JP2009140670A - Direct methanol fuel cell using metal porous body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct methanol fuel cell that delivers a high power output by improving the discharging performance of product materials and the supplying performance of reactant materials. <P>SOLUTION: A membrane electrode assembly has a polymer electrolyte membrane disposed at its center, and electrodes consisting of an anode and a cathode disposed at both outer sides of the polymer electrolyte membrane. A separator has a surface in contact with the membrane electrode assembly that is replaced by a metal porous body. On a separator for a conventional direct methanol fuel cell, a trench-like passage has been provided on a surface in contact with the membrane electrode assembly, and discharge of product materials and supply of reactant materials have been performed through such a passage. On the other hand, the present invention requires no passage because the metal porous body substitutes for such a capability. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a direct methanol fuel cell in which a part of a separator is replaced with a porous metal body.

  A direct methanol fuel cell (DMFC) that directly uses an aqueous methanol solution as a fuel is advantageous in that it has a simple structure and uses a liquid fuel that is excellent in portability and energy density. Compared to fuel cells, the power density and power generation efficiency are inferior.

In order to improve the performance of the direct methanol fuel cell, it is necessary to smoothly discharge the product (carbon dioxide at the anode and water at the cathode). In other words, it is required to reduce the contact resistance between the separator and the membrane electrode assembly, and to secure the flow rate of the product flowing in the separator channel, and attempts to devise the width and number of channels (non- Attempts have been made to use a metal porous body in Patent Document 1) and gas diffusion layers (Patent Document 1).
JP2003-282068A Toshio Shudo: Relationship between anode and cathode separator channel shape and output in DMFC, Material Stage, Vol. 2, no. 10, pp. 60-63, (2003).

  However, even when the above-described conventional method is used, a separator having a flow path has a problem that it is difficult to supply reactants (methanol aqueous solution at the anode and air or oxygen at the cathode) to the membrane electrode assembly at the rib portion. Remains.

  This invention is made | formed in view of this point, and it aims at solving the discharge | emission problem of a product, and the supply problem of a reactant simultaneously, and providing a high output direct methanol fuel cell.

  The direct methanol fuel cell of the present invention comprises a membrane electrode assembly and a separator installed outside the membrane electrode assembly, and the separator surface joined to the membrane electrode assembly is replaced with a porous metal body. ing.

  According to the present invention, the product discharge performance and the reactant supply performance can be improved, so that the power generation efficiency and output of the direct methanol fuel cell can be improved.

  The direct methanol fuel cell of the present invention is a direct methanol fuel cell comprising a membrane electrode assembly (1) and a separator (2) installed outside thereof.

  FIG. 1 is a schematic cross-sectional view showing an example of a direct methanol fuel cell 100 of the present invention. FIG. 2 shows a state where each component is separated in order to explain FIG. Hereinafter, the configuration of the present invention will be described in detail with reference to FIG.

  In FIG. 2, a membrane electrode assembly 200 has a polymer electrolyte membrane 210 at the center and electrodes arranged on both outer sides thereof, one of which is an anode 220 and the other is a cathode 230. Here, each member which comprises a membrane electrode assembly should just satisfy the performance of a standard direct methanol fuel cell. Further, the separator 250 has a surface in contact with the membrane electrode assembly 200 replaced with a metal porous body 160. The material forming the metal porous body 260 is desirably an alloy having corrosion resistance and a porosity of 85% or more. For example, the metal porous body described in Patent Document 1 may be used.

  The contact surface with the membrane electrode assembly in the separator of the conventional direct methanol fuel cell is provided with a groove-like channel for discharging the product and supplying the reactant. Does not require this flow path.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Separator configuration]
The difference between the conventional separator 300 and the separator 400 of the present invention will be described. FIG. 3 shows an example of a conventional separator 300. The conventional separator 300 maintains its function by providing a flow path 310 for discharging products and supplying reactants. On the other hand, the separator 400 of the present invention substitutes its function by inserting a metal porous body 410 instead of providing a flow path as shown in FIG.

[experimental method]
In the experiment, a direct methanol fuel cell for test was used in combination with the separators shown in FIGS. A 5 wt% aqueous methanol solution was used as the fuel, and was supplied to the anode by a diaphragm electromagnetic metering pump (ProMinet GVLA1000). Oxygen was used as the cathode gas, and the flow rate was measured with a thermal gas mass flow meter (Yamatake CMS0005). The anode flow rate was 10 cc / min, and the cathode flow rate was 1000 cc / min. The power generation characteristics were measured using a fuel cell impedance meter (Kikusui KFM2030). A thermostat (40-80 ° C.) was used for temperature control of the battery and anode fuel. As the polymer electrolyte membrane, Nafion (registered trademark, manufactured by DuPont, film thickness of 175 μm) was used. The other specifications of the membrane electrode assembly and the specifications of the reactant are shown in Table 1.

The metal porous body used for the separator (porous separator) of the present invention has specifications as shown in Table 2. The member manufactured using this was attached to a separator as shown in FIG. For comparison, an experiment using a conventional stainless steel separator (flow channel separator) having a normal flow channel as shown in FIG. 3 was also performed. The thickness of the porous separator member was the same as the channel depth of the channel separator. The space volume in the separator is about 2.9 cc for the conventional type and about 5 cc for the metal porous body.

[Experimental result]
The result at the time of comparing the case where a porous separator is used and the case where a flow path type separator is used is shown. The battery temperature at this time was maintained at 80 ° C. FIG. 5 shows current density-voltage characteristics (IV characteristics), and FIG. 6 shows current density-output density characteristics. In both cases, the performance is similar up to about 0.1 A / cm ² , but it was shown that when a porous separator was used, operation at a higher current density was possible compared to a flow path separator. . Further, it can be seen that the output peak is greatly improved and changes to the higher current density side.

FIG. 7 shows an AC impedance measurement result (Cole-Cole plot). The measured current density condition was 0.3 A / cm ² , and the battery temperature at this time was maintained at 80 ° C. It can be inferred that the porous separator has a smaller arc diameter in the plot and the reaction resistance is reduced compared to the flow-path separator. This is considered to have improved the output. Reaction resistance measured by AC impedance measurement includes diffusion polarization related to material diffusion and activation polarization related to fuel activation. In the porous separator, there is no channel rib, so that uniform reactant can be supplied to the entire reaction surface, and the product discharge is improved by high porosity, so that diffusion polarization is reduced and high current density is achieved. It is considered that a voltage difference has occurred.

FIG. 8 shows the measurement results of battery temperature-voltage characteristics. The measured current density condition is 0.2 A / cm ² , and the battery temperatures at this time are 40 ° C., 60 ° C., and 80 ° C. It can be seen that the porous separator shows a higher voltage value than the flow-path separator at any battery temperature, and the voltage difference increases as the battery temperature decreases. Although the water produced by the cathode reaction is likely to condense at a low temperature, the power generation performance is improved by using a porous separator having excellent water discharge properties.

  The direct methanol fuel cell according to the present invention exhibits superior output performance as compared with the conventional direct methanol fuel cell, and in particular, since it can be expected to improve the power generation performance in a low temperature region, safety is required. It is suitable for application to power sources such as notebook computers and portable music players, and external chargers for mobile phones.

The cross-sectional schematic diagram of the direct methanol type fuel cell of this invention. The cross-sectional schematic diagram of the direct methanol type fuel cell of this invention. Schematic diagram of a conventional separator (channel separator). The schematic diagram of the separator (porous separator) of the present invention. Measurement results of current density-voltage characteristics (IV characteristics). Measurement results of current density-power density characteristics. AC impedance (Cole-Cole plot) measurement results. Measurement results of battery temperature-voltage characteristics.

Explanation of symbols

100 Direct Methanol Fuel Cell 200 Membrane Electrode Assembly 210 Polymer Electrolyte Membrane 220 Electrode (Anode)
230 Electrode (Cathode)
250, 300, 400 Separator 260, 410 Porous metal 310 Flow path

Claims (2)

  A direct methanol fuel cell comprising a membrane electrode assembly and a separator installed outside the membrane electrode assembly. The direct methanol fuel cell, wherein the separator surface is a porous metal body.

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