JP2009245641A - Fuel cell system - Google Patents

Abstract

A fuel cell system that suppresses a decrease in oxygen diffusion capacity of a cathode due to flooding and maintains a stable output for a long period of time.
A power generation unit including an anode that oxidizes a fuel that is a mixed solution of water and alcohol, a cathode that reduces an oxidant-containing gas, and a solid polymer electrolyte membrane sandwiched between the anode and the cathode; A fuel supply unit that supplies fuel to the anode, an oxidant-containing gas supply unit that supplies an oxidant-containing gas to the cathode, and an oxidant-containing gas supply unit that is interposed between the oxidant-containing gas and the cathode to humidify the oxidant-containing gas. A first control for adjusting the humidity of the oxidant-containing gas supplied to the cathode based on information obtained from the voltage measurement unit, a voltage measurement unit for measuring a voltage between the anode and the cathode, And a fuel cell system.
[Selection] Figure 1

Description

  The present invention relates to a fuel cell system, and more particularly to a polymer electrolyte fuel cell system.

    In recent years, fuel cells have been actively developed along with the expansion of applications of portable devices. In particular, in fuel cells for portable devices, development of a direct methanol fuel cell (DMFC) that supplies methanol directly to the cell is being researched and developed for use as a power source for portable devices, particularly cellular phones and notebook PCs.

    In a fuel cell, a required output is obtained by connecting a plurality of single cells in series. Depending on the connection method of the single cells, it can be divided into a three-dimensional stack called a stack type and a two-dimensional layout called a planar type. The stack type can effectively use heat generated by power generation to obtain high output, but has a problem that it cannot be made compact in volume as a portable device. The flat type has advantages such as being able to be compact in volume and suppressing the use of auxiliary equipment in air distribution, and has been intensively studied for portable devices.

    In general, in the DMFC currently developed, a single cell is obtained by heating an electrode member made of a carbon porous plate coated with a catalyst layer to a solid polymer proton conductive film (for example, Nafion film (registered trademark) manufactured by Dupont). It is manufactured by bonding by crimping or the like.

    A Pt—Ru alloy catalyst and a Pt catalyst are used for the anode electrode and the cathode electrode, respectively. In particular, a large amount of catalyst is used for obtaining high output in the DMFC.

    In DMFC, since fuel is directly supplied to a cell to generate power, it is attracting attention as a fuel cell that is superior in portability and safety as compared with fuel cells that use hydrogen or other fuels.

  However, the DMFC has a problem that a power generation output (voltage) decreases with time when power is generated continuously for a long period of time. Reasons for this decrease in output include reduced activity of the anode and cathode catalyst, deterioration of the electrolyte membrane, and decrease in the ability to diffuse fuel and oxygen at the anode and cathode, and the cause of deterioration varies depending on the power generation conditions. I know it.

  As described above, among the factors that reduce the output of the fuel cell system, the phenomenon in which the oxygen diffusing capacity of the cathode decreases due to the retention of water at the cathode is commonly known as cathode flooding.

  In particular, in the case of a fuel cell that generates power by supplying liquid fuel directly to the anode, such as DMFC, water in the liquid fuel tends to remain in the cell excessively. This excess water is excellent in terms of suppressing a decrease in proton conductivity due to drying of the electrolyte membrane, but causes power generation characteristics to deteriorate due to flooding of the cathode.

  As described above, the decrease in output due to the flooding of the cathode accounts for the majority of the decrease in output of the DMFC. Therefore, a technique for establishing stabilization of the power generation output by avoiding this is technically required.

  On the other hand, even if the fuel supply is controlled so that water is not supplied excessively, the amount of water remaining in the cell may decrease depending on the state of the power generation cell (hereinafter abbreviated as a cell) during power generation. When the amount of water remaining in the cell is reduced, the water in the electrolyte membrane is deficient, resulting in an increase in cell resistance, resulting in a decrease in output.

As a technique for managing the water of the fuel cell system in this way, there is Patent Document 1.
JP 2001-143732 A

  The technique shown in Patent Document 1 controls moisture in the air supplied to the cathode while monitoring the humidity in the system. However, Patent Document 1 is used for a fuel cell using hydrogen as a fuel. For example, in a DMFC using a mixed solution of methanol and water as a fuel, the cell voltage is a methanol crossover amount, a cell temperature. Affected by flooding. That is, since Patent Document 1 does not control the humidity at the time of air supply, it is inappropriate control for DMFC.

  The present invention has been made to solve such problems, and by controlling the humidity in the oxidant-containing gas (for example, air) supplied to the cathode while monitoring the voltage of the power generation unit of the fuel cell system. An object of the present invention is to provide a fuel cell system that maintains a stable output for a long period of time by preventing a decrease in the oxygen diffusing capacity of the cathode due to flooding by preventing excessive water from staying at the cathode.

  A fuel cell system according to the present invention includes an anode that oxidizes a fuel that is a mixed solution of water and alcohol, a cathode that reduces an oxidant-containing gas, and a solid polymer electrolyte membrane that is sandwiched between the anode and the cathode. A power generation unit, a fuel supply unit for supplying fuel to the anode, an oxidant-containing gas supply unit for supplying an oxidant-containing gas to the cathode, an oxidant-containing gas supply unit and the cathode, Adjust the humidity of the oxidant-containing gas supplied to the cathode based on the information obtained from the voltage measurement unit, the voltage measurement unit that measures the voltage between the anode and the cathode, and the oxidant-containing gas humidification unit that humidifies the oxidant-containing gas And a control unit.

  According to the present invention, there is provided a fuel cell system capable of maintaining a stable output for a long period of time by suppressing a decrease in oxygen diffusion capacity of a cathode due to flooding.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  Further, the embodiments described below exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention includes the material, shape, structure, The arrangement is not limited to the following. The technical idea of the present invention can be variously modified within the scope of the claims.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In the following description, a direct methanol fuel cell system (DMFC) using a methanol aqueous solution as a fuel will be described as an example.

  FIG. 1 shows the configuration of the fuel cell system according to the first embodiment.

  The fuel cell system 10 according to the first embodiment shown in FIG. 1 controls the fuel supply unit 42 and optimizes the structure of the membrane electrode assembly (MEA) so that excessive water does not remain in the cell. First, the fuel cell system 10 is driven by controlling the fuel supply unit 42, the oxidant-containing gas supply unit 52, and the oxidant-containing gas humidification unit 53 so that excessive water is not supplied to the power generation unit 4. To do.

  The amount of fuel 41 (water and methanol) supplied to the cell can be changed by controlling the fuel supply and the shape of the MEA. The fuel 41 used in the anode reaction during power generation of DMFC is water: methanol = 1: 1 (molar ratio). However, when protons generated at the anode move to the cathode, about three waters move as entrained water. Therefore, in the DMFC, the water / methanol ratio (molar ratio) actually supplied to the cell is not 1, but varies from about 1 to 19 depending on the fuel control and MEA structure. The excess water described above is water that moves with protons, and is reduced as much as possible.

  For example, in fuel supply, an aqueous methanol solution (3 to 10 mol / L) having a higher methanol concentration than usual (1 to 2 mol / L) is used, and the supply amount of the fuel 41 per unit time is reduced. In the MEA structure, a carbon porous plate with high water repellency is used for the anode 2, or an MPL layer (Micro Porous Layer) is provided between the anode catalyst layer 21 and the anode porous plate (anode gas diffusion layer 22 described later). ) To prevent unnecessary water for the reaction at the anode 2 from entering the cell.

  The fuel cell system according to the embodiment of the present invention includes an anode 2 that oxidizes fuel 41, a cathode 3 that reduces oxidant-containing gas 51, and an electrolyte sandwiched between anode 2 and cathode 3 (solid polymer). A power generation unit 4 composed of the membrane 1, a fuel supply unit 42 for supplying fuel 41 to the anode 2, an oxidant-containing gas supply unit 52 for supplying an oxidant-containing gas 51 to the cathode 3, and an oxidant-containing gas An oxidant-containing gas humidifying unit 53 that is interposed between the supply unit 52 and the cathode 3 and humidifies the oxidant-containing gas 51, a voltage measuring unit 6 that measures the voltage between the anode 2 and the cathode 3, and a voltage measurement And a control unit 7 that adjusts the humidity of the oxidant-containing gas 51 supplied to the cathode 3 based on the information obtained from the unit 6.

  Hereinafter, a description will be given with reference to FIG.

(Power generation part)
The power generation unit 4 has an electrolyte membrane 1 sandwiched between an anode 2 and a cathode 3.

(Electrolyte membrane)
In the case of a direct methanol fuel cell system (DMFC), the electrolyte membrane 1 may be, for example, a Dupont Nafion membrane (registered trademark). The electrolyte membrane 1 functions as a medium for transferring protons (H ⁺ ) generated in the catalyst layer 21 of the anode 2 (hereinafter referred to as the anode catalyst layer 21) to the catalyst layer of the cathode 3 (hereinafter referred to as the cathode catalyst layer 31). .

(Anode catalyst layer / Cathode catalyst layer)
An anode catalyst layer 21 and a cathode catalyst layer 31 are disposed on both sides of the electrolyte membrane 1. When an aqueous methanol solution is used as the fuel 41, for example, a Pt—Ru catalyst can be used for the anode catalyst layer 21. Further, a noble metal catalyst such as a Pt catalyst can be used for the cathode catalyst layer 31.

  The anode catalyst layer 21 is obtained by mixing a Pt-Ru catalyst with a perfluorosulfonic acid resin solution (Nafion solution (trademark)), water, and ethylene glycol, and then dispersing the mixture on the electrolyte membrane by a spray method. Can be produced.

  The cathode catalyst 31 is prepared by mixing a Pt catalyst with a perfluorosulfonic acid resin solution (Nafion solution (trademark)), water, and ethylene glycol, and then applying the mixture onto the electrolyte membrane by a spray method. can do.

(Anode gas diffusion layer, cathode gas diffusion layer)
An anode gas diffusion layer 22 and a cathode gas diffusion layer 32 are disposed on the opposite sides of the anode catalyst layer 21 and the cathode catalyst layer 31 from the electrolyte membrane 1, respectively. For the anode gas diffusion layer 22 and the cathode gas diffusion layer 32, carbon paper, carbon cloth, carbon non-woven fabric, or the like can be used. Each gas diffusion layer may be provided with a carbon dense water repellent layer (microporous layer: MPL) mainly composed of carbon powder and PTFE.

  The anode gas diffusion layer 22 provides a function of smoothly supplying fuel to the anode catalyst layer 21, discharging a product, and collecting current. The cathode gas diffusion layer 32 provides a function of smoothly supplying air to the cathode catalyst layer 31, discharging a product, and collecting current.

  A structure in which the anode gas diffusion layer 22, the anode catalyst layer 21, the electrolyte membrane 1, the cathode catalyst layer 31, and the cathode gas diffusion layer 32 are sequentially laminated is often referred to as a membrane electrode assembly (MEA) 5.

(Stacking method of membrane electrode composite)
The membrane electrode assembly 5 is produced, for example, by joining the electrolyte membrane 1 having the anode catalyst layer 21 and the cathode catalyst layer 31 applied on both surfaces, and the anode gas diffusion layer 22 and the cathode gas diffusion layer 32. Alternatively, the electrolyte membrane 1 may be joined to the anode gas diffusion layer 22 coated with the anode catalyst layer 21 and the cathode gas diffusion layer 32 coated with the cathode catalyst layer 31. By joining at a high pressure, the contact resistance at the interface contacting the anode catalyst layer 21 and the cathode catalyst layer 31 can be reduced.

  Here, “joining” means that both members are integrated by being compressed in advance using a press or the like, and a part of one member and another member facing each other is fused to use a simple tool. This means a processing method that is difficult to separate without deformation of the member to a certain extent, or a resulting state. For example, this also applies to the membrane electrode assembly 5. The member after joining as the membrane electrode assembly 5 has a reduced thickness on the entire surface compared to the thickness of the original member. On the other hand, “contact” described later means a state in which both can be easily separated when the membrane electrode assembly 5 is disassembled without being previously integrated by compression. Are distinguished.

(Anode channel plate)
An anode flow path plate 23 is disposed on the opposite side of the anode gas diffusion layer 22 from the anode catalyst layer 21. The anode flow path plate 23 has fuel anode flow paths 25 (25a, 25b, 25c). The anode channel 25 provided in the anode channel plate 23 can be, for example, a serpentine channel or a parallel channel in which a plurality of channels run in parallel.

The anode channel plate 23 is an anode channel for the purpose of supplying fuel to the anode catalyst layer 21 through the anode diffusion layer 22 and for discharging the product (CO ₂ etc.) generated by the anode reaction (Formula 1). 25 is provided. In addition, it is also possible to give the function of the current collecting plate of the anode 2 by using conductive carbon or the like for the anode flow path plate 23.

  Thus, the anode current collector to the electrolyte membrane 1 and the boundary are used as the anode 2. That is, in the present embodiment, the anode flow path plate 23, the anode gas diffusion layer 22, and the anode catalyst layer 21 correspond to the anode 2.

(Cathode channel plate)
On the opposite side of the cathode gas diffusion layer 32 from the cathode catalyst layer 31, a cathode flow path plate 33 is disposed. The cathode channel plate 33 has a cathode channel 35 (35a, 35b, 35c) of an oxidizing agent-containing gas. The cathode channel 35 provided in the cathode channel plate 33 can be, for example, a serpentine channel or a parallel channel in which a plurality of channels run in parallel.

The cathode flow path plate 33 is used for supplying an oxidant supply gas to the cathode catalyst layer 31 through the cathode gas diffusion layer 32 and for discharging products (H ₂ O, etc.) generated by the cathode reaction (formula 2). Therefore, a cathode channel 35 is provided. The cathode channel plate 33 can be provided with the function of a cathode current collecting plate by using conductive carbon or the like.

Thus, the cathode 3 is defined from the cathode channel plate 33 to the electrolyte membrane 1 and the boundary. That is, in the present embodiment, the cathode flow path plate 33, the cathode gas diffusion layer 32, and the cathode catalyst layer 31 correspond to the cathode 3.
(Fuel supply part)
The fuel cell system according to the present embodiment includes a fuel supply unit 42 that supplies fuel 41 to the anode 2. The fuel supply unit 42 has a function of sending the fuel 41 from the fuel container 43 in which the fuel 41 is stored to the anode flow path 25 (25a to 25c) of the anode 2. For example, a pump can be used as the fuel supply unit 42. As the fuel 41, an aqueous methanol solution adjusted to a predetermined concentration (for example, 4 mol-CH ₃ OH / L) can be used.

(Oxidant-containing gas supply unit)
The fuel cell system according to the present embodiment includes an oxidant-containing gas supply unit 52 that supplies the oxidant-containing gas 51 to the cathode 3. The oxidant-containing gas supply unit 52 has a function of sending an oxidant-containing gas 51, for example, oxygen-containing air, to the cathode flow path 35 (35 a to 35 c) of the cathode 3. For example, a pump can be used for the oxidant gas supply unit 52. Or the cylinder etc. which pressurized and stored the oxidizing agent containing gas can also be used.

(Oxidant-containing gas humidifier)
The fuel cell system according to the present embodiment includes an oxidant-containing gas humidifying unit 53 that is interposed between the oxidant-containing gas supply unit 52 and the cathode 3 and humidifies the oxidant-containing gas 51. The oxidant-containing gas humidifying unit 53 has a function of relatively changing the humidity of the oxidant-containing gas 51.

  For example, as shown in FIG. 1, it can be comprised from the switching valve | bulb 54 and the container 55 which stored water. The container 55 storing water has a function of bubbling water with the oxidant-containing gas 51 sent from the oxidant-containing gas supply unit 52 and humidifying the oxidant-containing gas 51. In order to change the humidity of the oxidant-containing gas 51 relatively, by switching the switching valve 54, when the oxidant-containing gas 51 passes through the container 55 storing water, the humidity is relatively high. When not going through, it can be realized by appropriately selecting a relatively low humidity state.

  Alternatively, an appropriate amount of water may be supplied to the cathode 3 together with the oxidant-containing gas 51 when the oxidant-containing gas 51 is supplied. This means is effective when the container 55 is bubbled and the oxidant-containing gas 51 is humidified and supplied. This is because when the water temperature inside the container 55 is 60 ° C. or less, it is difficult to supply sufficient water to the cathode 3 together with the oxidant-containing gas even if bubbling (because the water vapor partial pressure of water is low). is there. Specifically, water is contained in a porous body such as sponge and oxygen-containing gas 51 is passed through the surface for humidification, or a small amount of water is supplied to the supply channel of the oxidant-containing gas 51 with a pump or the like. Thus, it is possible to apply a method of directly supplying the oxidant-containing gas 51 and water droplets to the cathode flow channel in the cell.

(Voltage measurement unit)
The fuel cell system according to the present embodiment has a voltage measuring unit 6 that measures the voltage between the anode 2 and the cathode 3. When the power generator 4 uses the anode current collector and the cathode current collector as described above, the voltage measuring unit 6 can measure the voltage between them by applying a known voltage measuring means. it can.

  In addition, the fuel cell system according to the present embodiment may include a temperature measurement unit 8 that measures the temperature of the power generation unit 4. The temperature measuring unit 8 can measure by applying a known temperature measuring means such as installing a thermocouple on the anode 2.

(Control part)
The fuel cell system according to the present embodiment includes a control unit 7 that adjusts the humidity of the oxidant-containing gas 51 supplied to the cathode 3 based on information obtained from the voltage measurement unit 6. Information (voltage information) obtained by the voltage measuring unit 6 is sent to the control unit 7 through the signal line E4.

  FIG. 3 shows the configuration of the control unit 7. The control unit 7 includes an external input unit 100, a determination unit 110, an adjustment unit 120, an information storage unit 130, and an arithmetic processing unit 140.

(External input section)
The external input unit 100 includes a voltage input unit 101 and a temperature input unit 102. The voltage input unit 101 is connected to the voltage measurement unit 6 through a signal line E4. The temperature input unit 102 is connected to the temperature measurement unit 8 through a signal line E3.

(Judgment part)
The determination unit 110 includes a voltage determination unit 111 and a temperature determination unit 112. Whether the voltage determination unit 111 relatively changes the humidity of the oxidant-containing gas 51 through the oxidant-containing gas humidification unit 53 based on information (voltage information) obtained from the voltage measurement unit 6 via the signal line E4. It has a function to determine whether or not.

  Further, the temperature determination unit 112 increases or maintains the supply amount of the fuel 41 per unit time through the fuel supply unit 42 based on information (temperature information) obtained from the temperature measurement unit 8 through the signal line E3. It has a function to determine the decrease.

(Adjustment part)
The adjustment unit 120 includes a humidity adjustment unit 121 and a fuel supply adjustment unit 122. The humidity adjusting unit 121 is connected to the oxidant-containing gas humidifying unit 53 through the signal line E2. In the first embodiment, the switching valve 54 switches the flow path of the oxidant-containing gas and has a function of adjusting the humidity of the oxidant-containing gas 51.

  The fuel supply adjustment unit 122 is connected to the fuel supply unit 42 through the signal line E1. The second embodiment is connected to the above-described fuel supply unit 42 (pump) and has a function of adjusting the fuel supply amount per unit time.

(Information storage)
The information storage unit 130 includes a voltage information storage unit 131 and a temperature information storage unit 132. Voltage information and temperature information for reference for determination performed by the determination unit 110 are stored. The information storage unit 130 can be a storage medium such as a hard disk.

(Calculation processing part)
The arithmetic processing unit 140 has functions for exchanging information with the external input unit 100, the determination unit 110, the adjustment unit 120, and the information storage unit 130, calculating and processing information, storing the information in the information storage unit 130, and the like. The arithmetic processing unit 140 can be a CPU such as an electronic computer.

(Function of fuel cell)
Next, the basic function of the power generation stack shown in FIG. 1 will be described. First, the fuel 41 (methanol aqueous solution) is supplied to the anode flow path 25 through the fuel supply unit 42 (pump), and is supplied to the anode catalyst layer 21 through the anode gas diffusion layer 22. In the anode catalyst layer 21 of the membrane electrode assembly 5, the above-described anode reaction (formula 1) occurs.

Based on (Formula 1), protons (H ⁺ ) generated in the anode catalyst layer 21 flow from the anode catalyst layer 21 through the electrolyte membrane 1 to the cathode catalyst layer 31. Electrons (e ⁻ ) are carried to the cathode catalyst layer 31 via the anode gas diffusion layer 22, the anode flow path plate 23, an external circuit (not shown), the cathode flow path plate 33, and the cathode gas diffusion layer 32. Carbon dioxide (CO ₂ ) generated in the anode catalyst layer 21 is discharged to the outside through the anode gas diffusion layer 22 and the anode flow path 25.

  By the air 12 supplied from the oxidant gas means 52, protons and electrons are consumed in the cathode catalyst layer 31 by the cathode reaction shown in (Formula 2) described above. In FIG. 1, the oxidant-containing gas 51 is supplied to the cathode catalyst layer 31 through the cathode channel 35 and the cathode gas diffusion layer 32 of the cathode channel plate 33.

In general, when the cathode reaction (formula 2) occurs, methanol (CH ₃ OH) and water (H ₂ O) also move through the electrolyte membrane 1 along with the movement of protons (the former is methanol crossover and the latter is water). Called a crossover). Of these, methanol that has permeated through the electrolyte membrane 1 undergoes an oxidation reaction shown in (Equation 3) in the cathode catalyst layer 31 by the air 51 supplied from the oxidant gas supply unit 52 to generate water.

  Further, the water generated in the cathode reaction (Formula 2) and a part of the permeated water are back-diffused through the electrolyte membrane 1 to the anode catalyst layer 21. The remaining water is discharged from the membrane electrode assembly 5 to the outside through the cathode channel plate 33.

  Here, when water generated by the cathode reaction shown in (Formula 2) and the oxidation reaction shown in (Formula 3) is not properly discharged from the cathode 3, the water stays in the cathode 3, and the oxidant-containing gas 41 becomes the cathode catalyst. 31 is not properly supplied. This is the cathode flooding described above.

  In the fuel cell system 10 according to the present invention, the amount of moisture remaining in the power generation unit 4 during power generation can be adjusted by including the fuel supply unit 42 and the oxidant-containing gas humidification unit 53. As a result, it is possible to suppress a reduction in output due to flooding of the cathode 3 caused by excess water remaining in the cathode 3.

  This flooding can be prevented by performing the following control in the control unit 7.

  Hereinafter, this procedure will be described with reference to FIG.

[Flooding]
FIG. 4 is a process flow showing a procedure for preventing flooding of the cathode 3. As a matter of course, flooding of the cathode 3 occurs when the fuel cell system 10 performs a predetermined output within the design range, so that the fuel cell system 10 is in an operating state. At this time, it is assumed that the voltage of the power generation unit 4 is constantly measured by the voltage measurement unit 6 and sent to the control unit 7 through the signal line E4. In addition, the measurement of the voltage of the electric power generation part 4 by the voltage measurement part 6 may be measured suitably as needed.

  The voltage information sent to the voltage input unit 101 of the control unit 7 is subjected to arithmetic processing by the arithmetic processing unit 140 or compared with temperature information stored in advance in the voltage information storage unit 131. The results of these arithmetic processes and comparison reference are stored in the voltage determination unit 111. Based on the result stored in the voltage determination unit 111, the oxidant-containing gas humidification unit 53 is controlled from the humidity adjustment unit 121 via the signal line E2.

  For convenience of explanation, the following four are defined as predetermined voltages.

V3: Minimum voltage value judged to be unrecoverable in operation of the fuel cell system V1: Minimum voltage value allowed in operation of the fuel cell system V2: Maximum voltage value allowed in operation of the fuel cell system V4: Fuel cell The maximum voltage value Vi (i = 1, 2, 3, 4) determined to be unrecoverable in the operation of the system is a preset value according to the type of the fuel cell system, and the voltage information storage unit 131. And is referred to as appropriate. Note that V3 <V1 ≦ V2 <V4.

(First non-humidifying step: S1)
First, as an initial state, a first non-humidification step S1 for supplying a non-humidified oxidant-containing gas to the fuel cell system 10 is performed. Here, the “non-humidified oxidant-containing gas” means that the oxidant-containing gas 51 is changed to the oxidant gas 51 having relatively low humidity by the operation of the oxidant-containing gas humidifying unit 53. On the other hand, the “humidified oxidant-containing gas” means that the oxidant-containing gas 51 is oxidized by the operation of the oxidant-containing gas humidifying unit 53 with a relatively high humidity compared to the previous “non-humidified oxidant-containing gas”. It means that it is the agent gas 51.

  For example, in the fuel cell system 10 shown in FIG. 1, the first non-humidifying step S1 can be performed by switching the valve 54 so that the oxidant-containing gas 51 does not pass through the container 55 storing water.

  After a predetermined time (for example, 5 to 10 minutes) has passed since the non-humidified oxidant-containing gas is supplied to the cathode 3 and the fuel cell system 10 has stabilized, the voltage value V is determined based on the information obtained from the voltage measurement unit 6. Ask. Here, “determining the voltage value V based on the information obtained from the voltage measuring unit 6” means that the information obtained from the voltage measuring unit is not necessarily the voltage value itself (for example, the voltage measuring unit 6 Information may be sent in the form of a signal of 0-5V), meaning that such information is arithmetically processed (converted) by the arithmetic processing unit 140 to obtain a correct value (voltage V).

  Depending on the voltage value V, the control unit 7 determines and controls in the following cases.

  (S1-1) V4 <V: A predetermined operation stop mode is entered.

  (S1-2) V2 <V ≦ V4: The first non-humidifying step S1 is continued.

  (S1-3) V1 ≦ V ≦ V2: The first non-humidifying step S1 is continued.

  (S1-4) V <V1: The humidification step S2 is performed.

(Humidification step: S2)
When it determines with the above (S1-4), humidification step S2 is performed as follows. For example, in the fuel cell system 10 shown in FIG. 1, the humidifying step S2 can be performed by switching the valve 54 so that the oxidant-containing gas 51 passes through the container 55 storing water.

  After the humidified oxidant-containing gas is supplied to the cathode 3 and a predetermined time (for example, 5 to 10 minutes) elapses and the fuel cell system 10 is stabilized, the voltage value V is obtained from the voltage information obtained from the voltage measuring unit 6. At this time, according to the voltage value V, the control unit 7 determines and controls in the following cases.

  (S2-1) V1 ≦ V: The first non-humidifying step S1 is performed.

  (S2-2) V <V1: It is determined that there is another cause.

  That is, when it is determined that the voltage value V obtained based on the information obtained from the voltage measurement unit 6 is smaller than a predetermined voltage value (in the above case, V1 corresponds to this), the control unit 7 performs the cathode 3 The humidity of the oxidant-containing gas 51 to be supplied to the cathode 3 is adjusted to be supplied to the cathode 3 (humidification step S2).

(Effects of the first embodiment)
Thus, according to 1st Embodiment, it is possible to perform 1st non-humidification step S1 and humidification step S2 by having the voltage measurement part 6, the control part 7, and the oxidizing agent containing gas humidification part 53. It becomes. As a result, the amount of moisture remaining in the power generation unit 4 during the power generation of the fuel cell system 10 can be adjusted. This also has the effect of suppressing a reduction in output due to flooding of the cathode 3 caused by excess water remaining in the cathode 3.

  Furthermore, when the output is reduced, it can be determined whether or not it is caused by flooding of the cathode 3. That is, except for the case of (S2-2), the decrease in the output of the fuel cell system 10 is caused by the flooding of the cathode 3, and the output can be recovered by the first non-humidification step S1 and the humidification step S2.

[Second Embodiment]
In the first embodiment, the case of (S2-2), that is, the case where it is determined that the decrease in the output of the fuel cell system 10 is not due to the flooding of the cathode 3 and that there is another cause. A second embodiment will be described.

  In the fuel cell system 10 in which the fuel 41 is directly supplied to the anode 2, the output (voltage) may not decrease due to the voltage decrease due to the flooding of the cathode 3. This is because the fuel 41 called “fuel crossover” is excessively supplied, or conversely, the fuel 41 is insufficiently supplied. In such a case, a state is observed in which the output (voltage) decreases even when the output (voltage) does not decrease due to flooding at the cathode 3.

  Here, when the fuel 41 is excessively supplied due to the fuel crossover, the temperature of the power generation unit 4 rises at the cathode 3 due to the oxidation reaction of the fuel 41 shown in (Equation 3). Conversely, when the fuel 41 is insufficiently supplied, the fuel 41 supplied to the oxidation reaction at the cathode 3 decreases, so the temperature of the power generation unit 4 decreases.

  In the second embodiment, this feature is utilized, and the voltage of the power generation unit 4 falls below the minimum voltage value (V1) allowed in the operation of the fuel cell system ((S2 in the first embodiment) 2)), whether the voltage drop due to the crossover of the fuel 41 or the voltage drop due to the shortage of the fuel 41 has occurred by controlling the fuel supply unit 42 is determined depending on the temperature of the power generation unit 4. Is measured by the temperature measuring unit 8 and determined by the control unit 7. Specifically, the cause of the decrease in output can be determined in detail by performing the following procedure based on the temperature information obtained from the temperature measurement unit 8 of the power generation unit 4.

  In addition to the second embodiment and the first embodiment, the power generation unit 4 has a temperature measurement unit 8 that measures the temperature of the power generation unit 4, and the control unit 7 is based on information obtained from the temperature measurement unit 8. In this fuel cell system, the fuel supply amount per unit time supplied to the anode 3 is adjusted.

  Here, the temperature of the power generation unit 4 by the temperature measurement unit 8 may be continuously measured while it is operating, or may be appropriately measured as necessary. The temperature information is sent to the control unit 7 through the signal line E3.

  The temperature information sent to the temperature input unit 102 of the control unit 7 is arithmetically processed by the arithmetic processing unit 140 or compared with temperature information stored in advance in the temperature information storage unit 132. The results of these calculation processes and comparison reference are stored in the temperature determination unit 112. Based on the result stored in the temperature determination unit 112, the fuel supply unit 42 is controlled from the fuel supply adjustment unit 122 via the signal line E1.

  For convenience of explanation, the following four are defined as predetermined temperatures.

T3: Minimum temperature judged to be unrecoverable in the operation of the fuel cell system T1: Minimum temperature allowed in the operation of the fuel cell system T2: Maximum temperature allowed in the operation of the fuel cell system T4: Operation of the fuel cell system The maximum temperature Ti determined to be unrecoverable in (i = 1, 2, 3, 4) is a preset value according to the type of the fuel cell system and the like, and is stored in the temperature information storage unit 131. Referenced as appropriate. Note that T3 <T1 ≦ T2 <T4.

(Anode temperature determination step: S3)
In the humidification step S2 (S2-2), when “determined that there is another cause” is determined, the following case classification is performed according to the temperature T measured by the temperature measurement unit 8 of the anode 2.

  (S3-1) T4 <T: A predetermined operation stop mode is entered.

  (S3-2) T2 <T ≦ T4: The fuel reduction step S4 is performed.

  (S3-3) T1 ≦ T ≦ T2: Voltage determination step S6 is performed.

  (S3-4) T3 ≦ T <T1: The fuel increase step S5 is performed.

  (S3-5) T <T3: Enters a predetermined operation stop mode.

  Whether the output of the fuel cell system 10 is reduced due to the anode temperature determination step S3 is due to the fact that the fuel 41 supplied to the power generation unit 4 is too much, causing a crossover. Alternatively, it is determined whether this is due to the fact that the temperature of the power generation unit 4 has decreased due to too little.

  In order to more accurately determine this, one of the following fuel reduction step S4 and fuel increase step S5 is performed according to the case classification in the anode temperature determination step S3.

(Fuel reduction step: S4)
When it is determined as (S3-2) above, the fuel reduction step S4 is performed as follows. For example, in the fuel cell system 10 shown in FIG. 1, the fuel reduction step S <b> 4 is performed by reducing the rotation speed of the pump of the fuel supply unit 42 and reducing the fuel 41 per unit time supplied to the power generation unit 4. Can do.

  Thus, after a predetermined time (for example, 5 minutes) has passed through the fuel reduction step S4 and the fuel cell system 10 is stabilized, the temperature of the power generation unit 4 is obtained from information obtained based on the temperature measurement unit 8. Here, “determining the temperature of the power generation unit 4 from the information obtained from the temperature measurement unit 8” is because the information obtained from the temperature measurement unit 8 is not necessarily the temperature value itself (for example, temperature measurement The information from the unit 8 may be sent in the form of a signal of 0-5V), which means that such information is arithmetically processed by the arithmetic processing unit 140 to obtain a correct value (temperature T). .

  At this time, it is determined and controlled by the control unit 7 in the following cases according to the temperature.

  (S4-1) T2 <T: The voltage determination step S6 is performed.

  (S4-2) T ≦ T2: The fuel reduction step S4 is continued.

  That is, when it is determined that the temperature value T obtained based on the information obtained from the temperature measuring unit 8 is included in the first range given in advance (corresponding to T2 <T <T4 in the above case). Further, an adjustment (fuel reduction step S4) is performed to reduce the supply of the fuel 41 per unit time supplied to the anode 3 by the control unit 7.

(Fuel increase step: S5)
When it is determined as (S3-4) above, the fuel increase step S5 is performed as follows. For example, in the fuel cell system 10 shown in FIG. 1, the fuel increase step S5 is performed by increasing the number of revolutions of the pump of the fuel supply unit 42 and increasing the fuel 41 per unit time supplied to the power generation unit 4. Can do.

  Thus, after a predetermined time (for example, 5 minutes) has passed through the fuel increasing step S5 and the fuel cell system 10 is stabilized, the temperature T is obtained from the temperature information obtained from the temperature measuring unit 8. At this time, it is determined and controlled by the control unit 7 according to the temperature T in the following cases.

  (S5-1) T1 ≦ T: Voltage determination step S6 is performed.

  (S5-2) T <T1: The fuel increase step S5 is continued.

  That is, when it is determined that the temperature value T obtained based on the information obtained from the temperature measuring unit 8 is included in the second range given in advance (corresponding to T3 <T <T1 in the above case). In addition, adjustment is performed to increase the supply of the fuel 41 per unit time supplied to the anode 3 by the control unit 7 (fuel increase step S5).

(Voltage judgment step: S6)
When it is determined as (S3-3), (S4-1), or (S5-1), the voltage determination step S6 is performed as follows.

  (S6-1) V3 ≦ V: The voltage determination step S6 is continued.

  (S6-2) V <V3: The second non-humidifying step S7 is performed.

(Second non-humidifying step: S7)
When it is determined as (S6-2), the second non-humidifying step S7 is performed as follows.

  (S7-1) V1 ≦ V: The second non-humidifying step S7 is continued.

  (S7-2) V3 ≦ V <V1: The first non-humidifying step S1 is performed.

  (S7-3) V <V3: Enters a predetermined operation stop mode.

(Effect of the second embodiment)
According to the second embodiment, if the output (voltage) seems to be lowered due to a malfunction of the fuel supply unit 42, after correcting it, the oxidant-containing gas humidification unit 53 is controlled again. As a result, when the temperature T of the power generation unit 4 recovers within the allowable range for operation of the fuel cell system 10 (T1 ≦ T ≦ T2), the oxidant-containing gas 51 is monitored while monitoring the voltage of the voltage measurement unit 6. By changing the humidity, the output (voltage) can be maintained in the stable region (V1 ≦ V ≦ V2) while suppressing flooding at the cathode 3.

  That is, the anode temperature determination step S3 can be performed by including the control unit 7, the temperature measurement unit 8, and the fuel supply unit 42. That is, the reason why the output of the fuel cell system 10 is reduced is that the fuel 41 supplied to the power generation unit 4 is too much to cause a crossover, or the power generation unit is too small. It is determined whether it is due to the temperature of 4 being lowered or due to other causes.

  In addition to this, by performing the fuel reduction step S4 or the fuel increase step S5 and the voltage determination step S6, the output decrease of the fuel cell system 10 can be recovered or cannot be recovered due to another cause. Can be determined. That is, except for the case of (S7-3), the output decrease of the fuel cell system 10 is caused by the crossover due to the excessive supply of the fuel 41 and the power generation unit 4 due to the insufficient supply of the fuel 41. This is due to the temperature drop, and the output can be recovered by the second non-humidifying step S7.

On the other hand, in the case of (S7-3), other than two causes (crossover due to excessive supply of fuel 41, temperature drop of power generation unit 4 due to insufficient supply of fuel 41) It can be determined that there is a cause.

The block diagram which shows the fuel cell system which concerns on this invention. Sectional drawing which shows the electric power generation part which concerns on this invention. The block diagram which shows the control part which concerns on this invention. The process flow figure concerning the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrolyte membrane 2 ... Anode 3 ... Cathode 4 ... Power generation part 5 ... Membrane electrode assembly (MEA)
6 ... Voltage measurement unit 7 ... Control unit (first control unit, second control unit)
DESCRIPTION OF SYMBOLS 8 ... Temperature measurement part 10 ... Fuel cell system 21 ... Anode catalyst layer 22 ... Anode gas diffusion layer 23 ... Anode flow path plate (anode current collecting plate)
24 ... Gaskets 25, 25a, 25b, 25c ... Anode channel 31 ... Cathode catalyst layer 32 ... Cathode gas diffusion layer 33 ... Cathode channel plate (cathode current collector plate)
34 ... Gasket 35, 35a, 35b, 35c ... Cathode channel 41 ... Fuel 42 ... Fuel supply part 43 ... Fuel container 51 ... Oxidant-containing gas (air)
52 ... Oxidant-containing gas supply unit 53 ... Oxidant-containing gas humidification unit 54 ... Valve (switching valve)
55 ... Containers E1, E2, E3, E4 ... Signal line

Claims (6)

A power generation unit including an anode that oxidizes a fuel that is a mixed solution of water and alcohol, a cathode that reduces an oxidant-containing gas, and a solid polymer electrolyte membrane sandwiched between the anode and the cathode;
A fuel supply unit for supplying the fuel to the anode;
An oxidant-containing gas supply unit for supplying the oxidant-containing gas to the cathode;
An oxidant-containing gas humidifying unit interposed between the oxidant-containing gas supply unit and the cathode and humidifying the oxidant-containing gas;
A voltage measuring unit for measuring a voltage between the anode and the cathode;
A control unit for adjusting the humidity of the oxidant-containing gas supplied to the cathode based on information obtained from the voltage measurement unit;
A fuel cell system comprising: The power generation unit has a temperature measurement unit for measuring the temperature of the power generation unit,
2. The fuel cell system according to claim 1, wherein the control unit adjusts a fuel supply amount per unit time supplied to the anode based on information obtained from the temperature measurement unit.   The fuel cell system according to claim 1 or 2, wherein the alcohol is methanol.   When it is determined that the voltage value obtained based on the information obtained from the voltage measurement unit is smaller than a predetermined voltage value, the humidity of the oxidant-containing gas supplied to the cathode by the control unit is set. The fuel cell system according to any one of claims 1 to 3, wherein an adjustment is made to raise and supply to the cathode.   When it is determined that the temperature value obtained based on the information obtained from the temperature measurement unit is included in the first range given in advance, the control unit supplies the anode with the unit time. The fuel cell system according to any one of claims 1 to 3, wherein adjustment is performed to reduce fuel supply.   When it is determined that the temperature value obtained based on the information obtained from the temperature measurement unit is included in the second range given in advance, the control unit supplies the anode to the anode. The fuel cell system according to any one of claims 1 to 3, wherein adjustment for increasing the supply of fuel is performed.

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