proton conductive composite electrolyte membrane comprising metal compound particles having proton conductivity, an organic polymer material having proton conductivity, and a dispersant having a sulfonic acid group,
The average primary particle diameter of the metal compound particles is 0.5 nm or more and 5 nm or less,
The average secondary particle diameter of the metal compound particles is 50 nm or less,
The average dispersed particle size of the metal compound particles is 30 nm or less,
The content of the metal compound particles is 30% by weight to 60% by weight with respect to the total weight of the electrolyte membrane,
A proton conductive composite electrolyte membrane, wherein a weight ratio of the dispersant to the metal compound particles is 0.1: 100 to 5: 100.   The proton conductive composite electrolyte membrane according to claim 1, wherein the dispersant has a number average molecular weight of 150 or more and 1000 or less.   The proton conductive composite electrolyte membrane according to claim 1, wherein the dispersant is an organic material having a benzene ring. The proton conductive composite according to claim 1, wherein the metal compound particles are zirconium oxide hydrate particles represented by a general formula ZrO ₂ · nH ₂ O (n ≧ 2.7). Electrolyte membrane.   The oxygen electrode including a catalyst layer that reduces oxygen, a fuel electrode including a catalyst layer that oxidizes fuel, and the oxygen electrode and the fuel electrode are disposed between the oxygen electrode and the fuel electrode. And a proton conductive composite electrolyte membrane.   A fuel cell comprising the membrane electrode assembly according to claim 5.

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