JP5229872B2 - Fuel cell - Google Patents

Description

  The present invention relates to a direct liquid fuel type fuel cell and a fuel cell system which are operated by directly supplying liquid fuel.

  Since the polymer electrolyte fuel cell has excellent features such as being able to obtain a high current density at low temperature operation and being able to be downsized, it is a power source for transportation equipment such as electric vehicles and aerospace equipment, Research and development is underway for portable power supplies.

As the fuel supplied to the polymer electrolyte fuel cell, hydrogen gas produced by reforming natural gas, methanol, gasoline, etc. is often used, but it is convenient as a liquid fuel for storage, transportation, etc. Therefore, a polymer electrolyte fuel cell (direct methanol fuel cell) that directly supplies methanol as fuel has recently attracted attention. In particular, methanol fuel cells are the mainstream for small power supplies and chargers for portable devices. In addition to methanol, ethanol (Non-patent Document 1), glycol (Patent Document 1), and other direct alcohol fuel cells using various alcohols such as fuel, and fuel cells using formic acid as fuel (Patent Document 2) And Patent Literature 3) have been studied. However, these fuels have safety problems and the electromotive force is not necessarily high, and it cannot be said that they have sufficient performance.

On the other hand, research on fuel cells (non-patent documents 3 to 6 and patent documents 4 to 6) using an alkaline aqueous solution of tetrahydroborate such as NaBH ₄ as a fuel has also been conducted, but this fuel has strong alkalinity. Therefore, there are problems such as safety and control of alkali concentration (pH value).

  Therefore, the realization of a fuel cell that can operate with high electromotive force by directly supplying safe and easy-to-handle fuel has become a major issue.

  An aqueous solution of ammonia borane or a derivative thereof is safe and easy to handle. By supplying it to a fuel electrode of a known polymer electrolyte fuel cell using a cation exchange membrane as an electrolyte membrane, a high electromotive force can be obtained. It has been found that a working fuel cell can be obtained (Non-patent Document 7, Patent Document 7).

  In a fuel cell using ammonia borane as fuel, it is considered that the following reaction proceeds at the negative electrode and the positive electrode.

The polymer electrolyte fuel cell of the known structure that utilizes such electrode reaction can not be the mobility of NH ₄ ⁺ ions in the electrolyte membrane to obtain a sufficient performance for low, also, NH ₄ in the positive electrode ⁺ NH ₃ is released from the ions, and this has problems such as adversely affecting the performance of the fuel cell.
C. Lamy, EM Belgsir, and J. -M. Legar, J. Appl. Electrochem., 31, 799 (2001). M. Weber, J.-T.Wang, S. Wasmus, and RF Savinell, J. Electrochem. Soc. 143, L158 (1996). SC Amendola, P. Onnerud, MT Kelly, PJ Petillo, SL Sharp-Goldman, M. Binder, J. Power Source, 84, 130, (1999). BH Liu, ZP Li, S. Suda, J. Electrochem. Soc. 150, A398 (2003). ZP Li, BH Liu, K. Arai, S. Suda, J. Electrochem. Soc. 150, A868 (2003). ZP Li, BH Liu, K. Arai, S. Suda, J. Power Source, 126, 28, (2004). X.-B. Zhang, S. Han, J.-M. Yan, M. Chandra, H. Shioyama, K. Yasuda, N. Kuriyama, T. Kobayashi, Q. Xu, J. Power Sources, 168, 1671 (2007). JP 2002-151132 A Japanese National Patent Publication No. 10-507572 JP 2001-219271 A U.S. Patent 5,804,329 JP 2003-132932 A JP 2004-356084 A JP 2006-286549 A

  The present invention has been made in view of the current state of the prior art described above, and its main purpose is to provide a novel fuel cell that is safe and easy to handle and has excellent performance. is there.

  The present inventor has intensively studied to achieve the above-described object. As a result, in the polymer electrolyte fuel cell, it has been found that the above-described object can be achieved by using an aqueous solution of ammonia borane or a derivative thereof as a fuel and an anion exchange resin membrane as an electrolyte membrane. The invention has been completed.

That is, the present invention provides the following fuel cell and fuel cell system.
1. A polymer electrolyte fuel cell comprising a positive electrode, a negative electrode, and an electrolyte membrane disposed between the positive electrode and the negative electrode,
The electrolyte membrane is an anion exchange membrane;
The negative electrode has a chemical formula: R _n NH _{3 -n} B _m H _{2m + 1} (wherein R is a monovalent hydrocarbon group, n is an integer of 0 to 3, and m is 1 or 3. However, two or three Rs may be bonded to each other to form a nitrogen-containing cyclic structure together with nitrogen atoms.) A direct liquid fuel type in which an aqueous solution of an ammonia borane compound represented by Fuel cell.
2. The above item wherein the ammonia borane compound is at least one compound selected from the group consisting of ammonia borane, dimethylamine borane, diethylamine borane, trimethylamine borane, triethylamine borane, t-butylamine borane, ammonia triborane, morpholine borane and pyridine borane. 2. The fuel cell according to 1.
3. Chemical formula: R _n NH _{3 -n} B _m H _{2m + 1} (wherein R is a monovalent hydrocarbon group, n is an integer of 0 to 3, and m is 1 or 3, provided that 2 or 3 R may be bonded to each other to form a nitrogen-containing cyclic structure together with a nitrogen atom.) An aqueous solution of an ammonia borane compound represented by the following formula: a solid polymer type having an anion exchange membrane as an electrolyte membrane A fuel cell system for supplying to a negative electrode of a fuel cell.
4). Chemical formula: R _n NH _{3 -n} B _m H _{2m + 1} (wherein R is a monovalent hydrocarbon group, n is an integer of 0 to 3, and m is 1 or 3, provided that 2 or 3 R may be bonded to each other to form a nitrogen-containing cyclic structure together with a nitrogen atom.) A solid polymer having an anion exchange membrane as an electrolyte membrane, which is an aqueous solution of an ammonia borane compound represented by Liquid fuel supplied to the negative electrode of a fuel cell.

  A fuel cell according to the present invention is a solid polymer fuel cell including a positive electrode, a negative electrode, and an electrolyte membrane disposed between the positive electrode and the negative electrode, using an anion exchange membrane as the electrolyte membrane, An aqueous solution of an ammonia borane compound is used.

  In the fuel cell having such a structure, the amine borane compound used as the fuel is safe and easy to handle, and can generate a high electromotive force by the negative electrode reaction, and has excellent performance as a liquid fuel. It is.

Furthermore, in the fuel cell of the present invention, it is necessary to use an anion exchange membrane as an electrolyte membrane in addition to using an aqueous solution of an amine borane compound as a fuel. As described above, by supplying oxygen or hydrogen to the positive electrode of the fuel cell, OH 2 ⁻ ions are generated by the positive electrode reaction. However, in the fuel cell of the present invention, by using an anion exchange membrane as the electrolyte membrane, The generated OH ^- ions can be used as conductive ions in the electrolyte membrane. In conventional fuel cells using cation exchange membranes as electrolyte membranes, NH ₄ ⁺ ions with low mobility become conductive ions, so it was difficult to produce high-performance fuel cells using amine borane compounds as fuel. According to the fuel cell, by using an anion exchange membrane as an electrolyte membrane, OH ^- ions with high mobility become conductive ions, and a high-performance fuel cell with high current and high voltage can be obtained. In addition, by using an anion exchange membrane, NH ₄ ⁺ ions do not move to the positive electrode, and the problem of NH ₃ emission at the positive electrode can be avoided.

Hereinafter, the fuel cell of the present invention will be described in detail.
(1) Fuel The fuel cell of the present invention has a chemical formula: R _n NH _{3 -n} B _m H _{2m + 1} (wherein R is a monovalent hydrocarbon group, n is an integer of 0 to 3, and m is 1 or 3. However, an aqueous solution of an ammonia borane compound represented by (2 or 3 R may be bonded to each other to form a nitrogen-containing cyclic structure together with a nitrogen atom) is used as a fuel. Is.

  In the above chemical formula, examples of the monovalent hydrocarbon group include a lower alkyl group. Specific examples of such a lower alkyl group include linear groups having about 1 to 5 carbon atoms such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, t-butyl group, and pentyl group. Or a branched alkyl group can be mentioned. In the above chemical formula, when two or more Rs are contained, all the Rs may be the same, or some or all of them may be different from each other.

  When two or three Rs are bonded to each other to form a nitrogen-containing cyclic structure together with a nitrogen atom, the formed cyclic structure may be either saturated or unsaturated, and other nitrogen atoms, An oxygen atom, a sulfur atom, etc. may be contained.

  The ammonia borane compound represented by the above chemical formula is a known compound, and can be transported and stored in a solid state in a lightweight and safe manner, and can be easily dissolved in water before being supplied to the fuel cell. Liquid fuel. In addition, the ammonia borane compound is soluble in water, but exists relatively stably without being easily reacted with water even when dissolved in water, and its handling is easy and safe. It has the convenience of.

Among the ammonia borane compounds represented by the above chemical formula, specific examples of the compound in which m is 1 include ammonia borane represented by NH ₃ BH ₃ and dimethylamine borane represented by (CH ₃ ) ₂ NHBH _3. , Diethylamineborane represented by (CH ₃ CH ₂ ) ₂ NHBH ₃ ,
Trimethylamine borane represented by (CH ₃ ) ₃ NBH ₃ , (CH ₃ CH ₂ ) ₃ NBH ₃
And t-butylamine borane represented by (CH ₃ ) ₃ CNH ₂ BH ₃ . A specific example of the compound in which m is 3 is ammonia triborane represented by NH ₃ B ₃ H ₇ .

  Moreover, as a specific example of the compound containing a nitrogen-containing cyclic structure,

Morpholine borane represented by

And pyridine borane represented by the formula:

  In the present invention, the ammonia borane compounds represented by the above chemical formulas can be used singly or in combination of two or more.

In the fuel cell of the present invention, the above-described ammonia borane compound is used as a fuel in the form of an aqueous solution. The concentration of the ammonia borane compound in the aqueous solution is not particularly limited, but can be, for example, a concentration range of about 10 ⁻⁴ mol / L to 8 mol / L, and about 10 ⁻³ mol / L to 2 mol / L. It is preferable to set the concentration range. In such a concentration range, a specific concentration may be determined according to the required electromotive force. This aqueous solution only needs to contain an ammonia borane compound which is an active ingredient, and may contain other ingredients at the same time as long as there is no adverse effect as fuel for the fuel cell.
(2) Electrolyte membrane In the fuel cell of the present invention, it is necessary to use an anion exchange membrane as the electrolyte membrane. By using an anion exchange membrane as the electrolyte membrane, the OH ^- ions generated by the negative electrode reaction described above become conductive ions, and a fuel cell with high performance at high current and high voltage can be obtained.

  The anion exchange membrane is not particularly limited, and various polymer compounds capable of conducting anions can be used. For example, various polymer compounds having an anion exchange group such as a quaternary ammonium group and a pyridinium group can be used. Such a polymer compound having an anion exchange group operates at a low temperature, and the apparatus can be miniaturized. The type of the resin skeleton in the anion exchange membrane is not particularly limited. For example, resins of various materials such as a fluorine resin and a hydrocarbon resin can be used.

The thickness of the anion exchange membrane may be usually determined in consideration of the strength of the membrane, electrical resistance, and the like. From the viewpoint of the film strength, the thickness is usually preferably about 5 μm or more, and more preferably about 10 μm or more in view of ease of handling at the time of manufacturing the fuel cell. Further, since the internal resistance of the battery increases as the film thickness increases, the film thickness is preferably about 200 μm or less.
(3) Structure of fuel cell The structure of the fuel cell of the present invention may be the same as that of a known solid polymer fuel cell except that an anion exchange membrane is used as the electrolyte membrane.

  That is, an anion exchange membrane is used as the electrolyte membrane, and the electrode catalyst, membrane-electrode assembly, cell structure, and the like may be the same as those of known solid polymer fuel cells.

  Each electrode of the negative electrode (fuel electrode) and the positive electrode (oxygen electrode) may have a structure that can supply reactants and discharge products, and further increase the electrode surface area in order to improve performance. It is preferable. Moreover, in order to promote oxidation-reduction, it is preferable to carry | support a catalyst in an electrode.

  For example, in order to secure the path to each reaction interface and increase the surface area of the electrode (and catalyst) for electrons, ions, liquid fuel and gas supplied from the outside, etc., mesh metal, carbon paper, An electrode having a structure in which a porous (network structure or structure having pores) electron conductive material such as a carbon cloth is used as a support, and a layer containing an electrolyte is formed on or bonded to the support. When the electrode includes a catalyst, the catalyst may be directly supported on the support made of the porous electron conductive material or may be supported on another electron conductive material and bonded to the support. As the catalyst metal, conventionally known various metals, metal alloys and the like can be used. Specific examples include various metal catalysts including platinum, palladium, iridium, rhodium, ruthenium, and platinum-ruthenium.

  The joined body of the anion exchange membrane and the electrode can be produced by a known method. For example, after thinning the catalyst ink prepared by mixing catalyst powder and electrolyte solution, hot pressing on the anion exchange membrane, or applying and drying on the anion exchange membrane, etc. are applied Is done. In addition, the catalyst can be directly attached to the anion exchange membrane by an adsorption reduction method, an electroless plating method, sputtering, CVD, or the like. Alternatively, the electrode may be produced by a method in which a catalyst ink is directly applied to a gas diffusion layer or a current collector and dried, or a method in which a metal complex as a precursor is impregnated or reduced.

  A fuel battery cell can be produced by sandwiching both surfaces of the obtained membrane-electrode assembly between current collectors such as carbon paper and carbon cloth and incorporating them into the cell.

  In the fuel cell of the present invention, the above-described aqueous solution of ammonia borane compound may be supplied as fuel to the negative electrode, and air or oxygen may be supplied or naturally diffused to the positive electrode side.

  The operating temperature of the fuel cell of the present invention varies depending on the electrolyte membrane to be used, but is usually about 0 ° C to 100 ° C, preferably about 10 ° C to 80 ° C.

  As described above, the ammonia borane compound used as a fuel in the fuel cell of the present invention can be transported and stored in a solid state in a lightweight and safe manner and can be dissolved in water before being supplied to the fuel cell. It can be a liquid fuel for batteries.

Further, in the fuel cell of the present invention, by using an anion exchange membrane as an electrolyte membrane, OH
^- ions can be a conducting ions, ion conductivity in the solid electrolyte is accelerated,
Moreover, the problem of NH ₃ emission at the positive electrode can be avoided.

  Therefore, the fuel cell of the present invention is a fuel cell that is highly safe and very convenient, and is a high-performance fuel cell that operates with high electromotive force.

  The present invention will be described more specifically with reference to the following examples.

Example 1
Platinum as an anode catalyst is added to a solution in which an anion exchange polymer electrolyte containing a quaternary ammonium group at the end of the side chain consisting of a hydrocarbon polymer in a mixed solvent of tetrahydrofuran and 1-propanol. In addition, mixing was performed to obtain a catalyst ink for a negative electrode. The catalyst ink was thinned to produce an electrode sheet for the negative electrode.

  As the electrolyte membrane, an anion exchange type polymer electrolyte membrane having a main chain made of a hydrocarbon polymer and having a quaternary ammonium group at the end of the side chain (film thickness 28 μm, ion exchange capacity 1.8 meq / g) is used. The electrode sheet obtained by the above method was hot pressed on one side of the polymer electrolyte membrane to obtain a membrane-electrode assembly.

  In addition, platinum as a positive electrode catalyst was added to a solution in which an anionic polymer electrolyte containing a quaternary ammonium group at the end of the side chain consisting of a hydrocarbon polymer in a mixed solvent consisting of tetrahydrofuran and 1-propanol. Were added and mixed to obtain a catalyst ink for positive electrode. The catalyst ink was thinned to produce a positive electrode sheet, and then hot-pressed on the other surface of the polymer electrolyte membrane to obtain a membrane-electrode assembly. A fuel cell was assembled by sandwiching both surfaces of the membrane-electrode assembly with carbon cloth.

A 0.1 mol / L ammonia borane (NH ₃ BH ₃ ) aqueous solution was supplied to the negative electrode of the fuel cell obtained by the above method, oxygen was supplied to the positive electrode, and the power generation performance of the fuel cell was evaluated at room temperature. The current-voltage characteristic is shown as a curve (c) in FIG.

Example 2
On the negative electrode side of the fuel cell produced in Example 1, 0.5 mol / L ammonia borane (NH ₃ BH ₃
) An aqueous solution was supplied, oxygen was supplied to the positive electrode, and the power generation performance of the fuel cell was evaluated at room temperature. The current-voltage characteristic is shown as a curve (d) in FIG.

Comparative Example 1
Platinum is used as the negative electrode catalyst, mixed with a cation polymer electrolyte solution (“Nafion solution”, manufactured by Aldrich) to form a catalyst ink, which is made into a thin film to produce an electrode sheet. A membrane-electrode assembly was obtained by hot pressing one side of a molecular electrolyte membrane (“Nafion-117”, manufactured by DuPont). Using platinum as the positive electrode catalyst, mixed with a solution of a cation type polymer electrolyte to form a catalyst ink, and after making the electrode sheet thin, hot press on the other surface of the polymer electrolyte membrane, A membrane-electrode assembly was obtained. A fuel cell was assembled by sandwiching both surfaces of the membrane-electrode assembly with carbon cloth.

A 0.1 mol / L aqueous solution of ammonia borane (NH ₃ BH ₃ ) was supplied to the negative electrode of the fuel cell obtained by the above method, oxygen was supplied to the positive electrode, and the power generation performance of the fuel cell was evaluated at room temperature. The current-voltage characteristics are shown as curve (a) in FIG.

Comparative Example 2
A 0.5 mol / L aqueous solution of ammonia borane (NH ₃ BH ₃ ) was supplied to the negative electrode side of the fuel cell produced in Comparative Example 1, oxygen was supplied to the positive electrode, and the power generation performance of the fuel cell was evaluated at room temperature. The current-voltage characteristic is shown as a curve (b) in FIG.

As is clear from the current-voltage curve shown in FIG. 1, when an aqueous solution of ammonia borane NH ₃ BH ₃ is directly supplied to a fuel cell using an anion exchange membrane as an electrolyte membrane (curves (c) and (d) ) Shows that the fuel cell using the cation exchange membrane as the electrolyte membrane exhibits higher performance than when the aqueous ammonia borane solution is supplied (curves (a) and (b)).

The graph which shows the current-voltage characteristic of each polymer electrolyte fuel cell obtained in Examples 1-2 and Comparative Examples 1-2.

Claims (4)

A polymer electrolyte fuel cell comprising a positive electrode, a negative electrode, and an electrolyte membrane disposed between the positive electrode and the negative electrode,
The electrolyte membrane is an anion exchange membrane;
The negative electrode has a chemical formula: R _n NH _{3 -n} B _m H _{2m + 1} (wherein R is a monovalent hydrocarbon group, n is an integer of 0 to 3, and m is 1 or 3. However, two or three Rs may be bonded to each other to form a nitrogen-containing cyclic structure together with nitrogen atoms.) A direct liquid fuel type in which an aqueous solution of an ammonia borane compound represented by Fuel cell.   The ammonia borane compound is at least one compound selected from the group consisting of ammonia borane, dimethylamine borane, diethylamine borane, trimethylamine borane, triethylamine borane, t-butylamine borane, ammonia triborane, morpholine borane and pyridine borane. 2. The fuel cell according to 1. Chemical formula: R _n NH _{3 -n} B _m H _{2m + 1} (wherein R is a monovalent hydrocarbon group, n is an integer of 0 to 3, and m is 1 or 3, provided that 2 or 3 R may be bonded to each other to form a nitrogen-containing cyclic structure together with a nitrogen atom.) An aqueous solution of an ammonia borane compound represented by the following formula: a solid polymer type having an anion exchange membrane as an electrolyte membrane A fuel cell system for supplying to a negative electrode of a fuel cell. Chemical formula: R _n NH _{3 -n} B _m H _{2m + 1} (wherein R is a monovalent hydrocarbon group, n is an integer of 0 to 3, and m is 1 or 3, provided that 2 or 3 R may be bonded to each other to form a nitrogen-containing cyclic structure together with a nitrogen atom.) A solid polymer having an anion exchange membrane as an electrolyte membrane, which is an aqueous solution of an ammonia borane compound represented by Liquid fuel supplied to the negative electrode of a fuel cell.

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