JP4831656B2 - Thin wood pieces for electrolyte membranes such as fuel cells impregnated with inorganic ion exchangers - Google Patents

Description

  The present invention relates to an electrolytic membrane of a fuel cell and an electrolytic membrane of a direct methanol fuel cell (DMFC). The present invention relates to a membrane that allows ion migration and eliminates methanol methanol crossover. The present invention relates to a membrane having a water shielding property of “generated water” at an oxidation electrode of a fuel cell. It relates to higher ion mobility membranes such as electrolytic membranes in electrolysis.

  Currently, the electrolyte membranes of fuel cells that are being developed are organic materials such as Nafion (registered trademark). These membranes have been originally used as separation membranes for industrial electrolysis. This membrane is made of an organic polymer and is hydrophilic as well as amphiphilic and permeates methanol. This methanol permeation is called crossover. Development research is underway to reduce this.

As a method for reducing methanol crossover at the present research stage, the permeability of methanol is suppressed by blending a silicone resin or by irradiating with a branch polymer to form a net. Although various improvements have been made, there has been no real way to eliminate methanol crossover.
Japanese Patent Application No. 2002-177095 (P2002-177095)

  As a result of intensive studies, the inventors have invented a method and a material in which the crossover of 100% methanol is almost completely eliminated and the water permeability from the oxidation electrode is very small. In addition, the present application has been achieved with good ionic conductivity.

Recent applications using zirconium phosphate for fuel cells include the following, which are very different from the present application. In addition, there has been an application for blending zirconium phosphate in order to improve the bonding property with the electrode of the polymer film, but this is greatly different from the present application using wood. Further, in order to improve the durability of the proton exchange material while maintaining the fuel cell performance, an application for mixing zirconium phosphate has been filed, but this is greatly different from the present application using wood.
Japanese Patent Application No. 2001-159066 (P2001-159066) Japanese Patent Application No. 2003-175029 (P2003-175029)

  As a problem in an electrolyte membrane of a fuel cell, there is a problem of eliminating leakage (crossover) of fuel to a counter electrode of methanol while allowing proton transfer. In addition, there has been a demand for what can prevent “water leakage” from the oxidation electrode capable of producing “water”. On the other hand, in electrolysis, it has been desired to have a higher ion mobility than that which is difficult in terms of gas separation and cost of an electrolytic membrane, is inexpensive, is superior in strength, and is easy to handle.

  The problem could be solved by producing an inorganic ion exchanger in the thin wood piece. That is, in order to shield and separate alcohol and water, the thickness of the wood is made as thin as possible to give a shielding effect, and in addition, when this thin wood piece is impregnated with metal acid chloride and then treated with phosphoric acid, It was discovered that inorganic ion exchangers that were produced only in irregular shapes could be coated into a stable glass.

  Moreover, this film is very chemically stable and withstands oxidizing atmospheres and high temperatures, so that it also has the effect of protecting thin wood pieces. In addition, since the shape of the separation membrane is a plate shape that can be independent without reinforcement, the handling problem and the inductiveness of the generated gas are added, thereby solving the above-mentioned problems.

  According to the present invention, by reducing the water shielding and the movement of methanol by a thin piece of wood and a glassy inorganic ion exchanger, the ability of electric fuel cells of the direct methanol system that has not been able to sufficiently demonstrate electric energy until now has been achieved. Unfolding "can be done reliably. In addition, raw materials and processing costs can be reduced, and the strength is excellent as can be imagined from a thin plate of wood.

  By producing an inorganic ion exchanger in a thin piece of wood, the thickness of the wood is made as thin as possible in order to shield and separate alcohol and water. It has been discovered that ion exchangers can be coated into a stable glass. In addition, this film is very chemically stable and withstands oxidizing atmospheres and high temperatures, so it also protects wood.

Zirconium phosphate is known as an inorganic cation exchanger. As a representative of acid salts, Non-Patent Document 1 describes the synthesis method, properties, ion exchange properties, and applications of zirconium phosphate. Thus, knowledge about the capture exchange of cations has been obtained for some time.
Published by Hidetake Kakibana and Kozo Narita “Latest Ion Exchange”, Yodogawa Shoten Co., Ltd., 7th Edition October 20, 1968 (first edition is July 15, 1960)

The synthesis of zirconium phosphate this time is as follows. When a phosphoric acid (or phosphate) solution is immersed in a piece of wood in a zirconyl nitrate (or zirconyl chloride) solution dissolved in 1N nitric acid (or hydrochloric acid) and treated with the phosphoric acid solution, a glassy film is formed. The ratio of phosphoric acid and zirconium involved in the reaction can vary considerably over a range greater than 0.5 (molar ratio). When PO ₄ /Zr=0.5 or less, a colloidal solution is formed and precipitation is not possible. Therefore, the phosphoric acid is always allowed to react in a molar ratio of more than 2. A more reliable reaction is possible when the liquid temperature of phosphoric acid is higher than room temperature.

By the way, in the usage method of zirconium phosphate, the powder is usually packed in a column and used. However, if it is made into a plate shape as in the present application, the container becomes unnecessary.
In addition, the cost of forming a zirconium phosphate film has come to be expected to be provided at a much lower price than the current organic electrode film by the method of the present application.

Next, wood is described. The advantages of wood include low specific gravity, ease of processing, low cost, extensive resources, and difficulty in transferring heat and electricity. On the other hand, disadvantages include repeated expansion and contraction due to changes in temperature and humidity, non-uniform fiber orientation, decay, flammability, and no resistance to chemicals.
Narusawa Kiyomizu "Wood" Power Company 2000

  As its use, it is used as an instrument and fixtures for pottery, barrels, aquariums, pots, pots, eggplants, and folk crafts. What should be noted is that the contents of the bowl can be isolated and preserved even if it contains alcohol, water, and high concentrations of salt, such as sake, water, miso and soy sauce. By the way, various processing methods have been proposed for wider use of this wood.

For example, as a method of processing wood, various techniques for impregnating with inorganic chemicals have been developed in order to impart flame retardancy, antiseptic / insect repellent, and stability. There are also applications for chemical treatment of wood. However, this application is very different from these applications in terms of content, purpose, type of medicine and usage, and is patentable and novel.
Japanese Patent Application No. 4-227605

The general strength of the cypress wood used this time is shown.
Air-dry specific gravity 0.44
Compressive strength 39.2 MPa (400 kg / square cm)
Tensile strength 117.7 MPa (1,200 Kg / square cm)
Bending strength 73.5MPa (750Kg / square cm)
Shear strength 7.4 MPa (75 Kg / square cm)
Narusawa Kiyomizu "Wood" Power Company 2000

  Some types of wood such as conifers and broadleaf trees and herbs can be made into a plate, so if wood can be processed into a plate with plants, it is not necessary to specify the species of wood and herbs. good. The thickness of the wood is not limited as long as the liquid can permeate, but paulownia and the like can penetrate even 10 mm. The thinness limit is desirably 100 microns or more, which can prevent the liquid from passing through. The size is not particularly limited as long as there is no problem with the size of the liquid layer in the processing reaction of the plate material. This time, the sample was cut out from a cypress-free sheet material.

This is a test for producing a film of an inorganic ion exchanger in and on a thin wood piece. Wood turns the cypress plate into a thin plate of 400-500 microns or less. It cut out to a size of 25 mmW × 50 mmL. This is washed with acetone to remove oils and fats and dried. Zirconyl nitrate ZrO (NO ₃ ) / 1NHNO ₃ solution (107 g of ZrO (NO ₃ ) ₂ .2H ₂ O / L) is put in 100 ml and the whole is depressurized for about 20 minutes. By reducing the pressure, the liquid is sufficiently immersed in the thin wood piece.

The pressure is returned to atmospheric pressure, and the mixture is placed in 200 mL of a H ₃ PO ₄ solution (phosphoric acid 100 ml / water 1) heated to room temperature or higher and allowed to react for 1 hour. Remove from phosphate solution and wash with distilled water. A “material” is obtained in which zirconium phosphate is soaked in a glass state in and on the surface of a thin wood piece. The increase in thickness was about 50 microns on average.

  A permeation test of an equimolar solution of 100% methanol, water and methanol water is performed. This test was performed by making the following test equipment. A 7 mm through hole is made in the same position on two sheets of 60 mmW × 150 mmL × 10 mmt PVC. A single PVC pipe (inner diameter: 22mmφ30mmL) is prepared and bonded vertically so that the 7mm through hole of the thick plate is on the inside of the single pipe. The sample prepared in Example 1 is sandwiched between the thick plate with a PVC single pipe and the PVC thick plate having only a through-hole, and a liquid is put into the single pipe to conduct a liquid permeation test using only gravity.

  A sheet of thin wood with zirconium phosphate deposited on the lower surface so that a thick pipe with a single PVC pipe is on the upper surface, along with an EPDM ring packing with an inner diameter of 12 mm, and another PVC thick plate through-hole Set them so that they match, and fix the two PVC thick plates with multiple spring clamps. Even if the EPDM is deformed, a spring system that can follow the deformation is better.

  In this horizontal set, 100% methanol is put into a single pipe pipe portion of polyvinyl chloride and left for 48 hours or more, and the amount of permeation is measured from the change at the liquid level. In addition, in order to eliminate the evaporation loss of methanol, the PVC single tube opening was covered with a wrap film and fixed with a rubber band.

  Although different from the conventional method of measuring and observing methanol dissolved in water, the observation was performed by a method close to the actual use as an electrode film. Passage area, 0.7 × 0.7 × π / 4 = 0.38 square cm, liquid depth, 3-4 cm (the thickness of the PVC thick plate and the length of the pipe), and the specific gravity of methanol is 0.8.

  The weight loss level of methanol after 51 hours was 3 mm. The permeation weight per 1 cm 2 per hour is calculated. A result of 0.047 g / hr.cm 2 is obtained.

  With the same apparatus, the permeation amount at 100% methanol of a Nafion® membrane having a thickness of about 100 microns formed from a commercially available Nafion® 5 wt% solution was measured. It swelled and permeated within 48 hours, and measurement was impossible.

  Perform the water permeation test using the same equipment and procedure. The weight loss level of water was 1.5 mm. The specific gravity of water is 1.0. A permeation weight of 1 cm 2 per hour results in 0.029 g / 1 hour · cm 2.

  With the same apparatus, the amount of water permeated through a membrane having a thickness of about 100 microns formed from a commercially available Nafion® 5 wt% solution was measured. Similarly, it swelled and permeated within 48 hours, and measurement was impossible.

  A permeation test of an equimolar solution of water and methanol was performed using the same equipment and procedure, but the results were the same as for water.

Conduct a chemical stability confirmation test. There is a pre-processing method for electrical conductivity measurement, which was submitted by the New Energy and Industrial Technology Development Organization (NEDO). The sample prepared in Example 1 was pretreated by this method.
1) Boiling in 3% hydrogen peroxide water (1 hour)
2) Boiling in distilled water (1 hour)
3) Boiling in 1M sulfuric acid (1 hour)
4) Boiling in distilled water (1 hour)
5) Store in distilled water at room temperature

  The sample prepared in Example 1 is processed under these conditions. In the case of only a thin piece of wood, the fibers in the edge portion vary at the stage of 3), but there was no abnormality in Example 1 coated with chemically stable zirconium phosphate.

  Conduct conductivity measurement test. The power source for the conductivity measurement was amplified by BMS120-2.5 of Takasago Seisakusho Co., Ltd., which was oscillated by the low-frequency transmitter KENWOODYMIAG-203D. A set frequency of 5000 Hz was passed through the sample to obtain the electrical resistance. The voltage / current measurement was performed with SANWACD800a and MT-31 of Mother Tool Co., Ltd. The electrodes were made by changing two platinum-plated titanium plates with an interelectrode distance of 1 to 2 cm. The width of the sample is 2 cm. The temperature is 20 ° C.

The samples were processed in Example 1 and Example 3, and the conductivity measurement results are as follows.
In Example 1, the film thickness is 450 microns, and the conductivity is 0.040 S / cm.
Example 3 pre-processed, film thickness 450 microns, conductivity = 0.020 S / cm.
It turns out that there is good ionic conductivity.
The catalog value introducing Nafion (registered trademark) is S / cm = 0.083.

Perform production tests with other chemicals. A thin piece of wood is put in 100 ml of a zirconyl nitrate ZrO (NO ₃ ) / 1NHNO ₃ solution (107 g of ZrO (NO ₃ ) ₂ .2H ₂ O / L), and the whole is depressurized for about 20 minutes. By reducing the pressure, the liquid is sufficiently immersed in the thin wood piece.

  It is returned to atmospheric pressure and placed in a sodium tungstate solution (73 grams of sodium tungstate dihydrate / 250 grams of water) heated to room temperature or higher and allowed to react for 1 hour. Remove from solution and decant with distilled water until pH is about 3. A “wood piece” is obtained, in which zirconium tungstate is formed into a glassy film and immersed in a thin piece of wood. Zirconium molybdate was similarly produced.

  A thin piece of wood is placed in a solution of 73 grams of sodium tungstate dihydrate in 250 grams of water and thoroughly soaked. When this piece of wood is placed in concentrated nitric acid, tungstic acid is formed in a colloidal form on the surface and inside of the piece of wood. Wash thoroughly with decantation until the pH reaches about 3. When dried at room temperature, a green tungstic acid film can be confirmed. This tungstic acid is a both ion exchanger and behaves the same as zirconium hydroxide. Molybdic acid could also be produced in the thin wood piece.

  Measurement of equivalent amount of PH and hydroxyl group for confirmation of ion exchange characteristics. Zirconium phosphate containing no wood chips was prepared under the same conditions as in Example 1, and the amount of hydroxyl groups per gram of sample and the change in PH were observed. A predetermined amount of hydroxyl group was added to each sample, and the pH was measured with the same water amount. The PH meter was measured with a Convoy HI98129 type.

The result was completely different from that of tribasic acid of phosphoric acid, and changes similar to those of monobasic acid in the neutral region as an ion exchanger were confirmed. Water temperature 20 ° C.
Measurement results of OH equivalent and PH value per gram of zirconium phosphate.

The PH at 0 meq is 1.20
The PH at 1 meq is 2.39
PH at 2 meq is 6.53
The PH at 3 meq is 10.26
The PH at 4 meq is 11.94.
The PH at 5 meq is 11.94.

This test confirms the ion permeability and separability of the separation membrane. An energization test by direct current using phosphoric acid acid (phosphoric acid 1 mL water 3 L) was performed. A 7 mm opening was made in the cap portion at the tip of a polyvinyl chloride single pipe pipe with an inner diameter of 50 mm and 50 mmL, and the thin wood piece prepared in Example 1 was loaded as a separation membrane and fixed so that the inside and outside of the pipe were not mixed. The electrode was a titanium platinum electrode 2 cm wide and 10 cm long, and the change in PH inside the isolation was measured. The energization conditions for energizing the cathode on the PVC pipe side are 40 vDC, 0.02 A.

The PH meter was measured with a Convoy HI98129 type.
The starting PH was 4.2, and the pH after 1 hour of this sample was 2.1. It became about 1.9 after 3 hours and 30 minutes from the start. Here, the result of observing the PH after 24 hours from stopping energization was the same as 1.9. Thus, it shows that it functions as a separation membrane with no return of hydrogen ions.

  A potential generation test as a fuel cell was conducted. The thin plate wood piece impregnated with the inorganic ion exchanger prepared in Example 1 was subjected to platinum plating. The inventors have been platinum-plated on titanium etc. on a daily basis to make this experience a know-how. The platinum adhesion amount of the sample of Example 1 is 1 mg / square cm.

  The platinum on the edge of the plate is cut off by about 1 mm to eliminate the electrical conductivity between the two surfaces. When this plate was loaded into the cap part used in Example 7 and an equimolar solution of methanol water was put into a single PVC pipe, a large amount of gas was observed on the methanol water side, and the oxidation electrode on the air side It was confirmed that a potential of about 0.7 V was generated between them. This confirmed the effect as a fuel cell.

  The present invention has led to the solution of the problems of direct methanol fuel cells, and is not only an electrical industry such as personal computers that require a mobile power supply, but also information related industries such as communications, as well as a composite material with wood, which contributes to the development of the wood industry. Can contribute.

It can make a wide range of contributions to the procurement of electrical energy during natural disasters.
In addition, various materials have been tried to solve problems, but what has been achieved with “wood” that makes use of nature's bounty can be used and deployed in a wide range of industries.

Claims (4)

An electrolyte membrane for a fuel cell, characterized in that a glassy inorganic ion exchanger is produced inside and on the surface of a plate-like piece of a plant belonging to woods or herbs. An electrolytic membrane for electrolysis, characterized in that a glassy inorganic ion exchanger is produced inside and on the surface of a plate-like piece of a plant belonging to trees or herbs. A plate-like piece of wood having a thickness of 10 mm or less is impregnated with a hydrochloric acid solution of zirconium oxychloride or a nitric acid solution of zirconium oxynitrate, and then treated with a phosphoric acid solution, whereby glassy zirconium phosphate is formed inside and on the surface of the plate-like piece of wood. Producing an electrolyte membrane having a liquid shielding property that hardly causes methyl alcohol and water to pass therethrough. After impregnating a plate-like piece of wood having a thickness of 10 mm or less with a hydrochloric acid solution of zirconium oxychloride or a nitric acid solution of zirconium oxynitrate, the glass is hydrated inside and on the surface of the plate-like piece by treating with a sodium tungstate solution. A method for producing an electrolyte membrane comprising producing an electrolyte membrane having a liquid shielding property in which methyl zirconate tungstate is formed to prevent methyl alcohol and water from passing therethrough.