JP5231737B2 - Fuel cell solid electrolyte - Google Patents

Description

  The present invention relates to a solid polymer electrolyte having proton conductivity used in a fuel cell.

In recent years, interest in fuel cells with high power generation efficiency has increased due to environmental and energy problems such as global warming. Also by the fuel cell to the cogeneration system to effectively utilize the exhaust heat or the like, it is possible to obtain a high primary energy utilization efficiency of overall efficiency, environmentally friendly, such as CO ₂ emissions for the suppression system It has been very attention as. Depending on the type of electrolyte used for the fuel cell, for example, an alkaline aqueous solution type, a solid polymer electrolyte type, a phosphoric acid type, etc., a low temperature operation type fuel cell, and a molten carbonate type, a solid oxide electrolyte type, etc. Broadly divided into batteries. Among these fuel cells, a solid polymer electrolyte type fuel cell using a polymer membrane having hydrogen ion (proton) conductivity as an electrolyte has been developed. According to this, a high power density can be obtained with a compact structure and the system can be operated with a simple system, and the electrolyte component which is a problem in a phosphoric acid fuel cell (PAFC) using a phosphoric acid solution as an electrolyte can be obtained. Since it does not scatter and is superior when driving stably for a long time, it has been attracting attention as a power source for vehicles, space, and home use.

In the proton conduction type fuel cell, the fuel electrode: H ₂ → 2H ⁺ + 2e ⁻ and the oxidant electrode: 1 / 2O ₂ + 2H are obtained by hydrogen gas supplied from the fuel electrode side and oxygen gas supplied from the oxidant side. ^An electrochemical reaction of ++ 2e ⁻ → H ₂ O occurs. In the above reaction formula, electrons move from the fuel electrode to the oxidant electrode through an external circuit, and protons move in the electrolyte. In a solid polymer electrolyte fuel cell such as an oxyhydrogen fuel cell, an electrolyte membrane having high proton conductivity that exhibits a conductivity of 10 ⁻⁵ S · cm ⁻¹ or more at room temperature is regarded as a promising solid electrolyte. Yes.
As a proton conductive electrolyte having practical stability, a polymer membrane represented by Nafion (registered trademark of Nafion, DuPont), that is, a perfluorocarbon sulfonic acid membrane has been developed. Applications to other electrochemical devices such as fuel cells have been proposed.

  However, in the perfluorocarbon sulfonic acid membrane, water for proton conduction in the membrane is indispensable, and this cannot be maintained at a high temperature of 100 ° C. or higher, so that there is a problem that the conductivity is greatly lowered.

  As a method for producing a high proton conductive solid electrolyte membrane that conducts ions even at a high temperature of 100 ° C. or higher, a method using a melting-quenching method, which is a normal glass production method, can be considered. However, in this method, since most of the water or hydrogen ions in the raw material evaporates and is lost because it melts at a high temperature, the molecular water and hydrogen ions are extremely small, and a high proton conductive membrane cannot be obtained. .

Therefore, for example, as in Japanese Patent Publication No. 8-119612, a method for obtaining a high proton conductive glass such as zirconium phosphate by low-temperature synthesis using a so-called sol-gel method has been studied. Japanese Patent Application Laid-Open No. 2003-192380 reports a method of leaving a large amount of water and hydrogen ions in a glass body by making the temperature during production much lower than that of a conventional melting method. However, the high proton conductive solid electrolyte produced in this way generally has a problem of poor chemical stability and lacks reliability for long-term use.
Japanese Patent Publication No. 8-119612 JP 2003-192380 A

  An object of the present invention is to provide a fuel cell solid electrolyte that exhibits higher proton conductivity than conventional ones and is superior in heat resistance and chemical stability to a perfluorocarbon sulfonic acid membrane.

As a result of intensive research on solid electrolytes in fuel cells, the present inventors have achieved excellent heat resistance, chemical stability, and high proton conductivity by using solid electrolytes mainly composed of phosphoric acid compounds containing nitrogen. The inventors have found that the present invention exhibits the properties, and have made the present invention. That is, according to the present invention, the following inventions are provided.
(1) A fuel cell solid electrolyte comprising a phosphoric acid compound containing nitrogen as a main component.
(2) The fuel cell solid electrolyte according to (1), wherein the phosphoric acid compound is mainly composed of condensed phosphoric acid or a salt thereof, or imidopolyphosphoric acid or a salt thereof.
(3) The fuel cell solid electrolyte according to (1) or (2), wherein the phosphoric acid compound is formed by heating imidopolyphosphoric acid or a salt thereof at 90 to 500 ° C.
(4) The fuel cell solid electrolyte according to any one of (1) to (3), wherein the phosphoric acid compound is an imide polyphosphoric acid or a salt thereof having a cyclic structure.
(5) The fuel cell solid electrolyte according to any one of (1) to (4), wherein the phosphoric acid compound is imide polyphosphoric acid or a salt thereof is tetracycloimide tetraphosphoric acid.
(6) The phosphoric acid compound containing nitrogen is described in any one of (1) to (5) having at least one amino group (—NH ₂ ), imino group (═NH, —NH—) or a triazine ring. Fuel cell solid electrolyte.
(7) The fuel cell solid electrolyte according to any one of (1) to (6), wherein the phosphoric acid compound containing nitrogen has ammonia.
(8) The fuel cell solid electrolyte according to any one of (1) to (6), wherein the phosphoric acid compound containing nitrogen has melamine.
(9) at room temperature ^{10 -4 ~10 -5 S · cm -1} , in any one of at 200 ° C. shows the proton conductivity of ^{10 -3 ~10 -5 S · cm -1} (1) ~ (8) The fuel cell solid electrolyte described.

According to the present invention, it exhibits high proton conductivity of about 10 ⁻⁴ to 10 ⁻⁵ S · cm ⁻¹ at room temperature and about 10 ⁻³ to 10 ⁻⁵ S · cm ⁻¹ at 200 ° C., and perfluorocarbon sulfone. An object of the present invention is to provide a fuel cell solid electrolyte that is superior in heat resistance and chemical stability to an acid film.

The nitrogen-containing phosphoric acid compound used in the present invention is preferably condensed phosphoric acid or imidopolyphosphoric acid. The condensed phosphoric acid is a group of compounds in which PO ₄ groups are basic structural units and the PO ₄ groups are linked two-dimensionally or three-dimensionally. As the condensed phosphoric acid, polyphosphoric acid having a chain structure, cyclophosphoric acid having a cyclic or long chain structure, and the like can be used. For example, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, hexaphosphoric acid, octaphosphoric acid, decalic acid, cyclotriphosphoric acid, cyclotetraphosphoric acid, cyclohexaphosphoric acid, cyclooctalonic acid, cyclodecalic acid, polyphosphoric acid, metaphosphoric acid, etc. At least one of these is used. Among these, pyrophosphoric acid and polyphosphoric acid that can provide high proton conductivity are preferable.

  In addition, imidopolyphosphoric acid in which the cross-linking oxygen of the P—O—P bond contained in the condensed phosphoric acid is substituted with an imino group can also be suitably used.

  When imidopolyphosphoric acid is used, a higher proton conductivity can be obtained by performing the heat treatment than when no heat treatment is performed. The heating temperature at this time is preferably 90 ° C to 500 ° C. More preferably, it is 100 degreeC-400 degreeC. Therefore, examples of the upper limit of the heating temperature include 500 ° C., 450 ° C., and 400 ° C. Furthermore, 350 degreeC, 300 degreeC, and 300 degreeC are illustrated. Examples of the lower limit that can be combined with this upper limit include 120 ° C., 150 ° C., and 200 ° C. In addition, urea may be added as a condensing agent during heating. The amount of urea to be added is not particularly limited, but is preferably 1 to 50%, more preferably 5 to 40%, and still more preferably 10 to 30% by mass ratio with respect to imidocyclotetraphosphate.

Imidopolyphosphoric acid can be broadly classified into a compound having a chain structure and a compound having a cyclic structure. Examples of the compound having a chain structure include imide diphosphate, diimide triphosphate, and imide polyphosphate, and at least one of these is used. Examples of the compound having a cyclic structure include cycloimidocyclotriphosphoric acid and imidocyclotetraphosphoric acid, and at least one of them is used. Among them, a compound having a cyclic structure capable of obtaining high proton conductivity is preferable, and imidocyclotetraphosphate is preferable.
As the phosphoric acid compound containing nitrogen, it is preferable to use one having at least one amino group, imino group or triazine ring. In this case, it is advantageous to obtain high proton conductivity.

  Examples of the compound having an amino group include ammonia, urea, ethylene urea, butyl urea, dicyandiamide, benzenesulfonyl hydrazide, lysine, arginine, polyamide resin, and the like, and at least one of these is used. Examples of the compound having an imino group include dianamide and guanidine, and at least one of them is used. Examples of the compound having a triazine ring include melamine, cyanuric acid, melamine cyanurate, benzoguanamine, acetoguanamine, acryloguanamine, and at least one of them is used. Among these, ammonia and melamine are preferable because they obtain high proton conductivity.

  A solid electrolyte prepared using such a phosphoric acid compound containing nitrogen as a main component is chemically stable and exhibits high proton conductivity at room temperature. Alternatively, high proton conductivity is exhibited at 100 ° C. or higher (100 to 200 ° C.).

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to this.

<Production Example 1> Production of Melamine Pyrophosphate Synthesis of melamine pyrophosphate is based on Japanese Patent Application Laid-Open No. 2004-155664.
(Step 1) Melamine and diammonium hydrogen phosphate were weighed so that the mixing molar ratio was 1: 1. Melamine is a compound having an NH ₂ group. They were pulverized and mixed in a mortar so that the particle diameter was as uniform as possible to obtain a solid raw material composition.
(Step 2) This solid raw material composition was put in a boat-shaped magnetic dish (container) and set in a tubular electric furnace (heating furnace). After the furnace temperature reached 200 ° C., this solid raw material composition was baked in the air atmosphere for 60 minutes (predetermined time) while maintaining this temperature to obtain a baked product. After the completion of firing, the fired product was taken out of the electric furnace and sufficiently cooled in a desiccator to obtain a fired product (white) of melamine pyrophosphate (a phosphoric acid compound having nitrogen). Since this fired product was a low-strength lump, it was crushed and ground for 1 hour in an automatic mortar. During firing, dry air was continuously flowed into the electric furnace, and a gas such as generated ammonia was introduced into a sulfuric acid aqueous solution (50% by mass) to be removed.

<Manufacture example 2> Manufacture of melamine polyphosphate Manufacture of melamine polyphosphate is based on Unexamined-Japanese-Patent No. 2004-10649.
(Step 1) Melamine, diammonium phosphate and urea were weighed so that the mixing molar ratio was 1: 1: 1. They were pulverized and mixed in a mortar so that the particle size was as uniform as possible to obtain a solid raw material composition.
(2 steps) This solid raw material composition is put in a boat-shaped magnetic dish (container), set in a tubular electric furnace (heating furnace), and at the furnace temperature (200 ° C.) in an atmospheric atmosphere, the first process is 60 Minute calcining was performed to obtain a calcined product. The calcined product was once cooled in a desiccator and pulverized again, then set in an electric furnace again, and baked for 60 minutes in an air atmosphere at a predetermined heating temperature (300 ° C.) as a second step. As a result, a fired product mainly composed of melamine polyphosphate was obtained. During the firing step, dry air was continuously flowed into the electric furnace, accompanied by a gas such as ammonia generated from the heated raw material composition, and contacted with a sulfuric acid aqueous solution (50% by mass) for removal.
(Step 3) Further, 4 parts of water was added to 1 part of the obtained fired product and mixed well to form a mixture. A washing step was performed by filtering the mixture. This wet cake was sufficiently dried at a predetermined drying temperature (105 ° C.) to obtain melamine polyphosphate (phosphate compound having nitrogen).

<Production Example 3> Production of tetraimidocyclotetraphosphate and ammonium tetraimidocyclotetraphosphate (1 step) 65 g of ammonium chloride and 200 g of phosphorus pentachloride are placed in a flask and 1,1,2,2-tetrachloroethane is used as a solvent. 500 cm ³ was added and heated and stirred. The stirring speed was about 300 rpm so that the reaction solution did not come to a high position. The reaction temperature was set at 130 ° C., and when the temperature exceeded 135 ° C., the ratio of by-products increased, and subsequent handling became difficult. Since hydrogen chloride gas was generated along with the vapor of tetrachloroethane from around 100 ° C., tetrachloroethane was condensed by a water-cooled reflux tube. Hydrogen chloride gas was drawn with an aspirator, dissolved in water and discharged. Thereafter, the reaction was continued at a predetermined temperature (130 ° C.), and the whole process was completed in about 20 hours. Ammonium chloride was separated from the resulting reaction product. Thereafter, the filtrate was put into a Claisen flask and heated under a predetermined reduced pressure (reduced pressure of 667 to 1333 Pa). Thereby, tetrachloroethane was distilled at a heating temperature (30 to 35 ° C.). After sufficiently distilling tetrachloroethane, it was quickly transferred to the flask before the concentrated solution 100-120 cm ³ did not harden before the residue cooled and hardened. Further, about 500 cm ³ of petroleum ether was added and refluxed for about 15 minutes. After cooling to 30 ° C. or lower, the mixture was allowed to stand for a while, the supernatant was separated into another container, and 500 cm ³ of petroleum ether was again poured into the flask, and the same operation was performed. After repeating this 3-5 times, the lower viscous liquid was cooled with ice to precipitate solid crystals. Here, petroleum ether was added again and refluxed. The extract so far was placed in a flask and distilled by heating. Distillation was stopped when the temperature exceeded 60 ° C., and about 60 cm ³ of a viscous solution brownish brown was taken out while warm. This solution was allowed to stand overnight in a freezer to sufficiently precipitate crystals, and then the crystals were separated. The crystals were washed 2-3 times with petroleum ether. This crystal was a mixture of phosphorus dichloronitride trimer, tetramer, etc., and the yield was about 50 g.
(Step 2) The mixture of phosphorus dichloronitride trimer, tetramer, etc. obtained in the above (Step 1) was distilled under reduced pressure to fractionate phosphorus dichloride nitride having each degree of polymerization. Monomer began to distill at a pressure of about 7-12 mmHg and a temperature of about 80 ° C. Distillation was continued to 100 ° C. to separate only the monomer. Thereafter, the temperature was increased to 160 to 170 ° C. to separate the tetramer.
(3 steps) 15 g of phosphorus dichloride nitride tetramer was dissolved in 200 cm ³ of dioxane. Separately, 120 g of sodium acetate trihydrate was dissolved in 40 cm ³ of pure water and immersed in a constant temperature bath at 45 to 50 ° C. After both solutions reached the same temperature, they were mixed with stirring. After a while, a white precipitate was formed, but the reaction was carried out for 3 hours. Thereafter, the precipitate was immediately separated, and then the sample was washed with 70% by volume ethanol aqueous solution and 90% by volume ethanol aqueous solution. Since the product takes various amounts of water of crystallization, in order to make this constant, further dissolve 1 g of sample in 40 cm ³ of water, add 2 g of sodium chloride therein, stir for 15 to 20 minutes, and again precipitate white. And was filtered to form a sample. This sample was washed with 70 volume% ethanol aqueous solution and 90 volume% ethanol aqueous solution, and finally washed with acetone. As a result, sodium tetraimidocyclotetraphosphate was obtained.
(Step 4) 0.5 g of sodium tetraimidocyclotetraphosphate obtained in Step ³ was dissolved in 50 cm ³ of pure water. Further, the pH was lowered to 1.0 or less with hydrochloric acid. The resulting precipitate was filtered and washed with an aqueous ethanol solution (70% by volume). Further, tetraimidecyclotetraphosphoric acid (a phosphoric acid compound containing nitrogen) was obtained by washing with acetone.
(Step 5) Next, tetraimidecyclotetraphosphoric acid was dissolved again in 50 cm ³ of pure water while adding aqueous ammonia to form an aqueous solution. This aqueous solution was adjusted to pH 10.0 or higher. Ethanol was added to this solution, and the resulting precipitate was separated to obtain tetraimidocyclotetraphosphate ammonium (a phosphate compound containing nitrogen).
(6 steps) After taking 1 g of the ammonium tetraimidecyclotetraphosphate obtained in the above 5 steps and mixing with 0.1 g of urea, a predetermined temperature (10
Heat treatment was performed at a temperature of ˜250 ° C. for a predetermined time (1 hour). As a result, a heated product of ammonium tetraimidocyclotetraphosphate was obtained.

  Moreover, the tetraimidocyclotetraphosphoric acid obtained by the above-mentioned 4 process was heated at each temperature of 100-250 degreeC (Unlike 5th process, ammonia water was not mixed). In this case, a sample heated in the atmosphere, a sample heated in nitrogen, and a sample heated in vacuum were prepared. FIG. 5 shows test result data of a sample heated in the atmosphere. FIG. 8 shows test result data of the sample heated in nitrogen. FIG. 9 shows test result data of a sample that has been heated in vacuum.

(Test Example 1)
According to Test Example 1, the sample was manufactured by performing the following operation using the melamine pyrophosphate manufactured in the above-described Preparation Example 1 as a sample.
(Step 1A) 0.2 g of melamine pyrophosphate produced in Production Example 1 was uniformly pulverized in a mortar.
(2A step) Using a KBr tablet molding machine (manufactured by Honko) and a manual pump (manufactured by Riken Kikai Co., Ltd.), the sample of (1A step) is pressed for 30 seconds, and a tablet-like sample having a diameter of 13 mm and a thickness of 1 mm It was created. The diameter and thickness of the sample were confirmed with a micrometer.
(3A process) About the sample produced in (2A process), JEE-400 VACUUM EVAPORATOR (made by JEOL) was used, and the gold | metal wire of diameter 0.5mm per side and length 10mm was vapor-deposited on both surfaces of the sample. At this time, the side surface of the sample was masked with a cellophane tape or the like.
(Step 4A) The sample was sandwiched between 10 × 20 mm platinum plates as electrodes. It was further insulated by sandwiching it with a ceramic plate, and the sample was fixed with a clip.
(Step 5A) The platinum plate was connected to an impedance meter 3532-80 (manufactured by HIOKI). The resistance characteristics of the samples were measured at room temperature, 100 ° C., 150 ° C., and 200 ° C., respectively.
(Step 6A) The resistance value of the measured sample was substituted in the following equation, and the electrical conductivity σ in the thickness direction of the sample was calculated. The electrical conductivity σ corresponds to the proton conductivity in the thickness direction of the sample. Here, L indicates the thickness of the sample, S indicates the surface area of one side of the sample, and R indicates resistance.

σ = (L / S) × (1 / R)
The measurement results are shown in FIG. The horizontal axis of FIG. 1 shows temperature parameters (10 ³ / T, absolute temperature, Celsius). The numerical value 2.5 on the horizontal axis means 1000K / 2.5 = 400K (127 ° C.). The vertical axis | shaft of FIG. 1 shows electrical conductivity (sigma) [S * cm < ^-1 >] (Conductivity). 1.00E-03 corresponds to 1 × 10 ⁻³ . As shown in FIG. 1, the electrical conductivity of melamine pyrophosphate is in the range of 10 ⁻⁴ · cm ⁻¹ to 10 ⁻³ S · cm ⁻¹ in the temperature range from room temperature to 200 ° C. Met. Specifically, it is 10 ⁻⁴ S · cm ⁻¹ at room temperature, and approaches 10 ⁻³ S · cm ⁻¹ at 200 ° C. Thus, Test Example 1 was a sufficient value as a membrane having high proton conductivity.

(Test Example 2)
According to Test Example 2, the same operation as in Test Example 1 was performed except that the melamine polyphosphate produced in Production Example 2 was used as a sample. The result of measuring the electrical conductivity of the sample is shown in FIG. As shown in FIG. 2, the electrical conductivity of melamine polyphosphate is in the range of 10 ⁻⁵ S · cm ⁻¹ to 10 ⁻⁴ S · cm ⁻¹ in the temperature range from room temperature to 200 ° C. It was good. Specifically, the electrical conductivity at room temperature is 10 ⁻⁴ S · cm ⁻¹ , ^exceeding 10 ⁻⁵ S · cm ⁻¹ at 200 ° C., and approaching 10 ⁻⁴ S · cm ⁻¹ . Thus, Test Example 2 was a sufficient value as a membrane having high proton conductivity.

(Test Example 3)
According to Test Example 3, the same procedure as in Test Example 1 was performed, except that the heated product of ammonium tetraimidecyclotetraphosphate manufactured in Production Example 3 was used as a sample, and the electrical conductivity was measured. The result of measuring the electrical conductivity of the sample is shown in FIG. As shown in FIG. 3, the electrical conductivity of this substance is in the range of 10 ⁻⁵ S · cm ⁻¹ to 10 ⁻³ S · cm ⁻¹ in the temperature range from room temperature to 200 ° C. Met. Specifically, it is about 10 ⁻⁵ S · cm ⁻¹ at room temperature, about 10 ⁻⁴ S · cm ⁻¹ at 100 ° C., and higher than 10 ⁻³ S · cm ⁻¹ at 200 ° C. . Thus, Test Example 3 was a sufficient value as a membrane having high proton conductivity. In particular, proton conductivity was high in the range of 100 to 200 ° C.

(Comparative Example 1)
As a polymer membrane, commonly used polymer type Nafion 117 (registered trademark of Nafion, DuPont) is connected to an impedance meter 3532-80 (manufactured by HIOKI), and room temperature, 100 ° C., 150 ° C., 200 ° C. The resistance characteristics were measured at the respective temperatures, and the electrical conductivity was calculated. The electric conductivity at room temperature was 10 ⁻² S · cm ⁻¹ . However, when the temperature of the sample was 100 ° C., the electric conductivity decreased rapidly. Electrical conductivity could not be measured above 150 ° C. Thus, when the polymer type Nafion exceeds 100 ° C., it lacks heat resistance and chemical stability.

(Test Example 4)
According to Test Example 4, tetraimidocyclotetraphosphate ammonium was used as a sample. The sample was assembled between the fuel electrode and the oxidant electrode as an electrolyte membrane of a single cell fuel cell, and the power generation characteristics of the fuel cell were measured. In power generation operation, humidified hydrogen gas (3% by volume, 97% hydrogen gas) was introduced into the fuel electrode, and dry air was introduced into the oxidizer electrode. The IV characteristics were measured at 25 ° C. using the sample made of ammonium tetraimidocyclotetraphosphate described above. The measurement results are shown in FIG. The horizontal axis of FIG. 4 shows current density (I / S [mA · cm ⁻² ]), and the vertical axis shows voltage E [V] and output density (P / S [mW · cm ⁻² ]). As shown in FIG. 4, the voltage E decreases as the current density increases. The maximum value of the power density (P / S) is 0.14 mW · cm ⁻² .

(Test Example 5)
According to Test Example 5, tetraimidocyclotetraphosphate was used as a sample. Tetraimidocyclotetraphosphate is produced in Production Example 3 described above. Tetraimidocyclotetraphosphate is heat-treated at 250 ° C. for 1 hour in the air. As in the case of Test Example 4, the sample was incorporated as an electrolyte membrane of a single cell fuel cell, and the power generation characteristics of the fuel cell were measured under the same power generation conditions. The measurement results are shown in FIG. The horizontal axis of FIG. 5 shows current density (Current Density), and the vertical axis shows voltage (Voltage) and output density (Power Density). As shown in FIG. 5, the voltage decreases as the current density increases. The maximum value of the power density was about 0.4 mW · cm ⁻² . Thus, the power density of Test Example 5 is considerably improved as compared with the power density of Test Example 4.

(Test Example 6)
According to Test Example 6, tetraimidocyclotetraphosphate was used as a sample. In this case, tetraimidecyclotetraphosphate is produced in Production Example 3 described above. Tetraimidocyclotetraphosphate is heat-treated at 200 ° C. for 1 hour.

The electrical conductivity was measured in the same manner as described above using a sample made of tetraimidocyclotetraphosphoric acid heat-treated as described above. The measurement results are shown in FIG. In this case, as shown in FIG. 6, room temperature (reference 1) → 200 ° C. (reference 2) → 100 ° C. (reference 3) → 150 ° C. (reference 4) → 200 ° C. (reference 5) → 150 ° C. (reference 6) The temperature of the sample was changed as indicated by 100 ° C. (symbol 7) → 100 ° C. (symbol 8). As shown in FIG. 6, even when the temperature of the sample was changed in this way, the reproducibility of the electrical conductivity was high. According to this test, the electrical conductivity is in the range of 10 ⁻⁵ S · cm ⁻¹ to 10 ⁻⁴ S · cm ⁻¹ when the test temperature is normal temperature. However, if the test temperature is 100 ° C., the temperature rises to around 10 ⁻⁴ S · cm ⁻¹ . Further, when the test temperature is 150 ° C., the temperature rises to around 10 ⁻⁴ S · cm ⁻¹ to 10 ⁻³ S · cm ⁻¹ . Furthermore, if the test temperature is 200 ° C., it approaches 10 ⁻³ S · cm ⁻¹ or becomes higher than this value. Thus, tetraimidocyclotetraphosphate exhibits high proton conductivity.

(Test Example 7)
According to Test Example 7, tetraimidocyclotetraphosphate was used as a sample. In this case, tetraimidecyclotetraphosphate is produced in Production Example 3 described above. Tetraimidocyclotetraphosphate is heat-treated at 350 ° C. for 1 hour. The electrical conductivity was measured in the same manner as described above using a sample made of tetraimidocyclotetraphosphoric acid heat-treated as described above. The measurement results are shown in FIG. In this case, as shown in FIG. 7, 150 ° C. (reference numeral 1) → 100 ° C. (reference numeral 2) → 75 ° C. (reference numeral 3) → 100 ° C. (reference numeral 4) → 120 ° C. (reference numeral 5) → 140 ° C. (reference numeral 6) ) → 150 ° C. (symbol 7), the temperature of the sample was changed. As shown in FIG. 7, even when the temperature of the sample was changed in this way, the reproducibility of the electrical conductivity was high. According to this test, the electrical conductivity is in the range of 10 ⁻⁵ S · cm ⁻¹ to 10 ⁻⁴ S · cm ⁻¹ when the test temperature is 75 ° C. However, if the test temperature is 100 ° C., it is higher than 10 ⁻⁴ S · cm ⁻¹ , and if the test temperature is 150 ° C., it is in the range of 10 ⁻³ S · cm ⁻¹ to 10 ⁻² S · cm ⁻¹ . It becomes considerably high.

(Test Example 8)
According to Test Example 8, tetraimidocyclotetraphosphate was used as a sample. In this case, it is manufactured in the manufacturing example 3 described above. Furthermore, using a reduction furnace, tetraimidecyclotetraphosphoric acid was heat-treated at 250 ° C. in a nitrogen atmosphere. In this case, the sample heated for 0.5 hour, the sample heated for 1 hour, the sample heated for 2 hours, the sample heated for 3 hours, the sample heated for 4 hours, the sample heated for 5 hours, and the like The electrical conductivity was measured respectively. In this case, the temperature of the sample was set to 373K (100 ° C.), 393K (120 ° C.), and 423K (150 ° C.).

The measurement results are shown in FIG. As shown in FIG. 8, the higher the measurement temperature of the sample, the higher the electrical conductivity. The electrical conductivity was particularly good for the samples at a heat treatment time of 250 ° C. for 3 hours (× mark), 4 hours (● mark), 2 hours (◇ mark), and 5 hours (Δ mark). In particular, when the temperature of the sample is 150 ° C., the electric conductivity is as high as 10 ⁻³ S · cm ⁻¹ to 10 ⁻⁴ S · cm ^−1, and high proton conductivity is obtained.

Even when the heat treatment time is 0.5 hours (circles) and 1 hour (squares), the electrical conductivity is low when the measured temperature of the sample is lower than 100 ° C., but the measured temperature of the sample is 100 ° C. The electric conductivity approaches 10 ⁻³ S · cm ⁻¹ and 10 ⁻⁴ S · cm ⁻¹ as the temperature rises to over 150 ° C. and high proton conductivity is obtained.

(Test Example 9)
According to Test Example 9, tetraimidocyclotetraphosphate was used as a sample. In this case, the first to fourth steps are carried out in Production Example 3 described above. Furthermore, using a reduction furnace, heat treatment was performed at 250 ° C. for 1 hour in a vacuum atmosphere (5 mmHg or less). The electrical conductivity of the sample was measured as described above. The measurement results are shown in FIG. As shown in FIG. 9, the higher the measured temperature of the sample is from about 373 K (100 ° C.) to about 454 K (181 ° C.), the higher the electrical conductivity is obtained.
(Application example)
The fuel cell shown in FIG. 10 includes a fuel electrode 102 to which fuel is supplied, an oxidant electrode 104 to which an oxidant is supplied, and a solid electrolyte 100 sandwiched between the fuel electrode 102 and the oxidant electrode 104. . Fuel (hydrogen) is supplied from the fuel distribution member 202 to the fuel electrode 102. An oxidant (oxygen) is supplied from the oxidant distribution member 204 to the oxidant electrode 104. The solid electrolyte 100 is formed of the solid electrolyte according to the above-described test example.

(Other)
The present invention is not limited to the embodiments described above and shown in the drawings, and can be implemented with appropriate modifications within the scope not departing from the gist. The following technical idea can be obtained from the above description.
(Additional Item 1) A solid electrolyte having proton conductivity mainly containing a phosphoric acid compound containing nitrogen.
(Additional Item 2) The solid electrolyte having proton conductivity according to claim 1, wherein the phosphoric acid compound is mainly composed of condensed phosphoric acid or a salt thereof, or imidopolyphosphoric acid or a salt thereof.
(Additional Item 3) The solid electrolyte having proton conductivity according to each additional item, wherein the phosphoric acid compound is formed by heating imidopolyphosphoric acid or a salt thereof at 90 to 500 ° C.
(Additional Item 4) The solid electrolyte having proton conductivity according to each additional item, wherein the phosphoric acid compound is an imidopolyphosphoric acid or a salt thereof having a cyclic structure.
(Additional Item 5) The solid electrolyte having proton conductivity according to each additional item, wherein the phosphoric acid compound is imide polyphosphoric acid or a salt thereof is tetracycloimide tetraphosphoric acid.
(Additional Item 6) The solid electrolyte having proton conductivity according to each additional item, wherein the phosphoric acid compound containing nitrogen has at least one amino group, imino group or triazine ring.
(Additional Item 7) The solid electrolyte having proton conductivity according to each additional item, wherein the phosphoric acid compound containing nitrogen has ammonia.
(Additional Item 8) The solid electrolyte having proton conductivity according to any one of the additional items, wherein the phosphoric acid compound containing nitrogen has melamine.
(Additional Item 9) The method for producing a solid electrolyte having proton conductivity according to each additional item, wherein imide polyphosphoric acid or a salt thereof is heat-treated at 90 to 500 ° C.
(Additional Item 10) A fuel electrode to which fuel is supplied, an oxidant electrode to which an oxidant is supplied, and a solid electrolyte sandwiched between the fuel electrode and the oxidant electrode. A fuel cell comprising the solid electrolyte described above.

  The solid electrolyte according to the present invention is not limited to a solid electrolyte for a fuel cell. In some cases, the solid electrolyte may be used as a solid electrolyte for a hydrogen detector, a hydrogen gas sensor, a hydrogen concentration cell, a hydrogen separation membrane, or an electrochromic display element. it can.

  The present invention can be used for a proton conductive membrane of a fuel cell.

It is a graph which shows the electrical conductivity in each temperature of a melamine pyrophosphate. It is a graph which shows the electrical conductivity in each temperature of a melamine polyphosphate. It is a graph which shows the electrical conductivity in each temperature of the heating thing of tetraimido cyclotetraphosphate ammonium. It is a graph which shows the electric power generation characteristic of tetraimidocyclotetraphosphate ammonium. It is a graph which shows the electric power generation characteristic of tetraimidocyclotetraphosphoric acid. It is a graph which shows the electrical conductivity of tetraimidocyclotetraphosphoric acid. It is a graph which shows the electrical conductivity of tetraimidocyclotetraphosphoric acid. It is a graph which shows the electrical conductivity of tetraimidocyclotetraphosphoric acid. It is a graph which shows the electrical conductivity of tetraimidocyclotetraphosphoric acid. It is a block diagram of a fuel cell.

Claims (3)

A fuel cell solid electrolyte having proton conductivity, the main component being a phosphoric acid compound containing nitrogen, wherein the phosphoric acid compound containing nitrogen has condensed phosphoric acid or imidopolyphosphoric acid, and melamine Fuel cell solid electrolyte. At room temperature ^{10 -4 ~10 -5 S · cm -1} , the fuel cell solid electrolyte according to claim 1, which shows a ¹⁰ -3 ^{to 10 -5} electrical conductivity of S · cm ^-1 at 200 ° C..   A fuel cell solid electrolyte having proton conductivity made of condensed ammonium phosphate or made of ammonium imidopolyphosphate.

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