JP2004079210A - Liquid-fuel direct feeding fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a liquid-fuel direct feeding fuel cell system in which a by-product, ion by-product or metal ion can be steadily removed from the liquid content produced by electrochemical reaction of a positive electrode and a negative electrode. <P>SOLUTION: A filter 6, which adsorbs or decomposes the by-product, the ion by-product or the metal ion from the liquid content, is provided at a liquid content recovery means 4 in which a reaction product produced by the electrochemical reaction of the negative electrode 12 and the liquid fuel that has not contributed to the reaction, and a reaction product produced by the electrochemical reaction of the positive electrode 13 and an oxidizer gas that has not contributed to the reaction, are supplied to a gas-liquid separation tank 3 and separated into a gas and a liquid by this gas-liquid separation tank 3, and the separated liquid content is recovered. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid fuel direct supply type fuel cell system, and more specifically, to a liquid fuel direct supply type fuel cell capable of directly supplying a liquid fuel and an oxidizing gas to generate power, and a distributed power supply. The present invention relates to an optimum structure when applied to a power supply for a mobile object and a small portable power supply.
[0002]
[Prior art]
In recent years, measures against environmental problems and resource problems have been highlighted, and as one of the measures, fuel cells are being actively developed.
[0003]
Fuel cells are equipped with a negative electrode and a positive electrode on both sides of the electrolyte, supply a reducing agent such as hydrogen to the negative electrode, supply an oxidizing agent such as oxygen in the air to the positive electrode, and generate electricity through an electrochemical reaction through the electrolyte. Because of its high power generation efficiency and high energy density, it has attracted attention as a power source to replace secondary batteries such as nickel-hydrogen batteries and lithium ion batteries. In particular, a liquid fuel direct supply type fuel cell represented by a direct methanol fuel cell, which uses a liquid fuel such as methanol as a reducing agent, can be used for direct power generation without reforming or gasifying the fuel. Therefore, since the structure can be simplified and the size and weight can be easily reduced, it has been studied as a power source for various mobile objects, a distributed power source, a portable power source, a consumer power source for computers, and the like.
[0004]
In such a direct methanol fuel cell, a negative electrode and a positive electrode are provided on both sides of the electrolyte, an aqueous methanol solution is supplied to the negative electrode, air is supplied to the positive electrode, and the fuel cell is formed by an electrochemical reaction of the cell. A plurality of stacked cell stacks via a separator having a flow channel and a manifold for discharging reaction products, or a negative electrode and a positive electrode are provided on both sides of an electrolyte, and a methanol aqueous solution is supplied to the negative electrode. A cell including a separator having a channel groove and a manifold for supplying air to the positive electrode and discharging a reaction product generated by an electrochemical reaction of the cell is defined as a power generation unit. When a methanol aqueous solution is supplied to the negative electrode and air is supplied to the positive electrode by this separator, carbon dioxide is generated as a reaction product by the electrochemical reaction of the negative electrode, and water is generated as a reaction product by the electrochemical reaction of the positive electrode. On the negative electrode side, the carbon dioxide is discharged to the outside together with the aqueous methanol solution that did not contribute to the reaction, and on the positive electrode side, the water is discharged to the outside together with air that did not contribute to the reaction.
[0005]
Further, in the direct methanol fuel cell described above, a type in which an external power such as a pump is used to supply air to the positive electrode, and an opening for introducing air from the atmosphere to the positive electrode are provided in the separator, and the opening is provided in the separator. Through the natural diffusion and natural convection of oxygen in the atmosphere through the use of natural gas, the latter has the disadvantage that it is more difficult to obtain an output than the former, but it is necessary to drive the pump. Since there is no need for electric power, there are advantages that the power generation efficiency can be increased, the system can be made simple and compact, and a quiet generator without pump driving noise can be obtained. For these reasons, the direct methanol fuel cell may be optimal as a small-sized consumer power supply for computers and the like.
[0006]
[Problems to be solved by the invention]
As described above, in the direct methanol fuel cell, an aqueous methanol solution that did not contribute to the reaction with carbon dioxide was discharged from the negative electrode side, air that did not contribute to the reaction with water was discharged from the positive electrode side, and further the above-mentioned electrochemical reaction was performed. In some cases, for example, by-products such as formaldehyde and formic acid are generated in a very small amount, or when these react with each other, by-products such as methyl formate may be generated in a very small amount. Since it is contained in a trace amount as an ion by-product such as formate ion, or may contain a trace amount of a metal ion such as platinum ion and ruthenium ion eluted from the negative electrode or the positive electrode, it does not contribute to the reaction with the carbon dioxide and water. How the aqueous methanol solution and air were treated, the by-products, ion by-products, How to process was the important practical application of direct methanol fuel cells. In a conventional direct methanol fuel cell, carbon dioxide and water, an aqueous methanol solution and air that did not contribute to the reaction, were introduced into the gas-liquid separation tank together with by-products, ion by-products, and metal ions. The gas-liquid separation tank separates the gas component and the liquid component, and the gas component removes by-products before discharging to the atmosphere.The liquid component removes by-products, ion by-products, and metal ions. Reused without removal. Therefore, a methanol aqueous solution containing such by-products, ion by-products, and metal ions is continuously used in an electrochemical reaction, and there is a problem that deterioration of battery characteristics is promoted.
[0007]
[Means for Solving the Problems]
The present invention has been made to solve the above problems, and has as its object to remove by-products mixed in a liquid component so as not to promote deterioration of battery characteristics. That is, the invention according to claim 1 has a configuration in which a negative electrode and a positive electrode are opposed to each other via an electrolyte made of a proton conductive solid polymer membrane, and a liquid fuel is supplied to the negative electrode and an oxidizing gas is supplied to the positive electrode. In the liquid fuel direct supply type fuel cell system, comprising a cell provided with or a cell stack in which a plurality of the cells are stacked, and obtaining an electromotive force by an electrochemical reaction of the positive and negative electrodes, A configuration is provided for separating gas and liquid from the reaction product generated by the electrochemical reaction and the liquid fuel and the oxidizing gas that have not contributed to the electrochemical reaction, and does not contribute to the reaction product and the electrochemical reaction. 3. A liquid component recovery means for recovering a liquid component separated from the liquid fuel and the oxidant gas is provided, wherein the liquid component recovery means is provided. Minute collection means, in the liquid component, positive, by-products generated by the electrochemical reaction of the negative electrode, ion by-products ionized part of the by-products, metal ions eluted from the negative electrode or the positive electrode, It is characterized by having a filter for adsorbing or decomposing at least one.
[0008]
That is, according to the first and second aspects of the present invention, the reaction product generated by the positive and negative electrode electrochemical reactions and the liquid component separated from the liquid fuel and the oxidizing gas that did not contribute to the electrochemical reaction are separated from each other. The liquid component is recovered by a liquid component recovery means, and the liquid component recovery means adsorbs or removes at least one of a by-product, an ion by-product in which a part of the by-product is ionized, and a metal ion eluted from a negative electrode or a positive electrode. Since it is equipped with a filter that decomposes, it is possible to prevent by-products such as formic acid, formaldehyde and methyl formate from being contained in the aqueous methanol solution to be reused, and to prevent ionic by-products such as formate ions from being contained in platinum aqueous solution. And metal ions such as ruthenium ions.
[0009]
The invention according to claim 3 is characterized in that the filter contains an adsorbent for adsorbing by-products, and the invention according to claim 4 includes the photochemical catalyst in which the filter decomposes by-products. The invention according to claim 5 is characterized in that the filter contains an ion exchange resin that adsorbs ion by-products or metal ions.
[0010]
That is, according to the invention of claim 3, by-products can be adsorbed by the adsorbent, and according to the invention of claim 4, the by-products can be decomposed by the photochemical catalyst. According to the fifth aspect of the present invention, since ion by-products or metal ions can be adsorbed by the ion exchange resin, by-products such as formic acid, formaldehyde and methyl formate, ion by-products such as formate ion, platinum ion and ruthenium The aqueous methanol solution from which metal ions such as ions have been removed can be reused.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described based on the embodiments.
[0012]
FIG. 1 is a configuration diagram of a direct methanol fuel cell system shown as an example of a liquid fuel direct supply type fuel cell system according to an embodiment of the present invention, and is characterized by a proton conductive solid polymer membrane. A cell 1 in which a negative electrode 12 and a positive electrode 13 are opposed to each other via an electrolyte 11 is a power generation unit, and a fuel tank 2 for storing an aqueous methanol solution as a liquid fuel in the negative electrode 12 at a concentration suitable for the electrochemical reaction. , And air as an oxidizing gas is supplied to the positive electrode 13, and a reaction product generated by the electrochemical reaction of the cell 1 is separated into a methanol aqueous solution and air which did not contribute to the electrochemical reaction. The gas is introduced into a separation tank 3, separated into a gas and a liquid in the gas-liquid separation tank 3, and water and an aqueous methanol solution as liquid components are returned to the fuel tank 2 via a liquid component recovery means 4. It is to have to be. In the liquid component, for example, formic acid, formaldehyde, by-products such as methyl formate, a part of the by-products are ionized, for example, ion by-products such as formate ion, and a negative electrode. Alternatively, metal ions such as platinum ions and ruthenium ions eluted from the positive electrode are contained. Note that air and carbon dioxide as gas components separated in the gas-liquid separation tank 3 are collected by the gas component collection unit 5.
[0013]
The liquid component recovery means 4 is provided with a filter 6 for adsorbing or decomposing at least one of the by-products, ion by-products and metal ions. Further, the gas component recovery means 5 may be provided with a filter for absorbing or decomposing by-products in the gas component.
[0014]
【Example】
(Example 1)
FIG. 2 shows a configuration diagram of a direct methanol fuel cell system shown as an example of the liquid fuel direct supply type fuel cell system according to the first embodiment of the present invention, and does not show air supplied to the positive electrode 13. The aqueous methanol solution which did not contribute to the reaction with the reaction product of the negative electrode 12 and the reaction product of the positive electrode 13 and air which did not contribute to the reaction are collectively supplied to the cell 1 by a pump or the like, and the gas-liquid separation tank 3, water and a methanol aqueous solution as liquid components are separated by the gas-liquid separation tank 3 and introduced into the liquid component recovery means 4, and air and carbon dioxide as gas components are separated and the gas component recovery means 5 is introduced.
[0015]
An aqueous methanol solution that did not contribute to the electrochemical reaction of the negative electrode 12 and water generated by the electrochemical reaction of the positive electrode 13 were introduced as liquid components into the liquid component collecting means 4 of the first embodiment. By the filter 6 built in 4, by-products such as formic acid, formaldehyde and methyl formate in the liquid component, ionic by-products such as formate ion in which a part of the by-products are ionized, the negative electrode or At least one of metal ions such as platinum ions and ruthenium ions eluted from the positive electrode is adsorbed or decomposed and sent to the fuel tank 2.
[0016]
(Example 2)
FIG. 3 is a configuration diagram of a direct methanol fuel cell system shown as an example of a liquid fuel direct supply fuel cell system according to a second embodiment of the present invention. It is supplied by diffusion or natural convection. In the second embodiment, since the positive electrode side of the cell 1 is open to the atmosphere, the entire cell 1 is put in a case, and only the reaction product of the negative electrode 12 and the aqueous methanol solution which has not contributed to the reaction are removed. This is introduced into the gas-liquid separation tank 3, and the aqueous methanol solution as a liquid component is separated by the gas-liquid separation tank 3 and introduced into the liquid component recovery means 4.
[0017]
An aqueous methanol solution that did not contribute to the electrochemical reaction of the negative electrode 12 was introduced as a liquid component into the liquid component recovery means 4 of the second embodiment, and the liquid component recovery means 4 was filtered by the filter 6 incorporated therein. Formic acid, formaldehyde, by-products such as methyl formate, ion by-products such as formate ions in which part of the by-products are ionized, and platinum ions and ruthenium ions eluted from the negative electrode or the positive electrode At least one of the metal ions is adsorbed or decomposed and sent to the fuel tank 2.
[0018]
If the filter 6 incorporated in the liquid component recovery means 4 of the first and second embodiments contains an adsorbent such as activated carbon or zeolite that adsorbs by-products such as formic acid, formaldehyde and methyl formate, When the by-product can be adsorbed and the filter 6 contains a photochemical catalyst such as titanium oxide that decomposes by-products such as formic acid, formaldehyde, and methyl formate, the by-product is converted to water. And the filter 6 adsorbs ion by-products such as formate ions and metal ions such as platinum ions or ruthenium ions. When the resin contains an ion exchange resin, the ion by-products and metal ions can be adsorbed. By-products such as, ion-products, it is possible to prevent the aqueous methanol solution in which the metal ion is contained is sent to the fuel tank 2.
[0019]
As a method for allowing the filter to contain the adsorbent, the photochemical catalyst, or the ion exchange resin, it is preferable that these are supported on the honeycomb layer. However, when the photochemical catalyst is supported on the honeycomb layer, the honeycomb is used. It is necessary to irradiate the layer with sunlight, or to arrange a chemical lamp near the honeycomb layer to irradiate the light.
[0020]
In addition, the above-mentioned adsorbent, photochemical catalyst or ion exchange resin may be used alone, or may be appropriately combined. In this case, a synergistic effect can be expected.
[0021]
In the above embodiments and examples, a direct methanol fuel cell system using an aqueous methanol solution as a liquid fuel has been described. However, a liquid fuel other than an aqueous methanol solution, for example, a liquid fuel using ethyl alcohol, butanol, dimethyl ether, etc. The present invention can also be applied to a direct supply type fuel cell.
[0022]
In the above-described embodiments and examples, the description has been given of the case where the power generation unit is composed of the cell 1. However, the power generation unit can be similarly applied even if the power generation unit is configured by a cell stack in which a plurality of the cells 1 are stacked. .
[0023]
In the above-described embodiments and examples, the liquid component collecting means 4 is provided with the filter 6, but the gas component collecting means 5 is also provided with the same filter so that the air after the reaction and the reaction product are generated. By-products contained in carbon dioxide as a substance may be absorbed or decomposed.
[0024]
In addition, the adsorbents, photochemical catalysts, and ion exchange resins exemplified in the above-described embodiments and examples are not limited thereto, and may be other types having the same function, The shape (for example, the particle size) is not limited, and the method of including them in the filter is not limited to the above-described method.
[0025]
【The invention's effect】
As described above, according to the present invention, a liquid fuel direct supply type fuel cell such as a direct methanol type fuel cell capable of generating electricity without reforming and gasifying a methanol aqueous solution can be used as a portable power source, a computer, When applied to small consumer applications such as power supplies for use, by-products, ion by-products or metal ions can be reliably removed from the methanol aqueous solution that is reused, so that the battery characteristics suitable for the above-mentioned applications are This can contribute to the configuration of the system in which the reduction can be suppressed.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a liquid fuel direct supply type fuel cell system according to an embodiment of the present invention.
FIG. 2 is a configuration diagram of a liquid fuel direct supply type fuel cell system according to a first embodiment of the present invention.
FIG. 3 is a configuration diagram of a liquid fuel direct supply type fuel cell system according to a second embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Cell 2 Fuel tank 3 Gas-liquid separation tank 4 Liquid component recovery means 5 Gas component recovery means 6 Filter

Claims (5)

A cell having a configuration in which a negative electrode and a positive electrode are opposed to each other via an electrolyte made of a proton conductive solid polymer membrane, and a liquid fuel is supplied to the negative electrode and an oxidizing gas is supplied to the positive electrode, or a plurality of such cells are stacked. A liquid fuel direct supply type fuel cell system comprising a power generation unit comprising a cell stack, wherein the positive and negative electrodes obtain an electromotive force by an electrochemical reaction. A configuration is provided for separating gas and liquid from the liquid fuel and the oxidizing gas that did not contribute to the electrochemical reaction, and the reaction product and the liquid fuel and the oxidizing gas that did not contribute to the electrochemical reaction were separated from the oxidizing gas. A liquid fuel direct supply type fuel cell system comprising a liquid component recovery means for recovering a liquid component. 2. The liquid fuel direct supply type fuel cell system according to claim 1, wherein the liquid component recovery means includes a by-product generated by an electrochemical reaction between positive and negative electrodes in the liquid component, and a part of the by-product is ionized. A liquid fuel direct supply type fuel cell system, comprising: a filter for adsorbing or decomposing at least one of selected ion by-products and metal ions eluted from a negative electrode or a positive electrode. 3. The liquid fuel direct supply type fuel cell system according to claim 2, wherein the filter contains an adsorbent for adsorbing by-products. 3. The liquid fuel direct supply type fuel cell system according to claim 2, wherein the filter contains a photochemical catalyst for decomposing by-products. 3. The liquid fuel direct supply type fuel cell system according to claim 2, wherein the filter contains an ion exchange resin that adsorbs ion by-products or metal ions.

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