Solid proton conductor and method for producing the same, electrolyte membrane for fuel cell, and fuel cell

Abstract

To provide a solid proton conductor having good proton conductivity in a medium temperature range of 100°C to 250°C under a non-humidified condition, a manufacturing method of the same, an electrolyte membrane for a fuel cell containing the solid proton conductor, and a fuel cell.SOLUTION: A solid proton conductor 1 according to the present invention includes a composite material including a particle portion 2 made of an inorganic oxide, and a covering portion 3 covering at least a portion of the particle portion 2 and containing a salt formed by a nitrogen atom-containing heterocyclic ring-containing compound and an acid, and the inorganic oxide is preferably at least one selected from SiO2, TiO2, SnO2, ZrO2, MnO2, WO3, and Al2O3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a solid proton conductor having good proton conductivity under medium-temperature, non-humidified conditions, a method for producing the same, an electrolyte membrane for a fuel cell containing the solid proton conductor, and a fuel cell. [Background technology]

[0002] Fuel cells are widely known as clean power generation systems, and one type of fuel cell that uses a fluoropolymer solid electrolyte and operates at a temperature of about 80°C under humidified conditions has been put into practical use. Furthermore, in recent years, there has been hope for the realization of a medium-temperature dry fuel cell (MTDFC) that has an electrolyte layer containing a solid electrolyte and liquid phosphoric acid and operates in the medium-temperature range of 100°C to 250°C under unhumidified conditions. Compared to fuel cells that use the aforementioned fluoropolymer solid polymer electrolyte, MTDFCs have the following advantages: (1) they do not require water for proton conduction, which eliminates the need for a humidifier and allows for the device to be more compact; (2) operation at temperatures above 100°C improves the catalyst's CO resistance, which means that catalyst poisoning can be significantly reduced, reducing the amount of Pt used and simplifying the reformed gas system; and (3) the increased operating temperature allows for the simplification of the cooling system and the use of waste heat, improving overall energy efficiency.

[0003] Patent Document 1 discloses an electrolyte membrane with a polybenzimidazole (PBI) skeleton as an electrolyte membrane for use in such MTDFCs. This electrolyte membrane contains PBI, an inorganic acid, and adenylic acid, and is doped with phosphoric acid to exhibit high proton conductivity.

[0004] On the other hand, ionic liquids have been proposed as proton conductors for use in the electrolyte of MTDFCs. Ionic liquids are substances that remain liquid at room temperature and are produced by adding an acidic substance to a basic solid, such as imidazole, that has proton conductivity. In general, ionic liquids have better thermal stability than basic solids alone, and their ionic conductivity is also significantly better than that of basic solids alone. For example, imidazole exhibits a proton conductivity of 10 -3 Scm -1 However, in the ionic liquid where imidazole is mixed with bistrifluoromethanesulfonyl imide (HTFSI) (imidazole / HTFSI=9 / 1), the proton conductivity is 10 -1 Scm -1 It has been reported that the temperature reaches 1000K. Furthermore, Patent Document 2 discloses a proton conductor produced by mixing this ionic liquid with a heteropolyacid, and attempts to achieve both improved stability as an electrolyte and high proton conductivity. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-218299 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-16156 [Non-patent literature]

[0006] [Non-Patent Document 1] A. Noda et al., J. Phys. Chem. B, 107, 4024 (2003) Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a solid proton conductor having good proton conductivity in the medium temperature range of 100°C to 250°C under non-humidified conditions, a method for producing the same, an electrolyte membrane for a fuel cell containing the solid proton conductor, and a fuel cell. [Means for solving the problem]

[0008] The present invention is illustrated below. [1] A solid proton conductor comprising a composite material having a particle portion made of an inorganic oxide and a coating portion that coats at least a portion of the particle portion and contains a salt formed from a heterocycle-containing compound containing a nitrogen atom and an acid. [2] The solid proton conductor according to [1] above, wherein the inorganic oxide is at least one selected from SiO2, TiO2, SnO2, ZrO2, MnO2, WO3 and Al2O3. [3] The solid proton conductor according to [1] or [2] above, wherein the number of nitrogen atoms constituting the heterocycle of the heterocycle-containing compound is 1 or 2. [4] The solid proton conductor according to any one of [1] to [3] above, wherein the salt is at least one selected from hydrochlorides, hydrobromides, nitrates, sulfates, phosphates, acetates, trifluoroacetates, carbonates, sulfonates, and trifluoromethanesulfonates. [5] The composite material for a battery electrode according to any one of [1] to [4] above, which satisfies the following formula (1): (logX 130 - logX 110 ) / (logY 130 - logY 110 )<0.9 (1) (In the formula, X 130 and X 110 are the electrical conductivities (S / cm) of the solid proton conductor at 130°C and 110°C, respectively, and Y 130 and Y 110 are the electrical conductivities (S / cm) of the salt at 130°C and 110°C, respectively. [6] A method for producing the solid proton conductor according to any one of [1] to [5] above, A method for producing a solid proton conductor, comprising a step of subjecting particles made of an inorganic oxide and a powder made of a salt formed from a heterocycle-containing compound containing a nitrogen atom and an acid to mechanical milling. [7] An electrolyte membrane for a fuel cell, comprising the solid proton conductor according to any one of [1] to [5] above. [8] An electrode for a fuel cell, comprising the solid proton conductor according to any one of [1] to [5] above. [9] A fuel cell comprising the electrolyte membrane for a fuel cell according to [7] above.

[10] A fuel cell comprising the fuel cell electrode according to [8] above. [Effects of the Invention]

[0009] The solid proton conductor of the present invention has good proton conductivity in the medium temperature range of 100° C. to 250° C. under non-humidified conditions, and is therefore suitable as a material (electrolyte membrane) for fuel cells, etc. Furthermore, according to the method for producing a solid proton conductor of the present invention, a solid proton conductor having the above properties can be efficiently produced. As described above, the electrolyte membrane for a fuel cell of the present invention contains a solid proton conductor having good proton conductivity in the intermediate temperature region, and therefore can provide a fuel cell (intermediate temperature non-humidified fuel cell) that maintains excellent output characteristics without having to previously humidify the fuel gas or oxidant gas to a high humidity before supplying them. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view showing the structure of a solid proton conductor of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view showing the structure of a fuel cell. [Figure 3] 1 shows X-ray diffraction images of the composite material obtained in Experimental Example 1. [Figure 4] 1 shows X-ray diffraction images of the composite material obtained in Experimental Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0011] The solid proton conductor of the present invention includes a composite material having particles made of an inorganic oxide and a coating covering at least a portion of the particles, and the coating comprising the composite material includes a salt formed from a heterocycle-containing compound containing a nitrogen atom and an acid.

[0012] The form of the solid proton conductor of the present invention is not particularly limited as long as it has the above-mentioned configuration, and it can be a powder (including granules) made of a composite material.

[0013] The particle portion constituting the composite material is made of an inorganic oxide. There are no particular limitations on the inorganic oxide, as long as it is stable at temperatures up to at least 200°C and stable to acids, particularly phosphoric acid. In the present invention, SiO2, TiO2, SnO2, ZrO2, MnO2, WO3, and Al2O3 are preferred. The particle portion may contain only one type of inorganic oxide, or two or more types.

[0014] The shape of the particle portion is not particularly limited and may be spherical, ellipsoidal, polyhedral, rod-like, etc. The particle portion may be solid or porous, and if solid, may be an aggregate of fine particles of, for example, 1 to 50 nm. The size of the particle portion is not particularly limited either, and the major axis thereof (the major axis of the aggregate in the case of an aggregate of fine particles) is preferably 0.005 to 5 μm, more preferably 0.01 to 1 μm.

[0015] The coating portion is formed directly on the surface of the particle portion without any other layer interposed therebetween, and includes a salt formed from a nitrogen-containing heterocycle-containing compound and an acid. The heterocycle-containing compound used to form the salt is a compound containing a nitrogen atom in the heterocycle, and the heterocycle may contain a heteroatom other than the nitrogen atom (oxygen atom, sulfur atom, etc.). The heterocycle-containing compound may also contain a nitrogen atom, oxygen atom, sulfur atom, etc. in a portion other than the heterocycle. The heterocycle-containing compound may also contain multiple heterocycles in one molecule, and in this case, the heterocycles may be the same or different.

[0016] Examples of the heterocycle containing a nitrogen atom include heterocycles containing one nitrogen atom, such as a pyrrole ring or a pyridine ring; heterocycles containing two nitrogen atoms, such as an imidazole ring, a pyrazole ring, a pyridazine ring, a pyrimidine ring, or a piperazine ring; heterocycles containing three nitrogen atoms, such as a triazine ring; fused heterocycles containing one nitrogen atom, such as an indolizine ring, an indole ring, a quinoline ring, a quinolizine ring, or a pyridocoline ring; fused heterocycles containing two nitrogen atoms, such as a pyrimidazole ring, a phthalizine ring, a naphthalizine ring, a quinoxaline ring, or a quinazoline ring; and fused heterocycles containing three or more nitrogen atoms, such as a purine ring.

[0017] Examples of heterocyclic rings containing a nitrogen atom and an oxygen atom include a morpholine ring and an isoxazole ring. Furthermore, examples of heterocyclic rings containing a nitrogen atom and a sulfur atom include a thiazole ring, an isothiazole ring, a thiazoline ring, a thiazine ring, a thiadiazine ring, and a thiadizole ring.

[0018] In the present invention, the heterocycle-containing compound is preferably a compound containing one or two nitrogen atoms in the heterocycle. Particularly preferred heterocycles constituting such compounds are represented by the following formula (2) or (3): [ka]

[0019] The acid used to form the salt may be either an inorganic acid or an organic acid, such as hydrochloric acid, hydrobromic acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, trifluoroacetic acid, carbonic acid, sulfonic acid, or trifluoromethanesulfonic acid.

[0020] The coating portion may contain other components in addition to the salt, if necessary.

[0021] The mass ratio of the particle portion and the coating portion constituting the composite material contained in the proton conductor of the present invention is not particularly limited. Since good proton conductivity can be obtained under unhumidified conditions in the medium temperature range of 100° C. to 250° C., the content ratios of the particle portion and the coating portion, when the total amount of both is 100% by mass, are preferably 5 to 70% by mass and 30 to 95% by mass, and more preferably 10 to 60% by mass and 40 to 90% by mass, respectively.

[0022] The structure of the solid proton conductor of the present invention is not particularly limited. The solid proton conductor of the present invention can have the structure shown in FIG. 1. FIG. 1(A) is an example of a solid proton conductor including one particle portion 2 in a coating portion 3. FIG. 1(B) is an example of a solid proton conductor including multiple particle portions 2 in a coating portion 3. In these figures, the particle portion 2 is provided with the coating portion 3 on the entire surface, but the solid proton conductor of the present invention is not limited to these embodiments, and part of the surface of the particle portion 2 may be exposed (not shown). Furthermore, in FIG. 1(B), all of the particle portions 2 do not need to be made of the same inorganic oxide particles.

[0023] In the present invention, when the conductivity (S / cm) of the proton conductor and the salt contained in the coating portion thereof is measured at 110° C. and 130° C. under non-humidified conditions, the following formula (1) is satisfied. (logX 130 - logX 110 ) / (logY 130 - logY 110 )<0.9 (1) (In the formula, X 130 and X 110are the electrical conductivities (S / cm) of the solid proton conductor at 130°C and 110°C, respectively, and Y 130 and Y 110 are the electrical conductivities (S / cm) of the salt at 130°C and 110°C, respectively. In the present invention, (logX 130 - logX 110 ) / (logY 130 - logY 110 )<0.7. The conductivity of proton conductors is generally highly temperature-dependent, with a significant decrease in conductivity as the temperature drops. In the case of actual fuel cell use, changes in conductivity as the temperature drops can lead to problems such as complicated control and reduced output. The solid proton conductor of the present invention exhibits a smaller change in conductivity at temperatures between 110°C and 130°C than the salt contained in the coating alone. While the mechanism behind this has not been fully elucidated, it is believed that mechanical milling refines the crystals of the salt formed from the nitrogen-containing heterocycle-containing compound and the acid, allowing them to adsorb onto the particle surfaces of inorganic oxide particles, and that this interface contributes to proton conduction, thereby suppressing temperature dependence.

[0024] The method for producing a solid proton conductor of the present invention (hereinafter referred to as the "production method of the present invention") includes a step of subjecting particles made of an inorganic oxide and a powder made of a salt formed from a nitrogen-containing heterocycle-containing compound and an acid to mechanical milling (hereinafter referred to as the "composite step"). This composite step makes it possible to obtain a composite made of inorganic oxide particles and a salt, which can be used as is as a solid proton conductor. Note that the production method of the present invention can also include a particle size adjustment step for adjusting the shape, a classification step for adjusting the size, and the like, after the composite step, as necessary.

[0025] The composite step is a step of subjecting inorganic oxide particles and salt powder to mechanical milling. The inorganic oxide particles are not particularly limited as long as they are stable at temperatures up to at least 200°C and made of an inorganic oxide that is stable against acids (particularly phosphoric acid). In the present invention, particles containing at least one selected from SiO2, TiO2, SnO2, ZrO2, MnO2, WO3, and Al2O3 are preferred. The shape of these particles is not particularly limited, and they can be spherical, ellipsoidal, polyhedral, rod-like, or the like. Furthermore, these inorganic oxide particles may be solid or porous, and if solid, they may be aggregates of fine particles of, for example, 1 to 50 nm. Inorganic oxide particles with a large particle surface area can also be preferably used. The size of the inorganic oxide particles is not particularly limited either, and the major axis thereof (the major axis of the aggregates in the case of aggregates of fine particles) is preferably 0.005 to 5 μm, more preferably 0.01 to 1 μm.

[0026] The salt powder is a powder comprising a salt formed from a heterocycle-containing compound containing a nitrogen atom and an acid, and can be a solid comprising the salt contained in the coating portion constituting the solid proton conductor of the present invention. The shape and size of this salt powder are not particularly limited.

[0027] The mass ratio of the inorganic oxide particles and the salt powder used in the composite step is not particularly limited, but the amount of salt powder used is preferably 40 to 2000 parts by mass, more preferably 60 to 950 parts by mass, relative to 100 parts by mass of the inorganic oxide particles. The inorganic oxide particles and salt powder used may each be of one type, or two or more types.

[0028] In the above-mentioned composite forming step, components other than the inorganic oxide particles and the salt powder may be used.

[0029] The specific method of mechanical milling used in the above-mentioned compounding step is not particularly limited. For example, a ball mill (such as a planetary ball mill), a vibration mill, a turbo mill, mechanofusion, a disk mill, or the like can be used. The atmosphere used for mechanical milling is preferably one that contains as little moisture as possible. For example, an atmosphere such as dry nitrogen or dry argon is preferred.

[0030] As described above, the production method of the present invention can include, after the compounding step, a sizing step for regulating the shape, a classification step for regulating the size, etc. In the sizing step, a method of crushing through a mesh, a method using a sizing machine, etc. can be applied.

[0031] The solid proton conductor of the present invention can also be produced by, for example, coating the surface of inorganic oxide particles with a heterocycle-containing compound containing a nitrogen atom, and then contacting the resulting coating with an acid such as hydrochloric acid, hydrobromic acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, trifluoroacetic acid, carbonic acid, sulfonic acid, or trifluoromethanesulfonic acid.

[0032] The electrolyte membrane for a fuel cell of the present invention is a membrane containing the solid proton conductor of the present invention. The electrolyte membrane for a fuel cell of the present invention may consist of only the solid proton conductor, or may consist of the solid proton conductor and a resin, as long as stability and strength are obtained under medium-temperature, unhumidified conditions. Furthermore, if necessary, it may further contain additives such as stabilizers. The electrolyte membrane for a fuel cell of the present invention may also contain other solid proton conductors.

[0033] The electrolyte membrane for a fuel cell of the present invention is usually in the form of a plate, and its thickness is preferably 5 to 100 μm.

[0034] When the electrolyte membrane for a fuel cell of the present invention is made of only a solid proton conductor, it can be produced by press molding.

[0035] When the fuel cell electrolyte membrane of the present invention contains a solid proton conductor and a resin, preferred resins include polybenzimidazole (PBI), sulfonated polyether ether ketone, sulfonated polysulfone (SPU or SPSU), sulfonated polyimide (SPI), polyamide, polyamic acid, polyimide (PI), polyamideimide, polyvinylpyridine, polyvinylpyrrolidone, etc. Among these, polybenzimidazole (PBI), sulfonated polyether ether ketone, sulfonated polysulfone (SPU or SPSU), and sulfonated polyimide (SPI) are preferred.

[0036] When the electrolyte membrane for a fuel cell of the present invention contains a solid proton conductor and a resin, the upper limit of the proportion of the resin is preferably 100 parts by mass per part by mass of the solid proton conductor of the present invention, from the viewpoint of the balance between electrical performance and mechanical properties.

[0037] When the electrolyte membrane for a fuel cell of the present invention contains a solid proton conductor and a resin, the following embodiments can be employed. (A) A solid proton conductor and a resin are uniformly mixed and molded. (B) A resin porous membrane with a solid proton conductor filled in the pores.

[0038] In the case of the above-mentioned aspect (A), the proton conductor can be produced, for example, by a method of press-molding a mixture of a solid proton conductor and a resin, or by a method of dispersing a solid proton conductor and a resin in a solvent to prepare a dispersion in which the solid proton conductor is dispersed in the resin solution, and then casting this dispersion onto a substrate made of glass or the like to form a film.

[0039] The electrolyte membrane for a fuel cell of the present invention can be used as it is as a raw material for a fuel cell. If necessary, a composite electrolyte membrane having other electrolyte layers on both sides of the electrolyte membrane for a fuel cell of the present invention, or a composite electrolyte membrane having electrolyte layers made of the electrolyte membrane for a fuel cell of the present invention on both sides of another electrolyte membrane, can also be used as a raw material. Depending on the structure of the electrolyte membrane, a binder or a reinforcing layer may be provided on both sides or inside the electrolyte membrane for the purpose of improving shape retention. Furthermore, it is also preferable to combine a solid proton conductor with an electrode catalyst such as Pt and use it as an ionomer in an electrode. This configuration makes it possible to efficiently guide protons to the catalyst material.

[0040] Fuel cells are usually provided with an electrolyte membrane impregnated with phosphoric acid, i.e., a phosphoric acid-doped electrolyte membrane. Such a phosphoric acid-doped electrolyte membrane can be produced, for example, by contacting the fuel cell electrolyte membrane of the present invention with phosphoric acid and then, if necessary, heat-treating it. In addition to phosphoric acid, electron-accepting substances that can act on both the acidic and basic sides, such as sulfuric acid and hydrochloric acid, may also be used.

[0041] In the phosphoric acid-doped electrolyte membrane, the doped phosphoric acid contributes to proton conduction. A fuel cell equipped with such a phosphoric acid-doped electrolyte membrane does not require humidification, and can therefore be suitably used under medium-temperature, non-humidified conditions. Furthermore, within this phosphoric acid-doped electrolyte membrane, the solid proton conductor of the present invention contributes to proton conduction together with phosphoric acid. Therefore, even when the doping amount of phosphoric acid is small, the phosphoric acid-doped electrolyte membrane exhibits high proton conductivity. Furthermore, since the impregnation amount of phosphoric acid can be suppressed in the phosphoric acid-doped electrolyte membrane, corrosion of the electrolyte membrane by phosphoric acid can be reduced, resulting in excellent durability.

[0042] The fuel cell of the present invention is an article including the electrolyte membrane for fuel cells (hereinafter referred to as "electrolyte membrane") of the present invention. When the electrolyte membrane is impregnated with phosphoric acid, the fuel cell essentially includes a phosphoric acid-doped electrolyte membrane. The doping amount of phosphoric acid is not particularly limited.

[0043] The fuel cell of the present invention includes a fuel cell 10 shown in Fig. 2. Fig. 2 is a schematic diagram of the fuel cell 10, which is a basic unit of a fuel cell, and includes an electrolyte membrane 11, an anode-side catalyst layer 12, a cathode-side catalyst layer 13, an anode-side gas diffusion layer 14, and a cathode-side gas diffusion layer 15. The fuel cell of the present invention may be configured as a stack by combining a plurality of fuel cells 10, and Fig. 2 shows a fuel cell 10 suitable for such an embodiment, which includes an anode-side separator 16 and a cathode-side separator 17 on the outside of the anode-side gas diffusion layer 14 and the cathode-side gas diffusion layer 15.

[0044] The anode catalyst layer 12 and the cathode catalyst layer 13 are electrodes formed on either side of the electrolyte membrane 11 and are also called a hydrogen electrode and an air electrode, respectively. The electrolyte membrane 11, the anode catalyst layer 12, and the cathode catalyst layer 13 form a membrane-electrode assembly 19. The anode electrode is composed of the anode catalyst layer 12 and the anode gas diffusion layer 14 disposed on the outer side of the anode catalyst layer 12 . The cathode side catalyst layer 13 and the anode side gas diffusion layer 15 disposed on the outer side of the cathode side catalyst layer 13 constitute a cathode electrode.

[0045] The anode-side catalyst layer 12 and the cathode-side catalyst layer 13 are preferably layers formed by supporting a catalyst material made of platinum, a platinum alloy, palladium, rhodium, or the like on a carrier made of carbon such as acetylene black or graphite, or alumina, silica, or the like, for example, by binding granular materials with a binder. The anode-side gas diffusion layer 14 and the cathode-side gas diffusion layer 15 are layers that are permeable to gases and liquids from one side to the other side, and are made of, for example, carbon cloth, in order to efficiently supply the fuel gas and oxidant gas from each flow path space to the anode-side catalyst layer 12 and the cathode-side catalyst layer 13, and to efficiently discharge water generated by the electrochemical reaction and unreacted raw materials to the outside.

[0046] The anode side separator 16 and the cathode side separator 17 are made of stainless steel, a nickel-based alloy, a chromium-based alloy, or the like from the viewpoints of proton conductivity and heat resistance.

[0047] When reactant gases (hydrogen gas, air) are supplied to the fuel cell 10, the following reactions occur at the anode and cathode, and electrical energy is output. That is, at the anode, hydrogen undergoes a catalytic reaction to produce electrons (e - ) and protons (H + ) and protons (H + ) moves through the electrolyte membrane 11. On the other hand, at the cathode, protons (H + ), electrons circulating from the outside, and oxygen (O2) from the air react to produce water. (Anode) H2→2H + +2e - (Cathode) 2H + +(1 / 2)O2+2e - →H2O

[0048] The fuel cell 10 is not limited to the one shown in FIG. 2, and may be configured such that the membrane-electrode assembly 19 is sandwiched between separators on both sides, and supply channels for hydrogen gas and air are provided on the surface of the separator facing the membrane-electrode assembly 19.

[0049] A solid polymer electrolyte membrane containing polybenzimidazole and phosphoric acid is known to have proton conductivity. However, since polybenzimidazole can only adsorb one phosphoric acid per unit, it is necessary to dope 6 to 13 times as much phosphoric acid as one unit of polybenzimidazole, resulting in a 1 × 10 -3 The solid proton conductor of the present invention exhibits a conductivity of about 100 S / cm (150°C). However, phosphoric acid that has been in contact with polybenzimidazole but has not been adsorbed thereon leaches out of the membrane and corrodes the catalyst, thereby reducing the durability of the fuel cell. However, when an electrolyte membrane containing the solid proton conductor of the present invention is used, the salt formed from the heterocycle-containing compound and the acid exists as a coating, which prevents phosphoric acid from leaching out of the membrane and maintains durability.

[0050] Furthermore, since the solid proton conductor of the present invention has a salt formed from a heterocycle-containing compound and an acid on the surface of an inorganic oxide, the temperature range in which high proton conductivity is exhibited is broadened. For example, the solid proton conductor exhibits high conductivity at about 150°C, but even at a slight temperature drop, the conductivity does not decrease significantly, and even at a temperature slightly lower than 150°C, the battery output is maintained at the same level as at 150°C. [Example]

[0051] 1. Manufacturing raw materials The raw materials used in the production of the solid proton conductor are as follows: 1-1. Silica particles "Fumed silica" (product name, catalog number SS130) manufactured by CVD by Aldrich was used. 1-2. Imidazole hydrochloride (C3N2H4·HCl) powder "Imidazole hydrochloride" (trade name) manufactured by Aldrich was used, hereinafter referred to as "ImiHCl." 1-3. Imidazole trifluoromethanesulfonate powder "Imidazole trifluoromethanesulfonate" (trade name, model number 515876) manufactured by Sigma Aldrich was used. 1-4.Heptane "Heptane" (trade name) manufactured by Aldrich was used.

[0052] 2. Fabrication and evaluation of solid proton conductors A solid proton conductor was produced using the above raw materials, and the conductivity was measured.

[0053] Experimental Example 1 ImiHCl powder and silica particles were blended at mass ratios of 90:10, 70:30, 60:40, and 40:60, respectively, and 1g of each mixture was prepared. Each mixture was then placed in a Fritsch Japan zirconia pod along with 40g of zirconia balls (4mm diameter) and 5ml of heptane. The mixture was milled in a Fritsch Japan planetary mill (model "Fritsch Pulverisette 7") at 450 rpm for 12 hours under an argon atmosphere. After milling, the heptane was removed by vacuum drying, followed by heat treatment at 100°C under an argon atmosphere to obtain four composite materials. In addition, the above milling treatment was carried out on 1 g of ImiHCl powder alone, without using silica particles.

[0054] X-ray diffraction measurements were performed on the milled material (diffraction angle 2θ = 10° to 50°, sampling width 0.02°, scan rate 5° / min, X-ray source: CuKα radiation) to obtain the X-ray diffraction pattern shown in Figure 3. In Figure 3, for example, "x = 60" refers to a composite material obtained using ImiHCl powder and silica particles in a mass ratio of 60:40 (xImiHCl-(100-x)SiO2). Furthermore, "BM ImiHCl" refers to a material obtained by subjecting only ImiHCl powder to the above-mentioned milling process.

[0055] As shown in Figure 3, the X-ray diffraction patterns of the composite materials with x = 60, x = 70, and x = 90 show peaks common to those of BM ImiHCl, but at different intensities. Furthermore, the X-ray diffraction patterns are different from those of the raw material ImiHCl, indicating that the ImiHCl in the coating formed on the surface of the silica particles has a novel crystalline structure.

[0056] In addition, the ionic conductivity (S / cm) of each composite material at 110°C and 130°C was measured using the following method, and the value was used to calculate the ionic conductivity (logX1 130 - logX1 110 ) / (logY1 130 - logY1 110) was calculated and shown in Table 1. X1 130 and X1 110 are the ionic conductivities (S / cm) of the solid proton conductor made of the composite material at 130°C and 110°C, respectively, and Y1 130 and Y1 110 are the ionic conductivities (S / cm) of ImiHCl at 130°C and 110°C, respectively. To prepare pellets (Φ12 mm) of each composite material, they were pressed at 60 MPa for 1 minute using a RIKEN press molding machine "P-16B" (model name). Next, the ionic conductivity (S / cm) of the pellets was measured under non-humidified conditions at 110°C and 130°C using a Solartron electrochemical measurement system "SI 1260" (model name).

[0057] [Table 1]

[0058] As is clear from Table 1, all of the solid proton conductors made from the three types of composite materials exhibited high conductivity (S / cm) at 130°C, and the difference between the conductivity (S / cm) at 130°C and the conductivity (S / cm) at 110°C was small.

[0059] Experimental Example 2 Imidazole trifluoromethanesulfonate powder and silica particles were mixed at mass ratios of 80:20, 60:40, 50:50, and 40:60, respectively, and 1 g of each mixture was prepared. Then, using each mixture, the same procedure as in Experimental Example 1 was carried out to obtain four types of composite materials. Furthermore, the above milling treatment was carried out on 1 g of imidazole trifluoromethanesulfonate powder alone, without using silica particles.

[0060] Next, X-ray diffraction measurement was performed on the material after the milling treatment, and the X-ray diffraction pattern shown in Figure 4 was obtained. In Figure 4, "BM-ImiITS" refers to the material obtained by performing the above-mentioned milling treatment on imidazole trifluoromethanesulfonate powder alone.

[0061] Figure 4 shows that the pattern of BM-ImiITS exhibited a peak shift compared to the raw material, imidazole trifluoromethanesulfonate. Furthermore, the pattern of the composite material showed a change in half-width and a peak shift compared to BM-ImiITS, indicating a slight change in the crystal structure.

[0062] In addition, in the same manner as in Experimental Example 1, the ionic conductivity (S / cm) of each composite material was measured at 110°C and 130°C, and the value was used to calculate (logX2 130 - logX2 110 ) / (logY2 130 - logY2 110 ) was calculated and shown in Table 2. X2 130 and X2 110 are the ionic conductivities (S / cm) of the solid proton conductor made of the composite material at 130°C and 110°C, respectively, and Y2 130 and Y2 110 are the ionic conductivities (S / cm) of ImiITS at 130°C and 110°C, respectively.

[0063] [Table 2]

[0064] As is clear from Table 2, all of the solid proton conductors made from the four types of composite materials had higher electrical conductivities (S / cm) at 130°C than BM-ImiITS. Furthermore, the composite materials with x=40 and x=50 had smaller differences between the electrical conductivities (S / cm) at 130°C and 110°C than the composite materials with x=60 and x=80. [Industrial Applicability]

[0065] The solid proton conductor of the present invention can be applied not only to the field of fuel cells but also to the field of sensors, lithium ion batteries, etc. In fuel cells and lithium ion batteries, it can be used as an electrolyte component. The fuel cell of the present invention is suitable as a fuel cell that can continue to operate without humidifying to high humidity (medium-temperature non-humidified fuel cell). [Explanation of symbols]

[0066] 1: Solid proton conductor 2: Particle part 3: Covering part 10: Fuel cell 11: Electrolyte membrane 12: Anode side catalyst layer 13: Cathode side catalyst layer 14: Anode side gas diffusion layer 15: Cathode side gas diffusion layer 16: Anode side separator 17: Cathode side separator 19: Membrane-electrode assembly

Claims

1. A solid proton conductor containing a composite material including a particle portion made of an inorganic oxide and a coating portion that coats at least a portion of the particle portion and contains a salt formed from a heterocycle-containing compound containing a nitrogen atom and an acid, The inorganic oxide is at least one selected from SiO 2 , SnO 2 , ZrO 2 , MnO 2 and WO 3 ; the number of nitrogen atoms constituting the heterocycle of the heterocycle-containing compound is 1 or 2; the salt is at least one selected from hydrochlorides, hydrobromides, nitrates, sulfates, phosphates, trifluoroacetates, carbonates, sulfonates, and trifluoromethanesulfonates; The solid proton conductor is a solid proton conductor that satisfies the following formula (1): (logX 130 - logX 110) / (logY 130 - logY 110) <0.9 (1) (In the formula, X 130 and X 110 are the electrical conductivities (S / cm) of the solid proton conductor at 130° C. and 110° C., respectively, and Y 130 and Y 110 are the electrical conductivities (S / cm) of the salt at 130° C. and 110° C., respectively.) A solid proton conductor characterized by:

2. An electrolyte membrane for a fuel cell, comprising the solid proton conductor according to claim 1.

3. An electrode for a fuel cell, comprising the solid proton conductor according to claim 1.

4. A fuel cell comprising the electrolyte membrane for a fuel cell according to claim 2.

5. A fuel cell comprising the fuel cell electrode according to claim 3.

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