JP2008059998A - Operation method of fuel cell, and fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an operation method of a fuel cell and a fuel cell system capable of applying the operation method which can control a hydrous state of an electrolyte film. <P>SOLUTION: The operation method the fuel cell provided with an MEA having a pair of catalyst layers and an electrolyte film fitted between the pair, a separator each fitted at either side of the MEA and equipped with a plurality electrode elements and gas flow channels covered with an insulating layer comprises a judgment process judging a hydrous state of the electrolyte film, a conveyance judgment process judging whether waterdrops existing in the gas flow channels should be conveyed, and a conveyance direction deciding process deciding a conveying direction of waterdrops in case the conveyance judgment process judges that the waterdrops be conveyed. Based on a result of the conveyance direction deciding process, voltage is impressed on the plurality of electrode elements to convey the waterdrops thereby. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell operation method and a fuel cell system to which the operation method can be applied. In particular, the fuel cell operation method capable of managing the water content of an electrolyte membrane and the operation method are applicable. The present invention relates to a fuel cell system.

  A fuel cell has a membrane electrode assembly (hereinafter referred to as “MEA (Membrane)” including an electrolyte layer (hereinafter referred to as “electrolyte membrane”) and electrode layers (anode and cathode) respectively disposed on both sides of the electrolyte membrane. The electrical energy generated by the electrochemical reaction in “Electrode Assembly”) is taken out to the outside through current collectors (hereinafter referred to as “separators”) disposed on both sides of the MEA. Among fuel cells, polymer electrolyte fuel cells (hereinafter sometimes referred to as “PEFC (Polymer Electrolyte Fuel Cell)”) used in household cogeneration systems and automobiles, etc., are used at low temperatures. Is possible. In addition, PEFC has attracted attention as an optimal power source for electric vehicles and portable power sources because of its high energy conversion efficiency, short start-up time, and small and lightweight system.

  A single cell of PEFC includes an electrolyte membrane that exhibits proton conduction performance in a water-containing state, a cathode and an anode including at least a catalyst layer, and a theoretical electromotive force thereof is 1.23V. In PEFC, a hydrogen-containing gas is supplied to the anode, and an oxygen-containing gas is supplied to the cathode. The hydrogen supplied to the anode is separated into protons and electrons on the catalyst contained in the catalyst layer of the anode (hereinafter referred to as “anode catalyst layer”), and the protons generated from the hydrogen are separated into the anode catalyst layer and the electrolyte membrane. To the cathode catalyst layer (hereinafter referred to as “cathode catalyst layer”). On the other hand, electrons reach the cathode catalyst layer through an external circuit. Then, the protons and electrons that have reached the cathode catalyst layer react with oxygen supplied to the cathode catalyst layer, thereby generating water. In addition, since the single-cell electromotive force alone is not sufficient as a power source for an electric vehicle or the like, a stack-type fuel cell (hereinafter referred to as a “stack”) is generally configured by connecting single cells electrically in series. Is sometimes used.).

  The electrolyte membrane provided in the PEFC exhibits good proton conductivity at a predetermined temperature (for example, around 80 ° C.). Therefore, PEFC maintains the temperature of the electrolyte membrane by circulating a heat medium through a fluid flow path provided in the separator. Here, when the water generated in the cathode catalyst layer during steady operation of the PEFC touches the separator cooled by the cooling medium, the water is condensed to form droplet water (hereinafter referred to as “water droplet”). The water droplets can be discharged to the outside of the cell together with the gas flowing through the gas flow path provided in the separator. However, when the amount of water drops increases, the water drops accumulate in the gas flow path, and a so-called flooding state occurs. When water droplets accumulate, gas diffusion is hindered and the electrochemical reaction is less likely to occur. As a result, the power generation performance of PEFC is reduced. Therefore, it is effective to prevent the occurrence of the flooding state in order to suppress the performance degradation of PEFC.

  On the other hand, as described above, since the electrolyte membrane of PEFC exhibits proton conduction performance in a water-containing state, a single cell has a humidified hydrogen-containing gas and oxygen-containing gas (or these are collectively referred to as “reaction gas”). May be provided). Here, in many cases, the reaction gas on the gas channel inlet side in the single cell is dried more than the reaction gas on the outlet side, and the electrolyte membrane on the gas channel inlet side of the single cell is easily dried. When the electrolyte membrane is dried, the proton conducting performance is lowered, so that the power generation performance of the fuel cell is lowered. Therefore, in order to improve the performance of PEFC, in addition to preventing the occurrence of the flooding state, it is important to suppress drying of the electrolyte membrane, in other words, to manage the moisture content of the electrolyte membrane.

Several techniques aimed at managing the water content of the electrolyte membrane have been disclosed so far. For example, Patent Document 1 discloses that oxygen in an oxidizing gas that passes through an oxidizing gas passage provided on the cathode side of an electrolyte membrane and hydrogen in a fuel gas that passes through a fuel gas passage provided on the anode side of the electrolyte membrane. A fuel cell that generates electricity by an electrochemical reaction with the fuel cell, and a static electricity that is provided in at least one of the fuel gas passage and the oxidizing gas passage and discharges water droplets in the gas passage out of the gas passage. There is disclosed a fuel cell system including an electric transfer means. According to such a technique, moisture in the gas passage (corresponding to the “gas passage” described above; the same applies hereinafter) is removed with a simple structure without disposing a movable member such as a vibrator in the gas passage. I can do it. In Patent Document 1, when it is determined that the operation state of the fuel cell detected by the operation state detection unit is a predetermined operation state that is determined in advance as a state in which water droplets are likely to be generated, It is disclosed that voltage is applied to a plurality of electrodes. Patent Document 2 discloses an apparatus for moving a fluid using an electrostatic force.
JP 2004-342562 A JP 2004-935 A

  However, when a voltage is applied to a plurality of electrodes by the technique disclosed in Patent Document 1, various forms are considered as criteria for applying the voltage, and the fuel cell according to the form disclosed in Patent Document 1 is considered. In the operation method, there is a problem that the water content of the electrolyte membrane may not be sufficiently managed. Furthermore, for example, when the water droplet is difficult to move due to the contact resistance between the gas passage and the water droplet, it is difficult to move the water droplet even if a voltage is applied by the technique disclosed in Patent Document 1. There was also. In addition, there is a problem that it is difficult to manage the water content of the electrolyte membrane simply by applying the technique disclosed in Patent Document 2 to the field of fuel cells.

  Therefore, an object of the present invention is to provide a fuel cell operation method capable of managing the water content of an electrolyte membrane, and a fuel cell system to which the operation method can be applied.

In order to solve the above problems, the present invention takes the following means. That is,
The invention according to claim 1 covers an MEA having a pair of catalyst layers and an electrolyte membrane provided between the pair of catalyst layers, and an insulating layer provided on one side and the other side of the MEA. A separator having a plurality of electrode elements and gas flow paths, and a method for operating a fuel cell comprising: a determination step for determining a water content state of an electrolyte membrane; and a determination result of the determination step, A transport determination step for determining whether or not to transport water droplets present in the gas flow path; and a transport direction determination step for determining a transport direction of water droplets when it is determined in the transport determination step that water droplets are transported. And a water cell is transported by applying a voltage to a plurality of electrode elements based on the result of the transport direction determining step.

  Here, “a pair of catalyst layers” means an anode catalyst layer and a cathode catalyst layer. Furthermore, the “insulating layer” means an insulating resin (for example, a fluororesin, a hydrocarbon resin, etc.) having good corrosion resistance, and the “electrode element” is made of gold, silver, copper or the like. Examples include metal wire elements. In addition, the “gas flow path” is a concept including a gas flow path formed in the separator and a structure that can be used as a gas flow path when the separator is provided in advance. . Furthermore, specific examples of criteria for determining the moisture content of the electrolyte membrane include the temperature of the single cell (or stack), the resistance value of the single cell (or stack), and the load of the single cell (or stack). And combinations thereof.

  The “catalyst layer” is not particularly limited as long as it is a catalyst layer used in PEFC. Examples of the catalyst provided in the catalyst layer include platinum and a platinum alloy. When the catalyst is supported on a carrier, Can illustrate carbon (for example, carbon black etc.) as a support | carrier. Further, as the ionomer having proton conductivity provided in the catalyst layer and the electrolyte membrane, a fluorine-based ionomer (for example, Nafion et al., “Nafion” is a registered trademark of DuPont, USA; hereinafter simply referred to as “Nafion”) and the like. Examples include hydrocarbon ionomers (for example, Selemion, etc., “Selemion” is a registered trademark of Asahi Glass Co., Ltd.). In addition, examples of the separator include metal separators made of stainless steel, hydrocarbon separators, and the like. When a diffusion layer is provided between the catalyst layer and the separator, carbon paper is used as the diffusion layer. A diffusion layer made of or the like can be exemplified.

  The invention according to claim 2 covers an MEA having a pair of catalyst layers and an electrolyte membrane provided between the pair of catalyst layers, and an insulating layer provided on one side and the other side of the MEA. A separator having a plurality of electrode elements and a gas flow path, a determination means capable of determining a water content state of the electrolyte membrane, and a gas passage based on a determination result of the determination means A transport determination unit capable of determining whether or not to transport a water droplet present, a transport direction determination unit capable of determining the transport direction of the water droplet when the transport determination unit determines that the water droplet is transported, and the water droplet, A fuel cell system comprising: a voltage applying unit capable of applying a voltage to the plurality of electrode elements so as to be transported in the transport direction determined by the transport direction determining unit.

  According to a third aspect of the present invention, in the fuel cell system according to the second aspect, the flow path surface of the gas flow path that comes into contact with the water droplets is made hydrophobic.

  According to the first aspect of the present invention, on the basis of the determination result of the water content state of the electrolyte membrane, the right and wrong of water droplet conveyance and the conveyance direction are determined. Therefore, it is possible to provide a fuel cell operation method capable of managing the water content of the electrolyte membrane.

  According to the second aspect of the present invention, on the basis of the determination result of the water content state of the electrolyte membrane, whether or not the water droplet is transported and its transport direction are determined. Therefore, it is possible to provide a fuel cell system capable of managing the water content of the electrolyte membrane.

  According to the third aspect of the present invention, since the flow channel surface of the gas flow channel that contacts the water droplet is made hydrophobic, the resistance between the flow channel surface and the water droplet can be reduced. Therefore, as a result of facilitating electrostatic conveyance of water droplets, it is possible to provide a fuel cell system that can easily manage the water content of the electrolyte membrane.

  Hereinafter, a fuel cell operation method of the present invention and a fuel cell system to which the operation method can be applied will be specifically described with reference to the drawings.

1. FIG. 1 is a flowchart schematically showing an example of an embodiment of a fuel cell operation method of the present invention (hereinafter referred to as “the operation method of the present invention”). In the operation method of the present invention according to the embodiment shown in FIG. 1, it is first determined whether or not the stack temperature is lower than a predetermined threshold (for example, 50 ° C.) (step S1). If an affirmative determination is made in step S1, it can be determined that water droplets are likely to accumulate in the gas flow path, so that the stack load continues to be a predetermined threshold value (for example, the pressure of the oxygen-containing gas supplied to the cathode). Is less than 1 kPa) (step S2). If an affirmative determination is made in step S2, for example, it is considered that it is difficult to move water droplets in the gas flow path with the reaction gas just after the start of the PEFC. Is determined to be prone to water immersion. Therefore, when an affirmative determination is made in step S2, it is determined that the water droplets in the gas flow path should be transported to the outlet side of the gas flow path by the transport determination means described later (step S3). A voltage application start signal is output to a voltage applying means (to be described later) to be conveyed to the channel outlet side (step S4). Then, when the voltage application start signal is output to the voltage application means, the process returns to step S2. Thereafter, if a negative determination is made in step S2, it means that the load on the stack is equal to or greater than the predetermined threshold value, and it becomes possible to move the water droplets in the gas flow path by the gas. Therefore, the determination unit determines that the electrolyte membrane is not in a state that is likely to be immersed in water, and the transfer determination unit determines that the water droplet is not in a state to be electrostatically transferred. Therefore, if a negative determination is made in step S2, an output signal is output to stop the operation of the voltage application unit, and the operation of the voltage application unit is stopped (step S5). Thereafter, it is determined whether or not the PEFC operation is continued (step S6). If an affirmative determination is made in step S6, the process returns to step S1, and a negative determination is made in step S6. Then, the processing relating to the operation of the voltage applying means is completed.

  On the other hand, when a negative determination is made in step S1, it can be determined that the stack temperature has risen and the electrolyte membrane is in a state of being easily dried, so whether or not the stack resistance value exceeds a predetermined threshold value. Is determined (step S7). If an affirmative determination is made in step S7, it is considered that the electrolyte membrane has dried and the resistance of the stack has increased, and therefore, the determination means determines that the electrolyte membrane is in a state of being easily dried. Therefore, when an affirmative determination is made in step S7, it is determined by the transfer determination means that the water droplets in the gas flow channel should be transferred to the inlet side of the gas flow channel that is easy to dry (step S8). A voltage application start signal is output to the voltage application means to be conveyed to the gas flow path inlet side (step S9). Then, when a voltage application start signal is output to the voltage application means, the process returns to step S7. After that, when a negative determination is made in step S7, it can be considered that the resistance of the stack is reduced as a result of the dry state of the electrolyte membrane being relaxed by water droplets or the like that have moved to the gas flow path inlet side. Then, it is determined that the electrolyte membrane is not in a state of being easily dried, and it is determined by the transport determination unit that the water droplet is not in a state of being electrostatically transported. Therefore, if a negative determination is made in step S7, an output signal is output to stop the operation of the voltage application means, and the operation of the voltage application means is stopped (step S5). Thereafter, it is determined whether or not the PEFC operation is continued (step S6). If an affirmative determination is made in step S6, the process returns to step S1, and a negative determination is made in step S6. Then, the processing relating to the operation of the voltage applying means is completed.

2. Fuel Cell System FIG. 2 is a schematic view showing an example of the fuel cell system according to the first embodiment of the present invention. As shown in FIG. 2, the fuel cell system 100 according to the first embodiment of the present invention includes a fuel cell stack (hereinafter referred to as “FC stack”) 20 including single cells 30, 30,. , 30,..., Temperature measuring means 21 capable of measuring the load of the FC stack 20, load measuring means 22 capable of measuring the load of the FC stack 20, resistance measuring means 23 capable of measuring the resistance value of the FC stack 20, and a single cell 30 , 30,... A voltage applying unit 24 capable of applying a voltage to an electrostatic conveying unit (an electrostatic conveying unit will be described later), and a control unit 50 capable of controlling the operation of the voltage applying unit 24. I have. The control means 50 includes determination means capable of determining the water content of the electrolyte membrane provided in the single cells 30, 30,..., Conveyance determination capable of determining whether or not water droplets in the single cells 30, 30,. The CPU 51 also has a function as a transport direction determining means capable of determining the transport direction of the water droplets, and includes a CPU 51 that controls the operation of the voltage applying means 24, and a storage device for the CPU 51. The CPU 51 is configured by combining a microprocessor unit and various peripheral circuits necessary for its operation, and a storage device for the CPU 51 is, for example, a ROM 52 that stores programs and various data necessary for determining the water content state of the electrolyte membrane. And a RAM 53 that functions as a work area of the CPU 51. In addition to this configuration, the control means 50 in the fuel cell system 100 of the present invention functions by combining the CPU 51 with software stored in the ROM 52.

  Output signals from the temperature measurement unit 21, the load measurement unit 22, and the resistance measurement unit 23 reach the CPU 51 as input signals via the input port 54. The CPU 51 controls an operation command to the voltage application unit 24 via the output port 55 based on the input signal and the program stored in the ROM 52. The voltage applying unit 24 applies a voltage to the electrode elements of the electrostatic transfer unit provided in the single cells 30, 30,... According to the operation command given from the CPU 51.

  In this embodiment, the temperature measuring means 21 is exemplified by a temperature sensor capable of measuring the temperature of the single cells 30, 30,. Furthermore, as the load measuring means 22, a pressure sensor capable of measuring the pressure of the oxygen-containing gas supplied to the single cells 30, 30,. In addition, as the resistance measuring unit 23, a resistance sensor capable of measuring the resistance value of the FC stack 20 is exemplified.

FIG. 3 is an enlarged cross-sectional view showing a part of a single cell provided in the fuel cell system of the present invention according to the first embodiment, and the straight arrow in FIG. 3 indicates the direction of gravity. 3, components having the same configuration as the members shown in FIG. 2 are denoted by the same reference numerals as those used in FIG.
As shown in FIG. 3, the single cell 30 includes an electrolyte membrane 1, an anode 2 provided on one side of the electrolyte membrane 1, a cathode 3 provided on the other side, a separator 5 provided on the anode 2 side, and And a separator 6 provided on the cathode 3 side. The anode 2 includes an anode catalyst layer 2a and an anode diffusion layer 2b, the cathode 3 includes a cathode catalyst layer 3a and a cathode diffusion layer 3b, and the MEA 4 includes a pair of catalyst layers (the anode catalyst layer 2a and the cathode catalyst layer 3a). And an electrolyte membrane 1 provided between the pair of catalyst layers. The separator 5 and the separator 6 are respectively provided with gas flow paths 7, 7,... And gas flow paths 8, 8,. A transport unit (hereinafter, also referred to as “electrostatic transport unit according to the first embodiment”) 9 is provided. The electrostatic transport means 9 includes a plurality of electrode elements 9b, and the electrode elements 9b are covered with an insulating layer 9a that has been subjected to water repellent treatment on the entire surface that contacts the water droplets.

  FIG. 4 is a front view schematically showing a separator provided in the fuel cell system of the present invention according to the first embodiment. The straight arrow in FIG. 4 indicates the direction of gravity, and the dotted arrow indicates a typical flow of the reaction gas. Each direction is shown. FIG. 5 is an enlarged cross-sectional view showing water droplets in the gas flow path and the electrostatic transfer means, and the interval between the adjacent electrode elements (hereinafter referred to as “electrode pitch”) and the width of the electrode elements (hereinafter referred to as “electrode pitch”). The concept of “electrode width” is also shown. In FIG. 5, in order to facilitate understanding, a part of the electrostatic transport unit is omitted, and a part of the electrostatic transport unit and the water droplet located below the direction of gravity of the water droplet are enlarged. 4 and 5, components having the same configuration as the members shown in FIG. 3 are denoted by the same reference numerals as those used in FIG. 3, and description thereof is omitted as appropriate. Hereinafter, the fuel cell system of the present invention will be described with reference to FIGS.

  As shown in FIG. 4, a separator (hereinafter sometimes referred to as “separator according to the first embodiment”) 6 provided in the fuel cell system of the present invention according to the first embodiment is in contact with the cathode diffusion layer 3 b. .. To be projected, and lattice-shaped recesses (gas flow paths) 8, 8,... Through which oxygen-containing gas (hereinafter referred to as “air”) supplied to the cathode 3 should flow. And the gas supply port 42 and the gas discharge port 43, and the electrostatic transfer means 9 is provided in the gas flow path 8x located at the lowermost part in the gravity direction. As shown in FIG. 5, the electrostatic transport means 9 includes, for example, a plurality of electrode elements 9b, 9b,... That form a six-phase parallel electrode array (af), and is covered with an insulating layer 9a. The plurality of electrode elements 9b, 9b,... Are connected to the voltage applying means 24.

  When the fuel cell system 100 is operated, a hydrogen-containing gas (hereinafter referred to as “hydrogen”) supplied through the gas flow paths 7, 7,... Reaches the anode catalyst layer 2a and is included in the anode catalyst layer 2a. Hydrogen separates into protons and electrons on the catalyst. Protons generated in this way pass through a proton conductive material (for example, Nafion) contained in the anode catalyst layer 2a, the electrolyte membrane 1, and the cathode catalyst layer 3a and onto the catalyst contained in the cathode catalyst layer 3a. And reach. On the other hand, the electrons generated in the anode catalyst layer 2a reach the catalyst contained in the cathode catalyst layer 3a via an external circuit. On the other hand, air is supplied to the cathode 3 through the gas flow paths 8, 8,..., And oxygen is supplied to the catalyst included in the cathode catalyst layer 3a. When protons, electrons, and oxygen are supplied onto the catalyst of the cathode catalyst layer 3a, they react to generate water.

  The single cells 30, 30,... Provided in the FC stack 20 of the fuel cell system 100 are arranged so that the stacking direction of the single cells 30, 30,. Therefore, for example, the single cells 30, 30,... Have a low internal temperature (for example, 50 ° C. or less), and the pressure of the air supplied to the gas flow paths 8, 8,. When the temperature is low (hereinafter referred to as “wet state”), the water generated by the above reaction moves downward in the direction of gravity and moves to the electrostatic transfer means 9 provided in the gas flow path 8x at the lowest part in the direction of gravity. And reach. Here, since the saturated vapor pressure is low in a wet state, water is likely to be droplets, and the pressure of air supplied to the gas flow paths 8, 8,. It is difficult to be transported. Therefore, in particular, the water droplets easily collect in the vicinity of the gas discharge port 43, so that a so-called flooding state is likely to occur. However, in the fuel cell system 100 of the present invention, in a wet state, the CPU 51 determines that water droplets present in the gas flow path 8x should be transported to the gas flow path outlet side (gas discharge port 43 side). A voltage is applied to the plurality of electrode elements 9b, 9b,... From the voltage applying means 24 that has received the operation command. In this way, when a voltage is applied to the plurality of electrode elements 9b, 9b,..., Water droplets present in the gas flow path 8x can be electrostatically transported toward the gas discharge port 43. Can be suppressed.

  On the other hand, the pressure of the air supplied to the gas flow paths 8, 8,... In the lattice form is relatively large, and the temperature inside the single cells 30, 30, ... is high (for example, 80 ° C. or more). In some cases (hereinafter referred to as “dry state”), the saturated vapor pressure in the single cell 30 is high. As described above, the water generated in the dry state condenses into droplet water by touching the separator 6 cooled by the cooling medium, and reaches the gas flow path 8x at the lowest part in the gravity direction. On the other hand, in the dry state, the water in the droplets tends to evaporate and become steam, and the water in the steam state is discharged from the gas discharge port 43 by the air flowing in the gas flow paths 8, 8. Therefore, the electrolyte membrane 1 in the vicinity of the gas outlet 43 is easily kept in a water-containing state. Here, in general, since the air supplied from the gas supply port 42 is dryer than the air discharged from the gas discharge port 43, the electrolyte membrane 1 in the vicinity of the gas supply port 42 is easy to dry, Proton conduction performance is likely to deteriorate. However, in the fuel cell system 100 of the present invention, in the dry state, the CPU 51 determines that the water droplets present in the gas flow path 8x should be conveyed to the gas flow path inlet side (gas supply port 42 side). A voltage is applied to the plurality of electrode elements 9b, 9b,... From the voltage applying means 24 that has received the operation command. In this way, when a voltage is applied to the plurality of electrode elements 9b, 9b,..., Water droplets existing in the gas flow path 8x can be electrostatically transported to the gas supply port 42 side (left side in FIG. 4). Therefore, drying of the electrolyte membrane 1 in the vicinity of the gas supply port 42 can be suppressed by the water droplet.

  Table 1 shows examples of voltage application by the voltage applying means. Hereinafter, it is assumed that the left side of FIG. 5 is the gas supply port side and the right side of the page is the gas discharge port side, and water droplets present in the gas flow path 8x are transferred to the gas discharge port 43 side by the electrostatic transfer means 9. The voltage application form in this case will be described with reference to FIGS.

  In accordance with the voltage application mode shown in Table 1, the voltage application means 24, for example, to a plurality of electrode elements 9b, 9b,... Forming a six-phase parallel electrode array (af), (a, b, c, d). , E, f) = (+, +, 0, −, −, 0) is applied (see No. 1 in Table 1). Thereafter, a voltage of (a, b, c, d, e, f) = (0, +, +, 0, −, −) is applied (see No. 2 in Table 1), and then (a, b , C, d, e, f) = (−, 0, +, +, 0, −) is applied (see No. 3 in Table 1), and (a, b, c, d, e) F) = (−, −, 0, +, +, 0) is applied (see No. 4 in Table 1). Then, a voltage of (a, b, c, d, e, f) = (0, −, −, 0, +, +) is applied (see No. 5 in Table 1), and then (a, b, c, d, e, f) = (+, 0, −, −, 0, +) is applied (see No. 6 in Table 1). In this embodiment, No. 1 in Table 1 is used. 1-No. 6 is defined as one cycle, and the above cycle is repeated by applying a six-phase rectangular wave voltage to the six-phase parallel electrode arrays (af). When a voltage is applied in such a form, positive / negative switching of the voltage proceeds from the gas supply port 42 side to the gas discharge port 43 side. When the positive / negative switching of the voltage proceeds in this way, the water droplet on the insulating layer 9a is charged by electrostatic induction. And according to the positive / negative transition of the said voltage, a water droplet is conveyed to the gas discharge port 43 side (electrostatic conveyance), repelling or attracting | sucking with the electrode elements 9b, 9b, ... near a water droplet.

  In Table 1, the voltage application form in the case of transporting water droplets present in the gas flow path 8x to the gas discharge port 43 side is illustrated, but the present invention is not limited to this form and exists in the gas flow path 8x. It is also possible to transport the water droplets to the gas supply port 42 side. When transporting water droplets to the gas supply port 42 side, for example, the voltage is applied in the reverse order of the above configuration (No. 6 → No. 5 → No. 4 → No. 3 → No. 2 → No. 1). What is necessary is just to apply.

  FIG. 6 is an enlarged view of a part of electrostatic transport means (hereinafter, also referred to as “electrostatic transport means according to the second embodiment”) provided in the fuel cell system of the present invention according to the second embodiment. FIG. In FIG. 6, components having the same configuration as the members shown in FIG. The surface of the electrostatic conveyance means 69 shown in FIG. 6 (all surfaces that can come into contact with water droplets) is subjected to water repellent treatment. FIG. 7 is a conceptual diagram showing the contact angle. FIG. 7A shows the contact angle θ between the flat surface and the water droplet, and FIG. 7B shows the contact between the uneven surface and the water droplet. Each angle θ ′ is shown. Hereinafter, the angle represented by θ ′ in FIG. 7B is referred to as “apparent contact angle”.

  The electrostatic transfer means 69 shown in FIG. 6 includes a plurality of electrode elements 9b, an insulating layer 69a having a surface to be brought into contact with water droplets (hereinafter referred to as “transport surface”) having a flooded surface with a contact angle of 90 ° or more. 9b is covered. According to the electrostatic conveyance means 69 of this form, the contact angle between the conveyance surface and the water droplet can be increased, and the contact area between the electrostatic conveyance means 69 and the water droplet is reduced. The contact resistance between the two can be reduced. Therefore, if the separator provided in the fuel cell system of the present invention is provided with the electrostatic transfer means 69, water droplets can be easily moved, so that the water content state of the electrolyte membrane can be easily managed. . Further, it is possible to reduce energy consumed when electrostatically transporting water droplets.

  FIG. 8 is a front view schematically showing a separator (hereinafter referred to as “separator according to the second embodiment”) provided in the fuel cell system of the present invention according to the second embodiment, and is a straight arrow in FIG. Indicates the direction of gravity, and the dotted arrow indicates the typical flow direction of air. In FIG. 8, the same reference numerals as those used in FIG. 4 or 6 are assigned to the same components as those shown in FIG. 4 or 6, and the description thereof is omitted. FIG. 9 is an enlarged cross-sectional view of a part of a single cell (hereinafter referred to as “single cell according to the second embodiment”) provided in the fuel cell system of the present invention according to the second embodiment. The straight arrow in FIG. 9 indicates the direction of gravity. 9, components having the same configuration as the members shown in FIG. 3 or FIG. 8 are denoted by the same reference numerals as those used in FIG. 3 or FIG. Hereinafter, the fuel cell system of the present invention will be described with reference to FIGS. 8 and 9.

  As shown in FIG. 8, the separator 86 according to the second embodiment includes the convex portions 81, 81,... That should be in contact with the cathode diffusion layer 3 b, and the linear gas that the air supplied to the cathode 3 should flow through. Are provided with flow paths 88, 88,..., Gas supply ports 42 and gas discharge ports 43, and electrostatic conveying means 69, 69,. ing. On the other hand, as shown in FIG. 9, the single cell 90 according to the second embodiment is provided with a separator 95 including straight gas flow paths 97, 97,... On the anode 2 side, and on the cathode 3 side. A separator 86 according to the second embodiment is provided. Here, when the straight gas flow paths 88, 88,... Are provided, water droplets are likely to accumulate on the upper surface side in the gravity direction of each of the convex portions 81, 81,. Therefore, as shown in FIGS. 8 and 9, by providing electrostatic transport means 69, 69,... On the upper surface side in the gravitational direction of each convex portion 81, 81,. , And can be easily electrostatically transferred to the gas discharge port 43 side. Furthermore, the single cell 90 according to the second embodiment is provided with electrostatic transfer means 69, 69,... Having a hydrophobic contact surface with water droplets. Therefore, according to the fuel cell system of the present invention including the single cell 90 according to the second embodiment, the water content of the electrolyte membrane 1 can be easily transported by the electrostatic transport means 69, 69,. Makes it easier to manage.

  FIGS. 10 and 11 are schematic views showing a separator (hereinafter referred to as “separator according to the third embodiment”) provided in the fuel cell system of the present invention according to the third embodiment. FIG. FIG. 11 is a sectional view taken along line XX in FIG. 10. The dotted arrows in FIG. 10 indicate the typical flow direction of air, and the straight arrows in FIG. 11 indicate the direction of gravity. 11, members having the same configuration as in FIG. 6 are assigned the same reference numerals as those used in FIG. Here, in order to prevent the figure from becoming complicated, the description of the electrostatic transfer means is omitted in FIG. FIG. 12 is an enlarged sectional view showing a part of a single cell (hereinafter referred to as “single cell according to the third embodiment”) provided in the fuel cell system of the present invention according to the third embodiment. Yes, the straight arrows in FIG. 12 indicate the direction of gravity. In FIG. 12, the same reference numerals as those used in FIG. 9 are assigned to the same components as those shown in FIG. 9, and the description thereof is omitted. Hereinafter, the fuel cell system of the present invention will be described with reference to FIGS.

  As shown in FIG. 10, the separator 106 according to the third embodiment includes so-called serpentine-shaped gas flow paths 108, 108,... And convex portions 101, 101 sandwiched between adjacent gas flow paths 108, 108,. ,..., And a gas supply port 102 and a gas discharge port 103. And the electrostatic transfer means 69, 69,... According to the second embodiment over the entire length of the gas flow paths 108, 108,... Connecting the gas supply port 102 and the gas discharge port 103 (see FIGS. 11 and 12). ) Is provided. As shown in FIG. 12, the separator 106 according to the third embodiment is arranged in a form substantially parallel to a horizontal plane, and electrostatic transporting means 69, 69,. … Is provided. 12, the single cell 120 according to the third embodiment is provided with a separator 125 including serpentine-shaped gas flow paths 127, 127,... On the anode 2 side, and on the cathode 3 side. A separator 106 according to the third embodiment is provided. As described above, when the single cell 120 according to the third embodiment is used in a form that is substantially parallel to the horizontal plane and the separator 106 according to the third embodiment is disposed below the MEA 4, Water droplets easily collect in the gas flow paths 108, 108,. Therefore, by providing electrostatic conveyance means 69, 69,... Having a hydrophobic contact surface at the location where water droplets tend to accumulate, the water droplets can be supplied to the gas supply port 102 side or the gas discharge port 103 side. Can be easily electrostatically conveyed. Therefore, according to the fuel cell system of the present invention including the single cell 120 according to the third embodiment, the water content of the electrolyte membrane 1 can be easily transported by the electrostatic transport means 69, 69,. Can be managed.

  In the present invention, the interval (electrode pitch) between the electrode elements provided in the separator is not particularly limited as long as it is an interval at which water droplets can be electrostatically conveyed, but the width (or depth) of the gas flow path in which the water droplets exist. When H) is H, it is preferably H / 3 or less from the viewpoint of easy transport of water droplets. On the other hand, the thickness is preferably 0.2 mm or more from the viewpoint of workability for arranging the electrode elements.

  In the above description regarding the present invention, the fuel cell system in which the resistance measurement unit capable of measuring the resistance value of the FC stack is illustrated, but the fuel cell system of the present invention is limited to the mode in which the resistance measurement unit is provided. Alternatively, for example, a resistance measuring unit capable of measuring the resistance value of a representative single cell that can grasp the situation of a plurality of single cells provided in the FC stack may be provided. Furthermore, instead of the resistance measurement means, a voltage measurement means capable of measuring the voltage value of the FC stack or the voltage value of the representative single cell may be provided. The resistance measurement means or the voltage measurement means Instead of the above, a form provided with a dew point measuring means capable of measuring the dew point of the typical single cell may be employed.

  When the fuel cell system of the present invention is provided with a resistance measuring means, the threshold value used for determining whether or not the electrolyte membrane is dry is a pre-measured FC at a low temperature and a low gas flow rate. A resistance value of a stack (or a single cell), a value obtained by adding a predetermined numerical value to the resistance value, or the like can be used. Furthermore, when the resistance measuring means is provided in the fuel cell system of the present invention, the environment in each single cell provided in the FC stack changes as the operation time elapses, and whether the dry state is determined based on the previously measured threshold value. If it is determined whether or not, the accuracy of the determination may be reduced. Therefore, from the viewpoint of making it possible to accurately determine whether or not it is in a dry state, for example, it is periodically determined whether or not the threshold is accurate, and the threshold is not accurate. In such a case, it is preferable to correct the threshold value so that it becomes an accurate threshold value, and to determine whether or not it is in a dry state using the corrected threshold value.

  In the above description, the electrostatic transport unit 9 according to the first embodiment or the electrostatic transport unit 69 according to the second embodiment (hereinafter, these may be collectively referred to as “electrostatic transport unit”). Although the fuel cell system of the form provided only in the gas flow path facing the cathode of the single cell is illustrated, the fuel cell system of the present invention is not limited to this form. Here, flooding may occur not only in the cathode but also in the anode. Therefore, the fuel cell system of the present invention can be configured such that electrostatic transport means is provided only in the gas flow path facing the anode, and the gas flow path facing the anode and the gas flow facing the cathode. It is also possible to adopt a form in which electrostatic conveyance means is provided on the path.

  Moreover, in the said description regarding the fuel cell system 100 of this invention concerning 1st Embodiment, although the separator 6 was illustrated with the form provided with the electrostatic conveyance means 9, this invention is not limited to the said form, It is a grid | lattice form. The electrostatic transport means 69 according to the second embodiment may be provided in the gas flow channel located at the lowest part in the gravity direction of the separator provided with the gas flow channel. With this configuration, water droplets accumulated in the gas flow channel located at the lowest position in the gravity direction can be easily electrostatically transported to the gas supply port side or the gas discharge port side. It becomes possible to make the fuel cell system easier to manage. Furthermore, in the above description regarding the fuel cell system 100 of the present invention according to the first embodiment, the mode in which the electrostatic transfer means 9 is provided only in the gas flow path 8x located at the lowest position in the gravitational direction is illustrated. It is not limited to the said form, For example, the electrostatic conveyance means may be provided in the gravity direction upper surface side of all the convex parts 41, 41, .... With this configuration, water droplets can be electrostatically transported more easily, so that the water content of the electrolyte membrane can be easily managed. However, if a large number of electrostatic transfer means are provided, the arrangement of the electrode elements may be complicated and the productivity of the separator may decrease, and as a result of the increase in the ratio of the insulating layer in the separator, the conductivity of the separator may be reduced. May decrease. Therefore, in the separator 6 according to the first embodiment, it is preferable that the electrostatic transfer means is provided only in the gas flow path 8x located at the lowest part in the gravity direction.

  On the other hand, in the above description regarding the fuel cell system of the present invention according to the second embodiment and the fuel cell system of the present invention according to the third embodiment, the electrostatic transport means 69 according to the second embodiment is provided. Although illustrated, this invention is not limited to the said form. Even when the separator is provided with a linear gas flow path or a serpentine-shaped gas flow path, the electrostatic transfer means 9 according to the first embodiment can be provided. Even if the separator according to the first embodiment includes the electrostatic transport means 9 according to the first embodiment, water droplets existing in the gas flow path are electrostatically transported to the gas supply port side or the gas discharge port side, and the electrolyte The water content of the membrane can be managed.

  In the present invention, the voltage applied to the electrode element and the speed at which the voltage is changed are not particularly limited, but when the fuel cell system is operated in a high load state, the load is low. Since a larger amount of reaction gas than the state is supplied to the single cell and a large amount of water is generated, it is preferable to operate so that a large amount of water droplets can be electrostatically conveyed. Here, it is considered that the higher the voltage applied to the electrode element, and the higher the speed at which the voltage is changed, the higher the transport speed of electrostatically transported water droplets. Therefore, in the present invention, it is preferable that the voltage is applied to the electrode element in a form that can increase the transport speed of the water droplets that are electrostatically transported as the load increases.

  In the above description, the fuel cell system including the electrostatic transfer means in a form in which water repellent treatment is performed on all surfaces (hereinafter referred to as “insulating layer surface”) that can come into contact with water droplets is illustrated. The electrostatic transport means provided in the fuel cell system of the present invention is not limited to this form. For example, the form in which the water-repellent treatment is performed only on the surface of the insulating layer located below the gravity direction of the water droplets, or the insulating layer The surface may be provided with electrostatic transfer means that is not subjected to water repellent treatment. However, from the viewpoint of reducing the contact resistance between water droplets and the surface of the insulating layer, the surface of the insulating layer is subjected to a water repellent treatment, or an electrostatic layer having a configuration in which an insulating layer made of a water repellent material is provided. It is preferable to use a conveying means. Specific examples of the water repellent treatment that can be used in the present invention include a method of spray-coating a fluorine-based water repellent treatment agent. Specific examples of the water-repellent substance that can form the insulating layer include a fluororesin such as polytetrafluoroethylene (PTFE), a hydrocarbon resin such as polypropylene (PP), and the like. Furthermore, in the above description, the U-shaped electrostatic transfer means is illustrated, but the electrostatic transfer means provided in the present invention is not limited to this form, and the insulating layer and the plurality of only the lower part in the gravity direction of the water droplet. It may be an electrostatic transfer means in a form in which an electrode element is provided.

1. Electrostatic transport test Water droplets are electrostatically transported by disposing water droplets in the gas flow path of the separator 6 according to the first embodiment and then applying a voltage to the plurality of electrode elements. Whether or not water droplets are electrostatically transported. Table 2 shows the configuration of the separator used for the investigation.

2. Relationship between temperature and resistance value Supplying hydrogen and air to a single cell to operate it, the ratio (ratio) of water droplet mass to the total mass of water discharged from the gas outlet and the resistance value of single cell (AC resistance value) And the temperature of the single cell was investigated. As a result, when the temperature in the single cell was 50 ° C., the ratio was 1, and the AC resistance value was 8.0 [mΩ · cm ² ]. On the other hand, when the temperature in the single cell was 80 ° C., the ratio was 0.2, and the AC resistance value was 12.0 [mΩ · cm ² ]. This is because when the temperature of the single cell is 50 ° C., the saturated vapor pressure is low, so the water in the single cell tends to exist as droplet water instead of steam, and the generated water is discharged in the state of droplet water. This means that the AC resistance value is low because the electrolyte membrane is difficult to dry. On the other hand, when the temperature of the single cell is 80 ° C., the saturated vapor pressure is high, so the water in the single cell tends to exist in a vapor state, and most of the generated water is discharged in the vapor state, and the electrolyte membrane Means that the AC resistance is high. From this test, it was confirmed that the resistance value of the single cell dried in a high temperature state is likely to increase. That is, it was confirmed that whether or not the electrolyte membrane is in a dry state can be determined depending on whether or not the resistance value exceeds a predetermined threshold value.

3. Relationship between water droplet mobility and unevenness Carbon powder and water repellent resin (dispersed in a fine powder such as fluororesin) are mixed and dispersed, and then sprayed onto the carbon plate by spraying. And it was made to dry and the test material concerning Example 1 was produced. On the other hand, a surface excellent in smoothness (for example, a metal flat plate mirror-polished) is applied to the surface produced by the same method as the test material of Example 1, and the temperature below the melting point (about 100 to 200 ° C.). The test material concerning Example 2 was produced by performing the press process which applies a pressure (about 100 kg / cm < ² >) on conditions. The sample material according to Example 1 and the sample material according to Example 2 thus produced were respectively placed on a horizontal plane, and water droplets were dropped on these sample materials. And the apparent contact angle of the water drop dripped on the test material concerning Example 1 and the test material concerning Example 2 is measured, and then the wind speed is zero on the water drop dripped on these test materials. It was investigated whether water droplets moved by blowing air of 2 [m / s]. The results are shown in Table 3. In Table 3, “(apparent) contact angle” means the above “apparent contact angle θ ′” in the test material according to Example 1, and “contact angle θ” in the test material according to Example 2. Respectively.

  From Table 3, the contact angle of the test material according to Example 1 was 150 °, and the contact angle of the test material according to Example 2 was 120 °. And, the water droplets dropped on the test material according to Example 1 moved when blowing air with a wind speed of 0.2 [m / s], but the water droplets dropped onto the test material according to Example 2 were: Didn't move much. That is, from this investigation, it was confirmed that water droplets were easier to move when the surface contact angle was larger.

  So far, an example in which the electrode exists only on one side has been described, but the form of the electrode is not limited to the above form. FIG. 13 schematically shows an example in which electrodes are provided in two directions. FIG. 13A is a cross-sectional view showing the case where electrodes are provided on the upper and lower sides, and the horizontal direction on the paper is the flow direction of the reaction gas supplied to the flow path. FIG. 13B is a cross-sectional view showing the case where electrodes are provided on the left and right, and the direction perpendicular to the paper surface is the flow direction of the reaction gas supplied to the flow path. For example, as shown in FIG. 13 (a), a ground side electrode is provided on the upper surface and an electrode for applying a traveling wave electric field is provided on the lower surface, or a ground side electrode shown in FIG. There may be a method in which electrodes are provided in two directions, such as a structure in which an electrode for applying an electric field is provided on the right side.

It is a flowchart which shows the example of the form of the driving | running method of this invention roughly. It is the schematic which shows the example of the form of the fuel cell system of this invention concerning 1st Embodiment. It is sectional drawing which expands and shows a part of single cell concerning 1st Embodiment. It is a front view showing roughly the separator concerning a 1st embodiment. It is the schematic which expands and shows the water droplet and electrostatic conveyance means in a gas flow path. It is sectional drawing which expands and shows a part of electrostatic conveyance means concerning 2nd Embodiment. It is a conceptual diagram which shows a contact angle. It is a front view which shows roughly the separator concerning 2nd Embodiment. It is sectional drawing which expands and shows a part of single cell concerning 2nd Embodiment. It is a front view which shows roughly the separator concerning 3rd Embodiment. It is XX sectional drawing of FIG. It is sectional drawing which expands and shows a part of single cell concerning 3rd Embodiment. It is the schematic which shows the example which provided the electrode in 2 directions.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrolyte membrane 2 Anode 2a Anode catalyst layer 2b Anode diffusion layer 3 Cathode 3a Cathode catalyst layer 3b Cathode diffusion layer 4 MEA
5, 6, 86, 95, 106, 125 Separator 7, 8, 88, 97, 108, 127 Gas flow path 9, 69 Electrostatic transfer means 9a Insulating layer 9b Electrode element 20 Fuel cell stack 21 Temperature measurement means 22 Load measurement Means 23 Resistance measurement means 24 Voltage application means 50 Control means 51 CPU (determination means, conveyance judgment means, conveyance direction determination means)
52 ROM
53 RAM
54 Input port 55 Output port 30, 90, 120 Single cell 42, 102 Gas supply port 43, 103 Gas exhaust port 100 Fuel cell system

Claims (3)

A MEA having a pair of catalyst layers and an electrolyte membrane provided between the pair of catalyst layers, and a plurality of electrode elements and gas flow covered with an insulating layer provided respectively on one side and the other side of the MEA A separator having a path, and a method of operating a fuel cell comprising:
A determination step of determining the water content of the electrolyte membrane;
A transport determination step for determining whether or not to transport water droplets present in the gas flow path based on the determination result of the determination step;
A transport direction determining step for determining a transport direction of the water droplets when it is determined in the transport determination step that the water droplets are transported;
The method of operating a fuel cell, wherein the water droplets are transported by applying a voltage to the plurality of electrode elements based on a result of the transport direction determining step. A MEA having a pair of catalyst layers and an electrolyte membrane provided between the pair of catalyst layers, and a plurality of electrode elements and gas flow covered with an insulating layer provided on one side and the other side of the MEA, respectively. A fuel cell comprising: a separator comprising a path;
Determination means capable of determining the water content of the electrolyte membrane;
A transport determination unit capable of determining whether or not to transport a water droplet present in the gas flow path based on a determination result of the determination unit;
A transport direction determining means capable of determining the transport direction of the water droplets when it is determined by the transport determining means to transport the water drops;
Voltage applying means capable of applying a voltage to the plurality of electrode elements so that the water droplets are transported in the transport direction determined by the transport direction determining means;
A fuel cell system comprising: The fuel cell system according to claim 2, wherein a flow path surface of the gas flow path in contact with the water droplet is made hydrophobic.

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