KR20070079531A - Membrane electrode assembly activation process - Google Patents

Abstract

Provided is a method for activating an electrolyte membrane electrode assembly for a direct methanol fuel cell to reduce the time required for the activation of an electrolyte membrane electrode assembly. The method comprises the step of supplying hydrogen to the anode of an electrolyte membrane electrode assembly which comprises an anode, a cathode, and an electrolyte membrane interposed between the anode and the cathode. Preferably the flux of the supplied hydrogen is 4-8 ccm per 1 cm^2 of the electrolyte membrane electrode assembly. Preferably hydrogen is humidified to an absolute humidity of about 90% and is supplied for about 2 hours.

Description

Method of activating an electrolyte membrane electrode assembly {membrane electrode assembly activation process}

1 is a performance comparison curve of an electrolyte membrane electrode assembly activated according to an activation process and a conventional activation process according to an embodiment of the present invention,

2 is a schematic view showing the action of an electrolyte membrane electrode assembly of a direct methanol fuel cell.

The present invention relates to a method of activating an electrolyte membrane electrode assembly used in a fuel cell, and more particularly, to a method of activating an electrolyte membrane electrode assembly used in a direct methanol fuel cell so as to generate a maximum output from an initial operation. .

A fuel cell is a power generation system that converts chemical energy directly into electrical energy by an electrochemical reaction between hydrogen and oxygen. The fuel cell is a polymer electrolyte type and direct methanol fuel cell operating at room temperature or below 100 ° C, a phosphate fuel cell operating at around 150 to 200 ° C, a molten carbonate fuel cell operating at a high temperature of 600 to 700 ° C, and 1000 ° C. It is classified into the solid oxide fuel cell etc. which operate at the high temperature mentioned above. Each of these fuel cells has basically the same operation principle of generating electricity, but different fuel types, catalysts, and electrolytes.

Among them, the direct methanol fuel cell (DMFC) can operate at a relatively low temperature, and since methanol is used as a direct fuel, it can be compactly constructed without using a reformer that generates hydrogen by reforming raw fuel. As a result, development for use as a power source for portable electronic devices is active.

In the direct methanol fuel cell, a portion where electricity is generated is an electrolyte membrane electrode assembly, and typically, the electrolyte membrane electrode assembly is configured in such a manner that an electrolyte membrane is interposed between an anode electrode and a cathode electrode. Methanol is supplied to the anode electrode through a fuel supply device, oxygen contained in normal air is supplied to the cathode electrode through an air supply device, and electricity is generated in the electrolyte membrane electrode assembly using methanol and oxygen.

Meanwhile, by directly facing the anode electrode with methanol and exposing the cathode electrode in the air, methanol and oxygen in the air can be supplied to the electrolyte membrane electrode assembly without the addition of a separate fuel supply device or air supply device. This type of fuel cell is commonly referred to as passive type direct methanol fuel cell (passive type DMFC). Fuel cells of the type which omit the fuel supply but add the air supply are commonly referred to as semi-passive direct methanol fuel cells (semi passive type DMFC). Passive direct methanol fuel cells or semi-passive fuel cells do not require a separate fuel supply and / or air supply, thus minimizing unnecessary power consumption. It has the advantage of being compact.

On the other hand, in the case of the electrolyte membrane electrode assembly used directly in the methanol fuel cell, if the power is produced immediately after manufacturing, the normal output is not obtained. Thus, conventionally, the electrolyte membrane electrode assembly was used after activating the electrolyte membrane electrode assembly through a pretreatment step of immersing the electrolyte membrane electrode assembly in water or methanol at a predetermined concentration. However, the above-mentioned activation method usually takes several days, and there is a problem that normal power generation is impossible during the pretreatment process.

The present invention has been proposed to solve the conventional problems as described above, to provide an activation method for reducing the time required for the pretreatment process of the electrolyte membrane electrode assembly used in a direct methanol fuel cell.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention.

2 is a schematic view showing the action of an electrolyte membrane electrode assembly of a direct methanol fuel cell.

Referring to FIG. 2, the electrolyte membrane electrode assembly of the direct methanol fuel cell is configured in such a manner that an electrolyte membrane 30 is interposed between the anode electrode 10 and the cathode electrode 20. Methanol (CH ₃ OH) and water (H ₂ O) (hereinafter, a mixture of methanol and water as fuel) supplied to the anode electrode 10 were carbon dioxide (CO ₂ ), hydrogen ions (H ⁺ ) and It is decomposed into ^- e (e). The hydrogen ions move to the cathode electrode 20 through the electrolyte membrane 30, and the electrons move to the cathode electrode 20 through an external wire. The cathode 20 is supplied with oxygen (O ₂ ) contained in ordinary air, and electrons, hydrogen ions, and oxygen moved from the anode electrode 10 react on the catalyst to generate water.

The electrochemical reaction occurring at the anode electrode 10 and the cathode electrode 20 is represented by the following reaction scheme.

The anode: H ₂ CH ₃ OH + O → CO ₂ + 6H ⁺ + 6e ^-

^{_{Cathode: 3/2 O 2 + 6H + +}} 6e - → 3H 2 O

Total: CH ₃ OH + 3/2 O ₂ → CO ₂ + 2H ₂ O

1 is a performance comparison curve of an electrolyte membrane electrode assembly activated according to an activation process and a conventional activation process according to an embodiment of the present invention.

Hereinafter, an activation process of an electrolyte membrane electrode assembly used in a direct methanol fuel cell will be described in detail with reference to FIG. 1. However, the present invention is not limited only to the following examples.

<Example>

Hydrogen (H ₂ ) humidified at an absolute humidity of 90% is supplied to the anode electrode of the electrolyte membrane electrode assembly having a width of 25 cm _{2 at} a flow rate of 100 to 200 cm (Cubic Centimeter per Minute). That is, the flow rate of the hydrogen supplied to the electrolyte membrane electrode assembly is 4 to 8 ccm per cm 2 of the electrolyte membrane electrode assembly.

If the electrolyte membrane electrode assembly is supplied less than the flow rate of hydrogen may not be enough electricity is produced, if more than the flow rate of hydrogen unreacted hydrogen is accumulated to inhibit the efficient use of hydrogen. On the other hand, when supplying less humidified hydrogen than the humidification amount, the hydration time of the electrolyte membrane electrode assembly is delayed, thereby requiring more time for the activation process. In addition, when supplying more humidified hydrogen than the humidification amount, water may condense on the surface of the electrolyte membrane electrode assembly, thereby preventing hydrogen flow. As a result, hydrogen is uniformly supplied to the electrolyte membrane electrode assembly, thereby providing a uniform activation process. Can't be done.

When hydrogen is supplied to the anode electrode of the electrolyte membrane electrode assembly as described above and air is supplied to the cathode electrode of the electrolyte membrane electrode assembly, electricity is produced so that the output voltage is maintained between 0.4 to 0.8V. Referring to FIG. 1, in this case, the maximum performance of the electrolyte membrane electrode assembly can be reached in about 1 to 2 hours and more specifically in about 2 hours.

Comparative Example

As in the conventional method, an activation process of supplying 3 M concentration of methanol fuel to the anode electrode of the electrolyte membrane electrode assembly is performed. At this time, air is supplied to the cathode of the electrolyte membrane electrode assembly. 1, the maximum performance of the electrolyte membrane electrode assembly can be reached in about 72 hours. Therefore, in the case of the above-described embodiment, there is an advantage that the activation time of the electrolyte membrane electrode assembly can be significantly shortened in comparison with the comparative example.

According to the present invention, when the electrolyte membrane electrode assembly of a direct methanol fuel cell is initially used, humidified hydrogen is supplied to the anode to activate the electrolyte membrane electrode assembly, thereby shortening the time taken to activate the electrolyte membrane electrode assembly. Therefore, the electrolyte membrane electrode composite can be used more efficiently.

Claims (4)

In a method for activating an electrolyte membrane electrode assembly, which is used in a direct methanol fuel cell and has an electrolyte membrane interposed between an anode electrode and a cathode electrode, And activating the electrolyte membrane electrode assembly by supplying hydrogen to the anode electrode of the electrolyte membrane electrode assembly. The method of claim 1, And activating the electrolyte membrane electrode assembly by supplying hydrogen at a flow rate of 4 to 8 ccm per cm 2 of the electrolyte membrane electrode assembly to the anode electrode. The method of claim 2, And the hydrogen is humidified at an absolute humidity of about 90%. The method of claim 3, Wherein said hydrogen is supplied for about 2 hours.

Images