JP6618242B2 - Conductive membrane and fuel cell - Google Patents

Description

  The present invention relates to a conductive membrane and a fuel cell.

  At present, from the viewpoint of cost reduction and simplification of the polymer electrolyte fuel cell system, there is a demand for an electrolyte material that operates at an operating temperature of 100 ° C. or higher and without humidification or under low humidification conditions. On the other hand, a conventional polymer electrolyte fuel cell includes an electrolyte that conducts ions through water as represented by perfluorocarbon sulfonic acid. Therefore, sufficient ionic conduction cannot be exhibited under operating conditions of 100 ° C. or higher, no humidification, or low humidification.

  Known examples of sol-gel porous glass (see Patent Document 1), phosphate hydrogel (see Patent Document 2), and the like that can suppress evaporation of moisture contained in an electrolyte even at high temperatures.

JP 2002-097272 A JP 2003-217339 A

  However, the techniques described in Patent Documents 1 and 2 require humidification close to the saturated water vapor pressure in order to suppress moisture evaporation, and the ionic conductivity and stability are not yet sufficient under low humidification conditions. As described above, in the conventional electrolyte material, good ionic conductivity and stability are not obtained under operating conditions of 100 ° C. or higher and no humidification or low humidification.

  The present invention has been made in view of the above points, and an object thereof is to provide a conductive membrane and a fuel cell that can be used at 100 ° C. or higher and without humidification.

  The conductive membrane of the present invention includes (A) a metal ion, an oxoanion, and a proton-coordinating molecule, and the oxoanion and / or the proton-coordinating molecule is coordinated with the metal ion to increase coordination. It includes a proton conductor forming molecules, and (B) a resin filler of a resin containing an engineering plastic.

  The conductive film of the present invention has high ionic conductivity even at high temperatures (for example, 100 ° C. or higher). Therefore, the fuel cell provided with the electrolyte made of the conductive film of the present invention can be used even at high temperatures.

  The conductive membrane of the present invention does not mediate water in ionic conduction. Therefore, the fuel cell including the electrolyte made of the conductive film of the present invention can be used in a non-humidified or low-humidified condition, and a system for managing the moisture of the electrolyte becomes unnecessary.

  In addition, the conductive film of the present invention can be easily thinned (for example, the film thickness is 500 μm). Therefore, the film resistance of the conductive film can be further reduced.

It is explanatory drawing showing the organic polymer which is 1 type of an additive material. It is explanatory drawing showing the result of the X-ray crystal structure analysis about the proton conductor X1. It is explanatory drawing showing the manufacturing method of the single cell of a fuel cell. It is a perspective view showing the structure of the single cell of a fuel cell.

  An embodiment of the present invention will be described. The conductive membrane of the present invention includes (A) a metal ion, an oxoanion, and a proton coordination molecule, and the oxoanion and / or proton coordination molecule coordinates to the metal ion to form a coordination polymer. A proton conductor, and (B) a resin filler of a resin containing an engineering plastic.

  The metal ion in the present invention is not particularly limited, but from the viewpoint of easy formation of a coordination bond with an oxoanion and / or a proton-coordinating molecule, a high-cycle transition metal ion or a typical metal ion is used. preferable. Of these, cobalt ions, copper ions, zinc ions, and gallium ions are preferred.

  Examples of the oxo anion in the present invention include phosphate ions and sulfate ions, and phosphate ions are preferred from the viewpoint of chemical stability against hydrogen. The phosphate ion may be in the form of a hydrogen phosphate ion in which one proton is coordinated or a dihydrogen phosphate ion in which two protons are coordinated. The oxoanion in the present invention is coordinated to a metal ion, for example, in the form of a monomer in which condensation does not occur, whereby the proton concentration is maintained at a high state and the stability to moisture is also excellent.

  The proton-coordinating molecule in the present invention is a molecule having preferably two or more coordination points for coordinating protons in the molecule. From the viewpoint of ion conductivity, imidazole, triazole, benzimidazole, benztriazole, and derivatives thereof having a coordination point with an excellent balance between proton coordination and release are preferable. Here, the derivative means one obtained by replacing a part of the chemical structure with another atom or atomic group, and specific examples thereof include 2-methylimidazole, 2-ethylimidazole, histamine, histidine with respect to imidazole. Etc.

Examples of the proton-coordinating molecule in the present invention include a primary amine represented by the general formula R—NH ₂ , a secondary amine represented by the general formula R ¹ (R ² ) —NH, And tertiary amines of the formula R ¹ (R ² ) (R ³ ) -N. Here, R, R ¹ , R ² , and R ³ are each independently any one of an alkyl group, an aryl group, an alicyclic hydrocarbon group, and a heterocyclic group.

Examples of such primary amines include lower alkyl amines such as methylamine, ethylamine and propylamine, and aromatic amines such as aniline and toluidine.
Examples of secondary amines include di-lower alkylamines such as dimethylamine, diethylamine and dipropylamine, and aromatic secondary amines such as N-methylaniline and N-methyltoluidine.

  Examples of the tertiary amine include tri-lower alkylamines such as trimethylamine and triethylamine. Examples of the proton-coordinating molecule in the present invention include carbon straight chain diamines such as ethylenediamine and its N-lower alkyl derivative (for example, tetramethylethylenediamine).

  Furthermore, as the proton-coordinating molecule in the present invention, pyrrolidine, N-lower alkylpyrrolidine (for example, N-methylpyrrolidine), piperidine, N-lower alkylpiperidine (for example, N-methylpiperidine), morpholine, N-lower alkylmorpholine. A saturated cyclic amine such as (for example, N-methylmorpholine) can be mentioned.

  Still further, as proton-coordinating molecules in the present invention, piperazine, N-lower dialkylpiperazine (for example, N, N-dimethylpiperazine), 1,4-diazabicyclo [2.2.2] octane (also known as triethylenediamine) ) And the like.

  The proton conductor in the present invention includes a metal ion, an oxoanion, and a proton-coordinating molecule, but in order for these constituents to efficiently form a coordination polymer, It is desirable that the mixing ratio is 1 to 4 mol for the oxoanion and 1 to 3 mol for the proton-coordinating molecule. When the amount of oxoanion and proton coordination molecule is less than 1 mole, a coordination polymer may not be formed. Also, when more than 4 moles of oxoanion and more than 3 moles of proton coordination molecules are blended. In this case, the proton conductor does not become solid, exhibits extremely high hygroscopicity, and the shape stability may be significantly reduced.

  The proton conductor in the present invention can be obtained by mixing and stirring a metal oxide as a metal ion source, an oxo acid, and a proton-coordinating molecule. In the mixing and stirring step, a solvent that can dissolve or uniformly disperse each raw material can be used, but it is preferably performed by a solvent-free reaction from the viewpoint of production cost. Moreover, in the said manufacturing process, when the said proton conductor is heat-processed at temperature higher than 200 degreeC, since condensation of the phosphate ion contained may occur, it is preferable to carry out at the temperature of 200 degrees C or less.

  The proton conductor in the present invention may contain an additive material in addition to the metal ion, oxoanion, and proton coordination molecule. Examples of the additive material include one or more selected from the group consisting of metal oxides, organic polymers, and alkali metal ions. When these additive materials are included, the ion conductivity at a low temperature (for example, less than 100 ° C.) is further increased without impairing the performance of the proton conductor at a high temperature (for example, 100 ° C. or more).

  The addition amount of the additive material is preferably in the range of 1 to 20 parts by weight when the total weight of the metal ion, oxoanion and proton coordination molecule is 100 parts by weight, and the additive material is a metal oxide or an organic polymer. In some cases, the range of 5-20 parts by weight is preferred. When the addition amount is within this range, the ionic conductivity at a low temperature (for example, less than 100 ° C.) is further increased without impairing the performance of the proton conductor at a high temperature (for example, 100 ° C. or more).

Examples of the metal oxide include one or more selected from the group consisting of SiO ₂ , TiO ₂ , Al ₂ O ₃ , WO ₃ , MoO ₃ , ZrO ₂ , and V ₂ O ₅ . When these metal oxides are used, the ionic conductivity at a low temperature (for example, less than 100 ° C.) is further increased without impairing the performance of the proton conductor at a high temperature (for example, 100 ° C. or higher). The particle diameter of the metal oxide is preferably in the range of 5 to 500 nm. When the particle diameter is within this range, the ionic conductivity at a low temperature (for example, less than 100 ° C.) is further increased without impairing the performance of the proton conductor at a high temperature (for example, 100 ° C. or more). The particle diameter is a value obtained by a method in which metal oxide particles are photographed using an electron microscope (SEM) and the obtained image is subjected to image analysis.

The organic polymer preferably has an acidic functional group. When an organic polymer having an acidic functional group is used, the ionic conductivity at a low temperature (for example, less than 100 ° C.) is further increased without impairing the performance of the proton conductor at a high temperature (for example, 100 ° C. or higher). Examples of the acidic functional group include any of a carboxyl group (—COOH), a sulfonic acid group (—SO ₃ H), and a phosphonic acid group (—PO ₃ H ₂ ). The pH of the organic polymer is preferably in the range of 4 or less. When the pH is within this range, the ionic conductivity at a low temperature (for example, less than 100 ° C.) is further increased without impairing the performance of the proton conductor at a high temperature (for example, 100 ° C. or more).

  Examples of the organic polymer include polyacrylic acid (PAA), polyvinyl phosphonic acid (PVPA), polystyrene sulfonic acid (PSSA), and deoxyribonucleic acid (DNA) shown in FIG.

  Examples of the alkali metal ion include one or more metal ions selected from the group consisting of Li, Na, K, Rb, and Cs. When these alkali metal ions are used, the ionic conductivity of the proton conductor becomes higher at low temperatures (for example, less than 100 ° C.) and high temperatures (for example, 100 ° C. or more).

  When the additive is included, the proton conductor in the present invention can be obtained, for example, by mixing and stirring a metal oxide as a metal ion source, an oxo acid, a proton-coordinating molecule, and an additive. In mixing and stirring, it is preferable to mix and stir all the raw materials at once.

  In the mixing and stirring step, a solvent that can dissolve or uniformly disperse each raw material can be used, but it is preferably performed by a solvent-free reaction from the viewpoint of production cost. Moreover, in the said manufacturing process, when the said proton conductor is heat-processed at temperature higher than 200 degreeC, since condensation of the phosphate ion contained may occur, it is preferable to carry out at the temperature of 200 degrees C or less.

In the present invention, the engineering plastics, degradation even 100 ° C. or higher, melting, satisfy the heat resistance is not damaged, and 500 kg / cm ² or more tensile strength, all the characteristics of the 20000 kg / cm ² or more flexural modulus resin Means. Examples of the engineering plastic include polycarbonate, polyvinylidene fluoride, polyether, polyether ketone, polyimide, polyether imide, and derivatives thereof.

In this invention, it is preferable that the weight ratio of a proton conductor and a resin filler exists in the range of 1: 0.1-3.
When the weight ratio of the resin filler to the proton conductor is 0.1 or more, the strength of the conductive film is further increased and the brittleness is reduced, so that it is easier to reduce the thickness of the conductive film. In addition, when the weight ratio of the resin filler to the proton conductor is 3 or less, the proton conductive particles easily form a conduction path in the conductive film, and the proton conductivity of the conductive film is further increased.

The conductive film of the present invention can be produced, for example, by the following method.
(i) Proton conductor powder and resin filler solution are mixed to prepare a mixed solution. Here, although the density | concentration of the resin filler in a resin filler solution is not specifically limited, For example, it can be 0.5-30 wt%. Moreover, the solvent in the resin filler solution is not particularly limited, and examples thereof include 1-methyl-2-pyrrolidone, acetone, ethanol, dimethylacetamide, and two or more mixed solvents selected from them.

After mixing the proton conductor and the resin filler solution, the proton conductor powder can be pulverized and further refined.
(ii) Place the mixture in a low pressure environment and degas. Moreover, a part of solvent is evaporated and the density | concentration of the resin filler in a liquid mixture is raised to a suitable density | concentration. The step (ii) may be omitted.

  (iii) The mixed solution is cast on the surface of a flat plate. Thereafter, when the solvent evaporates, a conductive film is obtained. The film thickness of the conductive film can be adjusted by the cast amount per unit area. A conductive film having a large film thickness can be obtained by providing a bank around the plate and holding a large amount of the liquid mixture on the plate. In addition, as a method for forming the conductive film from the mixed solution, a known method other than the casting method may be used.

  The film thickness of the conductive film can be, for example, 500 μm or less, preferably 100 μm or less. When the film thickness is within the above range, the film resistance is further reduced. Moreover, the film thickness of a conductive film can be 1 micrometer or more, for example, Preferably it can be 10 micrometers or more. In this case, the film strength of the conductive film is further improved.

The fuel cell of the present invention uses the conductive membrane as an electrolyte.
(Example)
1. Production of Proton Conductor X1 210 mg of zinc oxide, 530 μL of 85% phosphoric acid, and 350 mg of imidazole were weighed into a mortar and stirred and mixed at room temperature for 15 minutes in an air atmosphere. Then, it was made to dry at 80 degreeC for 15 hours, and white powder (proton conductor X1) was obtained.

  Table 1 shows the types of metal ions, the types of proton-coordinating molecules, and the blending ratio in the proton conductor X1.

X-ray crystal structure analysis of this powder was conducted. One-dimensional coordination polymer in which phosphate ion was coordinated to zinc ion and imidazole were crystallized by hydrogen bonding via phosphate ion and proton of the coordination polymer. It was confirmed that. The result of the X-ray crystal structure analysis is shown in FIG. Further, ³¹ P-MAS-NMR measurement was performed, and it was confirmed that condensed phosphoric acid was not present in the powder.

  Further, powder X-ray diffraction measurement was performed on the proton conductor X1, and lattice parameters were measured. The conditions of the powder X-ray diffraction measurement are as follows. Table 2 shows the measurement results of the lattice parameters.

X-ray source: CuKα ray Measurement range: 5 ° ≦ 2θ ≦ 40 °
Step width: 0.04 °

2. Production of proton conductor X2 The production method is basically the same as the production method of proton conductor X1, but the levels shown in Table 1 are changed by changing the type of metal ion, the type of proton-coordinating molecule, and the mixing ratio. Proton conductor X2 was produced. And about the proton conductor X2, the X-ray crystal structure analysis and the measurement of the lattice parameter were performed. The measurement results of the lattice parameters are shown in Table 2 above.

3. Production of Conductive Film Y1 Conductive film Y1 was produced as follows.
(i) The proton conductor X1 powder and the resin filler solution were mixed to prepare a mixed solution. Table 3 shows the resin filler type, the solvent type, and the resin filler concentration in the resin filler solution used here. The weight ratio of the resin filler to the proton conductor X1 in the prepared mixed liquid is as shown in Table 3.

  In Table 3, the column “resin filler” represents the type of resin filler, the column “solvent” represents the type of solvent, the column “resin concentration” represents the concentration of resin filler in the resin filler solution, and “ The column “B / A ratio” represents the weight ratio of the resin filler to the proton conductor X1.

(ii) The mixture was placed in a low pressure environment and degassed. Further, a part of the solvent was evaporated to adjust the concentration of the resin filler in the mixed solution.
(iii) The mixed solution was cast on the surface of a flat plate. Thereafter, when the solvent was evaporated, a conductive film Y1 was obtained. As shown in the “film thickness” column in Table 3, the film thickness of the conductive film Y1 was 50 μm. This film thickness is a value measured with a micrometer or a value obtained based on observation with an optical microscope or a scanning electron microscope. If the amount of the mixed liquid to be cast is reduced, the film thickness of the conductive film Y1 can be reduced, and if the amount of the mixed liquid to be cast is increased, the film thickness of the conductive film Y1 can be increased.

4). Production of conductive films Y2 to Y12 The production method is basically the same as the production method of conductive film Y1, but the type of proton conductor, the type of resin filler, the type of solvent in the resin filler solution, the resin in the resin filler solution Conductive membranes Y2 to Y12 shown in Table 3 were manufactured by varying the concentration of the filler and the weight ratio of the resin filler to the proton conductor in the mixed solution.

  However, the conductive membranes Y8 and Y12 are not mixed with the resin filler solution in the proton conductor, only the proton conductor powder is put in a circular mold having a diameter of 20 mm, and the force is 370 MPa from the direction perpendicular to the circle at room temperature. It is a film produced by press molding.

  The film thicknesses of the conductive films Y2 to Y12 are values shown in the “film thickness” column in Table 3. The film thickness of the conductive films Y2 to Y7 could be 100 μm or less. In any of the conductive films Y2 to Y12, an attempt was first made to form a thin film with a film thickness of 100 μm or less. However, the conductive films Y8 to Y12 were too brittle, so that such a thin film could not be formed. . Therefore, for the conductive films Y8, Y10, Y12, films having a film thickness of 1000 μm were formed.

5). Evaluation of Conductive Films Y1 to Y12 (1) Measurement of Film Resistance Conductive films Y1 to Y12 were cut into a circular sheet having a diameter of 10 mm as shown in FIG. Then, plate-shaped platinum-supported carbon electrodes 3 and 5 having a diameter of 9 mm were pressure-bonded from both sides of the electrolyte 1 at a load of 130 kg at 120 ° C. to produce a single cell 7 of the fuel cell shown in FIG.

AC impedance measurement was performed on the single cell 7 manufactured as described above, and the membrane resistance was measured. The measurement was performed under the conditions of a temperature of 120 ° C. and a non-humidified condition under a nitrogen gas stream, a frequency region of 0.1 Hz to 1 MHz, and a voltage amplitude of 10 mV. The measurement results are shown in the column “Membrane Resistance” in Table 3 above. As shown in Table 3, the film resistance of the conductive films Y1 to Y7 was remarkably low.
(2) Measurement of film strength The film strength of the conductive films Y1 to Y12 was measured. The measuring method is as follows.

  As the equipment used, Tensilon RTC-1310A type manufactured by A & D Co., Ltd. was used. The specimen width was 10 mm and the specimen length was 35 mm. The measurement was carried out at room temperature, the sample was pulled at a rate of 10 mm / min in the length direction of the test piece, the stress with respect to the elongation of the test piece was measured, and the tensile strength was calculated from the value. This tensile strength was taken as the film strength.

The measurement results of the film strength are shown in the “film strength” column in Table 3 above. As shown in Table 3, the film strengths of the conductive films Y1, Y2, and Y4 were remarkably high. In Table 3, “x” in the “film strength” column indicates that the film was too brittle to measure the film strength.
(3) Heat resistance test at 120 ° C. The heat resistance test at 120 ° C. was performed on the conductive films Y1 to Y12. The test method and the judgment criteria for heat resistance are as follows.

  Thermogravimetric analysis was performed in a nitrogen atmosphere, and the weight loss when the sample was heated to 120 ° C. was measured. As a result, (b) no weight loss due to thermal decomposition is observed, and (b) no damage occurs when the film is heated to 120 ° C. on a hot plate. Was judged to be good, and if one of the above (a) and (b) was not satisfied, it was judged that there was no heat resistance.

The results of the heat test are shown in the “heat test” column in Table 3 above. As shown in Table 3, the heat resistance of the conductive films Y1 to Y7 was remarkably high.
6). Effects produced by the conductive films Y1 to Y7 (1) As described above, the conductive films Y1 to Y7 have low film resistance even at high temperatures. Therefore, the fuel cell provided with the electrolyte composed of the conductive films Y1 to Y7 can be used even under high temperature conditions (for example, 100 ° C. or higher). As a result, the temperature of the fuel cell can be increased to suppress poisoning of the electrode catalyst. Moreover, exhaust heat efficiency can be improved by raising the temperature of the fuel cell.

  (2) The conductive films Y1 to Y7 do not mediate water in ionic conduction. Therefore, the fuel cell including the electrolyte composed of the conductive films Y1 to Y7 can be used under non-humidified or low humidified conditions. In addition, a system for managing the water content of the electrolyte becomes unnecessary.

  (3) Since the conductive films Y1 to Y7 are in a solid state, in the fuel cell including the electrolyte composed of the conductive films Y1 to Y7, the problem of the liquid oozing out and the liquid that oozes out react with the electrode. There is no problem that the output is lowered due to deterioration or a mixed potential.

  (4) The conductive films Y1 to Y7 can be easily thinned, have high film strength, and high heat resistance.

  DESCRIPTION OF SYMBOLS 1 ... Electrolyte, 3, 5 ... Platinum carrying carbon electrode, 7 ... Single cell of fuel cell

Claims (8)

(A) a proton including a metal ion, an oxoanion, and a proton coordination molecule, wherein the oxoanion and / or the proton coordination molecule is coordinated to the metal ion to form a coordination polymer A conductor,
(B) a resin filler of a resin containing engineering plastic;
Including
The resin is at least one selected from the group consisting of polyvinylidene fluoride, polyetherimide, and derivatives thereof;
The weight ratio of the proton conductor to the resin filler is in the range of 1: 0.1-3;
A proton conductive membrane having a thickness of 50 μm or more and 500 μm or less. The proton conducting membrane according to claim 1, wherein the oxoanion is a monomer. The oxo anion is phosphate ion, hydrogen phosphate ion, and proton conductive membrane according to claim 1 or 2, characterized in that at least one member selected from the group consisting of dihydrogen phosphate ions. The proton-coordinating molecule is at least one selected from the group consisting of imidazole, triazole, benzimidazole, benzotriazole, and derivatives thereof. Proton conducting membrane. It said proton coordinating molecules, Formula primary amine represented by R-NH _2, the general formula R ¹ (R ²⁾ a secondary amine represented by -NH, general formula R ¹ (R ²⁾ It is 1 or more types chosen from the group which consists of tertiary amine represented by (R < ³ >)-N, carbon linear diamine, saturated cyclic amine, and saturated cyclic diamine, The proton conducting membrane according to any one of the above.
(R, R ¹ , R ² and R ³ each independently represents an alkyl group, an aryl group, an alicyclic hydrocarbon group, or a heterocyclic group.) The proton conductive membrane according to claim 1, wherein the metal ions are at least one selected from the group consisting of cobalt ions, copper ions, zinc ions, and gallium ions. The said proton conductor contains the additive material which is 1 or more types chosen from the group which consists of a metal oxide, an organic polymer, and an alkali metal ion, The any one of Claims 1-6 characterized by the above-mentioned. Proton conducting membrane. A fuel cell comprising an electrolyte comprising the proton conducting membrane according to claim 1.