JP2009076331A - Polymer nanosheet integrated electrolyte membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymer nanosheet integrated electrolyte membrane having high gas barrier properties and low proton conductive resistance. <P>SOLUTION: The polymer nanosheet integrated electrolyte membrane is composed of a laminated membrane obtained by developing and compressing an amphipatic polymer having an acid group on the water surface to form a monomolecular membrane, and by accumulating monomolecular membranes on a substrate. The amphipatic polymer having the acid group is preferably a copolymer of alkylacrylamide monomer, perfluoroalkyl acrylamide monomer, alkylmethacrylamide monomer or perfluoroalkyl methacrylamide monomer with the carbon number of 4 or more, and sulfonic acid content acrylic monomer. Moreover, the polymer nanosheet integrated electrolyte membrane is preferably obtained by heat-treating the laminated membrane at the glass transition temperature or more. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a polymer nanosheet-integrated electrolyte membrane, and more particularly, to a polymer nanosheet-integrated electrolyte membrane obtained by laminating nanosheets in which polymer chains having acid groups are closely packed.

  When an organic compound (amphiphile) having both a hydrophobic part and a hydrophilic part is dropped onto the water surface, the amphiphile spreads to the surface of the water with the hydrophilic part facing the water, and a thin film It becomes. Such a film is called a monomolecular film on the water surface or a Langmuir film (L film). When the L film spreading on the water surface is compressed in the plane direction and the area of the L film is reduced, the L film eventually becomes a “two-dimensional solid” state in which molecules that have spread on the water surface are densely packed. Become. Furthermore, when the monomolecular film is developed on the water surface, and the operation of sinking the substrate in water and the operation of pulling up the substrate from the water while keeping the monomolecular film in a solid state is repeated, the hydrophobic parts and the hydrophilic parts are respectively The monomolecular film can be copied onto the substrate one after another while facing each other. The obtained film is called a monomolecular cumulative film or a Langmuir-Blodgett film (LB film).

Conventionally, the LB method has been generally applied to low molecular organic compounds. The obtained LB film has begun to be applied to diffraction gratings, optical ion sensors, gas sensors, biosensors, and the like.
Furthermore, an example in which the LB method is applied to an inorganic compound is also known. For example, Patent Document 1 discloses that
(1) The interlaminar ions of the sukumetite clay are exchanged with hydrophobic long-chain polymer ions to swell and exfoliate the interlaminar layers, and at the same time impart hydrophobicity to the surface,
(2) Disperse hydrophobized sukumite clay mineral in chloroform,
(3) The dispersion is dropped onto the water surface and developed to form a film on the water surface;
(4) Laminating the obtained film a plurality of times on a hydrophobized substrate;
A method for producing a layered particle thin film is disclosed.
This document describes that a thin film of an inorganic compound having a complicated composition and structure can be obtained by such a method.

JP-A-8-57406

  Solid polymer electrolyte membranes are used in various electrochemical devices such as fuel cells, water electrolysis devices, hydrohalic acid electrolysis devices, salt electrolysis devices, oxygen and / or hydrogen concentrators, humidity sensors, and gas sensors. Various materials are used for the solid polymer electrolyte membrane according to the application. For example, sulfonic acid electrolyte membranes such as Nafion (registered trademark, manufactured by DuPont) and sulfonated aromatic electrolytes are used as electrolyte membranes for polymer electrolyte fuel cells.

Conventionally, this type of electrolyte membrane is generally manufactured by a melt stretching method, a casting method, a spin coating method, or the like. However, in the conventional method, since the polymer in the film becomes a random coil shape, there is a problem that the free volume increases and it is difficult to obtain a high-density and homogeneous thin film. A decrease in the density and homogeneity of the electrolyte membrane causes a decrease in gas barrier properties. On the other hand, when the film thickness is increased in order to improve the gas barrier property, the proton conduction resistance of the film increases.
Furthermore, when the LB method is applied to a low molecular compound or an inorganic substance, an ultrathin film that is homogeneous and dense and has an extremely small thickness can be obtained. However, there has never been an example in which the LB method is applied to a polymer electrolyte.

The problem to be solved by the present invention is to provide a polymer nanosheet integrated electrolyte membrane having a high gas barrier property and a low proton conduction resistance.
Another problem to be solved by the present invention is to provide a polymer nanosheet integrated electrolyte membrane having high homogeneity and denseness.

In order to solve the above problems, a polymer nanosheet-integrated electrolyte membrane according to the present invention forms an monomolecular film by developing and compressing an amphiphilic polymer having an acid group on a water surface, and the monomolecular film is formed on a substrate. It is made of a laminated film obtained by accumulating in the above.
The polymer integrated nanosheet electrolyte membrane is preferably obtained by heat-treating the laminated film at a glass transition temperature or higher.

  When the LB method is applied to an amphiphilic polymer having an acid group, a high-density and homogeneous thin film can be obtained. This is considered to be because the polymer is most closely packed by compressing the membrane developed on the water surface. Furthermore, when the obtained laminated film is heat-treated under predetermined conditions, the proton conduction resistance is further reduced. This is presumably because the hydrophilic portion is phase-separated by the heat treatment.

Hereinafter, an embodiment of the present invention will be described in detail.
The polymer nanosheet integrated electrolyte according to the present invention is a laminated film obtained by developing and compressing an amphiphilic polymer having an acid group on a water surface to form a monomolecular film, and accumulating the monomolecular film on a substrate. Consists of.
In the present invention, the term “laminated film” refers to not only a so-called “LB film” in which the film thickness can be determined from the cumulative total number (XRD reflection is observed), but also a nano thin film in which the film thickness cannot be determined from the cumulative total number. These laminates are also included.

“Amphiphilic polymer” refers to a polymer having a hydrophilic part and a hydrophobic part in the side chain. The hydrophilic portion may be on the main chain side or on the terminal side of the side chain. That is, the amphiphilic polymer may have a side chain having a hydrophilic part and a hydrophobic part bonded to the main chain in the vicinity of the hydrophilic part, or may be bonded to the main chain in the vicinity of the hydrophobic part. It may be what you have.
Examples of the hydrophilic portion include an amide group (—CO—NH—), a hydroxyl group (—OH), a quaternary ammonium group (—N ⁺ R ₃ , R is an alkyl group, etc.), a carboxyl group (—COOH), and a sulfonic acid. Groups (—SO ₃ H), phosphate groups (—P (OH) ₂ ), and the like. In particular, an amide group is suitable as a hydrophilic portion because the molecules are likely to be closely packed by hydrogen bonding.
Examples of the hydrophobic moiety include an alkyl group having 4 or more carbon atoms, a fluoroalkyl group, and a substituted phenyl group.
The main chain and the side chain are not particularly limited, and can have various structures. For example, the main chain and the side chain may each have either a C—F bond or a C—H bond, or may have both. In addition to the C—F bond and / or the C—H bond, the main chain and the side chain are each composed of a chlorocarbon structure (—CCl ₂ —) and other structures (eg, —O—, —S—). , -C (= O)-, -N (R)-, etc., provided that "R" is an alkyl group).

The “amphiphilic polymer having an acid group” refers to an acid group introduced into the side chain of the amphiphilic polymer. The acid group may be introduced into a side chain having a hydrophilic part and a hydrophobic part, or may be introduced into a different side chain.
The kind of acid group introduced into the amphiphilic polymer is not particularly limited. Specific examples of the acid group include a sulfonic acid group, a carboxylic acid group, a phosphonic acid group, and a sulfonimide group. The amphiphilic polymer may contain only one of these acid groups, or may contain two or more.
The amount of acid groups introduced into the amphiphilic polymer can be arbitrarily selected according to the purpose. In general, the proton conduction resistance can be lowered as the amount of acid groups increases.

  The amphiphilic polymer having an acid group can be produced by various methods. In particular, a method of copolymerizing a monomer having an LB film-forming ability (that is, having a hydrophilic part and a hydrophobic part) and an unsaturated bond (amphiphilic monomer) with a monomer having an acid group and an unsaturated bond Is preferred. The copolymerization method of the amphiphilic monomer and the monomer having an acid group is not particularly limited, and a known method can be used.

Specific examples of the amphiphilic monomer include alkyl acrylamide monomers having 4 or more carbon atoms, perfluoroalkyl acrylamide monomers having 4 or more carbon atoms, alkyl methacrylamide monomers having 4 or more carbon atoms, and carbon numbers. And perfluoroalkyl methacrylamide monomers that are 4 or more.
As alkyl acrylamide monomer, specifically,
(1) N-dodecylacrylamide (pDDA) monomer,
(2) tert-pentylacrylamide (ptPA) monomer,
(3) adamantylacrylamide (pADA) monomer,
and so on.
As a perfluoroalkyl acrylamide monomer, specifically,
(4) N- (1H, 1H-pentadecafluorooctyl) acrylamide (pC7F15AA) monomer,
(5) (2- (perfluorooctyl) ethyl) acrylamide (pC8F17AA) monomer and the like.
Specifically, as the alkyl methacrylamide monomer,
(6) N-tetradecyl methacrylamide (pTDMA) monomer,
(7) neo-pentyl methacrylamide (pnPMA) monomer,
and so on.
Specific examples of perfluoroalkyl methacrylamide monomers include:
(8) N- (1H, 1H-pentadecafluorooctyl) methacrylamide (pC7F15MA) monomer,
and so on.

As the monomer having an acid group, specifically,
(1) a sulfonic acid-containing monomer (for example, 2-acrylamido-2-methylpropanesulfonic acid monomer),
(2) styrene sulfonic acid monomer,
(3) an acrylic monomer having a phosphoric acid group or a phosphonic acid group,
and so on.

Among these, the amphiphilic polymer having an acid group is preferably a copolymer of an alkylacrylamide monomer having 4 or more carbon atoms and a sulfonic acid-containing monomer.
The amphiphilic polymer having an acid group is preferably a copolymer of an N-dodecylalkylacrylamide monomer and a 2-acrylamido-2-methylpropanesulfonic acid monomer.

  The amphiphilic monomer and the monomer having an acid group are commercially available, or can be produced by applying a well-known method to a monomer having a similar molecular structure.

When an amphiphilic polymer having an acid group is dissolved in an appropriate solvent (for example, chloroform) to form a solution, and this solution is dropped on the water surface, the amphiphilic polymer having an acid group has a hydrophobic portion in the air. In the state facing the side, it spreads to the full water surface and becomes a thin L film. When this L film is compressed in the plane direction, the polymer developed on the water surface becomes a two-dimensional solid L film.
From this state, when a substrate having a hydrophobic surface (for example, a glass substrate, a silicon substrate, etc.) is submerged in water, the first L film is copied onto the substrate with the hydrophobic portion facing the substrate side. Can do. Subsequently, when the substrate is lifted from the water, the second L film can be copied onto the substrate in a state where the hydrophilic portion exposed on the substrate surface and the hydrophilic portion of the second L film face each other. it can. Hereinafter, when such an operation is repeated, a laminated film having an arbitrary thickness can be formed on the substrate.
The obtained laminated film can be used for various applications as it is, but the obtained laminated film may be further heat-treated at a temperature equal to or higher than the glass transition temperature. When the laminated film is heat-treated under predetermined conditions, there is an effect that the proton conduction resistance is further reduced.

Next, the operation of the polymer nanosheet integrated electrolyte membrane according to the present invention will be described.
When the LB method is applied to an amphiphilic polymer having an acid group, a high-density and homogeneous thin film can be obtained. This is considered to be because the polymer is most closely packed by compressing the membrane developed on the water surface. In particular, an amphiphilic polymer having an amide group easily obtains a high-density and uniform thin film. This is presumably because the molecules are likely to be close packed by hydrogen bonds.
Furthermore, when the obtained laminated film is heat-treated under predetermined conditions, the proton conduction resistance is further reduced. This is presumably because the hydrophilic portion is phase-separated by the heat treatment.

Example 1
[1. Preparation of sample]
[1.1 Synthesis of p (DDA / AMPS)]
First, as shown in Scheme 1, p (DDA / AMPS) is synthesized by copolymerization of N-dodecylacrylamide (DDA) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) having a sulfonic acid at its terminal. did. Copolymerization was performed using AlBN as the initiator and a THF / H ₂ O mixed solution as the solvent. A polymerization solution was prepared with a monomer concentration of 0.2M and an initiator concentration of 0.004M. The polymerization solution was frozen with liquid nitrogen, vacuum degassing, and nitrogen substitution were repeated three times to remove dissolved oxygen, and then polymerized for 17 hours in a 60 ° C. constant temperature bath. After polymerization, the produced and precipitated polymer was collected by centrifugation, dissolved in chloroform, reprecipitated with acetonitrile, and collected by centrifugation at 3000 rpm for 30 minutes.
The copolymer composition was determined by trace element analysis (AMPS S element). The molecular weight and the degree of dispersion were measured by GPC and determined in terms of polystyrene.

[1.2 Surface treatment of accumulated substrates]
The glass or silicon substrate was sequentially ultrasonically washed with acetone and chloroform, and then immersed in 2-propanol for 30 minutes. Next, the taken out substrate was subjected to ozone cleaning for 25 min (Nippon Laser Electronics, UV-O ₃ cleaner), and immersed in distilled chloroform. A few drops of octadecyltrichlorosilane (OTS) (Shin-Etsu Silicone) were added thereto, and the surface was subjected to hydrophobic treatment by leaving it for 30 minutes. After the reaction, the substrate was taken out and ultrasonically washed with chloroform, and this was used as a cumulative substrate.

[1.3 Measurement of π-A isotherm and production of LB film]
Langmuir Rough (USI, FDS-110) was used for the measurement of the π-A isotherm and the production of the LB film. FIG. 1 shows a conceptual diagram thereof.
The synthesized p (DDA / AMPS) copolymer was dissolved in chloroform (Dotite, Spectrozole) to prepare a 1 mM polymer solution. This was dropped dropwise onto a trough filled with ion-exchanged water (18 MΩ), and then allowed to stand for 30 minutes to evaporate the solvent. The monomolecular film developed on the water surface was compressed by a polytetrafluoroethylene barrier at a constant speed of 14 cm ² / min, and simultaneously the surface pressure was monitored by the Wilhelmy plate method to measure the π-A isotherm. During the compression of the monomolecular film, the temperature was kept constant by a thermostatic bath. Accumulation on the substrate was carried out by standing for 30 minutes after reaching a predetermined accumulated pressure and moving the substrate up and down at a transfer speed of 10 mm / min. Further, the standing time after the substrate was lowered was 3 min, and the standing time after the substrate was raised was 50 min.

[2. Test method]
[2.1 Surface shape observation using atomic force microscope (AFM)]
The surface shape was observed by a tapping mode using AFM (SII SPA-400), with a measurement sample obtained by accumulating a predetermined layer of a monomolecular film on a water surface on a hydrophobically treated silicon substrate. The observation was performed using a surface irregularity (Topo mode) image and a phase difference (Phase mode) image.
[2.2 X-ray diffraction measurement]
Using a sample obtained by accumulating 30 monolayers on the water surface on a hydrophobically treated glass substrate, the orientation state of p (DDA / AMPS) was examined by XRD measurement (source CuKα, wavelength 0.154 nm).

[3. result]
[3.1 Synthesis of p (DDA / AMPS) Copolymer]
From the elemental analysis, the AMPS content in the synthesized p (DDA / AMPS) copolymer was 15%, the number average molecular weight Mn = 4000, and the degree of dispersion Mw / Mn = 1.5.
FIG. 2 shows a π-A curve of a monomolecular film on the p (DDA / AMPS) water surface where n = 0.15. As the surface area decreased, a sharp rise in surface pressure and a high collapse pressure were shown, indicating that a good monolayer on the water surface was obtained. From this, the average ultimate occupation area (A _average ) was determined to be 0.25 nm ² / monomer unit. The “average limit occupation area” means an area obtained by extrapolating from 0 mN / m where the surface pressure rises most sharply.

Here, in the copolymer monomolecular film, it is assumed that each component of the copolymer has a specific occupied area, and from A _average and composition, the ultimate occupied area per unit of AMPS is expressed by the following formula (1). Calculated according to
A _average = (1-n) A _DDA + nA _AMPS (1)
A _average , A _DDA , and A _AMPS represent the average ultimate occupied area, the ultimate occupied area per DDA unit, and the occupied area per _AMPS unit, respectively, and n represents the AMPS composition. From the result of the π-A isotherm, the ultimate occupied area of the DDA monomer is determined to be A _DDA = 0.28 nm ² . From this, A _AMPS calculated using the formula (1) is determined to be approximately 0 nm ² / monomer unit, and it is considered that AMPS exists below the water surface.

  FIG. 3 shows an AFM image of a film accumulated in two layers at a cumulative pressure of 35 and 45 mN / m. At 35 mN / m (FIGS. 3A and 3B), many defects having a depth of about 3.9 nm were observed. On the other hand, at 45 mN / m (FIGS. 3C and 3D), it was found that a highly condensable film surface was formed, and the RMS value (root mean square) also increased. Therefore, 30 layers were accumulated at 45 mN / m on the glass substrate, and XRD measurement was performed (FIG. 4). A prominent Bragg peak was observed at a position of 2θ = 2.47 (d = 3.57 nm). This is almost the same as the Bragg peak (d = 3.48 nm) derived from the pDDA bilayer spacing, so the p (DDA / AMPS) LB film has a layered structure similar to p (DDA). It was suggested that

  Therefore, 20 layers of p (DDA / AMPS) monomolecular film were accumulated on the silicon substrate, a part of the surface was removed with tweezers, and the film thickness was measured from the cross-sectional profile (FIG. 5). Although many agglomerates are seen on the surface of the laminated film, it can be seen that the film thickness of 20 layers laminated in a flat part is 41 nm. From this, the film thickness per layer was 2.1 nm, which was in good agreement with the XRD results.

(Example 2)
[1. experimental method]
[1.1 Production of measurement cell]
An Au comb electrode was used as a measurement substrate. The glass substrate was subjected to a hydrophobic treatment according to the procedure of [1.2] in Example 1, covered with a mask, and set in a vacuum vapor deposition machine (Osaka Vacuum, V-KS200). First, Cr was deposited as an adhesive layer on glass at a rate of 1 nm / s (0.1 nm / s) by an electron gun (Anelva, single-shot E-type electron gun) at a thickness of 5 nm. Next, Au was vapor-deposited at 2 nm / s (0.2 nm / s) by 45 nm by resistance heating to produce an electrode having a total thickness of 50 nm. The film thickness was monitored by a quartz crystal microbalance (QCM) (INFICON, DepositionMonitor XTM / 2).
Subsequently, 30 layers of p (DDA / AMPS) (n = 0.15) on the electrode substrate were accumulated. Since the film thickness per layer was determined to be 2.1 nm by AFM, it is considered that the Au electrode was almost completely covered with the LB film for all samples.

[1.2 Impedance measurement in ion-exchanged water (IEW)]
Connect both electrodes of the cell produced in [1.1] to an impedance analyzer (Toyo Technica, Solartron SI1280B) as CE and WE, respectively, immerse the measurement cell in IEW (18 MΩ) for 1 h, and then start measurement did. FIG. 6 shows a measurement cell and measurement conditions.
The impedance in a frequency range of 20000 to 0.1 Hz was measured, and the ionic conductivity was calculated using the equation (1) from the resistance value in the film obtained by the Nyquist plot and the board plot.
σ = 1 / Rs · d / S (S / cm) (1)
σ: ion conductivity (S / cm), Rs: bulk resistance (Ω), d: distance between electrodes (cm), S: electrode area (cm ² )

[1.3 Impedance measurement under high humidity atmosphere and temperature control]
Using the p (DDA / AMPS) (n = 0.15) 30-layer sample prepared in [1.1], changes in proton conductivity with respect to temperature under the condition of relative humidity RH = 100% were examined. . FIG. 7 shows measurement cells and measurement conditions.
Using p (DDA / AMPS) (n = 0.15) as a measurement sample, 30 layers were accumulated on the Au comb electrode. This was put in a container, sealed, and left for 12 hours. Thereafter, the temperature was raised from room temperature to 70 ° C., and the impedance was measured in the frequency range of 100,000 to 10 Hz with an LCR meter (Hiki, LCR HiTESTER 3522) every time the temperature was raised to 10 ° C. After the measurement, the Nyquist plot was obtained by fitting with an equivalent circuit using ZsimpWin ™ (Princeton Applied Research) to obtain the resistance value inside the film, and the ionic conductivity was calculated from Equation (1).

[2. result]
[2.1 Ionic conductivity of polymer nanosheets with ion-conducting side chains in IEW]
Generally, in a proton conduction mechanism in a solid, it is necessary to dissociate protons of sulfonic acid and phosphoric acid by containing water. Therefore, in order to calculate proton conductivity in a state where polymer nanosheets having various ionic groups are sufficiently hydrated, impedance measurement was performed on the nanosheets in IEW. FIG. 8A and FIG. 8B show a Nyquist plot and a Bode plot in the frequency range 20000 to 0.1 Hz, respectively. FIG. 9 shows a Nyquist plot in the high frequency quantity region.
In FIG. 8, a perfect semicircle was not seen at a frequency of 20000 to 0.1 Hz, but Z tends to increase monotonously without drawing a semicircle on the low frequency side of 100 Hz or less from the board plot. It was. This is thought to be because charge transfer at the membrane-electrode interface due to the use of Au having a high blocking property as the electrode is suppressed.

On the other hand, on the high frequency side of 20000 to 200 Hz, an inflection point appeared as shown in FIG. Assuming that an arc appearing on the higher frequency side than the inflection point is an impedance component in the film, the ionic conductivity is a resistance value obtained by extrapolating the arc to the real axis. Therefore, the ion conductivity was found to be 2.6 × 10 ⁻³ (S / cm) from the film thickness of the p (DDA / AMPS) 30 layer and the distance between the electrodes. Since Nafion (registered trademark) exhibits a conductivity of the order of 10 ⁻² (S / cm) in water at room temperature, it is clear that the nanosheet prepared in this example exhibits a conductivity that is an order of magnitude lower than this. Became.

[2.2 Temperature dependence of ionic conductivity under high humidity]
In [2.1], the produced nanosheets were immersed in water and examined for proton conductivity in a sufficiently wet state. In order to apply such a nanosheet as a proton conducting membrane, it is important to examine proton conductivity under conditions that are actually close to the operating conditions of the fuel cell. The operating temperature of a mobile fuel cell is from room temperature to around 100 ° C. Currently, Nafion (registered trademark) used as a proton conducting membrane has been shown to exhibit proton conductivity of about 0.1 to 0.2 (S / cm) under saturated humidification conditions at 80 ° C. Yes. Therefore, in this example, the temperature dependence of the impedance was measured using a p (DDA / AMPS) LB film under an atmosphere of relative humidity RH = 100%.

FIG. 10A and FIG. 10B show a Bode plot and a change corresponding to the frequency f of the phase difference θ when the temperature is changed from room temperature to 70 ° C., respectively. From FIG. 10A, it was found that | Z | decreased with temperature change and decreased greatly at 60 ° C. In addition, from 20 ° C. to 50 ° C., at 10 ⁵ to 10 ⁴ Hz, | Z | increases linearly as the frequency decreases, and shows a substantially constant value on the low frequency side of 10 ⁴ Hz or less. I understood. On the other hand, at 60 ° C., Z gradually increased as the frequency decreased from 10 ⁵ to 10 ³ Hz, and at 70 ° C., the constant region disappeared in the range of 10 ⁵ to 10 ¹ Hz.
Furthermore, when the phase change of FIG.10 (b) was examined, it became clear that a clear peak appears above 60 degreeC. From this, it is considered that a large change occurs in the ion conduction path at 60 ° C. or higher.

Therefore, the conductivity of the p (DDA / AMPS) LB film was analyzed from the Nyquist plot (FIG. 11). In the range of 20 ° C. to 40 ° C., a relatively continuous impedance plot was obtained on the high frequency side from 10 ⁵ to 10 ⁴ Hz. On the other hand, the plots varied greatly on the low frequency side of 10 ³ Hz or less. This is thought to be because the absolute value of the impedance increased on the low frequency side and reached the measurement limit. When the temperature was raised to 50 ° C., a consistent plot was obtained in the entire measurement frequency region of 10 ⁵ to 10 ¹ Hz, and impedance derived from the electrode interface appeared. Furthermore, when the temperature is raised, the semicircle becomes smaller, and the one similar to the Nyquist plot obtained in [2.1] is obtained at 70 ° C, and the impedance component in the film and the impedance component at the electrode interface are clearly Appeared. This is considered to be due to an increase in proton hopping property due to a temperature rise.

Therefore, these Nyquist plots were fitted with an equivalent circuit, and an attempt was made to calculate the ionic conductivity at each temperature by using the resistance value in the obtained film and Equation (1). FIG. 12 shows the equivalent circuit used.
The impedance in the film was expressed as a parallel circuit of a capacitive component (CPE _b ) derived from polymer polarization and a resistance component (R _b ) derived from ionic conduction. These components appear as semicircles on the high frequency side, and R _b corresponds to the diameter of the semicircle. CPE _b represents an ideal capacitive component that takes into account the dielectric relaxation of the polymer.

On the other hand, the impedance at the electrode interface is expressed as a series circuit of the capacitance (Ci) derived from the electric double layer and the cell resistance (Ri). In general, Ri is 20Ω or less, and therefore it can be assumed that R≈0 in a high-resistance material such as the present ionic conductor. Except at 70 ° C., the Nyquist plot obtained in FIG. 11 appeared as a single arc in the measurement frequency region, so fitting was performed only with a parallel circuit of CPE _b and R _b ignoring impedance at the electrode interface. Tried.
FIG. 13 shows the impedance behavior when the Nyquist plot obtained at each temperature is fitted with the equivalent circuit of FIG. At this time, in the Nyquist plots at temperatures of 20 ° C. and 40 ° C., plots having a frequency of 500 Hz or less that reached the measurement limit were excluded, and in the Nyquist plots from 50 ° C. to 70 ° C., plots of impedance components at the electrode interface were excluded (T = 497 Hz or less at 50 or 60 ° C., and 2000 Hz or less was excluded at T = 70 ° C.).

As shown in FIG. 12, for the plot of T = 20-50 ° C., CPE _b is an ideal capacitance component C _b, and for T = 60, 70 ° C., CPE _b is a polymer, trapped ions, etc. Good fitting was performed by setting Cb _′ taking into account the relaxation process. This is because the orientational polarization process of the polymer is uniformly performed on the low temperature side of 50 ° C. or lower, and the ionic conductivity and the polymer mobility are high on the high temperature side of 60 to 70 ° C. This is thought to be due to an overlap in the frequency domain where the orientation polarization process and ionic conduction follow due to the increase in.

Next, from the resistance values in the membranes obtained by these fittings, an attempt was made to calculate proton conductivity using Equation (1). FIG. 14 is a plot of ionic conductivity calculated from R _b versus temperature (A 1st is the ionic conductivity calculated from R _{b in} FIG. 13, B to D are the same number of layers, and the same It was found that the change in proton conductivity with increasing temperature causes a large error of about two orders of magnitude, but in either case, ion conduction increases with increasing temperature. The degree increased significantly in the range of 50-60 ° C.
On the other hand, Nafion (registered trademark) has been shown to exhibit proton conductivity of the order of 10 ⁻² (S / cm) at room temperature, and log σ increases linearly with respect to 1 / T. According to Arrhenius's equation (equation (2)).
lnσ = lnσ ₀ −Ea / RT (2)
(Σ: ion conductivity, Ea: activation energy, T: temperature)

The activation energy E _a of the proton conduction in Nafion®, from this equation, to be a 5.1~8.7kJ / mol has been revealed. Similarly, the activation energy Ea _AMPS of p (DDA / AMPS) at 40 to 60 ° C. is obtained by the following equation (3) from the slope.
Ea _AMPS = 43.3 lnσ _{T = 60 °} C./σ _{T = 50 ° C.} (kJ / mol) (3)
Therefore, Ea _AMPS = 108 to 198 kJ / mol, and the activation energy was 20 times higher than that of Nafion (registered trademark). From this, it is considered that the increase in proton conductivity at 50 to 60 ° C. is not only due to the increase in proton hopping property but also due to the structural change in the film.

Therefore, the sample A was cooled from 70 ° C. to room temperature after measurement, and the temperature dependence of proton conductivity was examined again. As a result, as shown in the plot of A 2nd, it was revealed that the proton conductivity was remarkably increased as compared with the first measurement, and the order of 10 ⁻³ (S / cm) was exhibited even at 45 ° C. From this, it is considered that an irreversible change occurs in the ion conduction path accompanying the temperature rise.

  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 polymer nanosheet integrated electrolyte membrane according to the present invention is 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. It can be used as an electrolyte membrane.

It is a conceptual diagram of Langmuir Rough. It is a π-A curve of a monomolecular film on the p (DDA / AMPS) water surface where n = 0.15. FIGS. 3A and 3B are AFM images ((a) 20 μm × 20 μm, (b) 5 μm × 5 μm) of the p (DDA / AMPS) laminated film accumulated two layers at a cumulative pressure of 35 mN / m. is there. FIG. 3 (c) is an AFM image of a p (DDA / AMPS) laminated film accumulated two layers at a cumulative pressure of 45 mN / m 5 minutes after the surface pressure reaches 45 mN / m, and FIG. FIG. 5 is an AFM image of a p (DDA / AMPS) laminated film in which two layers are accumulated at a cumulative pressure of 45 mN / m 60 minutes after the surface pressure reaches 45 mN / m. It is an XRD pattern of a p (DDA / AMPS) laminated film in which 30 layers are accumulated. It is a cross-sectional profile of a p (DDA / AMPS) laminated film in which 20 layers are accumulated at an accumulated pressure of 45 mN / m. It is the conceptual diagram and measurement conditions of the measurement cell used for the impedance measurement in ion-exchange water. It is the conceptual diagram and measurement conditions of the measurement cell used for the impedance measurement in a high-humidity atmosphere. FIG. 8A and FIG. 8B are a Nyquist plot and a Bode plot of a p (DDA / AMPS) LB film in ion-exchanged water, respectively (frequency range: 20000 to 0.1 Hz). It is a Nyquist plot in the high frequency region of the p (DDA / AMPS) LB film. FIG. 10A and FIG. 10B are a Bode plot and a θ plot of a p (DDA / AMPS) laminated film in which 30 layers are accumulated, which are measured at different temperatures (20 to 70 ° C.), respectively. It is a Nyquist plot (FIG. 11 (a): 20-50 degreeC, FIG.11 (b): 60-70 degreeC) of the p (DDA / AMPS) laminated film which accumulated 30 layers measured at different temperature. It is an equivalent circuit used for fitting the Nyquist plot. Nyquist plots measured at different temperatures and fitting results using equivalent circuits. It is a figure which shows the temperature dependence of the proton conductivity of the p (DDA / AMPS) laminated film which accumulated 30 layers.

Claims (4)

  A polymer nanosheet integrated electrolyte membrane comprising a laminated film obtained by spreading and compressing an amphiphilic polymer having an acid group on a water surface to form a monomolecular film, and accumulating the monomolecular film on a substrate.   The amphiphilic polymer having an acid group is a copolymer of an alkylacrylamide monomer, a perfluoroalkylacrylamide monomer, an alkylmethacrylamide monomer or a perfluoroalkylmethacrylamide monomer having 4 or more carbon atoms, and a sulfonic acid-containing monomer. The polymer nanosheet integrated electrolyte membrane according to claim 1.   2. The polymer nanosheet-integrated electrolyte membrane according to claim 1, wherein the amphiphilic polymer having an acid group is a copolymer of an N-dodecylalkylacrylamide monomer and a 2-acrylamido-2-methylpropanesulfonic acid monomer.   The polymer nanosheet integrated electrolyte membrane according to any one of claims 1 to 3, obtained by heat-treating the laminated film at a glass transition temperature or higher.

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