JP2005011691A - Direct liquid type fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct liquid type fuel cell system capable of easily and efficiently removing impurities like salt content or metal ion infiltrated into the system. <P>SOLUTION: The direct liquid type fuel cell system is enabled to remove the impurities like salt content or metal ion infiltrated into the direct liquid type fuel cell system through an air filter 6 by an impurity removing device 3 mounted on a circulation part 9, and prevented from the lowering of battery characteristics. By the above, reliability of the direct liquid type fuel cell system is improved and a life thereof is prolonged. It is economical because an ion exchanging body or the like used for the impurity removing device 3 can be easily exchanged. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a direct liquid fuel cell system including a battery unit that generates water by supplying water and proton-producing liquid fuel.
[0002]
[Prior art]
In recent years, countermeasures against environmental problems and resource problems have become important, and development of direct liquid fuel cell systems has been actively conducted as one of the countermeasures.
The direct liquid fuel cell system includes a fuel electrode, an air electrode, and a proton conductive polymer solid electrolyte membrane disposed therebetween in a battery unit, and water and a proton-generating liquid fuel are supplied to the fuel electrode. Electric power is generated by supplying an oxidant gas to the electrode. Moreover, the structure which reuses the water produced | generated by the air electrode by the series of reaction of a fuel electrode and an air electrode as the water supplied to a fuel electrode is provided.
[0003]
By the way, in such a direct liquid fuel cell system, when impurities such as metal ions are contained in the oxidant gas, impurities may be mixed in the water generated at the air electrode. Since this water is reused, water mixed with impurities reaches the proton conductive polymer solid electrolyte membrane. As a result, there is a problem in that the proton conductivity of the catalyst layer of the electrolyte membrane, the fuel electrode, and the air electrode is lowered and the battery characteristics are lowered. This deterioration in battery characteristics becomes very large when air taken from the outside is used as the oxidant gas.
[0004]
The direct methanol fuel cell system is particularly promising as a compact power source that can be easily refueled, and is used as an auxiliary power source for ships and power sources that operate near the sea such as buoys. Since the air in the above contains a large amount of metal ions and the like, the deterioration of the battery characteristics is more remarkable.
[0005]
[Problems to be solved by the invention]
This decrease in battery characteristics will be described using a direct methanol fuel cell system as an example.
In the direct methanol fuel cell system, when a methanol aqueous solution having a concentration of about 3% is supplied to the fuel electrode and oxygen is supplied to the air electrode, electric power is generated by a series of cell reactions. The water generated at the air electrode by a series of battery reactions is circulated and used for adjusting the concentration of the aqueous methanol solution that supplies the fuel electrode.
[0006]
Therefore, if the direct methanol fuel cell system is used in the air at or near the sea, alkali and alkaline earth metal ions such as sodium ions, potassium ions, magnesium ions, calcium ions and iron ions contained in the air In addition, transition metal ions such as nickel ions directly enter the air electrode of the methanol fuel cell. Most of these impurities flow out of the battery due to water generated at the air electrode, but since the generated water is circulated and used, salt and metal ions are mixed in the methanol aqueous solution. When the aqueous methanol solution containing this impurity is supplied, the metal ions are adsorbed to a part of the proton conductive polymer solid electrolyte membrane used directly for the electrolyte of the methanol fuel cell. As a result, the proton conductivity of the catalyst layer of the electrolyte membrane, the fuel electrode, and the air electrode is lowered, so that the battery characteristics are lowered.
[0007]
As a means for removing impurities such as fine dust and salt contained in the air supplied to the air electrode of the fuel cell, there is a method of providing a wet filter at the air intake (see Patent Document 1). However, in this method, once impurities are mixed in water, it can no longer be removed, and deterioration of battery characteristics cannot be avoided.
[0008]
[Patent Document 1]
JP 2001-185193 A (page 2-5).
[0009]
In view of the above problems, an object of the present invention is to easily and efficiently remove impurities once mixed in water to prevent deterioration of battery characteristics and prolong battery life.
[0010]
[Means for Solving the Problems]
As a means for solving this problem, the present invention includes a fuel electrode to which water and a proton-generating liquid fuel are supplied, an air electrode to which an oxidant gas arranged to face the fuel electrode is supplied, A proton conductive polymer solid electrolyte membrane disposed between the fuel electrode and the air electrode, and reacting water and a proton-generating liquid fuel at the fuel electrode to generate electrons and protons; A battery unit that generates electric power by a series of reactions in which the proton and the oxidant gas are reacted at the air electrode to generate water, and water generated at the air electrode of the battery unit is circulated to the fuel electrode. In the direct liquid fuel cell system including a circulation unit, the system includes means for removing impurities from at least one of water supplied to the cell unit and proton-generating liquid fuel or oxidant gas. Special It provides a direct liquid fuel cell system according to.
The impurity is a metal ion present in water generated in the air electrode, and the impurity removing device is provided with a circulation unit having means for removing the impurity. This impurity removal device may be an ion exchanger or an adsorbent or a combination thereof.
The impurities are fine particles mixed in the oxidant gas, and the means for removing the impurities is an air filter provided in the supply path of the oxidant gas. The air filter may be an ion exchanger or adsorbent or microporous membrane filter or air shower or a combination thereof.
[0011]
When impurities such as metal ions are mixed in the oxidant gas supplied to the air electrode, the generated water to be circulated contains impurities. However, according to the present invention, the impurities can be removed by the impurity removing device provided in the circulation section or the air filter provided in the supply path for the oxidant gas, so that the impurities are proton conductive polymer solid electrolyte membrane or fuel. It can suppress reaching the catalyst layer of the electrode and the air electrode.
Therefore, it is possible to prevent the battery characteristics from deteriorating and prolong the battery life.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
As shown in FIG. 1, the direct liquid fuel cell system of the present invention includes a fuel electrode to which water and a proton-generating liquid fuel are supplied, an air electrode to which an oxidant gas is supplied, the air electrode and the fuel electrode. A battery unit 4 having a proton conductive polymer solid electrolyte membrane disposed between the fuel electrode and the fuel electrode so that the water generated in the air electrode is reused as water to be supplied to the fuel electrode. And a circulation part 9 for circulation.
[0013]
The fuel electrode and the air electrode have a plate shape and are arranged to face each other.
[0014]
The proton conductive polymer solid electrolyte membrane is formed in a thin film, and as a polymer constituting the proton conductive polymer solid electrolyte membrane, a side chain having a sulfonic acid group attached to the end of a Teflon skeleton, A perfluorosulfonic acid polymer (Nafion) having a hanging structure is used.
[0015]
In the fuel electrode, a catalyst layer that promotes a reaction between water and a proton-generating fuel is disposed on the surface of the proton conductive polymer solid electrolyte membrane, and water and a proton-generating liquid fuel are diffused on the surface of the catalyst layer. It is comprised by the laminated structure in which the diffusion layer for making it contact with a catalyst layer was provided.
The catalyst layer generally includes a catalyst in which fine powder of platinum or ruthenium alloy is supported on carbon powder, and PTFE (polytetrafluoroethylene) powder for imparting water repellency to the catalyst layer to facilitate gas diffusion. And a proton conductive resin for forming an ion conductive path in the catalyst layer.
A porous carbon material such as a porous carbon sintered body is used for the diffusion layer.
The proton-generating liquid fuel supplied to the fuel electrode means an organic fuel that reacts with water in the presence of a catalyst to release electrons and protons. Examples of the proton-generating liquid fuel include usually methanol and ethanol. Alcohols and hydrazines are used.
In this embodiment, the proton-producing liquid fuel and water are mixed and supplied in the form of an aqueous solution.
[0016]
In the air electrode, a catalyst layer for promoting a reaction between oxygen, electrons and protons is disposed on the surface of the proton conductive polymer solid electrolyte membrane side, and oxygen molecules are diffused on the surface of the catalyst layer to contact the catalyst layer. It is comprised by the laminated structure in which the diffused layer to be provided was provided.
The catalyst layer generally includes a catalyst supporting platinum fine powder, PTFE (polytetrafluoroethylene) powder for imparting water repellency to the catalyst layer and facilitating gas diffusion, and an ion conduction path in the catalyst layer. The proton conductive resin for forming is contained. As the diffusion layer, a porous carbon material such as a porous carbon sintered body is used.
As the oxidant gas, air introduced from the outside is usually used.
[0017]
In the direct liquid fuel cell system of the present embodiment, the proton-generating liquid fuel reacts with water at the fuel electrode to generate protons and electrons, and the generated protons move through the proton-conductive polymer solid electrolyte membrane and air. By a series of battery reactions in which water is generated by combining oxygen and electrons at the pole, current is extracted to an external circuit.
[0018]
The circulation unit 9 includes a fuel tank 1 that stores an aqueous solution of proton-generating liquid fuel to be supplied to the battery unit 4, a return system 10 that returns water generated in the battery unit 4 to the fuel tank 1, and It comprises a supply system 11 for supplying an aqueous solution of proton-producing liquid fuel from the fuel tank 1 to the battery unit 4.
The fuel tank 1 is connected to a high-concentration fuel tank 7 for supplying a high-concentration proton-producing liquid fuel when the concentration of the proton-producing liquid fuel in the fuel tank 1 is lowered.
[0019]
In the direct liquid fuel cell system of this embodiment, the return system 10 includes a gas-liquid separator 5, and the supply system 11 includes a fuel supply pump 2 and an impurity removal device 3.
[0020]
The gas-liquid separation device 5 converts water and unreacted air generated on the air electrode side of the battery unit 4, gas generated on the fuel electrode side and an aqueous solution of unreacted proton-generated liquid fuel into gas and liquid. To separate.
The fuel supply pump 2 supplies an aqueous solution of proton-generating liquid fuel from the fuel tank 1 to the fuel electrode of the battery unit 4.
The impurity removing device 3 passes an aqueous solution of proton-generating liquid fuel and removes impurities such as metal ions contained in the aqueous solution of proton-generating liquid fuel. In the system of the present embodiment, the impurity removal device 3 is provided in the supply system 11, but at least one or more of the circulation units 9 can be provided.
[0021]
The impurity removing device 3 includes an ion exchanger or an adsorbent, and is configured to remove impurities through an aqueous solution of proton-generating liquid fuel through the ion exchanger or adsorbent. As the ion exchanger, ion exchange resins, ion exchange membranes, zeolites and the like can be used. As the ion exchange resin, a mixture of a cation exchange resin and an anion exchange resin can be used. As the mixture of the cation exchange resin and the anion exchange resin, a one-to-one mixture or a mixture whose ratio is adjusted depending on the place of use can be used.
As the adsorbent, activated carbon, silica gel or the like can be used.
The impurity removing device 3 may include both an ion exchanger and an adsorbent. The ion exchanger and adsorbent may be in various shapes such as granular, porous, cloth or felt, but in order to reduce pressure loss, it is preferable to use a porous, cloth or felt shape. .
[0022]
In the system of the present embodiment, an air blower 8 forcibly taking in external air and an air filter 6 for removing fine particles such as fine dust contained in the taken-in air are provided on the air electrode side of the battery unit 4. I have.
The air filter 6 is preferably provided with the above-described ion exchanger, adsorbent, or a combination thereof, but removes fine particles, particularly components such as salt that become metal ions by the reaction in the battery unit 4. For this purpose, it is preferable to provide a microporous membrane filter, an electrostatic filter, an air shower, or a combination thereof. Thereby, components such as salt that become metal ions by the reaction in the battery unit 4 can be removed before being taken into the battery unit 4.
[0023]
The movement of the direct liquid fuel cell system of this embodiment will be described using methanol as the proton-generating liquid fuel.
In the direct methanol fuel cell system of the present embodiment, external air is supplied to the air electrode by the air blower 8 through the air filter 6, and an aqueous methanol solution is supplied to the fuel electrode, and power is generated by a cell reaction.
Water and unreacted air generated on the air electrode side in this battery reaction, and carbon dioxide gas and unreacted methanol aqueous solution generated on the fuel electrode side are discharged from the battery unit 4, and the carbon dioxide gas is separated from the gas-liquid separator 5. The unreacted aqueous methanol solution is returned to the fuel tank 1 through the return system 10. Again, the aqueous methanol solution in the fuel tank 1 is supplied from the fuel tank 1 to the fuel electrode of the battery unit 4 via the fuel supply pump 2 of the supply system 11 and the impurity removing device 3.
[0024]
Most of the impurities such as salt and metal ions contained in the external air are removed together with the suspended fine particles by the air filter 6 and are not introduced into the air electrode side of the battery unit 4. And metal ions are introduced into the air electrode side of the battery unit 4 together with air, and the salt and metal ions are dissolved in the water generated by the battery reaction and pass through the return system 10 to the fuel tank 1. It goes back and dissolves in the methanol aqueous solution. However, since the aqueous methanol solution in which the metal ions and the like are dissolved is ion-exchanged by the impurity removing device 3 disposed in the supply system 11, the aqueous methanol solution does not contain metal ions and the like and is supplied to the fuel electrode. become. Therefore, if the air filter 6 is provided with an ion exchanger, an adsorbent, a microporous membrane filter, an electrostatic filter, or an air shower, more salt and metal ions can be removed together with suspended fine particles. Therefore, if the air filter 6 and the impurity removing device 3 are used in combination, the above-described effects can be further enhanced.
[0025]
As described above, according to the present embodiment, once mixed metal ions can be removed, it is possible to prevent deterioration of battery characteristics caused by mixing metal ions or the like. The impurity removing device 3 and the ion exchanger of the air filter 6 are preferably installed in a removable state. According to such a configuration, it can be exchanged at regular intervals, and the direct methanol fuel cell system can be stably operated for a long period of time.
In addition, ion exchangers and the like can be recycled and are economical.
[0026]
In this embodiment, an example of application to a fuel cell system in which air is forcibly supplied using the air blower 8 has been shown. However, as described above, metal ions dissolved in an aqueous methanol solution are removed. Therefore, the present invention can also be applied to a natural diffusion type direct methanol fuel cell system.
[0027]
Hereinafter, the following tests were conducted to confirm the effects of the present invention using the direct methanol fuel cell system of the above embodiment.
Test example 1
FIG. 2 shows cell characteristics when seawater is mixed in the fuel of a direct methanol fuel cell.
The characteristics are as follows. In a direct methanol fuel cell unit having an effective area of 60 cm 2, air was supplied at 3 liters / minute under a temperature condition of 90 ° C., and 3% methanol aqueous solution as fuel was supplied at 6 ml / minute, and 0.3V It shows the change in the output current value when operating with a constant voltage output.
In addition, the battery characteristics are compared when 2% and 5% of seawater is added under the same conditions.
[0028]
It can be seen from FIG. 2 that when seawater is mixed in the fuel, the battery characteristics are greatly reduced, and when 2% of seawater is added, the battery characteristics are reduced by about 30%. This deterioration in battery characteristics is because salt, metal ions, and the like in seawater are directly adsorbed on the proton conductive polymer solid electrolyte membrane used in the electrolyte of the methanol fuel cell.
As a result, proton conductivity of the electrolyte membrane and the like is lowered, and battery characteristics are lowered.
[0029]
Test example 2
FIG. 3 compares changes in battery characteristics when the direct methanol fuel cell system according to the present invention and a conventional direct methanol fuel cell system are operated at the seaside (installed in a warehouse 30 m away from the coast). It is a thing.
The same single electrode battery as in Test Example 1 was used as the battery part, air was supplied at 3 liters / minute, and 3% methanol aqueous solution was supplied at 6 ml / minute as a fuel at a temperature of 90 ° C., and a constant voltage of 0.3V. Was operated.
The direct methanol fuel cell system of the present invention is provided with an impurity removing device 3 filled with 50 g of an ion exchange resin (manufactured by Organo, Amberlite EG-4) between the fuel supply pump 2 and the battery unit 4. This is not provided in the conventional system.
[0030]
As can be seen from FIG. 3, according to the system of the present invention, the battery characteristics were slightly lowered even during long-term operation.
It is recognized that the direct methanol fuel cell system of the present invention can suppress deterioration of battery characteristics and is excellent in reliability.
This is because salt, metal ions, and the like that have entered from the air electrode are directly ion-exchanged by the ion exchange resin of the impurity removal device 3 provided in the methanol fuel cell system, and proton conductivity such as a proton conductive polymer solid electrolyte membrane. This is because the deterioration of the property can be suppressed.
[0031]
【The invention's effect】
According to the direct liquid fuel cell system of the present invention, it is possible to suppress the deterioration of the battery characteristics and to prolong the battery life.
[Brief description of the drawings]
FIG. 1 is a flow diagram of the present invention.
FIG. 2 is a comparison of changes in cell characteristics when seawater is mixed into direct methanol fuel cell fuel.
FIG. 3 is a comparison between the system of the present invention and a conventional system.
[Explanation of symbols]
1. 1. Fuel tank 2. Fuel supply pump Impurity removing device 4. Battery part 5. Gas-liquid separator 6. 6. Air filter 7. High concentration fuel tank Air blower9. Circulation unit 10. Return system 11. Supply system

Claims (4)

A fuel electrode to which water and a proton-generating liquid fuel are supplied, an air electrode to which an oxidant gas is provided so as to face the fuel electrode, and the fuel electrode and the air electrode. A proton conductive polymer solid electrolyte membrane, wherein water and a proton-generating liquid fuel are reacted at the fuel electrode to generate electrons and protons, and the proton and the oxidant gas are generated at the air electrode. A battery unit that generates electricity by a series of reactions that cause water to react with each other, and
In a direct liquid fuel cell system comprising a circulation unit that circulates water generated at an air electrode of the battery unit to the fuel electrode so that the water can be reused as water supplied to the fuel electrode.
The direct liquid fuel cell system is characterized in that the system includes means for removing impurities from at least one of water, proton-generating liquid fuel, and oxidant gas supplied to the battery unit. The impurity is a metal ion present in the water generated in the air electrode, and the impurity removing device is provided with a circulation unit as a means for removing the impurity, and the impurity removing device is an ion exchanger or an adsorbent. 2. The direct liquid fuel cell system according to claim 1, which is a combination thereof. The impurities are fine particles mixed in the oxidant gas, and the means for removing the impurities is an air filter provided in the supply path of the oxidant gas, and the air filter is an ion exchanger, an adsorbent or a micropore. 2. The direct liquid liquid fuel cell system according to claim 1, which is a membrane filter, an air shower, or a combination thereof. 4. The direct liquid liquid fuel cell system according to claim 3, wherein the air filter has a function of removing salt.

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