GEL-LIKE FUEL FOR FUEL CELL
According to one embodiment, a gel-like fuel for a fuel cell includes a network macromolecular compound formed by cross-linking a macromolecular compound having at least one group selected from an OH group and a COOH group, or a C═N bond with a cross-linking agent, a liquid fuel component incorporated into the network macromolecular compound, and a co-catalyst incorporated into the network macromolecular compound.
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This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2008-078989, filed Mar. 25, 2008, the entire contents of which are incorporated herein by reference.
BACKGROUND1. Field
One embodiment of the present invention relates to a gel-like fuel used for fuel cells.
2. Description of the Related Art
Fuel cells using methanol or diethyl ether as the liquid fuel each have the electromotive section which comprises an anode (fuel electrode) to which the above fuel is fed, a cathode (air electrode) to which an oxidizer (oxygen or air) is fed, and a polymer electrolyte membrane interposed between the anode and the cathode. The anode comprises a catalyst layer, which is in contact with the polymer electrolyte membrane, and a diffusion layer such as carbon paper laminated on the catalyst layer.
In the above fuel cell, methanol or diethyl ether to be used as the liquid fuel is volatile and flammable, thus it is necessary to handle these fuels with care.
From the above fact, Jpn. Pat. Appln. KOKAI Publication No. 2007-242367 discloses technologies that improve the handling ability of liquid fuel by using a microcapsule to include the liquid fuel to thereby put the fuel into a solid form.
However, the microcapsules included within the fuel cell reduce the speed of the methanol that needs to reach the catalyst layer of the fuel electrode. As a result, the oxidation reaction necessary for power generation is reduced, causing a reduction in output.
A general architecture that implements the various feature of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention.
Various embodiments according to the invention will be described hereinafter. In general, according to one embodiment of the invention, there is provided a gel-like fuel for a fuel cell comprising: a network macromolecular compound formed by cross-linking a macromolecular compound having at least one group selected from an OH group and a COOH group, or a C═N bond with a cross-linking agent; a liquid fuel component incorporated into the network macromolecular compound; and a co-catalyst incorporated into the network macromolecular compound.
A typical fuel cell comprises an anode (fuel electrode) to which the above gel-like fuel is fed, a cathode (air electrode) to which an oxidizer (oxygen or air) is fed, and a polymer electrolyte membrane interposed between the anode and the cathode. The anode comprises a catalyst layer, which is in contact with the polymer electrolyte membrane, and a diffusion layer such as carbon paper formed on the catalyst layer. The cathode comprises a catalyst layer, which is in contact with the polymer electrolyte membrane, and a diffusion layer such as carbon paper formed on the catalyst layer.
The macromolecular compound is preferably an aliphatic macromolecular compound containing at least one group selected from an OH group and COOH group or a C═N bond. Examples of the aliphatic macromolecular compound having an OH group include a polyvinyl alcohol and polyethylene glycol. Examples of the aliphatic macromolecular compound having a COOH group include a polyacrylic acid. The aliphatic macromolecular compound having an OH group and COOH group is for example, a polyalginic acid. The aliphatic macromolecular compound having a C═N bond is for example, a polyethyleneimine.
The cross-linking agent is preferably, for example, an isocyanate in which a NCO group is bound with a long-chain alkyl group.
Examples of the fuel component include lower alcohols such as methanol and ethanol or ethers such as dimethyl ether.
The co-catalyst has the ability to activate an oxidation reaction when a fuel component in the gel-like fuel reaches the fuel electrode of the fuel cell. Such a co-catalyst is for example, a porphyrin.
The liquid fuel component is preferably incorporated into the network macromolecular compound in an amount of 15 to 99.5% by weight based on the total amount of the network macromolecular compound and the liquid fuel component. A gel-like fuel for a fuel cell in which the liquid fuel component is incorporated into the network macromolecular compound on such an amount can better promote the speed required for the liquid fuel component to reach the catalyst layer of the fuel electrode, when applied to a fuel cell.
The co-catalyst is preferably incorporated into the network macromolecular compound in an amount of 0.001 to 30% by weight based on the total amount of the network macromolecular compound and the co-catalyst.
The gel-like fuel according to the embodiment preferably has a shearing viscosity of 100 to 1500000 dyne·s/cm2. The shearing viscosity of the gel-like fuel primarily is compatible, in the degree of cross-linking, with the network macromolecular compound. When the shearing viscosity is designed to be less than 100 dyne·s/cm2, there is a fear that the network macromolecular compound is deteriorated in the ability to incorporate the liquid fuel component. On the other hand, the shearing viscosity of the gel-like fuel exceeds 1500000 dyne·s/cm2, the network macromolecular compound is deteriorated in the ability to release the liquid fuel component and there is therefore a fear of a decrease in the speed required for the network macromolecular compound to reach the catalyst layer of the fuel electrode, when applied to a fuel cell. The shearing viscosity of the gel-like fuel for a fuel cell is more preferably 1000 to 300000 dyne·s/cm2.
The gel-like fuel for a fuel cell according to the embodiment may be produced, for example, by the following method.
First, a reaction container is charged with the macromolecular compound and a cross-linking agent together with a solvent and the mixture is stirred and mixed under heating to allow the macromolecular compound to undergo a cross-linking reaction. Subsequently, the reaction product is put in the heated state to distill solvents under reduced pressure, thereby obtaining a network macromolecular compound. In the case of, for example, an aliphatic macromolecular compound having an OH group, this OH group reacts with the cross-linking agent to cross-link, thereby producing a network macromolecular compound. Then, the liquid fuel component is gradually added to the network macromolecular compound with stirring, and after all the liquid fuel component is added, the stirring is further continued and stopped when all of the gel is made uniform, to thereby produce a gel-like fuel for a fuel cell. In this case, the co-catalyst may be added either in the raw material stage of preparing a network macromolecular compound or before the liquid fuel component is added after the network macromolecular compound is prepared.
The macromolecular compound and the cross-linking agent are preferably compounded in an amount of 0.3 to 60% by weight and in an amount of 0.01 to 20% by weight respectively. The network macromolecular compound which is cross-linked between macromolecular compound and the cross-linking agent in such a compounding ratio to form a network is well balanced between the ability to incorporate the liquid fuel component and the ability to release the liquid fuel component.
The gel-like fuel for a fuel cell according to the embodiment as mentioned above has the following ability and effect when applied to a fuel cell.
(1) The gel-like fuel for a fuel cell comprises a network macromolecular compound formed by cross-linking a macromolecular compound having at least one group selected from an OH group and a COOH group, or a C═N bond with a cross-linking agent, a liquid fuel component incorporated into the network macromolecular compound, and a co-catalyst incorporated into the network macromolecular compound. Therefore, when the fuel is fed to the catalyst layer of the fuel electrode in the fuel cell, the liquid fuel component is rapidly released from the network macromolecular compound and reaches the catalyst layer. Specifically, the speed required for the liquid fuel component to reach the catalyst layer can be increased. As a result, the oxidation reaction necessary for power generation can sufficiently proceed in the catalyst layer, making it possible to improve the output density of the fuel cell.
(2) The crossover phenomenon, in which an unreacted liquid fuel component retained in the catalyst layer diffuses into the polymer electrolyte membrane to reach the oxidizing electrode, can be reduced. Specifically, a proper amount of the liquid fuel component is released from the network macromolecular compound and reaches the catalyst layer of the fuel electrode, where the oxidation reaction of the fuel can proceed. Therefore, such a phenomenon that an unreacted liquid fuel component is retained in the catalyst layer can be further limited. Also, the co-catalyst is likewise released from the network macromolecular compound and reaches the catalyst layer to activate the liquid fuel component which has already reached there to promote the oxidation reaction. Therefore, such a phenomenon that an unreacted liquid fuel component is retained in the catalyst layer can be even further limited. Since such a phenomenon that an unreacted liquid fuel component is retained in the catalyst layer can be limited, the above crossover phenomenon can be reduced.
(3) Since the retention of an unreacted liquid fuel component can be limited as explained in the above (2), the generation of heat is suppressed, and the efficiency of power generation can be improved.
(4) The damage of devices mounted on the fuel cell which are caused by the leakage of the liquid fuel component can be further reduced than in the case of singly using a liquid fuel.
(5) A reduction in the size of the fuel cell can be attained by the effects of the above (1) to (3).
The present invention will be explained in more detail by way of examples. However, these examples are not intended to be limiting of the present invention.
EXAMPLE 1 Preparation of a Network Macromolecular CompoundA reaction container obtained by equipping a three-neck flask having a circular bottom with a homogenizer (trade name: Homogenizer PH91, manufactured by MST (Corp.), a Liebig condenser and a dropping funnel was soaked in a silicon oil bath.
30 parts by weight of a polyvinyl alcohol (manufactured by Aldrich Corporation, weight average molecular weight: 31000 to 50000) used as a macromolecular compound, 5 parts by weight of methylene diisocyanate (manufactured by Aldrich Corporation) used as a cross-linking agent and 0.5 parts by weight of porphyrin used as a co-catalyst were added in 64.5 parts by weight of 1,2-dichloroethylene (manufactured by Aldrich Corporation), to prepare a solution. This solution was poured into the reaction container and stirred at 550° C. at 3000 rpm by using a homogenizer for 2 hours. The mixture in the reaction container was poured into an eggplant-shape flask and then, a rotary evaporator (trade name: RI-210, manufactured by Shibata Rika Kiki)) was set to the flask to distill 1,2-dichloroethylene which was a solvent component under reduced pressure in the hot-water bath to prepare a porphyrin-dispersed network macromolecular compound. The obtained network macromolecular compound has a number average molecular weight of 100000.
[Production of a Fuel]
10 g of the obtained porphyrin-dispersed network macromolecular compound was poured into a 300 mL beaker and then 90 g of methanol was gradually added with stirring the network macromolecular compound in the beaker by a homogenizer (trade name: Homogenizer PH91, manufactured by MST (Corp.)). After the above methanol was all added, the stirring was continued for 30 minutes to produce a gel-like fuel for a fuel cell which was uniformed as a whole.
EXAMPLES 2 TO 8Gel-like fuels for a fuel cell were produced in the same manner as in Example 1 except that the materials shown in the following Table 1 were used as the macromolecular compound, cross-linking agent, co-catalyst and solvent used to prepare a co-catalyst dispersed network macromolecular compound in each amount shown in Table 1, and the network macromolecular compound and methanol used in the production of the gel-like fuel were formulated in the ratios shown in Table 1. The polyethyleneimine, polyalginic acid and polyacrylic acid, which were the macromolecular compounds, had weight average molecular weights of 2000 to 350000, 3000 to 450000 and 2500 to 200000 respectively.
The shearing viscosity of each of the gel-like fuels obtained in Examples 1 to 8 is described in Table 1 below.
50 mL of a 1 wt % sodium alginate methanol solution was poured into a 100 mL beaker. 10 g of calcium chloride was placed in a 100 mL beaker and distilled water was added in the beaker to make a volume of 100 mL. The sodium alginate methanol solution was gradually added dropwise to this aqueous calcium chloride solution by using a syringe while the solution was stirred by a homogenizer (trade name: Homogenizer PH91, manufactured by MST (Corp.)) at 100 rpm. The produced microparticles were filtered using a 25 mesh gauze and the particles on the gauze were collected as a methanol solid fuel (microcapsule fuel).
[Evaluation of the Fuel Cell]
<Fabrication of a Unit Cell>
A platinum-ruthenium catalyst layer and a diffusion layer of carbon powder-carbon paper were thermally bound to one surface of a polymer electrolyte membrane in this order under pressure to form an anode (fuel electrode). The polymer electrolyte membrane was formed from a perfluoroalkylsulfone membrane (trade name: Nafion 112 film, manufactured by Du Pont.). A platinum-ruthenium catalyst layer and a diffusion layer of carbon powder-carbon paper were thermally bound to the other surface of the perfluoroalkylsulfone membrane in this order under pressure to form a cathode (air electrode). With the formations of the anode and cathode on the polymer electrolyte membrane, a membrane electrode having an electrode area of 5 cm2 was manufactured. Subsequently, a carbon separator provided with a column flow passage and a current collector were laminated in this order on both surfaces of the membrane electrodes, followed by fastening with bolts to fabricate a unit cell for evaluation.
<Evaluation of the Unit Cell>
Each fuel obtained in Examples 1 to 8 and Comparative Example 1 was fed to the anode side of the fabricated unit cell for evaluation at a flow rate of 7 mL/min and air was fed to the cathode side of the unit cell at a flow rate of 14 mL/min to measure the current-voltage characteristic of the unit cell of 50° C. The results are shown in
As is clear from
While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
Claims
1. A gel-like fuel for a fuel cell comprising:
- a network macromolecular compound formed by cross-linking a macromolecular compound comprising at least one group selected from an OH group and a COGH group, or a C=N bond with a cross-linking agent, the cross-linking agent consisting of an isocyanate in which an NCO group is bonded with a long-chain alkyl group;
- methanol incorporated into the network macromolecular compound; and
- a co-catalyst,
- wherein a shearing viscosity of the fuel is 3000 to 290000 dyne·cm2.
2. The gel-like fuel of claim 1, wherein the macromolecular compound is a polyvinyl alcohol.
3. (canceled)
4. The gel-like fuel of claim 1, wherein the macromolecular compound is a polyalginic acid.
5. The gel-like fuel of claim 1, wherein the macromolecular compound is a polyethyleneimine.
6.-11. (canceled)
12. The gel-like fuel of claim 1, wherein the co-catalyst is porphyrin.
13.-15. (canceled)
Type: Application
Filed: Jan 13, 2009
Publication Date: Oct 1, 2009
Applicant: KABUSHIKI KAISHA TOSHIBA (Tokyo)
Inventor: Tomoaki ARIMURA (Hamura-shi)
Application Number: 12/353,094
International Classification: C10L 7/04 (20060101);
