WO2010058811A1

WO2010058811A1 - Fuel cell

Info

Publication number: WO2010058811A1
Application number: PCT/JP2009/069617
Authority: WO
Inventors: 西村　勝憲; 安藤　慎輔; 貢中原; 正義菅野
Original assignee: 株式会社日立製作所
Priority date: 2008-11-21
Filing date: 2009-11-19
Publication date: 2010-05-27
Also published as: JPWO2010058811A1

Abstract

Provided is a fuel cell that uses a liquid organic compound as a fuel, wherein a concentration measuring element having a methanol oxidation electrode and a fuel circulation passage formed on the methanol oxidation electrode are provided in a fuel circulation pipe for circulating the fuel, and a fuel control circuit for controlling the fuel concentration according to the methanol concentration detected by the concentration measuring element is provided. The fuel concentration is monitored and controlled by means of a fuel detection unit having a flow cell structure which is provided in the fuel supply line.

Description

Fuel cell

The present invention relates to a fuel cell using a liquid organic compound as a fuel.

For fuel cells that use liquid organic compounds as fuel, solid polymer fuel cells that use liquid organic compounds such as methanol, ethanol, and formic acid as fuels have low noise and low operating temperatures (about 70-80 ° C). The fuel supply is easy. Therefore, a wide range of uses are expected as a portable power source, a power source for an electric vehicle, or a power source for an electric motorcycle, an assisted bicycle, and a light vehicle such as a wheelchair or a senior car for medical care.

Among these uses, a direct methanol fuel cell (hereinafter referred to as DMFC) using methanol as a fuel can eliminate a reformer, can supply fuel at room temperature, and has a fuel cost relative to output such as gasoline. It has advantages such as a cheaper point and a short start-up time because it can generate power at a low temperature of 50-60 ° C. In particular, an “active” DMFC that forcibly distributes fuel using a pump or the like can obtain a high output of several tens of watts to several hundred watts, and is suitable for feeding relatively low power devices such as electronic devices and lighting fixtures. Yes. Moreover, if a DMFC of 1 kW or more is used due to an increase in cell size and an increase in the number of stacked cells, the present invention can be applied to a moving body.

Thus, while the DMFC has excellent environmental adaptability, the electrolyte membrane used in the cell has a problem that the permeation of fuel such as methanol from the fuel electrode to the oxidation electrode cannot be completely prevented. As a result, methanol and oxidant (for example, oxygen contained in the air) permeated through the oxidation electrode directly react to cause a problem of output reduction and fuel loss.

According to the conventional technique, a control method is disclosed in which the methanol concentration is controlled to be relatively low, and the operation is performed while reducing a decrease in output (Patent Document 1 or 2).

US6254748 JP 2004-95376 A

An object of the present invention is to provide a fuel cell equipped with a fuel control method using an oxidation current of fuel. In particular, an object of the present invention is to realize control of a fuel concentration range wider than that in the conventional fuel cell that requires large load fluctuations.

Requirement for an element for measuring fuel concentration is that an object can be detected in a wide concentration range, and the detection signal does not greatly decrease with respect to the concentration.

For example, according to the conventional technique, when the methanol concentration is in the range of 1 mol / liter, the detected current is almost proportional to the concentration, and the sensitivity does not change in this concentration range (for example, FIG. 7 of Non-Patent Document 1). However, when the concentration increases, the current does not increase in proportion and the sensitivity decreases (FIGS. 6 and 8 of the same document).

In addition, it is important that sufficient sensitivity can be obtained even if the amount of noble metal such as platinum used is small. If the amount of catalyst such as platinum increases, the current density per platinum unit area decreases, and the sensitivity is relatively maintained. However, an increase in the amount of catalyst leads to an increase in the price of the measuring element, which is not desirable.

One of the objects of the present invention is to obtain sufficient detection sensitivity even when the amount of noble metal such as platinum used is small. In other words, both detection sensitivity and cost are compatible.

An even more important requirement is that the fuel can be controlled so that the required output can be supplied in a short time to the load requested by the user.

For example, in DMFC, an appropriate methanol concentration is determined for a frequently used output range, and the methanol concentration is managed within a predetermined range based on the concentration. However, when there is an output request exceeding the range, it is necessary to quickly increase the methanol concentration and to output the output to the outside. Conversely, after the output returns to the original level, it is necessary to lower the methanol concentration. In order to cope with such output fluctuations, methanol concentration control as quickly as possible is required.

According to the conventional technology, a system is adopted in which a fuel tank is temporarily stored and a methanol tank is installed to supply the fuel to the DMFC, and the fuel is circulated by connecting the methanol tank and the DMFC with a pipe. Yes.

In the conventional method of installing a concentration sensor in a methanol tank, there is a time delay in changing the concentration of methanol added to the solution contained in the tank, and it is not possible to follow a high load requirement. On the other hand, when returning to a low load, the methanol concentration reaches an excessive level due to a time delay, and it takes time to adjust the concentration.

Therefore, in order to perform fuel control that quickly follows load fluctuations, a concentration control technique based on a concept different from the conventional one is required.

An object of the present invention is to provide a fuel cell system capable of accurately controlling the fuel concentration in a wide range in a fuel cell using liquid fuel.

Therefore, as a result of intensive studies on a method for controlling the fuel concentration in a wide concentration range, the inventors have established a new fuel control technique.

In a fuel cell having a solid polymer electrolyte membrane, an electrode joined to the surface of the electrolyte membrane, and a groove through which a fuel or an oxidant flows, and using a liquid organic compound as a fuel, A fuel control circuit for installing a concentration measuring element having a methanol oxidation electrode and a fuel flow passage formed on the electrode in the middle of a fuel circulation pipe for circulating the fuel, and controlling the fuel concentration according to the methanol concentration detected by the element It is to provide.

The second solution means is that the concentration measuring element of the first solution means is added with a configuration comprising a methanol oxidation electrode and a hydrogen generation electrode.

The third solution means that, in the second solution means, the hydrogen generating electrode is provided with a function of improving water repellency as compared with the methanol oxidation electrode.

The fourth solution is to install a porous membrane that does not allow liquid methanol to permeate but allows methanol vapor to permeate on the methanol oxidation electrode of the first solution.

According to a fifth solution means, in the second solution means, a methanol oxidation electrode and a hydrogen generation electrode are formed on respective surfaces of the hydrogen ion conductor, and the hydrogen ion conductor has a flow path through which fuel flows. And the members are electrically insulated from each other.

The sixth solution is that, in the second solution, the amount of platinum used for the methanol oxidation electrode or the hydrogen generation electrode is 1 mg or less per 1 cm ^{2 of} electrode area.

The seventh solution means that in the first solution means, the fuel control circuit has a function of storing and calculating the amount of electricity generated and the methanol concentration, and changes the methanol concentration or flow rate of the fuel flowing through the fuel circulation pipe. That is.

An eighth solution is a membrane electrode joint comprising a solid polymer film, a cathode formed on one surface of the solid polymer film, and an anode formed on the other surface of the solid polymer film. And a fuel tank that stores a fuel made of a liquid organic compound that is supplied to the fuel cell. The fuel cell includes a separator that sandwiches the membrane electrode assembly. And a fuel circulation system that circulates the fuel between the fuel tank and the fuel cell, and a concentration measuring element that is disposed in the fuel circulation pipe and measures an oxidation current of the fuel And a fuel control circuit for detecting the fuel concentration from the oxidation current measured by the concentration measuring element and controlling the fuel concentration of the fuel tank based on the fuel concentration.

The present invention can provide a fuel cell system capable of accurately controlling the concentration of liquid fuel in a wide range.
Other objects, features and advantages of the present invention will become apparent from the following description of embodiments of the present invention with reference to the accompanying drawings.

The structure of the fuel cell system of this invention is shown. The structure of the fuel detection part of this invention is shown. The top view of the density | concentration measuring element of this invention is shown. 2 shows a cross-sectional structure of a concentration measuring element of the present invention. 2 shows a cross-sectional structure of a concentration measuring element of the present invention. 1 shows a cross-sectional structure of a fuel cell main body of the present invention. The relationship between the methanol concentration and the current ratio in the flow cell structure device of the present invention is shown. The structure of the fuel cell system of this invention is shown. The result of the active fuel control of this invention is shown.

The principle of the fuel detection method of the present invention is to calculate the fuel from the oxidation current of the fuel. The fuel used for the DMFC, that is, methanol, will be described as an example as follows.

Methanol is oxidized according to (Equation 1) on the methanol oxidation electrode constituting the concentration measuring element of the present invention. Here, the generated carbon dioxide is dissolved or released as a gas in the fuel near the methanol oxidation pole. The hydrogen ions pass through the hydrogen ion conductor and are reduced at the hydrogen generation electrode provided on the opposite surface of the methanol oxidation electrode (Formula 2).

CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (Formula 1)
^{^{_{6H + + 6e - → 3H 2}}} ····· ( Equation 2)
In the entire concentration measuring element of the present invention, a reaction in which methanol is decomposed into carbon dioxide and hydrogen proceeds (Formula 3).

CH ₃ OH + H ₂ O → CO ₂ + 3H ₂ (Formula 3)
In the present invention, the oxidation current (formula 1) associated with the methanol decomposition reaction (formula 3) is measured, and this utilizes the property defined by the methanol concentration.

In the case of other fuels, if the oxidation reaction is determined, the reaction proceeds by the same mechanism. When the fuel is formaldehyde, the combination of (Formula 4) and (Formula 5)
HCHO + H ₂ O → CO ₂ + 4H ⁺ + 4e ⁻ (Formula 4)
4H ⁺ + 4e ⁻ → 2H ₂ (Formula 5)
In the case of formic acid, it consists of a combination of (Formula 6) and (Formula 7).

_{^{HCOOH → CO 2 + 2H + +}} 2e - ····· ( Equation 6)
2H ⁺ + 2e ⁻ → H ₂ (Formula 7)
In addition, with respect to ethanol, dimethyl ether, dimethoxyethane, dioxane, and the like, an oxidation reaction formula that involves generation of carbon dioxide and hydrogen ions can be obtained.

The fuel in which hydrogen ions are generated by the oxidation reaction can be detected as an oxidation current in combination with the hydrogen generation reaction of (Equation 2) using a hydrogen ion conductor. In the case of a fuel that generates other ions, a material that conducts the ions is selected.

In these reactions, in order to increase the fuel oxidation current in proportion to the concentration over a wide concentration range, carbon dioxide at the oxidation electrode (Equation 1), (Equation 4), (Equation 6), at the hydrogen generation electrode It is important to prevent hydrogen (formula 2), (formula 5), and (formula 7) from inhibiting the overall reaction rate. Therefore, in order to clarify the method for extending the measurable concentration range, DMFC will be described as an example.

Since carbon dioxide generated from the fuel oxidation reaction (formula 1) has high solubility in water, the oxidation reaction (formula 1, formula 4, formula 6, etc.) is not easily inhibited by the dissolution of carbon dioxide. On the other hand, at the hydrogen generation electrode, the solubility of hydrogen is low (25 ° C., 1/5 the value of carbon dioxide at 1 atmosphere), and the ratio of the hydrogen generation amount to the carbon dioxide generation amount is greater than 1. (In the case of methanol oxidation, the ratio is 3 from (Equation 3)), hydrogen bubbles tend to accumulate near the electrode. As a result, reaction inhibition due to gas generation becomes significant at the hydrogen generation electrode.

Therefore, if the liquid present in the vicinity of the methanol oxidation electrode and the hydrogen generation electrode always flows and the gas generated from the electrode is continuously removed, the reaction on the electrode is not easily disturbed by the gas. In particular, gas removal measures are extremely effective at the hydrogen generation electrode.

Therefore, in the present invention, the concentration measuring element has a flow cell structure, and the measurable concentration range is expanded. In the flow cell structure, since the fuel is flowing on the electrode surface, the gas generated from the electrode is removed from the electrode surface together with the fuel. Thereby, it can suppress that reaction on an electrode is obstructed by generated gas. Further, since the fuel near the electrode is always replaced, the fuel is oxidized on the oxidation electrode (Equation 3, Equation 4, and Equation 6), and the concentration near the electrode does not decrease. Compared to when it is left in the fuel tank, the oxidation current increases and the fuel detection sensitivity is improved.

A concentration measuring element characterized by measuring a fuel concentration from an oxidation current accompanying a decomposition reaction of fuel, and a concentration measuring element having a flow cell structure, and a specific configuration in which the concentration measuring element is applied to a fuel cell will be described in detail. .

FIG. 1 shows the configuration of a fuel cell (DMFC) system 101 equipped with a methanol concentration control mechanism using the concentration measuring element 112 of the present invention.

There is a DMFC main body 102 at almost the center of the fuel cell system 101. The fuel used for power generation of the DMFC main body 102 is filled in the methanol container 103. The methanol stored in the methanol container 103 may be 100% methanol, but generally an aqueous methanol solution diluted with water is used. A required amount of methanol is introduced into the fuel tank 108 by the fuel supply means 104 including a valve and a pump. The fuel supply means 104 operates when the methanol concentration becomes a predetermined concentration or less. A control circuit 120 such as a microcomputer is used for these controls.

The methanol concentration measuring element 112 is installed in the middle of the fuel circulation line 105 that connects the fuel tank 108 and the fuel supply port of the DMFC main body 102. The control circuit 120 monitors that the methanol fuel supplied to the DMFC main body 102 has a predetermined value. By providing it in the vicinity of the fuel tank, it is possible to avoid a measurement time delay and to perform concentration control quickly.

Alternatively, it may be installed in the middle of the fuel circulation line 105 that connects the fuel outlet of the DMFC main body 102 and the fuel tank 108. In this case, the consumption rate calculated from the current flowing in the DMFC main body 102 or the loss rate of methanol permeating the electrolyte membrane (loss rate due to methanol crossover) is added to the methanol concentration consumed in the DMFC main body 102. ) Etc., add the concentration of methanol consumed. The control circuit 120 determines whether or not the sum is a predetermined value.

When the control circuit 120 determines that the methanol concentration in the fuel tank 108 exceeds the upper limit value, the pure water supply means 107 is operated. In this case, necessary water is supplied from the pure water container 106 to the fuel circulation line 105 or the fuel tank 108, and the methanol concentration is maintained in an appropriate range.

The fuel tank 108 has a function of temporarily storing a methanol aqueous solution controlled to a predetermined concentration range, and also makes the fuel concentration uniform when fuel and water are replenished from the methanol container 103 and the pure water container 106 described above. It also has a function to

Some of the methanol aqueous solution is supplied to the DMFC main body 102 via the fuel circulation line 105 by the fuel circulation pump 109. In the DMFC main body 102, methanol is oxidized at the anode (Formula 8). Thereafter, the methanol drainage is returned to the fuel tank 108 again.

CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (Formula 8)
Carbon dioxide generated by the oxidation reaction of methanol (Formula 8) exists in the DMFC main body 102 in a state dissolved in the fuel or as fine bubbles. The carbon dioxide moves to the fuel tank 108 via the fuel circulation line 105, and most of the carbon dioxide is released into the gas phase in the fuel tank 108. Further, when the pressure in the gas phase increases, the gas is discharged to the outside of the fuel cell system 101 through the gas-liquid separator 110 installed at the upper part of the fuel tank 108. The gas-liquid separator 110 may be provided with a mechanism for removing a trace amount of organic substances by providing a catalyst treatment reactor.

Air is supplied from the fan or other air supply means 111 to the DMFC main body 102, and water is generated (formula 9). The hydrogen ions shown on the left side of (Equation 9) are the hydrogen ions produced by the methanol oxidation reaction (Equation 8) at the anode permeating through the electrolyte membrane.

3 / 2O ₂ + 6H ⁺ → 3H ₂ O (formula 9)
The exhaust gas after power generation is released to the outside of the fuel cell system 101 through the oxidant discharge system 124. A method of installing a gas-liquid separation membrane and a cooler at the air exhaust gas outlet, collecting water, and returning it to the cooling water tank 106 can also be adopted.

1 can be supplied from the fuel tank 108 to the DMFC main body 102 by the DMFC system configuration shown in FIG.

The fuel detector 217 of the concentration measuring element of the present invention has a configuration shown in FIG. A fuel oxidation electrode 215 and a gas generation electrode 216 are stacked on each surface of the ion conductor 214. When ethanol is detected, a methanol oxidation reaction (formula 1) proceeds at the fuel oxidation electrode 215, and a hydrogen generation reaction (formula 2) occurs at the gas generation electrode 216. As the ion conductor 214, a solid polymer electrolyte membrane that allows hydrogen ions to pass therethrough can be selected. Depending on the type of fuel, the materials of the fuel oxidation electrode 215 and the ion conductor 214 can be changed.

When the fuel detection unit 217 shown in FIG. 2 is housed in a pipe through which fuel is circulated and has a flow cell structure, it is possible to avoid the inhibition of the decomposition reaction (formula 3) due to gas generation.

The flow cell structure of the present invention is illustrated in FIGS. 3A and 3B. FIG. 3A is a view of the fuel oxidation electrode 315 as viewed from above. FIG. 3B shows a cross-sectional structure of the flow cell.

The fuel oxidation electrode 315 is installed on the upper part of the ion conductor 314, and the gas generating electrode is under the ion conductor 314. In FIG. 3A, it is omitted because it is hidden behind the ion conductor 314. In FIG. 3B showing a cross-sectional structure, a gas generating electrode 316 is shown.

A current terminal 318 for taking out electricity is connected to the fuel oxidation electrode 315. Since the current terminal 318 is exposed to the potential of the fuel oxidation electrode 315, the current terminal 318 is required to have corrosion resistance. Further, when the current terminal 318 is electrochemically active with respect to the fuel, an oxidation current on the current terminal 318 is generated as an error in the oxidation current at the fuel oxidation electrode 315. Therefore, it is preferable that the current terminal 318 is electrochemically inactive with respect to the fuel in order to improve the fuel measurement accuracy. Even when the fuel is electrochemically active, the error can be minimized by limiting the wire diameter and length so that the surface area of the current terminal 318 is reduced.

A current terminal 319 is also connected to the gas generating electrode (316 in FIG. 3B) from the lower surface of the ion conductor 314 so that a current can be taken out to the outside. Since the current terminal 319 is not in an oxidized state like the fuel oxidation electrode 315, any conductive material is selected as long as it is a material that does not naturally corrode even when immersed in the fuel without applying a voltage. be able to. Further, since hydrogen generation occurs at the gas generating electrode 316, it is preferable to be electrochemically inert to these reactions in order to improve the fuel measurement accuracy. However, even if there is electrochemical activity with respect to the gas generation reaction, it is possible to avoid the problem of error if the wire diameter and length are limited so that the surface area of the current terminal 319 is reduced.

The entire fuel detection unit is housed inside the fuel flow pipe 320, and the fuel oxidation electrode 315 and the gas generation electrode 316 are always in contact with the fuel. The fuel flow pipe 320 is electrically in non-contact with the

current terminals

318 and 319 or the fuel oxidation electrode 315 and the gas generation electrode 316 to ensure insulation. The material of the fuel flow pipe 320 can be arbitrarily selected as long as it is not affected by the fuel, and stainless steel or plastic can be used.

Next, a configuration in which the flow cell of FIGS. 3A and 3B is changed to a more practical form will be described. FIG. 4 is an example of a side view of the flow cell. The left figure shows a side view and the right figure shows a cross-sectional view.

The fuel flow pipe 420 corresponds to the fuel flow pipe 320 of FIG. It is desirable to manufacture with a low cost material that is durable against fuel penetration and heat. Further, since a voltage is applied to the fuel oxidation electrode and the gas generation electrode, it is particularly desirable that the electrode is manufactured from an insulator or a high resistance material.

A laminated body composed of a fuel oxidation electrode, an ion conductor, and a gas generation electrode is collectively shown as a fuel detection unit 417. This has a radius smaller than the outer diameter of the fuel flow pipe 420 and is sandwiched from above and below the fuel detection unit 417 by

graphite parts

421 and 422 having an arch shape. The graphite parts can be changed to other materials. A material other than graphite can be used as long as it is conductive and does not corrode with fuel or water. For example, it can be replaced with titanium or a titanium-coated metal laminate.

A counterbore 423 having a depth corresponding to the thickness of the

graphite parts

421 and 422 is provided so that the inner diameters of the

graphite parts

421 and 422 coincide with the inner diameter of the fuel flow pipe 420, and the

graphite parts

421 and 422 are fitted therein. Like that. In this way, as shown in the cross-sectional view on the right side of FIG. 4, the inner wall of the fuel flow pipe 420 has a smooth shape with no irregularities. This is effective for reducing the pressure loss during the flow of the fuel and preventing the adhesion of the gas generated by the fuel detector 417. Airtightness can be secured by applying an adhesive or sealant that is not attacked by the fuel and does not deteriorate at the fuel temperature to the contact surface between the spot facing portion 423 and the

graphite parts

421 and 422.

Part of the

graphite parts

421 and 422 is exposed from the opening window of the fuel flow pipe 420, and

current terminals

418 and 419 are connected from the part to apply a voltage to the fuel detection unit 417.

The upper and lower fuel flow pipes 420 may be manufactured in a semicircular shape, and the end portions of the semicircle may be bonded or welded together, or the entire side surface may be covered with a heat shrinkable tube and crimped. It is more preferable to provide a notch at the end of the semicircle so that the two semicircular ends engage with each other (so-called notch structure), so that misalignment can be avoided.

4 is incorporated in the fuel cell system of the present invention shown in FIG. 1 (112 in FIG. 1), and is connected to the control circuit 120 shown in FIG. 1 through

current terminals

418 and 419.

Current terminals

418 and 419 are represented by current signal lines 121 in FIG.

Although only one fuel detection unit 417 is provided in FIG. 4, it is also possible to form a plurality of counterbore portions 423 at different positions of the same fuel flow pipe 420 and provide a plurality of fuel detection units 417. In this way, in the process of fuel flowing through the fuel flow pipe 420, the upstream fuel detection unit 417 measures the oxidation current, and the downstream fuel detection unit 417 measures the oxidation current in the fuel after the concentration change. Become. As a result, it is possible to employ a method of measuring methanol with higher accuracy from the difference in oxidation current between the two fuel detection units.

Referring back to FIG. 1, the operation method of the concentration measuring element of FIG. 4 will be described. The control circuit 120 has a DC power source. This has a function of applying a voltage to the fuel detection unit 417 of FIG. 4 via the current signal line 121 and measuring the flowing current. An arithmetic process is executed based on the current, and the fuel concentration is calculated.

The temperature data measured by the thermocouple for measuring the battery temperature provided in the DMFC main body 102 or the thermocouple for measuring the fuel temperature inserted in the fuel circulation line 105 (both are omitted in FIG. 1) The signal can be taken into the control circuit 120 as a signal. By adding the temperature data to the calculation process, the temperature dependence of the current can be corrected. As a result, the accuracy of fuel concentration can be improved.

If a sensor for measuring the volume of the fuel is installed in the fuel tank 108, a signal representing the volume measurement result can be taken into the control circuit 120 from the sensor. In this way, the number of moles of methanol can be calculated from the fuel volume and the methanol concentration. As a result, it is possible to execute methanol concentration control in which both the fuel volume and the number of moles of methanol are monitored.

When it is determined that the fuel concentration is lower than the target value based on the calculation result of the control circuit 120, a methanol supply command signal is output from the fuel control line 122 to the fuel supply means 104. Conversely, when it is determined that the fuel concentration is higher than the target value, a pure water supply command signal is output from the pure water control line 123 to the pure water supply means 107.

When the fuel volume of the fuel tank 108 is insufficient, the control circuit 120 outputs both a fuel supply command and a pure water supply command.

Next, the configuration of the DMFC main body 102 of the present invention will be described. FIG. 5 shows a cross-sectional structure of the DMFC main body.

Methanol oxidation reaction (Formula 8) or oxygen reduction reaction (Formula 9) proceeds on the anode and cathode surfaces of a membrane electrode assembly (hereinafter referred to as MEA), respectively. The MEA 502 has a three-layer structure in which an anode is stacked on one surface of an electrolyte membrane and a cathode is stacked on the other surface. A structure in which the MEA 502 is sandwiched between two separators 504 is referred to as a single cell 501. A flow path through which fuel flows is formed on one side of the separator, and a flow path through which oxidant flows is formed on the other side.

Between the two separators 504, the gasket 505, the electrolyte membrane portion of the MEA 502, and the gasket 505 are laminated and pressed to prevent leakage of fuel and oxidant. The separator 504 was formed with a fuel channel on one side and an oxidant channel on the other side. The gasket 505 can be made of an oxidation resistant, reduction resistant, water resistant elastic body such as ethylene / propylene rubber, fluorine rubber, or silicon rubber. An epoxy resin may be used as an adhesive and cured to replace the gasket.

A plurality of single cells 501 are connected in series, current collecting

plates

513 and 514 are installed at both ends, and further tightened with an end plate 509 from the outside via an insulating plate 507. If the end plate is made of an insulating material, the insulating plate 507 can be omitted.

In the

separators

531 and 532 at the end in contact with the current collector plate, a channel was formed inward of the battery, and no channel was formed on the surface in contact with the current collector plate. This is because if the flow path is formed on the surface in contact with the current collector plate, the current collector plate may corrode. However, if the

current collector plates

513 and 514 are corrosion resistant, a channel may be formed on the surface.

ボルト Bolts 516, springs 517, and nuts 518 are used as tightening parts.

Fuel is supplied from the fuel supply line 105 in FIG. 1 to a fuel supply connector 510 on the fuel supply side provided on the end plate 509 in FIG. Then, the fuel is oxidized on the MEA anode while passing through each single cell 501. Thereafter, the fuel is discharged from the fuel discharge connector 522 provided on the opposite end plate 509. The discharged fuel is sent to the fuel tank 108 of FIG. As the fuel of this system, liquid organic fuel such as methanol can be used. Furthermore, it is possible to use a liquid fuel such as a methanol aqueous solution.

The oxidant is supplied from the air supply means 111 of FIG. 1 from the oxidant supply connector 511 on the oxidant supply side provided on the left end plate 509 shown in FIG. 5, and the oxidant discharge side of the opposite end plate 509. The oxidizer pipe connector 523 is discharged. Air was supplied from an air fan (air supply means 111 in FIG. 1) installed outside the battery.

A cell stack composed of 25 single cells 501 was manufactured with such a component structure.

The first embodiment is a DMFC system in which the cell stack is incorporated so as to have the configuration shown in FIG. Electric power from the DMFC main body is supplied to the DC-DC converter 520 or the inverter 520 via the external power line 519 connected to the

current collector plates

513 and 514, and the load 521 installed outside can be operated. This system is referred to as S1.

The specifications of the concentration measuring element used in the system S1 are as follows. The shape of the concentration measuring element is a cylindrical flow cell shown in FIG. The outer diameter of the fuel flow pipe 420 was 8 mm, the inner diameter was 6 mm, and the total length was 50 mm. The size of the fuel detector 417 was 6 mm × 4 mm. Further, the Pt loading was 0.5 mg / cm ^{2 for} both the fuel oxidation electrode and the hydrogen generation electrode. A perfluorosulfonic acid electrolyte membrane (thickness 25 μm) was used as the electrolyte membrane, and a porous carbon sheet (thickness 0.2 mm, porosity 75%) mainly composed of carbon fibers was used as the gas diffusion layer. Only the gas diffusion layer used for the hydrogen generation electrode was made of a porous carbon sheet impregnated with 10% PTFE dispersion and dried.

The amount of Pt supported used for the fuel oxidation electrode and the hydrogen generation electrode is preferably 5 mg / cm ² or less in order to prevent a decrease in the diffusion rate of methanol or hydrogen due to an increase in the thickness of the electrode layer. This is because when the amount is high, the oxidation current decreases with high concentration of methanol. Further, it is preferable that the amount is 1 mg / cm ² or less in order to reduce the cost of the fuel detection unit while maintaining the detection sensitivity.

It is desirable that the voltage applied to the fuel oxidation electrode and the hydrogen generation electrode be equal to or higher than the fuel oxidation start voltage and the oxygen generation current by water electrolysis does not exceed the fuel oxidation current. Therefore, the voltage applied to both electrodes when the organic fuel is methanol is suitably 0.2 V or more and 1.3 V or less. Particularly, 0.6 V or more is suitable for avoiding CO poisoning at the methanol oxidation electrode, and 1.2 V or less is suitable for increasing the ratio of the methanol oxidation current to the oxygen generation current. In this example, the applied voltage was set to 1.1V.

The methanol concentration of the aqueous methanol solution stored in the fuel tank 103 in FIG. 1 is 50%, the aqueous methanol solution when flowing through the fuel circulation line 105 is 5% as a control reference value, and the control accuracy range is 3 to 6%. . Further, an external data input port is provided in the control circuit 120 so that data can be written to and changed in the microcomputer in the control circuit 120 so that the control reference value can be adjusted from the outside as needed. The volume of fuel stored in the fuel tank was 100 cc.

The voltage that is the air supply means 111 was set so that the oxidant utilization rate would be 10%.

The system S1 was operated with the above configuration. The data of the method of the present invention in FIG. 6 is the result of examining whether or not the fuel control value of the system S1 is in accordance with the reference value according to the value transferred from the external personal computer to the microcomputer. The current ratio representing the oxidation current on the vertical axis is displayed as a relative value based on the current at a methanol concentration of 3%. According to this data, it was found that the current increased monotonously at a high concentration of 10% by weight concentration or 3.1 mol / liter or more at a molar concentration, and the rate at which the current increase rate decreased at a high concentration was small. . In addition, the accuracy range of control during continuous power generation was within a range of ± 1% (± 0.3 mol / liter) at any control reference value.

For comparison, a concentration measuring element in which the

current terminals

418 and 419 in FIG. 4 were sealed with a fluorine tube so as not to come into contact with the fuel was manufactured, and a system was also manufactured in which it was placed in the fuel tank 108 in FIG. In addition, the length of the pipe | tube of a density | concentration measuring element left about 2 mm from the counterbore part 423, and produced the short density | concentration measuring element which made 8 mm in total length. By shortening the concentration measuring element, methanol in the fuel tank can reach the fuel detector 417 in a short time. However, although the fuel reaches the fuel detector 417 by natural diffusion to the fuel detector 417 of the concentration measuring element, the difference is that the fuel does not always flow as in S1. Let this system be S2.

As with the system S1, the control reference value was changed from the external personal computer to the microcomputer, and it was examined whether the fuel control value of the system S2 was in accordance with the reference value. According to this data, it was observed that the rate of increase in current decreased from around 5% (1.5 mol / liter) and reached saturation. In particular, the increase in current was small near the 10% (3.1 mol / liter) concentration or higher, and it was found that the concentration measurement error increased, and it was found that the methanol concentration cannot actually be controlled. . In addition, the control accuracy range during continuous power generation has been expanded to ± 2% (± 0.6 mol / liter) at any control reference value. One reason is that the density detection error tends to increase due to natural diffusion. Another major factor is that the concentration at the time point measured by the concentration measuring element and the target concentration to be controlled by the control circuit are likely to be shifted, that is, the time lag between the measurement and the control.

Next, the system was generated with a current of 20 A (current density was 0.2 A / cm ² ), and a rated output of 200 W was obtained. The battery temperature was controlled at 55 to 60 ° C. In the system S1, the methanol concentration could be controlled within a control standard value of 4% and variation of ± 1% within the range of the rated current of 20A. On the other hand, in the system S2, even when the control reference value is the same, the variation is expanded to ± 2%.

As a second embodiment, a fuel control method using a concentration measuring element in which a porous film is bonded to the upper surface of a catalyst layer of a fuel oxidation electrode (methanol oxidation electrode) 215 in FIG. 2 will be described.

2 A polyethylene porous film or a fluorine-based porous film is used on the upper surface of the catalyst layer of the fuel oxidation electrode 215 in FIG. Although a thickness of about 1 mm can be used, a porous film having a thickness of 0.05 mm to 0.3 mm is particularly preferable from the viewpoint of easy adhesion to the electrode and shortening of the methanol diffusion time. The conditions for selecting the membrane include that the liquid permeation amount is extremely small relative to the gas permeation amount, that no melting or alteration occurs at the fuel temperature, and that no impurities affecting the fuel cell are released. Any material can be selected as long as these conditions are satisfied. Further, it may be a film, a sheet, a plate, or a multilayer laminate, and the outer shape may be any shape such as a square shape or a round shape.

As a bonding method, thermocompression bonding, a fluorine binder solution is thinly applied to the surface of the porous membrane, the coated surface is pressure-bonded to the fuel oxidation electrode 215, and dried to bond the porous membrane and the fuel oxidation electrode 215. Can do. Any method can be adopted as long as it does not block the pores of the porous membrane and does not inhibit the oxidation reaction on the fuel oxidation electrode 215.

With such a configuration, since the fuel liquid does not directly contact the fuel oxidation electrode 215, measurement up to a high concentration is possible. Since the liquid does not permeate and only methanol vapor reaches the electrode, the current is smaller than when the porous membrane is not used, but the electrode surface is covered with droplets and the three-layer interface inside the electrode is Since it becomes difficult to decrease, it is possible to measure even pure methanol. Moreover, since water vapor permeates through the porous membrane, the electrolyte membrane can be appropriately moisturized, so that an increase in the resistance of the concentration measuring element can also be suppressed.

A new system in which the concentration measuring element using the porous membrane of the present embodiment is replaced with the concentration measuring element of the system S1 is referred to as S3. Other configurations are the same as those of the system S1.

As with the system S1, the control reference value was changed from the external personal computer to the microcomputer, and it was examined whether the fuel control value of the system S2 was in accordance with the reference value. In the case of a concentration measuring element using a porous membrane for the fuel detection part, the oxidation current decreased to about 1/10 overall with respect to the current value at each concentration shown in FIG. However, the oxidation current with respect to the methanol concentration became almost proportional, and the linearity was improved. Furthermore, it has been found that the oxidation current increases almost linearly in the high concentration range up to 60% methanol, and high concentration fuel control is possible.

When the gas diffusion layer laminated on the fuel oxidation electrode is a carbon sheet that has not been subjected to water repellency treatment by adding a binder having high water repellency, such as tetrafluoropolyethylene, it has electrical conductivity and water repellency. Fewer electrodes can be formed. In this way, current can be taken out from the entire methanol oxidation electrode, and the generated carbon dioxide can be excluded to the liquid phase, so that methanol can be easily detected.

When the thickness of the carbon sheet used as the gas diffusion layer of the fuel oxidation electrode is in the range of 0.05 to 4 mm, a relationship in which the oxidation current with respect to the methanol concentration increases monotonously is obtained, and the methanol concentration can be easily detected from the oxidation current. . In particular, when the thickness of the carbon sheet is 0.1 mm or more, the strength of the carbon sheet is increased and the entire methanol oxidation electrode can be pressure-bonded. As a result, the contact resistance between the methanol oxidation electrode and the carbon sheet can be reduced. If the thickness of the carbon sheet is 0.3 mm or less, the methanol diffusion time in the thickness direction of the carbon sheet can be shortened. As a result, the responsiveness of the oxidation current to changes in methanol concentration is improved.

In addition, since a reduction reaction of hydrogen ions that permeate the electrolyte membrane occurs at the hydrogen generation electrode (Equation 2), the reaction rate is not governed by the rate of the substance that diffuses in the gas diffusion layer as in the methanol oxidation reaction. That is, the reaction rate of (Equation 2) is governed by the diffusion rate of hydrogen ions in the electrolyte membrane. Therefore, it is sufficient that the gas diffusion layer facilitates the release of the generated hydrogen gas into the liquid phase. As described above, since the gas generation is prioritized in the hydrogen generation electrode, the gas diffusion layer to which a binder with high water repellency such as tetrafluoropolyethylene is added is used to facilitate the hydrogen release. In this way, the oxidation current is unlikely to decrease at a high methanol concentration of 10% or more, and the methanol concentration can be easily detected.

The thickness of the carbon sheet used as the gas diffusion layer of the hydrogen oxidation electrode is set in the range of 0.05 to 5 mm. In order to obtain a high diffusion rate of hydrogen in the gas diffusion layer and to obtain adhesion between the gas diffusion layer and the hydrogen generation electrode, the thickness of the carbon sheet is preferably in the range of 0.15 to 0.3 mm.

The third embodiment uses a concentration measuring element comprising a methanol oxidation electrode in which a platinum catalyst layer is formed on a polymer solid electrolyte that allows hydrogen ions to permeate, and a conductive porous layer (such as a carbon sheet) is omitted on the top. It was the way. It is excellent in that the time for which methanol contacts the methanol oxidation electrode can be shortened and quick response can be obtained.

The methanol oxidation electrode can extract current by pressure bonding with the

graphite component

421 or 422 of FIG. The distance between the two contact portions of the graphite part and the electrode is determined by the electric resistance in the surface direction of the methanol oxidation electrode. The distance can be increased when the catalyst layer is thick, and conversely the distance is decreased when the catalyst layer is thin. . The interval is preferably 0.5 to 5 mm, particularly 1 to 2 mm.

In contrast, the conductive porous layer (carbon sheet or the like) may be omitted even on the hydrogen generation electrode side. However, hydrogen is generated directly from the hydrogen generation electrode and does not consume water or methanol contained in the fuel. Therefore, it is advantageous to use the conductive porous layer because the conductive porous layer can function the entire catalyst layer of the hydrogen generating electrode.

Next, in the fourth embodiment, an example of the construction of a system that can quickly respond to a user's output request using a plurality of concentration measuring elements of the present invention will be described. In the present invention, this is referred to as “active fuel control”. FIG. 7 shows a configuration in which the flow cell type

concentration measuring elements

712 and 713 of the present invention are installed in the fuel circulation line 705 on the supply side and the discharge side of the DMFC main body 702.

There is a DMFC main body 702 almost at the center of the fuel cell system 701. Methanol-containing fuel used for power generation of the DMFC main body 702 is stored in a methanol container 703. The methanol stored in the methanol container 703 may be 100% methanol, but generally an aqueous methanol solution diluted with water is used. A required amount of methanol is introduced into the fuel tank 708 by a fuel supply means 704 including a valve and a pump. The fuel supply means 704 operates when the methanol concentration becomes a predetermined concentration or less. A control circuit 720 such as a microcomputer is used for these controls.

Further, when the methanol concentration in the fuel tank 708 exceeds the upper limit value, the pure water supply means 707 operates, and necessary water is supplied from the pure water container 706 to the fuel circulation line 705, and the methanol concentration is maintained in an appropriate range. Is done.

The fuel tank 708 has a function of temporarily storing an aqueous methanol solution controlled to a predetermined concentration range, and also makes the fuel concentration uniform when fuel or water is replenished from the methanol container 703 and the pure water container 706 described above. It also has a function to In the present embodiment, the volume of fuel stored in the fuel tank is reduced from 100 cc to 20 cc in order to execute “active fuel control”. Accordingly, when fuel is supplied from the fuel supply unit 704 or pure water is supplied from the pure water supply unit 707, it is possible to quickly adjust the fuel concentration to a predetermined level.

The methanol aqueous solution in the fuel tank 708 is supplied to the DMFC main body 702 via the fuel circulation line 705 by the operation of the fuel circulation pump 709. At the anode, methanol is oxidized (Equation 8). Thereafter, the methanol drainage is returned to the fuel tank 708 again.

Carbon dioxide generated by the oxidation reaction of methanol (formula 8) exists in the DMFC main body 702 as dissolved or fine bubbles. The carbon dioxide moves to the fuel tank 708 via the fuel circulation line 705, and most of the carbon dioxide exists in the gas phase in the fuel tank 708. Further, when the pressure in the gas phase increases, the gas is discharged to the outside of the fuel cell system 701 through the gas-liquid separator 710 installed at the upper part of the fuel tank 708.

The air is supplied from the fan or other air supply means 711 to the DMFC main body 702 to generate water (Formula 9). The hydrogen ions are the hydrogen ions generated by the methanol oxidation reaction (Equation 8) at the anode permeating through the electrolyte membrane. The exhaust gas after power generation is released to the outside of the fuel cell system 701 via the oxidant discharge system 725.

The

concentration measuring elements

712 and 713 of the present invention are one in the middle of the fuel circulation line 705 connecting the DMFC main body 702 and the fuel tank 708, and the fuel circulation line 705 connecting the fuel tank 708 from the fuel discharge port of the DMF main body 702. Another concentration measuring element was installed between them. The voltage applied to the methanol oxidation electrode and the hydrogen generation electrode in each concentration measuring element was 1.1V.

The current terminals connected to the

concentration measuring elements

712 and 713 of the present invention are the

current terminals

418 and 419 in FIG. 4 and are shown as current signal lines 721 and 724 in FIG. The current signal lines 721 and 724 are connected to the control circuit 720.

The control circuit 720 has a DC power supply, and has a function of applying a voltage to the

concentration measuring elements

712 and 713 through the current signal lines 721 and 724 and measuring the flowing current. The measured fuel concentration data is converted into an electrical signal, and the signal is transmitted to the control circuit 720 from the current signal lines 721 and 724, and arithmetic processing based on the fuel data is started.

When it is determined that the fuel concentration is lower than the target value based on the calculation result of the control circuit 720, a methanol supply command signal is output from the fuel control line 722 to the fuel supply means 704. Conversely, when it is determined that the fuel concentration is higher than the target value, a pure water supply command signal is output from the pure water control line 723 to the pure water supply means 707.

The thermocouple for monitoring the battery temperature and the like, and the sensor for measuring the fuel volume of the fuel tank 708 can be used in the same manner as in the first embodiment described above. These additional sensors enable appropriate fuel concentration adjustment according to temperature, and output both a fuel supply command and a pure water supply command from the control circuit 720 when the fuel volume of the fuel tank 708 is insufficient. Then, fuel can be replenished.

With such a configuration, the upstream concentration measuring element 712 monitors the concentration of methanol supplied to the DMFC main body 702, and the downstream concentration measuring element 713 uses the power consumption and the amount of methanol loss (loss due to evaporation, methanol crossover, etc.). The concentration of methanol containing all of the amount can be monitored.

The methanol concentration detected by the upstream concentration measuring element 712 is C1 (mol / liter), the methanol concentration detected by the downstream concentration measuring element 713 is C2 (mol / liter), the fuel circulation flow rate is V (liter / minute), and methanol is generated by power generation. When the consumption is Q1 (value converted from the amount of electricity to the number of moles) and the amount of methanol loss is Q2 (number of moles), the following relational expression (Formula 10) is established.

V × (C1−C2) = Q1 + Q2 (Equation 10)
Since Q1 increases when the load current is increased, the fuel supply means 704 of FIG. 7 is driven to increase C1 so that the concentration of C1 increases accordingly. On the contrary, when the load current is lowered, Q1 becomes small. Therefore, the pure water supply means 707 may be operated to dilute the methanol in the fuel tank 708, or the fuel supply means 704 may be paused until it reaches a predetermined concentration. Further, even when the fuel circulation flow rate V is changed, the methanol concentration can be monitored according to (Equation 10). This is effective for increasing the system efficiency by performing variable flow control that lowers the fuel circulation flow rate when the output is low and increases the flow rate when the output is high. The means described above is a concentration control method whose main purpose is to manage the methanol concentration of the DMFC main body 702. This method can also be applied to organic fuels other than methanol. Note that Q2 in (Equation 10) is arithmetically processed by the control circuit 720 based on functions such as methanol concentration, temperature, and load current, and is taken into account when controlling C1.

Next, changing the viewpoint and focusing on the management of the methanol concentration in the fuel tank 708, it can be seen that the concentration in the fuel tank 708 can be predicted from the values of C1 and C2. That is, the methanol concentration Ct and volume of the fuel tank 708 are Vt, the piping volume from the fuel tank 708 to the DMFC main body 702 of the fuel circulation line 705 is Vi, the total volume of the fuel flow path of the DMFC main body 702 is Vc, and the DMFC main body 702 If the piping volume of the fuel circulation line 705 is set to Vo, it can be approximated that the following relational expression (formula 11) holds. Here, the methanol concentration inside the fuel cell was the average value of the methanol concentration at the inlet and outlet ((C1 + C2) / 2).

Vi * C1 + Vc * (C1 + C2) / 2 + Vo * C2 = Vt * Ct
(Equation 11)
Here, the concentration of the fuel flow path of the DMFC main body 702 is an average value of the concentrations detected by the

concentration measuring elements

712 and 713. Separately, a correction formula for the current may be obtained by measuring the methanol concentration at each load current, and the concentration calculated from the concentration function may be substituted. According to (Equation 11), the concentration of the fuel tank 708 can be estimated even when the fuel supply unit 704 and the pure water supply unit 707 are in operation.

In (Equation 11), the methanol concentration inside the fuel cell is the average value of the methanol concentration at the inlet and outlet. If there is a loss due to methanol crossover, add Q2 to the right side of (Equation 11). The calculation accuracy can be increased by using the corrected value.

When a device for measuring the temperature and flow rate of fuel is added to the fuel cell system, a space that is not calculated in (Equation 11) is generated. If fuel exists in that portion, the volume and concentration may be corrected in (Equation 11).

According to the conventional technique in which the sensor is immersed in the fuel tank, the concentration when methanol is uniformly dissolved cannot be determined until the fuel tank 708 has a uniform methanol concentration. However, according to the control method of the present invention, the methanol concentration (more strictly speaking, the total number of moles of methanol) is obtained even if the concentration in the tank is transiently changing (equation 11). ). As a result, it is possible to quickly adjust the fuel in response to the load request. In this respect, there is an advantage of the “active density control” of the present invention.

In this embodiment, the program of the above (formula 11) was stored in the microcomputer of the control circuit 720, and the driving test was performed. FIG. 8 shows the results of a three-stage output fluctuation test with a maximum current of 20 A. The methanol concentration was adjusted substantially in steps by adjusting the flow rate of the fuel supply means 704 in FIG. The flow rate of the fuel supply means 704 was increased so that the concentration change rate was 5 seconds per 1% change width (0.3 mol / liter). When lowering the methanol concentration, water was added by the pure water supply means 707 to dilute the methanol. In the case of diluting the methanol concentration, since the methanol concentration deficiency causes deterioration of the anode of the DMFC main body 702, the dilution rate is slightly reduced. In this embodiment, the range of change in the dilution direction was 10 seconds per 1% (0.3 mol / liter).

On the other hand, the load current was set to be 10 seconds per change width of 1A.

When the methanol concentration was controlled under these conditions, it was found that the methanol concentration could be controlled according to the load demand as shown in FIG.
While the above description has been made with reference to exemplary embodiments, it will be apparent to those skilled in the art that the invention is not limited thereto and that various changes and modifications can be made within the spirit of the invention and the scope of the appended claims.

101, 701

Fuel cell system

102, 702

Fuel cell

103, 703 Container for storing

fuel stock solution

104, 704 Fuel supply means 105, 705

Fuel circulation line

106, 706

Pure water container

107, 707 Pure water supply means 108, 708

Fuel tank

109, 709

Fuel circulation pump

110, 710 Gas-liquid separator 111, 711 Air supply means 112, 712, 713

Concentration measuring element

120, 720

Control circuit

121, 721, 724

Current signal line

122, 722

Fuel control line

123, 723 Pure

Water control line

124, 725

Oxidant discharge system

214, 314

Ion conductor

215, 315

Fuel oxidation electrode

216, 316

Gas generation electrode

217, 417

Fuel detector

318, 319, 418, 419

Current terminal

320, 420

Fuel flow pipe

421 , 422 Graphite parts 423 Counterbore part 501 Single cell 502 Membrane-electrode assembly (MEA)
504 Separator having fuel flow path and oxidant flow path 505 Gasket (seal)
507 Insulating plate 509

End plate

510, 522

Fuel piping connector

511, 523

Oxidant piping connector

513, 514 Current collecting plate 516 Bolt 517 Spring 518 Nut 519 External power line 520 DC-DC converter or inverter 521 Load 531 installed outside Separator having fuel flow path 532 Separator having oxidant flow path

Claims

A solid polymer electrolyte membrane; an electrode joined to the surface of the electrolyte membrane; a separator formed with a groove for circulating a fuel or an oxidant; a fuel supply port; and a fuel discharge port. In the fuel cell
A concentration measuring element having a methanol oxidation electrode and a fuel flow passage formed on the electrode is installed in the middle of a fuel circulation pipe for circulating fuel between the fuel supply port and the fuel discharge port. A fuel cell provided with a fuel control circuit for controlling the fuel concentration according to the detected methanol concentration.
The fuel cell according to claim 1, wherein the concentration measuring element has a methanol oxidation electrode and a hydrogen generation electrode.
3. The fuel cell according to claim 2, wherein the hydrogen generating electrode is provided with a function of increasing water repellency as compared with a methanol oxidation electrode.
The fuel cell according to claim 1, wherein a porous membrane that suppresses permeation of liquid methanol and permeates methanol vapor is installed on the methanol oxidation electrode.
The methanol oxidation electrode and the hydrogen generation electrode are formed on respective surfaces of a hydrogen ion conductor, the hydrogen ion conductor is sandwiched between two conductive members having a flow path for flowing fuel, and the member The fuel cell according to claim 2, wherein the two are electrically insulated from each other.
The fuel cell according to claim 2, wherein the amount of platinum used for the methanol oxidation electrode or the hydrogen generation electrode is 1 mg or less per 1 cm 2 of electrode area.
The fuel cell according to claim 1, wherein the fuel control circuit has a function of storing and calculating a generated electricity amount and a methanol concentration, and changes a methanol concentration or a flow rate of the fuel flowing through the fuel circulation pipe.
A membrane electrode assembly comprising a solid polymer membrane, a cathode formed on one surface of the solid polymer membrane, an anode formed on the other surface of the solid polymer membrane, and a fuel or an oxidant A fuel cell having a separator that sandwiches the membrane electrode assembly;
A fuel tank for storing fuel comprising a liquid organic compound supplied to the fuel cell;
In a fuel cell system comprising a fuel circulation pipe for circulating the fuel between the fuel tank and the fuel cell,
A concentration measuring element disposed in the fuel circulation pipe for measuring an oxidation current of the fuel;
A fuel cell system comprising: a fuel control circuit that detects a fuel concentration from an oxidation current measured by the concentration measuring element and controls the fuel concentration of the fuel tank based on the fuel concentration.
9. The fuel cell system according to claim 8, wherein the concentration measuring element includes a hydrogen ion conductor, a fuel oxidation electrode on one surface of the hydrogen ion conductor, and a hydrogen generation electrode on the other surface. And a current terminal for taking out the current from the fuel detection part to the outside of the element.
10. The fuel cell system according to claim 9, wherein the concentration in the fuel is increased or decreased according to a change in an output value of the fuel cell.
10. The fuel cell system according to claim 9, wherein the fuel oxidation electrode has a porous membrane on the surface of the fuel oxidation electrode that has a characteristic of suppressing liquid permeation and allowing vapor to permeate.
10. The fuel cell system according to claim 9, wherein the concentration measuring element has a flow cell structure.
The fuel cell system according to claim 8, wherein
A fuel concentration adjusting tank storing fuel or water having a predetermined concentration for adjusting the concentration of fuel stored in the fuel tank, and supplying fuel or water having a predetermined concentration from the fuel concentration adjusting tank to the fuel tank. Supply means,
The fuel control circuit controls a supply amount of fuel or water having a predetermined concentration supplied from the supply means to a fuel tank.
9. The fuel cell system according to claim 8, wherein a plurality of the concentration measuring elements are arranged in the fuel circulation pipe.
9. The fuel cell system according to claim 8, wherein the fuel is any one of methanol, ethanol, dimethyl ether, dimethoxyethane, dioxane, formaldehyde, and formic acid.