JP2007323981A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct methanol type fuel cell in which power generation characteristics are improved and catalyst poisoning of a fuel electrode by carbon monoxide generated in oxidation reaction of methanol is suppressed. <P>SOLUTION: In the direct methanol type fuel cell in which electromotive force is obtained by electrochemical reaction by arranging a fuel electrode 3 and an air electrode 4 on both sides of a solid polymer electrolyte membrane, at least any one of the electrode of the air electrode 4 and the fuel electrode 3 has a catalyst, and an oxidizing material is supplied to the air electrode and a mixed solution 51 in which ozone is mixed in methanol as a fuel material is supplied to the fuel electrode 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a direct methanol fuel cell that obtains an electromotive force by a chemical reaction.

  The membrane electrode assembly 1 of this type of direct methanol fuel cell (DMFC) is configured as shown in FIG. A membrane electrode assembly 1 of a fuel cell has a fuel electrode 3 and an air electrode 4 formed on both sides of a solid polymer electrolyte membrane 2 and supplies a methanol aqueous solution 7 to the fuel electrode 3 on one side of the solid polymer electrolyte membrane 2. The air 8 is supplied to the air electrode 4 on the other side of the solid polymer electrolyte membrane 2.

  The power generation principle of the direct methanol fuel cell will be described below.

  When the aqueous methanol solution 7 is supplied to the fuel electrode 3 of the membrane electrode assembly 1, a chemical reaction proceeds in the electrode catalyst layer of the fuel electrode 3, and carbon dioxide, protons (H +), and electrons are generated.

CH3OH + H2O-> CO2 + 6H ++ 6e- (1)
Proton (H +) passes through the solid polymer electrolyte membrane 2, and electrons pass through an external circuit, and a chemical reaction proceeds between proton (H +), electrons, and oxygen contained in the air 8 supplied to the air electrode 4. Then, water is generated in the electrode catalyst layer of the air electrode 4.

3 / 2O2 + 6H + + 6e− → 3H2O (2)
The electrode catalyst layer of the fuel electrode 3 and the air electrode 4 has a structure in which catalyst-supporting carbon in which 2-3 nm catalyst particles 10 are supported on 20 to 40 nm carbon particles 9 is fixed to the solid polymer electrolyte membrane 2 with a polymer electrolyte. is there.

  In the fuel electrode 3, as shown by the chemical formula (1), carbon dioxide, protons and electrons are generated from methanol and water. This reaction is a multistage reaction, and produces carbon monoxide as a reaction intermediate product accompanying power generation. It is known that the generated carbon monoxide is strongly adsorbed on platinum as an electrode catalyst to cause poisoning of the catalyst, so that the reaction activity is greatly reduced. As a catalyst poison countermeasure for this electrode catalyst, a platinum (Pt) -ruthenium (Ru) binary catalyst material is generally used as the catalyst material for the fuel electrode of a direct methanol fuel cell. However, even when a platinum-ruthenium binary catalyst is used, energy is used when carbon monoxide strongly bonded to the platinum surface is desorbed from the platinum surface, and the overvoltage corresponding to this energy loss is large. Therefore, the electromotive force that can be taken out as a direct methanol fuel cell becomes smaller than the voltage value of 1.21 (V), which is a thermodynamic theoretical value, and there is a problem that it is largely separated from the theoretical value.

  As a method of removing a substance that poisons a catalyst in a conventional electrode, an electromotive force is obtained by electrochemically reacting a fuel substance and an oxidizing substance via an electrolyte disposed between a fuel electrode and an air electrode. A fuel cell in which at least one of the fuel electrode and the air electrode includes a catalyst; and a substance that poisons the catalyst to a fuel material or an oxidizing material supplied to the fuel electrode or the air electrode including the catalyst; Shown is a fuel cell characterized in that it is mixed with a poison remover that reacts to remove the substance. Further, there is shown a fuel cell device characterized in that the fuel substance is methanol, the catalyst contains platinum, and the poisoning substance removing agent is an oxidizing agent that releases oxygen atoms or oxygen ions. Yes. Furthermore, a fuel cell device is shown in which the poisoning substance removing agent is carbonic acid (see, for example, Patent Document 1).

In addition, as a means for oxidizing the CO produced at the conventional fuel electrode and converting it into CO2 harmless to the catalyst, the oxidizer weight selected from hydrogen peroxide, sulfur dioxide, sulfur trioxide, nitrogen dioxide, manganese peroxide, etc. A fuel cell operating method is shown in which a part is supplied in a liquid state to a fuel electrode of the fuel cell together with 100 to 1000 parts by weight of fuel (see, for example, Patent Document 2).
JP 2000-21426 A JP 2002-343403 A

  However, in the conventional configuration, since the oxidizing power of carbonic acid and hydrogen peroxide is weak, a sufficient effect cannot be obtained for the oxidation of carbon monoxide that is poisoned by the catalyst. It had the problem of not being able to contribute.

  An object of the present invention is to solve the conventional problems and to provide a fuel cell capable of suppressing catalyst poisoning of a fuel electrode and improving power generation characteristics.

  In order to solve the conventional problems, the fuel cell of the present invention is a direct methanol fuel cell in which a fuel electrode and an air electrode are disposed on both sides of a solid polymer electrolyte membrane, and an electromotive force is obtained by electrochemical reaction. A catalyst is provided in at least one of the air electrode and the fuel electrode, an oxidizing material is supplied to the air electrode, and a mixed solution in which ozone is mixed with methanol as a fuel material is supplied to the fuel electrode. This is characterized in that the power generation characteristics of the direct methanol fuel cell are improved.

  According to the fuel cell of the present invention, the oxidation reaction of the fuel electrode can be promoted by the oxidizing power of ozone, and the power generation characteristics of the direct methanol fuel cell can be improved.

  Further, according to the fuel cell of the present invention, by containing carbon dioxide as an ozone decomposition inhibitor, the decomposition of ozone can be suppressed and the oxidizing power of ozone can be maintained.

  Further, according to the configuration of circulating the carbon dioxide of the fuel cell of the present invention, it is possible to stably supply the carbon dioxide that is an ozone decomposition inhibitor, and further to reduce the amount of carbon dioxide discharged from the fuel cell. Can be reduced.

  Furthermore, according to the fuel cell operation method of the present invention, the fuel cell is coupled with platinum without stopping the fuel cell operation by the operation method of supplying the methanol aqueous solution containing ozone to the fuel electrode while generating power. Carbon monoxide can be easily removed.

  Embodiments of a fuel cell according to the present invention will be described below in detail with reference to the drawings.

  FIG. 1 shows a configuration diagram of a fuel cell in Example 1 of the present invention.

  FIG. 2 shows a flowchart of a method for preparing a mixed solution in Example 1 of the present invention.

  FIG. 3 shows a time-voltage characteristic diagram of an experimental example in Example 1 of the present invention.

  FIG. 4 is a voltage characteristic diagram of the concentration range of the experimental example in Example 1 of the present invention.

  FIG. 5 shows a configuration diagram in which a methanol aqueous solution cartridge is mounted in Example 1 of the present invention.

  In FIG. 1, a fuel electrode 3 and an air electrode 4 are arranged on both sides of a solid polymer electrolyte membrane 2, a mixed solution 51 in which ozone is mixed with a fuel substance is mixed in the fuel electrode 3, and air 8 is respectively mixed in the air electrode 4. The direct methanol fuel cell is configured to supply an electromotive force by an electrochemical reaction between the fuel electrode 3 and the air electrode 4, and the methanol aqueous solution 7 is supplied from the methanol aqueous solution cartridge 13 to the mixer 22. The ozone 21 generated by the generator 23 is supplied to the mixer 22. The aqueous methanol solution 7 and the ozone 21 are mixed in the mixer 22 to prepare a mixed solution 51, and the mixed solution 51 is supplied to the fuel electrode 3.

  In FIG. 2, the first step shows a step of supplying the methanol aqueous solution 7 of the methanol aqueous solution cartridge 13 to the mixer 22. The second step shows a step of preparing the mixed solution 51 by supplying the ozone 21 to the mixer 22 and mixing the aqueous methanol solution 7 and the ozone 21. The third step shows a step of supplying the mixed solution 51 to the fuel electrode 3. The flowchart which supplies the aqueous solution of methanol containing ozone to a fuel electrode by these three processes is shown.

  In FIG. 3, a time representing a change in voltage with the passage of time when the fuel cell is generated under the condition of using the mixed solution of the present invention (Experimental Example 1) and the conventional aqueous methanol solution (Comparative Example 1). -The graph of the experimental result of a voltage characteristic is shown. The horizontal axis indicates the passage of time, and the unit is H (hours). The vertical axis indicates the voltage change, and the unit is V (volt).

  In FIG. 4, the graph of the experimental result when making a fuel cell generate electric power on the conditions which changed the ozone concentration of the mixed solution of this invention is shown. The horizontal axis indicates four types of ozone concentrations of 0 (zero), 0.001, 0.01, and 0.1, and the unit is weight percent (% by weight). The vertical axis represents voltage, and the unit is V (volt).

  In FIG. 5, the same components as those in FIG. In advance, the methanol aqueous solution cartridge 14 is mixed with the ozone 21 generated by the ozone generator 23 in addition to the methanol aqueous solution 7 to prepare the mixed solution 51. When starting the power generation of the fuel cell, the methanol aqueous solution cartridge 14 is connected to the fuel electrode supply port of the fuel cell, and the mixed solution 51 in the methanol aqueous solution cartridge 14 is supplied to the fuel electrode 3 of the fuel cell. ing.

  About the structure of the above direct methanol fuel cells and the preparation method of a mixed solution, the operation | movement and an effect | action are demonstrated below.

Ozone has a strong oxidizing power, the chemical reaction formula when the oxidation reaction of ozone proceeds,
O3 + 2H ++ 2e-> O2 + H2O (3)
Indicated by The oxidation-reduction potential of this oxidation reaction is
E ○ = + 2.07V vs. SHE (4)
It is. SHE is a standard hydrogen electrode.

  A solution in which ozone having such oxidizing power is dissolved in water is called ozone water. It is known that ozone water reacts with hydroxide ions generated by the dissociation of water molecules to generate reactive oxygen species (ROS = Reactive Oxygen Species) such as hydroxy radicals and superoxide ions, which act on various substances. It has been. As practical examples using the action of active oxygen species by ozone water, fields such as sterilization, deodorization, food storage, clothing bleaching, semiconductor washing water in fields such as water supply and sewerage, medical care and food production processes Is widely used.

  The present embodiment is characterized in that ozone is mixed in an aqueous methanol solution and a mixed solution of ozone and the aqueous methanol solution is directly supplied to the methanol fuel cell. In other words, carbon monoxide that is strongly bound to the platinum catalyst surface of the fuel electrode can be easily desorbed from the platinum without spending energy by the action of the active oxygen species generated by the ozone water. The overvoltage can be reduced by the smaller amount, and the voltage drop that can be taken out by the fuel electrode can be suppressed.

  In addition, since the product when ozone decomposes | disassembles produces | generates only water and oxygen, it cannot be overemphasized that even if ozone is supplied to a fuel cell, there is no bad influence, such as degradation by a decomposition product.

Next, the effect of the present embodiment will be specifically described with reference to FIG. FIG. 3 is a graph summarizing experimental results of voltage change with time when using the mixed solution of this example and a conventional aqueous methanol solution in a time-voltage characteristic diagram.
(Experimental example 1)
In this embodiment, operations other than supplying a mixed solution obtained by mixing ozone in a methanol aqueous solution to the fuel electrode are operated by a known fuel cell operation method.

  In Experimental Example 1, a membrane electrode assembly (manufactured by Electrochem) having a fuel electrode and an air electrode formed on both surfaces of an electrolyte membrane is used. This membrane electrode assembly has a square electrode shape of 5 cm × 5 cm.

  As the material of the electrolyte membrane, a known cation exchange resin ion exchange membrane is used. Specifically, perfluorosulfonic acid ion exchange membranes such as Nafion membrane (trademark of DuPont), Flemion membrane (trademark of Asahi Glass Co., Ltd.) and Aciplex membrane (trademark of Asahi Kasei Co., Ltd.) are used.

  As the electrode catalyst material for the fuel electrode, a fuel electrode is formed by adding a binder of an electrolyte membrane to a material in which a catalyst material is supported on conductive carbon using a metal or an alloy. Specifically, an alloy of platinum and ruthenium is desirable as a material used as a catalyst. A ternary alloy may be used. Reaction mechanisms such as “bifunctional mechanism” and “Rideal mechanism” have been proposed as the reason why the activity of the methanol oxidation reaction is increased by alloying the catalyst material of the fuel electrode.

  The fuel supplied to the fuel electrode is desirably alcohols, more preferably methanol. Needless to say, alcohols other than methanol can also be used. Further, a substance that is a gas at normal temperature and pressure, such as dimethyl ether, or a substance that becomes liquid by pressurization can be supplied to the fuel electrode.

  On the other hand, platinum is used as an electrode catalyst material for the air electrode, and an air electrode is formed by adding a binder of an electrolyte membrane to a conductive carbon supported platinum. The gas supplied to the air electrode is not necessarily limited to air, but may be a gas containing an oxidizing substance such as oxygen.

  The membrane electrode assembly is sandwiched between two carbon separators, and the two carbon separators are fixed with screws. Use a torque wrench to tighten all screws with a constant torque of 3 (N · m). This stack is installed upright in a fuel cell evaluation device (manufactured by Toyo Technica).

  A pipe for supplying the mixed solution of this embodiment is connected to the carbon separator of the fuel electrode, and a pipe for supplying air from an air cylinder (not shown) is connected to the carbon separator of the air electrode.

  The positional relationship between the electrode supply port and the discharge port will be described. In the fuel electrode, the supply port is connected to the lower part of the electrode and the discharge port is connected to the upper part of the electrode. In the air electrode, the supply port is connected to the upper part of the electrode and the discharge port is connected to the lower part of the electrode. The reason for the connection in such a vertical position is that a methanol aqueous solution or a mixed solution containing a methanol aqueous solution is supplied to the fuel electrode, so that liquid is gradually stored from the bottom of the electrode, and the methanol aqueous solution is stably fed to the electrode. This is to make it happen. On the other hand, at the air electrode, water is generated as the electrode reaction proceeds, and the generated water flows downward due to gravity, so that the generated water is quickly drained from the lower part of the electrode.

A mixed solution of 0.01% by weight of ozone and 3% by weight of methanol mixed according to this example is supplied to the fuel electrode at 0.8 ml / min. On the other hand, the supply amount of air is supplied at 1000 ml / min. As a result of voltage measurement when the fuel cell is generated at a temperature of 25 ° C., the open circuit voltage after 48 hours is 0.723 (V).
(Comparative Example 1)
Experiments were performed using a 3 wt% aqueous methanol solution (conventional aqueous methanol solution) that did not contain ozone, and all other experimental conditions were the same as in Experimental Example 1. As a result of the voltage measurement, the open circuit voltage after 48 hours is 0.681 (V).
(Experimental example 2)
The same procedure as in Experimental Example 1 is performed except that a mixed solution containing 0.001% by weight of ozone and 3% by weight of methanol is used. As a result of the voltage measurement, the open circuit voltage after 48 hours is 0.693 (V).
(Experimental example 3)
The same procedure as in Experimental Example 1 is performed except that a mixed solution containing 0.1% by weight of ozone and 3% by weight of methanol is used. As a result of the voltage measurement, the open circuit voltage after 48 hours is 0.683 (V).
(Experimental example 4)
The same procedure as in Experimental Example 1 is performed except that a mixed solution containing 1% by weight of ozone and 3% by weight of methanol is used. As a result of the voltage measurement, the open circuit voltage after 48 hours is 0.256 (V), and the voltage that can be taken out by the fuel cell is extremely low (not shown).

  FIG. 4 shows the experimental results of Experimental Examples 1 to 3 and Comparative Example 1.

  Comparing the experimental results between Experimental Example 1 and Comparative Example 1, it can be seen that the voltage increase of about 6.2% is observed under the experimental condition of this example (Experimental Example 1).

  In the fuel cell of this example, since the mixed solution supplied to the fuel electrode contains ozone, the oxidation reaction of carbon monoxide that is strongly bonded to the platinum surface is promoted. The overvoltage corresponding to the energy loss used is reduced. As a result, since the voltage that can be directly taken out from the fuel electrode of the methanol fuel cell is improved, the output characteristics of the fuel cell are improved as compared with a conventional aqueous methanol solution.

  Comparing the experimental results of FIG. 4, when the power generation voltage due to the ozone concentration is arranged in descending order, they are 0.01 wt%, 0.001 wt%, 0.1 wt%, 0 wt%, and 1 wt%. It can be seen that the most remarkable effect is observed when the ozone content in Experiment 1 is 0.01% by weight.

  From the experimental results of Experimental Example 4, when a large amount of ozone is contained in the aqueous methanol solution, the voltage that can be taken out as a fuel cell greatly decreases. This is because oxygen is generated by the decomposition of ozone, and the generated oxygen reacts at the fuel electrode, and it is understood that the effect of this example cannot be sufficiently obtained.

  From these results, there is an optimum range for the content of ozone in the aqueous methanol solution. Therefore, if the voltage when using the aqueous methanol solution that does not contain ozone is used as a reference, the effect of this embodiment is sufficiently obtained. It can be seen that the concentration of ozone for expression is in the range of 0.001 wt% or more and less than 0.1 wt%.

  As described above, in the first embodiment, the description has been given using the fuel cell having the configuration including the ozone generator and the mixer, but the configuration of the fuel cell device does not include the ozone generator and the mixer. Even if it exists, a present Example can be implemented. In other words, the ozone generated by the ozone generator is previously injected into the methanol aqueous solution in the methanol aqueous solution cartridge, and the methanol aqueous solution cartridge is attached to the fuel cell device when starting the power generation of the fuel cell. Since the first embodiment can be implemented, the operation and action will be described below.

  Generally, in a direct methanol fuel cell, a methanol aqueous solution cartridge is used as a container for storing an aqueous methanol solution. The methanol aqueous solution cartridge is configured to be separable from the fuel cell, and when the power generation of the fuel cell is started, the methanol aqueous solution cartridge is inserted into a predetermined position of the fuel cell to connect the methanol aqueous solution cartridge and the fuel cell. The methanol aqueous solution in the cartridge is supplied to the fuel cell to generate power. The fact that the present embodiment can be realized even with such a configuration will be described with reference to FIG.

  In advance, the methanol aqueous solution cartridge 14 is mixed with the ozone 21 generated by the ozone generator 23 in addition to the methanol aqueous solution 7 to prepare the mixed solution 51. When starting the power generation of the fuel cell, the methanol aqueous solution cartridge 14 is connected to the fuel electrode supply port of the fuel cell, and the mixed solution 51 in the methanol aqueous solution cartridge 14 is supplied to the fuel electrode 3 of the fuel cell. When the power generation of the fuel cell is started in this manner, the aqueous methanol solution mixed with ozone is supplied to the fuel electrode, so that the effect of this embodiment can be obtained.

  With such a configuration, this embodiment can be implemented even if the configuration of the fuel cell does not include an ozone generator or a mixer, and the direct methanol fuel cell without an ozone generator or a mixer can be used. Since the device configuration can be reduced in size and weight, it is suitable for use as a portable fuel cell.

  As described above, in Example 1, by supplying a mixed solution containing ozone in a methanol aqueous solution to the fuel electrode, the oxidation of carbon monoxide is promoted by the oxidizing power of ozone, and the catalyst coverage at the fuel electrode is increased. Poison poison can be removed. As a result, the activity of the oxidation reaction at the fuel electrode is increased, the overvoltage consumed by the oxidation reaction at the fuel electrode is reduced, and a large electromotive force can be extracted from the fuel cell. Can be improved.

  FIG. 6 shows a block diagram of a fuel cell in Example 2 of the present invention.

  FIG. 7 shows a flowchart of a method for preparing a mixed solution in Example 2 of the present invention.

  FIG. 8 is an explanatory diagram of an experimental result in Example 2 of the present invention.

  In FIG. 6, the same components as those in FIG. The mixed solution 52 is prepared by mixing the methanol aqueous solution 7 with the carbon dioxide 31 in the mixer 24, and the mixer 24 is provided with a pH meter 41 to measure the concentration of the carbon dioxide 31 in the mixed solution 52. The mixed solution 52 is supplied to the mixer 25, the ozone 21 generated by the ozone generator 23 and the mixed solution 52 are mixed to prepare the mixed solution 53, and the mixed solution 53 is supplied to the fuel electrode 3. It has become.

  In FIG. 7, the first step shows a step of supplying the methanol aqueous solution 7 of the methanol aqueous solution cartridge 13 to the mixer 24. The second step shows a step of preparing the mixed solution 52 by supplying the carbon dioxide 31 to the mixer 24 and mixing the aqueous methanol solution 7 and the carbon dioxide 31. The third step shows a step of supplying the mixed solution 52 to the mixer 25. The fourth step shows a step of preparing the mixed solution 53 by supplying the ozone 21 generated by the ozone generator 23 to the mixer 25 and mixing the mixed solution 52 and the ozone 21. The fifth step shows a step of supplying the mixed solution 53 to the fuel electrode 3. The flowchart which supplies the methanol aqueous solution containing ozone and a carbon dioxide to a fuel electrode by these five processes is shown.

  FIG. 8 shows a graph of experimental results when the fuel cell is generated under the conditions when the mixed solution of the present invention (Experimental Examples 1 and 5) and the conventional aqueous methanol solution (Comparative Example 1) are used. ing. The horizontal axis indicates the experiment name of each experiment. The vertical axis represents voltage, and the unit is V (volt).

  About the structure of the above direct methanol fuel cells and the preparation method of a mixed solution, the operation | movement and an effect | action are demonstrated below.

  Ozone is a chemically unstable substance and is known to have self-degrading properties. Therefore, in order to fully develop the effect of the present embodiment, a mixed solution supplied to the fuel electrode is mixed with a substance that suppresses decomposition of ozone. Specifically, carbon dioxide is mixed as an ozone decomposition inhibitor.

  Next, the process of mixing ozone and carbon dioxide with a methanol aqueous solution will be specifically described.

  The mixed solution 53 supplied to the fuel electrode of this embodiment is composed of an aqueous methanol solution 7, ozone 21, and carbon dioxide 31. In this mixed solution preparation method, first, the first step of supplying the aqueous methanol solution 7 to the mixer 24, and then the carbon dioxide 31 is supplied to the mixer 24 to mix the aqueous methanol solution 7 and the carbon dioxide 31. Then, the second step of preparing the mixed solution 52, the third step of supplying the mixed solution 52 to the mixer 25, and the ozone 21 generated by the ozone generator 23 are then mixed with the mixer 25. The mixed solution 52 and the ozone 21 are mixed to prepare the mixed solution 53, and then the fifth step of supplying the mixed solution 53 to the fuel electrode 3 is performed. The fuel cell is generated using the mixed solution mixed in such a manner.

  The reason why the mixed solution supplied to the fuel electrode is mixed in the above order is that the solubility of carbon dioxide is larger in methanol aqueous solution than water, and carbon dioxide, which is an ozone decomposition inhibitor, is mixed in advance before adding ozone. This is due to three reasons, that is, the reason why the ozone is a substance that is easily decomposed chemically, and the reason that ozone is added last, and this embodiment is characterized by mixing in the order of these steps. .

  Ozone supplied to the fuel cell can be stably supplied by the preparation method in which ozone and the ozone decomposition inhibitor are mixed with the methanol aqueous solution in this order. As a result, the oxidizing power of ozone contained in the methanol aqueous solution is maintained, the oxidation reaction at the fuel electrode is promoted, and the reaction efficiency of the oxidation reaction at the fuel electrode can be improved.

  In addition, since the carbon dioxide mixed as ozone decomposition suppression increases as reaction of a fuel electrode advances, it cannot be overemphasized that decomposition | disassembly of ozone becomes difficult and the effect of a present Example is maintained.

  In addition, when the mixed liquid containing ozone is acidic, that is, when the pH is less than 7, there is an action of suppressing decomposition of ozone. Generally, water in which carbon dioxide is dissolved is called carbonated water, but the pH of carbonated water is less than 7. The present embodiment is characterized in that carbon dioxide is mixed with a mixed liquid containing ozone, and the mixed solution in which carbon dioxide is mixed exhibits acidity, and therefore the pH of the mixed solution in which carbon dioxide is mixed is measured. By means, the concentration of carbon dioxide can be known. In this embodiment, since the pH meter 41 is attached to the mixer for mixing the aqueous methanol solution and carbon dioxide, the concentration of carbon dioxide in the mixed solution can be known. Can be confirmed.

  As a specific pH control method, the pH value of the pH meter 41 is set to 5.5 in advance, and when carbon dioxide is mixed with an aqueous methanol solution, the pH gradually decreases from 7, so the pH is 5 If the supply of carbon dioxide is stopped when .5 is indicated, a mixed solution in which carbon dioxide having a predetermined concentration is mixed can be prepared.

  In addition, although the structure provided with the pH meter is shown in FIG. 6, it cannot be overemphasized that it is not always necessary to provide the pH meter in the second embodiment. It is also possible to prepare the mixed solution 52 by mixing predetermined carbon dioxide.

Next, the effect of the present invention will be specifically described with reference to FIG. FIG. 8 shows the results of an experiment in which a fuel cell was generated using the mixed solution of the present invention and a conventional aqueous methanol solution.
(Experimental example 5)
A membrane / electrode assembly (manufactured by Electrochem) having electrodes formed on both sides of a Nafion 117 membrane (trademark of DuPont) is used. This membrane electrode assembly has a square electrode shape of 5 cm × 5 cm. The membrane / electrode assembly is sandwiched between two carbon separators, and the two carbon separators are screwed and fixed to form a stack. This stack is installed in a fuel cell evaluation device (manufactured by Toyo Technica) in an upright state. A pipe for supplying the mixed solution of this embodiment is connected to the fuel electrode, and a pipe for supplying air from an air cylinder (not shown) is connected to the air electrode. The positional relationship between the supply port and the discharge port of the electrode is such that, at the fuel electrode, the supply port is connected to the lower part of the electrode and the discharge port is connected to the upper part of the electrode. Connect to the bottom of the electrode.

  A mixed solution of 0.01% by weight of ozone, 0.1% by weight of carbon dioxide and 3% by weight of methanol prepared by the mixing procedure of the process of this example is supplied to the fuel electrode at 0.8 ml / min. As a method of mixing carbon dioxide, carbon dioxide can be mixed into an aqueous methanol solution by a method of bubbling carbon dioxide in an aqueous methanol solution or a method of absorbing carbon dioxide in the atmosphere. As a method of mixing ozone, ozone can be mixed with a methanol aqueous solution containing carbon dioxide by a method of bubbling ozone in a methanol aqueous solution containing carbon dioxide. Moreover, the supply amount of air is supplied at 1000 ml / min. As a result of voltage measurement when the fuel cell is generated at a temperature of 25 ° C., the open circuit voltage after 48 hours is 0.741 (V).

  In FIG. 8, when the result of Experimental Example 5 is compared with the result of Experimental Example 1, a voltage increase of about 2.5% is observed under the experimental condition of this Example (Experimental Example 5). In addition, a voltage increase of about 8.8% is observed as compared with the result obtained when the conventional aqueous methanol solution is used (conventional example 1).

  From these experimental results, in the fuel cell of this example, the mixed solution supplied to the fuel electrode contains not only ozone but also carbon dioxide, so that the output characteristics of the fuel cell are improved as compared with the conventional aqueous methanol solution. This indicates that the oxidation of carbon monoxide by ozone is promoted and the activity of the platinum catalyst is improved.

  As described above, in the second embodiment, by supplying a mixed solution containing ozone and carbon dioxide in a methanol aqueous solution to the fuel electrode, it is possible to suppress the decomposition of ozone, and to oxidize by the oxidizing power of ozone. The oxidation of the carbon can be promoted, and the poisoning substance of the catalyst poisoning at the fuel electrode can be removed. As a result, the oxidizing power of ozone contained in the methanol aqueous solution is maintained. This increases the activity of the oxidation reaction at the fuel electrode, reduces the overvoltage consumed by the oxidation reaction at the fuel electrode, and can extract a large electromotive force from the fuel cell. Characteristics can be improved. Furthermore, carbon dioxide to be mixed as an ozone decomposition inhibitor is very advantageous for the present embodiment due to carbon dioxide produced at the fuel electrode, and is therefore suitable as an aqueous methanol solution supplied directly to a methanol fuel cell.

  FIG. 9 shows a configuration diagram of a fuel cell in Example 3 of the present invention.

  9, the same components as those in FIG. 6 are denoted by the same reference numerals, and description thereof is omitted. The carbon dioxide 31 is configured to collect and reuse the exhaust material 11 of the fuel electrode 3. A gas-liquid separator 32 is used to separate the carbon dioxide 31, which is a gaseous component, from the exhaust material 11 of the fuel electrode 3, and the separated carbon dioxide 31 is supplied to the mixer 24.

  The operation and action of the configuration of the direct methanol fuel cell as described above will be described below.

  In the fuel electrode 3 of the direct methanol fuel cell, carbon dioxide is generated by the progress of the reaction represented by the chemical formula (1). The discharge material 11 of the fuel electrode is a gas / liquid mixture containing the generated carbon dioxide and an unreacted aqueous methanol solution, and the gas component is carbon dioxide 31. The discharged substance 11 is separated into a gas component and a liquid component 33 by using a gas-liquid separator, and the carbon dioxide 31 which is a gas component is recovered and reused and mixed with the aqueous methanol solution 7.

  As a specific example of a gas-liquid separator, as described in Japanese Patent Application Laid-Open No. 2005-238217, a liquid extraction material that restricts the passage of gas by allowing a liquid to pass therethrough and a passage of liquid that restricts the passage of gas by passing a gas. It is preferable to use a method in which a gas-liquid mixture is fed into a gas-liquid separation chamber composed of a gas extraction material that performs gas-liquid separation.

  As described above, in Example 3, since carbon dioxide is recovered and used from the emissions generated by the power generation of the fuel cell, the ozone decomposition inhibitor carbon dioxide can be stably supplied. The oxidative power it has can be sustained. Oxidizing power of ozone promotes the oxidation of carbon monoxide, and the poisoning substance of catalyst poisoning at the fuel electrode can be removed. As a result, the activity of the oxidation reaction at the fuel electrode is increased, the overvoltage consumed by the oxidation reaction at the fuel electrode is reduced, and a large electromotive force can be extracted from the fuel cell. Can be improved.

  In addition, carbon dioxide to be mixed for suppressing ozone decomposition works very favorably in the present embodiment due to carbon dioxide produced at the fuel electrode, and is therefore optimal as an aqueous methanol solution supplied directly to a methanol fuel cell.

  Furthermore, the configuration of this embodiment has the advantage that the amount of carbon dioxide released from the fuel electrode into the atmosphere as the fuel cell generates power can be reduced, thereby contributing to the prevention of global warming.

  FIG. 10 shows a configuration diagram of a fuel cell in Example 4 of the present invention.

  FIG. 11 shows a flowchart of a method of operating a fuel cell in Example 4 of the present invention.

  FIG. 12 is an explanatory diagram of an experimental result in Example 4 of the present invention.

  10, the same components as those in FIG. 6 are denoted by the same reference numerals, and description thereof is omitted. A valve 27 is installed in a pipe for mixing carbon dioxide with the mixer 24, and a valve 26 is installed between the ozone generator 23 and the mixer 25.

  In FIG. 11, the first step is a normal operation step in which the valve 26 and the valve 27 are closed and the aqueous methanol solution 7 is supplied to the fuel electrode 3. The second step is a step of detecting that the electromotive force of the fuel cell is lower than a predetermined set voltage. The third step is a step of supplying the mixed solution 53 of the aqueous methanol solution 7, the ozone 21, and the carbon dioxide 31 to the fuel electrode 3 by opening the valve 27 and the valve 26. The fourth step is a step of closing the valve 26 and the valve 27 and returning to the normal operation of supplying the aqueous methanol solution 7 to the fuel electrode 3. The operation method of supplying a methanol aqueous solution containing ozone to the fuel electrode while generating power from the fuel cell through these four steps is shown.

  FIG. 12 shows a graph of experimental results when the fuel cell is generated under the conditions when the mixed solution of the present invention (Experimental Examples 1 and 6) and the conventional aqueous methanol solution (Comparative Example 1) are used. ing. The horizontal axis indicates the experiment name of each experiment. The vertical axis represents voltage, and the unit is V (volt).

  The operation and action of the direct methanol fuel cell operation method as described above will be described below.

  When a direct methanol fuel cell is allowed to generate power for a long time, there is a problem that the electromotive force gradually decreases due to catalyst poisoning of the catalyst surface with carbon monoxide. The present embodiment has an excellent feature that the catalyst poisoning of the fuel electrode can be removed without stopping the power generation of the fuel cell by the operation method of supplying ozone and the ozonolysis inhibiting substance.

  A method for operating the fuel cell will be specifically described.

  As a normal operation of the direct methanol fuel cell, the valve 26 and the valve 27 are closed, and the aqueous methanol solution 7 is supplied to the fuel electrode 3 as a fuel material. However, when the fuel cell is continuously operated by such an operation method, the voltage gradually decreases due to catalyst poisoning even in the case of a catalyst material using a platinum ruthenium binary alloy. Therefore, a predetermined electromotive force value is set in advance, and operation conditions are switched as shown in this embodiment when the electromotive force falls below the set voltage. In the operation method of this embodiment, the valve 26 and the valve 27 are opened, and the mixed solution 53 in which the ozone 21 and the carbon dioxide 31 are mixed is supplied to the fuel electrode 3 of the fuel cell. As a result, the catalyst poisoning of the platinum catalyst can be easily removed by the oxidizing power of the ozone 21. In addition, while the ozone 21 is supplied to the fuel electrode 3, the power generation voltage of the fuel cell hardly decreases. After the catalyst poisoning has been removed, the valve 26 and the valve 27 are closed and the methanol aqueous solution 7 is supplied to the fuel electrode 3 to return to the normal operation.

Next, the effect of the present invention will be specifically described with reference to FIG. FIG. 12 shows the results of an experiment in which the fuel cell is generated by generating power with the operation method of the present invention and the conventional operation method.
(Experimental example 6)
A membrane / electrode assembly (manufactured by Electrochem) having electrodes formed on both sides of a Nafion 117 membrane (trademark of DuPont) is used. This membrane electrode assembly has a square electrode shape of 5 cm × 5 cm. The membrane / electrode assembly is sandwiched between two carbon separators, and the two carbon separators are screwed and fixed to form a stack. This stack is installed in a fuel cell evaluation device (manufactured by Toyo Technica) in an upright state. A pipe for supplying the mixed solution of this embodiment is connected to the fuel electrode, and a pipe for supplying air from an air cylinder (not shown) is connected to the air electrode. The positional relationship between the supply port and the discharge port of the electrode is such that, at the fuel electrode, the supply port is connected to the lower part of the electrode and the discharge port is connected to the upper part of the electrode. Connect to the bottom of the electrode.

  As a normal operation, an aqueous methanol solution is supplied to the fuel electrode at 0.8 ml / min. Further, air is supplied at 1000 ml / min, the temperature of the fuel cell is set to 25 ° C., and the fuel cell is continuously operated.

  When a direct methanol fuel cell is operated continuously for a long time, the catalyst surface of the fuel electrode is poisoned and the generated voltage gradually decreases. Therefore, a predetermined switching voltage is set in advance, and the generated voltage is When the voltage drops below the switching voltage, the operation method of this embodiment is switched. Specifically, if the direct methanol fuel cell has an electromotive force of 0.70 (V), the operation switching voltage is set to 0.65 (V) in advance. When this fuel cell is allowed to generate power for a long time, it eventually shows a voltage lower than 0.65 (V) due to catalyst poisoning. After detecting this voltage value, the valve 26 and the valve 27 are opened to prepare a mixed solution in which ozone and carbon dioxide are mixed with an aqueous methanol solution, and this mixed solution is added to the fuel electrode at 0.8 ml / min for 10 minutes. Supply. After 10 minutes, the valve 26 and the valve 27 were closed, the mixed solution was returned to the methanol aqueous solution, and the fuel cell was generated to measure the voltage. As a result, the open circuit voltage after 48 hours was 0.721 (V). is there.

  In FIG. 12, three experimental results of Experimental Example 6, Experimental Example 1, and Comparative Example 1 are shown.

  When the experimental example 6 is compared with the comparative example 1, a voltage increase of about 5.9% is observed under the experimental condition of this example (experimental example 6). From this experimental result, in the fuel cell of the present example, the platinum poisoning of the fuel electrode can be removed by ozone without stopping the power generation of the fuel cell, so that the activity of the platinum catalyst is improved again. Is shown.

  As described above, in Example 4, by performing the operation method of supplying the methanol aqueous solution containing ozone to the fuel electrode while generating power from the fuel cell, the poisoning substance of catalyst poisoning at the fuel electrode is removed. Can do. As a result, the activity of the oxidation reaction at the fuel electrode is increased, the overvoltage consumed by the oxidation reaction at the fuel electrode is reduced, and a large electromotive force can be extracted from the fuel cell. Can be improved. Furthermore, since catalyst poisoning can be easily removed while generating a constant voltage, stable power generation can be maintained without stopping the operation of the fuel cell.

  In Examples 1 to 4 above, specific examples of experiments based on experiments of a direct methanol fuel cell that supplies an aqueous methanol solution as a fuel have been described. In addition to methanol used as a fuel, for example, Needless to say, the present invention can be applied to fuel cells that generate electricity by supplying alcohols such as ethanol, propanol, and ethanediol.

  Furthermore, it goes without saying that the present invention can be applied to a fuel cell that generates power by supplying liquid fuel other than alcohol.

  Furthermore, it goes without saying that the present invention can be applied to a small analyzer using MEMS such as microchemical analysis.

  The fuel cell according to the present invention has a feature that prevents catalyst poisoning of the fuel electrode, and is useful as a direct methanol fuel cell or the like. The fuel cell according to the present invention can also be applied to uses such as a direct methanol fuel cell that needs to improve the electromotive force of the fuel cell.

Configuration diagram of a direct methanol fuel cell in Example 1 of the present invention The flowchart of the preparation method of the mixed solution of the direct methanol type fuel cell in Example 1 of this invention Time-voltage characteristic diagram of a direct methanol fuel cell in Example 1 of the present invention The figure which shows the output voltage characteristic with respect to the ozone concentration of the direct methanol type fuel cell in Example 1 of this invention. 1 is a configuration diagram of a direct methanol fuel cell according to a first embodiment of the present invention attached with an aqueous methanol cartridge. Configuration diagram of direct methanol fuel cell in Example 2 of the present invention The flowchart of the preparation method of the mixed solution of the direct methanol type fuel cell in Example 2 of this invention The figure which shows the output voltage of the direct methanol type fuel cell in Example 2 of this invention. Configuration diagram of direct methanol fuel cell in Example 3 of the present invention Configuration diagram of direct methanol fuel cell in Example 4 of the present invention Flowchart of a method for operating a direct methanol fuel cell in Example 4 of the present invention The figure which shows the output voltage of the direct methanol type fuel cell in Example 4 of this invention. Configuration diagram of membrane electrode assembly of direct methanol fuel cell

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Membrane electrode assembly 2 Solid polymer electrolyte membrane 3 Fuel electrode 4 Air electrode 7 Methanol aqueous solution 8 Air 9 Carbon particle 10 Catalyst particle 11 Fuel electrode discharge substance 12 Air electrode discharge substance 13 Methanol aqueous solution cartridge 14 Methanol aqueous solution mixed with ozone Cartridge 21 Ozone 22 Mixer (mixes ozone and aqueous methanol)
23 Ozone generator 24 Mixer (Methanol aqueous solution and carbon dioxide mixed)
25 Mixer (mixed aqueous solution of methanol and carbon dioxide with ozone)
26 Valve (ozone supply valve)
27 Valve (CO2 supply valve)
31 Carbon dioxide (Ozone decomposition inhibitor)
32 Gas-liquid separator 33 Exhaust gas 41 pH meter 51 Mixed solution (Methanol aqueous solution and ozone mixed solution)
52 Mixed solution (Methanol aqueous solution and carbon dioxide mixed solution)
53 Mixed solution (Methanol aqueous solution, carbon dioxide and ozone mixed solution)

Claims (6)

In a direct methanol fuel cell in which a fuel electrode and an air electrode are arranged on both sides of a solid polymer electrolyte membrane and an electromotive force is obtained by electrochemical reaction,
Having a catalyst on at least one of the air electrode and the fuel electrode;
Supplying an oxidizing substance to the air electrode;
A direct methanol fuel cell, characterized in that a mixed solution in which ozone is mixed with methanol as a fuel material is supplied to the fuel electrode. 2. The direct methanol fuel cell according to claim 1, wherein the mixed solution is mixed with ozone after mixing carbon dioxide with methanol. 3. The direct methanol fuel cell according to claim 2, wherein the carbon dioxide is obtained by mixing carbon dioxide obtained by collecting the exhaust material of the fuel electrode with the methanol. 3. The direct methanol fuel cell according to claim 2, further comprising a first valve for controlling the carbon dioxide supply and a second valve for controlling the ozone supply. 5. The direct methanol fuel cell according to claim 4, wherein when a decrease in the electromotive force is detected, the first valve and the second valve are opened to mix carbon dioxide and ozone. 6. 2. The direct methanol fuel cell according to claim 1, wherein the ozone concentration contained in the mixed solution is in the range of 0.001 wt% to 0.1 wt%.

Images