JP2002208419A - Operation method of direct methanol fuel cell and direct methanol fuel cell suitable for it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an operation method of a direct methanol fuel cell with which the stability of oxidization electrode can be secured and which can contribute to improvement of output characteristics, and to provide a direct methanol fuel cell suitable for it. SOLUTION: The direct methanol fuel cell which uses a proton conductive solid polymer membrane as an electrolyte, methanol solution as a fuel supplied to a fuel electrode and air as an oxidizer gas to be supplied to an oxidization electrode, is operated so that a value of the supply volume per unit time of oxidizer gas divided by the cross section of a separator for the oxidization electrode through which the oxidizer gas passes (average linear velocity) may be not less than 0.5 m/s and not more than 10.0 m/s.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for operating a direct methanol fuel cell and a direct methanol fuel cell suitable for the method.

[0002]

2. Description of the Related Art In recent years, importance has been placed on measures against environmental problems and resource problems, and as one of the measures, fuel cells are being actively developed. In particular, direct methanol fuel cells that utilize fuel alcohol directly for power generation without reforming or gasification are portable and distributed power sources because they have a simple structure and are easy to reduce in size and weight. It is attracting attention.

A direct methanol fuel cell is constituted by stacking a large number of unit cells each having a joined body in which a fuel electrode and an oxidizing electrode are joined on both sides of an electrolyte membrane and sandwiching them by a separator. And a channel groove through which the fuel supplied to the fuel cell and the oxidant gas supplied to the oxidation electrode flow.

In the direct methanol fuel cell, when a liquid fuel is supplied to the fuel electrode, carbon dioxide gas is generated by an electrode reaction, and when air as an oxidant is supplied to the oxidizing electrode, water is generated by the electrode reaction. It is known that liquid fuel that has passed through the electrolyte membrane from the fuel electrode side is mixed into the fuel cell.

[0005] The flow channel of the separator discharges the carbon dioxide gas generated at the fuel electrode together with the liquid fuel, and the water generated at the oxidizing electrode and the liquid fuel permeated through the electrolyte membrane together with the oxidizing gas out of the fuel cell. It also plays a role.

While the electrical characteristics of the above-described fuel cell depend on operating conditions such as operating temperature and fuel concentration, if the product stays in the flow channel of the separator, it greatly decreases.
It can be said that whether or not the separator can uniformly supply the liquid fuel or the oxidizing gas to the reaction interface between the fuel electrode and the oxidizing electrode affects the characteristics of the fuel cell. In particular, on the oxidizing electrode side of a direct methanol fuel cell, since the liquid fuel permeating the electrolyte membrane from the fuel electrode side mixes with water generated by the electrode reaction, the structure of the oxidizing electrode side separator and the oxidizing gas Whether the removal of water and liquid fuel is smoothly carried out affects the electrical characteristics of the fuel cell.

[0007] With respect to such a channel groove of the separator on the oxidation electrode side, there is one described in Japanese Patent Application Laid-Open No. 12-90947.

That is, in the above-mentioned Japanese Patent Application Laid-Open No. 12-90947, an oxidizing gas flow path 60 is formed in the second separator 16 located at the cathode 22.
In this case, the path from the inlet holes 34a and 34b to the outlet hole 38 is meandered so that the flow rate of the oxidizing gas flowing through the hole increases.

[0009]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Laid-Open No. 12-90 is disclosed.
No. 947, in which the path from the inlet holes 34a, 34b to the outlet hole 38 is meandering, when the supply amount of the oxidizing gas is reduced, the flow rate of the oxidizing gas in the flow path 60 is reduced. There is a problem that the fuel cell is insufficient and stagnation occurs, and the characteristics of the fuel cell are significantly reduced.

[0010]

In order to solve the above-mentioned problems, the invention according to claim 1 uses a proton conductive solid polymer membrane as an electrolyte, uses a methanol aqueous solution as a fuel to be supplied to a fuel electrode, and uses a methanol aqueous solution as a fuel. In a direct methanol fuel cell using air as the oxidizing gas supplied to the fuel cell, the value obtained by dividing the supply amount of the oxidizing gas per unit time by the sectional area of the oxidizing electrode separator (average linear velocity) is 0. .5m / s or more,
An operation method of a direct methanol fuel cell, wherein the operation is performed at 10.0 m / s or less.

That is, according to the first aspect of the present invention, when the average linear velocity of the oxidizing gas flowing through the oxidizing electrode separator increases, the ability to discharge water generated at the oxidizing electrode and liquid fuel permeated through the electrolyte membrane increases. That is, it has been found that the water and the liquid fuel, which are present so as to cover the surface of the oxidation electrode, are removed, thereby improving the characteristics of the fuel cell.

The invention according to claim 2 uses a proton conductive solid polymer membrane for the electrolyte, uses an aqueous methanol solution for the fuel supplied to the fuel electrode, and uses air for the oxidant gas supplied to the oxidation electrode. In the direct methanol fuel cell, the value (average linear velocity) obtained by dividing the supply amount of the oxidizing gas per unit time by the cross-sectional area of the oxidation electrode separator through which the oxidizing gas flows is 2.
An operation method of a direct methanol fuel cell, wherein the operation is performed so as to be 0 m / s or more and 6.0 m / s or less.

[0013] That is, according to the invention of claim 2, the fuel cell has the best characteristics, and the average line of the oxidizing gas which can discharge the water generated at the oxidizing electrode and the liquid fuel permeated through the electrolyte membrane most efficiently. Due to finding speed.

The invention according to claim 3 uses a proton conductive solid polymer membrane for the electrolyte, uses an aqueous methanol solution for the fuel supplied to the fuel electrode, and uses air for the oxidant gas supplied to the oxidation electrode. In the direct methanol fuel cell, the value (average linear velocity) obtained by dividing the supply amount of the oxidizing gas per unit time by the cross-sectional area of the oxidation electrode separator through which the gas flows is 0.
An operation method of a direct methanol fuel cell, wherein the operation is performed so as to be 5 m / s or more and 0.8 m / s or less.

That is, according to the third aspect of the present invention, the ability of the separator for an oxidizing electrode through which an oxidizing gas flows to discharge water generated at the oxidizing electrode and liquid fuel permeated through the electrolyte membrane depends on the shape of the separator. Rather, it depends on the average linear velocity of the oxidizing gas.

The invention according to claim 4 uses a proton conductive solid polymer membrane for the electrolyte, uses an aqueous methanol solution for the fuel supplied to the fuel electrode, and uses air for the oxidant gas supplied to the oxidation electrode. In a direct methanol fuel cell, the width of one channel groove of the separator for the oxidation electrode through which the oxidizing gas supplied to the oxidation electrode flows is 0.5 mm or more,
It is a direct methanol fuel cell characterized by being 1.2 mm or less.

That is, the invention of claim 4 is based on the finding that the pressure loss of the oxidizing gas is determined by the flow channel of the oxidizing electrode separator through which the oxidizing gas flows.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on its embodiments.

The following evaluation tests were conducted to confirm the features of the operation method of the direct methanol fuel cell according to the embodiment of the present invention.

(Evaluation Test 1) The cross-sectional area of one channel groove is 1
mm ² (1 mm × 1 mm), and the shape is as shown in FIG.
An oxidation electrode separator (D) was prepared. FIG. 1
FIG. 1A shows a structure in which 31 flow grooves are arranged in parallel, and FIG. 1B shows a structure in which four flow grooves meander, and FIG. FIG. 1D shows a structure in which three flow grooves are meandering, and FIG. 1D shows a structure in which two flow grooves are meandering. Is 126 mm, that of FIG. 1B is 614 mm, that of FIG. 1C is 735 mm, and that of FIG.
The cross-sectional area of each channel is 31 mm ² in FIG. 1 (A), 4 mm ² in FIG. 1 (B), and FIG.
(C) 3 mm ² , FIG. 1 (D) 2 mm ² . In order to measure the amount of water and methanol removed by the flow of air, the filter paper impregnated with 2 g of a 1 mol / L aqueous methanol solution at a temperature of 80 ° C. While the air flow was changed for 60 seconds while changing the flow rate between the material and the end plate, the amount of removal was investigated, and the results are shown in FIG.

FIG. 2 shows that the removal amount of water / methanol increases as the flow rate of air increases.

The result of FIG. 2 is plotted again as a value (average linear velocity) obtained by dividing the supply amount of air by the sectional area (number of parallel passages × cross-sectional area of passage) of the oxidizing electrode separator through which the air flows. Is shown in FIG.

FIG. 3 shows that if the average linear velocity is 0.5 m / s or more, the removal amount of water / methanol can be made substantially constant or more.

(Evaluation Test 2) Air mixed with 2 cm ^{3 of} water per minute was flowed at a flow rate of 1.5 liter / minute through the separator for an oxidizing electrode shown in FIGS. 1A to 1D. The relationship between the structure and the pressure loss was investigated by measuring the pressure difference, and the results are shown in FIG.

FIG. 4 shows that the pressure difference increases as the flow rate of air increases. Increasing the pressure difference means that the energy consumed to operate pumps for supplying air etc. increases, and from an overall efficiency point of view, it is an unfavorable way to operate a direct methanol fuel cell. It can be said that

(Evaluation Test 3) Nafion 11 was used as the electrolyte.
No. 7 was prepared by applying a platinum-ruthenium / carbon catalyst to carbon paper for the fuel electrode and a platinum / carbon catalyst applied to carbon paper for the oxidation electrode, and these were joined by hot pressing to form an electrolyte. An electrode assembly was obtained. This electrolyte-electrode assembly is obtained by combining a graphite separator as shown in FIGS. 1A to 1D made of graphite and a fuel electrode separator as shown in FIG. 1C made of graphite. 36cm effective electrode area
⁽²⁾ A direct methanol fuel cell was manufactured, and at a temperature of 90 ° C., a 1 mol / liter aqueous methanol solution was supplied to the fuel electrode at 6 cm ³ / min, and air was supplied to the oxidation electrode at 3 liter / min. The battery voltage and the output density were investigated by changing the values of. And the results are shown in FIG.

From FIG. 5, it can be seen that the battery voltage and output density of the structures of FIGS. 1 (B) to 1 (D) are almost the same when the air velocity is constant.

FIG. 5 shows that the current density was 200 mA / c.
For the case of m ² , FIG. 6 shows a plot of the average linear velocity of air as a parameter, the addition of water / methanol removal to the battery voltage, and re-plotting.

FIG. 6 shows that the change in the battery voltage and the removal amount of water / methanol almost coincide with each other.

From the evaluation tests 1 to 3 described above, the average linear velocity of the air as the oxidizing gas supplied to the oxidizing electrode separator is determined by the pressure loss and the obtained battery voltage within a range that does not complicate the structure of the flow channel. 0.5 m / s or more in consideration of
m / s or less, and more preferably, 2.0 m / s from which the battery characteristics are good in view of the amount of water and methanol removed.
s or more and 6.0 m / s or less.

(Evaluation Test 4) One cross-sectional area is 1 mm
² 7 with 30 present a flow grooves is (1 mm × 1 mm)
Air as an oxidizing gas is applied to the separator for an oxidation electrode of 9.0 cm ³ / s,
5.0cm ³ /s,24.0cm ³ /s,30.0cm ³
/ S, and their average linear velocities are 0.3 m / s,
The battery was operated at 0.5 m / s, 0.8 m / s, and 1.0 m / s, and the battery voltage (mV) and the output per unit cross-sectional area (output density) (mW / cm ² ) were investigated. FIG. 8 shows the results.

FIG. 8 shows that when the operation was performed so that the average linear velocity was 0.5 m / s or more, both the battery voltage and the output density were good, and the average linear velocity was 0.5 m / s. At 0.3 m / s, which is smaller than s, the battery voltage and the power density decrease as the output current density increases,
It can be seen that when the average linear velocity is 1.0 m / s, which is larger than 0.8 m / s, the battery voltage and the output density hardly change. From this, the supply amount of the oxidizing gas per unit time was divided by the cross-sectional area of the oxidizing electrode separator through which the oxidizing gas flowed so that the average linear velocity became 0.5 m / s or more and 0.8 m / s or less. It can be said that it is better to set the value. In other words, the ability to discharge the water generated at the oxidizing electrode and the liquid fuel that has passed through the electrolyte membrane depends not on the shape of the separator but on the average linear velocity of the oxidizing gas.

(Evaluation Test 5) One cross-sectional area is 1 mm
^{2 to a} separator for an oxidation electrode having three (1 mm × 1 mm) flow grooves as shown in FIG. 9 and a separator for a fuel cell having a fuel electrode separator having the same shape as that of FIG.
0.9 cm ³ / s of air as oxidant gas, 1.5 c
supplied in ^{m 3 /s,2.4cm 3 /s,3.0cm 3 / s} , the average linear velocity, each 0.3 m / s, 0.5 m /
s, 0.8m / s, driving to 1.0m / s,
The battery voltage (mV) and the output per unit sectional area (output density) (mW / cm ² ) were investigated, and the results are shown in FIG.

From FIG. 10, it can be seen that when the operation was performed so that the average linear velocity was 0.5 m / s or more, both the battery voltage and the output density were good results, and the average linear velocity was 0.5 m / s. At 0.3 m / s less than s, the battery voltage and power density decrease with increasing output current density, and the average linear velocity is 1.0 m / s greater than 0.8 m / s.
, It can be seen that the battery voltage and the output density hardly change. From this, the average linear velocity is 0.5 m / s
As described above, it can be said that a value obtained by dividing the supply amount of the oxidizing gas per unit time by the cross-sectional area of the oxidizing electrode separator through which the oxidizing gas flows is 0.8 m / s or less.

In the above-mentioned evaluation test 5, the same test was carried out for the case where the number of the flow channel grooves was four and the case where the number of the flow channel grooves was two, but the tendency was almost the same.

(Evaluation Test 6) One cross-sectional area is 1 mm
² , the width of the channel groove is 0.5 mm, 0.8 mm, 1.2 m
11 (a), 11 (b), and 11 (c), and an oxidant gas as an oxidant gas in an oxidant electrode separator of a fuel cell including the oxidant electrode separator as shown in FIGS. Air was supplied at 16.7 cm ³ / s, and the average linear velocities were 1.52 m / s, 0.70 m / s and 0.3, respectively.
The operation was performed at 9 m / s, and the battery voltage (mV) and the output per unit sectional area (output density) (mW / cm ² ) were investigated. The results are shown in FIG.

FIG. 12 shows that the width of one channel groove is 0.5 m.
m, the battery voltage and the power density decrease with an increase in the output current density, and if it is 1.2 mm, the battery voltage and the power density tend to be lower than when it is 0.8 mm. You can see that there is. From the viewpoint of the average linear velocity, it can be said that the best result is obtained when the average linear velocity is 0.70 m / s, and it is also understood that the result matches the results of the evaluation tests 1 and 2 described above. In other words, the ability to discharge the water generated at the oxidizing electrode and the liquid fuel that has passed through the electrolyte membrane should preferably have an average linear velocity in the above-described range, and further reduce the pressure loss due to the flow of the oxidizing gas. That is, it is preferable that the width of the flow channel groove be good.

[0038]

As described above, the operation method of the direct methanol fuel cell of the present invention and the direct methanol fuel cell suitable for the method can efficiently supply the fuel and the oxidant, and A fuel cell that can prevent stagnation on the oxidized electrode side due to excessive gas supply, secure the stability of the electrode surface, and contribute to improvement in output performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a view showing an oxidizing electrode separator used in an evaluation test for supporting an operation method of a direct methanol fuel cell according to an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the removal amount of water / methanol and the flow rate of air.

FIG. 3 is a diagram in which the result of FIG. 2 is re-plotted using the average linear velocity of air as a parameter.

FIG. 4 is a view showing a result of an examination of a relationship between a structure of a flow path of an oxidation electrode separator and a loss pressure by measuring a pressure difference.

FIG. 5 is a diagram illustrating an investigation of a cell voltage and an output density according to an operation method of a direct methanol fuel cell according to an embodiment of the present invention.

FIG. 6 is a diagram in which the results of FIG. 5 are plotted again with the average linear velocity of air as a parameter and the amount of water / methanol removed added to the battery voltage.

FIG. 7 is a plan view of an oxidation electrode separator provided with 30 flow channel grooves, which was used in Evaluation Test 4.

FIG. 8 is a diagram showing the results of evaluation test 4.

FIG. 9 is a plan view of an oxidation electrode separator provided with three flow channel grooves and subjected to an evaluation test 5.

FIG. 10 is a diagram showing the results of evaluation test 5.

FIG. 11 shows a flow path groove having a width of 0.5 m, which was subjected to evaluation test 6.
It is a top view of the separator for oxidation electrodes which set m, 0.8 mm, and 1.2 mm.

FIG. 12 is a diagram showing the results of evaluation test 6.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Daisuke Shimizu 2-3-1, Kosobe-cho, Takatsuki-shi, Osaka F-term in Yuasa Corporation (reference) 5H026 AA08 CC03 CX05 HH03 5H027 AA08 MM03

Claims (4)

[Claims] 1. A proton conductive solid polymer membrane is used as an electrolyte, and a methanol aqueous solution is used as a fuel to be supplied to a fuel electrode.
In a direct methanol fuel cell using air as the oxidizing gas supplied to the oxidizing electrode, the value obtained by dividing the amount of oxidizing gas supplied per unit time by the cross-sectional area of the oxidizing electrode separator flowing through the cell (average linear velocity) Is 0.5 m / s or more and 10.0 m / s
A method for operating a direct methanol fuel cell, characterized by operating as follows. 2. A proton conductive solid polymer membrane is used as an electrolyte, and a methanol aqueous solution is used as a fuel to be supplied to a fuel electrode.
In a direct methanol fuel cell using air as the oxidizing gas supplied to the oxidizing electrode, the value obtained by dividing the amount of oxidizing gas supplied per unit time by the cross-sectional area of the oxidizing electrode separator flowing through the cell (average linear velocity) The method for operating a direct methanol fuel cell, wherein the fuel cell is operated so that the pressure is 2.0 m / s or more and 6.0 m / s or less. (3) using a proton conductive solid polymer membrane as an electrolyte, and using an aqueous methanol solution as a fuel to be supplied to a fuel electrode;
In a direct methanol fuel cell using air as the oxidizing gas supplied to the oxidizing electrode, the value obtained by dividing the amount of oxidizing gas supplied per unit time by the cross-sectional area of the oxidizing electrode separator flowing through the cell (average linear velocity) The method for operating a direct methanol fuel cell, wherein the fuel cell is operated such that the pressure is 0.5 m / s or more and 0.8 m / s or less. 4. Use of a proton conductive solid polymer membrane as an electrolyte, and use of an aqueous methanol solution as a fuel to be supplied to a fuel electrode,
In a direct methanol fuel cell using air as the oxidizing gas supplied to the oxidizing electrode, the width of one channel groove of the separator for the oxidizing electrode through which the oxidizing gas supplied to the oxidizing electrode flows is 0.5 mm or more, A direct methanol fuel cell having a diameter of 1.2 mm or less.