Proton conductor, method for producing same, proton conductor composite film, and method for producing same

Abstract

Provided is a method for producing a proton conductor, the method comprising: hydrolyzing and polycondensing a compound represented by formula (1) and a compound represented by formula (2) so as to form a siloxane bond, thereby obtaining a precursor 1 that has an -SH group and a group represented by formula (3); oxidizing the -SH group of the precursor 1 so as to obtain a precursor 2 that has a sulfonic acid group and a group represented by formula (3); and subsequently crosslinking the precursor 2 by means of polyvalent metal ions.　Formula (1): R1 s(OR2)3-sSi-Q1-SH, Formula (2): R3 t(OR4)3-tSi-Q2-P(=O)R5 u(OR6)2-u, Formula (3): -P(=O)R5 u(OR6)2-u

Description

Proton conductor and method for manufacturing the same, and proton conductor composite membrane and method for manufacturing the same

[0001] The present invention relates to a proton conductor, a method for producing the same, and a proton conductor composite membrane, and a method for producing the same. This application claims priority based on Japanese Patent Application No. 2024-038496, filed on March 12, 2024, the contents of which are incorporated herein by reference.

[0002] Proton conductors are known to be used in various devices such as fuel cells, electrochromic elements, sensors, etc. Various materials for such proton conductors have been investigated.

[0003] For example, Patent Document 1 discloses a proton conductor containing a metal ion, an oxoanion, and a proton-coordinating molecule, in which the oxoanion and / or the proton-coordinating molecule is coordinated to the metal ion to form a coordination polymer. Although the proton conductor disclosed in Patent Document 1 has high proton conductivity, it is easily soluble in water and has concerns about durability and shape retention, particularly in high-humidity environments.

[0004] Furthermore, proton conductors using silsesquioxanes or siloxanes are known from the viewpoint of imparting durability and shape retention. For example, Patent Document 2 discloses a proton conductor in which a phosphate group is introduced at the end of a silsesquioxane derivative having a so-called double-decker structure. Furthermore, Non-Patent Document 1 discloses a proton conductor made of a ladder-type polysilsesquioxane having sulfonic acid groups in its side chains.

[0005] JP 2017-33704 A JP 2013-7007 A

[0006] Chem.Eur.J.2014,20,p9394-9399

[0007] However, the proton conductor of Patent Document 2 exhibits high proton conductivity under humidified conditions, but low proton conductivity under non-humidified conditions. Furthermore, the proton conductor of Non-Patent Document 1 is thought to have difficulty retaining water at temperatures above 100°C, resulting in a decrease in proton conductivity. The present invention has been made in view of the above circumstances, and aims to provide a proton conductor and a proton conductor composite membrane that have high proton conductivity under various conditions.

[0008] In order to achieve the above object, the present invention employs the following configuration: [1] A method for producing a proton conductor, comprising hydrolyzing and polycondensing a compound represented by the following formula (1) with a compound represented by the following formula (2) to form a siloxane bond, thereby obtaining a precursor 1 having an -SH group and a group represented by the following formula (3), oxidizing the -SH group of the precursor 1 to obtain a precursor 2 having a sulfonic acid group and a group represented by the following formula (3), and then crosslinking the precursor 2 with a polyvalent metal ion. １ ｓ (OR ２ ) ３－ｓ Si-Q １ -SH...Formula (1) R ３ ｔ (OR ４ ) ３－ｔ Si-Q ２ -P(=O)R ５ ｕ (OR ６ ) ２－ｕ ...Formula (2) -P(=O)R ５ ｕ (OR ６ ) ２－ｕ ... Formula (3) [In the above formulas (1) to (3), R １ , R ２ , R ３ , R ４ , R ５ , R ６ are each independently H, CH ３ , C ２ H ５ , C ３ H ７s is 0, 1, or 2. However, in at least some of the compounds represented by formula (1), s is 0 or 1. When s is 2, R １ may be the same or different, and when s is 0 or 1, R ２ may be the same or different. t is 0, 1, or 2. However, in at least some of the compounds represented by formula (2), t is 0 or 1. When t is 2, R ３ may be the same or different, and when t is 0 or 1, R ４ may be the same or different from each other. u is 0 or 1, and when u is 0, R ６ may be the same or different. １ , Q ２ are each independently an alkylene group or a fluoroalkylene group having 1 to 20 carbon atoms, or an arylene group or a fluoroarylene group having 1 to 20 carbon atoms, and these groups may have one or more of an oxygen atom, a nitrogen atom, a boron atom, a phosphorus atom, a sulfur atom, and a silicon atom.] [2] The method for producing a proton conductor according to [1], wherein the compound represented by formula (1) is (3-sulfanylpropyl)trimethoxysilane. [3] The method for producing a proton conductor according to [1] or [2], wherein the compound represented by formula (2) is (2-diethylphosphatoethyl)triethoxysilane. [4] The method for producing a proton conductor according to any one of [1] to [3], wherein the metal element that becomes the polyvalent metal ion is one or more selected from Al, Ti, Zr, Fe, and Ce. [5] The method for producing a proton conductor according to any one of [1] to [3], wherein the polyvalent metal ion is Ce ３＋ ions and Ce ４＋[6] A method for producing a proton conductor according to any one of [1] to [5], wherein the ratio of the compound represented by formula (1) to the total amount of the compound represented by formula (1) and the compound represented by formula (2) is 5 to 95 mol %. [7] A method for producing a proton conductor according to any one of [1] to [6], wherein the crosslinking with the polyvalent metal ion is carried out in the presence of a compound having a group represented by the following formula (4): -P(=O)R ７ ｖ (OR ８ ) ２－ｖ ... Formula (4) [In the above formula (4), R ７ , R ８ are each independently H, CH ３ , C ２ H ５ , C ３ H ７ v is 0 or 1, and when v is 0, R ８ may be the same or different.] [8] The method for producing a proton conductor according to [7], wherein the compound having a group represented by formula (4) is one or more compounds selected from phosphoric acid, methylphosphonic acid, 1,2-ethylenediphosphonic acid, nitrilotris(methylenephosphonic acid), and complete or partial alkyl esters thereof. [9] An oligomer having a siloxane bond, which has a sulfonic acid group and a group represented by the following formula (3), and at least a part of R in the group represented by formula (3) ６ is eliminated, and the eliminated R ６ A proton conductor in which at least some of the phosphorus atoms of the group represented by the following formula (3) are bonded to polyvalent metal ions via oxygen atoms at positions where -P(=O)R was previously bonded. ５ ｕ (OR ６ ) ２－ｕ ... Formula (3) [In the above formula (3), R ５ , R ６ are each independently H, CH ３ , C ２ H ５ , C ３ H７ u is 0 or 1, and when u is 0, R ６ may be the same or different.]

[10] The proton conductor according to [9], wherein the metal element that forms the polyvalent metal ion is one or more selected from Al, Ti, Zr, Fe, and Ce.

[11] The polyvalent metal ion is Ce ３＋ ions and Ce ４＋

[12] The proton conductor according to any one of [9] to

[11] , wherein the ratio of the sulfonic acid groups to the total amount of the group represented by formula (3), the group derived from the group represented by formula (3) bonded to the polyvalent metal ion, and the sulfonic acid groups is 5 to 95 mol %.

[13] The proton conductor according to any one of [9] to

[11] , further comprising a compound having a group represented by formula (4) below, wherein at least a part of R in the group represented by formula (4) below is ８ is eliminated, and the eliminated R ８ The proton conductor according to any one of [9] to

[12] , wherein at least some of the phosphorus atoms in the group represented by the following formula (4) are bonded to the polyvalent metal ion via oxygen atoms at positions where -P(=O)R was previously bonded: ７ ｖ (OR ８ ) ２－ｖ ... Formula (4) [In the above formula (4), R ７ , R ８ are each independently H, CH ３ , C ２ H ５ , C ３ H ７ v is 0 or 1, and when v is 0, R ８may be the same or different.]

[14] A method for producing a proton conductor composite membrane, comprising impregnating a hydrophilic porous membrane with the proton conductor obtained by the method for producing a proton conductor according to any one of [1] to [8].

[15] A method for producing a proton conductor composite membrane, comprising impregnating a hydrophilic porous membrane with the proton conductor according to any one of [9] to

[13] .

[16] A method for producing a proton conductor composite membrane according to

[14] or

[15] , wherein the porous membrane is a porous polytetrafluoroethylene membrane that has been hydrophilized.

[17] A proton conductor composite membrane, comprising a hydrophilic porous membrane impregnated with the proton conductor obtained by the method for producing a proton conductor according to any one of [1] to [8].

[18] A proton conductor composite membrane, comprising a hydrophilic porous membrane impregnated with the proton conductor according to any one of [9] to

[13] .

[19] The proton conductor composite membrane according to

[17] or

[18] , wherein the porous membrane is a porous polytetrafluoroethylene membrane that has been hydrophilically treated.

[0009] According to the proton conductor and its manufacturing method of the present invention, a proton conductor having high proton conductivity under various conditions can be provided. According to the proton conductor composite membrane and its manufacturing method of the present invention, a proton conductor composite membrane having high proton conductivity under various conditions can be provided.

[0010] 1 is a diagram showing a proton conductor according to an embodiment of the present invention; ２９ The results of Si-NMR analysis are shown below. １ 1H-NMR analysis results. 1A and 1B show the results of molar mass distribution measurement of precursor 1a. 1B and 1C show the results of X-ray diffraction measurement of precursor 1a and precursor 2a. 1C and 1D show the results of H-NMR analysis of precursor 1a. ３１ The molar ratio of Al to Si (z Ａｌ The results are shown in Table 1. The ionic conductivity of each proton conductor A was measured in a non-humidified atmosphere when the molar ratio of phosphoric acid to Si (z ＰＡ) in a non-humidified atmosphere. The ionic conductivity of proton conductor A is measured in a humidified atmosphere. The TGA-DTA measurement results of proton conductor A are shown. The molar ratio of P to Si (z ＴＭＰ The results are shown in Table 1. The ionic conductivity of each proton conductor B is measured under a non-humidified atmosphere when the molar ratio of P to Si (z ＤＭＰ ) in a non-humidified atmosphere. The results of measurement of ionic conductivity of proton conductor C, which has a different structure, in a non-humidified atmosphere. The results of measurement of ionic conductivity of proton conductor D, which has a different structure, in a non-humidified atmosphere. The results of measurement of ionic conductivity of proton conductor A-2 and proton conductor composite membrane A, which has a non-humidified atmosphere. The results of measurement of ionic conductivity of proton conductor E, which has a non-humidified atmosphere. The results of measurement of ionic conductivity of proton conductor F, which has a non-humidified atmosphere.

[0011] <Method for Proton Conductor Production> The method for producing a proton conductor according to this embodiment includes the following steps 1 to 3. Step 1: A step of forming a siloxane bond by hydrolyzing and polycondensing a compound represented by formula (1) described below with a compound represented by formula (2) described below to obtain precursor 1 having an —SH group and a group represented by formula (3) described below. Step 2: A step of oxidizing the —SH group of precursor 1 to obtain precursor 2 having a sulfonic acid group and a group represented by formula (3) described below. Step 3: A step of crosslinking precursor 2 with a polyvalent metal ion.

[0012] [Step 1] Step 1 is a step of forming a siloxane bond by hydrolysis and polycondensation of a compound represented by formula (1) described below (hereinafter may be referred to as "compound (1)") and a compound represented by formula (2) described below (hereinafter may be referred to as "compound (2)"), thereby obtaining a precursor 1 having an -SH group and a group represented by formula (3) described below.

[0013] Compound (1) is represented by the following formula (1): １ ｓ (OR ２ ) ３－ｓ Si-Q １ -SH Formula (1) In the above formula (1), R １, R ２ are each independently H, CH ３ , C ２ H ５ , C ３ H ７ s is 0, 1, or 2. However, in at least some of the compounds represented by formula (1), s is 0 or 1. When s is 2, R １ may be the same or different, and when s is 0 or 1, R ２ may be the same or different. １ represents an alkylene group or a fluoroalkylene group having 1 to 20 carbon atoms, or an arylene group or a fluoroarylene group having 1 to 20 carbon atoms, and these groups may contain one or more of an oxygen atom, a nitrogen atom, a boron atom, a phosphorus atom, a sulfur atom, and a silicon atom.

[0014] R １ is CH ３ , C ２ H ５ Preferably, either of CH ３ It is more preferable that R ２ is CH ３ , C ２ H ５ Preferably, either of CH ３ It is more preferable that s is 0 or 1, and particularly preferable that s is 0. Compound (1) in which s is 0 is likely to form a three-dimensional structure through siloxane bonds, and SiOH groups that exhibit hydrophilicity are likely to remain. Compound (1) in which s is 1 is likely to form a chain structure through siloxane bonds.

[0015] The proportion of compound (1) in which s is 0 in compound (1) is preferably 10 to 100 mol %, more preferably 50 to 100 mol %. When the proportion of compound (1) in which s is 0 is equal to or greater than the preferred lower limit, a proton conductor that is hydrophilic, has a three-dimensional structure, and is excellent in mechanical strength is easily obtained.

[0016] The proportion of compound (1) in which s is 0 or 1 is preferably 50 to 100 mol %, more preferably 80 to 100 mol %. When the proportion of compound (1) in which s is 0 or 1 is equal to or greater than the preferred lower limit, a proton conductor that is hydrophilic, has a three-dimensional structure, and is excellent in mechanical strength is easily obtained.

[0017] Q １ is preferably an alkylene group having 1 to 10 carbon atoms, a fluoroalkylene group, an arylene group, or a fluoroarylene group, and more preferably an alkylene group having 3 carbon atoms. １ may contain the heteroatom. １ When Q has an oxygen atom, it can be contained as —OH bonded to one carbon atom constituting the alkylene group or as —O— present between two carbon atoms. １ When the group has a nitrogen atom, —NH ２ , -NH- between two carbon atoms, or ≡N between three carbon atoms.

[0018] Q １ When a boron atom is contained, -B(OH) is bonded to one carbon atom constituting an alkylene group or the like. ２ , =BOH between two carbon atoms, or ≡B between three carbon atoms. １ When a group has a phosphorus atom, it is —P(═O)(OH) bonded to one carbon atom constituting an alkylene group or the like. ２ , =P(=O)OH between two carbon atoms, or ≡PO between three carbon atoms.

[0019] Q １ has a sulfur atom, -SH or -SO bonded to one carbon atom constituting the alkylene group or the like ３ H, or —S—, —SO—, or —SO , which is present between two carbon atoms. ２ - can be included as Q １ When the alkylene group has a silicon atom, the —Si(OH) bonded to one carbon atom constituting the alkylene group or the like is３ , present between two carbon atoms = Si(OH) ２ , ≡Si(OH) between three carbon atoms, or Si between four carbon atoms.

[0020] Specific examples of compound (1) include (sulfanylmethyl)trimethoxysilane, (2-sulfanylethyl)trimethoxysilane, (3-sulfanylpropyl)trimethoxysilane, (4-sulfanylbutyl)trimethoxysilane, (sulfanylmethyl)triethoxysilane, (2-sulfanylethyl)triethoxysilane, (3-sulfanylpropyl)triethoxysilane, and (4-sulfanylbutyl)triethoxysilane. Among these, (3-sulfanylpropyl)trimethoxysilane is preferred because of its easy availability.

[0021] Compound (2) is represented by the following formula (2): ３ ｔ (OR ４ ) ３－ｔ Si-Q ２ -P(=O)R ５ ｕ (OR ６ ) ２－ｕ ... Formula (2) In the above formula (2), R ３ , R ４ , R ５ , R ６ are each independently H, CH ３ , C ２ H ５ , C ３ H ７ t is 0, 1, or 2. However, t in at least some of the compounds represented by formula (2) is 0 or 1. When t is 2, R ３ may be the same or different, and when t is 0 or 1, R ４ may be the same or different from each other.

[0022] u is 0 or 1, and when u is 0, R ６ may be the same or different. ２are each independently an alkylene group or a fluoroalkylene group having 1 to 20 carbon atoms, or an arylene group or a fluoroarylene group having 1 to 20 carbon atoms, and these groups may have one or more of an oxygen atom, a nitrogen atom, a boron atom, a phosphorus atom, a sulfur atom, and a silicon atom.

[0023] R ３ is CH ３ , C ２ H ５ Preferably, either of CH ３ It is more preferable that R ４ is CH ３ , C ２ H ５ It is preferable that R ５ is CH ３ , C ２ H ５ Preferably, either of CH ３ It is more preferable that R ６ is CH ３ , C ２ H ５ It is preferable that either of the above is used.

[0024] t is preferably 0 or 1, and particularly preferably 0. Compound (2) in which t is 0 is likely to form a three-dimensional structure through siloxane bonds and tends to leave residual SiOH groups that exhibit hydrophilicity. Compound (2) in which t is 1 is likely to form a chain structure through siloxane bonds.

[0025] The proportion of compound (2) in which t is 0 in compound (2) is preferably 10 to 100 mol %, more preferably 50 to 100 mol %. When the proportion of compound (2) in which t is 0 is equal to or greater than the preferred lower limit, a proton conductor that is hydrophilic, has a three-dimensional structure, and is excellent in mechanical strength is easily obtained.

[0026] The proportion of compound (2) in which t is 0 or 1 in compound (2) is preferably 50 to 100 mol %, more preferably 80 to 100 mol %. When the proportion of compound (2) in which t is 0 or 1 is equal to or greater than the preferred lower limit, a proton conductor that is hydrophilic, has a three-dimensional structure, and is excellent in mechanical strength is easily obtained.

[0027] Preferably, u is 0. Compound (2) in which u is 0 easily forms a network structure due to crosslinking with polyvalent metal ions, and a proton conductor with excellent mechanical strength is easily obtained. ２ is preferably an alkylene group having 1 to 10 carbon atoms, a fluoroalkylene group, an arylene group, or a fluoroarylene group, and more preferably an alkylene group having 2 carbon atoms. ２ may contain the heteroatom. ２ A specific embodiment in which Q contains a heteroatom is １ This is the same as in the case of

[0028] Specific examples of compound (2) include (dimethylphosphatomethyl)trimethoxysilane, (2-dimethylphosphatoethyl)trimethoxysilane, (3-dimethylphosphatopropyl)trimethoxysilane, (4-dimethylphosphatobutyl)trimethoxysilane, (diethylphosphatomethyl)triethoxysilane, (2-diethylphosphatoethyl)triethoxysilane, (3-diethylphosphatopropyl)triethoxysilane, and (4-diethylphosphatobutyl)triethoxysilane. Among these, (2-diethylphosphatoethyl)triethoxysilane is preferred because of its easy availability.

[0029] The proportion of compound (1) relative to the total amount of compound (1) and compound (2) is preferably 5 to 95 mol%, more preferably 10 to 90 mol%, even more preferably 30 to 90 mol%, and particularly preferably 50 to 90 mol%. When the proportion of compound (1) is equal to or greater than the preferred lower limit, high proton conductivity is easily obtained. When the proportion of compound (1) is equal to or less than the preferred upper limit, crosslinking points by polyvalent metal ions are easily secured, and the mechanical strength and water resistance of the resulting proton conductor are improved.

[0030] Compound (1) and compound (2) are subjected to hydrolysis and polycondensation to form a siloxane bond, thereby obtaining precursor 1 having a -SH group derived from compound (1) and a group represented by the following formula (3) (hereinafter sometimes referred to as "functional group (3)"): -P(=O)R ５ ｕ (OR ６ ) ２－ｕ ... Formula (3) Since the functional group (3) is a group derived from the compound (2), R in the above formula (3) ５ , R ６ are R in formula (2), respectively. ５ , R ６ is the same as

[0031] The hydrolysis polycondensation reaction in step 1 is preferably carried out under acidic conditions. The pH during the reaction is preferably 0 to 6, more preferably 1 to 3. Examples of pH adjusters include hydrochloric acid, nitric acid, sulfuric acid, formic acid, and acetic acid. The temperature during the reaction in step 1 is preferably 20 to 100°C, more preferably 60 to 80°C. The reaction time, which varies depending on the reaction temperature, is preferably 1 to 72 hours, more preferably 6 to 48 hours.

[0032] Precursor 1 is liquid. Although Precursor 1 contains a large amount of unreacted SiOH, polycondensation between SiOH groups is slow, and the viscosity remains almost unchanged even after storage at room temperature for two months. X-ray diffraction measurements conducted to investigate the reason for this revealed that Precursor 1 is composed of oligomer particles of relatively uniform size with an average particle size of approximately 1 nm, and that the particles have a core-shell structure consisting of an amorphous silica core containing a large amount of SiOH groups and an organic functional group moiety covering the outside. In other words, it is believed that because unreacted SiOH is present inside the oligomer particles, polycondensation between the oligomer particles is less likely to occur, thereby preventing viscosity increase.

[0033] [Step 2] Step 2 is a step in which the -SH group of precursor 1 obtained in step 1 is oxidized to obtain precursor 2 having a sulfonic acid group and functional group (3). Examples of the oxidizing agent include aqueous hydrogen peroxide and sodium hypochlorite. Of these, aqueous hydrogen peroxide is preferred because it is easy to remove any remaining oxidizing agent. The reaction temperature in step 2 is preferably 10 to 60°C, more preferably 20 to 40°C. The reaction time varies depending on the reaction temperature, but is preferably 1 to 96 hours, more preferably 12 to 72 hours.

[0034] The oxidizing agent generates active oxygen, and if it remains in the proton conductor, it may attack the organic functional groups and cause deterioration of the proton conductor, so it is not preferable. When hydrogen peroxide water is used as the oxidizing agent, it is preferable to insert a platinum plate to remove the hydrogen peroxide remaining after the reaction.

[0035] The temperature when the platinum plate is introduced and the remaining hydrogen peroxide is removed is preferably 20 to 80°C, more preferably 30 to 60°C. The time required for removal depends on the temperature, but is preferably 1 to 96 hours, more preferably 12 to 48 hours. It is also possible to proceed to step 3 as an aqueous solution without drying the solution at the end of step 2. In this case, if removing the oxidizing agent does not have any adverse effect on the proton conductor, or if the adverse effect is negligible, the step of removing the oxidizing agent in step 2 may be omitted.

[0036] [Step 3] Step 3 is a step of crosslinking precursor 2 obtained in step 2 with polyvalent metal ions. When precursor 2 obtained in step 2 is an aqueous solution, polyvalent metal ions and the like are added to the aqueous solution of precursor 2. When precursor 2 obtained in step 2 is dried and in a solid state, precursor 2 is dissolved in water together with polyvalent metal ions and the like. Note that when the step of removing the oxidizing agent in step 2 is omitted and drying is performed in step 3, it is preferable to remove the oxidizing agent before drying.

[0037] The metal element that becomes the polyvalent metal ion can be selected from metal elements of the 3rd to 6th periods of Group 2, metal elements of the 3rd to 5th periods of Group 4 and later, or rare earth elements. Among them, one or more metal elements selected from Al, Ti, Zr, Fe, and Ce are preferred. Examples of ions of these metals include Al, ３＋ , Ti ４＋ , Zr ４＋ , and Fe ３＋ , Ce ３＋ , Ce ４＋ etc.

[0038] In particular, Ce ３＋ and Ce ４＋ It is preferable that the polyvalent metal ion contains one or both of Ce. ３＋ and Ce ４＋ It is particularly preferred that all or part of the polyvalent metal ions are Ce. ３＋ and Ce ４＋ If either or both of ３＋ and Ce ４＋ Since active oxygen is removed by one or both of the above, it is possible to omit the step of removing hydrogen peroxide, etc. There are no particular limitations on the counter ions of the polyvalent metal ions, but chloride ions, nitrate ions, sulfate ions, acetate ions, etc., whose salts are water-soluble, can be used.

[0039] The ratio of the number of moles of polyvalent metal ions to the number of moles of Si atoms constituting precursor 2 is preferably 5 to 100 mol %, more preferably 10 to 50 mol %, although it depends on the type of polyvalent metal ion. If the ratio of the number of moles of polyvalent metal ions is equal to or greater than the preferred lower limit, the mechanical strength and water resistance of the resulting proton conductor are improved. On the other hand, if the ratio is equal to or less than the preferred upper limit, a proton conductor with higher proton conductivity and excellent flexibility is easily obtained.

[0040] Step 3 is preferably carried out in the presence of a compound having a group represented by the following formula (4) (hereinafter, sometimes referred to as "compound (4)"). That is, it is preferable to add a polyvalent metal ion and compound (4) to precursor 2 and allow them to react. Note that, since it may be difficult to uniformly mix the polyvalent metal ion and compound (4) when they are added to precursor 2 simultaneously, it is preferable to appropriately change the order in which they are added to precursor 2 depending on the type of polyvalent metal ion and compound (4).

[0041] -P(=O)R ７ ｖ (OR ８ ) ２－ｖ ... Formula (4) In the above formula (4), R ７ , R ８ are each independently H, CH ３ , C ２ H ５ , C ３ H ７ v is 0 or 1, and when v is 0, R ８ may be the same or different from each other.

[0042] R ７ is CH ３ , C ２ H ５ Preferably, either of CH ３ It is more preferable that R ８ is CH ３ , C ２ H ５By carrying out step 3 in the presence of compound (4), a proton conductor with excellent flexibility can be easily obtained. Increased flexibility of the proton conductor is preferred because it facilitates good contact with the electrode.

[0043] Specific examples of compound (4) include one or more selected from phosphoric acid, methylphosphonic acid, 1,2-ethylenediphosphonic acid, nitrilotris(methylenephosphonic acid), and their complete or partial alkyl esters. Compound (4) may be a complete alkyl ester in which all of the phosphoric acid (-POH) groups are esterified with alkyl groups, or a partial alkyl ester in which only some of the phosphoric acid (-POH) groups are esterified with alkyl groups. The alkyl groups used for alkyl esterification are preferably methyl or ethyl groups.

[0044] The ratio of the group represented by formula (4) in compound (4) to the number of moles of Si atoms constituting precursor 2 is preferably 10 to 200 mol %, more preferably 20 to 100 mol %, depending on the type of compound (4). If the ratio of the group represented by formula (4) is equal to or greater than the preferred lower limit, a proton conductor with excellent flexibility is easily obtained. If it is equal to or less than the preferred upper limit, the mechanical strength and water resistance of the resulting proton conductor are improved.

[0045] The reaction temperature in Step 3 is preferably 50 to 200° C., more preferably 80 to 150° C. The reaction time, which varies depending on the reaction temperature, is preferably 6 to 96 hours, more preferably 24 to 72 hours. The proton conductor of this embodiment is obtained by Step 3.

[0046] Steps 1 to 3 will be specifically described using as an example a case where compound (1) is (3-sulfanylpropyl)trimethoxysilane (hereinafter sometimes referred to as “compound (1a)”) represented by the following formula (1a), compound (2) is (2-diethylphosphatoethyl)triethoxysilane (hereinafter sometimes referred to as “compound (2a)”) represented by the following formula (2a), and step 3 is crosslinked using aluminum chloride in the presence of phosphoric acid (hereinafter sometimes referred to as “compound (4a)”).

[0047] In step 1, compound (1a) and compound (2a) are subjected to hydrolysis polycondensation to obtain precursor 1a having a unit represented by the following formula (5a) and a unit represented by the following formula (6a): The unit represented by the following formula (5a) has an —SH group derived from compound (1a), and the unit represented by the following formula (6a) has a group represented by the following formula (3a) derived from compound (2a).

[0048]

[0049] In the formula (5a), the three O atoms bonded to the Si atom are bonded to other units represented by the formula (5a) or units represented by the formula (6a), and the O atoms are shared between the bonded units. Alternatively, they are bonded to hydrogen atoms to form -OH groups. It is also believed that a small number of methoxy groups bonded to methyl groups remain.

[0050] In the formula (6a), the three O atoms bonded to the Si atom are bonded to the unit represented by the formula (5a) or other units represented by the formula (6a), and the O atoms are shared between the bonded units. Alternatively, they are bonded to hydrogen atoms to form -OH groups. It is also believed that a small amount of ethoxy groups bonded to ethyl groups remain.

[0051] In step 2, the —SH group in the unit represented by formula (5a) is oxidized to a sulfonic acid group, thereby obtaining a precursor 2a having a unit represented by formula (7a) below and a unit represented by formula (6a):

[0052]

[0053] In the formula (7a), the three O atoms bonded to the Si atom are bonded to other units represented by the formula (7a) or units represented by the formula (6a), and the O atoms are shared between the bonded units. Alternatively, they are bonded to hydrogen atoms to form -OH groups. Note that in precursor 2a, the methoxy groups bonded to the methyl groups are considered to have almost disappeared.

[0054] As in precursor 1a, in formula (6a), the three O atoms bonded to the Si atom are bonded to a unit represented by formula (7a) or another unit represented by formula (6a), and the O atoms are shared between the bonded units. Alternatively, they are bonded to hydrogen atoms to form -OH groups. In precursor 2a, the ethoxy groups bonded to the ethyl groups are considered to have almost disappeared.

[0055] In step 3, the units represented by formula (6a) in precursor 2a become crosslinking points and are crosslinked by Al ions. Compound (4a) also bonds to the Al ions. This gives proton conductor A of this example.

[0056] <Proton Conductor> The proton conductor of this embodiment is an oligomer having a siloxane bond, and is a sulfonic acid group and at least a part of R ６ is eliminated, and the eliminated R ６ At least some of the phosphorus atoms in the group represented by formula (3) are bonded to polyvalent metal ions via oxygen atoms at positions where the "R" was bonded. ６ The oxygen atom at the position where R was bonded is ６ may be the oxygen atom to which R was bonded, or the oxygen atom to which R was ６ The oxygen atom to which R was bonded is ６ This means that another oxygen atom may be substituted in its place.

[0057] In addition, at least a part of R in the group represented by the formula (4) ８ is eliminated, and the eliminated R ８ It is preferable that at least some of the phosphorus atoms in the group represented by formula (4) are bonded to the polyvalent metal ion via the oxygen atom at the position where the "R ８ The oxygen atom at the position where R was bonded is ８ may be the oxygen atom to which R was bonded, or the oxygen atom to which R was ８ The oxygen atom to which R was bonded is ８ This means that another oxygen atom may be substituted in its place.

[0058] The oligomer having a siloxane bond is a silsesquioxane or a siloxane, preferably a silsesquioxane. It may also be a hybrid oligomer of a silsesquioxane and a siloxane. The number of Si atoms constituting the oligomer is preferably 3 to 100, more preferably 5 to 50.

[0059] The ratio of the sulfonic acid groups to the total amount of the group represented by formula (3), the group derived from the group represented by formula (3) bonded to the polyvalent metal ion, and the sulfonic acid groups is preferably 5 to 95 mol%, more preferably 10 to 90 mol%, even more preferably 30 to 90 mol%, and particularly preferably 50 to 90 mol%. The ratio of the number of moles of polyvalent metal ions to the number of moles of Si atoms constituting the oligomer varies depending on the type of polyvalent metal ion, but is preferably 5 to 100 mol%, more preferably 10 to 50 mol%. The ratio of the total number of moles of the group represented by formula (4) in compound (4) and the group derived from the group represented by formula (4) bonded to the polyvalent metal ion to the number of moles of Si atoms constituting the oligomer varies depending on the type of compound (4), but is preferably 10 to 200 mol%, more preferably 20 to 100 mol%.

[0060] Figure 1 shows a schematic structure of proton conductor A, which is obtained by reacting compound (1a) with compound (2a), followed by oxidation, and then crosslinking using aluminum chloride in the presence of phosphoric acid (compound (4a)). As shown in Figure 1, proton conductor A is a silsesquioxane oligomer, and the sulfonic acid and phosphonic acid groups are thought to be located on the outside of the oligomer. Furthermore, the phosphonic acid groups in precursor 2a serve as crosslinking points, which are crosslinked by Al ions. Compound (4a) also bonds to Al ions.

[0061] <Method for manufacturing proton conductor composite membrane> The method for manufacturing a proton conductor composite membrane of this embodiment is a method for impregnating a hydrophilic porous membrane with the proton conductor obtained by the method for manufacturing a proton conductor of the above embodiment, or a method for impregnating a hydrophilic porous membrane with the proton conductor of the above embodiment.

[0062] To ensure fluidity that allows impregnation, the proton conductor is preferably used as an impregnation solution by dissolving it in a medium. The medium is preferably an aqueous medium. Specific examples include water, a mixed solvent of water and ethanol, and a mixed solvent of water and methanol. It is also preferable to use a proton conductor in which crosslinking is in progress (crosslinking is not complete), as needed.

[0063] Examples of materials for the hydrophilic porous membrane used in this embodiment include polytetrafluoroethylene (PTFE), polyimide, polyallyl ether, polybenzazole, polyether ether ketone, etc. These materials can be used by subjecting them to hydrophilic treatment, chemical modification, or introduction of side chains as necessary to make them hydrophilic (surface energy of 30 dynes / cm or more = 30 mN / m or more).

[0064] Among the above-mentioned hydrophilic porous membranes, a hydrophilically treated porous polytetrafluoroethylene membrane (hereinafter sometimes referred to as a "hydrophilic porous PTFE membrane") is preferred. The hydrophilic porous PTFE membrane is a hydrophilically treated porous polytetrafluoroethylene membrane.

[0065] Because untreated polytetrafluoroethylene membranes are hydrophobic, it is difficult to impregnate them with an aqueous solution of an oligomer having a siloxane bond. Hydrophilic porous PTFE membranes are made hydrophilic by being subjected to a hydrophilization treatment. Examples of hydrophilization treatments include plasma treatment and coating with a hydrophilic compound.

[0066] The average thickness of the hydrophilic porous PTFE membrane is preferably 0.1 to 200 μm, and more preferably 1 to 100 μm. When the average thickness is equal to or greater than the preferred lower limit, the strength of the proton conductor composite membrane is improved. When the average thickness is equal to or less than the preferred upper limit, a decrease in membrane resistance can be expected. The average thickness is the average value obtained by measuring three randomly selected locations with a micrometer.

[0067] The hydrophilic porous PTFE membrane preferably has a high porosity as long as the strength of the proton conductor composite membrane can be maintained. Higher porosity allows the membrane to be sufficiently impregnated with the oligomer having a siloxane bond, thereby improving the proton conductivity of the proton conductor composite membrane.

[0068] The hydrophilic porous PTFE membrane may be a commercially available product, such as the hydrophilic PTFE membrane filter H100A manufactured by Advantec Toyo Co., Ltd.

[0069] In order to thoroughly impregnate the hydrophilic porous PTFE membrane with the impregnation solution, it is preferable to carry out the impregnation under reduced pressure.

[0070] <Proton conductor composite membrane> The proton conductor composite membrane of this embodiment is a composite membrane in which a hydrophilic porous PTFE membrane is impregnated with the proton conductor obtained by the method for producing a proton conductor of the above embodiment, or a composite membrane in which a hydrophilic porous PTFE membrane is impregnated with the proton conductor of the above embodiment.

[0071] <Mechanism of Action> In the proton conductor of the above embodiment, the sulfonic acid groups and the POH groups remaining in the functional groups derived from compound (2) and compound (4) function as proton charge carriers. Furthermore, the functional groups derived from compound (2) serve as crosslinking points, forming a three-dimensional network structure with the polyvalent metal ions. This makes it easy to obtain a proton conductor with excellent mechanical strength. Furthermore, even if the amount of functional groups derived from compound (2) is reduced, a sufficient three-dimensional network structure can be formed by crosslinking with the polyvalent metal ions. This allows for a larger amount of sulfonic acid groups that do not contribute to crosslinking, thereby achieving high proton conductivity.

[0072] Furthermore, since the oligomer contains hydrophilic functional groups such as sulfonic acid groups, phosphonic acid groups, and hydroxyl groups, it is believed that it can easily retain water around it, and as a result, it can maintain its function as a proton conductor even under non-humidified and high-temperature conditions. Furthermore, when compound (4) is used, the network formation due to crosslinking is moderately alleviated, which is believed to impart flexibility to the resulting proton conductor.

[0073] Furthermore, in the method for producing a proton conductor according to the above embodiment, precursor 1 obtained in step 1 is liquid, facilitating the subsequent reaction in step 2. Precursor 1 is resistant to thickening despite containing many hydroxyl groups. This is thought to be because precursor 1 is made of oligomer particles of uniform size, and has a core-shell structure consisting of an amorphous silica core containing many hydroxyl groups and an organic functional group moiety covering the outside. Adjacent oligomer particles are thought to have a structure in which they are in contact with each other through a shell layer consisting of organic functional groups on the surface.

[0074] The proton conductor composite membrane of the above embodiment is impregnated with the oligomer, which makes it easy to maintain the required strength while reducing the overall thickness of the proton conductor. Furthermore, since a hydrophilic porous PTFE membrane is used as the impregnated membrane, the oligomer can be sufficiently impregnated into the membrane. Therefore, high proton conductivity similar to that of the proton conductor of the above embodiment can be obtained.

[0075] <Synthesis of Proton Conductor A-1> [Step 1] Dilute hydrochloric acid was added to a mixture of 8 mmol of (3-sulfanylpropyl)trimethoxysilane (compound (1a), manufactured by Tokyo Chemical Industry Co., Ltd.) and 2 mmol of (2-diethylphosphatoethyl)triethoxysilane (compound (2a), manufactured by Gelest) to prepare a solution with a molar ratio of compound (1a):compound (2a):water:HCl of 0.8:0.2:3:0.002, and the container was sealed and stirred at 20°C for 3 hours. The resulting solution was aged at 80°C for 1 day while the container was sealed, and then the container was opened and dried in the air at 60°C for 3 hours, and then vacuum dried at 60°C for 1 day to obtain liquid precursor 1a.

[0076] [Step 2] Precursor 1a was treated with 30% by mass of hydrogen peroxide solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to give compound (1a):H２ O ２ The solution was added so that the molar ratio was 1:5, the vessel was sealed, and the mixture was stirred at 20°C for 2 days. The vessel was then opened, and a platinum plate was placed in the solution to remove unreacted hydrogen peroxide. The solution was then left to stand at 20°C for 2 days, and further dried in the air at 40°C for 1 day to obtain Precursor 2a.

[0077] [Step 3] Precursor 2a, aluminum (III) chloride hexahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and phosphoric acid (PA, 85% by mass, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed in a solution containing 20% ​​aluminum (III) chloride and 20% phosphorus (PA) in a ratio of 1:1 to 1:1, where the molar ratio of Al and P (phosphorus) relative to Si in precursor 2a is z shown in Tables 2 and 3 and Figures 7 to 9, respectively. Ａｌ , z ＰＡ The solution was dissolved in 5 mL of distilled water so that the ＰＡ The molar ratio of P shown is the molar ratio of P contained in PA, and does not include P contained in precursor 2a.

[0078] The resulting solution was aged in a sealed container at 100° C. for one day, and then the container was opened and dried in the air at 100° C. for one day. Of the resulting proton conductors A-1, those in a solid state were redissolved in 5 mL of distilled water and dried in the air at 60° C. for one day to prepare flat plate samples with a diameter of 30 mm and a thickness of 1.0 to 1.5 mm.

[0079] <Analysis of Precursor 1a and Precursor 2a> [Average number of bridging oxygen atoms] Figure 2 shows the average number of bridging oxygen atoms in Precursor 1a and Precursor 2a. ２９ Si-NMR analysis (59.7 MHz, solvent for precursor 1a: CDCl ３ , solvent of precursor 2a: D ２ The results of O) are shown.

[0080] T in Figure 2 ２ From the peak intensity, the ratio of Si with 2 siloxane bonds f ２ To, T ３ From the peak strength of ３ The results are shown in Table 1. Note that no peak corresponding to Si with one siloxane bond was observed for any of the precursors. From these results, the average number of bridging oxygen atoms per Si atom, m, was calculated to be 2.65 (2 × 0.35 + 3 × 0.65) for precursor 1a and 2.68 (2 × 0.32 + 3 × 0.68) for precursor 2a.

[0081]

[0082] [Hydrolysis rate] Figure 3 shows the hydrolysis rate of precursor 1a and precursor 2a. １ H-NMR analysis (300 MHz, solvent for precursor 1a: CDCl ３ , solvent of precursor 2a: D ２ The symbols attached to each peak in FIG. 3 correspond to the hydrogen atoms at the corresponding symbol positions in the structural formula shown in FIG. 3, and the peak intensity corresponding to each symbol x is shown as I ｘ It is expressed as:

[0083] The residual ratio f of the methoxy group contained in the compound (1a) in the precursor 1a ＳｉＯＭｅ and the residual rate f of the ethoxy group contained in compound (2a) ＳｉＯＥｔ is calculated by the following formulas (k1) and (k2): ＳｉＯＭｅ =I ｅ / (9 x 0.8) x 2 / I ｂ　　 ...(k1) f ＳｉＯＥｔ =I ｈ / (6 × 0.2) × 2 / I ｂ　　 ...(k2)

[0084] Similarly, the residual ratio f of the methoxy group contained in the compound (1a) in the precursor 2a ＳｉＯＭｅ and the residual rate f of the ethoxy group contained in compound (2a) ＳｉＯＥｔ is calculated by the following formulas (k'1) and (k'2): ’ＳｉＯＭｅ =I ｅ’ / (9 x 0.8) x 2 / I ｂ’　　 ...(k'1) f ’ＳｉＯＥｔ =I ｈ’ / (6 × 0.2) × 2 / I ｂ’　　 ...(k'2)

[0085] The "9" in formula (k1) and formula (k'1) represents the number of hydrogen atoms constituting the methoxy group on the Si atom in compound (1a). The "0.8" in formula (k1) and formula (k'1) represents the ratio of compound (1a) used in step 1. The "6" in formula (k2) and formula (k'2) represents the ratio of CH out of the hydrogen atoms constituting the ethoxy group on the Si atom in compound (2a). ２The "0.2" in formula (k2) and formula (k'2) represents the ratio of compound (2a) used in step 1. In each formula, the peak intensity of the hydrogen atom of b or b', which is not affected by hydrolysis, is normalized (I ｂ , I ｂ’ is 2.00), so "2 / I ｂ " or "2 / I ｂ’ " is multiplied.

[0086] The measurement results of precursor 1a in FIG. ｅ is 0.07, I ｈ is 0.07) into equations (k1) and (k2), and calculate: ＳｉＯＭｅ = 0.0097 f ＳｉＯＥｔ = 0.0583

[0087] Considering that the molar ratio of the methoxy group or the hydrolyzed group thereof on the Si atom of compound (1a) to the ethoxy group or the hydrolyzed group thereof on the Si atom of compound (2a) in precursor 1a is 0.8:0.2, the proportion of alkoxy groups on Si atoms remaining unhydrolyzed in precursor 1a as a whole is calculated to be 1.94% according to the following formula: 0.0097 x 0.8 + 0.0583 x 0.2 = 0.0194

[0088] Therefore, it was confirmed that about 98 mol % of the alkoxy groups bonded to Si were hydrolyzed. On the other hand, in precursor 2a, no peaks corresponding to h' and i' were observed (f ’ＳｉＯＭｅ = f ’ＳｉＯＥｔ = 0), it was confirmed that almost 100 mol % of the alkoxy groups bonded to Si were hydrolyzed.

[0089] [Yield of Sulfonic Acid Groups Bonded to Si Atoms] The molar ratio of sulfonic acid groups bonded to Si atoms to the compound (1a) used as the raw material (hereinafter referred to as "yield of bound sulfonic acid groups") is １ Using the results of H-NMR analysis, it can be calculated using the following formula (k3): The yield of sulfonic acid groups calculated from formula (k3) was 0.94, and it was confirmed that most of the —SH groups were oxidized to sulfonic acid groups.

[0090]

[0091] [Number of hydroxyl groups] The rate f of alkoxy groups on Si atoms of precursor 1a converted to hydroxyl groups ＳｉＯＨ and the rate f' of alkoxy groups on Si atoms of precursor 2a being converted to hydroxyl groups. ＳｉＯＨ was calculated using the average number of bridging oxygen atoms m and the percentage of residual alkoxy groups calculated above, according to the following formulas (k4) and (k'4): ＳｉＯＨ = 1 - (0.8f ＳｉＯＭｅ +0.2f ＳｉＯＥｔ +m / 3)=0.1...(k4) f' ＳｉＯＨ = 1 - (0.8f' ＳｉＯＭｅ +0.2f' ＳｉＯＥｔ +m / 3)=0.1...(k'4)

[0092] f ＳｉＯＨ = 0.1, f' ＳｉＯＨ = 0.1 corresponds to 0.9 (0.1 × 3 × 3) SiOH groups per three Si atoms, respectively, and therefore it was confirmed that both precursor 1a and precursor 2a have approximately one hydroxyl group per three Si atoms.

[0093] [Molecular Weight Measurement] The molar mass distribution of precursor 1a is shown in Figure 4. The measurement was carried out by gel permeation chromatography (GPC) using tetrahydrofuran (40°C) as an eluent, and the molar mass distribution was calculated using a standard polystyrene polymer with a known molar mass.

[0094] As shown in Figure 4, a molar mass distribution was obtained with peaks near 3.0 (molar mass, approximately 1000 g / mol) and 3.3 (molar mass, approximately 2000 g / mol) in logarithmic values. The average molar mass per unit, consisting of 0.8 mol of units represented by the aforementioned formula (5a) and 0.2 mol of units represented by the formula (6a), is 145.2 g / mol. Therefore, the peak near 3.0 corresponds to 7 units in standard polystyrene equivalent, and the peak near 3.3 corresponds to 14 units in standard polystyrene equivalent.

[0095] That is, it was estimated that precursor 1a mainly consisted of an oligomer of about 7 units and an oligomer of about 14 units. The number-average molar mass Mn of precursor 1a was 1.6 × 10 ３ g / mol, and the mass-average molar mass Mm is 2.0 × 10 ３ The molar mass distribution Mm / Mn was 1.25.

[0096] [X-ray Diffraction Measurement] X-ray diffraction measurements were carried out on precursor 1a and precursor 2a. The obtained diffraction patterns are shown in FIG. 5. For comparison, silica glass (a-SiO ２ ), polysilsesquioxane having a linear propyl group as a functional group (Poly(Pr-SQ)), and polysilsesquioxane obtained by hydrolysis and polycondensation of compound (1a) alone (Poly(3-SP-SQ)).

[0097] As shown in FIG. 5, both precursor 1a and precursor 2a were silica glass (a-SiO ２ ) as well as 1.5 Å －１ Peak Q nearby １ This is due to the periodicity (d １ = 2π / Q １ = 4 Å).

[0098] In addition, the precursor 1a and Poly(3-SP-SQ) exhibited a 0.5 to 0.6 Å junction, similar to Poly(Pr-SQ). －１ Another peak Q nearby ０ Peak Q ０ The periodicity (d ０ = 2π / Q ０ = 10.4 to 12.5 Å) correlates with the chain length of the linear alkyl group. ０ is about 0.3 Å －１ This is because the -SH group shifted to -SO ３ This shows an increase in the thickness of the shell layer due to the conversion to H groups.

[0099] These results suggest that precursors 1a and 2a are oligomer particles of relatively uniform size with an average particle size of approximately 1 nm, that they have a core-shell structure consisting of an amorphous silica core containing many SiOH groups and an organic functional group moiety covering the outside, and that adjacent oligomer particles are in contact with each other through a shell layer consisting of organic functional groups on the surface.

[0100] <Crosslinking by Aluminum Ions> [Confirmation of Crosslinking] Figure 6 shows the molar ratio of Al and phosphoric acid to Si in precursor 2a (z Ａｌ , z ＰＡ ) of the proton conductor A-1 obtained as ３１ P-NMR analysis (122MHz, solvent: D ２ In precursor 2a, the group represented by formula (3a) derived from compound (2a) (in FIG. 6, "RPO(OEt) ２ A peak corresponding to the hydroxybenzoate (described as "H2O3") was observed.

[0101] In contrast, in each proton conductor A-1, the group represented by the formula (3a) is hydrolyzed (in FIG. 6, "RPO(OEt)(OH)" and "RPO(OH)" ２ ") was observed. In addition, peaks corresponding to groups derived from the group represented by formula (3a) bonded to Al or phosphate ions bonded to Al (two peaks indicated by "{" in Figure 6) were observed, confirming that the group represented by formula (3a) was hydrolyzed and bonded to Al, and that a portion of the phosphoric acid (PA) was also bonded to Al.

[0102] <Evaluation of Proton Conductor A-1> [Confirmation of State Depending on Crosslinking Conditions] The molar ratio of Al to Si in precursor 2a and phosphoric acid (z Ａｌ , z ＰＡ The state of each plate sample of proton conductor A-1 obtained was checked and classified according to the following criteria. The results are shown in Table 2.

[0103] (Evaluation criteria) ◯: A flexible, solid, flat plate sample was obtained. △: A brittle, solid, flat plate sample was obtained. ×: The sample was liquid, and no solid, flat plate sample was obtained.

[0104]

[0105] As shown in Table 2, z Ａｌ is 0.2 to 0.4, z ＰＡ In the range of z = 0.3 to 0.5, a flexible, solid, flat plate sample was obtained. Ａｌ As z increases, the toughness of the plate specimens tends to increase. ＰＡ As z increases, the flexibility of the plate specimens tends to increase. However, as shown in Table 2, ＰＡ If the value is too large, the proton conductor A-1 becomes a viscous liquid, and a solid flat sample cannot be obtained.

[0106] [Water Resistance] The molar ratio of Al to Si in precursor 2a and phosphoric acid (z Ａｌ , z ＰＡ ) were changed in various ways, and the resulting plate samples of each proton conductor A-1 and a container containing water were placed in a sealed container so that the sample and water would not come into direct contact, and left to stand overnight at room temperature. The state of the plate samples after standing was checked and classified according to the following criteria. The results are shown in Table 3.

[0107] (Evaluation criteria) ◯: The plate sample maintained its solid state. ×: The plate sample deliquesced and became liquid.

[0108]

[0109] As shown in Table 3, z Ａｌ The water resistance of the plate specimens tends to increase as z increases. ＰＡ The results in Tables 2 and 3 show that by promoting cross-linking by Al ions while appropriately relaxing it with phosphoric acid, a flexible solid can be obtained and high water resistance can be achieved.

[0110] [Ionic conductivity in a non-humidified atmosphere] The molar ratio of Al to Si in precursor 2a and phosphoric acid (z Ａｌ , z ＰＡThe molar ratio of Al to Si (z) was varied, and the resulting plate samples of each proton conductor A-1 were sandwiched between gold electrodes with a diameter of 5 mm and placed in a blower dryer (Yamato Scientific Co., Ltd., DKN-300), and AC impedance measurements were performed under the following conditions: Ａｌ ) is shown in Figure 7. ＰＡ The results of changing the values ​​are shown in FIG.

[0111] (Conditions) AC voltage amplitude: 50 mV. Frequency: 1 MHz to 0.1 Hz. Temperature: 40 to 120°C, holding time before measurement: 1 hour. Relative humidity at 40°C: 20%, no humidity.

[0112] As shown in FIG. Ａｌ As shown in Figure 8, the ionic conductivity decreased as z increased. ＰＡ The ionic conductivity tended to increase as the value of (z Ａｌ , z ＰＡ The flat sample with σ = (0.2, 0.5) showed high ionic conductivity under non-humidified and high-temperature conditions. This indicates that high proton conductivity can be achieved by promoting cross-linking by Al ions while appropriately relaxing the cross-linking with phosphoric acid.

[0113] [Ionic Conductivity in Humidified Atmosphere] The molar ratio of Al to Si in precursor 2a and phosphoric acid (z Ａｌ , z ＰＡ A flat plate sample of proton conductor A-1 with a ρ = (0.3, 0.3) was sandwiched between 5 mm diameter gold electrodes, and a beaker containing water was placed in a ventilated oven to maintain a relative humidity of 100%, and AC impedance measurements were performed under the same conditions as in Figures 7 and 8. The results are shown in Figure 9. For comparison, Figure 9 also shows the results of the same flat plate sample measured under the non-humidified conditions shown in Figure 7. As shown in Figure 9, it was confirmed that proton conductor A-1 exhibits even higher ionic conductivity under humidified conditions.

[0114] [Heat resistance] The molar ratio of Al to Si in precursor 2a and phosphoric acid (z Ａｌ , z ＰＡThermogravimetric analysis (TGA) and differential thermal analysis (DTA) were simultaneously performed on a flat plate sample of proton conductor A-1 with a ratio of 1.0 to 1.0 (ratio of 1.0 to 1.0) = (0.2, 0.5). The results are shown in Figure 10. For comparison, TGA and DTA were also simultaneously performed on precursor 2a. The results are shown in Figure 11.

[0115] As shown in Figure 11, an endothermic peak was observed in precursor 2a at 50 to 100°C. This means that in the absence of crosslinking, the adsorbed water is lost at temperatures below 100°C. In contrast, as shown in Figure 10, when the molar ratio of Al to phosphoric acid (z Ａｌ , z ＰＡ For a flat sample of proton conductor A-1 with a temperature of (K) = (0.2, 0.5), the initial weight loss and endothermic peak associated with the desorption of adsorbed water were observed at 170 to 190°C. This confirmed that proton conductor A-1 can retain adsorbed water even in an environment of around 150°C. The weight loss of proton conductor A-1 at 320 to 400°C was accompanied by heat generation, and is therefore thought to be due to the combustion of organic functional groups.

[0116] <Synthesis of Proton Conductor A-2> [Step 1] A liquid precursor 1a was obtained in the same manner as in step 1 of the synthesis of proton conductor A-1.

[0117] [Step 2] Precursor 1a was treated with 30% by mass of hydrogen peroxide solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to give compound (1a):H ２ O ２ The solution was added so that the molar ratio was 1:4, the container was sealed, and the solution was left standing at 40°C for 1 day. After that, the lid of the container was opened, and a platinum plate was placed in the solution to remove unreacted hydrogen peroxide. The solution was then left standing at 40°C for 2 days to obtain an aqueous solution containing precursor 2a.

[0118] [Step 3] Aluminum chloride (III) hexahydrate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and phosphoric acid (PA, 85% by mass, manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were added to an aqueous solution containing precursor 2a, and the molar ratios of Al and P (phosphorus) to Si in precursor 2a were adjusted to z Ａｌ = 0.2, z ＰＡ The solution was added so that z = 0.5 and dissolved.ＰＡ The molar ratio of P shown is the molar ratio of P contained in PA, and does not include P contained in precursor 2a.

[0119] The resulting solution was aged in a sealed container at 120°C for one day, and then the container was opened and dried in the air at 100°C for one day to obtain proton conductor A-2. The resulting proton conductor A-2 was redissolved in 5 mL of distilled water and dried in the air at 60°C for one day to obtain a plate sample with a diameter of 30 mm and a thickness of 1.0 to 1.5 mm.

[0120] <Evaluation of Proton Conductor A-2> [Ionic Conductivity in a Non-Humidified Atmosphere] A flat sample of the obtained proton conductor A-2 was sandwiched between gold electrodes with a diameter of 5 mm, and AC impedance measurement was carried out under the same conditions as in Figures 7 and 8. The results are shown in Figure 15. As shown in Figure 15, good ionic conductivity was obtained.

[0121] <Production of proton conductor composite membrane A> Proton conductor A-2 was obtained in the same manner as in the synthesis of proton conductor A-2. The obtained proton conductor A-2 was dissolved in ethyl alcohol (EtOH) and water (H ２ O) mixed solvent (EtOH:H ２ 0=1:3, mass ratio) to obtain an impregnation solution with a solid content of 20 mass %.

[0122] The obtained impregnation solution was impregnated into a hydrophilic porous PTFE membrane (hydrophilic PTFE membrane filter H100A090C manufactured by Advantec Toyo Co., Ltd.) having a length and width of approximately 30 mm, a thickness of 35 μm, and an average pore size of 1 μm. The ratio of the mass of the hydrophilic porous PTFE membrane to the mass (solid content equivalent) of the proton conductor A-2 in the impregnation solution was 1:9.

[0123] The impregnation was carried out by immersing a hydrophilic porous PTFE membrane, which had been wetted with water in advance, in the impregnation solution placed in a petri dish, placing the membrane in a desiccator, and reducing the pressure in the desiccator for 3 minutes using a diaphragm pump (LABOPORT N840.3, manufactured by KNF Corp.), and then returning the pressure to atmospheric pressure. After the reduced-pressure impregnation, the membrane was dried in the atmosphere at 60°C for 1 hour to obtain a thin film sample with a thickness of approximately 100 μmm.

[0124] <Evaluation of proton conductor composite membrane A> [Ionic conductivity in non-humidified atmosphere] The obtained proton conductor composite membrane A (thin film sample using proton conductor A-2) was sandwiched between gold electrodes with a diameter of 5 mm, and AC impedance measurement was carried out under the same conditions as in Figures 7 and 8. The results are shown in Figure 15. As shown in Figure 15, good ionic conductivity equivalent to that of the flat sample of proton conductor A-2 was obtained.

[0125] <Synthesis of Proton Conductor B> A precursor 1a was obtained in the same manner as in step 1 in the synthesis of proton conductor A-1, and then a precursor 2a was obtained in the same manner as in step 2 in the synthesis of proton conductor A-1.

[0126] In step 3, precursor 2a, aluminum chloride (III) hexahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and trimethyl phosphate (TMP, manufactured by Tokyo Chemical Industry Co., Ltd.) were mixed so that the molar ratios of Al and P (phosphorus) to Si in precursor 2a were z shown in Table 4 and FIG. Ａｌ , z ＴＭＰ It was dissolved in 5 mL of distilled water so that the ＴＭＰ The molar ratio of P shown is the molar ratio of P contained in TMP and does not include P contained in precursor 2a. The obtained solution was treated in the same manner as in the synthesis of proton conductor A-1 to prepare a plate sample having a thickness of 1.0 to 1.5 mm.

[0127] <Evaluation of Proton Conductor B> [Confirmation of State Depending on Crosslinking Conditions] The molar ratio of Al to Si in precursor 2a and P contained in TMP (z Ａｌ , z ＴＭＰ The state of each of the obtained plate samples of proton conductor B was confirmed and classified according to the same criteria as in Table 2. The results are shown in Table 4.

[0128]

[0129] As shown in Table 4, z Ａｌ is 0.2 to 0.4, z ＴＭＰ In the range of z = 0.3 to 0.4, a flexible, solid, flat plate sample was obtained. Ａｌ As z increases, the toughness of the plate specimens tends to increase. ＴＭＰ As the value of σ increases, the flexibility of the flat plate specimens tends to increase.

[0130] [Ionic conductivity in a non-humidified atmosphere] z ＴＭＰ Plate samples of each proton conductor B with different z were sandwiched between gold electrodes with a diameter of 5 mm, and AC impedance measurements were performed under the same conditions as in Figures 7 and 8. The results are shown in Figure 12. As shown in Figure 12, ＴＭＰ The larger the ionic conductivity, the higher the ionic conductivity, especially at high temperatures.

[0131] <Synthesis of Proton Conductor C> A precursor 1a was obtained in the same manner as in step 1 in the synthesis of proton conductor A-1, and then a precursor 2a was obtained in the same manner as in step 2 in the synthesis of proton conductor A-1.

[0132] In step 3, precursor 2a, aluminum (III) chloride hexahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and dimethyl methylphosphonate (DMP, manufactured by Tokyo Chemical Industry Co., Ltd.) were mixed in a manner such that the molar ratio of Al and P (phosphorus) to Si in precursor 2a was z shown in Table 5 and FIG. Ａｌ , z ＤＭＰ It was dissolved in 5 mL of distilled water so that the ＤＭＰ The molar ratio of P shown is the molar ratio of P contained in DMP and does not include P contained in precursor 2a. The obtained solution was treated in the same manner as in the synthesis of proton conductor A-1 to prepare a plate sample having a thickness of 1.0 to 1.5 mm.

[0133] <Evaluation of Proton Conductor C> [Confirmation of State Depending on Crosslinking Conditions] ＤＭＰ The state of the plate samples of each proton conductor C with different z was confirmed and classified according to the same criteria as in Table 2. The results are shown in Table 5. As shown in Table 5, Ａｌ is 0.2, z ＤＭＰ In the range of z = 0.4 to 0.5, a flexible, solid, flat plate sample was obtained. ＤＭＰ As the value of σ increases, the flexibility of the flat plate specimens tends to increase.

[0134]

[0135] [Ionic conductivity in a non-humidified atmosphere] z ＤＭＰPlate samples of each proton conductor C with different z were sandwiched between gold electrodes with a diameter of 5 mm, and AC impedance measurements were performed under the same conditions as in Figures 7 and 8. The results are shown in Figure 13. As shown in Figure 13, ＤＭＰ The larger the ionic conductivity, the greater the tendency.

[0136] <Synthesis of Proton Conductor D> A precursor 1a was obtained in the same manner as in step 1 in the synthesis of proton conductor A-1, and then a precursor 2a was obtained in the same manner as in step 2 in the synthesis of proton conductor A-1.

[0137] In step 3, precursor 2a, aluminum chloride (III) hexahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 1,2-ethylenediphosphonic acid (EDPA, manufactured by Tokyo Chemical Industry Co., Ltd.) were mixed so that the molar ratios of Al and P (phosphorus) to Si in precursor 2a were z Ａｌ = 0.2, z ＥＤＰＡ It was dissolved in 5 mL of distilled water so that z = 0.2. ＥＤＰＡ The molar ratio of P shown is the molar ratio of P contained in EDPA, and does not include P contained in precursor 2a. The obtained solution was treated in the same manner as in the synthesis of proton conductor A-1 to prepare a plate sample having a thickness of 1.0 to 1.5 mm.

[0138] <Evaluation of Proton Conductor D> [Ionic Conductivity in a Non-Humidified Atmosphere] The obtained flat plate sample was sandwiched between gold electrodes with a diameter of 5 mm, and AC impedance measurement was performed under the same conditions as in Figures 7 and 8. The results are shown in Figure 14. As shown in Figure 14, sufficient ionic conductivity was obtained.

[0139] <Synthesis of proton conductor E> [Step 1] A liquid precursor 1a was obtained in the same manner as in step 1 of the synthesis of proton conductor A-1. [Step 2] An aqueous solution containing precursor 2a was obtained in the same manner as in step 2 of the synthesis of proton conductor A-2.

[0140] [Step 3] Zirconium oxide chloride octahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to an aqueous solution containing precursor 2a at a molar ratio of Zr to Si in precursor 2a, z ＺｒThe resulting solution was sealed in a container and aged at 100°C for 40 hours. Then, 5 mL of distilled water and phosphoric acid (PA, 85% by mass, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added to the precursor 2a in a molar ratio of P (phosphorus) to Si of the precursor 2a, z ＰＡ It was added so that z was 0.6. ＰＡ The molar ratio of P shown is the molar ratio of P contained in PA, and does not include P contained in precursor 2a.

[0141] The resulting solution was dried in the air at 40° C. for 1 day. Each of the resulting proton conductors E was redissolved in 5 mL of distilled water and dried in the air at 60° C. for 1 day to prepare a plate sample having a diameter of 30 mm and a thickness of 1.0 to 1.5 mm.

[0142] <Evaluation of Proton Conductor E> [Ionic Conductivity in a Non-Humidified Atmosphere] The obtained flat plate sample was sandwiched between gold electrodes with a diameter of 5 mm, and AC impedance measurement was performed under the same conditions as in Figures 7 and 8. The results are shown in Figure 15. As shown in Figure 15, sufficient ionic conductivity was obtained.

[0143] [Ionic Conductivity in a Humidified Atmosphere] The obtained flat plate sample was sandwiched between gold electrodes having a diameter of 5 mm, and AC impedance measurement was performed using a thermo-hygrostat (IW223, manufactured by Yamato Scientific Co., Ltd.) under the same conditions as those shown in FIGS. 7 and 8, except that the conditions were 80°C and a relative humidity of 50%. As a result, a high ionic conductivity of 126 mS / cm was obtained.

[0144] <Synthesis of proton conductor F> [Step 1] A liquid precursor 1a was obtained in the same manner as in step 1 of the synthesis of proton conductor A-1. [Step 2] 30% by mass of hydrogen peroxide solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the precursor 1a to obtain compound (1a):H ２ O ２ The solution was added so that the molar ratio was 1:4, and the container was sealed and left to stand at 40° C. for 1 day to obtain an aqueous solution containing precursor 2a. Note that no platinum plate was added to remove unreacted hydrogen peroxide.

[0145] [Step 3] Cerium (III) chloride heptahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and trimethyl phosphate (TMP, manufactured by Tokyo Chemical Industry Co., Ltd.) were added to an aqueous solution containing precursor 2a, and the molar ratios of Ce and P (phosphorus) to Si in precursor 2a were adjusted to z Ｃｅ = 0.15, z ＴＭＰ It was added so that z = 0.3. ＴＭＰ The molar ratio of P shown is the molar ratio of P contained in TMP, and does not include P contained in precursor 2a.

[0146] The resulting solution was aged in a sealed container at 120°C for 16 hours, and then dried in air at 100°C for 1 day. The resulting proton conductor F was redissolved in 5 mL of distilled water and dried in air at 60°C for 1 day to prepare a plate sample with a diameter of 30 mm and a thickness of 1.0 to 1.5 mm.

[0147] <Evaluation of Proton Conductor F> [Ionic Conductivity in a Non-Humidified Atmosphere] The obtained flat plate sample was sandwiched between gold electrodes with a diameter of 5 mm, and AC impedance measurement was performed under the same conditions as in Figures 7 and 8. The results are shown in Figure 16. As shown in Figure 16, sufficient ionic conductivity was obtained.

Claims

1. A method for producing a proton conductor, comprising hydrolyzing and polycondensing a compound represented by the following formula (1) with a compound represented by the following formula (2) to form a siloxane bond, thereby obtaining a precursor 1 having an -SH group and a group represented by the following formula (3), oxidizing the -SH group of said precursor 1 to obtain a precursor 2 having a sulfonic acid group and a group represented by the following formula (3), and then crosslinking said precursor 2 with a polyvalent metal ion. １ ｓ (OR ２ ) ３－ｓ Si-Q １ -SH...Formula (1) R ３ ｔ (OR ４ ) ３－ｔ Si-Q ２ -P(=O)R ５ ｕ (OR ６ ) ２－ｕ ...Formula (2) -P(=O)R ５ ｕ (OR ６ ) ２－ｕ ... Formula (3) [In the above formulas (1) to (3), R １ , R ２ , R ３ , R ４ , R ５ , R ６ are each independently H, CH ３ , C ２ H ５ , C ３ H ７ s is 0, 1, or 2. However, in at least some of the compounds represented by formula (1), s is 0 or 1. When s is 2, R １ may be the same or different, and when s is 0 or 1, R ２ may be the same or different. t is 0, 1, or 2. However, in at least some of the compounds represented by formula (2), t is 0 or 1. When t is 2, R ３ may be the same or different, and when t is 0 or 1, R ４ may be the same or different from each other. u is 0 or 1, and when u is 0, R ６ may be the same or different. １ , Q ２ are each independently an alkylene group or a fluoroalkylene group having 1 to 20 carbon atoms, or an arylene group or a fluoroarylene group having 1 to 20 carbon atoms, and these groups may have one or more of an oxygen atom, a nitrogen atom, a boron atom, a phosphorus atom, a sulfur atom, and a silicon atom.

2. The method for producing a proton conductor according to claim 1, wherein the compound represented by formula (1) is (3-sulfanylpropyl)trimethoxysilane.

3. The method for producing a proton conductor according to claim 1, wherein the compound represented by formula (2) is (2-diethylphosphatoethyl)triethoxysilane.

4. The method for producing a proton conductor according to claim 1, wherein the metal element that becomes the polyvalent metal ion is one or more selected from the group consisting of Al, Ti, Zr, Fe, and Ce.

5. The polyvalent metal ion is Ce ３＋ ions and Ce ４＋ The method for producing a proton conductor according to claim 1 , wherein the proton conductor is one or both of the ions.

6. The method for producing a proton conductor according to claim 1, wherein the ratio of the compound represented by formula (1) to the total amount of the compound represented by formula (1) and the compound represented by formula (2) is 5 to 95 mol %.

7. The method for producing a proton conductor according to claim 1, wherein the crosslinking with the polyvalent metal ion is carried out in the presence of a compound having a group represented by the following formula (4): -P(=O)R ７ ｖ (OR ８ ) ２－ｖ ... Formula (4) [In the above formula (4), R ７ , R ８ are each independently H, CH ３ , C ２ H ５ , C ３ H ７ v is 0 or 1, and when v is 0, R ８ may be the same or different.

8. The method for producing a proton conductor according to claim 7, wherein the compound having a group represented by formula (4) is at least one selected from phosphoric acid, methylphosphonic acid, 1,2-ethylenediphosphonic acid, nitrilotris(methylenephosphonic acid), and complete or partial alkyl esters thereof.

9. An oligomer having a siloxane bond, which has a sulfonic acid group and a group represented by the following formula (3), and at least a part of R in the group represented by the following formula (3) ６ is eliminated, and the eliminated R ６ A proton conductor in which at least some of the phosphorus atoms of the group represented by the following formula (3) are bonded to polyvalent metal ions via oxygen atoms at positions where -P(=O)R was previously bonded, thereby forming a bridge. ５ ｕ (OR ６ ) ２－ｕ ... Formula (3) [In the above formula (3), R ５ , R ６ are each independently H, CH ３ , C ２ H ５ , C ３ H ７ u is 0 or 1, and when u is 0, R ６ may be the same or different.

10. The proton conductor according to claim 9, wherein the metal element that forms the polyvalent metal ion is one or more selected from the group consisting of Al, Ti, Zr, Fe, and Ce.

11. The polyvalent metal ion is Ce ３＋ ions and Ce ４＋ 10. The proton conductor of claim 9, wherein the proton conductor is one or both of the ions.

12. The proton conductor according to claim 9, wherein the proportion of the sulfonic acid groups relative to the total amount of the group represented by formula (3), the group derived from the group represented by formula (3) bonded to the polyvalent metal ion, and the sulfonic acid groups is 5 to 95 mol %.

13. Further, it includes a compound having a group represented by the following formula (4), wherein at least a part of R in the group represented by the following formula (4) ８ is eliminated, and the eliminated R ８ 10. The proton conductor according to claim 9, wherein at least some of the phosphorus atoms in the group represented by the following formula (4) are bonded to the polyvalent metal ion via oxygen atoms at positions where -P(=O)R was previously bonded: ７ ｖ (OR ８ ) ２－ｖ ... Formula (4) [In the above formula (4), R ７ , R ８ are each independently H, CH ３ , C ２ H ５ , C ３ H ７ v is 0 or 1, and when v is 0, R ８ may be the same or different.

14. A method for producing a proton conductor composite membrane, comprising impregnating a hydrophilic porous membrane with the proton conductor obtained by the method for producing a proton conductor according to claim 1.

15. A method for producing a proton conductor composite membrane, which comprises impregnating a hydrophilic porous membrane with the proton conductor according to claim 9.

16. The method for producing a proton conductor composite membrane according to claim 14 or 15, wherein the porous membrane is a porous polytetrafluoroethylene membrane that has been hydrophilically treated.

17. A proton conductor composite membrane in which the proton conductor obtained by the method for producing a proton conductor according to claim 1 is impregnated into a hydrophilic porous membrane.

18. A proton conductor composite membrane in which the proton conductor according to claim 9 is impregnated into a hydrophilic porous membrane.

19. The proton conductor composite membrane according to claim 17 or 18, wherein the porous membrane is a porous polytetrafluoroethylene membrane that has been hydrophilically treated.

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