JP2009170272A - Maintenance method of fuel cell stack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for preventing elution of polymer electrolyte from an electrode and restraining degradation of an output of a fuel cell stack. <P>SOLUTION: In the maintenance method of the fuel cell stack containing polymer electrolyte as an electrode material, for instance, structured by pinching a film made of polymer electrolyte with a pair of catalyst layers, the electrode is heated up to above a glass transition temperature of the polymer electrolyte, for instance, from 100°C to 180°C, after elapse of each given period, for instance, each month to each 5 years. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for maintaining a fuel cell stack that includes a polymer electrolyte material in an electrode material.

  In recent years, a hydrogen electrode and an oxygen electrode are configured by disposing catalyst layers on both sides of the polymer electrolyte membrane, respectively, and a fuel gas such as hydrogen gas is supplied to the hydrogen electrode side while air is supplied to the oxygen electrode side, for example. Development of a fuel cell stack that can supply chemical gas by oxidation-reduction reaction of fuel gas and oxidant gas (hereinafter also referred to as reaction gas) directly as electric energy is being promoted.

In such a fuel cell stack, deterioration with time of electrodes due to long-term use becomes a problem. For example, Patent Document 1 discloses that the ionic conductivity of a polymer electrolyte membrane is modified and regenerated by heating and humidifying the polymer electrolyte membrane without applying a potential.
JP 2005-294173 A

  Here, the present inventor has confirmed the phenomenon that the polymer electrolyte contained as the electrode material of the fuel cell stack is eluted from the electrode after a long period of use.

  However, in the conventional method, it is difficult to prevent deterioration of the electrode with time due to elution of the polymer electrolyte. The elution of the polymer electrolyte causes a decrease in the proton carrying capacity of the electrode, resulting in a decrease in the output of the fuel cell stack.

  Accordingly, the present invention has been made in view of the above-described problems of the prior art, and provides a fuel cell stack maintenance method that prevents elution of a polymer electrolyte from an electrode and suppresses a decrease in output of the fuel cell stack. For the purpose.

  In the present invention, the following means are adopted in order to solve the above-mentioned problems. That is, the present invention is a maintenance method of a fuel cell stack that includes a polymer electrolyte in an electrode material, and the electrode is brought to a temperature equal to or higher than the glass transition temperature of the polymer electrolyte every time a predetermined period has elapsed since the use of the fuel cell stack. It is designed to warm up.

  With this configuration, the molecular chains of the polyelectrolyte in which the molecular chain entanglement has become weaker after long-term use can be rearranged to strengthen the bond. As a result, elution of the polymer electrolyte from the electrode can be prevented, a decrease in the output of the fuel cell stack can be suppressed, and as a result, the life of the fuel cell stack can be extended.

  In the above configuration, the electrode may be configured by sandwiching a membrane made of a polymer electrolyte between a pair of electrode catalyst layers.

  With the above configuration, elution of the polymer electrolyte from the membrane that greatly contributes to the proton carrying capacity of the electrode can be suppressed.

  Moreover, the said structure WHEREIN: You may make it the said catalyst layer contain a polymer electrolyte.

  The polymer electrolyte in the catalyst layer is formed from a solution state and often has a low molecular chain entanglement state, and the polymer electrolyte is likely to elute, so the molecular chain of the polymer electrolyte is rearranged to strengthen the bond. The usefulness of the configuration of the present invention that can be performed is high.

  In the above configuration, the predetermined period may be set between one month and five years.

  With the above configuration, the molecular chains of the polymer electrolyte can be rearranged every time period from 1 month to 5 years to strengthen the bond, so that elution of the polymer electrolyte can be suppressed over a long period of time, and the length of the fuel cell stack Life expectancy can be realized.

  Moreover, the said structure WHEREIN: You may make it the said heating be performed between 100 degreeC and 180 degreeC.

  With the above configuration, the polymer electrolyte generally used in the fuel cell stack can be heated to a temperature higher than the glass transition temperature and lower than the melting temperature of the polymer electrolyte membrane.

  In the above configuration, the heating may be performed by applying heat to the entire fuel cell stack from the outside.

  With the above configuration, since heating can be realized by applying heat to the entire fuel cell stack, maintenance of the fuel cell stack is facilitated.

  ADVANTAGE OF THE INVENTION According to this invention, the elution of the polymer electrolyte from an electrode can be prevented, and the maintenance method of a fuel cell stack which suppresses the output fall of a fuel cell stack can be provided.

Hereinafter, a maintenance method for a fuel cell stack according to an embodiment of the present invention will be described in the following order with reference to the drawings.
1. 1. Configuration of fuel cell stack 2. Structure of single cell of fuel cell stack 3. Maintenance method of fuel cell stack Modified example

  In the present embodiment, a solid polymer fuel cell stack suitable for a vehicle will be described as an example. Of course, a fuel cell system including a fuel cell stack can be mounted not only on a vehicle but also on a self-propelled mobile body such as a robot, a ship, an aircraft, etc., and for a building (house, building, etc.) It can also be used as a stationary power generation system used as a power generation facility. In addition, in each drawing, the same code | symbol is attached | subjected to the same components.

1. Configuration of Fuel Cell Stack First, the overall configuration of the fuel cell stack according to the present embodiment will be described with reference to FIG. Here, FIG. 1 is a side view of the fuel cell according to the embodiment of the present invention.

  The fuel cell stack 1 in the present embodiment includes a cell stack 3 formed by stacking a plurality of single cells 2, and is sequentially attached to the outer side in the stacking direction of the single cells located at both ends of the cell stack 3. The terminal plate 4, the insulator (insulating plate) 5, and the end plate 6 are further provided. A predetermined compressive force in the stacking direction is applied to the cell stack 3 by a tension plate 7 that is bridged so as to connect both end plates 6.

  Further, a pressure plate 8 and a spring mechanism 8a are provided between the end plate 6 on one end side of the cell stack 3 and the insulator 5 so that the fluctuation of the load acting on the single cell 2 is absorbed. It has become.

  The terminal plate 4 is a member that functions as a current collecting plate, and is formed in a plate shape from a metal such as iron, stainless steel, copper, or aluminum. The rigidity of the terminal plate 4 is higher than that of the single cell 2 (particularly, a separator as will be described later).

  The insulator 5 is a member that functions to electrically insulate the terminal plate 4 from the end plate 6 and the like. In order to perform such a function, the insulator 5 is formed in a plate shape from a resin material such as polycarbonate.

  As with the terminal plate 4, the end plate 6 is formed in a plate shape with various metals (iron, stainless steel, copper, aluminum, etc.). For example, in the present embodiment, the end plate 6 is formed using copper, but this is only an example, and the end plate 6 may be formed of another metal.

  The tension plate 7 is provided so as to bridge between both end plates 6, 6. For example, a pair of the tension plates 7 is disposed so as to face both sides of the cell stack 3. The tension plate 7 is fixed to each end plate 6.6 with a bolt or the like, and maintains a state in which a predetermined fastening force (compression force) is applied in the stacking direction of the single cells 2. An insulating film is formed on the inner surface of the tension plate 7 (the surface facing the cell stack 3) in order to prevent leakage and sparks. Specifically, the insulating film is formed by, for example, an insulating tape attached to the inner surface of the tension plate 7 or a resin coating applied so as to cover the surface.

2. Next, the detailed structure of the single cell 2 will be described with reference to FIG. Here, FIG. 2 is a cross-sectional view of a single cell of the fuel cell stack according to the embodiment of the present invention.

  As shown in FIG. 2, the single cell 2 includes a membrane / electrode / diffusion layer assembly (hereinafter also referred to as “MEGA”) 20 and a pair of separators 22 </ b> A and 22 </ b> B. The MEGA 20, the separator 22A, and the separator 22B are integrated by, for example, adhesion.

  The MEGA 20 includes a polymer electrolyte membrane 30, a catalyst layer 36 and a diffusion layer 38 that are arranged so as to sandwich the polymer electrolyte membrane 30 from both sides.

  The polymer electrolyte membrane 30 is made of an ion exchange membrane made of a polymer material. In this embodiment, the polymer electrolyte membrane 30 is a perfluorosulfonic acid polymer having a structure in which a side chain having a sulfonic acid group attached to the end of a Teflon (registered trademark) skeleton is suspended. It is configured.

  The catalyst layer 36 is a matrix in which the catalyst-supporting carbon and the polymer electrolyte are mixed. An electrode reaction is performed at the interface between the catalyst on the catalyst-supporting carbon and the polymer electrolyte, and the catalyst layer 30 functions as an anode (hydrogen electrode) and a cathode (oxygen electrode). For example, platinum is used as the catalyst. The catalyst layer 36 is formed, for example, by solidifying a catalyst-supported carbon and a polymer electrolyte solution in an appropriate amount to make a paste.

  The diffusion layer 38 is made of, for example, a porous material such as carbon cloth or carbon paper, and has a function of diffusing the reaction gas supplied via the separators 22A and 22B and flowing it to the catalyst layer 30. The diffusion layer 38 also has a conductive function for conducting the catalyst layer 36 and the separators 22A and 22B.

  The separators 22A and 22B are made of a gas impermeable conductive material. Examples of the conductive material include carbon and a hard resin having conductivity, and metals such as aluminum and stainless steel. The separator 22A has a fuel gas channel 40 on the front surface and a refrigerant channel 44A on the back surface. The separator 22B has an oxidizing gas channel 42 on the front surface and a refrigerant channel 44B on the back surface.

  The fuel gas channel 40 supplies the fuel gas to the anode side of the MEGA 20, and the oxidizing gas channel 42 supplies the oxidizing gas to the cathode side of the MEGA 20, thereby causing an electrochemical reaction in the MEGA 20. Thereby, the electromotive force of the single cell 2 is obtained. In addition, water is generated on the cathode side by this electrochemical reaction. The refrigerant reduces the heat of the single cell 2 generated by the electrochemical reaction, and suppresses the temperature rise of the fuel cell stack 1.

3. Fuel Cell Stack Maintenance Method Next, a fuel cell stack maintenance method according to an embodiment of the present invention will be described.

  Since the fuel cell stack 1 deteriorates over time in use, it is necessary to perform maintenance periodically. The maintenance method in the present embodiment pays particular attention to the deterioration mechanism of the electrode material.

  This mechanism will be described more specifically. The polymer electrolyte contained in the polymer electrolyte membrane 30 and the catalyst layer 36 constituting the electrode repeats expansion and contraction during the operation of the fuel cell stack 1. For this reason, the intermolecular chains constituting the polymer electrolyte gradually weaken after long-term use, and gradually escape from the polymer electrolyte membrane 30 and the catalyst layer 36. Thereby, the proton carrying capacity of the polymer electrolyte membrane 30 and the catalyst layer 36 is lowered, and the output voltage of the fuel cell stack 1 is lowered.

  In the embodiment of the present invention, the following maintenance is performed based on the deterioration mechanism of the electrode material.

  First, the fuel cell stack 1 is taken out from a vehicle or the like on which the fuel cell stack 1 is mounted. The timing of taking out is 1 month to 5 years after using the fuel cell stack 1, and more preferably once every 1 to 3 years in consideration of maintenance.

  Next, heat of 100 ° C. or more and less than 180 ° C. is applied to the entire fuel cell stack 1 with a heat source such as an external heater for about several minutes to one hour. This temperature is set so that the polymer electrolyte contained in the polymer electrolyte membrane 30 and the catalyst layer 36 constituting the electrode has a glass transition temperature or higher and lower than the melting temperature. At this time, humidification is not performed. When humidifying at 100 ° C. or higher, it is necessary to increase the pressure. However, if humidification is performed at a high pressure, elution of the polymer electrolyte is rather promoted.

  Next, the heated fuel cell stack 1 is cooled and mounted again on the vehicle. Thereby, the maintenance is completed. In addition, you may implement another maintenance work as needed before heating or after heating.

  Due to the above heating and cooling, rearrangement of the molecular chains of the polymer electrolyte contained in the polymer electrolyte membrane 30 and the catalyst layer 36 occurs, and the entanglement of the molecular chains increases (crystallization progresses). As a result, the elution of the polymer electrolyte from the polymer electrolyte membrane 30 and the catalyst layer 36 can be prevented, the output decrease of the fuel cell stack 1 can be suppressed, and the life of the fuel cell stack can be extended. .

(Example)
FIG. 3 shows the change over time in the amount of voltage drop when the electrode material is heated and when it is not heated every certain time. Example 1 shows the voltage drop amount (%) per unit cell when heating is performed at 130 degrees every 100 hours, and Comparative Example 1 is the voltage drop per unit cell when heating is not performed. Indicates the amount. In either case, the fuel cell stack was operated in an alternating power generation cycle of 0.6 A / cm ² and no load (OCV). The heating interval, temperature, etc., of course, differ from fuel cell stack to fuel cell stack. However, the figure also shows that the amount of voltage drop per unit cell and the amount of change over time are smaller when heated regularly. I understand that.

4). Although the embodiment of the present invention has been described above, the present invention is not limited to this embodiment, and can be implemented in various modes without departing from the scope of the present invention. For example, the following modifications are possible.

  In the above embodiment, the single cell 2 provided with the membrane / electrode / diffusion layer assembly (MEGA) 20 has been described. However, the present invention is not limited to this. For example, the membrane / electrode assembly without the diffusion layer ( MEA) is also acceptable. The present invention is widely applicable to fuel cell stacks containing a polymer electrolyte as an electrode material.

  In the above embodiment, the fuel cell stack 1 is periodically removed from the vehicle and heated, but the present invention is not limited to this. For example, a heat source may be prepared in the vehicle or the fuel cell stack, and the fuel cell stack 1 may be periodically heated. Further, for example, a liquid (for example, oil) heated from 100 ° C. to less than 180 ° C. is allowed to flow through the refrigerant flow paths 44A and 44B in the fuel cell stack 1 to directly heat the single cells 2 of the fuel cell stack 1. It may be. Also, regarding the maintenance timing, for example, the usage time or voltage drop amount of the fuel cell stack 1 may be detected in the vehicle, and the user may be notified or the maintenance may be automatically performed.

1 is a side view of a fuel cell stack according to an embodiment of the present invention. Sectional drawing of the single cell of the fuel cell stack concerning the embodiment. The figure which shows the time-dependent change of the voltage fall amount of a fuel cell stack.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell stack 2 ... Single cell 3 ... Cell laminated body 4 ... Terminal plate 4a ... Output terminal 5 ... Insulator 6 ... End plate 7 ... Tension plate 8 ... Pressure plate 8a ... Spring Mechanism 20 …… MEGA
22A ... Separator 22B ... Separator 30 ... Polymer electrolyte membrane 36 ... Catalyst layer 38 ... Diffusion layer 40 ... Fuel gas passage 42 ... Oxidation gas passage 44A ... Refrigerant passage 44B ... Refrigerant flow Road

Claims (6)

A fuel cell stack maintenance method including a polymer electrolyte in an electrode material,
A fuel cell stack maintenance method in which the electrode is heated to a glass transition temperature or higher of the polymer electrolyte every predetermined period.   The method for maintaining a fuel cell stack according to claim 1, wherein the electrode is configured by sandwiching a membrane made of a polymer electrolyte between a pair of catalyst layers.   The fuel cell stack maintenance method according to claim 2, wherein the catalyst layer includes a polymer electrolyte.   4. The fuel cell stack maintenance method according to claim 1, wherein the predetermined period is set between one month and five years.   The fuel cell stack maintenance method according to any one of claims 1 to 4, wherein the heating is performed between 100 ° C and 180 ° C.   The fuel cell stack maintenance method according to claim 1, wherein the heating is performed by applying heat to the entire fuel cell stack from the outside.

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