JP2007280667A - Liquid fuel direct supply fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To collect formaldehyde in by-products of a liquid fuel direct supply fuel cell. <P>SOLUTION: A cell having a negative electrode 6 to be supplied with liquid fuel and a positive electrode 7 to be supplied with oxidant gas set in opposition through an electrolyte 5, or a cell stack laminating a plurality of such cells 1 is to be a power generating unit, and diatomaceous filter 4 is arranged in a gas/liquid mixture tub 3 so that formaldehyde as a by-product from reaction products by electrochemical reaction of the anode 6 and the cathode 7 is absorbed and removed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid fuel direct supply type fuel cell system. More specifically, the present invention relates to a distributed power source, a mobile power source, and a small portable power source capable of generating power by directly supplying liquid fuel and oxidant gas to a power generation unit. The present invention relates to a structure of a liquid fuel direct supply type fuel cell suitable for an electric power source.

  In recent years, measures against environmental problems and resource problems have been highlighted, and fuel cells have been actively developed as part of such measures. Particularly, a liquid fuel direct supply type fuel cell such as a direct methanol type fuel cell using a proton conductive solid polymer membrane as an electrolyte can generate electric power by directly supplying the fuel without gasification or reforming. Therefore, the structure is simple, and it is easy to reduce the size and weight, and is attracting attention as a distributed power source, a mobile power source, and a small portable power source.

  In this direct methanol fuel cell, a cell in which a positive electrode and a negative electrode are joined to both sides of an electrolyte of a proton conductive polymer solid polymer membrane is sandwiched by a graphite separator, or the cell is interposed via a graphite separator. A large number of power generation units are stacked. The positive electrode is formed by applying a carbon powder carrying a platinum catalyst on the surface of a porous carbon paper, and the negative electrode is formed by applying a carbon powder carrying a platinum-ruthenium catalyst on the surface of the same carbon paper.

  The direct methanol fuel cell described above is to supply an aqueous methanol solution as a reducing agent to the negative electrode, supply oxygen in the air as an oxidant to the positive electrode, and generate power by an electrochemical reaction via an electrolyte. In terms of its power generation efficiency and energy density, it has attracted attention as a power source that can replace secondary batteries such as nickel-hydrogen batteries and lithium ion batteries. That is, when a methanol aqueous solution having a concentration of about 3% is supplied to the negative electrode and air is supplied to the positive electrode, carbon dioxide is generated by the electrochemical reaction of the negative electrode, and water is generated by the electrochemical reaction of the positive electrode. The aforementioned carbon dioxide is discharged together with the methanol aqueous solution, and the aforementioned water is discharged together with air from the positive electrode side.

  Such a direct methanol fuel cell recovers a methanol aqueous solution discharged together with carbon dioxide and water discharged together with air in a gas-liquid mixing tank, removes carbon dioxide and air as gas components, A system in which an aqueous methanol solution and water as components are returned to a fuel tank for storing an aqueous methanol solution to be supplied to the negative electrode, its concentration is adjusted to about 3%, and then supplied to the negative electrode again, that is, a liquid It is configured as a fuel direct supply type fuel cell system.

However, in the above system, since the operating temperature of the direct methanol fuel cell is about 80 ° C., most of the water discharged from the positive electrode side goes out of the system as water vapor, and together with this, the electrochemical reaction There is a problem that formaldehyde and formic acid, which are by-products generated in the above, or methyl formate generated by the reaction thereof is also released from the system. Among such by-products, in particular, formaldehyde causes sick house syndrome. Therefore, it is one of the problems to be solved in spreading the liquid fuel direct supply type fuel cell system for general households. A proposal as disclosed in Patent Document 1 has been made.
JP, 2003-223920, A The proposal of patent documents 1 provides an adsorption agent which absorbs or decomposes the above-mentioned by-product while separating a gas ingredient from a reaction product by gas ingredient recovery means. It is a thing.

  The above-described method of providing an adsorbent that absorbs or decomposes by-products in the gas component recovery means recovers the aqueous methanol solution discharged together with carbon dioxide and the water discharged together with air in a gas-liquid mixing tank, Since the gas component separated in (1) is sent to the gas component recovery means to absorb or decompose the by-product, there is a problem that the configuration becomes complicated. In addition, activated carbon and zeolite exemplified as an adsorbent that absorbs or decomposes such a by-product also has a problem that its adsorption performance deteriorates early when it comes into contact with a high-humidity gas component.

  In order to solve the above-described problems, the present invention provides a negative electrode and a positive electrode that are opposed to each other via an electrolyte composed of a proton conductive solid polymer membrane, and a liquid fuel is supplied to the negative electrode and an oxidant gas is supplied to the positive electrode. A power generation unit comprising a cell or a cell stack in which a plurality of the cells are stacked, water generated by the electrochemical reaction of the positive electrode, and carbon dioxide generated by the electrochemical reaction of the negative electrode, In the liquid fuel direct supply type fuel cell system, wherein the gas-liquid mixing tank includes a liquid fuel that does not contribute to the gas and a gas-liquid mixing tank that is recovered together with the oxidant gas, and obtains an electromotive force by an electrochemical reaction between the positive and negative electrodes Is provided with a diatomaceous earth filter that adsorbs formaldehyde generated by the electrochemical reaction (claim 1).

  According to the present invention, the gas-liquid mixing tank is provided with a diatomaceous earth filter whose adsorption performance does not decrease even in a high-humidity atmosphere, so that formaldehyde is not separated in the gas-liquid mixing tank without separating gas components. Since it can be removed, the above causative substance of sick house syndrome can be removed with a simple system.

  Hereinafter, the present invention will be described based on the embodiments.

  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, which is characterized by a proton conductive solid polymer membrane. A cell 1 in which a negative electrode 6 and a positive electrode 7 are arranged with an electrolyte 5 interposed therebetween is used as a power generation unit. A methanol aqueous solution as a liquid fuel is applied to the negative electrode 6 at a concentration (about 3%) suitable for the electrochemical reaction. This is that the fuel is supplied from the fuel tank 2 to be stored, and air as an oxidant gas is supplied to the positive electrode 7 by a pump (not shown). In the positive electrode 7, water is generated by the electrochemical reaction, and in the negative electrode 6, carbon dioxide is generated by the electrochemical reaction, which contributes to the reaction with air and the carbon dioxide that did not contribute to the reaction with the water. The methanol aqueous solution that has not been introduced is introduced into the gas-liquid mixing tank 3, and water and methanol aqueous solution as liquid components are introduced into the fuel tank 2 by a pump (not shown). The gas-liquid mixing tank 3 is provided with a diatomaceous earth filter, and adsorbs formaldehyde in a mixture of water, air that did not contribute to the reaction, carbon dioxide, and aqueous methanol solution that did not contribute to the reaction. In the mixture after formaldehyde is adsorbed, the gas component is released into the atmosphere and the liquid component is introduced into the fuel tank 2.

  The diatomaceous earth filter of the above-described embodiment is mainly composed of aluminum and silicon, and is preferably processed into a plate shape and provided in the gas-liquid mixing tank 3. You may process into a shape.

  Next, the concentration of about 3% of the embodiment in which the diatomaceous earth filter processed into a plate shape is arranged in the gas-liquid mixing tank 3 and the conventional one in which the diatomaceous earth filter is not arranged in the gas-liquid mixing tank 3 Aqueous methanol solution of 8 ml / min. , Air at 1 l / min. When the amount of formaldehyde in the gas component released from the gas-liquid mixing tank 3 was detected by the Kitagawa type gas detector tube, it was not detected in the embodiment. On the other hand, it was found that 2 ppm was detected in the conventional one.

  From this, it can be seen that the direct methanol fuel cell of the present invention provided with a diatomaceous earth filter in the gas-liquid mixing tank 3 can remove most of the by-product formaldehyde.

  In the above-described embodiment, the methanol aqueous solution in the fuel tank 2 has a concentration (about 3%) suitable for the electrochemical reaction by the water supplied from the gas-liquid mixing tank 3 and the methanol aqueous solution. Separately, a high-concentration methanol tank for storing a high-concentration (for example, about 60%) aqueous methanol solution may be separately provided, and a high-concentration methanol aqueous solution may be introduced from the high-concentration methanol tank to control the concentration to the above-described concentration. .

  In the above-described embodiment, the power generation unit is composed of a single cell 1. However, a cell stack in which a plurality of cells 1 are stacked may be used, and this may be a power generation unit.

  As described above, according to the present invention, a liquid fuel direct supply type fuel cell typified by a direct methanol type fuel cell capable of generating power without reforming and gasifying a methanol aqueous solution, a portable power source, When applied to small consumer applications such as computer power supplies, formaldehyde in by-products can be removed with a simple system configuration, which contributes to the spread of direct methanol fuel cell systems especially for home use. be able to.

1 is a configuration diagram of a liquid fuel direct supply type fuel cell system according to an embodiment of the present invention.

Explanation of symbols

1 Cell 2 Fuel Tank 3 Gas-Liquid Mixing Tank 4 Diatomaceous Earth Filter 5 Electrolyte 6 Negative Electrode 7 Positive Electrode 8 Heat Exchanger

Claims (1)

A cell in which a negative electrode and a positive electrode are opposed to each other through an electrolyte composed of a proton conductive solid polymer membrane, liquid fuel is supplied to the negative electrode, and an oxidant gas is supplied to the positive electrode. A power generation unit comprising a stack of cell stacks, and water produced by the electrochemical reaction of the positive electrode and carbon dioxide produced by the electrochemical reaction of the negative electrode, liquid fuel and oxidant gas that did not contribute to the electrochemical reaction A liquid fuel direct supply type fuel cell system that obtains an electromotive force by an electrochemical reaction between the positive and negative electrodes, wherein the gas-liquid mixing tank contains formaldehyde generated by the electrochemical reaction. A liquid fuel direct supply type fuel cell system comprising an adsorbing diatomite filter.

Images