JP2005340022A - Aging method and manufacturing method of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aging method of a fuel cell capable of shortening an aging period, imparting stable output property to a fuel cell after aging, and to provide a manufacturing method of a fuel cell shortening a period necessary for aging and reducing manufacturing cost. <P>SOLUTION: The aging method of a fuel cell composed of an anode, a cathode, and a polymer electrolyte interposed between the anode and the cathode comprises (i) a process of making the fuel cell start power generation by supplying fuel to the anode and oxidant gas to the cathode, (ii) a process of stabilizing the output property of the fuel cell by impressing a periodically changing electric load on the fuel cell which has just started power generation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for aging a fuel cell including an electrolyte, an anode, and a cathode, and a method for manufacturing the same. More specifically, the present invention relates to a polymer electrolyte fuel cell aging method in which the electrolyte is a polymer electrolyte, and a method for manufacturing the same.

  In recent years, fuel cells have been actively developed as a power source having excellent power generation efficiency and environmental characteristics. Like a general battery, a fuel cell includes a negative electrode (anode), a positive electrode (cathode), and an electrolyte sandwiched between the anode and the cathode. However, unlike general batteries, electrochemically reactive species are supplied from the outside. Fuel cells are roughly classified into solid oxide type (SOFC), molten carbonate type (MCFC), phosphoric acid type (PAFC), alkaline type (AFC), polymer electrolyte type (PEFC), etc., depending on the type of electrolyte. The temperature range suitable for power generation, the suitable catalyst, fuel, etc. differ depending on each type. Among them, the direct methanol fuel cell (DMFC), which is one of PEFC and PEFC, has an operable temperature of about −40 ° C. to 100 ° C. (preferably 50 ° C. to 100 ° C.), which is lower than other fuel cells. It is expected to be applied to stationary power sources such as household power supply systems, mobile power sources such as electric vehicles, and power sources for small portable devices such as personal computers and mobile phones.

  In PEFC, fuel such as hydrogen supplied to the anode is dissociated into electrons and hydrogen ions (protons) by a catalyst such as platinum contained in the anode. The generated hydrogen ions move to the cathode side through an electrolyte (generally a membrane electrolyte), and at the cathode, the hydrogen ions react with water by reacting electrochemically with oxidants and electrons such as oxygen supplied to the cathode. Become. Electrons generated at the anode move to the cathode side via an external circuit as the electrons are consumed at the cathode. Thus, in a fuel cell, electric energy can be directly extracted from an electrochemical reaction.

  Generally, after a fuel cell is manufactured, it is necessary to perform an aging operation (hereinafter also referred to as “aging process” or simply “aging”) until a predetermined output voltage designed as a battery characteristic is reached. The performance of the fuel cell immediately after manufacture is often lower than the design performance, and aging is performed as a process for ensuring the initial performance of the fuel cell. For this reason, it is difficult to quickly evaluate the quality of the fuel cell after production, and the cost required for the aging process (especially, capital investment) is very large. For this reason, shortening the aging time is a big problem.

  Factors that determine the aging time include the water content of the polymer electrolyte, the hydrogen ion migration rate in the polymer electrolyte, the gas diffusion rate in the gas diffusion layer, and the electrochemical reaction rate on the catalyst surface. These values are low immediately after production and are considered to be suitable for power generation only by aging treatment.

For example, Patent Document 1 discloses a method for realizing shortening of the aging time by paying attention to the water content in the polymer electrolyte. In the aging method described in Patent Document 1, the water content of the polymer electrolyte in the fuel cell is improved by generated water and condensed water generated by power generation by generating power so that flooding occurs. In addition, in order to suppress a decrease in power generation performance due to flooding, when the output voltage (cell voltage) of each cell in the fuel cell falls below a predetermined lower limit value, the flow rate of air supplied to the cathode is increased. To suppress excessive flooding. In addition to the lower limit value, if the time until the cell voltage next falls below the lower limit value is shorter than the predetermined time interval, the gas pressure is set to the lower limit value of the cell voltage to promote the recovery of the cell voltage. Control is performed such that the increase is adjusted until the value exceeds.
JP 2003-217622 A

  However, in reality, fuel cells that have once flooded often exhibit unstable cell voltage behavior, depending on the degree of flooding, and often perform aging operation for several tens of hours or more, and in some cases, several hundred hours or more. It has been found that otherwise the cell voltage will not be stable (eg, sudden and instantaneous voltage drops are observed). Therefore, although the method disclosed in Patent Document 1 is excellent from the viewpoint of shortening the aging time, it is considered that there is much room for improvement from the viewpoint of the output characteristics of the fuel cell obtained by aging. Thus, there is a need for an aging method for a fuel cell that can shorten the aging time and has stable output characteristics of the obtained fuel cell.

A fuel cell aging method of the present invention is an aging method for a fuel cell comprising an anode, a cathode, and a polymer electrolyte sandwiched between the anode and the cathode,
(I) starting power generation of the fuel cell by supplying fuel to the anode and supplying oxidant to the cathode;
(Ii) including a step of stabilizing the output characteristics of the fuel cell by applying an periodically changing electric load to the fuel cell that has started power generation.

The fuel cell aging method of the present invention is an aging method for a fuel cell comprising an anode, a cathode, and an electrolyte sandwiched between the anode and the cathode,
(I) starting power generation of the fuel cell by supplying fuel to the anode and supplying oxidant to the cathode;
(II) reducing the output voltage of the fuel cell by decreasing the supply amount of the oxidant to the cathode while maintaining the supply amount of the fuel to the anode;
And (III) returning the output voltage of the fuel cell by increasing the supply amount of the oxidant to the cathode.

  Next, a method for manufacturing a fuel cell according to the present invention is a method for manufacturing a fuel cell including an anode, a cathode, and a polymer electrolyte sandwiched between the anode and the cathode. A battery aging method is included.

  ADVANTAGE OF THE INVENTION According to this invention, the aging time can be shortened and the aging method of the fuel cell with which the output characteristic of the fuel cell obtained after aging was stabilized can be provided. Further, by using the fuel cell aging method of the present invention, it is possible to provide a fuel cell manufacturing method in which the time required for the aging treatment is shortened and the manufacturing cost is reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description of the embodiments, the same members may be denoted by the same reference numerals, and redundant descriptions may be omitted.

  A fuel cell aging method of the present invention (hereinafter also simply referred to as “aging method”) includes a fuel cell (that is, a polymer electrolyte type) including an anode, a cathode, and a polymer electrolyte sandwiched between the anode and the cathode. This is an aging method of a fuel cell (PEFC). Here, the aging method of the present invention includes (i) a step of starting power generation of the fuel cell by supplying fuel to the anode and supplying fuel to the cathode, and (ii) a fuel cell having started power generation. And applying an electrical load that fluctuates periodically to stabilize the output characteristics of the fuel cell.

  By using such an aging method, the time required for aging can be shortened. For this reason, the investment to the aging process considered to require the most investment in the manufacturing process of the fuel cell can be reduced, and a fuel cell with a further reduced manufacturing cost can be obtained. Further, since aging can be performed without causing flooding, an aging method in which the output characteristics of the fuel cell obtained after aging is more stable than when the method disclosed in Patent Document 1 is used. It can be.

  In addition, for example, when power is regenerated after a fuel cell is suspended (especially after a long period of suspension), or when output characteristics such as electromotive force are reduced due to long-term power generation, It has been found that the output characteristics of the fuel cell may be recovered by performing the aging process. At this time, if the time required for the aging process can be shortened, a fuel cell with reduced maintenance costs can be obtained.

  Although the reason why the aging time can be shortened by the aging method of the present invention is not clear, for example, the following reasons can be considered. In the aging method of the present invention, periodic and electrical load fluctuations are applied to each cell in the fuel cell. When the fuel cell is generating electric power, an electrochemical reaction proceeds in each cell. When the load fluctuation is applied here, it is considered that a non-equilibrium state of a partial electrochemical reaction is formed inside each cell. When a non-equilibrium state is formed, it is considered that micro pulsation and diffusion effects of reactive species related to electrochemical reactions such as hydrogen, oxygen, water, and hydrogen ions can be obtained inside the polymer electrolyte membrane and catalyst layer. . For this reason, it is thought that the effect of raising the moisture content of a polymer electrolyte membrane in a shorter time, for example is acquired.

  As described above, aging refers to power generation that is performed, for example, after a fuel cell is manufactured until its output characteristics reach a predetermined designed output characteristic. At this time, for example, in PEFC, it is considered that the polymer electrolyte membrane, which is an electrolyte, is sufficiently humidified to cause a phenomenon that a channel that conducts hydrogen ions is sufficiently formed. In addition, not only after production but also when the fuel cell is restarted after storage, or when the output characteristic is lowered by continuing power generation for a long period of time, power generation performed for the purpose of recovering the output characteristic at any time is also included.

  The structure and configuration of the PEFC to which the aging method of the present invention can be applied are not particularly limited. Any fuel cell can be applied as long as the electrolyte is a polymer electrolyte membrane. An example of a specific fuel cell will be described later.

  In step (i), the method of starting the power generation of the fuel cell by supplying fuel to the anode and supplying oxidant to the cathode is not particularly limited. What is necessary is just to start electric power generation using a general method. For example, power generation may be initiated by connecting the fuel cell to an aging device and supplying fuel and oxidant to the fuel cell. Further, for example, the fuel cell may be connected in advance to a system itself in which the fuel cell after aging is installed, and power generation may be started by supplying fuel and an oxidant to the connected fuel cell. In addition, if necessary, cooling water may be supplied to the fuel cell.

  The fuel supplied to the fuel cell is not particularly limited, and may be at least one selected from hydrogen and methanol, for example. The oxidizing agent supplied to the fuel cell is not particularly limited, and may be a gas containing oxygen, for example.

  In step (ii), there is no particular limitation on the method of applying an periodically changing electric load to the fuel cell that has started power generation. For example, a load may be connected to the fuel cell, and the magnitude of the load may be periodically changed. More specifically, for example, the fuel cell may be connected to a resistor (or a group of the resistors) such as a fixed resistor or a variable resistor, and the magnitude of the resistor may be periodically changed.

  At this time, the variable resistor may be, for example, an electronic load device. When an electronic load device is used, it is possible to more easily apply an periodically changing electric load to the fuel cell. For example, a control unit in which a load pattern to be applied to the fuel cell is set in advance and an electronic load device connected so that a load pattern signal can be sent from the control unit are prepared, and the electronic load device and the fuel cell are electrically connected. After connecting to, a preset load pattern may be executed. In addition, at this time, the control unit monitors arbitrary parameters such as the output voltage of the fuel cell, the output current, the flow rate of the fuel and the flow rate of the oxidant, and the application of the load is stopped according to the values of these parameters, Fuel and / or oxidant flow rates may be varied, and yet another load pattern may be implemented. In addition, the same effect can be acquired as long as the load is not limited to the electronic load device and can execute the load pattern sent from the control unit.

  For example, in step (ii), a periodically varying load may be applied to the fuel cell so that the output voltage of the fuel cell maintains a value equal to or higher than a preset output voltage threshold value. During aging of the fuel cell, if the output voltage of the fuel cell becomes too small, the fuel cell may be damaged. By applying a load so that the output voltage of the fuel cell does not fall below a preset output voltage threshold, it is possible to suppress such damage during aging. The threshold value may be set arbitrarily.

  Further, for example, in the step (ii), when the fuel cell is flooded, at least one utilization rate selected from the utilization rate of the fuel and the utilization rate of the oxidant may be decreased. In other words, the step (ii) may be performed under the condition that the fuel cell does not cause flooding as much as possible (preferably, the condition that does not cause flooding). Flooding refers to a phenomenon in which liquid water stays inside a fuel cell (for example, a fuel flow path or an oxidant flow path in the separator, which will be described later) depending on the power generation conditions of the fuel cell. As described above, when flooding occurs, the output characteristics of the fuel cell after aging may be lowered, depending on the degree of flooding. Therefore, in step (ii), when at least one utilization rate selected from the utilization rate of the fuel and the utilization rate of the oxidant is reduced when the fuel cell is flooded, the output of the fuel cell after aging is reduced. An aging method with more stable characteristics can be obtained.

  For example, in step (ii), when the fuel cell is flooded, the load applied to the fuel cell may be reduced. In other words, the step (ii) may be performed under the condition that the fuel cell does not cause flooding as much as possible (preferably, the condition that does not cause flooding). Similarly, an aging method with more stable output characteristics of the fuel cell after aging can be achieved.

  Further, for example, in step (ii), a load that fluctuates periodically may be applied until the output voltage of the fuel cell satisfies a preset aging termination condition. The aging end condition is not particularly limited and may be set arbitrarily. Specifically, for example, the aging end condition may be set so that the output voltage of the fuel cell reaches a preset output voltage.

  In step (ii), there is no particular limitation on the pattern (load pattern) of the electrical load that periodically changes and is applied to the fuel cell. For example, a rectangular wave load pattern 51 as shown in FIG. 1A may be applied to the fuel cell. In addition, a sawtooth wave load pattern 52 as shown in FIG. 1B may be applied to the fuel cell, or a wave load pattern 53 as shown in FIG. 1C (for example, a sine wave load pattern). ) May be applied to the fuel cell. In addition, a load pattern having a waveform corresponding to the charge / discharge characteristics of the capacitor may be applied to the fuel cell. Further, for example, a load pattern obtained by mixing a plurality of load patterns having different shapes may be applied to the fuel cell. Further, for example, after a certain load pattern is applied to the fuel cell, different load patterns may be applied continuously (or at intervals). In addition, the vertical axis | shaft in Fig.1 (a)-FIG.1 (b) is not specifically limited, For example, it is a current density.

  The maximum value of the electrical load applied to the fuel cell may be arbitrarily set as long as it does not exceed the maximum load value calculated based on the stoichiometry from the amount of fuel and oxidant supplied to the fuel cell. For example, what is necessary is just to set so that the output voltage (cell voltage) per cell of a fuel cell may be set to the range of about 0.1V-1.2V. In addition, the maximum value and the minimum value of the electric load applied to the fuel cell are not particularly limited. For example, the cell voltage of the fuel cell varies within a range of about 0.3V to 0.9V. You only have to set it. The period of load fluctuation is not particularly limited, and may be in the range of, for example, about 5 seconds to 300 seconds.

  In step (ii), a load smaller than the fluctuating load may be applied stepwise before applying a periodically fluctuating load to the fuel cell. In the initial stage of power generation, when a large load is suddenly applied, the output voltage of the fuel cell may be greatly reduced. For this reason, if a load that fluctuates periodically is applied to the fuel cell when a small load is applied in stages and then the output characteristics are stabilized to some extent, such a decrease in output voltage can be suppressed. it can.

In the aging method of the present invention, between step (i) and step (ii),
(A) reducing the output voltage of the fuel cell by reducing the amount of oxidant supplied to the cathode while maintaining the amount of fuel supplied to the anode;
(B) The method may further include a step of returning (recovering) the output voltage of the fuel cell by increasing the supply amount of the oxidant to the cathode. Note that “returning the output voltage” in the step (B) means raising the output voltage to the extent before the amount of oxidant supplied to the cathode is reduced in the step (A).

  By using such an aging method, the time required for aging can be further shortened. For this reason, the fuel cell whose manufacturing cost was further reduced can be obtained. Further, an aging method in which the output characteristics of the fuel cell obtained after aging is more stable can be obtained.

  In step (A), the supply amount of the oxidant to the cathode may be reduced to such an extent that the output voltage of the fuel cell is lowered. For example, the supply amount of the oxidizer may be reduced so that the cell voltage of the fuel cell is in the range of about 0.1V to 0.3V. At this time, a load may or may not be applied to the fuel cell. From the viewpoint of safety, it is preferable not to apply a load. Further, the amount of fuel supplied to the anode need not be exactly the same as before the amount of oxidant supplied to the cathode is decreased, and may be increased or decreased slightly.

  In step (B), the amount of oxidant supplied to the cathode may be increased to the extent that the output voltage of the fuel cell is restored. For example, what is necessary is just to increase the supply amount of an oxidizing agent to the level before performing a process (A).

  The reason why the time required for aging can be shortened by performing step (A) and step (B) is not clear, but for example, the following reasons are conceivable.

  Carbon particles are widely used as a base material for supporting a catalyst and a conductive material in a catalyst layer (an anode catalyst layer and a cathode catalyst layer) which is one of the members constituting each cell in a fuel cell. In general, carbon particles have a porous structure that easily adsorbs chemical substances and the like. For this reason, there is a possibility that the carbon particles used in the catalyst layer adsorb and hold a wide variety of chemical substances depending on the storage before manufacture or the atmosphere at the time of manufacture. That is, when the fuel cell is assembled, there is a possibility that many impurities remain inside each cell of the fuel cell. These residual impurities may deteriorate the output characteristics of the fuel cell. In addition, if the fuel cell continues to generate electricity over a long period of time, impurities from piping that supplies fuel and oxidant will gradually accumulate in the catalyst layer and polymer electrolyte membrane, and as in the case of residual impurities, Output characteristics may be degraded. In addition, it has been pointed out that during the long-term power generation and long-term suspension of the fuel cell, the output characteristics of the fuel cell may be degraded due to accumulation of microorganisms and organic substances.

  By performing aging based on the above-described aging method of the present invention, these impurities are considered to be discharged out of the fuel cell by, for example, generated water. At this time, if the step (A) and the step (B) are further performed, it is considered that discharge of impurities is promoted by containing more hydrogen ions in the catalyst layer and the polymer electrolyte membrane. For this reason, it is considered that the time required for aging can be further shortened.

  In the aging method of the present invention, step (A) and step (B) may be performed independently of step (i) and step (ii). Even when the step (A) and the step (B) are performed independently, the time required for aging can be shortened.

That is, the aging method of the present invention is a fuel cell aging method comprising an anode, a cathode, and an electrolyte sandwiched between the anode and the cathode,
(I) starting power generation of the fuel cell by supplying fuel to the anode and supplying oxidant to the cathode;
(II) reducing the output voltage of the fuel cell by reducing the amount of oxidant supplied to the cathode while maintaining the amount of fuel supplied to the anode;
(III) The step of returning (recovering) the output voltage of the fuel cell by increasing the supply amount of the oxidant to the cathode may be included. By using such an aging method, the time required for aging can be shortened.

  Next, the manufacturing method of this invention is demonstrated.

  The manufacturing method of the present invention is a method of manufacturing a fuel cell including an anode, a cathode, and a polymer electrolyte sandwiched between the anode and the cathode, and includes the above-described fuel cell aging method of the present invention. It is a feature. As described above, in the aging method of the present invention, the time required for aging can be shortened. For this reason, by setting it as such a manufacturing method, the manufacturing cost can be reduced more and / or the fuel cell with the stable output characteristic can be manufactured.

  In the production method of the present invention, the steps other than aging are not particularly limited. It only has to include steps used in a general method for manufacturing a fuel cell. For example, a step of laminating an anode catalyst layer and a cathode catalyst layer on a polymer electrolyte membrane to form a membrane electrode assembly (MEA), a step of laminating MEA and a pair of separators to form a cell, Steps such as the step of stacking the cells to form a fuel cell stack may be included in any combination. In addition, since it is thought that an aging process is indispensable in order to manufacture a fuel cell, even when only the aging method of this invention is included, it can be considered that it is a manufacturing method of a fuel cell.

  The specific structure and configuration of the fuel cell using the aging method of the present invention and the fuel cell manufactured by the manufacturing method of the present invention are not particularly limited. The aging method of the present invention can be applied to general polymer electrolyte fuel cells (including direct methanol fuel cells).

  FIG. 2 shows an example of a fuel cell. In FIG. 2, the fuel cell is shown in a partially disassembled state for easy understanding.

  The fuel cell 2 shown in FIG. 2 is a general polymer electrolyte fuel cell (PEFC), and has a structure in which a plurality of cells 15 are stacked. Such a fuel cell 2 may be generally called a fuel cell stack. The cell 15 includes an MEA (membrane electrode assembly) 11 in which an anode is formed on one main surface of a polymer electrolyte membrane and a cathode is formed on the other main surface. The polymer electrolyte membrane is not particularly limited as long as it has hydrogen ion conductivity. For example, a membrane (PFSA membrane) made of polyperfluorocarbon sulfonic acid may be used. More specifically, for example, Nafion (registered trademark) manufactured by DuPont. Generally, the anode and the cathode may have any structure or configuration used for PEFC. For example, the anode may be constituted by an anode catalyst layer or a diffusion layer, and the cathode may be constituted by a cathode catalyst layer or a diffusion layer. Further, as the anode catalyst and the cathode catalyst, for example, Pt (platinum), Ru (ruthenium), etc., as the base material and the conductive material supporting the catalyst, for example, as a carbon material such as carbon, as the ion conductor For example, the polyperfluorocarbon sulfonic acid described above may be included.

  The MEA 11 is sandwiched between an anode separator 13 and a cathode separator 14 via a gasket 12 that prevents leakage of fuel and oxidant supplied to the MEA 11. The anode separator 13 is disposed on the anode side of the MEA 11, and the cathode separator 14 is disposed on the cathode side of the MEA 11. On the main surfaces of the anode separator 13 and the cathode separator 14 facing the MEA 11, a fuel flow path and an oxidant flow path are formed, respectively. A cooling water flow path is formed on the main surface of the cathode separator 14 opposite to the main surface facing the MEA. Thus, the structure in which the MEA 11 is held between the pair of separators 13 and 14 is called a cell 15. The cell 15 is the minimum unit of the fuel cell 2, and the output voltage of the fuel cell 2 can be increased by stacking a plurality of cells 15 so as to be electrically connected in series. For example, the anode separator 13 and the cathode separator 14 may be formed of a conductive material such as a metal such as stainless steel or a carbon material.

  In the fuel cell 2 shown in FIG. 2, a plurality of cells 15 are stacked via a seal 16 for preventing leakage of fuel and oxidant between the cells 15. A cathode side current collector 17 and an anode side current collector 18 for collecting electric power generated in the cell 15 are arranged at both ends of the stacked body of the cell 15. The cathode side current collector 17 and the anode side current collector 18 may be formed using a conductive material such as metal. Each current collector is provided with a cathode terminal 19 and an anode terminal 20, and the electric power generated in the fuel cell 2 can be taken out of the fuel cell 2 via both terminals. The laminated body of the cell 15, the cathode side current collector 17, and the anode side current collector 18 is sandwiched by an insulating plate 21 having an insulating property. 29, the washer 32 and the nut 30 are fastened to constitute the fuel cell 2.

  In the fuel cell 2 shown in FIG. 2, a fuel inlet 23, an oxidant inlet 24, a fuel outlet 25, an oxidant outlet 26, a cooling water inlet 27 and a cooling water outlet 28 are formed in the insulating plate 21. Each separator has a through hole (a fuel through hole, an oxidant through hole, and a cooling water through hole) formed in a direction perpendicular to the main surface of the separator. The oxidant and the cooling water can be supplied to the cell 15. Further, the unused fuel and oxidant that have passed through the cell 15 and the cooling water that has cooled the cell can be discharged from the fuel cell 2 through the respective outlets. A spring 31 is disposed between the end plate 22 and the insulating plate 21, and the pressure for stacking the cells 15 can be adjusted. For each member described above in the fuel cell 2, a material generally used for PEFC may be used. 2 is merely an example, and the fuel cell to which the aging method of the present invention is applied or the fuel cell manufactured by the manufacturing method of the present invention is different from the fuel cell shown in FIG. You may have the structure of.

  The aging method of the present invention may be applied to a fuel cell system as shown in FIG. 3, for example.

  A fuel cell system 1 shown in FIG. 3 includes a fuel cell 2 including an anode, a cathode, and an electrolyte sandwiched between the anode and the cathode. The fuel cell 2 can generate electric power by supplying fuel to the anode of the fuel cell 2 and supplying an oxidant to the cathode. In addition to the fuel cell 2, the fuel cell system 1 includes a connection unit 3 for taking out the generated electric power to the outside of the fuel cell system 1 (for example, the external circuit 6 shown in FIG. 3), the fuel cell 2, The load part 4 connected in general, and the control part 5 which controls the magnitude | size of the load in the load part 4 are provided. In the fuel cell system 1, the load unit 4 can apply an electrical load to the fuel cell 2 by consuming at least a part of the generated power according to the control of the control unit 5. That is, if a load that varies periodically is applied to the fuel cell 2 by the load unit 4, aging based on the aging method of the present invention can be performed. In the fuel cell system 1, a load unit 4 that applies an electrical load to the fuel cell 2 is built in the fuel cell system 1 itself. For this reason, aging can be performed without using an external device for aging. The fuel cell system 1 is not limited to the fuel cell system 1 shown in FIG.

  In the fuel cell 2 in the fuel cell system 1 shown in FIG. 3, a pipe 37 and a connection port 38 are arranged corresponding to the fuel inlet 23, the oxidant inlet 24, the fuel outlet 25, and the oxidant outlet 26, respectively. . For this reason, the fuel and the oxidant can be supplied to the fuel cell 2 from the outside of the fuel cell system 1 through the respective connection ports 38. Further, unused fuel and oxidant can be discharged to the outside of the fuel cell system 1 through the connection ports 38.

  As long as the connection part 3 can take out the electric power which generate | occur | produced in the fuel cell outside, the structure, structure, etc. are not specifically limited. In the example shown in FIG. 3, the connection portion 3 includes a − (minus) terminal 41 and a + (plus) terminal 42 that are electrically connected to the anode terminal 20 and the cathode terminal 19 in the fuel cell 2 via the wiring 43. The terminal part containing is included. The electric power generated in the fuel cell 2 can be supplied to the external circuit 6 via the − terminal 41 and the + terminal 42.

  When the fuel cell system 1 is a stationary fuel cell system used in a home or factory, the external circuit 6 is, for example, a group of electrical devices in the home or factory. When the fuel cell system 1 is a portable fuel cell system used for a portable device such as a personal computer or a mobile phone, the external circuit 6 is, for example, an electric circuit, a memory device, a storage device, or the like in the portable device. When the fuel cell system 1 is a mobile body-loaded fuel cell system used for a mobile body such as an automobile, the external circuit 6 is, for example, an electronic device group mounted on the automobile or various drive motors.

  The structure and configuration of the load unit 4 are not particularly limited. For example, a fixed resistor may be included or a variable resistor may be included. When the variable resistor is an electronic load device, for example, the control of the load pattern by the control unit 5 can be performed more easily.

  An electrical connection method between the load unit 4 and the fuel cell 2 is not particularly limited. For example, as shown in FIG. 3, it is only necessary that the cathode terminal 19 and the anode terminal 20 of the fuel cell 2 and the load portion 4 are electrically connected by a wiring 44. The wiring 43 that electrically connects the fuel cell 2 and the connection portion 3 may be branched to electrically connect the fuel cell 2 and the load portion 4.

  As long as the control part 5 can control the load pattern in the load part 4, the structure, a structure, etc. are not specifically limited. For example, the control unit 5 is a control unit (for example, a program control device) in which a control program is built in advance, and the load unit 4 may execute the load pattern based on a command from the program. In the example shown in FIG. 3, the control part 5 and the load part 4 are connected by the information line 45 which conveys the said instruction | command.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, this invention is not limited to the Example shown below.

  In this embodiment, an aging test is performed by applying a square-wave load pattern that periodically fluctuates as shown in FIG. 1A to an unpowered fuel cell, and output characteristics of the fuel cell after aging is completed. Evaluated.

-Sample 1-
First, a fuel cell used for an aging test was prepared. The fuel cell was a fuel cell as shown in FIG. Specifically, a porous anode catalyst layer and a cathode catalyst layer are formed by using a Nafion membrane as the electrolyte membrane, applying a mixed slurry of Pt catalyst + Ketjen black + Nafion solution on the electrolyte membrane, and drying it. An MEA was produced. The produced MEA was sandwiched between a pair of carbon separators (a fuel or oxidant flow path is formed on the main surface on the MEA side) to produce a cell. Thereafter, the produced cells were laminated to produce a fuel cell (fuel cell stack) having 10 cells. The effective membrane area of MEA was 400 cm ² .

An aging process as shown in FIG. 4 was performed on the fuel cell thus prepared. Specifically, first, the fuel cell is supplied with 3SLM per cell of hydrogen with a purity of 99.99% (SLM: 20 ° C. standard volume), and air is supplied as an oxidizer with 10 SLM per cell to start power generation. did. After power generation was started, a load was applied to the fuel cell stepwise using an electronic load device connected to the fuel cell. After that, when 5 minutes passed from the start of power generation, application of a square-wave load that fluctuates periodically to the fuel cell was started. Load pattern, as shown in FIG. 4, at a current density in terms applied to each cell in the fuel cell, maximum 0.3 mA / cm ^2, and the minimum 0.2 mA / cm ^2. Moreover, 1 cycle was made into 1 minute and 15 cycles were performed. At this time, the voltage per cell (cell voltage) in the fuel cell fluctuated periodically in the range of 0.75V to 0.9V. The square wave load was applied for 15 minutes, and then a steady power generation state in which a load of 0.15 mA / cm ^{2 in} terms of current density was continuously applied was obtained. Note that no flooding was observed during the aging process.

-Sample 2-
An aging treatment as shown in FIG. 5 was performed on the fuel cell prepared in the same manner as Sample 1. Specifically, first, hydrogen having a purity of 99.99% as a fuel was supplied to a fuel cell at 3 SLM per cell, and an oxygen-nitrogen mixed gas having an oxygen concentration of 21% by volume as an oxidant was supplied at 10 SLM per cell. Power generation started. Next, when the cell voltage reached 1.0 V, the oxygen concentration in the oxidant was reduced to 2% by volume, and the cell voltage was lowered. Subsequently, when the cell voltage dropped to 0.1V, the oxygen concentration in the oxidant was increased to 21% by volume, and the cell voltage was returned to about 1.0V. This step was repeated twice (that is, two sets of the above-described step (A) and step (B) were performed), and a square wave load that fluctuates periodically was applied to the fuel cell in the same manner as in sample 1. Note that, like the sample 1, application of the square wave load started 5 minutes after the start of power generation. Similarly to Sample 1, a square wave load was applied for 15 minutes, and then a steady power generation state in which a load of 0.15 mA / cm ^{2 in} terms of current density was continuously applied was obtained. No flooding was observed during the aging process.

-Comparative sample-
Aging was performed on the fuel cell prepared in the same manner as Sample 1 without applying a load that fluctuates periodically. Specifically, first, the fuel cell was supplied with 3SLM per cell of hydrogen having a purity of 99.99% as a fuel and 10 SLM per cell as an oxidant, and power generation was started. After starting power generation, a constant load (0.2 mA / cm ² in terms of current density) was applied for 8 hours using an electronic load device connected to the fuel cell. As in the case of Sample 1, application of the load started 5 minutes after the start of power generation. In addition, after application for 8 hours, a state of steady power generation in which a load of 0.15 mA / cm ^{2 in} terms of current density was continuously applied was obtained.

  For the three samples subjected to the aging process in this way, the degree of decrease in the cell voltage in the state of steady power generation performed following the aging process was evaluated. As a result, the cell voltage decrease in sample 1 was -1.3 mV / h, the cell voltage decrease in sample 2 was -0.7 mV / h, and the cell voltage decrease in the comparative sample was -5.3 mV / h. Met. Compared with the comparative sample, it can be seen that in Sample 1 and Sample 2, the time required for aging can be shortened and a fuel cell having stable output characteristics after aging was obtained. In addition, sample 2 was a fuel cell with more stable output characteristics than sample 1.

Moreover, about the sample 1 and the comparative sample, the density | concentration (total organic carbon material density | concentration: TOC) of the organic substance in the cathode discharge water in an aging process was evaluated. At the same time, aging treatment was performed on two types of samples (samples 3 and 4) that were subjected to aging by applying a load that varies periodically as in sample 1 to a fuel cell prepared in the same manner as in sample 1. The concentration of organic substances in the cathode discharge water was evaluated. However, in the sample 3, it was varied in a range value at a current density in terms of 0.1mA / cm ² ~0.2mA / cm ² load (fluctuation range of the cell voltage, similarly to the sample 1 0.15V) . In Sample 4, was varied in a range value at a current density in terms of 0.1mA / cm ² ~0.3mA / cm ² load, the fluctuation range of the cell voltage was 0.25 V. The results are shown in FIG.

  As shown in FIG. 6, it was found that the TOC in the cathode discharge water increased in Sample 1 at an earlier stage as compared with the comparative sample. Further, in the comparative sample, the TOC continued to increase, whereas in the sample 1, the TOC started to decrease after 8 minutes from the start of aging. From this, it is considered that the discharge of impurities contained in the fuel cell is promoted in the sample 1 as compared with the comparative sample. In addition, sample 3 and sample 4 showed a greater tendency than sample 1.

  As described above, according to the present invention, it is possible to provide a fuel cell aging method in which the aging time can be shortened and the output characteristics of the fuel cell obtained after aging are stable. Further, by using the fuel cell aging method of the present invention, it is possible to provide a fuel cell manufacturing method in which the time required for the aging treatment is shortened and the manufacturing cost is reduced.

It is a schematic diagram which shows an example of the load which can be used for the aging method of the fuel cell of this invention which fluctuates periodically. It is a schematic diagram which shows an example of the fuel cell which can apply the aging method of the fuel cell of this invention. 1 is a schematic diagram showing an example of a fuel cell system including a fuel cell to which the fuel cell aging method of the present invention can be applied. It is a figure for demonstrating an example of the aging method of the fuel cell implemented in the Example. It is a figure for demonstrating an example of the aging method of the fuel cell implemented in the Example. It is a figure which shows the relationship between the aging time in each sample of an Example, and the total organic carbon substance density | concentration in discharge water.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell system 2 Fuel cell 3 Connection part 4 Load part 5 Control part 6 External circuit 11 MEA
12 Seal 13 Anode Separator 14 Cathode Separator 15 Cell 16 Gasket 17 Cathode Side Current Collector 18 Anode Side Current Collector 19 Cathode Terminal 20 Anode Terminal 21 Insulating Plate 22 End Plate 23 Fuel Inlet 24 Oxidant Inlet 25 Fuel Outlet 26 Oxidant Outlet 27 Cooling water inlet 28 Cooling water outlet 29 Bolt 30 Nut 31 Spring 32 Washer 37 Piping 38 Connection port 51, 52, 53 Load pattern

Claims (8)

A fuel cell aging method comprising an anode, a cathode, and a polymer electrolyte sandwiched between the anode and the cathode,
(I) starting power generation of the fuel cell by supplying fuel to the anode and supplying oxidant to the cathode;
(Ii) a step of stabilizing the output characteristics of the fuel cell by applying a periodically varying electric load to the fuel cell that has started the power generation. . In the step (ii),
2. The fuel cell aging method according to claim 1, wherein the periodically varying load is applied so that the output voltage of the fuel cell maintains a value equal to or higher than a preset output voltage threshold value. 3. In the step (ii),
2. The fuel cell aging method according to claim 1, wherein when the fuel cell is flooded, at least one utilization rate selected from the utilization rate of the fuel and the utilization rate of the oxidant is decreased. In the step (ii),
2. The fuel cell aging method according to claim 1, wherein the periodically varying load is applied until an output voltage of the fuel cell satisfies a preset aging termination condition. Between the step (i) and the step (ii),
(A) reducing the output voltage of the fuel cell by decreasing the supply amount of the oxidant to the cathode while maintaining the supply amount of the fuel to the anode;
2. The fuel cell aging method according to claim 1, further comprising: (B) returning the output voltage of the fuel cell by increasing the supply amount of the oxidant to the cathode. A method for aging a fuel cell comprising an anode, a cathode, and an electrolyte sandwiched between the anode and the cathode,
(I) starting power generation of the fuel cell by supplying fuel to the anode and supplying oxidant to the cathode;
(II) reducing the output voltage of the fuel cell by decreasing the supply amount of the oxidant to the cathode while maintaining the supply amount of the fuel to the anode;
(III) A method of aging a fuel cell, comprising a step of returning the output voltage of the fuel cell by increasing the supply amount of the oxidant to the cathode. The method for aging a fuel cell according to any one of claims 1 to 6, wherein the fuel is at least one selected from hydrogen and methanol, and the oxidant is a gas containing oxygen. A method for producing a fuel cell, comprising: an anode; a cathode; and a polymer electrolyte sandwiched between the anode and the cathode,
A fuel cell manufacturing method comprising the fuel cell aging method according to claim 1.

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