JP2006236776A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems of alkaline fuel cells in which hydrogen H2 and oxygen O2 used as fuel can not be supplied without completely excluding carbon dioxide CO2 contained as impurities because the electrolyte of hydrogen H2 and oxygen O2 is changed in quality and increased in an electrical resistance by the carbon dioxide CO2, or an alkaline solution should be neutralized with an acid agent and a neutralized salt should be excluded before being drained away. <P>SOLUTION: This fuel cell (HIWFC) is structured by using hydroxide ion water as electrolyte. The hydroxide ion water has a boiling point of about 100°C and low corrosive. Therefore, the fabric of cotton 100% is used as a matrix (an substance is impregnated into which the hydroxide ion water of an electrolyte), and polypropylaene can be used as a structure material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hydroxide ion water fuel cell (HIWFC) characterized by using hydroxide ion water as an electrolyte.

  A fuel cell basically comprises three elements: an anode (fuel, hydrogen) electrode, an electrolyte, and a cathode (air, oxygen) electrode. When fuel cells are classified based on the type of electrolyte, there are alkaline fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, solid polymer fuel cells, and the like. (For example, refer nonpatent literature 1, 2, and 3.).

  An alkaline fuel cell (AFC) is composed of Pt (• Ag), an aqueous potassium hydroxide solution, and Pt (• Au) and operates from room temperature to about 80 ° C. Since an alkaline electrolyte is used, it is easy to select an electrode catalyst and a battery constituent material, and it can be produced at low cost, and exhibits excellent battery performance. However, carbon dioxide CO2 alters the electrolyte and increases electrical resistance, so carbon dioxide CO2 contained as an impurity in hydrogen H2 and oxygen O2 supplied as fuel must be completely removed. There is a problem that it cannot be supplied.

The effect of carbon dioxide can be explained as follows. (1) According to the scientific chronology, 0.8 cc of carbon dioxide CO2 dissolves at 20 ° C per cc of water H2O. (2) The dissolved carbon dioxide becomes carbonic acid by the reaction of CO2 + H2O-> H2CO3. (3) Carbonic acid reacts with potassium hydroxide KOH to form water and potassium carbonate. That is, H2CO3 + 2KOH-> K2CO3 + 2H2O. (4) Since potassium carbonate K2CO3 is an insoluble salt and precipitates, carbonate ions disappear from the water. (5) When the carbonate ions disappear, the carbon dioxide CO2 in the air is dissolved in water again.
This process repeats and carbon dioxide continues to dissolve until the potassium ion K + is finally gone. When potassium ions disappear, the concentration of carbonic acid increases and carbon dioxide reaches a dissolution equilibrium and does not dissolve in water.

  As long as potassium ion K + is present, carbonic acid reacts. Therefore, it can be seen that carbon dioxide does not affect the alkaline solution if potassium ion K + can be eliminated.

Even when the fuel cell is discarded, the alkaline agent is neutralized with acid to make it below the water quality standard, and even if it is drained, the neutralized salt continues to accumulate in the river and the sea. The neutralized salt is ionized in water, and water molecules surround each ion. In general, since 4 to 5 water molecules are coordinated to one ion, free water molecules decrease as the neutralization salt increases. It has a problem of acting on microorganisms like seawater instead of fresh water, and having a great influence on the ecosystem in the aquatic environment. In addition, neutralized salts in wastewater that meet water quality standards are concentrated by the ecological food chain, which affects the ecosystem.
In general, asbestos, which has been widely used as a diaphragm material, has recently been reported to have a carcinogenic problem.

  The polymer electrolyte fuel cell (PEFC) is composed of Pt (・ C), fluororesin proton exchange membrane, Pt (・ C), and a solid proton exchange membrane (Proton Exchange Membrane) in the electrolyte. (Solid Polymer Electrolyte Membrane) is used, and the operating temperature is from room temperature to 80 ° C. Since PEFC uses a strongly acidic ion exchange membrane, CO2 may be contained in H2 and O2 which are active materials. However, there is a problem that the electrolyte is highly corrosive, the electrode catalyst is limited to platinum, and CO becomes a catalyst poison. Proton exchange membranes are expensive (trade name Nafion Nafion membranes are approximately 50,000 yen at 25cm x 25cm), and if they do not contain moisture, the ionic conductivity is significantly reduced, so evaporation of moisture must be avoided during battery operation. There is. In addition, since the proton exchange membrane uses a toxic substance at the time of manufacture, there is a problem that it is harmful to the human body and is not friendly to the environment.

  In the polymer electrolyte fuel cell, it is considered that the following phenomenon occurs on the anode (fuel, hydrogen) electrode surface and the cathode (air, oxygen) electrode surface.

  When a hydrogen molecule approaches the platinum surface of the anode (fuel) electrode, the outermost molecular orbital of the hydrogen molecule and the outermost electron orbit of the platinum atom overlap, and the hydrogen molecule forms an active complex with the platinum atom. The hydrogen molecules forming the active complex are adsorbed on the platinum surface. The adsorbed hydrogen molecules become two atomic hydrogens. Electrons in the outermost electron orbit of atomic hydrogen transition to the outermost electron orbit of platinum atoms. The transitioned electrons travel to the external circuit and reach the air electrode. The atomic hydrogen that released the electrons becomes hydrogen ions. Hydrogen ions are attracted to oxygen ions at the air electrode by the electric Coulomb force, approaching, and hydrogen ions combine with oxygen ions to become water.

  When an oxygen molecule approaches the platinum surface of the cathode (air) electrode, the outermost molecular orbital of the oxygen molecule and the outermost electron orbit of the platinum atom overlap, and the oxygen molecule forms an active complex with the platinum atom. Oxygen molecules forming an active complex are adsorbed on the platinum surface. The adsorbed oxygen molecules become two atomic oxygen. Electrons coming from the fuel electrode through the external circuit reach the outermost electron trajectory of platinum atoms on the cathode (air) electrode surface. Electrons in the outermost electron orbit of the platinum atom transition to the outermost electron orbit of atomic oxygen. When atomic oxygen receives these transition electrons, the atomic oxygen becomes oxygen ions. Oxygen ions are attracted to the hydrogen ions at the fuel electrode due to the electric Coulomb force, approaching, and oxygen ions combine with the hydrogen ions to become water.

  Electrons flow from the fuel (hydrogen) electrode through the external circuit to the air electrode. However, since the direction of current is opposite to the direction of flow of electrons, the current flows from the air electrode to the hydrogen electrode. Therefore, the electromotive force has a positive potential at the cathode (air, oxygen) electrode and a negative potential at the anode (fuel, hydrogen) electrode.

  The overall fuel cell reaction is given by the formula H2 + (1/2) O2-> H2O (liquid) + 68.3 kcal. On the other hand, the heat of vaporization of water is 9.72 kcal / mol, and the heat required to heat water from room temperature 20 ° C. to 100 ° C. is 18 cc × 80 ° C. = 1.44 kcal / mol. The amount of heat required to evaporate is 11.16 kcal / mol.

  Supplying 1 mol of hydrogen gas generates 1 mol of water and 68.3 kcal of heat, but only absorbs 11.16 kcal of heat when 1 mol of water evaporates, so the fuel cell is held at a constant value of about 80 ° C. To do so, it is necessary to remove 57.14kcal heat. As one method for removing the heat of 57.14 kcal / mol, 57.14 kcal / 11.6 kcal / mol = 5.12 mol of room temperature (20 ° C.) water may be supplied. Or you may air-cool or water-cool through a heat sink and a heat pipe.

  Cellulose, which is the main component of wood chips and cotton, is known to dissolve in hydrochloric acid having a concentration of 40% or higher, and in sulfuric acid, it is dissolved in a concentration of 75% or higher. (Refer nonpatent literature 4.).

  Sulfuric acid having a concentration of 75% has a specific gravity of 1.62 g / cc, is a strong electrolyte, and has a pH of -1.09. In addition, 40% hydrochloric acid has a density of 1.198 g / cc and a pH of −1.12. Therefore, it is considered that there is a critical value of hydrogen ion concentration in which cellulose dissolves in the vicinity of −1 pH.

  The conductivity σ of the electrolyte is given by σ = Qnμ. Here, Q is the carrier charge, n is the carrier density, and μ is the carrier mobility. In a fuel cell using hydroxide ion water as an electrolyte, the carrier of electricity is hydroxide ion OH-. The resistivity ρ of the electrolyte is given by ρ = 1 / σ. The electrical resistance R of the electrolyte is given by R = ρl / A. Here, l is the distance between the electrodes, and A is the effective sectional area of the electrodes.

  In the flue gas desulfurization method that removes sulfurous acid gas in exhaust gas from boilers, etc., the Ni-base alloys include c-276 alloy, 625 alloy, c-22 alloy, G Examples of the alloy, 825 alloy, 20 alloy, 904L alloy, and stainless steel include 6Mo stainless steel, 255 duplex stainless steel, 2205 duplex stainless steel, and 317LMN stainless steel. (Refer nonpatent literature 5.).

  Conventionally, high purity platinum Pt, iridium Ir, osmium Os and other platinum group elements such as platinum electrode, carbon electrode, graphite electrode, glassy carbon electrode, etc. It is used. (For example, refer to Patent Document 1).

  Catalytic combustion is a combustion system in which a catalyst is used instead of a high-temperature flame, and fuel and oxygen are reacted on the surface. Hydrocarbon fuels such as methane and propane, even when using palladium or platinum catalysts, do not cause catalytic combustion unless the temperature is 300 ° C. or higher, but hydrogen also occurs at room temperature. This point was noticed by catalytic combustion of hydrogen, which has the following advantages. (1) A temperature from room temperature to around 400 ° C. can be freely obtained by adjusting the output. (2) Since it is flameless combustion, there is little risk of fire and NOx is not generated. (3) Dilute hydrogen below the flame combustion limit can also be used. (4) While the hydrogen flame is transparent and has little heat radiation, the catalyst becomes a heat radiator and it is easy to obtain radiant heat. (For example, refer nonpatent literature 6.).

  When hydrogen is used as fuel, many substances are effective combustion catalysts at low temperatures, unlike hydrocarbon fuels that are difficult to burn. When using a highly active catalyst such as platinum Pt or palladium Pd, combustion starts just by flowing hydrogen at room temperature, and only by changing the hydrogen flow rate from about 50 ° C to the flame ignition temperature (500 to 600 ° C) with complete combustion. To adjust the temperature. In addition to Pt, Pd, Ir, Ru, PdO, PtO2, and RuO2 are known as highly active catalysts.

  The cryogenic catalytic combustion of hydrogen is attracting attention as a means of automatic ignition of rocket liquid hydrogen fuel. Of various precious metals and their alloys, Ir has the highest catalytic activity at cryogenic temperatures. In the case of Pt, even if the loading amount is increased, the combustion start temperature is about -120 ° C, and the activity hardly changes. Hydrogen catalytic combustion is possible even at a nitrogen temperature (−196 ° C.).

In catalytic combustion of hydrogen in the presence of platinum, the following phenomenon is considered to occur on the surface of platinum.
As the hydrogen molecule approaches the platinum surface, the hydrogen molecule forms an active complex with the platinum atom. The hydrogen molecules forming the active complex are adsorbed on the platinum surface. The adsorbed hydrogen molecules become two atomic hydrogens. Electrons in the outermost electron orbit of atomic hydrogen transition to the outermost electron orbit of platinum atoms. The atomic hydrogen that released the electrons becomes hydrogen ions.

  At the same time, when an oxygen molecule approaches the platinum surface, the oxygen molecule forms an active complex with the platinum atom. Oxygen molecules forming an active complex are adsorbed on the platinum surface. The adsorbed oxygen molecules become two atomic oxygen. The electrons in the outermost electron orbit of the platinum atom transition to the outermost electron orbit of atomic oxygen, and the atomic oxygen becomes oxygen ions. Oxygen ions are attracted to hydrogen ions by electric Coulomb force, approaching, and oxygen ions combine with hydrogen ions to become water.

  Therefore, from the viewpoint of the chemical reaction in which oxygen ions are combined with hydrogen ions, it can be seen that hydrogen catalytic combustion is equivalent to a fuel cell. That is, the state of catalytic combustion of hydrogen corresponds to a case where the fuel electrode and the air electrode in the fuel cell are extremely close to each other. Therefore, there is a possibility that a highly active catalyst in catalytic combustion of hydrogen can be used as a fuel electrode of a fuel cell.

  The property of platinum adsorbing hydrogen is considered to be based on one of electric force, magnetic force, nuclear force, and gravity. However, the hydrogen atom is composed of a combination of hydrogen ions and electrons, and has already been electrically neutralized, so it is considered that the electric force is not the cause. In addition, hydrogen atoms are considered not to be caused by magnetic force because hydrogen atoms are magnetically coupled to each other. Nuclear power will cause nuclear fusion, but the nuclear force of platinum and hydrogen is not fused, so it is thought that nuclear power is not the cause. Therefore, it is derived that the property of platinum adsorbing hydrogen is caused by gravity.

Here, assuming that the property that platinum adsorbs hydrogen is caused by gravity, it is expected that the higher the density of the substance, the larger the adsorbing force. Platinum is a substance with heavy nuclei and high density, which is consistent with this expectation. Further, it is expected that catalytic combustion occurs at a lower temperature as the density of the substance increases. Since iridium Ir has a higher density than platinum Pt (the density of platinum is 21.45 g / cc and the density of iridium is 22.61 g / cc), catalytic combustion at a lower temperature of iridium Ir than platinum Pt It is consistent with the fact that
Patent Publication 2001-96273 Technical trend survey on fuel cells, JPO technical research section, May 31, 2001, 2P State-of-the-art hydrogen energy technology, supervised by Tokio Ota, NTS Co., Ltd. Corrosion Protection Handbook, Corrosion Protection Association, Maruzen Co., Ltd. February 29, 2000, 749p. The latest technology of Wood Chemicals, supervised by Keisuke Iizuka, CM Co., Ltd., 2000, 39p. Corrosion Protection Handbook, Corrosion Protection Association, Maruzen Co., Ltd. February 29, 2000, 768p. Hydrogen Energy State-of-the-art Technology, NTS Co., Ltd., January 31, 1995, first printing, p.570

  In alkaline fuel cells, the carbon dioxide CO2 changes the electrolyte and increases the electrical resistance, so the carbon dioxide CO2 contained as an impurity in the hydrogen H2 and oxygen O2 supplied as fuel is completely removed. There was a problem that it could only be supplied after that. In addition, when the fuel cell is discarded or an accident in which the alkaline solution is scattered occurs, it is necessary to neutralize the alkaline solution with an acid agent and then remove the neutralized salt to drain the solution. . However, even if neutralized salt is removed below the water quality standard, there is a problem in rivers where neutralized salt accumulates due to the concentration by the food chain, affecting the ecosystem. In addition, asbestos, which has been widely used as a diaphragm, has recently had a problem of being carcinogenic. On the other hand, in the polymer electrolyte fuel cell that operates at 100 ° C. or less and has no problem of neutralization salt, there is a problem that the price of the polymer membrane is high. In addition, since the polymer film uses a hazardous substance at the time of manufacture, there is a problem that it is harmful to the human body and is not friendly to the environment. On the other hand, when using cellulose that is environmentally friendly and low in cost as a matrix (a diaphragm for holding the electrolyte), and when a strongly acidic electrolyte solution is used, the pH of the electrolyte solution is −1 pH or less. However, there is a problem that the cellulose may be dissolved too much.

The present invention solves this problem, and is a fuel cell characterized in that hydroxide ion water is used as an electrolyte in an alkaline fuel cell.
Further, in the fuel cell, a cellulose or 100% cotton cloth is used as a diaphragm for impregnating the electrolyte, and polypropylene is used as a structural material of a portion in contact with hydroxide ion water of the fuel cell. is there.
In other words, by using hydroxide ion water as an electrolyte for alkaline fuel cells, it does not contain potassium ions K +, sodium ions Na +, etc., so carbon dioxide is not neutralized. Is suppressed.
In addition, since the boiling point of hydroxide ion water is about 100 ° C. and does not contain a catalyst such as potassium ion K + or sodium ion Na +, the corrosiveness is low. 100% cotton cloth can be used as the base material to be impregnated with polypropylene, and polypropylene can be used as the structural material in contact with the hydroxide ion water.

  FIG. 1 shows a schematic diagram of a hydroxide ion water fuel cell. The hydrogen gas passes through the fuel electrode gas diffusion layer 1, becomes hydrogen ions H + (protons) in the fuel electrode catalyst layer 2, and enters the electrolyte solution holding layer (cellulose or cloth) 3. The oxygen gas passes through the air electrode gas diffusion layer, becomes oxygen ions O 2− in the air electrode catalyst layer, and enters the electrolyte solution holding layer (cellulose or cloth) 3. The structural material 6 in contact with the hydroxide ion water is polypropylene. The electrolyte solution can be put in from the electrolyte solution introduction port 7 and taken out from the electrolyte solution discharge port 8.

Hydrogen atom H consists of electron e- and proton H + (= hydrogen ion).
Proton water is pure water or water generated near the anode when electrolyzing water, and means water that contains a large amount of protons H + (= hydrogen ions) and shows acidity.
Hydrogen ion water and proton water mean the same thing.
The hydroxide ion water is pure water or water in the vicinity of the cathode in the electrolysis of water, and means water containing a lot of hydroxide ions OH-.

The proton powder is a powder obtained by removing moisture from proton water and drying it.
The hydrogen ion powder is a powder obtained by removing moisture from hydrogen ion water and drying it.
The hydroxide ion powder is a powder obtained by removing moisture from hydroxide ion water and drying it.
It is desirable to use hydroxide ion powder for pH adjustment of 13 pH hydroxide ion water used as an electrolyte solution.

  Furthermore, if 14 pH or 15 pH hydroxide ion water is used as the electrolyte solution, the electrical resistance is lowered and a large current can be extracted efficiently, but on the other hand, the corrosivity of the hydroxide ion water is also increased. The disadvantage is that it cannot be made of low-cost materials. Accordingly, the pH value of hydroxide ion water is desirably about 13 pH.

  The thicker the cellulose or 100% cotton cloth impregnated with the electrolyte is, the higher the mechanical strength is. However, if it is 3 mm or more, the electrical resistance is also increased, leading to a reduction in efficiency. On the other hand, if the thickness of the cloth is reduced, the electrical resistance is lowered and the efficiency is increased. However, if it is less than 10 μm, it is difficult to maintain the mechanical strength, and it is too thin to easily cause a short circuit accident. Accordingly, the thickness of the 100% cotton cloth impregnated with the electrolyte may be 20 μm to 3 mm, preferably 50 μm to 2 mm, and more preferably 0.1 mm to 1 mm.

  Since the resistance of the fuel cell electrolyte is kept low while pure water is supplied, the chemical reaction of the formula H2 + (1/2) O2-> H2O (liquid) + 68.3kcal proceeds and generates heat. If the supply of pure water is inadequate, the electrical resistance at the electrolyte portion will increase, making it difficult for current to flow, reducing the amount of proton H + (: hydrogen ion) or hydroxide ion OH- transfer, Fever is also reduced. Therefore, the upper limit of the operating temperature of the fuel cell is 100 ° C., which is the boiling point of water.

  However, when the electrolyte part is completely dehydrated and dried, hydrogen gas and oxygen gas that have passed through the gas diffusion electrode (porous electrode) meet on the surface of a highly active catalyst such as platinum, and catalytic combustion of hydrogen occurs. Wake up and continue to generate heat, and over 100 ° C may cause a burning accident, so install a moisture sensor in the electrolyte part and adjust it so that it does not lose moisture when supplying hydrogen gas There is a need.

  The catalytic combustion of hydrogen is a combination reaction of hydrogen and oxygen at room temperature, and it can be seen that the thermochemical reaction formula is equal to the thermochemical reaction formula in the fuel cell. This indicates that the hydrogen reaction at the surface of the highly active catalyst in the catalytic combustion of hydrogen is equal to the hydrogen reaction at the fuel electrode surface in the fuel cell. Therefore, a highly active catalyst in catalytic combustion of hydrogen may be used as a fuel electrode in a fuel cell.

  In addition to Pt, Pd, Ir, Ru, PdO, PtO2, and RuO2 are known as highly active catalysts in catalytic combustion of hydrogen. Furthermore, even a material that is not known today can be used as a material for the fuel electrode of a fuel cell if it is a highly active catalyst in catalytic combustion of hydrogen and has high corrosion resistance.

  The material of the fuel electrode is preferably a material that is a highly active catalyst for catalytic combustion of hydrogen, has high corrosion resistance, and is difficult to elute. Specific examples include platinum Pt and iridium Ir.

  Since the air electrode needs to withstand a high potential state of about 1 V during or after operation of the fuel cell, it is desirable that the material of the air electrode is a material that has high corrosion resistance and is difficult to elute. Specific examples include platinum Pt and iridium Ir.

When the hydroxide ion water fuel cell is discarded, the electrolyte ion hydroxide ion water is neutralized with proton powder (hydrogen ion powder) or proton water (hydrogen ion water) to obtain pH 7 water. It is desirable to dispose of it so as not to affect the environment.
Place hydrogen ion powder on the outside of the fuel cell so that it can be neutralized with hydrogen ion powder immediately in the event of a hydroxide ion water leakage accident at the time of a hydroxide ion water fuel cell failure accident It is desirable to keep it. Furthermore, it is desirable to design based on fail-safe policy so that the neutralization reaction automatically proceeds in the event of an accident.

When fuel cells are mass-produced, the impact on the environment will increase, so it is desirable to change the manufacturing process up to a single component to an environmentally friendly green process.
In addition, it is desirable to evaluate the environmental impact of each relevant component throughout the lifetime of the fuel cell: manufacturing, operation, periodic inspection, accidents, fault repairs, and disposal.

When operating at about room temperature (20 ° C.) as an operating condition, a cooling device for cooling the heat generated at 68.3 kcal per 1 mol of flowing hydrogen is required.
At the same time, one mole of water is produced in the electrolyte solution per mole of hydrogen flowing in. Accordingly, the hydrogen ion concentration in the electrolyte solution increases, and the pH value of the hydroxide ion water becomes smaller than 13 pH. For this reason, after taking out electrolyte solution outside once, pH adjustment is needed to adjust pH and to return to an electrolyte part again.

  As operating conditions, if the temperature is maintained at about 100 ° C., the moisture becomes water vapor and evaporates, so that the pH value of the electrolyte solution increases. For this reason, it is necessary to replenish pure water in an electrolyte solution, and a pH adjuster or a replenisher of pure water is required. Furthermore, it is necessary to heat the fuel cell to 100 ° C. with a heating device before the start of operation.

  Between 100 ° C. and room temperature, there is a temperature at which the amount of water produced and the amount of water evaporated are just balanced. This temperature is referred to herein as the critical temperature Tc. Tc depends on the heat capacity, structure and operating state of the fuel cell, and is a unique value of the fuel cell.

  By controlling the temperature to be constant at the critical temperature Tc as the operating condition, the amount of water in the electrolyte can be maintained at a constant value, and it is not necessary to replenish water or adjust pH. However, a heating device and a cooling device are required to keep the temperature constant at Tc. Examples of the heating device include an electric heater and a gas heater.

  In order to adjust the pH of the electrolyte solution, the fuel cell preferably includes an electrolyte solution inlet and an electrolyte solution outlet. In order to adjust the pH value of the electrolyte solution taken out from the fuel cell to the set value, it is equipped with pH measuring means for measuring the pH value of the electrolyte solution, and hydroxide ion water or hydroxide ion powder that is strong against the electrolyte solution It is desirable to provide a pH adjusting means including an adding means for adding.

  The fuel cell preferably includes temperature measuring means for measuring the temperature of the electrolyte solution and temperature adjusting means for adjusting the temperature of the electrolyte solution in order to adjust the temperature of the electrolyte solution. In order to adjust the power generation output of the fuel cell, supply means for supplying air or oxygen to the air electrode, or supply means for supplying fuel or hydrogen to the fuel electrode is provided with adjusting means for adjusting the pressure or flow rate. It is desirable to provide. In order to separate the electrolyte solution and gas of the fuel cell, it is desirable to use gas diffusion electrodes for the fuel electrode and the air electrode.

  Can be used for power generation. Since hydroxide ionized water has a boiling point of about 100 ° C and is not corrosive, use a 100% cotton cloth for the matrix (base material impregnated with electrolyte hydroxide ionized water) or use inexpensive materials such as polypropylene. It can be used as a structural material. Since no carcinogenic substances such as asbestos are used as the diaphragm, it is safe for the human body. Also, when the fuel cell is discarded, the hydroxide ion water can be neutralized with proton water to pH 7 water, so there is no problem of neutralization salt, the drainage can be cleaned and the environment is good. . Compared to an expensive proton exchange membrane of about 50,000 yen for a 25cm square, cotton cloth is cheaper. Furthermore, compared to proton exchange membranes that use hydrofluoric acid, which is a hazardous substance in the manufacturing process, 100% cotton fabric is good for the environment because it does not use any harmful substances in the manufacturing process. Hydroxide ion water is also good for the environment because it does not contain harmful substances in its production process. The entire manufacturing process of the fuel cell including each component is close to the green process, which is good for the environment. Since the pH of the electrolyte solution is close to 13 pH, there is no possibility that the cellulose dissolves. Therefore, there is an advantage that the durability of the cellulose diaphragm is increased and the life is extended.

  By limiting the electrolyte solution of the fuel cell to hydroxide ion water, it is possible to use a safe and inexpensive material such as cotton or polypropylene as the structural material, and the fuel cell has the same performance as the conventional type. Was able to be realized.

  Platinum was used for the cathode and the anode, hydroxide ion water was used as the electrolyte, and a 100% cotton cloth was used for the matrix (base material impregnated with the electrolyte hydroxide ion water). A fuel cell was manufactured as follows.

  A cloth of 100% cotton having a thickness of 0.2 mm was spread and fixed in position, and a polypropylene (A) having a thickness of 0.2 mm and a diameter of 9 cm was placed on the cloth and fixed with cellophane tape. A hole with a diameter of 4 cm was made with a soldering iron in the center position of polypropylene (A) with a diameter of 9 cm. After melting the polypropylene along the circumference of the hole with a diameter of 4 cm and fusing it to the cloth, the excess cloth outside the hole with a diameter of 4 cm was cut off.

  A platinum wire (1) having a diameter of 0.3 mm and a length of 30 cm was spirally wound on a cloth having a hole with a diameter of 4 cm. A 3 cm outermost platinum wire was pulled out to be a terminal. Three 1 mm × 1 mm × 10 cm thin polypropylene bars placed at equal intervals on the platinum wire were welded and fixed on the cloth.

  The polypropylene (A) having a diameter of 9 cm was turned upside down and fixed with cellophane tape, and a platinum wire (2) having a diameter of 0.3 mm and a length of 22 cm was spirally wound on the cloth having a hole of 4 cm in diameter. A 3 cm outermost platinum wire was pulled out to be a terminal. Three 1 mm × 1 mm × 10 cm thin polypropylene bars placed at equal intervals on the platinum wire were welded and fixed on the cloth.

  A polypropylene (A) having a diameter of 9 cm was horizontally placed and fixed so that a platinum wire (1) having a length of 30 cm came to the lower side and a platinum wire (2) having a length of 22 cm to the upper side. The position of the nozzle of the hydrogen gas was fixed at a height of 1 cm below the center axis of the spiral of the platinum wire (1). Hydrogen gas was arranged to blow out from the bottom to the top.

  The platinum wire terminal was sandwiched between clips, the tester's negative terminal was connected to the lower platinum wire (1), and the positive terminal was connected to the upper platinum wire (2). When the electric resistance between the platinum wires was measured with a tester, it could not be measured at 20 M ohms or more. When a few drops of tap water were dropped on the cloth to wet the cloth and platinum wire, the electrical resistance became 2M ohms.

  When hydrogen gas was blown onto the platinum wire (1) on the lower side of the polypropylene (A) having a diameter of 9 cm, the open circuit voltage was 0.6V to 0.7V. However, the internal resistance of the voltmeter which measured the open circuit voltage is 10M ohm. The voltage decreased when the moisture that had wetted the cloth decreased, and increased when moisture was added. When the hydrogen gas was turned off, the voltage approached 0V.

  Even when the flow rate of hydrogen was changed from about 10 ml / min to about 200 ml / min, the open-circuit voltage of the fuel cell was about 0.7 V and hardly changed. This is presumably because the effective area of platinum in contact with hydrogen gas is as small as 0.03 cm × 20 cm = 0.6 cm 2.

  When a load resistance of 1 ohm was connected to the fuel cell and hydrogen gas was allowed to flow, the voltage across the load resistance was 0.12 mV. According to Ohm's law, the value of the current flowing through a load resistance of 1 ohm is 0.12 mV / 1 ohm = 0.12 mA.

The conductivity σ of the electrolyte is given by σ = Qnμ. The resistivity is ρ = 1 / σ. The hydrogen ion concentration of 7 pH pure water is 1e-7 mol / l, and the hydrogen ion concentration of 13 pH hydroxide ion water is 1e-13 mol / l.
Since the electrical conductivity σ of the electrolyte is proportional to the hydroxide ion concentration and inversely proportional to the hydrogen ion concentration, in the fuel cell having the configuration of the present invention, the electrical resistance of the electrolyte in the case of 7 pH pure water is 1 M ohm. In this case, the electrical resistance of the electrolyte in the case of 13 pH hydroxide ion water is 1 ohm.

  Assuming that the electromotive force of the fuel cell is 0.6 V and the effective cross-sectional area of platinum is 0.6 cm 2, according to Ohm's law, when the resistance of the electrolyte is 1 M ohm, a current of 0.6 V / 1 M ohm = 0.6 μA (current density 0.6 μA / 0.6cm2 = 1μA / cm2) is obtained, and when the resistance of the electrolyte is 1 ohm, current solidity (current density 0.6A / 0.6cm2 = 1A / cm2) of about 0.6V / 1 ohm = 0.6A is obtained . The current density of 1 A / cm 2 in the case of 13 pH hydroxide ion water is comparable to the performance of conventional polymer electrolyte fuel cells.

  In order to know the requirements for fuel cell operation, we replaced platinum with several other metals and found that the anode must always be platinum. Furthermore, it was discovered that the air electrode need not be platinum.

  The effective diameter of the cloth placed horizontally is 6 cm. On the upper side, three 2 mm x 1 mm x 6 cm pieces of stainless steel wire having a diameter of 0.3 mm and a length of 1 m are spirally wound on the cloth. While pressing with a polypropylene rod, it was welded and fixed. A platinum wire having a diameter of 0.1 mm and a length of 1 m was spirally wound under the cloth and placed on a 6 cm circle of the cloth. The two 2 mm × 1 mm × 6 cm polypropylene bars placed at equal intervals were welded and fixed while being pressed.

Tap water was dropped to wet the platinum wire and cloth.
When hydrogen was blown against the platinum wire from the bottom, an open circuit voltage of about 0.6 V was output. However, the internal resistance of the voltmeter which measured the open circuit voltage is 10M ohm.
When the cloth is turned upside down, the platinum wire is on the top and the stainless steel wire is on the bottom of the cloth, and hydrogen is blown onto the stainless steel wire from the bottom, the voltage changes only slightly to several tens of mV. In comparison with 0.6V, the change was negligible.

  I tried platinum and platinum, gold and gold, stainless steel and stainless steel, copper and copper, or a combination of different metals as a combination of air electrode and fuel electrode. It was found that an open circuit voltage of V to 0.6V can be obtained. Conversely, when the fuel electrode was stainless steel, copper, or gold, the open circuit voltage was almost 0V. That is, when the fuel electrode was platinum, power could be generated regardless of whether the air electrode was stainless steel, copper, or gold.

  It is desirable that the unit cell (unit cell) of the hydroxide ion water fuel cell HIWFC has a plate-like structure in which a matrix holding hydroxide ion water is sandwiched between gas diffusion electrodes (air electrode and fuel electrode). . The battery is supplied with oxygen (including air) on the air electrode side and hydrogen (including reformed gas) on the fuel electrode side to generate power. The operating temperature is from room temperature to 100 ° C. Since the voltage of a single cell is about 1V, it is usually used as a cell stack in which a plurality of cells are stacked in series electrically. In that case, a separator is used to prevent gas mixture between the air electrode and the fuel electrode. Sandwiched between cells.

  Further, it is desirable that a hydroxide ion water holding plate (reservoir) for replenishing hydroxide ion water scattered in the gas with a small amount is sandwiched between the separator and the cell. It is desirable to form a groove serving as a reaction gas channel on the cell side surface of the hydroxide ion water holding plate.

  In the cell stack, it is desirable to provide a cooling plate for removing exhaust heat during power generation every 5 to 8 cells. It is desirable that the cooling plate has a structure in which a cooling water pipe is embedded in a carbon plate, and the cooling water is managed to have an ultrapure water class low electrical conductivity in order to ensure insulation between cells.

  Hydroxide ion water fuel cell HIWFC has high electrical and thermal conductivity, and carbon, which is relatively corrosion resistant to 13 pH hydroxide ion water, is the main constituent material (catalyst carrier, electrode substrate, separator, reservoir) It is desirable to use as a cooling plate. However, care must be taken because carbon may also be subjected to electrochemical corrosion. For example, corrosion of the catalyst carrier leads to deterioration of characteristics due to isolation of catalyst particles, etc., and corrosion of the separator is caused by deficiency of hydroxide ions or excessive hydroxide ions accompanying electrochemical movement of hydroxide ions through the separator. It leads to characteristic deterioration by.

  In order to suppress this corrosion reaction, it is desirable to use a carbon material that has been graphitized by high-temperature treatment at 2000 ° C. to 3000 ° C. and that has improved corrosion resistance in contact with hydroxide ions. However, the corrosion rate increases as the electrochemical potential rises even at high temperature. Therefore, it is important to prevent a high potential state in each part of the cell stack regardless of a transitional state such as a normal operation state, start and stop, and output change.

  In addition to carbon corrosion, in a high potential state at the operating temperature, there is a problem of reduction of the catalyst surface area due to dissolution and reprecipitation of Pt of the catalyst metal in hydroxide ion water. In particular, the damage in the no-load state (potential around 1 V) at the operating temperature is great, and the battery performance is lowered in a short time. Although there is a high possibility that such a state will occur immediately after the power generation is stopped, it is desirable to take measures such as quick oxygen concentration reduction by nitrogen purge and potential control by adding resistance.

  Corrosion of the piping material by hydroxide ion water in the exhaust gas from the cell may lead to gas leakage or clogging by corrosion products. In particular, it is desirable to take measures such as coating the gas manifold of the cell stack with a large amount of hydroxide ion condensation with a corrosion-resistant resin. In addition, it is necessary to pay attention to the corrosion of heat exchangers related to cooling water for heat recovery.

  Assuming that the cloth diaphragm thickness is 0.2 mm, hydroxide ion water is filled so that the cloth gets wet. Therefore, assuming that the size of one diaphragm portion is 100 cm × 100 cm × 0.02 cm = 200 cc, there are 10 cells of 0.6V. A total of 2 liters of hydroxide ion water is required in a 6V stack.

13 pH hydroxide ion water contains 1 mol (17 g) of hydroxide ions per liter. Boil 10 liters of 12 pH hydroxide ion water to make 1 liter of 13 pH hydroxide ion water. 100 liters of 11 pH hydroxide ion water can be boiled to make 1 liter of 13 pH hydroxide ion water. 1000 liters of 10 pH hydroxide ion water can be boiled to make 1 liter of 13 pH hydroxide ion water.
Since pure water (purified water) costs 3000 yen for 20 liters, it costs 150,000 yen for 1000 liters.

So far, the inventor has produced 1 liter of hydroxide ion water with a maximum pH of 10 at 100 V and 1 mA at 1 H, so if 1 kW is 30 yen, the electricity charge is 3 yen.
Therefore, the cost of 1000 liters of 10 pH hydroxide ion water is 150003 yen.

  Furthermore, to make 1 liter of 13 pH hydroxide ion water by boiling 1000 liters of 10 pH hydroxide ion water, raise the temperature of the water from 20 ° C to 100 ° C and further evaporate the heat of vaporization 9.7 kcal / mol is required. In order to evaporate 999 liters of water, (100-20 ° C) x 999 liters x 1000 cc = 79920 kcal and 999000/18 x 9.7 kcal = 538350 kcal are required. It costs 21536 yen from 1kwH = 861kcal. Therefore, 2 liters of 13 pH hydroxide ion water costs (21536 yen + 150003 yen) x 2 = 343078 yen.

  Since the price of the polymer electrolyte membrane of 25 cm × 25 cm was about 50,000 yen, it would be 200,000 yen at 100 cm × 100 cm, and 1.2 million yen for 6 stacks. Therefore, the total cost of the electrolyte and the diaphragm is about 4 times cheaper than the conventional one.

  As a fuel cell operating from room temperature to 100 ° C. or less, a polymer electrolyte fuel cell PEFC is mainstream, but there is a problem that the cost of the polymer electrolyte membrane is high. If hydroxide ion water is used as the electrolyte, the corrosiveness is lowered, and instead of the polymer electrolyte membrane, 100% cotton cloth is used as a matrix (base material impregnated with electrolyte hydroxide ion water). In addition, since polypropylene can be used as a structural material, a low-cost fuel cell can be produced, and there is a high possibility that it can be used as an industry.

The schematic diagram of the hydroxide ion water type fuel cell of the present invention is shown.

Explanation of symbols

1 Fuel electrode gas diffusion layer 2 Fuel electrode catalyst layer 3 Electrolyte solution holding layer (cellulose or cloth)
4 Air electrode catalyst layer 5 Air electrode gas diffusion layer 6 Structural material (polypropylene)
7 Electrolyte solution inlet 8 Electrolyte solution outlet

Claims (2)

A fuel cell characterized in that hydroxide ion water is used as an electrolyte in an alkaline fuel cell. 2. The method according to claim 1, wherein a cloth made of 100% cotton or cellulose is used as a diaphragm for impregnating an electrolyte, and polypropylene is used as a structural material of a portion in contact with hydroxide ion water of a fuel cell. Fuel cell.

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