fuel cell system

Abstract

To provide a hydrophilic processing method for an anode diffusion layer and a fuel battery system configured to be capable of performing the method, the method being capable of improving hydrophilicity of a surface and the inside of the anode diffusion layer using a simple procedure.SOLUTION: A hydrophilic processing method is applied to an anode diffusion layer 114 of a fuel battery 1 configured to be capable of using formic acid as fuel, the fuel battery including a membrane-electrode assembly 11 comprising an electrolyte membrane 111, an anode 112 and a cathode 113 that are provided on the electrolyte membrane 111, and the anode diffusion layer 114 provided on the anode 112. Bringing formic acid having a concentration equal to or higher than 20 mass% and equal to or lower than 98 mass% into contact with the anode diffusion layer 114 can enhance hydrophilicity of the region of the anode diffusion layer 114 in contact with the formic acid.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a hydrophilic treatment method and a fuel cell system. [Background technology]

[0002] Fuel cells, such as polymer electrolyte fuel cells, have a membrane electrode assembly (MEA) that includes an electrolyte membrane, an anode provided on one side of the electrolyte membrane, and a cathode provided on the other side of the electrolyte membrane. Fuel cells can generate electrode reactions at each electrode by supplying fuel to the anode of the MEA and an oxidant to the cathode. These electrode reactions generate an electromotive force between the anode and the cathode, enabling electricity generation.

[0003] The anode in the MEA is sometimes covered with an anode diffusion layer made of a material with pores and gaps. Examples of the anode diffusion layer include carbon cloth or carbon paper that has been made hydrophilic by irradiating it with ultraviolet light or plasma. Patent Document 1 describes a method for producing a direct methanol fuel cell, which includes an immersion step of immersing a gas diffusion layer in water and a lamination step of laminating the gas diffusion layer so that it is in contact with a membrane-electrode assembly. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-138276 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, direct formic acid fuel cells, which use formic acid as the fuel supplied to the anode, have attracted attention from the viewpoint of improving the energy density of fuel cells. Formic acid, the fuel for direct formic acid fuel cells, has a lower affinity with the anode diffusion layer than methanol, the fuel for direct methanol fuel cells. Therefore, the anode diffusion layer used in direct formic acid fuel cells must be more hydrophilic than the anode diffusion layer used in direct methanol fuel cells. Therefore, it is difficult to directly apply the manufacturing method for direct methanol fuel cells described in Patent Document 1 to the manufacturing method for direct formic acid fuel cells.

[0006] Furthermore, when the anode diffusion layer is subjected to hydrophilic treatment using ultraviolet light, plasma, or the like, it is difficult for the ultraviolet light, etc., to reach the interior of the anode diffusion layer, making it difficult to improve the hydrophilicity of the pores and gaps in the anode diffusion layer. On the other hand, increasing the irradiation intensity of ultraviolet light, etc., in order to allow the ultraviolet light, etc., to reach the interior of the anode diffusion layer may lead to deterioration of the anode diffusion layer. Furthermore, when performing treatment by irradiating the anode diffusion layer with ultraviolet light, plasma, etc., the hydrophilic treatment must be performed using dedicated equipment, which can complicate the fuel cell manufacturing process.

[0007] The present invention has been made in view of the above-mentioned problems, and aims to provide a method for hydrophilizing an anode diffusion layer, which can improve the hydrophilicity of the surface and the interior of the anode diffusion layer while suppressing deterioration of the anode diffusion layer, and a fuel cell system configured to be able to carry out this method. [Means for solving the problem]

[0008] One aspect of the present invention reference One aspect is a method for hydrophilizing the anode diffusion layer in a fuel cell that includes a membrane electrode assembly including an electrolyte membrane, an anode and a cathode provided on the electrolyte membrane, and an anode diffusion layer provided on the anode, and that is configured to be able to use formic acid as a fuel, the method comprising: The method for hydrophilizing an anode diffusion layer includes contacting the anode diffusion layer with formic acid having a concentration of 20% by mass or more and 98% by mass or less, thereby increasing the hydrophilicity of the region of the anode diffusion layer that comes into contact with the formic acid.

[0009] The present invention 1st One aspect of the present invention is a fuel cell that includes a membrane electrode assembly including an electrolyte membrane, an anode and a cathode provided on the electrolyte membrane, and an anode diffusion layer provided on the anode, and is configured to be able to use formic acid as a fuel; Formic acid having a concentration of 20 mass % or more and 98 mass % or less is fed to the fuel cell. directly a formic acid tank configured to be able to supply the formic acid; a fuel tank configured to be able to supply formic acid as fuel to the fuel cell; Equipped with the formic acid tank is configured to be able to supply formic acid to the fuel cell and the fuel tank, Formic acid in the formic acid tank is supplied to the anode diffusion layer. and bringing the anode diffusion layer into contact with formic acid having a concentration of 20% by mass or more and 98% by mass or less, thereby increasing the hydrophilicity of the region of the anode diffusion layer that comes into contact with the formic acid. The present invention relates to a fuel cell system configured to be able to: A second aspect of the present invention provides a fuel cell that includes a membrane electrode assembly including an electrolyte membrane, an anode and a cathode provided on the electrolyte membrane, and an anode diffusion layer provided on the anode, and is configured to be able to use formic acid as a fuel; a formic acid tank configured to be able to directly supply formic acid having a concentration of 20% by mass or more and 98% by mass or less to the fuel cell; a concentration meter configured to be able to measure the concentration of formic acid in the formic acid tank; a formic acid pump disposed on a formic acid path from the formic acid tank to the fuel cell and configured to be able to deliver formic acid to the fuel cell; a control device connected to the concentration meter and the formic acid pump; a fuel tank configured to be able to supply formic acid as fuel to the fuel cell, the formic acid tank is configured to be able to supply formic acid to the fuel cell and the fuel tank, the control device is configured to set the amount of formic acid to be sent from the formic acid pump to the fuel cell based on the concentration of formic acid obtained from the concentration meter, The fuel cell system is configured to supply formic acid from the formic acid tank to the anode diffusion layer and bring the anode diffusion layer into contact with formic acid having a concentration of 20% by mass or more and 98% by mass or less, thereby increasing the hydrophilicity of the region of the anode diffusion layer that comes into contact with the formic acid. A third aspect of the present invention provides a fuel cell including a membrane electrode assembly having an electrolyte membrane, an anode and a cathode provided on the electrolyte membrane, and an anode diffusion layer provided on the anode, the fuel cell being configured to be able to use formic acid as a fuel; a formic acid tank configured to be able to supply formic acid having a concentration of 20% by mass or more and 98% by mass or less to the fuel cell; a fuel tank configured to be able to supply formic acid as fuel to the fuel cell; a formic acid pump disposed between the formic acid tank and the fuel tank on the formic acid path and configured to be able to deliver formic acid in the formic acid tank to the fuel tank; a concentration meter configured to be able to measure the concentration of formic acid in the fuel tank; a fuel pump disposed between the fuel tank and the fuel cell on the path of formic acid, the fuel pump being configured to be able to deliver the formic acid in the fuel tank to the fuel cell; a control device connected to the concentration meter, the formic acid pump, and the fuel pump, the fuel cell system is configured to be able to supply formic acid in the formic acid tank to the fuel cell via the fuel tank, the control device is configured to be able to set the amount of formic acid to be delivered from the formic acid pump to the fuel tank and the amount of formic acid to be delivered from the fuel tank to the fuel cell based on the concentration of formic acid acquired from the concentration meter, The fuel cell system is configured to supply formic acid from the formic acid tank to the anode diffusion layer and bring the anode diffusion layer into contact with formic acid having a concentration of 20% by mass or more and 98% by mass or less, thereby increasing the hydrophilicity of the region of the anode diffusion layer that comes into contact with the formic acid. [Effects of the Invention]

[0010] In the method for hydrophilizing the anode diffusion layer, formic acid having a concentration within the specific range is brought into contact with the anode diffusion layer. Because formic acid is a liquid, it can easily penetrate into pores, gaps, and the like in the anode diffusion layer. Furthermore, by bringing the anode diffusion layer into contact with formic acid having a concentration within the specific range, the surface and interior of the anode diffusion layer can be modified while suppressing deterioration of the anode diffusion layer.

[0011] The fuel cell system of the above aspect includes the fuel cell and a formic acid tank configured to supply the formic acid to the fuel cell, and thus, by supplying formic acid having a concentration within the specific range from the formic acid tank to the fuel cell, the anode diffusion layer can be easily hydrophilized.

[0012] As described above, the above aspects provide a method for hydrophilizing an anode diffusion layer, which can improve the hydrophilicity of the surface and the interior of the anode diffusion layer while suppressing deterioration of the anode diffusion layer, and a fuel cell system configured to be able to carry out this method. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a partial cross-sectional view showing a main part of a fuel cell according to a first embodiment. [Figure 2] FIG. 2 is an explanatory diagram showing the amount of water retained in the anode diffusion layer after hydrophilization treatment in the first embodiment. [Figure 3] FIG. 3 is an explanatory diagram showing the power density-current density characteristics of a fuel cell using an anode diffusion layer after hydrophilization treatment in the first embodiment. [Figure 4] FIG. 4 is an explanatory diagram showing the overall configuration of a fuel cell system according to the second embodiment. [Figure 5] FIG. 5 is an explanatory diagram showing the overall configuration of a fuel cell system according to a third embodiment, which includes a formic acid tank and a fuel tank. [Figure 6]FIG. 6 is an explanatory diagram showing the overall configuration of a fuel cell system according to a fourth embodiment, which is equipped with a formic acid tank, a fuel tank, and a water tank. [Figure 7] FIG. 7 is an explanatory diagram showing the overall configuration of a fuel cell system in which a formic acid tank is connected to a fuel cell via a fuel tank in a fifth embodiment. [Figure 8] FIG. 8 is an explanatory diagram showing the overall configuration of a fuel cell system according to a sixth embodiment, which includes a formic acid tank, a fuel tank, and a water tank. DETAILED DESCRIPTION OF THE INVENTION

[0014] (Embodiment 1) An embodiment of the hydrophilization treatment of the anode diffusion layer will be described with reference to FIGS. 1 to 3. The hydrophilization treatment method of the anode diffusion layer in this embodiment can be applied to the anode diffusion layer 114 of a fuel cell 1 that includes a membrane electrode assembly 11 (hereinafter referred to as "MEA") including an electrolyte membrane 111, an anode 112 and a cathode 113 provided on the electrolyte membrane 111, and an anode diffusion layer 114 provided on the anode 112, as shown in FIG. 1. The membrane electrode assembly 11 is configured to use formic acid as a fuel. In the hydrophilization treatment method of the anode diffusion layer 114, the anode diffusion layer 114 is brought into contact with formic acid having a concentration of 20% by mass or more and 98% by mass or less. This increases the hydrophilicity of the region of the anode diffusion layer 114 that comes into contact with formic acid.

[0015] The anode diffusion layer 114 to be hydrophilized in the hydrophilization method can be an anode diffusion layer 114 applicable to a direct formic acid fuel cell. More specifically, the anode diffusion layer 114 can be made of a conductive carbon material having pores and gaps, such as carbon paper, which is a composite material of conductive carbon fiber and carbon, or carbon cloth made of conductive carbon fiber.

[0016] The concentration of formic acid used in the hydrophilic treatment method is 20% by mass or more and 98% by mass or less. By contacting the anode diffusion layer 114 with formic acid at a concentration of 20% by mass or more, the surface and interior of the anode diffusion layer 114 can be rapidly modified, thereby shortening the time required for the hydrophilic treatment. From the perspective of further shortening the time required for the hydrophilic treatment, the concentration of formic acid is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more. If the concentration of formic acid used in the hydrophilic treatment method is less than 20% by mass, the time required for the hydrophilic treatment of the anode diffusion layer may be prolonged.

[0017] On the other hand, if the concentration of formic acid contacting the anode diffusion layer 114 is excessively high, the anode diffusion layer 114 may be excessively oxidized by the formic acid, which may lead to deterioration of the anode diffusion layer 114. This problem can be easily avoided by setting the concentration of formic acid contacting the anode diffusion layer 114 to 98% by mass or less. From a similar perspective, the concentration of formic acid contacting the anode diffusion layer 114 is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and particularly preferably 60% by mass or less. Furthermore, formic acid with a concentration of 90% by mass or less is easier to handle than formic acid with a higher concentration. Therefore, using formic acid with a concentration of 90% or less in the hydrophilization treatment method can more easily carry out the hydrophilization treatment method.

[0018] In the hydrophilization treatment method, the contact time between the anode diffusion layer 114 and formic acid is preferably 10 seconds or more and 4 hours or less. By setting the contact time between the anode diffusion layer 114 and formic acid within the above-mentioned specific range, the hydrophilicity of the anode diffusion layer 114 can be enhanced while easily avoiding deterioration of the anode diffusion layer 114. From the viewpoint of further enhancing the hydrophilicity of the anode diffusion layer 114 and easily achieving the performance of the direct formic acid fuel cell in a short time, the contact time between the anode diffusion layer 114 and formic acid is more preferably 1 minute or more and 2 hours or less, even more preferably 1 minute or more and 1 hour or less, and particularly preferably 1 minute or more and 30 minutes or less.

[0019] The hydrophilic treatment method for the anode diffusion layer 114 in this embodiment can be applied to both the anode diffusion layer 114 before and after it is incorporated into the fuel cell 1. That is, the hydrophilic treatment method for the anode diffusion layer 114 can be applied to the anode diffusion layer 114 before it is incorporated into the fuel cell 1 as part of the assembly process of the fuel cell 1. Furthermore, the hydrophilic treatment method for the anode diffusion layer 114 can also be applied to the anode diffusion layer 114 after it has been incorporated into the fuel cell 1 as part of the conditioning performed before the start of operation of the fuel cell 1, for example.

[0020] Furthermore, for example, if a fuel cell 1 having a hydrophilized anode diffusion layer 114 is stored without being operated for a long period of time, the hydrophilicity of the anode diffusion layer 114 may decrease for some reason. Even in such a case, the hydrophilization method described above allows the anode diffusion layer 114 to be hydrophilized at the installation site of the fuel cell 1 by supplying formic acid having a concentration within the specific range to the fuel cell 1.

[0021] From the viewpoint of suppressing an increase in the number of steps in the manufacturing process of the fuel cell 1 and improving the productivity of the fuel cell 1, it is preferable to subject the anode diffusion layer 114 after it has been incorporated into the fuel cell 1 to the hydrophilic treatment method for the anode diffusion layer 114.

[0022] Next, the fuel cell 1 incorporating the anode diffusion layer 114 will be described. The fuel cell 1 may be configured as a direct formic acid fuel cell that uses formic acid as fuel. A direct formic acid fuel cell can generate electricity by supplying formic acid as fuel to the anode 112 and an oxidant to the cathode 113. The concentration of the formic acid as fuel supplied to the anode 112 is usually lower than the concentration of formic acid used in the hydrophilization treatment method. The concentration of the formic acid used as fuel is, for example, 5% by mass or more and less than 50% by mass. The oxidant supplied to the fuel cell 1 can be, for example, air or oxygen gas.

[0023] The fuel cell 1 has one or more unit cells 14, which are its constituent units. When the fuel cell 1 has a plurality of unit cells 14, these unit cells 14 may be stacked on top of each other to form a cell stack. When the fuel cell 1 has a plurality of unit cells 14, each unit cell 14 may be electrically connected in series or in parallel with the other unit cells 14.

[0024] As shown in FIG. 1, the unit cell 14 of the fuel cell 1 includes an MEA 11, an anode-side separator 12, and a cathode-side separator 13. The MEA 11 includes an electrolyte membrane 111, an anode 112 provided on one side of the electrolyte membrane 111, a cathode 113 provided on the other side of the electrolyte membrane 111, and an anode diffusion layer 114 provided on the anode 112. The electrolyte membrane 111 is electrically insulating and has a high conductivity, and is resistant to hydrogen ions (H + The cation exchange resin is made of a cation exchange resin that is configured to be selectively permeable to cations such as ammonium nitrate, ammonium nitrate, etc. As the cation exchange resin, for example, a perfluoroalkylsulfonic acid polymer (for example, "Nafion (registered trademark)" manufactured by DuPont) can be used.

[0025] The anode 112 and the cathode 113 are disposed in the center of the electrolyte membrane 111 and are formed in layers on the electrolyte membrane 111. The anode 112 and the cathode 113 are configured to be able to catalyze an electrode reaction. For example, the anode 112 and the cathode 113 may contain catalyst-supported carbon that supports a precious metal catalyst such as palladium (Pd) or platinum (Pt). The anode 112 and the cathode 113 may also contain a binder configured to hold the catalyst-supported carbon.

[0026] An anode diffusion layer 114 is provided on the anode 112 of the MEA 11. The anode diffusion layer 114 is electrically conductive and has minute voids. By using an electrically conductive material for the anode diffusion layer 114, the anode 112 and the anode-side separator 12 are electrically connected, allowing the power generated in the MEA 11 to be extracted to the outside. Furthermore, by providing minute voids in the anode diffusion layer 114, fuel supplied to the unit cell 14 can be diffused within the anode diffusion layer 114 and guided to the anode 112. As a result, the fuel can be brought into contact with the anode 112 more efficiently, improving power generation efficiency.

[0027] The MEA 11 may further include a cathode diffusion layer 115 disposed on the cathode 113. The cathode diffusion layer 115 may be made of a conductive carbon material having pores and gaps, such as carbon paper, which is a composite material of conductive carbon fiber and carbon, or carbon cloth made of conductive carbon fiber. The use of an electrically conductive material for the cathode diffusion layer 115 electrically connects the cathode 113 and the cathode-side separator 13, allowing the electricity generated by the MEA 11 to be extracted to the outside. Furthermore, the provision of minute voids in the cathode diffusion layer 115 allows the oxidant supplied to the unit cell 14 to be guided to the cathode 113 while diffusing within the cathode diffusion layer 115. This allows the oxidant to come into contact with the cathode 113 more efficiently, improving power generation efficiency.

[0028] The anode-side separator 12 is provided on the surface of the MEA 11 on the side having the anode 112. The anode-side separator 12 may be made of an electrical conductor such as a metal material such as gold-plated stainless steel, a conductive non-metallic material such as conductive carbon, or a conductive composite material. The electrically conductive anode-side separator 12 functions as a current collector that collects electrons generated by the electrode reaction in the MEA 11, and can conduct the electricity generated by the MEA 11 to the outside.

[0029] The anode-side separator 12 has a fuel flow channel 122 on its electrode contact surface 121, which contacts the anode diffusion layer 114, that is configured to be able to supply fuel to the anode 112. The shape and arrangement of the fuel flow channel 122 may take various forms. For example, the fuel flow channel 122 may be a groove provided in the anode-side separator 12, having a cross-sectional shape such as a rectangular, triangular, or semicircular shape. The fuel flow channel 122 may have, for example, a plurality of straight sections aligned parallel to one another and folded sections connecting the ends of each straight section to the ends of the adjacent straight sections, and may be arranged in a serpentine pattern in a plan view from the contact surface side, although other arrangements are also possible.

[0030] A cathode-side separator 13 is provided on the surface of the MEA 11 on which the cathode 113 is provided. Like the anode-side separator 12, the cathode-side separator 13 may be made of an electrical conductor such as a metal material such as gold-plated stainless steel, a conductive non-metallic material such as conductive carbon, or a conductive composite material. The electrically conductive cathode-side separator 13 functions as a current collector that collects electrons generated by the electrode reaction in the MEA 11, and can conduct the electricity generated by the MEA 11 to the outside.

[0031] An oxidant channel 132 is provided on the electrode contact surface 131 of the cathode-side separator 13, which contacts the cathode diffusion layer 115. The shape and arrangement of the oxidant channel 132 may take various forms, similar to the fuel channel 122. For example, the oxidant channel 132 may have a cross-sectional shape such as a rectangular, triangular, or semicircular shape, and may be a groove provided in the anode-side separator 12. The oxidant channel 132 may have, for example, a plurality of straight sections arranged parallel to one another and folded sections connecting the end of each straight section to the end of an adjacent straight section, and may be arranged in a serpentine shape in a plan view seen from the contact surface side, although other arrangements are also possible.

[0032] A sealant 15 may be provided between the electrolyte membrane 111 of the MEA 11 in the unit cell 14 and the anode-side separator 12, and between the electrolyte membrane 111 and the cathode-side separator 13. By providing the sealant 15 in this manner, the gap between the MEA 11 and the anode-side separator 12 and the gap between the MEA 11 and the cathode-side separator 13 can be sealed, thereby preventing the fuel and oxidant from leaking from these gaps.

[0033] In the hydrophilization treatment method for the anode diffusion layer 114 in this embodiment, formic acid having a concentration within the above-mentioned specific range is brought into contact with the anode diffusion layer 114. Because formic acid is a liquid, it can easily penetrate into the pores, gaps, and the like in the anode diffusion layer 114. Therefore, the surface and interior of the anode diffusion layer 114 can be hydrophilized by the simple method of bringing the anode diffusion layer 114 into contact with formic acid.

[0034] Below, we will explain specific examples of the hydrophilic treatment method, as well as examples of the water retention capacity of the anode diffusion layer 114 that has been hydrophilic treated and the power density-current density characteristics of the fuel cell 1 that incorporates the anode diffusion layer 114.

[0035] The amount of water held by the anode diffusion layer 114 Carbon cloth (thickness: 0.38 mm, bulk density: 1.75 g / cm) used as the anode diffusion layer 114 3After thoroughly drying the carbon cloth, a circular test piece with a diameter of 25 mm is prepared. The test piece is immersed in formic acid with a concentration of 20% by mass (5 mol / L), 40% by mass (10 mol / L), or 60% by mass (15 mol / L). The test piece is then removed from the formic acid after a predetermined time has elapsed since the start of immersion. The test piece is then washed three times with distilled water to remove the formic acid, and the test piece is then thoroughly saturated with distilled water.

[0036] The difference between the mass of the test piece after soaking in distilled water and the mass of the test piece in a dry state obtained as described above is taken as the amount of water retained by the test piece. Figure 2 shows the variation in the amount of water retained by each test piece when the time from the start of immersion is varied. The vertical axis of Figure 2 represents the amount of water retained by the test piece (unit: g), and the horizontal axis represents the treatment time for hydrophilization (unit: minutes), i.e., the contact time between the test piece and formic acid. The data points shown in Figure 2 are for test pieces subjected to hydrophilization treatment under the same conditions. 3 pieces The error bars indicate the maximum and minimum values ​​of water retention for these test specimens.

[0037] ·Output density-current density characteristics The output density-current density characteristics are measured using a fuel cell evaluation device (an electrochemical measurement system "HZ-7000" manufactured by Hokuto Denko Corporation). First, a carbon cloth (thickness 0.38 mm, bulk density 1.75 g / cm) that has not been subjected to hydrophilic treatment is placed on the anode 112 and the cathode 113 of the MEA 11. 3 ) are stacked together to form the anode diffusion layer 114 and the cathode diffusion layer 115. Next, an evaluation cell is constructed using this MEA 11.

[0038] Next, 60% by mass formic acid is supplied to the fuel flow channel 122 of the evaluation cell for 30 minutes, and the portion of the anode diffusion layer 114 facing the fuel flow channel 122 is brought into contact with the formic acid to perform a hydrophilization treatment. After the hydrophilization treatment is completed, 10% by mass formic acid is supplied as fuel to the fuel flow channel 122, and air is supplied as an oxidant to the oxidant flow channel 132, and the power density-current density characteristics are evaluated.

[0039] Furthermore, for comparison with the anode diffusion layer 114 that had been subjected to hydrophilic treatment, an evaluation cell was prepared that had the same configuration as the above-described one except that an anode diffusion layer 114 that had not been subjected to hydrophilic treatment was used, and the power density-current density characteristics were evaluated using this evaluation cell. Figure 3 shows the power density-current density characteristics of each evaluation cell. The vertical axis of Figure 3 represents the power density (unit: mW / cm 2 ), and the horizontal axis is the current density (unit: mA / cm 2 )

[0040] The carbon cloth used to measure water retention and evaluate power density-current density characteristics had low hydrophilicity before hydrophilization, and therefore retained almost no water even when immersed in distilled water. In contrast, as shown in Figure 2, hydrophilization using formic acid with a concentration of 20% by mass to 60% by mass improved the hydrophilicity of the carbon cloth, enabling the carbon cloth to retain water. Figure 2 also shows that when hydrophilization is performed using formic acid with a concentration of 20% by mass to 60% by mass, contacting the anode diffusion layer 114 with formic acid for at least 15 minutes can improve the hydrophilicity of the anode diffusion layer 114. Figure 2 also shows that the higher the formic acid concentration, the shorter the time required to hydrophilize the anode diffusion layer 114. Furthermore, when using formic acid with a concentration of 20% by mass to 60% by mass, contacting the anode diffusion layer 114 with formic acid for at least one hour can sufficiently improve the hydrophilicity of the anode diffusion layer 114.

[0041] 3, the test cell using the hydrophilized carbon cloth as the anode diffusion layer 114 exhibits a significantly higher power density than the test cell using the untreated carbon cloth as the anode diffusion layer 114. This is thought to be because the hydrophilization treatment makes it easier for the fuel to spread across the anode diffusion layer 114, increasing the contact area between the fuel and the anode diffusion layer 114 and the amount of fuel that reaches the anode 112. Furthermore, FIG. 3 reveals that the degradation of the anode diffusion layer 114 can be suppressed when the hydrophilization treatment is performed using formic acid with a concentration within the specified range.

[0042] As described above, by subjecting the anode diffusion layer 114 to hydrophilic treatment using formic acid whose concentration is within the above-mentioned specific range, it is possible to improve the hydrophilicity of the anode diffusion layer 114 while suppressing deterioration of the anode diffusion layer 114.

[0043] (Embodiment 2) In this embodiment, an example of a fuel cell system 2 configured to be able to carry out the hydrophilic treatment method will be described. Note that, among the symbols used in the second and subsequent embodiments, the same symbols as those used in the previous embodiments represent the same components as those in the previous embodiments, unless otherwise specified.

[0044] As shown in Fig. 4, the fuel cell system 2 of this embodiment includes a fuel cell 1 configured to use formic acid as a fuel, including an MEA 11 with an electrolyte membrane, an anode and a cathode provided on the electrolyte membrane, and an anode diffusion layer provided on the anode, and a formic acid tank 3 configured to supply formic acid with a concentration of 20% by mass or more and 98% by mass or less to the fuel cell 1. The fuel cell system 2 is configured to perform the hydrophilization treatment method for the anode diffusion layer of the above-mentioned embodiment by supplying formic acid from the formic acid tank 3 to the anode diffusion layer. Note that, for convenience, the electrolyte membrane, anode, cathode, and anode diffusion layer are not shown in Fig. 4.

[0045] 4, the fuel cell 1 of this embodiment has a cell stack 16 formed by stacking a plurality of unit cells 14 on top of each other. The unit cells 14 that make up the cell stack 16 are arranged so that the anode-side separator 12 of each unit cell 14 and the cathode-side separator 13 of the unit cell 14 adjacent to that unit cell 14 abut against each other. As a result, the plurality of unit cells 14 are electrically connected in series via the anode-side separator 12 and the cathode-side separator 13.

[0046] A pair of holding plates 161 (161a, 161b) for holding the cell stack 16 may be arranged on both ends of the cell stack 16 in the stacking direction. In the fuel cell 1 of this embodiment, a fastening member 162 is inserted into one holding plate 161a of the pair of holding plates 161. The fastening member 162 penetrates the cell stack 16 in the stacking direction of the unit cells 14, and one holding plate 161a and the other holding plate 161b are fastened together by the fastening member 162. In this way, the cell stack 16 is held between the pair of holding plates 161. In addition, each holding plate 161 has a terminal 163 for extracting the electric power generated from the fuel cell 1 to an external circuit.

[0047] The fuel cell system 2 may be configured to directly supply the formic acid in the formic acid tank 3 to the fuel cell 1, or may be configured to indirectly supply the formic acid in the formic acid tank 3 to the fuel cell 1 via another tank, etc. Regardless of the manner of connection between the formic acid tank 3 and the fuel cell 1, the hydrophilization treatment method can be carried out as long as formic acid having a concentration within the specific range can be supplied to the anode diffusion layer 114 of the fuel cell 1.

[0048] The fuel cell system 2 of this embodiment is configured to be able to directly supply formic acid in a formic acid tank 3 to the fuel cell 1. Specifically, as shown in Fig. 4, the fuel cell system 2 has a formic acid tank 3 configured to be able to hold formic acid, and the formic acid tank 3 is connected to the cell stack 16 via a formic acid supply pipe 31. In addition, on the path of formic acid from the formic acid tank 3 to the fuel cell 1, i.e., on the formic acid supply pipe 31, a formic acid pump 32 configured to be able to deliver formic acid to the fuel cell 1 is provided. The formic acid tank 3 is provided with a concentration meter 33 configured to be able to measure the concentration of formic acid in the formic acid tank 3.

[0049] A control device 4 is connected to the concentration meter 33 and the formic acid pump 32, and the control device 4 is configured to be able to control the operation of the formic acid pump 32. The control device 4 may be configured to be able to set the amount of formic acid to be sent from the formic acid pump 32 to the fuel cell 1 based on the concentration of formic acid obtained from the concentration meter 33, for example.

[0050] More specifically, the control device 4 may be configured to operate the formic acid pump 32 for a preset time when the concentration of formic acid obtained from the concentration meter 33 is within the specific range, thereby supplying formic acid from the formic acid tank 3 to the fuel cell 1 and performing hydrophilization treatment. The time for operating the formic acid pump 32 may be, for example, a value stored in advance in the control device 4, or a value input to the control device 4 from an external device. Such an operation can be realized, for example, by an electronic circuit provided in the control device 4, a program for operating the control device 4, or the like.

[0051] After the hydrophilization treatment of the anode diffusion layer is completed, the formic acid tank 3 of this embodiment can be used as a fuel tank for supplying formic acid as fuel to the fuel cell 1. When using the formic acid tank 3 as a fuel tank, the concentration of formic acid in the formic acid tank 3 can be adjusted to a range suitable for use as a fuel by adding water to the formic acid tank 3 to dilute the formic acid in the tank.

[0052] The fuel cell system 2 of this embodiment also includes a formic acid recovery tank 21 that recovers formic acid and fuel discharged from the cell stack 16, a blower 22 that supplies air as an oxidant to each unit cell 14 that constitutes the cell stack 16, and a drain tank 23 that recovers water produced by electrode reactions in each unit cell 14. The formic acid recovery tank 21, the blower 22, and the drain tank 23 are connected to the cell stack 16 via a formic acid recovery pipe 211, an oxidant supply pipe 221, and a water recovery pipe 231, respectively.

[0053] To carry out the hydrophilic treatment method using the fuel cell system 2 of this embodiment, formic acid having a concentration within the specific range is first placed in the formic acid tank 3. In this state, the control device 4 is operated, and the formic acid in the formic acid tank 3 is pumped to the fuel cell 1 by the formic acid pump 32. The formic acid that has entered the fuel cell 1 comes into contact with the anode diffusion layer via the fuel flow path and modifies the surface and interior of the anode diffusion layer. After a time preset in the control device 4 has elapsed, the formic acid pump 32 is stopped. This completes the hydrophilic treatment of the anode diffusion layer.

[0054] After the hydrophilization treatment of the anode diffusion layer is completed, fuel is supplied from the formic acid tank 3 to the fuel cell 1, and an oxidant is supplied from the blower 22 to the fuel cell 1, thereby generating electricity in the MEA 11. To generate electricity, for example, water or diluted formic acid is placed in the formic acid tank 3, and the concentration of formic acid in the formic acid tank 3 is adjusted to a range suitable for use as fuel. Then, the formic acid pump 32 is operated to send the fuel in the formic acid tank 3 to the fuel cell 1, and air is supplied as an oxidant to the fuel cell 1 from the blower 22.

[0055] In this embodiment, the formic acid and fuel that have passed through the fuel cell 1 are recovered in the formic acid recovery tank 21, but it is also possible to return the formic acid and fuel that have passed through the fuel cell 1 to the formic acid tank 3 and reuse them as formic acid or fuel to be supplied to the fuel cell 1. In this embodiment, the generated water discharged from the fuel cell 1 is recovered in the drain tank 23, but it is also possible to connect the drain tank 23 and the formic acid tank 3 and use the generated water discharged from the fuel cell 1 to dilute the formic acid. Note that because the generated water discharged from the fuel cell 1 is harmless, it may be discharged outside the fuel cell 1 without being recovered as in this embodiment.

[0056] (Embodiment 3) In this embodiment, an example of a fuel cell system 203 will be described in which a formic acid tank 3 for supplying formic acid used in the hydrophilization treatment to the fuel cell 1 and a fuel tank 5 for supplying formic acid used as a fuel to the fuel cell 1 are separately provided. As shown in Fig. 5, the fuel cell system 203 of this embodiment has the fuel cell 1, the formic acid tank 3, and a fuel tank 5 configured to be able to supply formic acid as a fuel to the fuel cell 1. The fuel cell system 203 is configured to be able to directly supply formic acid from the formic acid tank 3 to the fuel cell 1, and is also configured to be able to supply formic acid from the formic acid tank to the fuel tank 5.

[0057] More specifically, the fuel cell system 203 of this embodiment has a formic acid tank 3, a formic acid pump 32, a fuel tank 5, a fuel pump 52, a control device 403, a three-way valve 34, and a blower 22. The formic acid tank 3 is connected to the formic acid pump 32 via a formic acid supply pipe 31. The formic acid pump 32 is also connected to the three-way valve 34 via a formic acid supply pipe 311. The other connection ports of the three-way valve 34 are connected to the fuel cell 1 via a formic acid supply pipe 312 and to the fuel tank 5 via a formic acid supply pipe 313. The three-way valve 34 is configured so that the open / closed states of the individual connection ports can be switched.

[0058] A fuel pump 52 is connected to the fuel tank 5 via a fuel supply pipe 51. The fuel tank 5 is also provided with a concentration meter 53 configured to be able to measure the concentration of formic acid in the fuel tank 5. The fuel pump 52 is configured to be able to deliver fuel from the fuel tank 5 to the fuel cell 1. A fuel delivery port of the fuel pump 52 is connected to a formic acid supply pipe 312 that connects the three-way valve 34 and the fuel cell 1. This allows the fuel delivered from the fuel pump 52 to join in the formic acid supply pipe 312 and be supplied to the fuel cell 1.

[0059] The control device 403 of the fuel cell system 203 is connected to the formic acid pump 32, the fuel pump 52, the three-way valve 34, and the concentration meter 53, and is configured to be able to control the operation of the formic acid pump 32, the fuel pump 52, and the three-way valve 34. The control device 403 may be configured, for example, to control the open / close state of the three-way valve 34 so that the formic acid pump 32 and the fuel cell 1 are connected, and to operate the formic acid pump 32 for a preset time to supply formic acid from the formic acid tank 3 to the fuel cell 1. The time for which the formic acid pump 32 is operated may be, for example, a value stored in advance in the control device 403, or a value input to the control device 403 from an external device. Such operation may be realized, for example, by an electronic circuit provided in the control device 403, a program for operating the control device 403, or the like.

[0060] Furthermore, the control device 403 may be configured to control the open / close state of the three-way valve 34 so that the formic acid pump 32 and the fuel tank 5 are connected based on the concentration of formic acid in the fuel tank 5 acquired from the concentration meter 53, for example, and to set the amount of formic acid sent from the formic acid pump 32 to the fuel tank 5 and the amount of formic acid sent from the fuel pump 52 to the fuel cell 1. In this way, by controlling the amount of formic acid sent from the formic acid pump 32 to the fuel tank 5 and the amount of formic acid sent from the fuel pump 52 to the fuel cell 1 based on the concentration of formic acid in the fuel tank 5, the concentration of formic acid in the fuel tank 5 can be adjusted to an appropriate range for use as a fuel, and the power generation efficiency of the fuel cell 1 can be improved.

[0061] The fuel cell system 203 of this embodiment has a formic acid recovery pipe 164 that connects the formic acid and fuel outlets in the cell stack 16 to the fuel tank 5, and a water recovery pipe 165 that connects the produced water outlet in the cell stack 16 to the fuel tank 5. The formic acid recovery pipe 164 allows the formic acid and fuel discharged from the cell stack 16 to flow into the fuel tank 5. The formic acid and fuel recovered via the formic acid recovery pipe 164 are reused as fuel. In addition, the water recovery pipe 165 allows the produced water discharged from the cell stack 16 to flow into the fuel tank 5. The produced water recovered via the water recovery pipe 165 is used to adjust the concentration of formic acid in the fuel tank 5.

[0062] To perform the hydrophilization treatment method using the fuel cell system 203 of this embodiment, formic acid having a concentration within the specific range is first placed in the formic acid tank 3. In this state, the control device 403 is operated to control the open / close state of the three-way valve 34 so that the formic acid tank 3 and the fuel cell 1 are connected. The formic acid pump 32 is then operated to deliver the formic acid from the formic acid tank 3 to the fuel cell 1. The formic acid directly supplied from the formic acid tank 3 to the fuel cell 1 comes into contact with the anode diffusion layer (not shown), thereby modifying the surface and interior of the anode diffusion layer. After a preset time has elapsed since the formic acid was supplied from the formic acid tank 3 to the fuel cell 1, the control device 403 stops the formic acid pump 32. This completes the hydrophilization treatment of the anode diffusion layer.

[0063] After the hydrophilization treatment of the anode diffusion layer is completed, power generation can be performed in the MEA (not shown) by supplying fuel to the fuel cell 1 from the fuel tank 5 and supplying an oxidant to the fuel cell 1 from the blower 22. To generate power, for example, a method can be employed in which formic acid having a concentration within a suitable range as a fuel is placed in the fuel tank 5 in advance, and the formic acid in the fuel tank 5 is supplied to the fuel cell 1 by the fuel pump 52 and the oxidant is supplied to the fuel cell 1 from the blower 22.

[0064] Furthermore, the fuel tank 5 can be filled in advance with water, dilute formic acid, or the like. In this case, the control device 403 is operated to switch the open / close state of the three-way valve 34 so that the formic acid pump 32 and the fuel tank 5 are connected, and then formic acid is supplied from the formic acid tank 3 to the fuel tank 5, thereby adjusting the concentration of formic acid in the fuel tank 5 to a range suitable for use as a fuel. After the concentration of formic acid in the fuel tank 5 has reached a range suitable for use as a fuel, the fuel pump 52 is operated to send the fuel in the fuel tank 5 to the fuel cell 1, and air is supplied as an oxidant from the blower 22 to the fuel cell 1, thereby generating electricity in the MEA.

[0065] When power is generated in the fuel cell 1, formic acid in the fuel is consumed, and therefore the concentration of formic acid in the fuel discharged from the fuel cell 1 becomes lower than the concentration of formic acid before it is supplied to the fuel cell 1. Furthermore, water produced as a result of power generation in the fuel cell 1 flows into the fuel tank 5. Therefore, as the operation of the fuel cell system 203 continues, the concentration of formic acid contained in the fuel in the fuel tank 5 gradually decreases. When the concentration of formic acid in the fuel tank 5 decreases, the formic acid pump 32 is operated to send high-concentration formic acid to the fuel tank 5, thereby adjusting the concentration of formic acid in the fuel tank 5 to a range suitable for use as a fuel.

[0066] (Embodiment 4) In this embodiment, an example of a fuel cell system 204 will be described, in which a water tank 6 is further provided in addition to the fuel cell system 203 of embodiment 3. As shown in Fig. 6, the fuel cell system 204 of this embodiment includes a fuel cell 1, a formic acid tank 3, a formic acid pump 32, a fuel tank 5, a fuel pump 52, a control device 404, a three-way valve 34, a blower 22, a water tank 6, and a water pump 62.

[0067] The water tank 6 and the water pump 62 are configured to be able to supply water to the fuel tank 5. For example, the water tank 6 and the water pump 62 may be arranged on the path of the produced water from the fuel cell 1 to the fuel tank 5, i.e., on the water recovery pipe 165, as shown in FIG. 6 . The water tank 6 connected in this manner can store the produced water discharged from the fuel cell 1. In addition, the water pump 62 is configured to be able to send water from the water tank 6 to the fuel tank 5. By sending the water from the water tank 6 to the fuel tank 5 and mixing it with the formic acid in the fuel tank 5, the concentration of formic acid in the fuel tank 5 can be adjusted.

[0068] The control device 404 in this embodiment is connected to the formic acid pump 32, the fuel pump 52, the three-way valve 34, the concentration meter 53, and the water pump 62, and is configured to be able to control the operations of the formic acid pump 32, the fuel pump 52, the three-way valve 34, and the water pump 62. The control device 404 may be configured, for example, similar to the control device 403 in embodiment 3, to control the open / close state of the three-way valve 34 so that the formic acid pump 32 and the fuel cell 1 are connected, and to operate the formic acid pump 32 for a preset time to supply formic acid from the formic acid tank 3 to the fuel cell 1.

[0069] Furthermore, the control device 404 may be configured to control the open / close state of the three-way valve 34 so that the formic acid pump 32 and the fuel tank 5 are connected based on the concentration of formic acid in the fuel tank 5 obtained from the concentration meter 53, and to set the amount of formic acid delivered from the formic acid pump 32 to the fuel tank 5, the amount of formic acid delivered from the fuel pump 52 to the fuel cell 1, and the amount of water delivered from the water pump 62 to the fuel tank 5. In this way, by controlling the amount of formic acid delivered from the formic acid pump 32 to the fuel tank 5, the amount of formic acid delivered from the fuel pump 52 to the fuel cell 1, and the amount of water delivered from the water tank 6 to the fuel tank 5 based on the concentration of formic acid in the fuel tank 5, the concentration of formic acid in the fuel tank 5 can be adjusted to an appropriate range for use as fuel, thereby improving the power generation efficiency of the fuel cell 1. The configuration of other parts of the fuel cell system 204 of this embodiment is the same as that of the fuel cell system 203 of embodiment 3.

[0070] The method for carrying out the hydrophilic treatment method using the fuel cell system 204 of this embodiment is the same as when the fuel cell system 203 of the third embodiment is used.

[0071] After the hydrophilization treatment of the anode diffusion layer is completed, power generation can be performed in the MEA (not shown) by supplying fuel to the fuel cell 1 from the fuel tank 5 and supplying an oxidant to the fuel cell 1 from the blower 22. More specifically, for example, a method can be employed in which formic acid having a concentration within a suitable range as a fuel is previously placed in the fuel tank 5, and the formic acid in the fuel tank 5 is supplied to the fuel cell 1 by the fuel pump 52 and the oxidant is supplied to the fuel cell 1 from the blower 22.

[0072] Alternatively, fuel can be prepared in the fuel tank 5 by, for example, filling the water tank 6 with water in advance and mixing the formic acid in the formic acid tank 3 with the water in the water tank 6 in the fuel tank 5, or by mixing the water produced during power generation and the formic acid in the formic acid tank 3 in the fuel tank 5. To prepare fuel in the fuel tank 5, for example, the control device 404 switches the open / close state of the three-way valve 34 so that the formic acid pump 32 connects to the fuel tank 5, and then supplies formic acid from the formic acid tank 3 to the fuel tank 5, and water from the water tank 6 to the fuel tank 5. This dilutes the formic acid in the fuel tank 5, adjusting the formic acid concentration to a range suitable for use as a fuel. After the formic acid concentration in the fuel tank 5 is adjusted to a range suitable for use as a fuel, the fuel pump 52 is operated to send the fuel in the fuel tank 5 to the fuel cell 1, and air is supplied as an oxidant from the blower 22 to the fuel cell 1, thereby generating power in the MEA.

[0073] (Embodiment 5) In this embodiment, an example of a fuel cell system 205 will be described in which a formic acid tank 3 is connected to a fuel cell 1 via a fuel tank 5. As shown in Fig. 7, the fuel cell system 205 of this embodiment includes a formic acid tank 3, a formic acid pump 32, a fuel tank 5, a fuel pump 52, a control device 405, and a blower 22. The formic acid pump 32 is disposed between the formic acid tank 3 and the fuel tank 5 on the formic acid path, and is configured to be able to deliver formic acid to the fuel tank 5.

[0074] The fuel tank 5 is provided with a concentration meter 53 configured to be able to measure the concentration of formic acid in the fuel tank 5. The fuel pump 52 is disposed between the fuel tank 5 and the fuel cell 1 on the formic acid path, and is configured to be able to send the formic acid in the fuel tank 5 to the fuel cell 1. The control device 405 is connected to the concentration meter 53, the formic acid pump 32, and the fuel pump 52, and is configured to be able to control the operations of the formic acid pump 32 and the fuel pump 52.

[0075] More specifically, the formic acid tank 3 is connected to a formic acid pump 32 via a formic acid supply pipe 31. Furthermore, the formic acid pump 32 is connected to the fuel tank 5 via a formic acid supply pipe 311, and is configured to be able to deliver formic acid in the formic acid tank 3 to the fuel tank 5. The fuel tank 5 is connected to the fuel pump 52 via a fuel supply pipe 51. Furthermore, the fuel pump 52 is connected to the fuel cell 1 via a fuel supply pipe 511, and is configured to be able to deliver the fuel in the fuel tank 5 and formic acid supplied from the formic acid tank 3 to the fuel cell 1.

[0076] The fuel cell system 205 of this embodiment also has a formic acid recovery pipe 164 that connects the formic acid and fuel outlets in the cell stack 16 to the fuel tank 5, and a water recovery pipe 165 that connects the produced water outlet in the cell stack 16 to the fuel tank 5. The formic acid recovery pipe 164 allows the formic acid and fuel discharged from the cell stack 16 to flow into the fuel tank 5. The formic acid and fuel recovered via the formic acid recovery pipe 164 are reused as fuel. The water recovery pipe 165 allows the produced water discharged from the cell stack 16 to flow into the fuel tank 5. The produced water recovered via the water recovery pipe 165 is used to adjust the concentration of formic acid in the fuel tank 5.

[0077] The control device 405 of this embodiment is configured to be able to set the amount of formic acid to be delivered from the formic acid pump 32 to the fuel tank 5 and the amount of formic acid to be delivered from the fuel pump 52 to the fuel cell 1 based on the concentration of formic acid in the fuel tank 5 obtained from the concentration meter 53. More specifically, the control device 405 may be configured to operate the formic acid pump 32 and the fuel pump 52 for a preset time when the concentration of formic acid in the fuel tank 5 is within the specific range, thereby supplying formic acid from the formic acid tank 3 to the fuel cell 1 via the fuel tank 5. In this way, even when formic acid is supplied via the fuel tank 5, the anode diffusion layer can be hydrophilized as long as the concentration of formic acid delivered from the fuel tank 5 to the fuel cell is within the specific range.

[0078] The time for which fuel pump 52 is operated may be, for example, a value stored in advance in control device 405, or may be a value input from outside to control device 405. Such an operation may be realized, for example, by an electronic circuit provided in control device 405, a program for operating control device 405, or the like.

[0079] Furthermore, the control device 405 may be configured to, for example, operate the formic acid pump 32 when the concentration of formic acid in the fuel tank 5 is lower than the specific range, and supply formic acid from the formic acid tank 3 to the fuel tank 5, thereby adjusting the concentration of formic acid in the fuel tank 5 to a range in which the hydrophilization treatment can be performed.

[0080] To perform the hydrophilization treatment method using the fuel cell system 205 of this embodiment, formic acid having a concentration within the specific range is first placed in the formic acid tank 3. In this state, the control device 405 is operated to pump the formic acid from the formic acid tank 3 to the fuel tank 5 via the formic acid pump 32, and then pump the formic acid from the fuel tank 5 to the fuel cell 1 via the fuel pump 52. The formic acid supplied to the fuel cell 1 in this manner comes into contact with the anode diffusion layer, thereby subjecting the anode diffusion layer to hydrophilization treatment. After a preset time has elapsed since the formic acid was supplied from the formic acid tank 3 to the fuel cell 1, the control device 405 stops the formic acid pump 32 and the fuel pump 52. This completes the hydrophilization treatment of the anode diffusion layer.

[0081] After the hydrophilization treatment of the anode diffusion layer is completed, fuel is supplied from the fuel tank 5 to the fuel cell 1, and an oxidant is supplied from the blower 22 to the fuel cell 1, thereby enabling power generation in the MEA. To generate power, for example, water or diluted formic acid is placed in the fuel tank 5, and the concentration of formic acid in the fuel tank 5 is adjusted to a range suitable for use as a fuel. Then, the fuel pump 52 is operated to send the fuel in the fuel tank 5 to the fuel cell 1, and air is supplied as an oxidant from the blower 22 to the fuel cell 1. Alternatively, after the hydrophilization treatment, the formic acid recovered via the formic acid recovery pipe 164 can be used directly for power generation, and the formic acid in the fuel tank 5 can be diluted with the water produced during power generation.

[0082] If the concentration of formic acid in the fuel tank 5 decreases during operation of the fuel cell system 205, the formic acid pump 32 is operated to send high-concentration formic acid to the fuel tank 5, thereby adjusting the concentration of formic acid in the fuel tank 5 to a range suitable for use as a fuel.

[0083] (Embodiment 6) In this embodiment, an example of a fuel cell system 206 will be described in which a water tank 6 is further provided in addition to the fuel cell system 205 of Embodiment 5. The fuel cell system 206 of this embodiment includes a fuel cell 1, a formic acid tank 3, a formic acid pump 32, a fuel tank 5, a fuel pump 52, a control device 406, a blower 22, a water tank 6, and a water pump 62, as shown in FIG.

[0084] The water tank 6 and the water pump 62 are configured to be able to supply water to the fuel tank 5. The water tank 6 and the water pump 62 may be arranged on the produced water path from the fuel cell 1 to the fuel tank 5, i.e., on the water recovery pipe 165, as shown in FIG. 8 , for example. The water tank 6 connected in this manner can store the produced water discharged from the fuel cell 1. The water pump 62 is also configured to be able to send the produced water in the water tank 6 to the fuel tank 5. By sending the produced water in the water tank 6 to the fuel tank 5 and mixing it with the formic acid in the fuel tank 5, the concentration of formic acid in the fuel tank 5 can be adjusted.

[0085] The control device 406 in this embodiment is connected to the formic acid pump 32, the fuel pump 52, the concentration meter 53, and the water pump 62, respectively, and is configured to be able to control the operations of the formic acid pump 32, the fuel pump 52, and the water pump 62. Similar to the control device 405 in the fifth embodiment, the control device 406 may be configured, for example, to operate the formic acid pump 32 and the fuel pump 52 for a preset time when the concentration of formic acid in the fuel tank 5 is within the specific range, thereby supplying formic acid from the formic acid tank 3 to the fuel cell 1 via the fuel tank 5, and performing a hydrophilization treatment on the anode diffusion layer (not shown).

[0086] Furthermore, the control device 406 may be configured to set the amount of formic acid delivered from the formic acid pump 32 to the fuel tank 5, the amount of formic acid delivered from the fuel pump 52 to the fuel cell 1, and the amount of water delivered from the water pump 62 to the fuel tank 5, based on the concentration of formic acid in the fuel tank 5 obtained from the concentration meter 53. In this way, by controlling the amount of formic acid delivered from the formic acid pump 32 to the fuel tank 5, the amount of formic acid delivered from the fuel pump 52 to the fuel cell 1, and the amount of water delivered from the water tank 6 to the fuel tank 5 based on the concentration of formic acid in the fuel tank 5, it is possible to adjust the concentration of formic acid in the fuel tank 5 to a desired range, perform a hydrophilic treatment on the anode diffusion layer, or adjust the concentration of formic acid in the fuel tank 5 to a range suitable for use as a fuel. The other configurations of the fuel cell system 206 of this embodiment are similar to those of the fuel cell system 205 of the fifth embodiment.

[0087] The method for carrying out the hydrophilic treatment method using the fuel cell system 206 of this embodiment is the same as when the fuel cell system 206 of the fifth embodiment is used.

[0088] After the hydrophilization treatment of the anode diffusion layer is completed, fuel is supplied to the fuel cell 1 from the fuel tank 5, and an oxidant is supplied to the fuel cell 1 from the blower 22, thereby enabling power generation in the MEA (not shown). To generate power, for example, water or diluted formic acid is placed in the fuel tank 5, and the concentration of formic acid in the fuel tank 5 is adjusted to a suitable range for use as fuel. Thereafter, the fuel pump 52 is operated to send the fuel in the fuel tank 5 to the fuel cell 1, and air is supplied to the fuel cell 1 as an oxidant from the blower 22.

[0089] Furthermore, the fuel can also be prepared in the fuel tank 5 by, for example, filling the water tank 6 in advance with water and mixing the formic acid in the formic acid tank 3 with the water in the water tank 6 in the fuel tank 5, or by mixing the water produced in the power generation and collected in the water tank 6 with the formic acid in the formic acid tank 3 in the fuel tank 5. To prepare the fuel in the fuel tank 5, for example, water can be supplied from the water tank 6 to the fuel tank 5 to dilute the formic acid in the fuel tank 5. After the concentration of formic acid in the fuel tank 5 is adjusted to a range suitable for use as a fuel, the fuel pump 52 is operated to send the fuel in the fuel tank 5 to the fuel cell 1, and air as an oxidant is supplied from the blower 22 to the fuel cell 1, thereby generating electricity in the MEA.

[0090] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments within the scope of the present invention. [Explanation of symbols]

[0091] 1 fuel cell 11 Membrane electrode assembly 111 Electrolyte membrane 112 Anode 113 Cathode 114 Anode diffusion layer

Claims

1. a fuel cell including a membrane electrode assembly including an electrolyte membrane, an anode and a cathode provided on the electrolyte membrane, and an anode diffusion layer provided on the anode, the fuel cell being configured to be capable of using formic acid as a fuel; a formic acid tank configured to be able to directly supply formic acid having a concentration of 20% by mass or more and 98% by mass or less to the fuel cell; a fuel tank configured to be able to supply formic acid as fuel to the fuel cell, the formic acid tank is configured to be able to supply formic acid to the fuel cell and the fuel tank, The fuel cell system is configured to supply formic acid from the formic acid tank to the anode diffusion layer and bring the anode diffusion layer into contact with formic acid having a concentration of 20% by mass or more and 98% by mass or less, thereby increasing the hydrophilicity of the region of the anode diffusion layer that comes into contact with the formic acid.

2. a fuel cell including a membrane electrode assembly including an electrolyte membrane, an anode and a cathode provided on the electrolyte membrane, and an anode diffusion layer provided on the anode, the fuel cell being configured to be capable of using formic acid as a fuel; a formic acid tank configured to be able to directly supply formic acid having a concentration of 20% by mass or more and 98% by mass or less to the fuel cell; a concentration meter configured to be able to measure the concentration of formic acid in the formic acid tank; a formic acid pump disposed on a formic acid path from the formic acid tank to the fuel cell and configured to be able to deliver formic acid to the fuel cell; a control device connected to the concentration meter and the formic acid pump; a fuel tank configured to be able to supply formic acid as fuel to the fuel cell, the formic acid tank is configured to be able to supply formic acid to the fuel cell and the fuel tank, the control device is configured to set the amount of formic acid to be sent from the formic acid pump to the fuel cell based on the concentration of formic acid obtained from the concentration meter, The fuel cell system is configured to supply formic acid from the formic acid tank to the anode diffusion layer and bring the anode diffusion layer into contact with formic acid having a concentration of 20% by mass or more and 98% by mass or less, thereby increasing the hydrophilicity of the region of the anode diffusion layer that comes into contact with the formic acid.

3. a fuel cell including a membrane electrode assembly including an electrolyte membrane, an anode and a cathode provided on the electrolyte membrane, and an anode diffusion layer provided on the anode, the fuel cell being configured to be capable of using formic acid as a fuel; a formic acid tank configured to be able to supply formic acid having a concentration of 20% by mass or more and 98% by mass or less to the fuel cell; a fuel tank configured to be able to supply formic acid as fuel to the fuel cell; a formic acid pump disposed between the formic acid tank and the fuel tank on the formic acid path and configured to be able to deliver formic acid in the formic acid tank to the fuel tank; a concentration meter configured to be able to measure the concentration of formic acid in the fuel tank; a fuel pump disposed between the fuel tank and the fuel cell on the path of formic acid, the fuel pump being configured to be able to deliver the formic acid in the fuel tank to the fuel cell; a control device connected to the concentration meter, the formic acid pump, and the fuel pump, the fuel cell system is configured to be able to supply formic acid in the formic acid tank to the fuel cell via the fuel tank, the control device is configured to be able to set the amount of formic acid to be delivered from the formic acid pump to the fuel tank and the amount of formic acid to be delivered from the fuel tank to the fuel cell based on the concentration of formic acid acquired from the concentration meter, The fuel cell system is configured to supply formic acid from the formic acid tank to the anode diffusion layer and bring the anode diffusion layer into contact with formic acid having a concentration of 20% by mass or more and 98% by mass or less, thereby increasing the hydrophilicity of the region of the anode diffusion layer that comes into contact with the formic acid.

Images