JP5343669B2 - Mesoporous electrolyte - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide mesoporous electrolyte of an organic/inorganic hybrid type in which a threshold value for the amount of acid radicals which is introduced is dramatically great compared with the conventional. <P>SOLUTION: The mesoporous electrolyte includes a mesoporous body composed from silica with mesopores in an ordered array and a perfluoro sulfonic acid group that is expressed by formula (1) that modifies the inner surfaces of the mesopores. The formula (1) is -[C(H,F)<SB>2</SB>]<SB>n</SB>-X-(CF<SB>2</SB>)<SB>m</SB>-SO<SB>3</SB>H when X is O or a direct bond and n, m are respectively integers of 1 or more and 3 or less. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a mesoporous electrolyte, and more specifically, various electrochemical devices such as a fuel cell, a water electrolysis apparatus, a hydrohalic acid electrolysis apparatus, a salt electrolysis apparatus, an oxygen and / or hydrogen concentrator, a humidity sensor, and a gas sensor. The present invention relates to a mesoporous electrolyte that can be used as an electrolyte used in the above.

  Various electrolytes exhibiting ionic conductivity are used in electrochemical devices such as fuel cells and electrolyzers. Among these, solid polymer electrolytes are widely used as electrolyte membranes for fuel cells and electrolytes in catalyst layers because they exhibit high ionic conductivity at relatively low temperatures. However, since the solid polymer electrolyte has low heat resistance, there is a limit to use at a high temperature advantageous in terms of efficiency. In addition, since the solid polymer electrolyte needs to be in an appropriate water-containing state in order to develop high ionic conductivity, there is a limit to its use under low humidification conditions. Further, the solid polymer electrolyte has a problem that when the acid group density is increased in order to increase the ionic conductivity, the polymer electrolyte easily swells or dissolves in water.

On the other hand, as an electrolyte for solving such a problem, for example, an organic / inorganic hybrid type in which an acid group such as a perfluoroalkylsulfonic acid group is introduced into a mesopore of a mesoporous body made of an inorganic material such as silica. Solid electrolytes have been proposed.
Inorganic / organic hybrid solid electrolyte
(1) Since a large amount of acid groups can be introduced into the mesopores, good proton conductivity is exhibited.
(2) Since moisture can be retained in the mesopores by capillary condensation, high proton conductivity is exhibited even under low humidification conditions.
(3) Since the base material is an inorganic material, the shape can be maintained regardless of the ratio of acid groups.
It is said.

Various proposals have heretofore been made for such inorganic / organic hybrid type solid electrolytes and methods for producing the same.
For example, Patent Document 1 discloses that
(1) A porous precursor containing a surfactant is synthesized by adding 1,4-bis (triethoxysilyl) benzene and reacting with an aqueous solution containing the surfactant and NaOH,
(2) the porous precursor particles hydrochloride - is dispersed in an ethanol solution mixture by extracting the _{surfactant, -C 6 H 4 -Si 2 O} 3 - a porous particle having a skeleton,
(3) A solid electrolyte obtained by adding fuming sulfuric acid to a porous particle to cause reaction to sulfonate and oxidize a part of a phenylene group (—C ₆ H ₄ —) contained in the skeleton is disclosed.
In the same document,
(A) By such a method, a solid electrolyte having a central pore diameter of 2.8 nm and a hydrogen ion of 5.5 × 10 ⁻⁴ eq / g is obtained, and
(B) In the obtained solid electrolyte, even if the relative pressure of water vapor is less than 1.0, the pores are sufficiently filled with water,
Is described.

In addition, in Patent Document 2,
(1) Tetraethoxysilane is added to a solution containing hydrochloric acid and a surfactant (F127) to form F127 / silica composite particles,
(2) F127 is burned and removed from the F127 / silica composite particles to form porous silica (SBA-16 particles).
(3) SBA-16 particles are added to a solution in which sultone (precursor) of 1,2,2-trifluoro-2-hydroxy-1-trifluoromethyl ethane sulfonate is dissolved, and silanol groups and precursors on the inner wall of the pores are added. An inorganic / organic hybrid solid electrolyte obtained by polycondensation with a body is disclosed.
This document describes that a solid electrolyte membrane obtained by pressure-molding such an inorganic / organic hybrid solid electrolyte exhibits high proton conductivity.

Non-patent document 1 discloses that a surface silanol group of mesoporous silica is reacted with sultone (cyclic precursor) of 1,2,2-trifluoro-2-hydroxy-1-trifluoromethylethanesulfonic acid. The resulting hybrid organic-inorganic mesoporous silica is disclosed.
In the same document,
(1) When a surface silanol group of mesoporous silica is reacted with a cyclic precursor, a sultone ring of the cyclic precursor is opened, and a perfluoroalkyl chain (—O—CF ₂₎ having a silica skeleton and a sulfonic acid group at the terminal is opened. A covalent bond is formed with —CF (CF ₃ ) —SO ₃ H),
(2) A hybrid organic compound having an S content of 0.51 mmol / g by changing the ratio of the cyclic precursor to the mesoporous silica by changing the ratio of the BET specific surface area of the mesoporous silica with the loading of the organic substance, and (3) -The point at which inorganic mesoporous silica is obtained,
Is described.

Non-Patent Document 2 discloses that silane 1 ((EtO) ₃ Si (CH ₂ ) ₃ (CF ₂ ) ₂ O (CF ₂ ) ₂ SO ₂ F) and silane 2 ((EtO) ₄ Si in the presence of a template. And mesoporous silica-perfluorosulfonic acid hybrid obtained by sol-gel copolycondensation polymerization.
In this document, when the molar ratio of silane 1: silane 2 is 0.02: 0.98, both silanes are completely incorporated and the sulfonic acid group loading is 0.2 mmol / g. It describes that a material having arranged pores is obtained.

Further, Non-Patent Document 3 discloses co-condensation polymerization of hydrolyzed tetraethoxysilane and (OH) ₃ —Si (CH ₂ ) ₃ (CF ₂ ) ₂ O (CF ₂ ) ₂ SO ₃ ⁻ M ^+. A high specific surface area material having a sulfonic acid group in the side chain, obtained by the above process, is disclosed.
In this document, the number of acid equivalents of a material obtained by such a method is 0.18 mequiv. The point of / g is described.

International Publication WO 2002/037506 JP 2007-141625 A

M. Alvaro et al., Chem. Commun., 2004, 956 D.J.Macquarrie et al., Chem. Commun., 2005, 2363 M.A.Harmer et al., Chem. Commun., 1997, 1803

In the method of introducing perfluorosulfonic acid to the inner surface of the mesoporous material, as described above,
(1) a first method of grafting perfluorosulfonic acid groups on the surfaces of pores of a pre-synthesized mesoporous silica; and
(2) Second method of co-condensation polymerization of a monomer having a long molecular length having a perfluorosulfonic acid group in the presence of a surfactant and a monomer (for example, tetraethoxysilane) that forms a skeleton of a mesopore wall ,
It has been known.
However, in the first method, it is difficult to uniformly introduce a precursor to be a perfluorosulfonic acid group into the mesopores. For this reason, the first method has a limit in the amount of acid groups that can be introduced into the pores, and remains at a maximum of 0.51 mmol / g.
In the second method, if the ratio of the monomer having a perfluorosulfonic acid group is too high, the pore structure is easily broken. For this reason, the amount of acid groups that can be introduced into the pores is also limited in the second method, and the maximum is only 0.2 mmol / g.

  The problem to be solved by the present invention is to provide an organic / inorganic hybrid type mesoporous electrolyte having a much larger limit value of the amount of acid groups that can be introduced than in the prior art.

In order to solve the above problems, the mesoporous electrolyte according to the present invention is
A mesoporous material composed of silica and regularly arranged mesopores;
The gist is that it comprises a perfluorosulfonic acid group represented by the formula (1) for modifying the inner surface of the mesopores.
- [C (H, F) 2] n -X- (CF 2) m -SO 3 H ··· (1)
However,
X is O or a direct bond,
n and m are each an integer of 1 or more and 3 or less.

  In the presence of a surfactant, the first precursor for forming the skeleton of the mesoporous material and the second precursor for modifying the inner surface of the mesopores with perfluorosulfonic acid groups are co-condensation polymerized. As a result, a mesoporous electrolyte in which the inner surface of the mesopores is modified with a perfluorosulfonic acid group is obtained. At this time, if a second precursor having a relatively short molecular length (specifically, having a total carbon number of 6 or less) is used, the amount of acid groups that can be introduced into the mesopores is dramatically increased. Increase. This is because co-condensation polymerization using a second precursor having a short molecular length alleviates the steric hindrance caused by the second precursor and makes it difficult to break the pore structure even when a large amount of acid groups are introduced. It is done.

FIG. 1A is a schematic configuration diagram of a four-terminal electrode substrate used for proton conduction measurement. FIG.1 (b) is a schematic block diagram of the apparatus used for the proton conduction measurement. It is an X-ray diffraction pattern of a perfluorosulfonic acid mesoporous membrane (TMOS / FTFEBS = 0.99 g / 1.6 g). 3 (a) and 3 (b) are a krypton adsorption isotherm and a pore distribution curve of a perfluorosulfonic acid mesoporous membrane (TMOS / FTTEBSBS = 0.99 g / 1.6 g), respectively. It is a figure which shows the relationship between the relative humidity and proton conductivity in 25 degreeC of the perfluorosulfonic acid mesopore membrane and Nafion (trademark) membrane from which an acid group density differs. It is a figure which shows the relationship between the sulfonic acid amount of a perfluorosulfonic acid mesopore membrane and a Nafion (trademark) membrane, and relative humidity when the proton conductivity in 25 degreeC becomes 0.01 S / cm.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Mesoporous electrolyte]
The mesoporous electrolyte according to the present invention includes a mesoporous body and a perfluorosulfonic acid group.

[1.1. Mesoporous material]
In the present invention, the “mesoporous material” refers to a material made of silica and having mesopores regularly arranged.
Silica is suitable as a material constituting the skeleton of the mesoporous material because it is relatively easy to produce the mesoporous material. The mesoporous material is preferably composed only of silica, but may contain inevitable impurities.

“Mesopore” refers to a nanospace (1.5 to 50 nm) larger than the space contained in zeolite. As will be described later, in the case of co-condensation polymerization of the first precursor that becomes the skeleton of the mesoporous material and the second precursor that becomes the perfluorosulfonic acid group, The agent forms micelles and self-assembles. As a result, a composite including a mesoporous material in which mesopores are regularly arranged and a surfactant filled in the mesopores is obtained.
The shape and arrangement state of micelles (ie, mesopores) can be controlled by the solution composition (particularly, the type, concentration and pH of the surfactant). For example, in general, spherical micelles are easily formed when the surfactant concentration is low, and pipe-like micelles are easily formed when the surfactant concentration is high. The micelles have various arrangement structures such as a three-dimensional cubic structure, a two-dimensional hexagonal structure, and a three-dimensional hexagonal structure depending on the solution composition.
In the present invention, the mesopores only need to be regularly arranged, and the shape and arrangement structure are not particularly limited.

[1.2. Perfluorosulfonic acid group]
In the present invention, the “perfluorosulfonic acid group” is an acid group that modifies the inner surface of the mesopore and has a structure represented by the formula (1).
- [C (H, F) 2] n -X- (CF 2) m -SO 3 H ··· (1)
However,
X is O or a direct bond,
n and m are each an integer of 1 or more and 3 or less.

(1) In the formula, “— [C (H, F) ₂ ] _n —” represents an alkylene group. The alkylene group may contain only a C—H bond, or all or part of H may be substituted with F. Further, the alkylene group may be linear or branched.
(1) In the formula, “— (CF ₂ ) _m —” represents a perfluoroalkylene group. When the SO ₃ H group is bonded to the terminal of the perfluoroalkylene group, the acid strength of the terminal SO ₃ H group is increased by the F atom having a high electronegativity.
The alkylene group and the perfluoroalkylene group may be directly bonded or may be bonded via an O atom.
If both the alkylene group and the perfluoroalkylene group have too many carbon atoms, the limit value of the amount of acid groups that can be introduced into the mesopores becomes small. Therefore, these carbon numbers are each preferably 3 or less.

The perfluorosulfonic acid group is in a state bonded to Si contained in the mesoporous material. The following formula (a) shows an example of a mesoporous electrolyte in which — (CH ₂ ) ₃ —O— (CF ₂ ) ₂ —SO ₃ H groups are bonded to the surface of a mesoporous material containing Si. .

[1.3. Acid group density]
In the present invention, since the inner surface of the mesopores is modified using the perfluorosulfonic acid group represented by the formula (1), the limit value of the amount of acid groups that can be introduced is smaller than that of the conventional method. It is much bigger. When a method described later is used, a mesoporous electrolyte having an acid group density of 0.52 mmol / g or more can be obtained.
In order to obtain a proton conductivity of 0.01 S / cm or more under conditions of 25 ° C. and a relative humidity of 40% RH or more, the acid group density is preferably 0.55 mmol / g or more.
In order to obtain a proton conductivity of 0.01 S / cm or more under conditions of 25 ° C. and a relative humidity of 35% RH or more, the acid group density is preferably 0.90 mmol / g or more.
In order to obtain a proton conductivity of 0.01 S / cm or more under conditions of 25 ° C. and a relative humidity of 30% RH or more, the acid group density is preferably 1.25 mmol / g or more.
Furthermore, in order to obtain a proton conductivity of 0.01 S / cm or more under conditions of 25 ° C. and a relative humidity of 27% RH or more, the acid group density is preferably 1.45 mmol / g or more.

[1.4. shape]
The mesoporous electrolyte according to the present invention takes the form of a film or powder depending on the production method. The membranous mesoporous electrolyte can be used as it is as an electrolyte membrane for various electrochemical devices. Further, the powdered mesoporous electrolyte can be used as it is as the electrolyte in the catalyst layer of various electrochemical devices.
On the other hand, in order to use a powdery mesoporous electrolyte as an electrolyte membrane for various electrochemical devices, it is necessary to form a powdery mesoporous electrolyte into a membrane.
As a method for forming a powdered mesoporous electrolyte into a membrane,
(1) A method of press-molding only mesoporous electrolyte powder,
(2) A method of mixing a mesoporous electrolyte powder and a polymer compound (for example, polytetrafluoroethylene) to form a film,
(3) A method of mixing a mesoporous electrolyte powder with a polymer electrolyte (for example, polyperfluorocarbon sulfonic acid) to form a film,
and so on.

[2. Method for producing mesoporous electrolyte]
The method for producing a mesoporous electrolyte according to the present invention includes a composite production process, a skeleton strengthening process, a surfactant removing process, and a protonation process.

[2.1. Complex production process]
In the composite production process, in the presence of a surfactant, a first precursor for forming a skeleton of a mesoporous body and a second precursor for modifying the inner surface of the mesopores with perfluorosulfonic acid groups Is obtained by co-condensation polymerization to obtain a composite in which the surfactant is filled in the mesopores of the mesoporous material.

[2.1.1. First precursor]
The “first precursor” refers to a raw material for forming a skeleton of a mesoporous material. The first precursor may be any mesoporous material that can form a skeleton of a mesoporous material mainly composed of silica and can be copolymerized with a second precursor described later.

Specific examples of the first precursor include the following. Any one of these may be used, or two or more may be used in combination.
(1) Tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, and dimethoxydiethoxysilane.
(2) Trimethoxysilanol, triethoxysilanol, trimethoxymethylsilane, trimethoxyvinylsilane, triethoxyvinylsilane, triethoxy-3-glycidoxypropylsilane, 3-mercaptopropyltrimethoxysilane, 3-chloropropyltrimethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, γ- (methacryloxypropyl) trimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, etc. Trialkoxysilane.
(3) Dialkoxysilanes such as dimethoxydimethylsilane, diethoxydimethylsilane, diethoxy-3-glycidoxypropylmethylsilane, dimethoxydiphenylsilane, and dimethoxymethylphenylsilane.
(4) Sodium metasilicate (Na ₂ SiO ₃ ), sodium orthosilicate (Na ₄ SiO ₄ ), sodium disilicate (Na ₂ Si ₂ O ₅ ), sodium tetrasilicate (Na ₂ Si ₄ O ₉ ), water Sodium silicate such as glass (Na ₂ O · nSiO ₂ , n = 2 to 4).
(5) Kanemite (NaHSi ₂ O ₅ .3H ₂ O), sodium disilicate crystals (α, β, γ, δ-Na ₂ Si ₂ O ₅ ), macatite (Na ₂ Si ₄ O ₉ ), eyelite ( _{Na 2 Si 8 O 17 · xH} 2 O), magadiite _{(Na 2 Si 14 O 17 ·} xH 2 O), kenyaite _{(Na 2 Si 20 O 41 ·} xH 2 O) layered silicates, such as.
(6) Fumed silica such as precipitated silica such as Ultrasil (Ultrasil), Cab-O-Sil (Cabot), HiSil (Pittsburgh Plate Glass), colloidal silica, Aerosil (Degussa-Huls).
(7) Tetrakis (hydroxyhydroxy) silane, tetrakis (3-hydroxypropoxy) silane, tetrakis (2-hydroxyproxy) silane, tetrakis (2,3-dihydroxypropoxy) silane and the like.
(8) Methyltris (2-hydroxyethoxy) silane, ethyltris (2-hydroxyethoxy) silane, phenyltris (2-hydroxyethoxy) silane, 3-mercaptopropyltris (2-hydroxyethoxy) silane, 3-aminopropyltris ( Tris (hydroxyalkoxy) silanes such as 2-hydroxyethoxy) silane and 3-chloropropyltris (2-hydroxyethoxy) silane.
Among these, tetramethoxysilane (Si (OCH ₃ ) ₄ ) and tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ ) can obtain a mesoporous material having good crystallinity, and therefore the first precursor. Is particularly suitable.

In addition, when using silane compounds, such as an alkoxysilane and a hydroxy alkoxysilane, as a 1st precursor, this is used as a starting material as it is.
On the other hand, when a compound other than the silane compound is used as the first precursor, the first precursor is added to water (or an alcohol aqueous solution to which alcohol is added if necessary) in advance, such as sodium hydroxide. Add basic material. The addition amount of the basic substance is preferably about equimolar to the silicon atom in the first precursor. When a basic substance is added to a solution containing a first precursor other than a silane compound, a part of the Si— (O—Si) ₄ bond already formed in the first precursor is cleaved, resulting in a uniform solution. can get. Since the amount of basic substance contained in the solution affects the yield and porosity of the complex, after a homogeneous solution is obtained, a dilute acid solution is added to the solution, and excess base present in the solution is added. Neutralize sex substances. The amount of the diluted acid solution added is preferably an amount corresponding to 1/2 to 3/4 times moles of silicon atoms in the first precursor.

[2.1.2. Second precursor]
The “second precursor” refers to a raw material for modifying the inner surface of the mesopores with a perfluorosulfonic acid group. In the present invention, the second precursor is represented by the following formula (2). The second precursor represented by the formula (2) has an advantage that co-condensation polymerization with the first precursor is easy, and that it is easy to introduce a large amount of acid groups into the mesopores. is there.
_{Z 3 Si- [C (H,} F) 2] n -X- (CF 2) m -SO 2 F ··· (2)
However,
Z is —OCH ₃ , —OC ₂ H ₅ , or halogen,
X is O or a direct bond,
n and m are each an integer of 1 or more and 3 or less.
(2) In formula, Z may mutually be the same or may differ.

  In the following formula (2a), a kind of second precursor, fluoro (1,1,2,2-tetrafluoro-2- (4,4,4-triethoxy-4-silaboxy) ethyl) sulfone) (FTFTESBS ) Is shown.

The second precursor represented by the formula (2) is commercially available, or can be synthesized by a known method using a compound having a similar molecular structure as a starting material.
For example, FTTEBS can be synthesized at room temperature by hydrosilylating CH ₂ = CHCH ₂ O (CF ₂ ) ₂ SO ₂ F with HSi (OEt) ₃ under dehydrated toluene using a platinum catalyst. Can do.

[2.1.3. Surfactant]
The surfactant serves as a template for forming mesopores. As the surfactant, any of a cationic surfactant, an anionic surfactant, and a nonionic surfactant can be used. Depending on the type of surfactant to be used, the pore structure in the mesoporous material can be changed.

Specific examples of the cationic surfactant include alkyl quaternary ammonium salts represented by the following formula (3).
CH ₃ — (CH ₂ ) _n —N ⁺ (R ₁ ) (R ₂ ) (R ₃ ) X ⁻ (3)
(3) In the formula, R _1, R _2, R ₃ are each carbon atoms represent a 1-3 alkyl group. R ₁ , R ₂ and R ₃ may be the same as or different from each other. In order to facilitate aggregation (formation of micelles) between alkyl quaternary ammonium salts, it is preferable that R ₁ , R ₂ , and R ₃ are all the same. Further, at least one of R ₁ , R ₂ , and R ₃ is preferably a methyl group, and all are preferably methyl groups.
(3) In formula, X represents a halogen atom. Although the kind of halogen atom is not particularly limited, X is preferably Cl or Br in view of availability.
(3) In formula, n represents the integer of 7-21.

Specific examples of the anionic surfactant include fatty acid salts, alkyl sulfonates, and alkyl phosphates.
Specific examples of nonionic surfactants include polyethylene oxide nonionic surfactants and primary alkylamines.

  When synthesizing the complex, one type of surfactant may be used, or two or more types may be used. However, since the surfactant serves as a template for forming mesopores in the composite, the type greatly affects the shape of the mesopores. In order to synthesize a complex having more uniform mesopores, it is preferable to use one type of surfactant.

[2.1.4. solvent]
As the solvent for dissolving the raw material, an optimal solvent is selected according to the types of the first precursor and the second precursor. As the solvent, water, alcohol, a mixed solvent of water and alcohol, or the like is usually used. The alcohol may be any of monovalent alcohols such as methanol, ethanol, and propanol, divalent alcohols such as ethylene glycol, and trivalent alcohols such as glycerin.

[2.1.5. catalyst]
In order to polycondensate the first precursor and the second precursor to obtain a mesoporous material, a catalyst is generally added to a solution containing the first precursor and the second precursor. The optimum catalyst is selected according to the types of the first precursor and the second precursor.
For example, when a particulate mesoporous material containing silica is synthesized, an alkali such as sodium hydroxide or aqueous ammonia is preferably used as the catalyst.
For example, when synthesizing a mesoporous film containing silica, an acid such as hydrochloric acid, nitric acid, boric acid, bromic acid, fluoric acid, sulfuric acid, or phosphoric acid is preferably used as the catalyst.

[2.1.6. Solution composition]
Solution compositions such as the type of solvent, the concentration and ratio of the first precursor and the second precursor, the type and concentration of the surfactant, the type and concentration of the catalyst are required for the type of starting material and the mesoporous electrolyte. It is preferable to select an optimum one according to the characteristics.

For example, when synthesizing particles, the alcohol content in the solvent affects the particle size and particle size distribution. In general, the smaller the alcohol content, the smaller the mesoporous material having a smaller particle size. However, it is difficult to control the particle size and the particle size distribution both when the alcohol content is too low and when the alcohol content is excessive.
For example, when synthesize | combining particle | grains, 30-80 vol% is preferable and, as for alcohol content in a solvent, More preferably, it is 40-70 vol%.

For example, the ratio of the first precursor and the second precursor affects the acid group density of the mesoporous electrolyte. In general, the higher the ratio of the second precursor to the first precursor, the higher the mesoporous electrolyte with a higher acid group density.
On the other hand, when the ratio of the second precursor is excessive, the pore structure is easily broken. However, in the present invention, since the second precursor that satisfies the above-described conditions is used, the amount of acid groups that can be introduced without breaking the pore structure is significantly increased as compared with the conventional method.

For example, when synthesizing a thin film, if the concentration of the precursor in the solution is too low, the viscosity of the solution is lowered and a uniform film cannot be obtained. Further, when the particles are synthesized, if the concentration of the precursor in the solution is too low, the yield of the particles is reduced, or it is difficult to control the particle size and particle size distribution of the particles.
On the other hand, when synthesizing a thin film, if the concentration of the precursor in the solution is too high, it becomes difficult to polycondense the precursor into a chain. Further, when the particles are synthesized, if the concentration of the precursor in the solution is too high, it is difficult to control the particle size and the particle size distribution, and the uniformity of the particle size decreases.
For example, when forming a thin film, the solvent is preferably 0.2 to 10 mol with respect to 0.1 mol of the precursor.

For example, if the amount of the surfactant is too small, the amount of the surfactant is insufficient and continuous micelles cannot be formed.
On the other hand, when the amount of the surfactant becomes excessive, a lamellar substance is generated, and when the surfactant is removed, only a laminate of sheets is obtained, and a mesoporous material cannot be obtained. For example, when a thin film is synthesized, The surfactant is preferably 0.005 to 0.05 mol with respect to 0.1 mol of the precursor.
Furthermore, in the case of producing a composite, the pore structure in the composite can be controlled by controlling the type and addition amount of the surfactant.

In addition, for example, when a thin film is synthesized, if the catalyst concentration in the solution is too low, the hydrolysis rate and the polycondensation rate are slowed, making it difficult to produce the thin film. In addition, when the particles are synthesized, if the catalyst concentration in the solution is too low, the yield of the particles is extremely reduced.
On the other hand, when synthesizing a thin film, if the catalyst concentration in the solution is too high, the hydrolysis rate and the polycondensation rate become too fast, and a homogeneous polymer cannot be obtained. Further, the crystallinity of the thin film, the smoothness of the surface, and the orientation of the pores are insufficient. Further, when the particles are synthesized, if the catalyst concentration in the solution is too high, it may be difficult to synthesize the mesoporous material.
For example, when synthesizing a thin film, the catalyst is preferably 1.0 to 5.0 × 10 ⁻⁴ mol, more preferably 2.0 to 4.0 × 10 ⁻⁴ mol, relative to 0.1 mol of the precursor. mol.

[2.1.7. Preparation of composite]
The powdery composite
(1) A surfactant and a catalyst (for example, an alkaline aqueous solution) are added to a mixed solution containing the first precursor and the second precursor to react them,
(2) separating the produced particles from the mixture;
Can be obtained.
In addition, the membrane complex is
(1) A catalyst (for example, an acid aqueous solution) is added to a mixed solution containing the first precursor and the second precursor to cause hydrolysis and partial polymerization of the first precursor and the second precursor,
(2) A surfactant is added to a solution containing a partial polymer of the first precursor and the second precursor to form a sol solution,
(3) A sol solution is applied to the substrate surface, and the solvent is volatilized.
Can be obtained.

  When an acid or alkali is added as a catalyst to the mixed solution containing the first precursor and the second precursor, hydrolysis and partial polymerization of the first precursor and the second precursor occur. When a surfactant is added to this solution, the surfactant forms micelles in the solution. This micelle becomes a supramolecular template, and the first precursor and the second precursor which are hydrolyzed or partially polymerized are adsorbed around the template. Since the partial polymer does not enter the interior of the micelle, the interior of the micelle eventually becomes a pore portion. Therefore, the pore diameter inside the mesoporous material can be controlled by controlling the molecular chain length of the surfactant.

  The micelles adsorbing the precursor will eventually be arranged in a stable direction. When this is dried or further reacted in solution, the precursor undergoes polycondensation between the arranged micelles. Moreover, the second precursor is adsorbed on the micelle exclusively with the perfluorosulfonyl fluoride group directed to the micelle side. As a result, a composite in which the surfactant is filled into the mesopores of the mesoporous material and the inner wall of the mesopore is modified with a perfluorosulfonyl fluoride group is obtained.

[2.2. Framework strengthening process]
The skeleton strengthening step is a step of strengthening the skeleton of the composite in which the surfactant is filled in the mesopores of the mesoporous material.
The composite immediately after co-condensation polymerization of the first precursor and the second precursor has a Si deficient part in a part of the skeleton. Therefore, when the surfactant is removed from the composite immediately after cocondensation polymerization, the pore structure tends to collapse. In order to prevent the collapse of the pore structure, it is necessary to supplement the deficient Si and form a Si—O—Si bond between the compensated Si and the skeleton of the composite.

There are various methods for reinforcing the skeleton of the composite.
Above all,
(1) Exposing the composite immediately after co-condensation polymerization to the vapor of the first precursor, filling the Si precursor with the first precursor,
(2) Exposing the composite filled with the first precursor to the vapor of the catalyst to form a Si—O—Si bond between the first precursor filled in the defect portion and the skeleton of the composite;
The method is preferred.

The contact between the composite and the vapor of the first precursor can be performed by placing the composite and the first precursor in an autoclave and holding the composite at a predetermined temperature for a predetermined time. The contact between the composite and the vapor of the catalyst can also be performed by the same method.
As for the contact temperature and the contact time with the vapor, optimum conditions are selected according to the structure of the composite, the type of the first precursor, the type of the catalyst, and the like.
For example, when an alkoxide such as TMOS or TEOS is used as the first precursor, the treatment is preferably performed at 80 to 200 ° C. for 100 to 150 hours.
For example, when using ammonia water as a catalyst, it is preferable to process at 50-120 degreeC for 1 to 20 hours.

[2.3. Surfactant removal process]
The surfactant removal step is a step of removing the surfactant from the complex. The method for removing the surfactant is not particularly limited, and it is preferable to select an optimum method according to the type of the surfactant, the structure of the complex, and the like.
As a method for removing the surfactant, specifically,
(1) A firing method of firing the composite at 300 to 1000 ° C. (preferably 300 to 600 ° C.) for 30 minutes or more (preferably 1 hour or more) in the air or under an inert atmosphere,
(2) The composite is immersed in a surfactant good solvent (for example, methanol containing a small amount of hydrochloric acid) and stirred while heating at a predetermined temperature (eg, 50 to 70 ° C.), and the interface in the composite An ion exchange method to extract the active agent,
and so on.
In the present invention, since the inner surface of the complex is modified with a perfluorosulfonyl fluoride group, the surfactant is preferably removed by an ion exchange method.

[2.4. Protonation process]
The protonation step is a step of converting a perfluorosulfonyl fluoride group that modifies the inner surface of the mesopores to a perfluorosulfonic acid group.
As a method for protonating a perfluorosulfonyl fluoride group, specifically,
(1) A method of treating a mesoporous material having a perfluorosulfonyl fluoride group with an acid,
(2) A method in which a mesoporous material having a perfluorosulfonyl fluoride group is treated with an alkali to form an alkali salt and then further treated with an acid,
and so on.

[3. Action of mesoporous electrolyte]
Any of the conventional methods for introducing perfluorosulfonic acid groups to the inner surface of a mesoporous material has a limit in the density of acid groups that can be introduced.
In contrast, in the presence of a surfactant, a first precursor for forming a skeleton of a mesoporous material and a second precursor for modifying the inner surface of the mesopores with a perfluorosulfonic acid group When co-condensation polymerization is performed, a mesoporous electrolyte in which the inner surface of the mesopores is modified with a perfluorosulfonic acid group is obtained. At this time, if a second precursor having a relatively short molecular length (specifically, having a total carbon number of 6 or less) is used, the amount of acid groups that can be introduced into the mesopores is dramatically increased. Increase. This is because co-condensation polymerization using a second precursor having a short molecular length alleviates the steric hindrance caused by the second precursor and makes it difficult to break the pore structure even when a large amount of acid groups are introduced. It is done.

Since the mesoporous electrolyte obtained by such a method has a very high acid group density, it exhibits high proton conductivity even under low humidity conditions. Specifically, by optimizing the acid group density, proton conductivity at a relative humidity of 10% RH is higher than that of a perfluorocarbon sulfonic acid membrane such as Nafion (registered trademark). Further, when the acid group density is optimized, the proton conductivity is 0.1 S / cm or more under the condition of relative humidity of 40% RH or more.
Furthermore, since the skeleton of the mesoporous electrolyte according to the present invention is made of silica, it has high heat resistance and is less likely to dissolve or swell in water. Therefore, if the mesoporous electrolyte according to the present invention is applied to an electrolyte membrane for a fuel cell, improvement in power generation efficiency under low humidification conditions or high temperature and low humidification conditions can be expected.

(Examples 1 to 3, Comparative Example 1)
[1. Sample synthesis]
[1.1 Preparation of sol solution]
Ethanol (5.0 mL) was added to tetramethoxysilane (TMOS) (0.99 g) as raw materials and FTESBS (1.6 g). H ₂ O (993 μL) and 2N-HCl (7 μL) were added thereto, and the mixture was stirred at room temperature for 1 hr (200 rpm). Further, a mixture of the surfactant octadecyltrimethylammonium chloride (C ₁₄ TMA ⁺ Cl ⁻ ) (1.3 g), ethanol (10 mL), H ₂ O (0.1 mL), 2N-HCl (10 μL) was added to TMOS / The mixture was added to the FTESBS sol solution and stirred (300 rpm) for 2 hr (Example 1, acid group density: 1.6 mmol / g).
Similarly, TMOS / FTFTESBS mixing ratio = 1.04 / 1.4 g (Example 2, acid group density: 1.2 mmol / g) or 1.34 g / 0.47 g (Example 3, acid group density: A sol solution was prepared in the same manner as in Example 1 except that 0.3 mmol / g).
For comparison, a commercially available Nafion (registered trademark) membrane was also used for the test (Comparative Example 1).

[1.2 Thin film production]
The four-terminal electrode substrate was coated with the sol solution prepared in [1.1] (see FIG. 1A). The electrode substrate coated with the thin film was placed in an autoclave, TMOS (150 μL) was added, and the substrate was treated at 120 ° C. for 2 hours. Next, 28% NH ₃ water (100 μL) was added and treated at 100 ° C. for 2 hr. After the treatment, the thin film was dried. Furthermore, the surfactant contained in the thin film was extracted at room temperature (1 wt% hydrochloric acid solution: diluted with ethanol).

[1.3 Thin film cleaning]
The thin film obtained by the above method was washed with 0.1N HCl aqueous solution (RT-2 hr) and pure water (80 ° C.-2 hr), dried at 60 ° C.-1 hr, and perfluorosulfonic acid mesopores. A membrane (mesoporous electrolyte membrane) was obtained.

[2. Test method]
[2.1 X-ray diffraction]
The X-ray diffraction pattern of the perfluorosulfonic acid mesoporous membrane was measured.
[2.2 Pore structure]
The BET specific surface area, pore volume, and pore size of the perfluorosulfonic acid mesoporous membrane were measured.
[2.3 Proton conductivity]
The electrode substrate coated with the perfluorosulfonic acid mesoporous membrane was inserted into an atmosphere prepared at 25 ° C. and a relative humidity of 10 to 90% under a flow of 1% H ₂ (diluted with nitrogen) (FIG. 1B). )reference). A picoammeter was attached to the two electrodes on both ends of the electrode substrate, and the current value when 0.5 V was applied was measured. Moreover, the voltmeter was attached to two center electrodes, and the voltage was measured. The resistance value was calculated from the measured current and voltage to determine the proton conductivity.

[3. result]
[3.1 X-ray diffraction pattern]
FIG. 2 shows an XRD pattern of a perfluorosulfonic acid mesoporous membrane (TMOS / FTTEBS = 0.99 g / 1.0 g, acid group density: 1.6 mmol / g). The diffraction peak corresponding to 2.48 nm is a peak attributed to mesopores.

[3.2 Pore structure]
FIG. 3 (a) and FIG. 3 (b) show krypton adsorption isotherms of perfluorosulfonic acid mesoporous membrane (TMOS / FTFEBS = 0.99 g / 1.6 g, acid group density: 1.6 mmol / g), respectively. Lines and pore distribution curves are shown.
The BET specific surface area and pore volume were 477 m ² / g and 0.22 mL / g, respectively. Moreover, the pore size by BJH method was 2.2 nm.

[3.3 Proton conductivity]
FIG. 4 shows the relationship between proton conductivity and relative humidity of perfluorosulfonic acid mesoporous membranes (acid group density: 1.6 mmol / g, 1.2 mmol / g) and Nafion (registered trademark) membrane at 25 ° C. Show.
From FIG.
(1) The proton conductivity of a perfluorosulfonic acid mesoporous membrane having an acid group density of 1.2 mmol / g is higher than that of Nafion (registered trademark) at 25 ° C. and a relative humidity of 35% RH or more.
(2) The proton conductivity of the perfluorosulfonic acid mesoporous membrane having an acid group density of 1.6 mmol / g is higher than that of Nafion (registered trademark) under conditions of 25 ° C. and a relative humidity of 10% RH or more.
(3) The proton conductivity of the perfluorosulfonic acid mesoporous membrane having an acid group density of 1.2 mmol / g or more is 0.1 S / cm or more under conditions of 25 ° C. and a relative humidity of 40% RH or more.
I understand that.

FIG. 5 shows the relationship between the amount of sulfonic acid in the perfluorosulfonic acid mesopore membrane and Nafion (registered trademark) membrane and the relative humidity when the proton conductivity at 25 ° C. is 0.01 S / cm.
From FIG. 5, in the perfluorosulfonic acid mesoporous membrane,
(1) When the acid group density is 0.55 mmol / g or more, a proton conductivity of 0.01 S / cm or more can be obtained at 25 ° C. and a relative humidity of 40% RH or more.
(2) When the acid group density is 0.90 mmol / g or more, proton conductivity of 0.01 S / cm or more is obtained at 25 ° C. and a relative humidity of 35% RH or more.
(3) When the acid group density is 1.25 mmol / g or more, a proton conductivity of 0.01 S / cm or more can be obtained under conditions of 25 ° C. and a relative humidity of 30% RH or more.
(4) When the acid group density is 1.45 mmol / g or more, a proton conductivity of 0.01 S / cm or more is obtained under conditions of 25 ° C. and a relative humidity of 27% RH or more.
I understand that.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

  The mesoporous electrolyte according to the present invention is an electrolyte used in various electrochemical devices such as a fuel cell, a water electrolysis apparatus, a hydrohalic acid electrolysis apparatus, a salt electrolysis apparatus, an oxygen and / or hydrogen concentrator, a humidity sensor, and a gas sensor. Can be used as

Claims (4)

A mesoporous material composed of silica and regularly arranged mesopores;
A mesoporous electrolyte comprising a perfluorosulfonic acid group represented by formula (1) that modifies the inner surface of the mesopores.
- [C (H, F) 2] n -X- (CF 2) m -SO 3 H ··· (1)
However,
X is O or a direct bond,
n and m are each an integer of 1 or more and 3 or less.   The mesoporous electrolyte according to claim 1, wherein the acid group density is 0.52 mmol / g or more. In the presence of a surfactant, the first precursor for forming the skeleton of the mesoporous material and the formula (2) for modifying the inner surface of the mesopores with a perfluorosulfonic acid group The mesoporous electrolyte according to claim 1 or 2, obtained by co-condensation polymerization with a second precursor.
_{Z 3 Si- [C (H,} F) 2] n -X- (CF 2) m -SO 2 F ··· (2)
However,
Z is —OCH ₃ , —OC ₂ H ₅ , or halogen;
X is O or a direct bond,
n and m are each an integer of 1 or more and 3 or less.   The mesoporous electrolyte according to any one of claims 1 to 3, wherein the mesoporous electrolyte is in the form of a film or particles.

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