JP3932549B2 - Electrolyte membrane for fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
It is used inside a fuel cell that has recently attracted particular attention due to its high energy generation efficiency.
[0002]
[Prior art]
Fuel cells are classified into four types according to the type of electrolyte used. Among these four types, solid oxide fuel cells (SOFCs) and polymer electrolyte fuel cells (PEFCs) are classified as being used in the intermediate temperature region rather than the low temperature region. In addition, these can be applied to a moving body because the electrolyte can be easily fixed. Recently, the most interest and the expansion of the application range have been studied.
[0003]
In the case of PEFC, applications such as small household power supplies, portable power supplies, and mobile power supplies are being developed by taking advantage of the high output at low temperatures. On the other hand, ions that have high heat resistance and do not require moisture management. There is a demand for the development of a selective polymer electrolyte membrane. In addition, the type that obtains hydrogen by reforming methanol fuel directly in the battery is easy to downsize, so it is expected to be a power source for portable devices, but it has high durability against methanol and ion selectivity. Development of high polymer electrolyte membranes is demanded.
[0004]
By the way, a fuel cell is basically composed of an anode electrode (fuel electrode), a cathode electrode (air electrode), and an electrolyte membrane. Fig. 1 shows the structure and operation principle of a fuel cell, taking PEFC as an example, from "Technical trend survey on fuel cells" by the Japan Patent Office Technical Research Section. The anode is formed by stacking a catalyst that takes electrons from hydrogen to form protons, a gas diffusion layer of hydrogen as a fuel, and a separator as a current collector. The cathode is formed by laminating a catalyst for causing a reaction between protons and oxygen, an air diffusion layer, and a separator. As the electrolyte membrane, a sulfonic acid proton conductive polymer electrolyte membrane is generally used. The reaction at each electrode is as follows.
[0005]
Anode reaction H ₂ → 2H ⁺ + 2e ⁻
Cathode reaction O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O
Well-known polymer electrolyte membranes for PEFC include proton conductive solid polymer membranes such as perfluorosulfonic acid (trade name: manufactured by Nafion DuPont). Such a membrane is provided with a large number of through-holes having a diameter of about 100 nm and having free OH ⁻ groups on the inner wall, and this OH ⁻ group allows protons to permeate from the anode side to the cathode side. . However, it is known that such a membrane allows not only protons but also hydrogen molecules, methanol and the like as raw materials to permeate the cathode side. When this occurs, the supplied fuel and oxidant react directly on the cathode side, and energy cannot be output as electric power. Therefore, there arises a problem that a stable output cannot be obtained.
[0006]
As a solution to these problems, there is a proton conductive membrane (electrolyte membrane) disclosed in JP-A-2002-110200. This proton conductive membrane is intended to suppress the permeation of methanol through the membrane while maintaining proton conductivity.
[0007]
Specifically, a composite of a proton conductive polymer and a specific polymer, or a proton conductive polymer and a specific polymer and Ti, Zr, Al, B, Mo, W, Ru, Ir, Ge, or V It is a composite of a copolymer with any oxide of the group.
[0008]
Although this proposed electrolyte membrane certainly has improved proton selectivity, it has a drawback that it cannot be heated to a temperature of 100 ° C. or higher because the material is a polymer or a polymer mainly like Nafion. For this reason, it cannot be applied to a stationary type for home use in which the specification of water vapor is being studied in order to increase efficiency. In this case, the use temperature is considered to be 150 to 250 ° C.
[0009]
[Problems to be solved by the invention]
The present invention has been made in view of the above situation, and an object of the present invention is an electrolyte membrane for fuel cells using hydrogen or methanol as a fuel, which has high proton selectivity and can be used at a temperature of 100 ° C. or higher. An electrolyte membrane for a fuel cell is provided.
[0010]
[Means for Solving the Problems]
The present invention for solving the above problems has a through hole having a diameter of 0.01 to 150 μm provided by anodizing a metal film or a silicon film, and a proton conductive functional group is modified on the inner wall of the through hole. It is characterized by this.
[0011]
The functional group of the present invention is preferably an OH group.
[0012]
What can be used as the metal film material of the present invention can form through holes by anodic oxidation. More preferred are aluminum, titanium, zinc, indium and alloys containing these as main components.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is an electrolyte membrane for a fuel cell which has a through hole having a diameter of 0.01 to 150 μm provided by anodizing a metal, and a proton conductive functional group is modified on the inner wall of the through hole. By doing so, it is possible to maintain a high proton selectivity and to improve the heat resistance, and to make an electrolyte membrane that can use 100 ° C. or higher, specifically, water vapor.
[0014]
Those using the electrolyte membrane of the present invention are an intermediate type between PEFC and SOFC in terms of conventional classification. Conventionally, coexistence of moisture is indispensable in PEFC, so that there is a limit to the operating temperature in fuel cells. However, in the present invention, the coexistence of water becomes indispensable by selecting the type and density of the functional group of the electrolyte membrane, and a very realistic fuel cell is obtained.
[0015]
In addition, if the electrolyte membrane of the present invention is used, a fuel cell that can be used up to a high temperature of 100 ° C. or higher can be produced, so that it can be used as a stationary fuel cell for in-vehicle use or at home.
[0016]
In the present invention, the electrolyte membrane is prepared by anodizing a metal film or a silicon film in order to improve the heat resistance of the film. What can be used as a metal film must be capable of forming a through hole having a diameter of 0.01 to 150 μm by anodization. From the viewpoint of ease of handling, economy, etc., it is preferable to use aluminum, titanium, zinc, indium or an alloy containing these as a main component as the metal film material. A through-hole is provided in such a metal film or silicon film by electrolytic oxidation, and the diameter of the through-hole can be adjusted by adjusting anodizing conditions such as voltage, electrode interval, time, and acid type.
[0017]
The anodic oxidation is a method in which a direct current voltage is applied in water or an electrolytic solution using a metal film or a silicon film as an anode. At this time, oxygen is usually generated at the anode, and through holes having a desired diameter are self-aligned in an orderly manner at intervals of several tens to 100 nm according to voltage, acid type, time, and the like.
[0018]
By the way, if the diameter of the through hole is too small, the proton selectivity is improved, but the passage resistance is increased, and the function as a battery is lowered. On the other hand, if it increases, the passage resistance of protons decreases, but hydrogen and methanol as raw materials also pass through, so the battery characteristics deteriorate. For these reasons, the electrolyte membrane is also required to function as a filter. That is, it is desirable to determine the diameter of the through hole depending on the raw material. Therefore, when a raw material having a large molecular size is used, the diameter may be around 150 nm. However, in the case of a raw material having a small molecular size, several tens of nm or less is required. When hydrogen is used as a raw material, it is desirable that the thickness be 0.01 to 1 nm.
[0019]
A proton conductive functional group is modified on the inner wall surface of the through hole. As the functional group, it is convenient to select an OH group. In addition, since the OH groups can be spaced closely, proton transmission can be improved.
[0020]
For example, when aluminum is selected as the electrolyte membrane material, the surface including the inner wall surface of the through hole is covered with the alumina membrane by electrolytic oxidation. In the case of an alumina membrane, anions and cations can be modified with pH = approximately 9 as a boundary. This is because when the pH is about 9 or more, the surface of the alumina film is charged to AlO ²⁻ , and when the pH is below about 9, it is charged to Al ³⁺ . Therefore, OH groups are supplied to the alumina surface with a pH of less than 9.
[0021]
Specifically, the aluminum film after electrolytic oxidation is first immersed in ion exchange water, and nitric acid is added to the ion exchange water to lower the pH to about 4. Thereafter, ammonia water is dropped into ion-exchanged water, the pH is returned to 7, and the ion-exchanged water is replaced and washed.
[0022]
In addition, when the alumina surface is dry, a good result is obtained when the above operation is attempted after applying steam to the surface and humidifying the surface.
[0023]
Further, when not only OH groups but also a catalyst layer is applied to the inner wall surface of the through hole, not only large molecules do not pass through, but also the raw material can be decomposed into protons inside the electrolyte membrane through hole.
[0024]
【Example】
Next, the present invention will be further described using examples.
Example 1
Sample 1—Alumina Electrolyte Membrane 1 Obtained Using Aluminum as the Base Material 50 mm wide, 50 mm long, 15 μm thick aluminum foil as the anode, platinum as the cathode, and 0.3 mol / l concentration of the electrolyte as the electrolyte Aluminum was electrolytically oxidized by performing constant voltage electrolysis at a voltage of 40 volts using an acid solution.
[0025]
A few seconds after the start of energization, the current value became substantially constant at 50 mA, but it became substantially 0 mA after about 60 minutes. Thereafter, the anode was pulled up, washed with water, the film was peeled off, and immersed in a mixed acid (6 wt% sulfuric acid + 1.8 wt% hydrochloric acid) for several tens of seconds, and immediately washed with water. The diameter of the obtained through hole was about 70 nm.
[0026]
Then, the anode surface was vapor-deposited with Pt so as not to fill the through hole. Thereafter, OH groups were modified on the inner wall surface of the through hole according to the above method.
[0027]
Sample 2-Preparation of an alumina electrolyte membrane 2 obtained by using aluminum as a base material An aluminum foil having a width of 50 mm, a length of 50 mm, and a thickness of 15 μm is used as an anode, platinum is used as a cathode, and a concentration of 0.3 mol / l is used as an electrolyte. Using an acid solution, aluminum was electrolytically oxidized by constant voltage electrolysis at a voltage of 50 volts.
[0028]
A few seconds after the start of energization, the current value became substantially constant at about 60 mA, but became substantially 0 mA after about 60 minutes. Thereafter, the anode was pulled up, washed with water, the film was peeled off, and immersed in a mixed acid (6 wt% sulfuric acid + 1.8 wt% hydrochloric acid) for several tens of seconds, and immediately washed with water. The diameter of the obtained through hole was 50 nm.
[0029]
Then, the anode surface was vapor-deposited with Pt so as not to fill the through hole. Thereafter, OH groups were modified on the inner wall surface of the through hole according to the above method.
[0030]
Sample 3-Preparation of alumina electrolyte membrane 3 obtained by using aluminum as the base material Aluminum foil having a width of 50 mm, a length of 50 mm, and a thickness of 15 μm is used as an anode, platinum is used as a cathode, and a concentration of 0.3 mol / l is used as an electrolyte. Aluminum was electrolytically oxidized by performing constant voltage electrolysis at a voltage of 40 volts using an acid solution.
[0031]
A few seconds after the start of energization, the current value became substantially constant at 50 mA, but it became substantially 0 mA after about 60 minutes. Thereafter, the anode was pulled up, washed with water, the film was peeled off, and immersed in a mixed acid (6 wt% sulfuric acid + 1.8 wt% hydrochloric acid) for several seconds, and immediately washed with water. The diameter of the obtained through hole was about 1 nm.
[0032]
Thereafter, the anode was pulled up and washed with ion exchange water. Then, the anode surface was vapor-deposited with Pt so as not to fill the through hole. Thereafter, OH groups were modified on the inner wall surface of the through hole according to the above method.
[0033]
Sample 4-Preparation of Alumina Electrolyte Membrane 4 Obtained Using Aluminum as Base Material Aluminum Oxide with a Width of 50 mm, Length of 50 mm, and Thickness of 15 μm as an Anode, Platinum as a Cathode, and 0.3 mol / l Oxalic Acid as an Electrolyte The solution was electrolyzed at a constant voltage of 40 V to electrolytically oxidize aluminum (same as document 1).
[0034]
The finally obtained membrane was immersed in a mixed acid (6 wt% sulfuric acid + 1.8 wt% hydrochloric acid) for about 1 second and immediately washed with water. As a result, a fine hole was formed at the end of the fine hole, and the diameter of the obtained through hole was about 0.5 nm when measured by TEM.
[0035]
Thereafter, the anode was pulled up and washed with ion exchange water. Then, the anode surface was vapor-deposited with Pt so as not to fill the through hole. Thereafter, OH groups were modified on the inner wall surface of the through hole according to the above method.
[0036]
Sample 5—Preparation of Titanium Oxide Electrolyte Membrane Obtained from Titanium as Base Material Titanium foil having a width of 50 mm, a length of 50 mm, and a thickness of 15 μm as an anode, platinum as a cathode, and an oxalic acid solution having a concentration of 0.5 mol / l as an electrolyte The titanium foil was electrolytically oxidized by constant voltage electrolysis at a voltage of 60 volts. The diameter of the obtained through hole was about 50 nm.
[0037]
The current value was 45 mA several seconds after the start of energization, but it became substantially 0 after 65 minutes. Thereafter, the anode was pulled up and washed with ion exchange water. Then, the anode surface was vapor-deposited with Pt so as not to fill the through hole. Thereafter, OH groups were modified on the inner wall surface of the through hole according to the above method.
[0038]
Sample 6—Preparation of Zinc Oxide Electrolyte Membrane Obtained Using Zinc as Base Material Zinc Foil with a Width of 50 mm, Length of 50 mm, and Thickness of 15 μm as an Anode, Platinum as a Cathode, and Oxalic Acid at a Concentration of 0.5 Mol / L as an Electrolyte The solution was used, and electrolysis was performed at a constant voltage of 50 volts, followed by zinc oxidation. The diameter of the obtained through hole was about 45 nm.
[0039]
A few seconds after the start of energization, the current value was 50 mA, but it was substantially zero after 50 minutes. Thereafter, the anode was pulled up and washed with ion exchange water. Then, the anode surface was vapor-deposited with Pt so as not to fill the through hole. Thereafter, OH groups were modified on the inner wall surface of the through hole according to the above method.
[0040]
Sample 7-Preparation of an indium oxide electrolyte membrane obtained by using indium as a base material An indium foil having a width of 50 mm, a length of 50 mm, and a thickness of 15 μm is used as an anode, platinum is used as a cathode, and 0.5 mol / l oxalic acid is used as an electrolyte. The indium foil was electrolytically oxidized by constant voltage electrolysis at a voltage of 45 V using the solution. The diameter of the obtained through hole was 50 nm.
[0041]
Although it showed 50 mA several seconds after the start of energization, it became substantially zero after about 60 minutes. Thereafter, the anode was pulled up and washed with ion exchange water. Then, the anode surface was vapor-deposited with Pt so as not to fill the through hole. Thereafter, OH groups were modified on the inner wall surface of the through hole according to the above method.
[0042]
Sample 8—Preparation of an electrolyte membrane made of silicon oxide obtained by using silicon as a base material A silicon foil provided on a copper foil electrode with a width of 50 mm, a length of 50 mm and a thickness of 100 μm as an anode, platinum as a cathode, and an electrolyte Using a hydrofluoric acid solution having a concentration of about 0.3 mol / l, the silicon foil was electrolytically oxidized by constant voltage electrolysis at a voltage of 40 volts. The diameter of the obtained through hole was 5 nm.
[0043]
The current value after starting energization was 50 mA, but it became substantially 0 after about 2 hours. Thereafter, the anode was pulled up and washed with ion exchange water. Thereafter, the copper foil was removed, the silicon oxide electrolyte membrane was separated, and the surface of the electrolyte membrane was vapor-deposited with Pt so as not to fill the through holes. Thereafter, OH groups were modified on the inner wall surface of the through hole according to the above method.
[0044]
(Example 2)
A fuel cell was constructed using the various electrolyte membranes obtained in Example 1, and the presence or absence of current generation and the permeability of methane gas to the air electrode side were measured.
[0045]
A mass spectrometer was used to check whether methane gas was introduced into the fuel electrode side and methane gas permeated into the air electrode side. Even after about 1 hour from the start of measurement, significant detection was possible within the detector performance range. I couldn't.
[0046]
However, when current was measured, current could be measured several seconds after energization. It is clear that the decomposition of methane gas occurs and the generated protons pass through the electrolyte membrane to the air electrode. Therefore, it was found that any electrolyte membrane has high ion selectivity. The generated currents were as follows.
A current of 1 kilohm was connected to the outside and the current was measured.
[0047]
Sample 1 0.57mA
Sample 2 0.78mA
Sample 3 0.76mA
Sample 4 0.79mA
Sample 5 0.63mA
Sample 6 0.65mA
Sample 7 0.58mA
Sample 8 0.60mA
(Comparative Example 2)
A fuel cell was constructed using Nafion 117, 1135, and 1035, and the presence or absence of current generation and the permeability of methane gas to the air electrode side were measured.
[0048]
Methane gas was introduced into the fuel electrode side, and whether or not methane gas permeated into the air electrode side was examined using a mass spectrometer. At about 10 seconds after the start of measurement, methane began to be detected, and was continuously detected thereafter. In the case of Nafion, current did not flow unless water was used.
[0049]
When methane gas was passed through water and measurement was made hydrophilic, currents were generated, and the generated currents were as follows.
[0050]
Nafion 117 0.5mA
Nafion 1135 0.45mA
Nafion 1035 0.55mA
[0051]
【The invention's effect】
As described above, the present invention has a through hole having a diameter of 0.01 to 150 μm provided by anodizing a metal, and has a proton conductive functional group modified on the inner wall of the through hole. It is an electrolyte membrane. In this way, while maintaining high proton selectivity, heat resistance can be improved, and it is possible to produce an electrolyte membrane that can generate power even in the absence of water at 100 ° C. or higher, and can be used even in a steam environment. It becomes. Further, in the present invention, the coexistence of water becomes indispensable by selecting the type and density of the functional groups of the electrolyte membrane, and a very realistic fuel cell is obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing the structure and operating principle of a PEFC type fuel cell.

Claims (3)

An electrolyte membrane for a fuel cell having a through hole having a diameter of 0.01 to 150 μm provided by anodizing a metal film or a silicon film, and a proton conductive functional group being modified on the inner wall of the through hole. 2. The electrolyte membrane for a fuel cell according to claim 1, wherein the metal membrane material is aluminum, titanium, zinc, indium or an alloy containing these as a main component. The electrolyte membrane for a fuel cell according to claim 1 or 2, wherein the functional group is an OH group.

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