JP2005166486A - Direct type fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct type fuel cell system capable of restraining the complication of the fuel cell system, an increase of size, the lowering of energy conversion efficiency caused by catalyst poisoning and cross-over of fuel, and the exhaustion of carbon dioxide. <P>SOLUTION: The direct type fuel cell system uses either phosphoric acid, solid organic electrolyte having heat resistance of ≥100°C, solid inorganic electrolyte, or organic hybrid electrolyte, as its electrolyte, operated at 100 °C to 400°C, and generates power by directly supplying or making directly contact the fuel composed of one or more kinds of methylcyclohexane, decalin, methyldecalin or the like, to or with a fuel electrode without reforming the fuel. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a novel fuel cell system. More specifically, the present invention relates to a direct fuel cell system that uses methylcyclohexane, decalin, methyldecalin, or the like as a fuel and uses a heat-resistant electrolyte and operates efficiently in a region of 100 ° C to 400 ° C.

  In a fuel cell system using a conventional polymer electrolyte fuel cell (hereinafter referred to as PEFC (Polymer Electrolyte Fuel Cell)), hydrogen gas is used as fuel gas or hydrogen obtained by steam reforming a hydrocarbon compound. Gas is used. In the case of using hydrogen gas, a cylinder that can withstand high pressure is required to secure a sufficient amount of hydrogen. In addition, when reforming a hydrocarbon compound, CO is also generated along with the reforming reaction, and a CO removal step is indispensable for the reduction.

  For example, a fuel cell system using methanol as a fuel is known which has a configuration as shown in FIG. In the fuel cell system, as shown in the figure, in order to store a mixed liquid of water and methanol in a water / methanol mixed liquid storage tank 15, and to generate hydrogen-rich fuel gas from this mixed liquid (fuel), The fuel vaporized by the evaporator 16 is introduced into the reformer 17 and steam reformed. Since the reformed gas reformed by the reformer 17 contains high-concentration CO, the CO is removed by the subsequent CO remover 18 and then supplied to the fuel cell 11 for power generation operation. .

  In the fuel cell 11, the fuel electrode and the air electrode are arranged to face each other through the electrolyte 11a. Air from the air supplier 14 is supplied to the air electrode. In the fuel cell system of the type described above, waste fuel is discharged from the fuel electrode of the fuel cell 11, water and waste air are discharged from the air electrode, and carbon dioxide is discharged from the reformer 17 and the CO remover 18. Is done. A fuel cell system incorporating such a reformer is disclosed in Japanese Patent Laid-Open Nos. 10-334935, 2000-340245, 2002-025591, and the like (see Patent Documents 1 to 3). ).

  FIG. 3 is an explanatory diagram showing a schematic configuration of a fuel cell system using a direct methanol fuel cell (hereinafter referred to as DMFC) that directly supplies methanol as fuel. As shown in the figure, in the DMFC, a mixed solution of methanol and water is directly supplied from the storage tank 5 to the fuel cell 11, and hydrogen is generated through a reforming reaction at the fuel electrode to perform a power generation operation. Carbon dioxide and waste fuel are discharged from the fuel electrode of the fuel cell 11, and water, waste air, and waste fuel are discharged from the air electrode and sent to the waste liquid separator 9.

  The fuel cell system using DMFC is simpler than the fuel cell system having the above reformer, but the catalyst activity of the fuel electrode is not sufficient, and methanol diffuses in the organic electrolyte and reaches the air electrode. There is a problem that a short circuit phenomenon (this phenomenon is called “crossover”) causes a direct reaction with an oxidant on the catalyst of the air electrode, resulting in a decrease in power generation efficiency (see Non-Patent Document 1).

In addition, research is also known in which power is generated by directly supplying cyclohexane and 2-propanol as fuel to a normal PEFC at a temperature of 70 to 80 ° C. (see Non-Patent Document 2). However, since the above method uses a polystyrene-based cation exchange membrane (trade name: Nafion) having a sulfonic acid group as an electrolyte, it cannot be operated at a higher temperature and cannot efficiently generate power.
JP-A-10-334935 JP 2000-340245 A JP 2002-025591 A [M. P. Hogarth and H.M. A. Hards Platinum Metals Rev. 40 (4) 150 (1996)]. British Chemical Society Bulletin (M. Ichikawa) Chem. Commun. 2003, 690-691)

  Among the conventional fuel cell systems shown above, in the fuel cell system having the reformer shown in FIG. 2, the reformer 17 and the CO remover 18 are larger as devices than the fuel cell 11, and the system becomes larger. . Furthermore, preheating is necessary to perform the power generation operation of the entire system. Since the operating temperatures of the reformer 17 and the CO remover 18 are 150 to 250 ° C., which is higher than the fuel cell 70 to 80 ° C., the preheating is performed. There is a problem of lowering the power generation efficiency. Furthermore, when hydrocarbons such as methanol are used as fuel, there is also an environmental problem of discharging carbon dioxide.

  In addition, the fuel cell system using the DMFC shown in FIG. 3 has the disadvantage that the output and efficiency of the fuel cell are low, although it is considerably improved by the simplification of the system. The reasons are that the electrode catalyst activity of the fuel electrode is not sufficient, and that the methanol crossover reacts directly with the oxidant on the air electrode catalyst, and the power generation efficiency of the fuel cell is limited. It is done. In addition, these fuel cell systems also have a problem that fuel is consumed and carbon dioxide is discharged, which adversely affects the environment.

  The conventional fuel cell system using cyclohexane and 2-propanol as the fuel has a low fuel reforming efficiency and a power generation efficiency using a reformer because the temperature of the fuel cell is as low as 70 to 80 ° C. There is a problem that it is lower than that of a fuel cell system (Chem. Commun., 2003, 690-691).

  The present invention has been made to solve the above-described problems, and its purpose is to make the energy of the fuel cell system more complicated and larger due to the provision of the reformer, catalyst poisoning, and fuel crossover. It is an object of the present invention to provide a direct fuel cell system capable of suppressing reduction in conversion efficiency and further emission of carbon dioxide.

  The inventors of the present application have made extensive studies in order to solve the above problems. As a result, it has been found that the above object can be achieved by directly supplying a hydrogen-containing compound substantially free of oxygen, that is, a hydrocarbon compound, as a fuel to the fuel cell, and the present invention has been completed.

  In order to solve the above-described problem, the direct fuel cell system according to claim 1 uses a hydrocarbon compound as a fuel, and an operating temperature is in a range of 100 ° C to 400 ° C. It is characterized in that it is supplied to the fuel cell or brought into contact with the electrode of the fuel cell.

  According to the above configuration, a reformer and a CO remover are required by using a hydrocarbon compound, which is a hydrogen-containing compound substantially free of oxygen, as a fuel, and by directly supplying fuel to the fuel cell. A simple fuel cell system that does not emit carbon dioxide can be constructed. Further, by setting the operating temperature within the above range, the dehydrogenation reaction of the fuel can be promoted by the heat generation of the fuel cell at 100 ° C. to 400 ° C., and the dehydrogenation reaction easily proceeds. A battery system can be constructed. Further, since the fuel generates power only by the dehydrogenation reaction, CO that becomes an electrode catalyst poison is not generated.

  The direct fuel cell system according to claim 2, wherein the hydrocarbon compound is at least one selected from an aliphatic hydrocarbon having a molecular weight of 40 or more and an alicyclic hydrocarbon having a molecular weight of 40 or more in order to solve the above-mentioned problem. It is characterized by being a compound of

  In the direct fuel cell system according to claim 3, in order to solve the above-mentioned problem, the hydrocarbon compound is composed of methylcyclohexane, dimethylcyclohexane, 1,3,5-trimethylcyclohexane, decalin, methyldecalin, and tetradecahydroanthracene. It is at least one compound selected from the group.

  According to said structure, since the molecular weight of a fuel is larger than methanol, the problem of the crossover which arises in the fuel cell system using DMFC can be avoided.

  The direct type fuel cell system according to claim 4 is characterized in that phosphoric acid is used as an electrolyte in order to solve the above-mentioned problems.

  According to said structure, the fuel cell system which operate | moves at 100 to 400 degreeC can be provided by making phosphoric acid into electrolyte.

  In order to solve the above problems, the direct fuel cell system according to claim 5 has one or two kinds of solid organic electrolyte membrane, solid inorganic electrolyte membrane, and organic-inorganic hybrid electrolyte membrane each having a heat resistance of 100 ° C. or higher. It is characterized by using it as an electrolyte.

According to said structure, the fuel cell which operate | moves at 100 to 400 degreeC by using as an electrolyte any one of the solid organic electrolyte membrane which has heat resistance of 100 degreeC or more, an inorganic solid electrolyte membrane, and an organic inorganic hybrid electrolyte membrane. It becomes possible to provide.

  The hydrocarbon compound used in the direct fuel cell system of the present invention refers to a hydrocarbon, that is, a compound consisting only of carbon and hydrogen, in other words, a hydrogen-containing compound substantially free of oxygen, and is a chain carbonization. Hydrogen (aliphatic hydrocarbon) and cyclic hydrocarbon (alicyclic hydrocarbon) are included.

  The hydrocarbon compound of the present invention is more preferably an aliphatic hydrocarbon having a molecular weight of 40 or more or an alicyclic hydrocarbon compound having a molecular weight of 40 or more. In any case, the molecular weight is more preferably 80 or more. These may use only 1 type and may mix and use 2 or more types. Specific examples of the hydrocarbon compound of the present invention include monocyclic hydrocarbons such as cyclohexane, methylcyclohexane, dimethylcyclohexane and 1,3,5-trimethylcyclohexane; bicyclic carbonization such as decalin and methyldecalin. And hydrogen; tricyclic hydrocarbons such as tetradecahydroanthracene; and the like. The hydrocarbon compounds exemplified above may be used alone or in combination of two or more.

  Examples of the electrolyte used in the fuel cell according to the present invention include solid organic electrolytes, inorganic solid electrolytes, and organic-inorganic hybrid electrolytes each having heat resistance of 100 ° C. or higher.

Examples of the solid organic electrolyte include aromatic proton electrolytes such as aromatic polyethers and polysulfides into which sulfonic acid groups or phosphonic acid groups are introduced. Examples of the solid inorganic electrolyte include proton conductive glass such as HZr ₂ (PO ₄ ) ₃ -glass composite, CsHSO ₄ -glass composite, and Pronton conductive ceramics. Examples of the organic-inorganic hybrid electrolyte include a porous ceramic material such as a zeolite-polytetrafluoroethylene composite material, a silica-ion exchange gel polymer composite material, and zeolite, and an inorganic acid, an organic acid, a proton conductive polymer material, or one of them. Examples include materials that contain more than one type. More preferably, the electrolyte is in the form of a membrane, plate, sandwich, or the like.

  The operating temperature of the fuel cell according to the present invention is not particularly limited, but is more preferably within a range of 100 ° C to 400 ° C. By setting the operating temperature within the above range, the dehydrogenation reaction of the fuel can be promoted by the heat generation of the fuel cell at 100 ° C. to 400 ° C., and the dehydrogenation reaction easily proceeds. A battery system can be constructed. In the case of the present invention, since the fuel generates power only by the dehydrogenation reaction, CO that becomes an electrocatalytic poison is not generated.

  In the fuel cell according to the present invention, it is more preferable to use phosphoric acid as an electrolyte in order to set the operating temperature within the range of 100 ° C. to 400 ° C.

  In order to preheat the fuel cell to 100 ° C. to 400 ° C., a combustor is installed in the fuel cell system and the fuel for the combustor is combusted or the fuel for the fuel cell is partially combusted and the combustion heat is used. The method to be used is used. In addition, the method of using the waste heat at the time of a power generation operation, the method of using the heating mechanism by the condensing device of sunlight, etc. are mentioned.

  As described above, according to the present invention, a hydrocarbon compound, which is a hydrogen-containing compound that does not substantially contain oxygen, such as methylcyclohexane, decalin, and methyldecalin, is used as the fuel, and the fuel is preheated to 100 ° C to 400 ° C. By supplying directly to the fuel cell, it is possible to perform a power generation operation of a simple and energy efficient fuel cell system that does not require a fuel reformer and a CO remover in an operating temperature range of 100 ° C. to 400 ° C. In addition, the problem of catalyst poisoning and crossover in the fuel cell system using DMFC is avoided, and the power generation efficiency is improved. In addition, there is an effect of improving environmental resistance without discharging carbon dioxide.

Embodiment 1
An embodiment of the present invention will be described below with reference to the drawings.

  FIG. 1 is an explanatory diagram showing a schematic configuration of a direct fuel cell system according to the present embodiment. In the fuel cell 1, the electrolyte 1a is filled with phosphoric acid as an electrolytic solution. In addition, carbon materials are used for the electrode substrates of the fuel electrode and the air electrode, and platinum, platinum--on the substrate formed using polytetrafluoroethylene (hereinafter referred to as PTFE) or phenolic resin as the binder. It consists of a carbon substrate holding a catalyst in which ruthenium, nickel, or platinum-rhodium is supported on carbon powder.

  The fuel storage tank 2 is for storing decalin as fuel, from which fuel is directly supplied to the fuel electrode of the fuel cell 1. Since dehydrogenated fuel is generated at the fuel electrode, it is recovered by the dehydrogenated fuel recovery tank 3. On the other hand, air is supplied from the air supplier 4 to the air electrode of the fuel cell 1.

  Next, the operation during the power generation operation of the first embodiment will be described. The fuel cell 1 needs to be preheated before supplying the fuel. Decalin is directly supplied from the fuel storage tank 2 to the fuel electrode of the fuel cell 1 preheated to 170 ° C. to 220 ° C. The heat of the fuel cell 1 preheated to 170 ° C. to 220 ° C. causes a desorption reaction of hydrogen stored in the form of a compound in the fuel at the fuel electrode. Hydrogen generated at the fuel electrode reacts with oxygen in the air supplied from the air supplier 4 to the air electrode to perform a power generation operation. At this time, heat is also generated at the same time. Due to the heat generated in the fuel cell 1 and appropriate heat retention, the fuel cell 1 continues the power generation operation while maintaining a temperature of 170 ° C. to 220 ° C. Although dehydrogenated fuel is generated at the fuel electrode by the power generation operation, it is recovered by the dehydrogenated fuel recovery tank 3, and water and waste air generated at the air electrode are discharged.

In Embodiment 1, the cell reaction when decalin is used as the fuel is shown in (Formula 1). The reaction between decalin and oxygen produces naphthalene, which is water and dehydrogenated fuel. The electromotive force of the fuel cell system of Embodiment 1 was 1.11V.
C ₁₀ H ₁₈ + 5 / 2O ₂ → 5H ₂ O + C ₁₀ H ₈ (Formula 1)
<< Embodiment 2 >>
Next, the second embodiment will be described. The configuration of the fuel cell system is the fuel cell system shown in FIG. However, in the fuel cell 1, the electrolyte 1a is filled with a film made of a mixture of CsHSO ₄ microcrystals and polytetrafluoroethylene as an organic-inorganic hybrid electrolyte having a heat resistance of 100 ° C. or higher, and an electrode substrate for a fuel electrode and an air electrode Consists of a carbon substrate holding a catalyst in which platinum, platinum-ruthenium, and platinum-rhodium are supported on carbon powder. At this time, the fuel cell is the same as the first embodiment in the components other than the electrolyte: the fuel storage tank, the dehydrogenated fuel recovery tank, the air supplier, and the fuel: decalin. In the power generation operation, the fuel cell 1 is preheated to 190 ° C., and the fuel is directly supplied to the fuel electrode from the fuel storage tank 2. Power generation is performed by reaction with oxygen in the air. The dehydrogenated fuel generated at the fuel electrode is recovered by the dehydrogenated fuel recovery tank 3, and the water and waste air generated at the air electrode are discharged.

  The present invention is particularly useful as a direct fuel cell system used in, for example, industrial waste heat recovery or household cogeneration power generation systems.

It is explanatory drawing which shows schematic structure of the fuel cell system in Embodiment 1 and Embodiment 2 of this invention. It is explanatory drawing which shows schematic structure of the fuel cell system provided with the conventional reformer and CO removal device. It is explanatory drawing which shows schematic structure of the conventional fuel cell system which supplies methanol directly.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 1a Electrolyte 2 Fuel storage tank 3 Dehydrogenation fuel recovery tank 4 Air supply device

Claims (5)

A hydrocarbon compound is used as a fuel, and an operating temperature is in a range of 100 ° C. to 400 ° C., and the fuel is supplied directly to a fuel cell or brought into contact with an electrode of the fuel cell. Direct fuel cell system. 2. The direct fuel cell system according to claim 1, wherein the hydrocarbon compound is at least one compound selected from an aliphatic hydrocarbon having a molecular weight of 40 or more and an alicyclic hydrocarbon having a molecular weight of 40 or more. The hydrocarbon compound is at least one compound selected from the group consisting of methylcyclohexane, dimethylcyclohexane, 1,3,5-trimethylcyclohexane, decalin, methyldecalin, and tetradecahydroanthracene. Or the direct type fuel cell system of 2. The direct fuel cell system according to any one of claims 1 to 3, wherein phosphoric acid is used as an electrolyte. Either one of the solid organic electrolyte membrane, the solid inorganic electrolyte membrane, and the organic-inorganic hybrid electrolyte membrane, each having a heat resistance of 100 ° C. or higher, is used as an electrolyte. 2. The direct fuel cell system according to item 1.

Images