JP5257994B2 - Measuring apparatus and measuring method - Google Patents

Description

  The present invention relates to a measuring apparatus and a measuring method using a nuclear magnetic resonance method, and more particularly to an apparatus and a method for measuring film characteristics using a nuclear magnetic resonance method.

  In order to grasp the characteristics of a certain type of functional membrane, it is important to evaluate the permeability of the protic solvent in the thickness direction of the functional membrane. For example, there is a case where it is desired to evaluate a change in the concentration of the protic solvent with time in a specific region in the thickness direction of the functional membrane.

  Specific examples of such a functional membrane include a solid polymer electrolyte membrane used in a direct methanol fuel cell. In a direct methanol fuel cell, a methanol aqueous solution having a predetermined concentration is supplied to the fuel electrode side, and air (oxygen) is supplied to the air electrode side. Both electrodes are partitioned by a solid polymer electrolyte membrane so that the fuel and oxidant do not react directly.

  However, in the direct methanol fuel cell, since the affinity between methanol and water is strong, methanol enters the polymer electrolyte membrane containing a large amount of water and reaches the oxygen electrode directly, regardless of power generation. Oxidizing “fuel crossover” occurs. The fuel crossover not only wastes fuel, but also reduces the cell voltage. Therefore, a direct methanol fuel cell is strongly required to reduce crossover.

  As a method for grasping the crossover characteristic of methanol in a solid polymer electrolyte membrane, there is a conventional method described in Patent Document 1. In this document, the amount of fuel crossed from the anode to the cathode is calculated by measuring the component of the gas discharged from the cathode of the fuel cell, and the fuel consumption is corrected based on the calculated value. Have been described.

Another technique for calculating the permeation characteristics of a protic solvent through a membrane is disclosed in Patent Document 2. This document describes a method for determining the ratio of the local amount of methanol in the plane of the membrane.
JP 2005-26215 A JP 2007-51990 A

However, none of the above-described conventional measuring methods has a configuration suitable for measuring a change with time in the methanol concentration penetrating into the polymer electrolyte membrane.
For example, Patent Document 1 is not a method for directly measuring the amount of methanol in the solid polymer electrolyte membrane.

  In Patent Document 2, although the solid polymer electrolyte membrane can be directly measured, the measurement was performed in an equilibrium state in which no substance is exchanged with the outside of the membrane.

  Here, the state in which the entire membrane is immersed in an aqueous methanol solution having a uniform concentration is greatly different from the environment where the membrane is placed as a fuel cell. In a fuel cell, one side of the membrane is in contact with an aqueous methanol solution and the other side is in contact with air. From the viewpoint of mass transfer, there is a high concentration of methanol on the fuel electrode side, and the methanol concentration on the air electrode side is almost zero. Therefore, methanol permeates to the air electrode side due to the concentration difference on both sides. Furthermore, water and methanol are evaporated from the polymer electrolyte membrane on the air electrode side. Due to the evaporation from the air electrode side, methanol and water always move from the fuel electrode side to the air electrode side in the polymer electrolyte membrane, and the state should be in a steady state. Therefore, originally, the methanol concentration in the electrolyte membrane when methanol is moving in the membrane should be measured. Also, it is required to evaluate the methanol permeation characteristics of the polymer electrolyte membrane in this state

  In this regard, the technique described in Patent Document 2 is such that a gas or aqueous methanol solution is supplied to the polymer electrolyte membrane, and methanol or water moves through the polymer electrolyte membrane, that is, in an operating state of the fuel cell or a state close thereto. However, the concentration of methanol penetrating into the polymer electrolyte membrane was not measured.

According to the present invention,
An apparatus for evaluating the permeation characteristics of a solvent in a membrane,
A membrane holder for holding the membrane ,
A gas supply for supplying gas to one side of the membrane; and
A measurement cell comprising a solvent supply unit for supplying a protic solvent containing a compound having a hydrogen atom in the molecular structure on the other surface of the membrane ;
A static magnetic field application unit that applies a static magnetic field to the film;
A small RF coil that applies an oscillating magnetic field for excitation to the film and acquires a nuclear magnetic resonance signal in a partial region in the thickness direction of the film;
The nuclear magnetic resonance acquired by the small RF coil in a state where the gas is supplied to the one surface of the membrane and the protic solvent is supplied to the other surface and the measurement cell is not generating power. Calculate the concentration of the protic solvent in the partial region based on the signal, and calculate the time or speed until the concentration of the protic solvent reaches a steady state based on the change over time of the concentration of the protic solvent An arithmetic unit to perform,
A measuring device is provided.

Moreover, according to the present invention,
A method for evaluating the permeation characteristics of a solvent in a membrane,
Performed using the measuring device described above,
The measurement cell generates power while supplying a gas to one side of the membrane placed in a static magnetic field and a protic solvent containing a compound having a hydrogen atom in the molecular structure to the other side of the membrane. Applying an oscillating magnetic field for excitation to the film using a small RF coil in a state where it is not, and obtaining a nuclear magnetic resonance signal in a partial region in the thickness direction of the film;
Based on the nuclear magnetic resonance signal acquired by the small RF coil, the concentration of the protic solvent in the partial region is calculated, and the concentration of the protic solvent is calculated based on the change over time of the concentration of the protic solvent. Calculating the time or speed to reach steady state ;
A measurement method is provided.

In the present invention, nuclear magnetic resonance (NMR) measurement of a film is performed in a state where a gas is supplied to one side of the film and a solvent is supplied to the other side. In NMR measurement, an excitation oscillating magnetic field is applied to a film disposed in a static magnetic field using a small RF coil, and a nuclear magnetic resonance signal is acquired in a partial region in the thickness direction of the film. . The small RF coil is used as the detection coil, and gas is supplied to one surface of the film and solvent is supplied to the other surface, so that the solvent supplied from the other surface of the film is directed toward one surface. It is possible to calculate the concentration of the solvent in a part of the region as it permeates, and the characteristic value of the film is calculated based on the change over time.
As described above, according to the present invention, it is possible to perform measurement while the solvent is moving in the film, and it is possible to measure a specific portion in the thickness direction of the film. Thus, while conventionally limited to measurement in an equilibrium state, the present invention makes it possible to evaluate the permeation characteristics of the solvent in the membrane in the dynamic state.
The solvent includes a compound having a hydrogen atom in the molecular structure, and specific examples include protic solvents such as alcohol. Therefore, for example, the structure is suitable for evaluating the crossover characteristics of the solid polymer electrolyte membrane of the fuel cell. If the technique of the present invention is used to evaluate the crossover characteristics of a solid polymer electrolyte membrane, the membrane characteristics in a system according to the actual operating state of the fuel cell can be evaluated.

Here, acquiring a nuclear magnetic resonance signal in a partial region in the thickness direction of the film means acquiring a nuclear magnetic resonance signal in a substantially specific portion in the thickness direction of the film. The measured value of the nuclear magnetic resonance signal acquired by the detection coil at this time is an integral value over the entire area where the magnetic resonance signal is emitted and can be received by the detection coil, and more specifically, the nuclear magnetic resonance from the sample. It is an integrated value of the signal obtained by applying a weighting coefficient in the thickness direction of the sample including the signal emission intensity and the reception sensitivity of the coil. For this reason, when measuring with the detection coil, the signal is obtained from a region other than the specific portion in the thickness direction of the film if the signal has a magnitude that does not substantially affect the measurement value. It is good.
In the present invention, the small RF coil is arranged on, for example, the one surface of the film, and outputs a nuclear magnetic resonance signal in a region from the one surface to a specific depth from the middle of the thickness of the film. The calculation unit calculates the concentration of the solvent in the region from one surface to a specific depth based on, for example, the nuclear magnetic resonance signal.

In addition, the time-dependent change in the concentration of the solvent (for example, protic solvent) in the membrane is a state where the concentration is changing with respect to time (transient state) and a state where the concentration is constant with respect to time (steady state). State). Further, as the characteristic value of the film calculated based on the change in concentration with time, for example,
(I) the temporal change rate of the concentration when the concentration of the protic solvent is in a transient state;
(Ii) the time until the concentration of the protic solvent reaches a steady state, and (iii) the steady concentration of the protic solvent,
Can be calculated.

Among these, in the above (i), the temporal change rate of the local concentration of the protic solvent in the thickness direction of the membrane in the transitional state from the start of supplying the protic solvent until the steady state is reached. It can be measured directly on the spot.
As for (ii) above, if the time change rate of the concentration becomes almost zero, it can be considered that the concentration of the protic solvent has reached the steady state in terms of time, and the time until the steady state is reached It can be measured by a technique.
When calculating the above (i) or (ii) in the present invention, for example, the calculation unit is configured to calculate the protic solvent in the region from one surface to a specific depth based on a change with time of the protic solvent concentration. It is good also as a structure including the steady state arrival parameter calculation part which calculates the time or speed | rate until the density | concentration of reaches a steady state.

In (iii) above, the protic solvent contained in the membrane in the steady state can be determined. At this time, the calculation unit includes a steady concentration calculation unit that calculates a concentration in a steady state of the protic solvent in the region from one surface to a specific depth based on a change with time of the protic solvent concentration. It is good.
Furthermore, by combining the above (i) to (iii), the permeation characteristics of the protic solvent in the membrane can be evaluated from multiple aspects.

  In the present invention, a specific example of the protic solvent supplied to the other surface of the membrane includes an aqueous alcohol solution. At this time, the calculation unit uses the ratio of the area of the signal derived from alcohol and water and the area of the signal derived from alcohol in the nuclear magnetic resonance spectrum obtained from the nuclear magnetic resonance signal, The concentration of the alcohol in may be calculated.

  It should be noted that any combination of these components, or a conversion of the expression of the present invention between a method, an apparatus, and the like is also effective as an aspect of the present invention.

  As described above, according to the present invention, it is possible to reliably evaluate the solvent permeation characteristics of the membrane.

  The above-described object and other objects, features, and advantages will become more apparent from the preferred embodiments described below and the accompanying drawings.

It is a perspective view which shows schematic structure of the measurement cell in embodiment. It is a top view which shows the structure of the measurement cell produced in the Example. It is a figure which shows the solid polymer electrolyte membrane used in the Example. It is a functional block diagram which shows the structure of the calculating part of the measuring apparatus in embodiment. It is a figure which shows the structure of the measuring apparatus used in the Example. It is a figure which shows LC resonance circuit of the measuring apparatus in embodiment. It is a figure which shows an example of the small surface coil of the measuring apparatus in embodiment. In an Example, it is a figure which shows a mode that the small surface coil installed in the cell which pinched | interposed the solid polymer electrolyte membrane was connected to the LC resonance circuit. It is a figure which shows the liquid sample used for the measurement of the methanol density | concentration in an Example. It is a figure which shows the result of the spectrum analysis of the methanol aqueous solution in an Example. It is a figure which shows the relationship between the methanol concentration in an Example, and the area ratio of CH spectrum. It is a figure which shows the time passage of the area ratio of CH spectrum in an Example. It is a figure which shows the time passage of the area ratio of the OH spectrum in an Example. It is a figure which shows the linear approximation result of the measurement data of the solid polymer electrolyte membrane in an Example. It is a figure which shows the relationship between the methanol density | concentration of the methanol aqueous solution supplied to the solid polymer electrolyte membrane in the Example, and the methanol osmosis | permeation rate into a polymer electrolyte membrane. It is a figure which shows the relationship between the methanol density | concentration of the methanol aqueous solution supplied to the solid polymer electrolyte membrane in the Example, and the methanol osmosis | permeation rate into a polymer electrolyte membrane. It is a figure which shows the relationship between the methanol aqueous solution concentration supplied to the solid polymer electrolyte membrane in the Example, and the methanol concentration in the polymer electrolyte membrane in a steady state. It is a figure which shows the relationship between the methanol concentration supplied to the solid polymer electrolyte membrane at the time of reaching a steady state in an Example, and the methanol concentration in a solid polymer electrolyte membrane. It is a figure which shows the time passage of the area ratio of the CH spectrum of the solid polymer electrolyte membrane in an Example. It is a figure which shows the time passage of the area ratio of the OH spectrum of the solid polymer electrolyte membrane in an Example. It is a figure which shows ratio of the methanol concentration supplied to the solid polymer electrolyte membrane at the time of reaching a steady state in an Example, and the methanol concentration in a solid polymer electrolyte membrane. It is a figure which shows the linear approximation result of the measurement data of the solid polymer electrolyte membrane in an Example. It is a figure which shows the methanol penetration rate of the solid polymer electrolyte membrane in an Example. It is a figure which shows the structure of the measuring apparatus in embodiment. It is a figure which shows the direction of the magnetic field formed with the measuring apparatus shown in FIG. It is a figure which shows the structure of the measuring apparatus in embodiment. It is a figure which shows the structure of the coil used for the measuring apparatus shown in FIG. It is a figure which shows the direction of the magnetic field formed with the measuring apparatus shown in FIG. It is a figure which shows the structure of the measuring apparatus in embodiment. It is a front view which shows the structure of the measurement cell in embodiment. It is a side view which shows the structure of the measurement cell in embodiment. It is a circuit diagram which shows an example of a structure of the switch part of the measuring apparatus in embodiment. It is a figure which shows the shape of the surface coil in an Example, and the coordinate system in an analysis. It is a figure which shows the geometric shape of the surface coil in an Example. It is a figure which shows the coordinate system used for the analysis in an Example. It is a figure which shows the parameter used for the division | segmentation of a coil by the analysis in an Example. It is a figure which shows the shape of the circular coil divided | segmented by the analysis in an Example. It is a figure which shows the space used for the analysis in an Example. It is a contour map which shows the analysis result of z direction magnetic field intensity Hz of the surface coil in an Example. It is sectional drawing which shows the positional relationship between the coil and sample in an Example. It is a figure which shows the analysis result of the excitation angle distribution in an Example. It is a figure which shows the analysis result of the excitation angle distribution in an Example. It is a contour map which shows reception intensity distribution of the FID signal of the surface coil in an Example. It is a figure which shows the receiving intensity distribution of the FID signal on the z-axis of the surface coil in an Example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  Embodiments of the present invention will be described below with reference to the drawings. In all the drawings, common constituent elements are denoted by the same reference numerals, and description thereof is omitted as appropriate.

  In the following embodiments, the permeation characteristics of the solvent in the membrane are evaluated. First, the measurement principle used in the following embodiments will be described. Here, a case where the measurement target membrane is a solid polymer electrolyte membrane will be described as an example, but the measurement target membrane is not limited thereto. Moreover, although the case where a solvent is protic solvents, such as aqueous methanol solution, is illustrated here, a solvent is not restricted to aqueous methanol solution or other alcohol aqueous solution.

(Measurement principle)
The permeation characteristics of the protic solvent in the membrane are evaluated by the following procedure.
Step 11: Supply a gas (for example, nitrogen gas) to one surface of a membrane (for example, a solid polymer electrolyte membrane) placed in a static magnetic field, and a solvent (for example, for example, a solid polymer electrolyte membrane) While supplying a methanol aqueous solution), an oscillating magnetic field for excitation is applied to the solid polymer electrolyte membrane using a small RF coil, and a nuclear magnetic resonance signal in a partial region in the thickness direction of the solid polymer electrolyte membrane Get
Step 12: Calculate the methanol concentration in the partial region based on the nuclear magnetic resonance signal acquired by the small RF coil, and calculate the permeation characteristic value of methanol in the solid polymer electrolyte membrane based on the change over time.

More specifically, in step 11, based on the NMR method,
(I) Using a measurement cell capable of supplying a gas (for example, dry nitrogen) to one surface of the polymer electrolyte membrane and allowing a protic solvent (for example, aqueous methanol solution) of a predetermined concentration to flow to the other surface,
(Ii) A small surface coil (small RF coil) is installed on one surface (gas electrode) side, and ¹ HNMR measurement is performed on a partial region in the thickness direction of the film.
In step 12,
(Iii) Measure the methanol concentration penetrating into the polymer electrolyte membrane,
(Iv) From the measurement results, an index (membrane characteristic value) representing the permeation characteristics of the protic solvent is calculated.
As the characteristic value calculated in (iv) above, for example, the time or speed from the start of supplying the methanol aqueous solution to one surface of the membrane until the methanol concentration reaches a steady state can be mentioned. These are parameters that reflect the permeation rate of methanol penetrating into the membrane. Another example of the characteristic value is a steady concentration of methanol, that is, a methanol concentration in a steady state.
The above (i) to (iii) will be described more specifically below.

(I) Measurement cell FIG.1, FIG.30 and FIG.31 is a figure which shows an example of a structure of the measurement cell in this embodiment. FIG. 1 is a perspective view showing a schematic configuration of a measurement cell. FIG. 30 is a front view of the measurement cell, and FIG. 31 is a side view thereof.

  The measurement cell 201 shown in FIGS. 1, 30, and 31 functions as a membrane holding unit that holds a membrane (Polymer Electrolyte Membrane (PEM) 203). The measurement cell 201 includes a first substrate 207 disposed in contact with one surface of the solid polymer electrolyte membrane 203 and a second substrate 205 disposed in contact with the other surface. The first substrate 207 and the second substrate 205 are fixed by bolts 217 and nuts 219 while facing each other with the solid polymer electrolyte membrane 203 interposed therebetween.

  The first substrate 207 is provided with a gas supply unit (gas channel 213) that supplies gas to one surface of the solid polymer electrolyte membrane 203. The gas channel 213 is provided in the first substrate 207 in a groove shape, and is a channel through which nitrogen gas, inert gas, or the like flows. For example, nitrogen gas in a gas cylinder (not shown) is supplied from one end (inlet 215) of the gas channel 213 to the gas channel 213. The supplied nitrogen gas flows along the surface of the solid polymer electrolyte membrane 203, and during that time, the protonic solvent and the like in the membrane move into the nitrogen gas and interact with each other. It is discharged from the end (discharge port).

  Similarly, the second substrate 205 is provided with a solvent supply unit (methanol channel 209) that supplies a protic solvent to the other surface of the solid polymer electrolyte membrane 203. The methanol channel 209 is provided in the second substrate 205 in a groove shape, and is a channel through which a protic solvent such as a methanol aqueous solution flows. For example, a methanol aqueous solution in a liquid tank (not shown) is supplied from one end (injection port 211) of the methanol channel 209 to the methanol channel 209. Part of the supplied aqueous methanol solution penetrates into the solid polymer electrolyte membrane 203, and the rest is discharged from the other end (discharge port).

  FIG. 1 shows an example in which the gas flow path 213 and the methanol flow path 209 are formed in a meander shape, but the shape of these flow paths supplies gas or solvent to the surface of the solid polymer electrolyte membrane 203. Any configuration can be used, and the configuration is not limited to this.

(Ii) Local measurement in the film thickness direction by a small surface coil When calculating the methanol concentration in the film, a small RF coil smaller than the film is disposed on one surface of the solid polymer electrolyte membrane as a detection coil. Then, an excitation oscillating magnetic field is applied to the solid polymer electrolyte membrane disposed in the static magnetic field, and a specific portion in the thickness direction of the solid polymer electrolyte membrane (from the surface of the solid polymer electrolyte membrane The NMR signal generated in the middle region of the thickness of the molecular electrolyte membrane is acquired.

Here, the spin resonance frequency in a magnetic field of 1 Tesla is about 43 MHz, and an LC resonance circuit is used to selectively detect the frequency band with high sensitivity.
FIG. 6 is a diagram showing an LC resonance circuit including a small surface coil. As shown in FIG. 6, since the measurement region is limited in the film thickness direction by using a small surface coil for the coil part (inductance part) of the LC resonance circuit, the NMR is measured only from a specific part in the film thickness direction. A signal (for example, FID (Free Induction Decay) signal) can be acquired. Furthermore, since the small surface coil has a planar shape unlike a normal solenoid type coil, as shown in FIG. 6, an NMR signal can be acquired simply by sticking on a planar film.

FIG. 7 is a diagram illustrating an example of a small surface coil. The small surface coil shown in FIG. 7 is a planar “spiral type” coil. According to the analysis result of the present inventor, the measurement area of such a spiral coil has a width of about the diameter of the coil and a depth of about a quarter of the diameter of the coil, for example. By using such a small surface coil, local measurement in the thickness direction of the film becomes possible.
In addition, about the measurement area | region of the FID signal of a small surface coil, an analysis result is demonstrated still in detail in the Example mentioned later.

(Iii) Measurement of methanol concentration in membrane In this embodiment, the concentration of aqueous methanol solution is calculated by the chemical shift method.
That is, in the NMR method, the movement of nuclear magnetization is detected as an NMR signal by the spin resonance phenomenon of a nucleus placed in a magnetic field. For example, from the ¹ HNMR signal, it is possible to know whether CH and OH are different from the resonance frequency as the chemical bonding state of the atom, and further to know the ratio of CH and OH and the number density of each. This difference in resonance frequency is called “chemical shift”, and separation of CH and OH using the chemical shift is called a chemical shift method.

Even in the case of the hydrogen nucleus ¹ H, if the nuclide and structure chemically bonded are different, the resonance frequency is different. In the case of methanol CH ₃ OH, the resonance frequency differs between CH and OH. On the other hand, water (H ₂ O) has a resonance frequency almost the same as OH of methanol.
Therefore, when measuring only methanol in an aqueous methanol solution, the obtained NMR signal is subjected to Fourier analysis to separate only the component of the resonance frequency of CH, and the area ratio to the OH component and its area are obtained. Thus, the ratio and amount of methanol can be calculated.

  In the present embodiment, as described in (ii) above, a small coil having a smaller dimension than the sample (film) is used so that the NMR signal is acquired only from the local region. A small surface coil has a small measurement area and relatively high uniformity of the static magnetic field. For this reason, the rotation of a sample generally performed in an ordinary NMR apparatus is unnecessary, and the NMR spectrum of methanol OH and CH can be clearly separated without rotating the sample.

In addition, when calculating the methanol concentration in the film, a methanol solution of a predetermined concentration is measured in advance with a small detection coil, and spectrum analysis is performed to obtain the relationship between the methanol concentration and the area ratio of the CH spectrum as a calibration curve. Also good.
Specific calculation results of the methanol concentration will be described in more detail in the examples described later.

  In the following embodiment, a specific example of an apparatus configuration capable of measurement based on the above-described measurement principle will be shown.

(First embodiment)
FIG. 29 is a diagram illustrating a configuration of a measurement apparatus according to the present embodiment.
A measuring apparatus 100 shown in FIG. 29 is an apparatus for evaluating the permeation characteristics of a protic solvent in a membrane (solid polymer electrolyte membrane 203). More specifically, the measuring apparatus 100 is an apparatus for evaluating the crossover characteristics of the solid polymer electrolyte membrane 203 of the fuel cell.

The measurement apparatus 100 includes a membrane holding unit (measurement cell 201) that holds the solid polymer electrolyte membrane 203;
A gas supply unit (gas channel 213) for supplying gas to one surface of the solid polymer electrolyte membrane 203;
A solvent supply unit (methanol channel 209) for supplying a solvent to the other surface of the solid polymer electrolyte membrane 203;
A static magnetic field application unit (magnet 113) for applying a static magnetic field to the solid polymer electrolyte membrane 203;
A small RF coil 114 that applies an oscillating magnetic field for excitation to the solid polymer electrolyte membrane 203 and acquires a nuclear magnetic resonance signal in a partial region in the thickness direction of the solid polymer electrolyte membrane 203; and a solid polymer Based on the nuclear magnetic resonance signal acquired by the small RF coil 114 in a state where gas is supplied to one surface of the electrolyte membrane 203 and solvent is supplied to the other surface, the change in the solvent concentration with time in the partial region is changed. The calculation part 130 which acquires and calculates the permeation | transmission characteristic value of the solvent in the solid polymer electrolyte membrane 203 is included.

First, the peripheral configuration of the solid polymer electrolyte membrane 203 will be described.
The solid polymer electrolyte membrane 203 to be measured is used as a solid polymer electrolyte membrane of a direct methanol fuel cell, for example. The material of the solid polymer electrolyte membrane 203 is not particularly limited, and for example, an ion exchange membrane such as a perfluoro type sulfonic acid membrane.
Moreover, the measuring apparatus 100 includes the measuring cell 201 shown in FIGS. 1, 30 and 31 as a measuring cell in which the solid polymer electrolyte membrane 203 is disposed.

  The magnet 113 is, for example, a permanent magnet, and applies a static magnetic field to the entire solid polymer electrolyte membrane 203. With this static magnetic field applied, an excitation oscillating magnetic field is applied to the solid polymer electrolyte membrane 203, and the methanol concentration in the solid polymer electrolyte membrane 203 is measured.

  The small RF coil 114 applies an oscillating magnetic field for excitation to a specific portion of the solid polymer electrolyte membrane 203. Further, an NMR signal corresponding to the excitation oscillating magnetic field is acquired. Specifically, the small RF coil 114 is disposed on one surface (gas supply surface) of the solid polymer electrolyte membrane 203 and acquires a nuclear magnetic resonance signal in a region from one surface to a specific depth. . As the small RF coil 114, for example, the flat spiral coil described above with reference to FIG. 7 is used. By using such a planar coil, the measurement region can be limited to a partial region in the film thickness direction in the depth direction of the solid polymer electrolyte membrane 203. Since the thickness of the measurement region in the solid polymer electrolyte membrane 203 changes according to the diameter of the small RF coil 114, the size of the small RF coil 114 is set according to the film thickness of the solid polymer electrolyte membrane 203. . Specifically, only the NMR signal in a region having a specific depth from the gas supply surface of the solid polymer electrolyte membrane 203 is substantially acquired.

Further, the excitation oscillating magnetic field H ₁ applied by the small RF coil 114 needs to be perpendicular to the static magnetic field H ₀ applied by the magnet 113.
The oscillating magnetic field (exciting oscillating magnetic field) applied by the small RF coil 114 is generated by the cooperation of the RF oscillator 102, the modulator 104, the RF amplifier 106, the control unit 169, the switch unit 161, and the small RF coil 114. That is, the excitation oscillating magnetic field oscillated from the RF oscillator 102 is modulated by the modulator 104 based on control by the control unit 169 functioning as a pulse control unit, and becomes a pulse shape. The generated RF pulse is amplified by the RF amplifier 106 and then transmitted to the small RF coil 114. The small RF coil 114 applies this RF pulse to a specific portion of the solid polymer electrolyte membrane 203 disposed in the measurement cell 201. And the small RF coil 114 detects the NMR signal emitted with respect to the applied RF pulse. This NMR signal is amplified by the preamplifier 112 and then sent to the phase detector 110. The phase detector 110 detects this NMR signal and sends it to the A / D converter 118. The A / D converter 118 performs A / D conversion on the NMR signal, and then sends the NMR signal to the calculation unit 130 via the data reception unit 131.

A sequence table 127 and a timer unit 128 are connected to the control unit 169. The sequence table 127 stores, for example, the application time of the high frequency pulse when measuring the methanol concentration in the film, the width, phase, and intensity of the applied high frequency pulse.
When the control unit 169 receives a measurement request from the operator, the control unit 169 controls the operation of the modulator 104 based on the sequence data acquired from the sequence table 127 and the measurement time in the time measuring unit 128 to control the high-frequency pulse. And an oscillating magnetic field for excitation is applied to the solid polymer electrolyte membrane 203.

  The application of the excitation oscillating magnetic field and the detection of the NMR signal have been described above, but these can be realized by an LC circuit including the small RF coil 114. As the LC circuit including the small RF coil 114, for example, the circuit described above with reference to FIG. 6 is used.

  The measuring apparatus 100 further includes a switch unit 161. The switch part 161 is provided in the branch part which connects the small RF coil 114, the RF excitation pulse generation part, and the NMR signal detection part.

  Here, the RF excitation pulse generation unit includes an RF oscillator 102, a modulator 104, and an RF amplifier 106, and generates an RF excitation pulse that causes the small RF coil 114 to generate an excitation oscillating magnetic field. The NMR signal detection unit includes a preamplifier 112, a phase detector 110, and an A / D converter 118. The NMR signal detection unit detects the NMR signal acquired by the small RF coil 114 and sends the NMR signal to the calculation unit 130.

  The switch unit 161 is connected to the first state in which the small RF coil 114 and the RF excitation pulse generation unit (RF amplifier 106) are connected, and to the small RF coil 114 and the NMR signal detection unit (phase detector 110). The second state is switched. That is, the switch unit 161 functions as a “transmission / reception switching switch”. Specifically, when transmitting the excitation pulse amplified by the RF power-amp to the surface coil, the switch unit 161 separates the pre-amp of the receiving system and protects it from a large voltage. Further, when receiving the NMR signal after excitation, the switch unit 161 blocks the noise generated by the large amplification transistor leaking from the RF power-amp so as not to be transmitted to the pre-amp of the receiving system.

In the measuring apparatus 100, since the small RF coil 114 is used as the detection coil, the received NMR signal is weak. Therefore, by providing the switch unit 161, the received signal can be detected more reliably.
Note that the switch unit 161 can employ various configurations. FIG. 32 is a circuit diagram illustrating an example of the configuration of the switch unit 161.

The apparatus configuration around the solid polymer electrolyte membrane 203 has been described above. Next, an NMR signal processing block will be described.
The NMR signal detected by the small RF coil 114 is detected by the phase detector 110 through the preamplifier 112, and is transmitted to the A / D converter 118 as an NMR signal in the audio frequency band. The A / D converter 118 A / D converts the NMR signal waveform and sends it to the data receiving unit 131. The data reception unit 131 sends the received data to the calculation unit 130. The control unit 169 controls the signal capturing timing of the A / D converter 118 and the operation of the data receiving unit 131.

  FIG. 4 is a functional block diagram illustrating a configuration example of the calculation unit 130. In FIG. 4, the calculation unit 130 includes an alcohol concentration calculation unit (methanol concentration calculation unit 221), a transmission characteristic evaluation parameter calculation unit 223, and a calculation parameter storage unit 225.

In the calculation parameter storage unit 225, for example,
Methanol mole fraction (methanol moles / (methanol moles + water moles)),
Spectra showing only methanol (spectrum of hydrogen nuclei bonded to C atoms) relative to the sum of the spectral intensities of water and methanol (the intensity of the spectrum of hydrogen nuclei bonded to C atoms and the intensity of the spectrum of hydrogen nuclei bonded to O atoms) ) Intensity ratio,
The relationship is remembered.

  The methanol concentration calculation unit 221 calculates the methanol concentration in a region from one surface of the solid polymer electrolyte membrane 203 to a specific depth, that is, a measurement region, from the FID signal detected by the small RF coil 114. For example, the methanol concentration calculation unit 221 refers to the calculation formula stored in the calculation parameter storage unit 225, and in the nuclear magnetic resonance spectrum obtained from the NMR signal, the area of the signal derived from methanol and water, and from the methanol. Using the ratio to the area of the signal, the concentration of methanol in the film in the measurement region is calculated. More specifically, the methanol concentration calculation unit 221 acquires a spectrum caused by water and methanol at a specific portion of the solid polymer electrolyte membrane 203 based on the FID signal acquired by the small RF coil 114. Then, the ratio of the intensity of the spectrum showing only methanol to the total value of the intensity of the spectrum caused by water and methanol at a specific location of the solid polymer electrolyte membrane 203 is calculated. Then, the methanol concentration calculation unit 221 calculates the mole fraction of methanol based on the correlation stored in the calculation parameter storage unit 225, and stores it in the methanol concentration calculation unit 221 in association with the parameter relating to time.

The methanol concentration calculation unit 221 acquires a data analysis unit (not shown) that performs a Fourier analysis of the FID signal acquired by the small RF coil 114 and a result obtained by analyzing the data analysis unit, and a spectrum indicating only methanol, that is, You may include the calculation part (not shown) which detects the spectrum corresponding to the chemical shift value of the hydrogen nucleus couple | bonded with C atom.
At this time, the calculation unit calculates the intensity of the spectrum of the hydrogen nucleus bonded to the C atom. The calculation unit also detects the intensity of the spectrum corresponding to the chemical shift value of the hydrogen nucleus bonded to the O atom. Next, the calculation unit calculates only the methanol with respect to the sum of the spectrum intensities of water and methanol (the sum of the spectrum intensity of the hydrogen nucleus bonded to the C atom and the spectrum intensity of the hydrogen nucleus bonded to the O atom). The ratio of the intensities of the spectra (the spectrum of hydrogen nuclei bonded to C atoms) is calculated. Thereafter, the calculation unit refers to the calculation parameter storage unit 225 and acquires the molar fraction of methanol corresponding to the calculated ratio. Thereby, the mole fraction of methanol as the methanol permeation characteristic of the solid polymer electrolyte membrane 203 can be grasped.
Note that the calculation unit may calculate not only the molar fraction of methanol but also the molar fraction of water.

  The transmission characteristic evaluation parameter calculation unit 223 calculates a characteristic value in a partial region (measurement region) of the membrane based on a change in methanol concentration with time. In the example illustrated in FIG. 4, the transmission characteristic evaluation parameter calculation unit 223 includes a steady state arrival parameter calculation unit 227 and a steady concentration calculation unit 229.

Among these, the steady state arrival parameter calculation unit 227 acquires data in which the methanol concentration stored in the methanol concentration calculation unit 221 is associated with the measurement time as data indicating a change in methanol concentration with time, and the acquired data is obtained. The time or speed until the concentration of the methanol concentration reaches a steady state in the region from one surface of the solid polymer electrolyte membrane 203 to a specific depth is calculated.
In addition, the steady concentration calculation unit 229 acquires data in which the methanol concentration stored in the methanol concentration calculation unit 221 is associated with the measurement time, and uses one surface of the solid polymer electrolyte membrane 203 using the acquired data. The concentration of the protic solvent in the steady state in the region from to a specific depth is calculated.

  The calculation unit 130 sends the characteristic value of the film calculated as described above to the output unit 138. The sent characteristic value is output from the output unit 138 and presented to the user. Various types of presentation types are possible, and there are no particular restrictions on display on the display, printer output, file output, and the like.

Next, the effect of this embodiment is demonstrated.
In the present embodiment, by using a small surface coil (small RF coil 114), the measurement region can be limited to only a region that is substantially thinner than the thickness of the solid polymer electrolyte membrane 203. That is, the NMR signal can be acquired only from the local area in the thickness direction of the film. Further, in the present embodiment, measurement using the small RF coil 114 is performed in a state where nitrogen gas is supplied to one surface of the solid polymer electrolyte membrane 203 and methanol aqueous solution is supplied to the other surface. According to this embodiment, according to the present embodiment, the methanol concentration penetrating into the inside of the membrane from the surface opposite to the membrane surface where the small surface coil is installed is measured on the spot, and the time series Measurement is possible. Further, a parameter indicating the ease of methanol permeation into the membrane when a methanol aqueous solution is supplied from one side of the solid polymer electrolyte membrane 203 as a characteristic value of the solid polymer electrolyte membrane 203 from a change in methanol concentration over time. As described above, the rate (permeation rate) or time until the steady state is reached and the methanol concentration in the steady state can be measured. Thereby, the permeation | transmission characteristic of methanol in a film | membrane can be evaluated effectively.

Further, according to the present embodiment, for example, the following operational effects can be obtained.
First, CH and OH are distinguished by the chemical shift method, and the local “ratio and amount of methanol” in the film thickness direction, not the entire sample, can be measured in a short time of several hundreds of milliseconds.
In addition, since the static magnetic field is highly uniform because only a minute region is measured, it is not necessary to rotate the sample to achieve high spectral resolution as in a normal chemical analysis NMR apparatus.
Moreover, non-invasive measurement using electromagnetic waves can be performed only by pasting on the surface of the polymer film.
In addition, a small detection coil is used to penetrate the polymer electrolyte membrane using a cell that can flow a gas (dry nitrogen) on one side of the polymer electrolyte membrane and a methanol aqueous solution of a predetermined concentration on the other side. By using a device capable of measuring the methanol concentration, the methanol concentration penetrating the polymer electrolyte membrane can be measured in time series by a small detection coil installed on the air side.
Further, by using the above apparatus and method, the methanol permeation rate permeating the polymer electrolyte membrane and the methanol concentration at the steady state can be measured from the methanol concentration obtained in time series.
In addition, using the apparatus and method described above, the methanol permeation rate and steady-state methanol concentration of electrolyte membranes with different molecular structures were measured under the same conditions, and the characteristics related to methanol permeability were directly compared and evaluated. can do.
In addition, the “ratio or amount of methanol” in the polymer electrolyte membrane is measured, and the methanol concentration is adjusted to minimize methanol crossover, and control is performed so that the optimum power generation state can always be maintained. be able to.

  The following embodiment will be described with a focus on differences from the first embodiment.

(Second embodiment)
In the first embodiment, the whole sample is measured by inserting it into the magnet. However, it is also possible to perform NMR measurement by applying a static magnetic field to only a part of the sample. In this embodiment, such a measuring apparatus will be described.
Although FIGS. 24 to 26 and FIG. 28 show the configuration in which the measurement apparatus includes the gradient magnetic field coil, the gradient magnetic field coil may not be provided in the present embodiment.

FIG. 24 is a diagram illustrating the configuration of the measurement apparatus according to the present embodiment. In FIG. 24, the magnets are arranged so that the static magnetic field is perpendicular to the central axis of the bar sensor. As a result, the direction H ₁ of the static magnetic field is perpendicular to the direction H _{1 of the} oscillating magnetic field for excitation of the spiral RF detection coil, and an NMR signal can be received. FIG. 25 is a diagram showing the direction of the magnetic field formed by the integrated sensor shown in FIG.

In FIG. 24, a spiral RF detection coil is placed on a protrusion formed at one end of the apparatus and placed in contact with a sample. A magnet is contained in the rod-shaped part, which forms a static magnetic field.
The rod-shaped sensor shown in FIG. 24 does not require a large magnet for applying a static magnetic field, and becomes an integrated sensor that can easily perform NMR measurement like a thermocouple.

  Moreover, a magnet can also be arrange | positioned so that a static magnetic field may become the same direction as the central axis of a rod-shaped sensor. FIG. 26 is a diagram showing a configuration of such a measuring apparatus, and FIG. 27 is a diagram showing a configuration of a coil used in the measuring apparatus shown in FIG. In FIG. 26 as well, as in FIG. 24, the detection coil is disposed on the protrusion and placed in contact with the sample.

However, in FIG. 26, the excitation oscillating magnetic field H ₁ needs to be applied in the direction perpendicular to the central axis of the rod. For this reason, in FIG. 26, the “8-shaped coil” (or “butterfly coil”, “Double-D coil”) shown in FIG. 27 is used as the RF detection coil. Also in FIG. 26, the direction H _{1 of} the static magnetic field H ₀ and the direction H _{1 of the} oscillating magnetic field for excitation of the 8-shaped coil are perpendicular, and an NMR signal can be received. FIG. 28 is a diagram showing the direction of the magnetic field formed by the integrated sensor shown in FIG.

  According to this embodiment, in addition to obtaining the operational effects of the first embodiment, the sensor that is not limited by the size of the magnet can be obtained by integrating the RF detection coil and the magnet. Become. Moreover, by making it rod-shaped, it is possible to reduce the size of the measuring apparatus and to easily perform NMR measurement like a thermocouple.

  As mentioned above, although embodiment of this invention was described with reference to drawings, these are the illustrations of this invention, Various structures other than the above are also employable.

  For example, in the above embodiment, the configuration in which the measurement apparatus has one small RF coil 114 has been described as an example, but a configuration including a plurality of small RF coils 114 may be employed. By doing so, the distribution and variation in the in-plane direction of the membrane can be further calculated for the methanol permeability in the membrane, so that the crossover characteristics of the solid polymer electrolyte membrane 203 can be evaluated in more detail.

  In the above embodiment, the example in which the small RF coil is disposed on the gas supply side surface of the solid polymer electrolyte membrane has been described. However, the small RF coil may be disposed on the liquid supply surface side.

  In the above embodiment, if a nuclide (for example, only CH or only OH) to be measured is excited and measured using a PGSE (Pulsed-Gradient Spin-Echo) method, the self-diffusion coefficient of the target nuclide Alternatively, the mobility can be further measured. If a small coil is used, local measurement is also possible.

Moreover, according to the above embodiment, the following effects can be obtained, for example.
(I) Provided with a small detection coil, using a cell that can flow a gas (dry nitrogen) on one side of the polymer electrolyte membrane and a methanol aqueous solution of a predetermined concentration on the other side, penetrate the polymer electrolyte membrane. By using a device that can measure the concentration of methanol going through, the polymer electrolyte membrane is not immersed in an aqueous methanol solution and the amount of methanol absorbed is measured in an equilibrium state. It is possible to measure the methanol concentration in a cell in which methanol or water can move through the polymer electrolyte membrane by supplying a methanol aqueous solution.
(Ii) By using the apparatus of (i) above, the methanol concentration penetrating the polymer electrolyte membrane can be measured in time series by a small detection coil installed on the air side. As a result, in the conventional NMR apparatus that measures the entire sample, measurement was possible only when the membrane was in an equilibrium state, whereas the state of methanol permeating through the membrane was measured as the amount of methanol permeation. Therefore, it is possible to accurately measure the crossover amount.
(Iii) The permeation rate of methanol permeating the polymer electrolyte membrane from the methanol concentration obtained in time series using the apparatus (i) and the method (ii), and when the steady state is reached. The methanol concentration can be measured. For this reason, it is possible to measure the permeation rate of methanol permeating into the polymer electrolyte membrane.
(Iv) Using the apparatus (i) and the methods (ii) and (iii), the methanol permeation rate and the methanol concentration in the steady state of electrolyte membranes having different molecular structures were measured under the same conditions. Properties relating to methanol permeability can be evaluated. Thereby, the methanol permeation rate into the polymer electrolyte membrane and the methanol concentration in the steady state can be quantified as the methanol permeability of the membrane, and compared with the membranes having different molecular structures.
(V) Methanol permeation characteristics can be evaluated in a short time in a situation close to the fuel cell structure.
(Vi) Based on the characteristic evaluation, it is useful for the development of a polymer electrolyte membrane with a reduced amount of methanol crossover.
(Vii) By constantly measuring methanol penetrating into the polymer electrolyte membrane, it is possible to supply a fuel with an optimal methanol concentration that reduces the amount of crossover and enables high-efficiency power generation.
(Viii) It is possible to monitor performance degradation due to deterioration of the polymer electrolyte membrane or the catalyst.
(Ix) Non-invasive measurement using electromagnetic waves is performed only by pasting on the surface of the polymer film.
(X) By integrating the small detection coil and magnet, it is not necessary to change the shape and size of the magnet according to the size of the sample, and conversely, the sample must be of a size that can be inserted into the magnet. There is no limitation, and the sensor has no limitation on the dimensions of the sample and the magnet. Moreover, if it is made into a rod shape, NMR measurement can be easily performed like a thermocouple.

Example 1
In this example, the cell with flow path shown in FIGS. 1 and 2 was produced as a measurement cell simulating a direct methanol fuel cell. FIG. 2 is a top view showing the configuration of the measurement cell produced in this example.

The dimensions of the gas supply channel and liquid supply channel of the measurement cell were both 1.0 mm wide and 1.0 mm deep. In Examples 2 to 4 described later, a polymer electrolyte membrane or a liquid sample is sandwiched between cells, nitrogen gas is supplied to the upper channel in the figure at 50 ml / min, and water or methanol aqueous solution is added to the lower channel. Flowed at 5 ml / min.
Further, as shown in FIG. 2, the small detection coil is embedded in the cell on the gas side, and is pressed against the surface of the polymer electrolyte membrane from this side.

Further, as shown in FIG. 2, a D ₂ O channel (temperature control channel in FIG. 2, not shown in FIG. 1) for adjusting the temperature passes through the measurement cell, and D By changing the temperature of ₂ O, the temperature environment of the polymer electrolyte membrane can be changed or controlled. The D ₂ O only passes through the inside of the cell and does not touch the polymer electrolyte membrane. In Examples 2 to 4 described later, the cell temperature was 20 ° C. in all cases.

(Example 2)
In this example, using the measurement cell produced in Example 1, local NMR measurement of a methanol aqueous solution having a predetermined concentration was performed. As shown in FIG. 2, a small circular surface coil (small detection coil in the figure) was arranged at the center of the cell.

FIG. 5 is a diagram showing the configuration of the measuring apparatus used in this example. The apparatus shown in FIG. 5 is configured in accordance with the apparatus shown in FIG. 29. In the switch unit 161 (“□” (open square in the drawing) described above in the first embodiment, “ It is indicated by a symbol of “×”. The apparatus shown in FIG. 5 further includes a gradient magnetic field coil, and is configured to be able to apply a gradient magnetic field to the solid polymer electrolyte membrane 203 as appropriate.
In this example, the LC resonance circuit (FIG. 6) including the small surface coil shown in FIG. 7 was used.

(Relationship between methanol concentration and CH spectrum area ratio)
Prior to measurement of the solid polymer electrolyte membrane, a methanol aqueous solution having a predetermined concentration was measured with the above-described small detection coil, and a spectrum analysis was performed to obtain a relationship between the methanol concentration and the area ratio of the CH spectrum as a calibration curve. .

  Methanol aqueous solutions with methanol concentrations of 0, 2.5, 5.0, 7.5 and 10 vol% were prepared. A 10 mm diameter hole is made in an acrylic plate with dimensions 18 mm x 18 mm and thickness 0.5 mm, and two cover glasses with dimensions 18 mm x 18 mm and thickness 0.12 mm are adhered to both sides of the acrylic to form a sealed container, An aqueous methanol solution was enclosed in the solution. FIG. 9 is a diagram showing the liquid sample used.

An excitation pulse was irradiated from the small surface coil with a pulse width of 40 μs, and the FID signal was received by the small surface coil. The sampling interval of the A / D converter was 40 μs, the number of data points was 8192, the measurement time was about 320 ms, and the NMR signal was acquired as a two-component signal of a real part and an imaginary part. Note that OH and CH differ in nuclear magnetic resonance frequency by several ppm.
The obtained FID signal was subjected to complex Fourier analysis, Fourier coefficients were calculated, and spectrum analysis was performed. Here, the Fourier coefficient is a value obtained by squaring the real and imaginary Fourier coefficients obtained by the complex Fourier analysis and taking the sum to obtain the square root.

  As a typical measurement example, the result of spectral analysis of a 5 vol% methanol aqueous solution is shown in FIG. In FIG. 10, the horizontal axis represents the frequency shift amount, and the peak of the OH spectrum is the origin. Here, the horizontal axis is normalized by the NMR frequency of 43.1 MHz, and the unit is shown in ppm. The frequency resolution is 0.142 ppm. It can be seen that the CH spectrum appears at about 1.5 ppm. Further, it can be seen from the OH spectrum of FIG. 10 that a spectrum having a line width of about 0.2 ppm is obtained using a small surface coil. Generally, a method is used in which the static magnetic field strength is increased to increase the spectral resolution. However, in the case of a small surface coil, the spatial uniformity of the static magnetic field in the measurement region becomes relatively high by reducing the diameter. Therefore, it is possible to improve the spectral resolution very easily, thereby enabling high-resolution NMR spectrum measurement.

With increasing methanol concentration, the intensity of the CH spectrum increased. When the methanol concentration was low, the base of the OH spectrum was widened and overlapped with the CH spectrum. Therefore, a method of extracting only the CH spectrum by extrapolating the OH spectrum distribution was used. The area of the spectrum was the area up to the position where each Fourier coefficient of the OH and CH spectra was half of the maximum value.
The relationship between the methanol concentration thus obtained and the area ratio of the CH spectrum (CH / (CH + OH)) is shown in FIG. FIG. 11 was used as a calibration curve relating both.

(Example 3)
In this example, the concentration of methanol penetrating into the polymer electrolyte membrane was measured by the measurement cell and measurement device used in Example 2.
As the solid polymer electrolyte membrane, a perfluoro sulfonic acid membrane (hereinafter referred to as membrane A) having a size of 15 mm × 15 mm and a thickness of 500 μm was used. The structural formula of the film A is shown in the following formula (1).

In the above formula (1), x, y, m and n are each independently zero or a positive number.
FIG. 3 is a diagram showing a sample of the film A used in this example. FIG. 8 is a diagram showing a state in which a small surface coil installed in a cell sandwiching the film A is connected to an LC resonance circuit in this example. In this example and example 4, no catalyst or the like is attached to the film surface.

  The polymer electrolyte membrane shown in FIG. 3 was sandwiched between cells with a flow path shown in FIG. 1, nitrogen gas was flowed at 50 ml / min in the upper flow path, and water was flowed in the lower flow path. This state was maintained for 2 hours to obtain a steady state. The cell temperature is 20 ° C. Since the NMR signal is acquired from the area of about 1/4 of the 1.3 mm diameter of the small detection coil, the methanol concentration on the nitrogen gas side in the polymer electrolyte membrane is measured by using this coil. become.

  The time when the methanol aqueous solution started flowing was set to zero, and the area ratio of the CH spectrum increasing with the passage of time was calculated. The results are shown in FIG. In this experiment, methanol aqueous solutions having three different concentrations of 10, 20, and 30 vol% were used. From FIG. 12, it can be seen that the methanol concentration in the electrolyte membrane increases with time, and becomes almost constant after 2500 seconds. This constant value state is considered to be in a steady state in which the aqueous methanol solution supplied from one side of the electrolyte membrane and the evaporation from the other side are balanced.

  In this measurement, when calculating the area ratio of the CH spectrum, the area ratio of the OH spectrum is also calculated. When both are added, the relationship is always 1. FIG. 13 is a diagram showing the time passage of the area ratio of the OH spectrum. From FIG. 13, it can be seen that the proportion of water decreases from the polymer electrolyte membrane with the passage of time, methanol permeates, and water is discharged accordingly.

Subsequently, the permeation rate of methanol penetrating into the polymer electrolyte membrane and the methanol concentration in a steady state were calculated.
That is, “the permeation speed tau [1 / s] of methanol penetrating into the polymer electrolyte membrane” is calculated based on the measurement result of FIG. The permeation rate tau is obtained as an increase rate of the area ratio of the CH spectrum obtained during the period from 0 to 2500 seconds after injecting the methanol aqueous solution. Here, the data for 0 to 2500 seconds was linearly approximated by the method of least squares, and the gradient was defined as the permeation speed tau [1 / s]. FIG. 14 is a diagram showing, as a typical example, a state in which measurement data in the case of a 30 vol% methanol aqueous solution is approximated by a straight line by the least square method. From this, the penetration rate is
tau (membrane A, 30 vol%) = 4.04 × 10 ⁻⁵ [1 / s]
And calculated.
In addition, although the vertical axis | shaft of FIG. 12 was made into the area ratio CH / (CH + OH) of CH spectrum, this can also be converted into methanol concentration using the relationship of FIG. However, in the case of this conversion, it is assumed that the relationship shown in FIG. 11 is substantially the same in both the polymer electrolyte membrane and the methanol aqueous solution. If this conversion is used, the vertical axis of FIG. 12 becomes the methanol concentration [vol%] from the CH spectrum area ratio CH / (CH + OH), and accordingly, the above-mentioned “permeation of methanol penetrating into the polymer electrolyte membrane”. “Unit of velocity tau” can also be written as [vol% / s].

  The same method as in the case of 30 vol% was also applied to the results of 10 and 20 vol% methanol aqueous solution to determine the permeation rate of each. 15 and 16 are diagrams showing the relationship between the methanol concentration of the supplied aqueous methanol solution and the methanol permeation rate into the polymer electrolyte membrane.

  Further, assuming that the “relation between the methanol concentration of the methanol aqueous solution and the area ratio of the CH spectrum” shown in FIG. 11 can be applied even inside the polymer electrolyte membrane, the CH spectrum after 2500 seconds in FIG. From the average value of the area ratio, the methanol concentration in the polymer electrolyte membrane was converted. The results are shown in FIG. FIG. 17 is a diagram showing the relationship between the supplied aqueous methanol solution concentration and the methanol concentration in the polymer electrolyte membrane in a steady state.

From the relationship shown in FIG. 17, the ratio between the methanol concentration C _PEM [vol%] in the polymer electrolyte membrane and the methanol concentration C _fuel [vol%] of the supplied aqueous methanol solution was calculated. The result is shown in FIG. FIG. 18 is a graph showing the relationship of the ratio C _PEM / C _fuel between the methanol concentration C _PEM [vol%] in the polymer electrolyte membrane and the methanol concentration C _fuel [vol%] of the supplied aqueous methanol solution. As shown in FIG. 18, when the polymer electrolyte membrane is evaporated from one side and the methanol aqueous solution is supplied from the other side and it is in a steady state, the ratio C _PEM / C _fuel of both is in the range of about 20-30%. I understood that.

Example 4
In this example, the methanol permeation characteristics of the polymer electrolyte membrane having a molecular structure different from that of the solid polymer electrolyte membrane used in Example 3 were evaluated and compared with the results of Example 3.

Specifically, the polymer electrolyte membrane is the same perfluoro type sulfonic acid membrane as the membrane A used in Example 3, and x, y, m and n in the above formula (1) are different from the membrane A. Membrane B was used.
The dimension of the membrane B was 17 mm × 17 mm and the thickness was 356 μm. In this example, two commercially available sheets having a thickness of 178 μm were laminated to a thickness of 356 μm. To laminate the two sheets, a polymer dispersion of the same material as membrane B was applied to the sheets and stacked, and then hot pressed in a vacuum.
For the obtained membrane B, the methanol permeation rate and the ratio C _PEM / C _fuel when supplying the same 20 vol% methanol aqueous solution as in Example 3 were obtained and compared with the results of the membrane A.

  Experiments were performed using the same cell and small detection coil as in Example 3. The membrane B was sandwiched between cells with a flow path shown in FIG. 1, nitrogen gas was flowed at 50 ml / min in the upper flow path, and water was flowed in the lower flow path. This state was maintained for 2 hours to obtain a steady state. The cell temperature is 20 ° C.

FIG. 19 shows the area ratio of the CH spectrum that increases with the passage of time, assuming that the time when the 20 vol% aqueous methanol solution started flowing is zero. FIG. 19 shows the time lapse of the area ratio of the CH spectrum when a 20 vol% methanol aqueous solution was passed through the membrane B, and for comparison, the 20 vol% methanol aqueous solution of the membrane A in Example 3 was used for comparison. The measurement results were also shown.
From FIG. 19, it can be seen that also in the membrane B, the methanol concentration in the membrane increases with time, and becomes substantially constant after 2500 seconds to 3000 seconds. However, there is a clear difference between the methanol penetration rate and the methanol concentration in the steady state.

  Also in the present embodiment, similarly to the third embodiment, when calculating the area ratio of the CH spectrum, the area ratio of the OH spectrum is also calculated. When both are added, the relationship is always 1. FIG. 20 is a diagram showing the time passage of the area ratio of the OH spectrum of film B. FIG. Also in FIG. 20, the time course of the area ratio of the OH spectrum in the case where a 20 vol% methanol aqueous solution was passed through the membrane A in addition to the membrane B is also shown. As can be seen from FIG. 20, the proportion of water decreases from the polymer electrolyte membrane with the passage of time, methanol permeates, and water is discharged accordingly.

  Next, the effect of the two samples (film A and film B) on the measurement results due to the different thicknesses was examined. As described above, the thickness of the film A is 500 μm, and the thickness of the film B is 356 μm.

Here, as a dimensionless number representing a phenomenon in which heat or a substance diffuses with time in a homogeneous substance, there is a Fourier number Fo represented by the following equation.
Fo = L ² / (D × t)
In the above formula, L is the film thickness [m], D is the diffusion coefficient [m ² / s] of the moving substance, and t is the time [s].

  The Fourier number Fo shows how the scale of time t changes when the film thickness L is different. If the boundary conditions are the same (in this case, the boundary conditions of the same concentration), it is shown that a completely similar phenomenon occurs when the Fourier numbers are the same. For example, consider material diffusion in a membrane. It is assumed that the concentration distribution at time t is reached when the thickness of the film is L. When the thickness of the film is halved (L / 2), the time required to obtain the same concentration distribution as before is ¼ (t / 4). The thinner the film, the shorter the time for the same concentration distribution.

Since the film thickness of film B is 356/500 of the film thickness of film A, assuming the same diffusion coefficient, the phenomenon is time
(356/500) ² = 0.51
It will be shortened and will proceed quickly. Although the membrane B is thin, the increase rate of the methanol concentration is slower than that of the membrane A, and it can be said that the methanol concentration when the steady state is reached is also small. From this, it can be said that the membrane B used this time has smaller methanol permeability than the membrane A.

Next, from the area ratio of the CH spectrum after 2500 seconds, which became almost steady (FIG. 19), the methanol concentration C _PEM [vol%] in the polymer electrolyte membrane and the methanol concentration C _{fuel of the} supplied aqueous methanol solution The ratio with [vol%] was calculated. The results are shown in FIG. FIG. 21 shows the ratio C _PEM / C _fuel with the methanol concentration C _PEM [vol%] when C _fuel = 20 vol% methanol aqueous solution [vol%] is supplied to the polymer electrolyte membrane (membrane A and membrane B). FIG.
FIG. 21 shows that when the polymer electrolyte membrane is evaporated from one side and the methanol aqueous solution is supplied from the other side and is in a steady state, the ratio C _PEM / C _fuel in the membrane B is compared with that in the membrane A. It was found that it was about two-thirds.

  Furthermore, based on the measurement result of FIG. 19, “the penetration rate tau [1 / s] of methanol penetrating into the polymer electrolyte membrane” was calculated. The permeation rate tau was determined as the rate of increase of the area ratio of the CH spectrum obtained during the period from 0 to 2500 seconds after injecting the methanol aqueous solution. Here, the data for 0 to 2500 seconds was linearly approximated by the method of least squares, and the gradient was defined as the permeation speed tau [1 / s].

FIG. 22 is a diagram illustrating a linear approximation result of the measurement data of the film B. From FIG. 22, the penetration rate is
tau (membrane B, 20 vol%) = 2.25 × 10 ⁻⁵ [1 / s]
And calculated.

The calculation results of tau for membranes A and B are summarized in FIG. FIG. 23 is a diagram showing a comparison of methanol permeation rates when a 20 vol% aqueous methanol solution was supplied to the polymer electrolyte membranes (membrane A and membrane B).
FIG. 23 shows that the membrane B has a lower permeation rate than the membrane A even though the membrane A has a thin film thickness of 356/500.

  As this result shows, using a cell equipped with a small detection coil and capable of flowing a gas (dry nitrogen) on one side of the polymer electrolyte membrane and a methanol aqueous solution of a predetermined concentration on the other side, the membrane A and The methanol permeation rate of the membrane B and the methanol concentration in the steady state were measured under the same conditions, and both of the properties relating to methanol permeability could be evaluated as numerical values.

  This example shows that the methanol permeation characteristics of the membrane A and the membrane B can be evaluated, and that the difference between the two can be quantitatively shown.

(Example 5)
In this example, the measurement region when the FID signal was acquired was analyzed for the small surface coil (FIG. 7) used in the measurement in the above example. In this analysis, the excitation magnetic field distribution created by the surface coil is obtained, the excitation angle of the magnetization vector at the coil center (x = 0, y = 0, z = 0) is set to 90 degrees, and the reception sensitivity of the NMR signal is taken into consideration. The intensity distribution of the FID signal was calculated by the following procedure.
(I) determine the geometry of the surface coil and introduce assumptions in the analysis;
(Ii) theoretically analyzing the magnetic field Hz (x _p , y _p , z _p ) created by the surface coil at the position (x _p , y _p , z _p ),
(Iii) theoretically analyzing the excitation angle distribution α (x _p , y _p , z _p ) when the excitation angle α at the center position of the surface coil is 90 degrees, and (iv) receiving the signal of the surface coil magnetic field Hz in sensitivity (ii) shall _{(x p, y p, z} p) is proportional to, FID signal intensity distribution S _FID also reception sensitivity distribution _{considering, Detect (x p, y p} , z p) of calculate.

(I) Geometric shape of surface coil and assumption at the time of analysis FIG. 33 is a diagram showing the shape of the surface coil and the coordinate system in the analysis. This small surface coil is a spiral coil having an outer diameter of 1.3 mm, an inner diameter of 0.91 mm, and three turns.
FIG. 34 is a diagram showing the geometric shape of a 3-turn surface coil. In FIG. 34, the center position of the copper wire is measured from FIG. 33. The center position of the outermost copper wire is 1.24 mm, the center position of the second copper wire is 1.08 mm, and the center position of the innermost copper wire. The position was 0.96 mm.

In addition, the following assumptions were made about the geometrical shapes of the coils shown in FIGS. 7, 33, and 34.
The coil wire diameter is zero. That is, the wire diameter is infinitely small.
It is assumed that there is no skin effect when conducting. Since the wire diameter is zero, the effect of current flowing only on the coil surface is ignored.
It is assumed that the 3-turn coil is not spiral but has a shape in which three circles having different diameters are concentrically arranged.
The coil is made of only conductive wire, and the coating film is ignored. As the dielectric constant and magnetic permeability, vacuum values are used.
It is assumed that there is no sample, and vacuum values are used for permittivity and permeability throughout the space.
Lead parts (wiring parts other than circular coils) are ignored.

(Ii) a surface coil makes the magnetic excitation field _{Hz (x p, y p,} z p) magnetic field H created by the current I flowing in the analysis conductor was calculated based on the Biot-Savart law. That is, when the surface coil is placed in a vacuum (permeability is 4π × 10 ⁻⁷ N / A ² ), the magnetic field H (x _p , x _p , y _p , z _p ) created by the surface coil at the position (x _p , y _p , z _p ). y _p , z _p ) is expressed by equation (51).

Symbols in the above formula (51) are as follows.
H: Magnetic field strength at position r [A / m] (vector)
r: position (x _p , y _p , z _p ) [m] (vector) of point P in space
r ′: position of the point Q on the coil (x _p , y _p , z _p ) [m] (vector)
I: Current [A] (scalar)
t: a unit vector [−] (vector) representing the direction in which the current flows. This represents the shape of the coil at point Q. 35 (a) and 35 (b), when the angle θ between the point Q and the x axis is t, t = (sin θ, cos θ, 0).
Meaning of integration: Line integration is performed over the entire circumference of the coil. The magnetic field generated at the point P is obtained by moving the point Q on the coil along the coil, and integrating (summing) the magnetic field generated at the position of each point Q over the entire circumference of the coil.
FIGS. 35A and 35B are diagrams showing a coordinate system in the above equation (51).

  Moreover, the following approximate calculation was used about the line integral of said Formula (51). That is, the coil is circular, and t changes smoothly as the angle θ increases, but this is divided into a number of sections and approximated by being represented by a straight line of length L [m] within the section. To do. This makes it possible to calculate Equation (51) numerically. Here, the circle was divided into 32 straight lines. FIG. 36 shows parameters at the time of division, and FIG. 37 shows a shape expressed by linear approximation when a circular coil is divided according to FIG.

Based on the above assumption, the z-direction magnetic field strength Hz (x _p , y _p , z _p ) was numerically analyzed by the equation (51) for the space shown in FIG. 38, that is, the xz plane with y _p = 0 mm. The current I flowing through the coil was set to 1.0A. In this calculation, since it is a singular point on the coil and cannot be calculated, it is not calculated in a region within a radius of 0.05 mm near the coil.
FIG. 39 is a contour map showing the z-direction magnetic field strength Hz (x _p , y _p , z _p ) of the 3-turn surface coil obtained in this analysis. From FIG. 39, it can be said that the isosurface shape of the magnetic field strength distribution is such that the isosurface spreads outward from the innermost coil, and the isosurface shape of the magnetic field is determined by the innermost coil. Note that since the value of the current passed through the coil set during this analysis is different from the experimental value, the absolute value of the magnetic field intensity shown in FIG. 39 has no direct meaning in NMR measurement.

(Iii) Theoretical analysis of excitation angle distribution α (x _p , y _p , z _p ) The following assumptions were made when analyzing the excitation angle α. That is, when PEM NMR measurement is performed using a surface coil, the sample is located slightly away from the center of the coil, as shown in FIG. FIG. 40 is a cross-sectional view showing the positional relationship between the coil and the sample. In FIG. 40, specifically, a polyimide film as an insulating film exists between the surface coil and the PEM, and further, a catalyst layer exists on the PEM surface. However, the diameter of the coil copper wire is 50 μm, the polyimide film is 30 μm, the catalyst layer is 10 μm, and even if all are added, it is sufficiently thin as 0.09 mm. Therefore, in this analysis, this thickness is ignored, and the reference point for setting the excitation angle α to 90 degrees is set as the center position of the surface coil (z _p = 0.0 mm).

Further, the nuclear magnetic resonance frequency of ¹ H in a magnetic field of ¹ Tesla is 42.6 MHz. One period at this time is 0.023 μs, which is sufficiently shorter than the irradiation time 64 μs of the oscillating magnetic field H1 for exciting the nuclear magnetization. From this, it was considered that the oscillating magnetic field H ₁ was formed with a strength equal to the static magnetic field strength Hz induced by flowing a steady current through the surface coil analyzed in the above section (ii).
Furthermore, since it regarded as oscillating magnetic field H ₁ in which the surface coil made is sufficiently smaller than the 1Tesla of the static magnetic field H _0, assuming both the resultant vector is equal to the static magnetic field H _0, of the nuclear magnetization excited angle α Was calculated.

Here, in order to relate the analysis result of the magnetic field intensity Hz described in the above (ii) to the excitation angle α of the nuclear magnetization generated by the hydrogen nucleus with an absolute value, a complicated analysis is required. Using only the relative relationship shown in the following formula (52), it was simplified as “excitation angle α is proportional to magnetic field strength Hz”. By using the relationship of the following formula (52), as shown in the following formula (52) ′, the spatial distribution α (x _p , x _p , _{p p} ) is obtained from the spatial distribution Hz (x _p , y _p , z _p ) of the magnetic field strength. y _p , z _p ) can be obtained.

41 and 42 are diagrams showing the analysis results of the excitation angle distribution α (x _p , y _p , z _p ). 41 theoretically shows the excitation angle distribution α (x _p , y _p , z _p ) when the excitation angle α at the reference point, that is, a point 0.0 mm on the central axis of the surface coil is 90 degrees. The isosurface of the excitation angle α (x _p , y _p = 0, z _p ) at the time of analysis is shown. FIG. 42 shows the distribution of the excitation angle α (z _p ) on the z axis.
41 and 42, the region where the excitation angle α, which is the measurement region, is 90 degrees plus or minus 5 degrees appears only in the vicinity of the center of the coil, and the spread in the z direction is narrow.

(Iv) Calculation of FID signal intensity distribution S _{FID, Detect} (x _p , y _p , z _p ) The signal intensity S _FID of the FID signal is the excitation angle α and S _FID = A (sin α)
There is a relationship. However, A in the above formula is a proportionality coefficient that relates the excitation angle and the signal intensity. By using this relational expression, the FID signal intensity distribution S _FID (x _p , y _p , z _p ) can be calculated.
Further, in the case of an FID sequence in which a nuclear wave excitation pulse (oscillating magnetic field intensity H _α ) is irradiated only once to excite nuclear magnetization at an excitation angle α, the relationship between the excitation angle α and the FID signal intensity S _FID . Is represented by the following formula (53).

As shown in the section (iii) above, the oscillating magnetic field strength of the surface coil has a distribution. Correspondingly, the coil also has a sensitivity distribution Det (x _p , y _p , z _p ) when receiving a signal. It may be considered that the sensitivity distribution of the signal reception is the same as the oscillating magnetic field strength. Therefore, as shown in the following equation (54), the analysis was performed assuming that the sensitivity Det (x _p , y _p , z _p ) is proportional to the magnetic field Hz (x _p , y _p , z _p ).

The reception intensity distribution S _{FID, Detect} (x _p , y _p , z _p ) of the FID signal was calculated in consideration of the equations (53) and (54). FIG. 43 is a contour diagram showing the received intensity distribution S _{FID, Detect} (x _p , y _p , z _p ) of the FID signal in the 3-turn surface coil. FIG. 44 is a diagram showing a profile S _{FID, Detect} (x _p , y _p = 0, z _p = 0) of the reception intensity distribution of the FID signal on the z-axis.

From FIG. 44, it was found that the position z _{p at} which the FID signal intensity is half (0.5) is 0.34 mm. Since the inner diameter of the coil is 0.91 mm, it can be said that the depth measured by the coil is a region from the coil installation surface to a depth of about one third of the inner diameter of the coil.
Further, when the same calculation is performed for a coil having an outer diameter of 1.3 mm, an area from the coil installation surface to a depth of about one quarter of the coil inner diameter is obtained.

  From this example, it was found that the area measured using a small surface coil of this size was approximately 70% deep of the film A (thickness 500 μm) used in Example 3.

(Example 6)
Here, by the measurement cell and measurement apparatus used in Example 2, the methanol permeability of the fluorine-based polymer electrolyte membrane (referred to as membrane C) and a membrane different from this membrane C and containing no fluorine The molecular electrolyte membrane (referred to as membrane D) was compared with the methanol permeability.
A small surface coil (small RF coil) is obtained by winding a polyurethane-coated copper wire having a wire diameter of 50 μm three times. The outer diameter of the coil is 1.3 mm, and the innermost coil inner diameter is about 0.96 mm. In order to maintain the shape, it was fixed by being sandwiched between polyimide films having a thickness of 30 μm. When the FID is obtained by attaching the coil to a 500 μm thick polymer electrolyte membrane, the measurement depth is about 70% of the thickness of the polymer electrolyte membrane. Thus, the concentration of methanol that has soaked into the polymer electrolyte membrane can be measured.
The dimensions of the films C and D are 15 mm × 15 mm and the thickness is 500 μm. No catalyst or the like is applied to the surface of each film.
Membrane C and membrane D were each sandwiched between cells with flow channels shown in FIG. The width of the flow path is 1.0 mm and the depth is 1.0 mm. The small coil was embedded in a cell on the nitrogen gas flow path side and pressed against the surface of each film. In this positional relationship, the NMR signal of the methanol aqueous solution that permeates into the film C and the film D can be acquired. The cell temperature during the experiment was 24 ° C. Nitrogen gas was flowed at 50 ml / min in the upper flow path, and water was flowed in the lower flow path. This state was maintained for 2 hours to obtain a steady state. Then, 30 vol% methanol aqueous solution was poured into the lower flow path at the start of measurement (time t = 0 s). At the same time, NMR signals were acquired. During the measurement, the methanol aqueous solution was kept flowing at 0.5 l / min. The area ratio of the CH spectrum that increases with the passage of time was calculated with the time when methanol began to flow being zero.
In both the film C and the film D, it was found that CH / (CH + OH), which is the area ratio of the CH spectrum, increased with substantially the same gradient. However, it was found that the time required for CH / (CH + OH) to be constant was longer in the film D than in the film C.
In this way, it was also possible to grasp that the time until the steady state varies depending on the type of film in this example.

Claims (8)

An apparatus for evaluating the permeation characteristics of a solvent in a membrane,
A membrane holder for holding the membrane ,
A gas supply for supplying gas to one side of the membrane; and
A measurement cell comprising a solvent supply unit for supplying a protic solvent containing a compound having a hydrogen atom in the molecular structure on the other surface of the membrane ;
A static magnetic field application unit that applies a static magnetic field to the film;
A small RF coil that applies an oscillating magnetic field for excitation to the film and acquires a nuclear magnetic resonance signal in a partial region in the thickness direction of the film;
The nuclear magnetic resonance acquired by the small RF coil in a state where the gas is supplied to the one surface of the membrane and the protic solvent is supplied to the other surface and the measurement cell is not generating power. Calculate the concentration of the protic solvent in the partial region based on the signal, and calculate the time or speed until the concentration of the protic solvent reaches a steady state based on the change over time of the concentration of the protic solvent An arithmetic unit to perform,
Including a measuring device. The measuring apparatus according to claim 1,
The small RF coil is arranged on the one surface of the film, and acquires a nuclear magnetic resonance signal in a region from the one surface to a specific depth to a middle position of the thickness of the film,
The measurement apparatus, wherein the calculation unit calculates a concentration of the protic solvent in the region from one surface to a specific depth based on the nuclear magnetic resonance signal. 3. The measuring apparatus according to claim 2 , wherein the calculation unit calculates a concentration of the protic solvent in a steady state in the region from one surface to a specific depth based on a change with time of the concentration of the protic solvent. A measuring device including a steady concentration calculation unit. In the measuring apparatus in any one of Claims 1 thru | or 3 ,
The protic solvent is an aqueous alcohol solution,
The arithmetic unit uses the ratio of the area of the signal derived from alcohol and water and the area of the signal derived from alcohol in the nuclear magnetic resonance spectrum obtained from the nuclear magnetic resonance signal to determine the alcohol in the region. A measurement device including an alcohol concentration calculation unit for calculating the concentration of the alcohol. The measuring apparatus according to claim 4 , wherein
The ratio of the area of the signal derived from alcohol and water to the area of the signal derived from the alcohol;
Having a storage unit that stores the relationship between alcohol concentration and alcohol concentration relative to water;
In the alcohol concentration calculation unit, the ratio of the area of the signal derived from alcohol and water and the area of the signal derived from the alcohol in the nuclear magnetic resonance spectrum obtained from the nuclear magnetic resonance signal, and the storage unit A measuring device that calculates the concentration of the alcohol in the region from the stored relationship. In the measuring apparatus in any one of Claims 1 thru | or 5 ,
The membrane is a solid polymer electrolyte membrane of a fuel cell,
A measuring apparatus, wherein the measuring apparatus is an apparatus for evaluating a crossover characteristic of the solid polymer electrolyte membrane. A method for evaluating the permeation characteristics of a solvent in a membrane,
Carried out using the measuring device according to claim 1,
The measurement cell generates power while supplying a gas to one side of the membrane placed in a static magnetic field and a protic solvent containing a compound having a hydrogen atom in the molecular structure to the other side of the membrane. Applying an oscillating magnetic field for excitation to the film using a small RF coil in a state where it is not, and obtaining a nuclear magnetic resonance signal in a partial region in the thickness direction of the film;
Based on the nuclear magnetic resonance signal acquired by the small RF coil, the concentration of the protic solvent in the partial region is calculated, and the concentration of the protic solvent is calculated based on the change over time of the concentration of the protic solvent. Calculating the time or speed to reach steady state ;
Including a measuring method. The measurement method according to claim 7 , wherein the membrane is a solid polymer electrolyte membrane.