JP2021136092A - Membrane-electrode composite - Google Patents

Abstract

To provide a membrane-electrode composite with improved flexibility against mechanical deformation.SOLUTION: A membrane-electrode composite is a laminate in which at least a portion of a carbon sheet electrode is bonded to at least one surface of an ion exchange membrane having a first surface and a second surface. The carbon sheet electrode is formed from two or more carbon sheets that contain carbon fiber as a component.SELECTED DRAWING: None

Description

The present invention relates to a membrane-electrode composite.

In recent years, as a measure against global warming, the introduction of power generation using renewable energy such as solar power and wind power has been promoted. Since the output of these power generations is greatly affected by the weather, there is a problem of destabilizing the voltage and frequency of the system power supply. Therefore, when introducing large-scale power generation, it is necessary to smooth the output and level the load by combining it with a large-capacity storage battery.

Examples of the large-capacity storage battery include lead storage batteries, sodium-sulfur batteries, metal-halogen batteries, and redox flow batteries. Among these, the redox flow battery is superior to other batteries in terms of reliability and economy, and is one of the batteries with the highest possibility of practical use.

FIG. 1 shows a schematic diagram of a general structure of a redox flow battery. As shown in this figure, the redox flow battery 100 includes an electrolytic cell 101, tanks 102 and 103 for storing the electrolytic cell, and pumps 104 and 105 for circulating the electrolytic cell between the tank and the electrolytic cell. Further, the electrolytic cell 101 has an electrode 112 composed of a positive electrode 112a and a negative electrode 112b separated by an ion exchange membrane 111, and is connected to the power supply 106.

In the redox flow battery 100, the electrolytic solution is circulated between the tanks 102 and 103 and the electrolytic cell 101 by the pumps 104 and 105, and electrochemical energy conversion is performed on the electrode 112 of the electrolytic cell 101. Charges and discharges.

In the redox flow battery 100 shown in FIG. 1, the ion exchange membrane 111 and the electrode 112 are separated from each other, but in order to increase the current density per unit area of the electrode, as shown in FIG. 2A. , The ion exchange membrane 11 and the electrode 12 are joined to form a film-electrode composite 10, and the film-electrode composite 10 is sandwiched between the current collector plate 14 via the separator 13 to form the cell shown in FIG. 2B. 20 is often formed, and a plurality of the cells 20 are provided to form a battery (cell stack).

In the cell 20 shown in FIG. 2B, a carbon fibrous structure is generally used as the electrode 12 because it is necessary to ensure conductivity, electrochemical stability, and flowability of the electrolytic solution.
For example, Patent Document 1 describes a membrane-electrode assembly in which an electrode is formed of a carbon fibrous structure and at least a part of the fibrous structure is embedded in a diaphragm.

JP-A-2018-101541

In a redox flow battery, in general, in the process of the active material passing through the porous carbon electrode and being discharged to the outside of the electrode, for example, an electrochemical reaction such as redox proceeds to charge the battery. Discharge is performed. At that time, mechanical deformation to the membrane-electrode composite due to the pulsation of the pump and the expansion and contraction of the membrane is repeatedly applied.
Patent Document 1 describes that the electrode of the membrane-electrode composite is peeled off from the membrane due to deformation of the membrane during battery operation, and the battery performance is deteriorated. Therefore, it is considered necessary to extend the life of the membrane-electrode composite so that the electrodes do not peel off even when the membrane-electrode composite is exposed to mechanical deformation and the adhesive state is maintained.

Regarding the electrode, since the viscosity of the electrolytic solution and the concentration of the unreacted active material differ between the inlet side and the outlet side of the electrolytic solution, the void ratio, surface area, and surface activity required for the electrode depend on the position on the electrode. The characteristics are different.
In the membrane-electrode assembly described in Patent Document 1, since a single porous carbon electrode is used, the electrochemical reaction of the electrodes is not uniform between the inlet side and the outlet side of the electrolytic solution, which is unnecessary. There is a risk that an electrochemical reaction will occur and the life of the electrode will be shortened.

Therefore, an object of the present invention is to provide a film-electrode composite having improved flexibility against mechanical deformation.

As a result of diligent studies on a film-electrode composite that can solve the above problems, the present inventors have imparted flexibility to the electrode film composite by forming the electrodes from a plurality of carbon sheets, and the machine. The electrode does not peel off from the film even if it is curved, and by combining carbon sheets with various different characteristics to form an electrode, it is possible to make the electrochemical reaction at the electrode uniform, and the reaction overvoltage distribution becomes uniform. It has been found that the life of the electrode can be extended by suppressing unnecessary electrochemical reactions, and the present invention has been completed.

That is, the present invention is as follows.
[1]
A laminate in which at least a part of a carbon sheet electrode is adhered to at least one surface of an ion exchange membrane having a first surface and a second surface.
The carbon sheet electrode is a film-electrode composite characterized in that it is formed of two or more pieces of carbon sheets containing carbon fibers as constituent elements.
[2]
The film-electrode composite according to [1], which is a laminate in which the carbon sheet electrode is adhered to the first surface and the second surface.
[3]
The film-electrode composite according to [1] or [2], wherein in the carbon sheet electrode, 30% or more of the surface facing the ion exchange membrane is adhered to the ion exchange membrane.
[4]
The membrane-electrode composite according to any one of [1] to [3], wherein the gap between the two or more carbon sheets adjacent to each other is 10 mm or less.
[5]
The membrane-electrode composite according to any one of [1] to [4], wherein the ratio of voids between the two or more carbon sheets adjacent to each other is 5% or less.
[6]
The film-electrode composite according to any one of [1] to [5], wherein the two or more carbon sheets have ^{different basis weights of 40 g / m 2 or more.}
[7]
The film-electrode according to any one of [1] to [6], wherein the depth of embedding of the carbon sheet electrode in the ion exchange membrane is 5 μm or less on the adhesive surface between the carbon sheet electrode and the ion exchange membrane. Complex.
[8]
The membrane-electrode composite according to any one of [1] to [7], wherein an electrolytic solution flow groove is formed at the edge of the carbon sheet electrode.
[9]
The film-electrode composite according to any one of [1] to [8], wherein the ion exchange membrane and the carbon sheet electrode are thermally pressure-bonded under a temperature condition equal to or lower than the decomposition temperature of the ion exchange membrane. How to make a body.
[10]
The membrane-electrode composite according to any one of [1] to [8] and an electrolyte circulation mechanism are provided.
An apparatus characterized in that, of the two or more carbon sheets, the one having the smaller basis weight of the two adjacent carbon sheets is arranged so as to be on the upstream side in the direction in which the electrolytic solution flows. ..
[11]
The membrane-electrode composite according to [8] and an electrolytic solution flow mechanism are provided.
An apparatus, characterized in that at least one extending direction of the electrolytic solution flow groove is provided along a direction in which the electrolytic solution flows.

According to the present invention, it is possible to provide a film-electrode composite having improved flexibility against mechanical deformation.

It is a schematic diagram of the general structure of a redox flow battery. It is a 1st schematic diagram of a general cell structure. It is a second schematic diagram of a general cell structure. It is a figure which shows an example of the membrane-electrode composite by this embodiment. FIG. 3 is a cross-sectional view of the film-electrode composite of FIG. 3A when cut along a plane along line I-I of FIG. 3A. It is a figure which shows an example of the membrane-electrode composite by this embodiment.

Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail, but the present invention is not limited to the following description and is within the scope of the gist thereof. It can be modified in various ways.

<Membrane-electrode complex>
The film-electrode composite of the present embodiment is a laminate in which at least a part of a carbon sheet electrode is adhered to at least one surface of an ion exchange membrane having a first surface and a second surface, and the carbon sheet. The electrode is characterized in that it is formed from two or more pieces of carbon sheets containing carbon fibers as constituent elements.

3A and 3B are examples of the membrane-electrode composite according to this embodiment. The membrane-electrode composite 1 shown in FIGS. 3A and 3B includes an ion exchange membrane 2 having a first surface and a second surface, and a carbon sheet electrode 3. The carbon sheet electrode 3 is formed of two pieces of carbon sheets 31 and 32 containing carbon fibers as components.
3A is a view of the membrane-electrode composite when viewed from the normal direction of the ion exchange membrane 2, and FIG. 3B is a view of the membrane-electrode composite of FIG. 3A taken along the line I-I of FIG. 3A. It is a cross-sectional view at the time of cutting by the plane along.

The membrane-electrode composite of the present embodiment is a laminate in which at least a part of a carbon sheet electrode is adhered to at least one surface of the first surface and the second surface of the ion exchange membrane. The carbon sheet electrode may be adhered to either the first surface or the second surface of the ion exchange membrane, but is adhered to both the first surface and the second surface of the ion exchange membrane. Is more preferable.
Here, the state in which the ion exchange membrane and the carbon sheet electrode are "adhered" means a state in which the carbon sheet electrode does not fall off due to its own weight when the ion exchange membrane is gripped.

In the membrane-electrode composite of the present embodiment, the ion exchange membrane and at least a part of the carbon sheet electrode are adhered to each other, so that when the membrane-electrode composite is used to assemble a cell or the like of a redox flow battery, The alignment between the carbon sheet electrode and the ion exchange membrane is improved, which leads to the suppression of leakage of the electrolytic solution from the cell.
Further, from the viewpoint of improving the long-term durability of a device such as a redox flow battery, it is preferable that 30% or more of the surface of the carbon sheet electrode facing the ion exchange membrane is adhered to the ion exchange membrane. 50% or more is more preferable, and 80% or more is further preferable.

Further, the film-electrode composite of the present embodiment is applied to the ion exchange membrane of the carbon sheet electrode (carbon fiber constituting the carbon sheet) from the viewpoint that the adhesion between the carbon sheet electrode and the ion exchange membrane improves energy efficiency. The embedding depth is preferably 7 μm or less, more preferably 5 μm or less, further preferably 4 μm or less, further preferably 3 μm or less, and even more preferably 2 μm or less.
The embedding depth of the carbon sheet electrode is 2000 times the magnification of the cross section of the composite cut parallel to the film thickness direction at any place where the carbon sheet electrode of the film-electrode composite and the ion exchange membrane are adhered. It can be evaluated from a scanning electron microscope (SEM) image.

《Ion exchange membrane》
The ion exchange membrane used for the membrane-electrode composite of the present embodiment is preferably a membrane having a structure that allows the desired ions to permeate, and is a perfluorocarbon polymer having an ion exchange group or carbonization having an ion exchange group. Examples include hydrogen membranes.
The ion-exchange group is not particularly limited, for example, -COOH group, -SO ₃ H group, _-PO 3 _{H 2} group, or salts thereof, and the like. The salt is not particularly limited, and examples thereof include alkali metal salts, alkaline earth metal salts, and amine salts.
Examples of the resin include a perfluorocarbon polymer and a hydrocarbon film, and a perfluorocarbon polymer is preferable from the viewpoint of good long-term durability.

(Equivalent mass EW)
The equivalent mass EW of the ion exchange membrane used in the present embodiment is preferably 600 g / eq or more, more preferably 700 g / eq or more, from the viewpoint of suppressing the permeation of active material ions to improve the current efficiency. Yes, more preferably 800 g / eq or more, and even more preferably 900 g / eq or more. The equivalent mass EW of the ion exchange membrane is preferably 2000 g / eq or less, more preferably 1700 g / eq or less, still more preferably 1500 g / eq, from the viewpoint that improvement of proton conductivity reduces resistance. It is eq or less, more preferably 1200 g / eq or less.
The equivalent mass EW means the dry mass (g) of the ion exchange membrane per one equivalent of the ion exchange group. The equivalent mass EW of the ion exchange membrane can be measured by substituting the ion exchange membrane with a salt and back titrating the solution with an alkaline solution. The equivalent mass EW can be adjusted by the copolymerization ratio of the monomer which is the raw material of the ion exchange membrane, the selection of the monomer type, and the like.

(Film thickness)
The film thickness of the ion exchange membrane used in the present embodiment is preferably 10 μm or more, and more preferably 20 μm or more, from the viewpoint of good shielding property of the active material when used as a battery. Further, the film thickness of the ion exchange membrane is preferably 180 μm or less, and more preferably 60 μm or less, from the viewpoint of improving the battery performance by reducing the resistance.

The film thickness uniformity of the ion exchange membrane used in this embodiment is such that the thickness unevenness of the ion exchange membrane is reduced in order to make the performance of the entire surface of the membrane-electrode composite uniform. From the viewpoint of improving the overall contact with the film, the average film thickness is preferably within ± 20%, more preferably within ± 15%, and even more preferably within ± 10%.
The film thickness uniformity of the ion exchange membrane is determined by allowing the ion exchange membrane to stand in a thermostatic chamber at 23 ° C. and a relative humidity of 65% for 12 hours or more, and then using a contact-type film thickness meter (for example, manufactured by Toyo Seiki Seisakusho Co., Ltd.). It can be evaluated by measuring the film thickness at any 6 points using.

《Carbon sheet electrode》
The carbon sheet electrode used in this embodiment is formed of two or more carbon sheets containing carbon fibers as components.
Among the two or more carbon sheets, the two adjacent carbon sheets may be the same or different.

The carbon sheet electrode used in the present embodiment may be adhered to at least one surface of the first surface and the second surface of the ion exchange membrane, but the first surface and the second surface of the ion exchange membrane may be adhered to. It is more preferable that the two surfaces are adhered to both surfaces (both sides). When the carbon sheet electrode of the present embodiment is adhered to both sides of the ion exchange membrane and used as a positive electrode and a negative electrode in this way, the uniformization of the electrochemical reaction in the film-electrode composite is further promoted, and the life of the electrode is extended. It leads to the promotion of.

By forming the carbon sheet electrode of the present embodiment from two or more pieces of carbon sheet, carbon sheets having different characteristics are arranged and combined according to the characteristics of the electrode required at each position on the electrode. Therefore, the electrochemical reaction at the electrode can be made uniform. With a single porous carbon electrode as used in the membrane-electrode assembly of Patent Document 1 described above, it is not easy to make a difference in density among them, and further when the surface characteristics are partially changed. Have difficulty. Since the electrochemical reaction can be made uniform in the carbon sheet electrode of the present embodiment, the reaction overvoltage distribution in the film-electrode composite can be made uniform, unnecessary electrochemical reaction can be suppressed, and the life of the electrode can be extended. can.
More specifically, carbon sheets having different characteristics have different void ratios or different appearances from the viewpoint of improving energy efficiency by reducing pressure loss of a device having an electrolyte circulation mechanism such as a redox flow battery. It is preferable to use the one having. Further, from the viewpoint that reduction of reaction resistance in the electrode improves energy efficiency, it is preferable to use carbon sheets having different surface activities.

Further, since the carbon sheet electrode of the present embodiment is formed of two or more carbon sheets, the boundary between the two adjacent carbon sheets is set as a bending line (see the bending line 4 in FIGS. 3A and 4). ), The carbon sheet electrode, and thus the membrane-electrode composite can be bent. This makes it possible to produce film-electrode composites having various shapes depending on the shape of the battery cell or device into which the membrane-electrode composite is incorporated.

Further, the carbon sheet electrode of the present embodiment preferably has an electrolytic solution flow groove that opens at the edge of the carbon sheet electrode. When the carbon sheet electrode has an electrolytic solution flow groove, the electrolytic solution passes through the electrolytic solution flow groove to make the diffusion of the electrolytic solution uniform, so that the electrochemical reaction in the carbon sheet electrode can be made uniform, as described above. It is possible to extend the life of the electrode as described above.
Further, when used in a device having an electrolytic solution circulation mechanism such as a redox flow battery, the film-electrode composite is installed so that the extending direction of at least one electrolytic solution flow groove is along the direction in which the electrolytic solution flows. It is preferable to arrange the electrolytic solution flow groove so that at least one opening is open on the inlet side of the electrolytic solution because the electrolytic solution is more efficiently and uniformly diffused between the carbon fibers constituting the carbon sheet electrode. ..

The electrolytic solution flow groove is a film-electrode composite in which at least one opening is opened on the upstream side in the flow direction of the electrolytic solution from the viewpoint of efficiently diffusing the electrolytic solution between the carbon fibers constituting the carbon sheet electrode. As long as the body can be arranged, the openings opened at the edge of the carbon sheet electrode may be provided only at one end of the electrolytic solution flow groove or at both ends.
The shape of the electrolytic solution flow groove is not particularly limited, and may be linear or curved. From the viewpoint of reducing the pressure loss during the transfer of the electrolytic solution, the linear shape is preferable. When there are a plurality of electrolytic solution flow grooves, the shape of each electrolytic solution flow groove may be the same or different.
The extending direction (longitudinal direction) of the electrolytic solution flow groove is not particularly limited, but is perpendicular to the edge of the carbon sheet electrode in which the electrolytic solution flow groove opens from the viewpoint of reducing the pressure loss during the electrolytic solution feeding. Is preferable. Further, when there are a plurality of electrolytic solution flow grooves, the extending directions of the electrolytic solution flow grooves may be the same or different.

FIG. 4 shows an example of the membrane-electrode composite of the present embodiment provided with a carbon sheet electrode having an electrolytic solution flow groove. In the film-electrode composite 1 of FIG. 4, the five electrolyte flow grooves having an opening at only one end of the carbon sheet electrode 3 are all parallel in the extending direction. The two adjacent electrolyte flow grooves are opened in opposite directions. In FIG. 4, the electrolytic solution flow groove has a width of 2.5 mm and a length of 22.5 mm, and the depth is the same as the thickness of the carbon sheet electrode 3 (100% of the thickness).

(Void)
In the carbon sheet electrode of the present embodiment, the voids between two carbon sheets adjacent to each other in the two or more carbon sheets are not particularly limited, but from the viewpoint of reducing cell resistance and improving energy efficiency. It is preferably 10 mm or less, more preferably 5 mm or less, further preferably 3 mm or less, and even more preferably 1 mm or less.
The voids between the carbon sheets are band-shaped voids sandwiched between the linear ends of the carbon sheets facing each other when viewed from the normal direction of the plane to which the carbon sheets are adhered, in other words, two pieces of carbon sheets. Includes voids where the spacing between the facing surfaces is constant. Further, the voids between the carbon sheets are surrounded by the curved edges of the carbon sheets when viewed from the normal direction, and the space where the carbon sheets (electrodes) do not exist, in other words, the facing surfaces of the two carbon sheets. It also includes spaces where the intervals fluctuate. The space in which the distance between the facing surfaces fluctuates is, for example, a space in which one facing surface is a flat surface and the other facing surface is surrounded by a curved surface. Further, the gap in which the distance between the facing surfaces fluctuates has a curved surface in which a part of both facing surfaces is a flat surface and the other part is recessed with respect to the plane, and the planes are adhered to each other. It also includes the space created between curved surfaces. In the case of the above-mentioned band-shaped voids when viewed from the normal direction, the width between the straight lines is defined as the voids between the carbon sheets, and in the case of a space where the above-mentioned carbon sheets (electrodes) do not exist when viewed from the normal direction, The farthest distance in the curve is the void between the carbon sheets.

(Void ratio)
Further, in the carbon sheet electrode of the present embodiment, the ratio of voids between two carbon sheets adjacent to each other in the two or more carbon sheets is not particularly limited, but reduction of cell resistance improves energy efficiency. From this viewpoint, it is preferably 7% or less, more preferably 5% or less, further preferably 3% or less, and even more preferably 1% or less.
This ratio indicates the ratio of the voids between the carbon sheets described above to the length of one side of the carbon sheet electrode perpendicular to the direction of the voids.

(Difference in basis weight)
In the carbon sheet electrode of the present embodiment, from the viewpoint of obtaining the flexibility of the film-electrode composite, the two or more carbon sheets adjacent to each other may have the same basis weight. No. From the viewpoint of suppressing the deterioration of the electrodes, the difference in basis weight between the two adjacent carbon sheets ^{is preferably 10 g / cm 2} or more, more preferably 20 g / cm ² or more, and 30 g / cm / cm. It is more preferably cm ^{2 or more.}

-Carbon sheet-
Examples of the carbon sheet containing carbon fiber as a component constituting the carbon sheet electrode of the present embodiment include carbon fiber paper.
Hereinafter, the requirements when carbon fiber paper is used as the carbon sheet electrode will be specifically described.

--Carbon fiber paper ---
(Fiber diameter of carbon fiber)
When the carbon sheet constituting the carbon sheet electrode is carbon fiber paper, the fiber diameter of the carbon fibers constituting the carbon fiber paper is preferably 3 μm or more, and more preferably 5 μm or more. As a result, the handleability when processing the fiber into paper can be improved. The fiber diameter of the carbon fiber is preferably 20 μm or less, and more preferably 12 μm or less. Thereby, when used as an electrode, the surface area per unit mass can be increased.

[Measuring method of average fiber diameter]
The average fiber diameter of the carbon fibers constituting the carbon paper is obtained by image analysis of a scanning electron microscope image. Specifically, the carbon foam is observed at a magnification of 10,000 times using a scanning electron microscope. From the obtained observation image, the thickness of the carbon fiber is randomly measured at 20 points. Assuming that the cross-sectional shape is circular, this average thickness is taken as the average fiber diameter.

(Average length of carbon fiber)
The average length of the carbon fibers in the carbon fiber paper is preferably 5 mm or more, more preferably 10 mm or more, and further preferably 15 mm or more. As a result, the mechanical strength can be increased by increasing the contact density between the fibers. The average length of the carbon fibers is preferably 50 mm or less, more preferably 40 mm or less, and even more preferably 30 mm or less. This makes it possible to facilitate the opening of fibers in the papermaking process.

(Bulk density)
The bulk density of the carbon fiber paper ^{is preferably 0.1 g / cm 3} or more, more preferably 0.15 g / cm ³ or more, and further preferably 0.2 g / cm ³ or more. .. As a result, the surface area can be increased when used as an electrode. The bulk density of the carbon fiber paper ^{is preferably 0.6 g / cm 3} or less, more preferably 0.5 g / cm ³ or less, and further preferably 0.4 g / cm ³ or less. .. This makes it possible to increase the porosity and facilitate the flow of the electrolytic solution when used as an electrode.

(Metsuke)
The basis weight of the carbon fiber paper ^{is preferably 10 g / m 2} or more, and more preferably 20 g / m ² or more. As a result, the electrochemical reaction field during charge / discharge increases, and the charge / discharge reaction can be made more efficient. The basis weight of the carbon fiber paper ^{is preferably 150 g / m 2} or less, and ^{more preferably 100 g / m 2} or less. Thereby, the pressure loss at the time of feeding the electrolytic solution can be effectively reduced.

(Thickness)
The thickness of the carbon fiber paper is preferably 50 μm or more, more preferably 100 μm or more, and further preferably 200 μm or more. As a result, a sufficient surface area of the electrode can be secured, and the resistance associated with the electrochemical reaction can be reduced. The thickness of the carbon fiber paper is preferably 600 μm or less, more preferably 500 μm or less, and even more preferably 400 μm or less. As a result, the resistance due to the movement of electrons in the electrode can be reduced, and the cell can be miniaturized.

<Manufacturing method of membrane-electrode composite>
The membrane-electrode composite can be produced, for example, by a hot press method in which the ion exchange membrane and the carbon sheet electrode are thermally pressure-bonded, a method in which the ion exchange membrane is bonded with a solution of the same polymer as the ion exchange membrane, or the like. Among these, the hot press method is preferable from the viewpoint of workability.
In the hot press method, the ion exchange membrane and the carbon sheet electrode are first laminated and placed between the pressure plates of the hot press machine together with the spacer of the desired thickness. Next, the pressure plate is heated to a predetermined temperature and then pressed. After holding for a predetermined time, the pressure plate is opened, the film-electrode composite is taken out, and the film-electrode composite is cooled to room temperature to obtain the membrane-electrode composite.

The heating temperature in the hot press method is preferably equal to or lower than the decomposition temperature of the ion exchange membrane from the viewpoint that the control of the embedding depth of the carbon sheet electrode suppresses the deterioration of the ion exchange membrane.
The thickness of the spacer is preferably 30 to 90%, more preferably 50 to 80%, based on the total thickness of the carbon sheet and the ion exchange membrane used.
The holding time during pressing is preferably 0.5 to 30 minutes, more preferably 2 to 10 minutes. As a result, the ion exchange membrane and the carbon sheet electrode can be firmly adhered to each other without causing a short circuit between the carbon sheet electrodes.

<Device>
The film-electrode composite of the present embodiment can be suitably used for devices such as a redox flow battery, a solid polymer film water splitting device, a direct methanol fuel cell, and a fuel cell. Above all, in the membrane-electrode composite of the present embodiment, carbon sheets having different characteristics can be arranged and combined according to the characteristics of the electrodes required at each position on the electrode, so that a redox flow battery or the like can be used. Suitable for devices with an electrolyte circulation mechanism.
The electrolyte circulation mechanism is not particularly limited as long as it circulates the electrolyte and supplies the electrolyte to the electrodes. For example, a mechanism composed of an electrolyte tank, a liquid feed pump, a pipe, or the like is used. Point to.

In a device having an electrolytic solution circulation mechanism such as a redox flow battery, the viscosity of the electrolytic solution and the viscosity of the electrolytic solution are not recorded on the inlet side (upstream side in the flow direction of the electrolytic solution) and the outlet side (downstream side in the flow direction of the electrolytic solution). The concentrations of the reactive active material are different, and the viscosity of the electrolytic solution and the concentration of the unreacted active material are higher on the inlet side of the electrolytic solution than on the outlet side, and the reactivity is higher. Therefore, a film-electrode composite having carbon sheet electrodes formed from carbon sheets having different textures is used, and the carbon sheet having the smaller texture of the two adjacent carbon sheets is arranged on the inlet side of the electrolytic solution. It is preferable to install the film-electrode composite so that the carbon sheet having the larger texture is arranged on the outlet side of the electrolytic solution. For example, in the membrane-electrode composite shown in FIG. 3A, the carbon sheet 31 located on the upstream side of the flow of the electrolytic solution has a smaller basis weight than the carbon sheet 32 located on the downstream side of the flow of the electrolytic solution. Is preferable. By arranging carbon sheets having different basis weights in this way, the electrochemical reaction in the carbon sheet electrode can be made uniform, the reaction overvoltage distribution is made uniform, and unnecessary electrochemical reaction is suppressed. The life can be extended.

Further, in a device having an electrolytic solution circulation mechanism such as a redox flow battery, as shown in FIG. 4, at least one electrolytic solution flow is used by using a film-electrode composite provided with a carbon sheet electrode having an electrolytic solution flow groove formed therein. The film-electrode composite is installed so that the extending direction of the groove is along the direction in which the electrolytic solution flows, and at least one opening of the electrolytic solution flow groove is on the inlet side of the electrolytic solution (upstream side of the flow of the electrolytic solution). It is preferable that By arranging the carbon sheet electrodes in this way, the diffusion of the electrolytic solution is made uniform, so that the electrochemical reaction at the carbon sheet electrodes can be made uniform, and the life of the electrodes can be extended as described above. Become.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples, and can be variously modified and implemented within the scope of the gist of the present invention. Needless to say.

The measurement method and evaluation method used in Examples and Comparative Examples will be described below.

<Embedding depth>
For the film-electrode composites produced in Examples and Comparative Examples, the embedding depth (μm) of the interface between the carbon sheet electrode and the ion exchange membrane was measured at a magnification of 2,000 times using a scanning electron microscope (SEM). It was obtained from the captured SEM image. The film-electrode composite was cut parallel to the film thickness direction, and images in the film thickness direction were arbitrarily imaged at three points. From the captured SEM image, when the ion exchange membrane side was deformed and the carbon sheet electrode was embedded, the embedding depth from the interface was measured, and the average value was taken as the embedding depth. When no embedding was observed in all three images, the embedding depth was set to 0 μm, and it was judged that the carbon sheet electrodes were adhered only on the surface.

<Adhesive area ratio>
For the membrane-electrode composites produced in Examples and Comparative Examples, only the ion exchange membrane portion was lifted by hand with the bonded carbon sheet electrode as the lower surface. At that time, if there is no appearance that the interface between the ion exchange membrane and the carbon sheet electrode is peeled off due to the weight of the carbon sheet electrode in all the composites of the bonded surfaces, it is judged as "whole surface adhesion (100%)". If even one of the composites on the adhered surface was peeled off and the carbon sheet electrode fell, it was judged as "no adhesion". Further, when the ion exchange membrane was bent and peeling was observed at a part of the end portion, it was judged that the ion exchange membrane was partially adhered, and the adhesive area ratio (%) was calculated from the total of the adhered areas.

<Flexibility>
The flexibility of the film-electrode composites prepared in Examples and Comparative Examples was evaluated by a MIT folding fatigue tester D type (Toyo Seiki Seisakusho).
Specifically, the film-electrode composites produced in Examples 1 to 7 and Comparative Examples 1 to 3 are about 8 to 12 mm below the upper end of the carbon sheet electrode (the end on the upstream side in the direction in which the electrolytic solution flows). The electrode portion was gripped with a clamp of R = 0.38, and the ion exchange membrane portion located about 30 mm below the lower end of the carbon sheet electrode (the end on the downstream side in the direction in which the electrolytic solution flows) was gripped with a flat plate clamp on the plunger side. Then, the membrane-electrode composite was bent at a load of 0.25 kgf and a test speed of 90 cpm. After stopping the test when the bending angle reached 90 °, the presence or absence of peeling of the carbon sheet electrode from the ion exchange membrane was visually confirmed. Those with no electrode peeling were rated as "○ (good)", and those with partial electrode peeling were rated as "× (poor)".
For the membrane-electrode composites produced in Example 8 and Comparative Example 4, the gripping position by the clamp of R = 0.38 and the gripping position by the flat plate clamp on the plunger side are set from the left end of the carbon sheet 33 in FIG. 4, respectively. The same method as in Examples 1 to 7 and Comparative Examples 1 to 3 above, except that the electrode portion on the right is about 4 to 8 mm and the ion exchange membrane portion is located on the right by about 10 mm from the right end of the carbon sheet 34 in FIG. And evaluated by the evaluation criteria.

<Redox flow battery evaluation (leakage, current efficiency, voltage efficiency, and power efficiency)>
To the electrolyte tank of the redox flow battery produced in Examples and Comparative Examples, 4 L of a vanadium sulfate solution having a vanadium ion concentration of 1.5 M, a vanadium ion valence of 3.5 valence, and a sulfate ion concentration of 4.5 M was added, and a flow velocity of 200 ml / Circulation was performed at min, and liquid leakage was evaluated.
The charge / discharge test was performed by the constant current method using a bipolar power supply manufactured by Kikusui Electronics Co., Ltd. The voltage range was 1.00-1.55V and the current density was 80mA / cm ² . The current efficiency CE, the voltage efficiency VE, and the power efficiency EE were obtained from the charge capacity Qc and the discharge capacity Qd at the time of 10 cycles, and the average voltage Vc and Vd at the time of charging and discharging, respectively, by the following equations. Further, in the same manner, the voltage efficiency VE at the time of 100 cycles was obtained.
CE: Qd / Qc (%)
VE: Vd / Vc (%)
EE: CE x VE (%)

<Electrode deterioration ratio>
The electrode deterioration rate of the redox flow batteries produced in Examples and Comparative Examples was calculated by the following formula.
Electrode deterioration rate (%) = voltage efficiency at 100 cycles (%) / voltage efficiency at 10 cycles (%) x 100

<Film thickness of ion exchange membrane>
The film thickness (μm) of the ion exchange membrane is defined as a contact-type film thickness meter (stock) at any 6 points of the ion exchange membrane to be used after allowing it to stand in a constant temperature room at 23 ° C. and a relative humidity of 65% for 12 hours or more. Measured using a company manufactured by Toyo Seiki Seisakusho).

The raw materials used in Examples and Comparative Examples will be described below.

<Carbon sheet electrode>
A carbon sheet electrode was formed using the carbon sheet materials shown in Table 1.

<Ion exchange membrane>
-Nafion212 (manufactured by Aldrich, average film thickness: 50 μm, film thickness uniformity: average film thickness ± 20%) was cut out to a length of 90 mm × a width of 45 mm and used.

(Example 1)
<Preparation of membrane-electrode composite>
The membrane-electrode composite shown in FIG. 3A was prepared. Specifically, first, four sheets having a length of 12.5 mm and a width of 20.0 mm were cut out from the carbon sheet material A. One carbon sheet material A cut out as the carbon sheets 31 and 32 of FIG. 3A was used and arranged on both sides of the ion exchange membrane so as to serve as a positive electrode and a negative electrode in the film-electrode composite. At that time, the positions of the carbon sheets 31 and 32 were arranged so as to coincide with each other on the positive electrode side and the negative electrode side. These were placed between the pressure plates of a hot press machine together with a spacer having a thickness of 0.5 mm, the pressure plates were heated to 120 ° C., and pressed at a pressure of 2 MPa. After holding in this state for 5 minutes, the pressure plate was opened and cooled to room temperature. In this way, the film-electrode composite according to Example 1 was prepared.
The evaluation results of the obtained membrane-electrode composite are shown in Table 2.
The ratio (%) of voids between the carbon sheets was determined as the ratio of voids to the length of one side (25.0 mm) of the carbon sheet electrode perpendicular to the boundary between the carbon sheets 31 and 32.
<Manufacturing of redox flow batteries>
The membrane-electrode composite obtained above and the cell components (gasket made of Baitton rubber, frame made of vinyl chloride, separator made of graphite, and end plate made of stainless steel) are combined in a predetermined order, and a predetermined number is used using a stainless bolt. It was fastened with torque and the cell of the redox flow battery was assembled. At that time, as shown in FIG. 3A, the above-mentioned carbon sheet 31 is on the electrolytic solution inlet side (upstream side in the electrolytic solution flow direction), and the carbon sheet 32 is on the electrolytic solution outlet side (downstream side in the electrolytic solution flow direction). The cells were assembled so that they would be placed in. The film thickness of the gasket was adjusted so that the compressibility of the electrodes was 67%. The obtained cell was connected to an electrolytic solution circulation mechanism composed of an electrolytic solution tank and a liquid feed pump. In this way, the redox flow battery according to Example 1 was produced.
Table 2 shows the evaluation results of the obtained redox flow battery.

(Example 2)
A film-electrode composite and a redox flow battery according to Example 2 were prepared in the same manner as in Example 1. However, the carbon sheet material A was used as the carbon sheet 31 in FIG. 3A, and the carbon sheet material B was used as the carbon sheet 32.
Table 2 shows the evaluation results of the obtained membrane-electrode composite and redox flow battery.

(Example 3)
A film-electrode composite and a redox flow battery according to Example 3 were prepared in the same manner as in Example 1. However, the carbon sheet material B was used as the carbon sheet 31 in FIG. 3A, and the carbon sheet material A was used as the carbon sheet 32.
Table 2 shows the evaluation results of the obtained membrane-electrode composite and redox flow battery.

(Example 4)
A membrane-electrode composite and a redox flow battery according to Example 4 were prepared in the same manner as in Example 2. However, the sizes of the sheets cut out from the carbon sheet materials A and B were set to 12.0 mm in length and 20.0 mm in width, respectively, and a space (void) having a width of 1 mm was provided between the sheets.
Table 2 shows the evaluation results of the obtained membrane-electrode composite and redox flow battery.

(Example 5)
A membrane-electrode composite and a redox flow battery according to Example 5 were prepared in the same manner as in Example 2. However, the sizes of the sheets cut out from the carbon sheet materials A and B were set to 11.75 mm in length and 20.0 mm in width, respectively, and a space (void) having a width of 1.5 mm was provided between the sheets.
Table 2 shows the evaluation results of the obtained membrane-electrode composite and redox flow battery.

(Example 6)
A film-electrode composite and a redox flow battery according to Example 6 were prepared in the same manner as in Example 2. However, in the hot press machine, the heating temperature of the pressure plate was 140 ° C., the press pressure was 2 MPa, and the holding time was 5 minutes.
Table 2 shows the evaluation results of the obtained membrane-electrode composite and redox flow battery.

(Example 7)
A membrane-electrode composite and a redox flow battery according to Example 7 were prepared in the same manner as in Example 2. However, in the hot press machine, the heating temperature of the pressure plate was 105 ° C., the press pressure was 2 MPa, and the holding time was 5 minutes.
Table 2 shows the evaluation results of the obtained membrane-electrode composite and redox flow battery.

(Example 8)
The membrane-electrode composite shown in FIG. 4 was prepared. Specifically, first, four sheets having a length of 25.0 mm and a width of 10.0 mm are cut out from the carbon sheet material A, and two sheets are used as the materials of the carbon sheets 33 and 34 of FIG. 4, respectively, and are shown in FIG. Processed into a shape. The processed carbon sheets 33 and 34 are combined so as to form five electrolyte flow grooves having a width of 2.5 mm and a length of 22.5 mm shown in FIG. 4, and arranged on both sides of the ion exchange membrane. Then, it became a positive electrode and a negative electrode in the membrane-electrode composite. These were placed between the pressure plates of a hot press machine together with a spacer having a thickness of 0.5 mm, and the pressure plates were heated to 115 ° C. and pressed at a pressure of 2 MPa. After holding in this state for 5 minutes, the pressure plate was opened and cooled to room temperature. In this way, the film-electrode composite according to Example 8 was prepared.
The evaluation results of the obtained membrane-electrode composite are shown in Table 2.
<Manufacturing of redox flow batteries>
Using the membrane-electrode composite obtained above, the redox flow battery according to Example 8 was produced in the same manner as in Example 1. When assembling the cell, as shown in FIG. 4, the film-electrode composite so that the extending direction (longitudinal direction) of the electrolytic solution flow groove of the carbon sheet electrode is along (parallel) the direction in which the electrolytic solution flows. Was placed.
Table 2 shows the evaluation results of the obtained redox flow battery.

(Comparative Example 1)
Two sheets having a length of 25.0 mm and a width of 20.0 mm were cut out from the carbon sheet material A, and one sheet was arranged on each side of the ion exchange membrane so as to be a positive electrode and a negative electrode in the film-electrode composite, respectively. At that time, the positions of the sheets were set to coincide with each other on the positive electrode side and the negative electrode side. These were placed between the pressure plates of a hot press machine together with a spacer having a thickness of 0.5 mm, the pressure plates were heated to 120 ° C., and pressed at a pressure of 2 MPa. After holding in this state for 5 minutes, the pressure plate was opened and cooled to room temperature. In this way, the film-electrode composite according to Comparative Example 1 was prepared.
The evaluation results of the obtained membrane-electrode composite are shown in Table 2.
<Manufacturing of redox flow batteries>
Using the membrane-electrode composite obtained above, a redox flow battery according to Comparative Example 1 was produced in the same manner as in Example 1.
Table 2 shows the evaluation results of the obtained redox flow battery.

(Comparative Example 2)
A film-electrode composite and a redox flow battery according to Comparative Example 2 were produced in the same manner as in Comparative Example 1. However, the carbon sheet material B was used instead of the carbon sheet material A.
Table 2 shows the evaluation results of the obtained membrane-electrode composite and redox flow battery.

(Comparative Example 3)
A film-electrode composite and a redox flow battery according to Comparative Example 3 were produced in the same manner as in Comparative Example 1. However, the carbon sheet and the ion exchange membrane were not adhered to each other and were simply overlapped.
Table 2 shows the evaluation results of the obtained membrane-electrode composite and redox flow battery.
When the redox flow battery was evaluated, the measurement was interrupted due to the occurrence of liquid leakage, and the current efficiency CE, the voltage efficiency VE, and the power efficiency EE were not calculated.

(Comparative Example 4)
Two sheets of 25.0 mm in length × 20.0 mm in width are cut out from the carbon sheet material A so that they all have the same shape as the shape of the carbon sheet electrode 3 in FIG. 4 (the shape of the carbon sheets 33 and 34 combined). That is, it was processed so that five electrolytic solution flow grooves having a width of 2.5 mm and a length of 22.5 mm were formed. Then, one sheet was arranged on each side of the ion exchange membrane. At that time, the positions of the sheets were set to coincide with each other on the positive electrode side and the negative electrode side. These were placed between the pressure plates of a hot press machine together with a spacer having a thickness of 0.5 mm, and the pressure plates were heated to 115 ° C. and pressed at a pressure of 2 MPa. After holding in this state for 5 minutes, the pressure plate was opened and cooled to room temperature. In this way, the film-electrode composite according to Comparative Example 4 was prepared.
The evaluation results of the obtained membrane-electrode composite are shown in Table 2.
<Manufacturing of redox flow batteries>
Using the membrane-electrode composite obtained above, a redox flow battery according to Comparative Example 4 was produced in the same manner as in Example 8. When assembling the cell, the film-electrode composite is formed so that the extending direction (longitudinal direction) of the electrolytic solution flow groove of the carbon sheet electrode is along (parallel) to the flowing direction of the electrolytic solution in the same manner as in Example 8. Placed the body.
Table 2 shows the evaluation results of the obtained redox flow battery.

According to the present invention, it is possible to obtain a film-electrode composite having improved flexibility against mechanical deformation, which is useful in the battery industry and the power generation industry.

1, 10 Membrane-electrode composite 2, 11, 111 Ion exchange membrane 3 Carbon sheet electrode 31 Carbon sheet 31
32 carbon sheet 32
33 Carbon sheet 33
34 Carbon sheet 34
4 Bending line 12, 112 Electrode 13 Separator 14 Current collector plate 20 Cell 100 Redox flow battery 101 Electrolytic cell 102, 103 Tank 104, 105 Pump 106 Power supply 112a Positive electrode 112b Negative electrode

Claims (11)

A laminate in which at least a part of a carbon sheet electrode is adhered to at least one surface of an ion exchange membrane having a first surface and a second surface.
The carbon sheet electrode is a film-electrode composite characterized in that it is formed of two or more pieces of carbon sheets containing carbon fibers as constituent elements. The film-electrode composite according to claim 1, which is a laminate in which the carbon sheet electrode is adhered to the first surface and the second surface. The film-electrode composite according to claim 1 or 2, wherein in the carbon sheet electrode, 30% or more of the surface facing the ion exchange membrane is adhered to the ion exchange membrane. The membrane-electrode composite according to any one of claims 1 to 3, wherein the gap between the two or more carbon sheets adjacent to each other is 10 mm or less. The membrane-electrode composite according to any one of claims 1 to 4, wherein in the two or more carbon sheets, the void ratio between the two adjacent carbon sheets is 5% or less. The membrane-electrode composite according to any one of claims 1 to 5, wherein the two or more carbon sheets have ^{different basis weights of 40 g / m 2 or more.} The film-electrode according to any one of claims 1 to 6, wherein the depth of embedding of the carbon sheet electrode in the ion exchange membrane is 5 μm or less on the bonding surface between the carbon sheet electrode and the ion exchange membrane. Complex. The membrane-electrode composite according to any one of claims 1 to 7, wherein an electrolytic solution flow groove is formed at the edge of the carbon sheet electrode. The film-electrode composite according to any one of claims 1 to 8, wherein the ion exchange membrane and the carbon sheet electrode are thermally pressure-bonded under a temperature condition equal to or lower than the decomposition temperature of the ion exchange membrane. How to make a body. The membrane-electrode composite according to any one of claims 1 to 8 and an electrolyte circulation mechanism are provided.
An apparatus characterized in that, of the two or more carbon sheets, the one having the smaller basis weight of the two adjacent carbon sheets is arranged so as to be on the upstream side in the direction in which the electrolytic solution flows. .. The membrane-electrode composite according to claim 8 and an electrolytic solution flow mechanism are provided.
An apparatus, characterized in that at least one extending direction of the electrolytic solution flow groove is provided along a direction in which the electrolytic solution flows.

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