Method for activating a polymer electrolyte fuel cell

Abstract

This invention provides a method for activating a polymer electrolyte fuel cell that can activate the fuel cell in a manner corresponding to the entire cathode electrode. [Solution] A method for activating a polymer electrolyte fuel cell, comprising an anode electrode and a cathode electrode, and a solid polymer membrane disposed between the anode electrode and the cathode electrode, the method comprising: a first step of uniformly supplying air to the entire cathode electrode; and a second step of, while uniformly supplying air to the entire cathode electrode, flowing a constant current from the anode electrode to the cathode electrode for a certain period of time using an external power source, and then stopping the flow of the current, wherein the combination of the first step and the second step is repeated two or more times.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for activating a polymer electrolyte fuel cell.

BACKGROUND ART

[0002] Conventionally, efforts aimed at mitigating or reducing the impacts of climate change have been ongoing, and research and development related to reducing carbon dioxide emissions have been conducted to achieve this goal. From such a perspective, fuel cell vehicles (FCV / Fuel Cell Vehicle) equipped with fuel cells have attracted attention. The reason is that what is discharged from a fuel cell vehicle is only water (H2O), and CO2, NO X , SO X and other gases are not discharged.

[0003] In general, a fuel cell mounted on a fuel cell vehicle has a fuel cell stack. The fuel cell stack is formed by stacking a plurality of flat plate-shaped fuel cell cells. Each fuel cell includes a membrane electrode assembly (MEA) and a pair of separators arranged on both sides of the membrane electrode assembly.

[0004] The membrane electrode assembly includes a polymer electrolyte membrane (hereinafter referred to as the electrolyte membrane) having a first end face and a second end face, an anode electrode (fuel electrode) provided on the first end face of the electrolyte membrane, and a cathode electrode (oxidant electrode) provided on the second end face of the electrolyte membrane. That is, the membrane electrode assembly is configured with the electrolyte membrane sandwiched between the anode electrode and the cathode electrode.

[0005] In a fuel cell, hydrogen is supplied as an anode gas (fuel) to the anode electrode of the membrane electrode assembly. Further, a cathode gas (oxidant) containing oxygen such as air is supplied to the cathode electrode of the membrane electrode assembly. Then, hydrogen ions generated by the reaction between hydrogen and the catalyst at the anode electrode pass through the electrolyte membrane and move to the cathode electrode, where an electrochemical reaction with oxygen in the cathode gas (O2+4H + +4e -It generates electricity by producing 2H2O (hydrogen ions). Therefore, water is produced in each fuel cell as electricity is generated.

[0006] In fuel cells, the fuel cell is typically activated (aged) before the first operation. Activating the fuel cell makes it easier for hydrogen ions and other elements to move within the cell, resulting in sufficient power generation performance. One method for activating fuel cell cells involves supplying hydrogen as the anode gas to the anode electrode and introducing a mixture of nitrogen and air as the cathode gas to the cathode electrode.

[0007] Paragraph 0059 (Example) of Patent Document 1 describes the aging process of a solid electrolyte fuel cell, stating: "...After starting power generation, a load was applied to the fuel cell in stages using an electronic load device connected to the fuel cell. Then, 5 minutes after the start of power generation, a periodically fluctuating square wave load was applied to the fuel cell. ...The load pattern is as shown in Figure 4...The square wave load was applied for 15 minutes, and thereafter, the current density was 0.15 mA / cm²." 2 It states, "The system was kept in a steady-state power generation state with the load continuously applied."

[0008] Paragraph 0033 of Patent Document 2 states, "...by short-circuiting the anode catalyst layer and the cathode catalyst layer, the fuel cell can be supplied with 2 A / cm²." 2 The description states that a short-circuit current with the above current density flows for a short time of less than 1 second (part III in Figures 4 and 5)... and that the process of steps S10 to S20 is repeated multiple times as shown in Figure 3.

[0009] Paragraph 0046 of Patent Document 3 describes "controlling the current source with a control device to control the current flowing out of the air electrode so that the potential of the air electrode becomes the potential waveform shown in Figure 9(B)," and paragraph 0052 describes periodically fluctuating the air electrode potential by applying a current. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2005-340022 [Patent Document 2] Japanese Patent Publication No. 2019-197690 [Patent Document 3] Japanese Patent Publication No. 2010-027296 [Overview of the project] [Problems that the invention aims to solve]

[0011] In conventional fuel cell activation methods, the amount of air supplied to the cathode electrode is insufficient, causing the electrochemical reaction described above to be biased upstream of the cathode electrode (the side where air is supplied), resulting in insufficient activation of the fuel cell downstream of the cathode electrode.

[0012] The present invention has been made in view of the above circumstances, and aims to provide a method for activating a polymer electrolyte fuel cell that can activate the fuel cell throughout the entire cathode electrode. [Means for solving the problem]

[0013] The present invention has the following aspects. [1] A method for activating a polymer electrolyte fuel cell, comprising an anode electrode and a cathode electrode, and a solid polymer membrane disposed between the anode electrode and the cathode electrode, A first step of uniformly supplying air to the entire cathode electrode, The process includes a second step in which, while uniformly supplying air to the entire cathode electrode, a constant current is passed from the anode electrode to the cathode electrode for a certain period of time using an external power source, and then the current is stopped. A method for activating a polymer electrolyte fuel cell, comprising repeating the combination of the first and second steps two or more times.

[0014] According to the above aspect, the fuel cell can be activated corresponding to the entire cathode electrode. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a method for activating a polymer electrolyte fuel cell that can activate the fuel cell corresponding to the entire cathode electrode. [Brief Description of the Drawings]

[0016] [Figure 1] This is a cross-sectional view schematically showing a fuel cell unit of a fuel cell activated by the method for activating a polymer electrolyte fuel cell according to one embodiment of the present invention. [Figure 2] This is a diagram for explaining the method for activating a polymer electrolyte fuel cell according to one embodiment of the present invention. [Modes for Carrying Out the Invention]

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0018] [Method for Activating Polymer Electrolyte Fuel Cell] A method for activating a polymer electrolyte fuel cell according to one embodiment of the present invention is a method for activating a polymer electrolyte fuel cell comprising an anode electrode, a cathode electrode, and a polymer electrolyte membrane disposed between the anode electrode and the cathode electrode, the method comprising: a first step of uniformly supplying air to the entire cathode electrode; and a second step of, in a state where air is uniformly supplied to the entire cathode electrode, causing a constant current to flow from the anode electrode to the cathode electrode for a certain period of time by an external power supply, then stopping the flow of the current, wherein the combination of the first step and the second step is repeated two or more times.

[0019] The method for activating a polymer electrolyte fuel cell of the present embodiment activates a plurality of stacked fuel cell units 30. The plurality of fuel cell units 30 are, for example, connected in series. In this embodiment, the case in which multiple fuel cell cells 30 are stacked is described as an example, but the fuel cell cells 30 may consist of only one layer. Also, as shown in Figure 1, when fuel cell cells 30 are stacked, the number of stacked fuel cell cells 30 is not particularly limited.

[0020] (30 fuel cell cells) As shown in Figure 1, the fuel cell cell 30 includes a first separator 21, a second separator 25, and a membrane electrode structure (MEA) 10 disposed between the first separator 21 and the second separator 25.

[0021] The first separator 21 and the second separator 25 are each made of known fuel cell separators such as a metal separator made of stainless steel, aluminum, titanium, etc., and a carbon separator, respectively. As shown in Figure 1, the membrane electrode structure 10 includes an anode electrode 14, a cathode electrode 16, and a solid polymer electrolyte membrane 12 sandwiched between the anode electrode 14 and the cathode electrode 16.

[0022] The solid polymer electrolyte membrane 12 consists of a proton-conducting ion-exchange membrane. Specifically, the solid polymer electrolyte membrane 12 can be made of, for example, a fluorine-based resin such as perfluorosulfonic acid, a hydrocarbon-based resin, or the like. As shown in Figure 1, the anode electrode 14 has a first electrode catalyst layer 18 and a first gas diffusion layer 20 for supplying gas to the first electrode catalyst layer 18. The cathode electrode 16 has a second electrode catalyst layer 22 and a second gas diffusion layer 24 for supplying gas to the second electrode catalyst layer 22.

[0023] The first electrode catalyst layer 18 and the second electrode catalyst layer 22 can each be, for example, a catalyst supported on a carrier such as carbon particles. Examples of catalysts included in the first electrode catalyst layer 18 and the second electrode catalyst layer 22 include platinum catalysts and platinum alloy catalysts composed of platinum and other metals. In this embodiment, it is preferable that one or both of the first electrode catalyst layer 18 and the second electrode catalyst layer 22 contain a platinum catalyst. This is because activating the fuel cell cell 30 results in a fuel cell with sufficient power generation performance.

[0024] For the first gas diffusion layer 20 and the second gas diffusion layer 24, known diffusion layers for fuel cells such as carbon cloth made of carbon nonwoven fabric and carbon paper can be used, respectively.

[0025] Between two adjacent fuel cell cells 30, a cooling water channel 23 is provided for circulating cooling water to cool the fuel cell cells 30.

[0026] Next, a method for activating the polymer electrolyte fuel cell of this embodiment will be described. This explains why fuel cells need to be activated (aged). Fuel cells have low initial power generation performance due to the resistance of the initially dried electrolyte membrane, the oxide film formed on the catalyst during the manufacturing process, and the poisoning of the catalyst by volatile organic matter. Therefore, after the manufacture of a fuel cell, a preliminary operation called aging is usually performed to bring out the desired power generation performance. Fuel cell aging involves generating power in the fuel cell preliminaryly after manufacture to wet the electrolyte membrane, reduce its resistance, and remove the oxide film and organic matter from the catalyst surface, thereby enabling the fuel cell to perform at the desired capacity. Furthermore, aging can be performed not only after manufacture, but also, for example, when restarting a fuel cell after it has been shut down (especially after a long period of shutdown), or when output characteristics such as electromotive force have deteriorated due to long-term power generation, in order to restore the output characteristics of the fuel cell.

[0027] "1st process" In the first step, air is supplied uniformly to the entire cathode electrode of the polymer electrolyte fuel cell. One way to supply air uniformly to the entire cathode electrode is to reduce the oxygen concentration in the air to 5% or less. Alternatively, the oxygen concentration in the air can be increased as much as possible, as long as it does not cause excessive current to flow through the cathode electrode. However, since increasing the oxygen concentration increases equipment costs, it is best to keep it to the minimum necessary, and the oxygen concentration should be set considering the target cost.

[0028] "Second process" In the second step, with air uniformly supplied to the entire cathode electrode, a constant current is passed from the anode electrode to the cathode electrode for a certain period of time using an external power supply, and then the current is stopped.

[0029] In the very beginning of the second process, there is a section at the cathode electrode where the current distribution is uniform. However, gradually, the current distribution becomes uneven, and it may become impossible to activate the fuel cell across the entire cathode electrode. Therefore, once the current distribution becomes constant, the flow of current from the anode electrode to the cathode electrode is temporarily stopped, and the first process is repeated, followed by the second process. This allows the fuel cell to be activated across the entire cathode electrode. The combination of the first and second processes is repeated at least twice. By repeating the combination of the first and second processes at least twice, the fuel cell can be activated across the entire cathode electrode by performing the combination of the first and second processes only once.

[0030] The number of repetitions and duration of the combination of the first and second steps are not particularly limited. Typically, the duration of repetitions of the combination of the first and second steps is, for example, between 10 and 40 minutes. If the duration of repetitions of the combination of the first and second steps is too short, the activation of the solid-state battery will not be completed to the predetermined output. On the other hand, if the duration of repetitions of the combination of the first and second steps is too long, it will lead to an increase in unnecessary repetition time. Therefore, the number of repetitions and duration of the combination of the first and second steps are determined by comprehensively considering the target output and repetition time.

[0031] In the activation method for the polymer electrolyte fuel cell of this embodiment, the completion of the activation of the polymer electrolyte fuel cell is determined by evaluating the output through power generation.

[0032] Referring to Figure 2, a specific example of the activation method for the polymer electrolyte fuel cell of this embodiment will be described. Figure 2 illustrates the activation method for the polymer electrolyte fuel cell of this embodiment. An indicator showing the oxygen concentration on one surface of the cathode electrode and the current flowing through the cathode electrode is displayed in the upper left of Figure 2. In the indicator, the oxygen concentration and current decrease from left to right across the page.

[0033] In Step 1, air is supplied to the cathode electrode of the polymer electrolyte fuel cell. In Step 1, the oxygen concentration is uniform throughout the cathode electrode. Also, in Step 1, no current is passed from the anode electrode to the cathode electrode.

[0034] In Step 2, when current is passed from the anode electrode to the cathode electrode, the current flowing through the cathode electrode increases throughout the entire cathode electrode. This is because oxygen is present throughout the entire cathode electrode, causing an electrochemical reaction between hydrogen ions and oxygen to proceed throughout the entire cathode electrode. On the other hand, as the electrochemical reaction progresses, the oxygen concentration throughout the cathode electrode decreases. Furthermore, as the electrochemical reaction progresses, the current flowing through the cathode electrode eventually becomes constant.

[0035] In Step 3, the amount of air supplied is greater upstream of the cathode electrode and less downstream of the cathode electrode, causing the electrochemical reaction described above to be biased towards the upstream side of the cathode electrode. As a result, a larger current flows upstream of the cathode electrode, and a smaller current flows downstream of the cathode electrode.

[0036] If this condition occurs, stop the flow of current from the anode electrode to the cathode electrode, return to Step 1, and uniformly supply air to the entire cathode electrode. Then, proceed to Steps 2 and 3.

[0037] If the activation of the polymer electrolyte fuel cell is confirmed to be complete, terminate Step 3. If the activation of the polymer electrolyte fuel cell is not confirmed to be complete, repeat Steps 1 through 3.

[0038] Although embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of Symbols]

[0039] 10 Membrane electrode structure 12 Solid polymer electrolyte membrane 14 Anode electrodes 16 Cathode electrodes 18 First electrode catalyst layer 20 First gas diffusion layer 21 First Separator 22 Second electrode catalyst layer 23 Cooling water flow path 24 Second gas diffusion layer 25 Second Separator 30. Solid polymer fuel cell (fuel cell)

Claims

[Claim 1] A method for activating a polymer electrolyte fuel cell, comprising an anode electrode and a cathode electrode, and a polymer electrolyte membrane disposed between the anode electrode and the cathode electrode, A first step is to uniformly supply air to the entire cathode electrode, The process includes a second step in which, while uniformly supplying air to the entire cathode electrode, a constant current is passed from the anode electrode to the cathode electrode for a certain period of time using an external power source, and then the current is stopped. A method for activating a polymer electrolyte fuel cell, comprising repeating the combination of the first and second steps two or more times.

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