JP2010114031A - Material recycling method of fuel cell mea - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To recover a platinum catalyst, and recover and reutilize an electrolyte membrane in no deformation by using milder ethanol aqueous solution of 25% or less for an organic solvent which is an immersion medium, and by carrying out peeling-off of a diffusion layer and peeling-off of PGM by two stages. <P>SOLUTION: In a material recycle method of an MEA to recover electrode agent particles comprised of carbon particles carrying platinum catalyst adhered to the electrolyte membrane, and the electrolyte membrane from the MEA of a fuel cell, in the first stage, in the ethanol aqueous solution of 25% or less or in the water, the diffusion layer is peeled off from the electrolyte membrane by agitation, and the electrode agent particles are recovered together with the diffusion layer, and in the second stage, from the electrolyte membrane of the MEA in which the diffusion layer is peeled off, in the ethanol aqueous solution of 25% or in the water, the electrode agent particles are peeled off and recovered from the electrolyte membrane by ultrasonic wave irradiation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a material recycling method for a membrane / electrode assembly (MEA) of a fuel cell.

  Since MEA electrolyte membranes and binders use fluororesin, hydrofluoric acid is generated when PGM (platinum catalyst) is recovered by heating, and dry scouring in large facilities and incineration concentration in small facilities are easily implemented. Can not do it.

  Moreover, when it is going to melt | dissolve PGM with a wet method etc. directly from MEA with aqua regia etc., the fluoropolymer which coat | covers the electrode material will become an obstacle, and ideal elution becomes difficult. Furthermore, under the present circumstances, the fluoride polymer film used for one MEA is as high as PGM, and it is also necessary to keep in mind the recovery of the fluoride polymer film during recycling.

  For the above reasons, when recycling, it is necessary to separate the PGM and the polymer membrane from the MEA in advance. Techniques for recovering the electrolyte membrane or electrode material from the MEA are divided into two parts: a chemical technique based on dissolution and combustion, and a physical technique based on a solid-solid separation technique.

  One of the typical chemical methods is to dissolve the electrolyte membrane under pressure by an autoclave in a solvent such as alcohol in the range of room temperature to 270 ° C., and then recover PGM from the insoluble component electrode material and dissolve the electrolyte membrane Is used again as a raw material for electrolyte membranes and binders (see Patent Document 1 “Recovery and Reuse Method for Polymer Electrolyte Fuel Cell Materials”).

  There is also a method in which MEA is introduced into a reaction fluid composed of water and oxygen in a supercritical state under high temperature and high pressure of 400 to 600 ° C. and 23 to 30 MPa to oxidize and dissolve the electrolyte membrane or the like (see “Patent Document 2”). "Recovery of precious metals from organic matter-noble metal compositions by supercritical water reactants").

  In a method for efficiently fixing hydrogen fluoride gas generated at the time of PGM incineration at low cost (see Patent Document 3, “Method and apparatus for recovering precious metal from waste”), MEA is pulverized together with powdered alkali metal, etc. The harmful gas generated by kneading and firing is made into a fluorine-containing solid. Thereafter, noble metal is extracted from the firing residue with aqua regia, but the electrolyte membrane component is discarded.

  On the other hand, as a physical method, there is a method in which the electrode material is peeled off with a water-soluble pressure-sensitive adhesive sheet, and then the pressure-sensitive adhesive sheet is dissolved with a predetermined solvent, and the electrolyte membrane is dissolved and reused as a raw material (see Patent Document 4). "Catalyst recovery method").

  In the method of injecting dry ice particles (refer to Patent Document 5 “Catalyst Recovery Method and Catalyst Recovery Device”), dry ice particles of about 1 to 50 μm are injected to the electrode material on the surface of the electrolyte membrane or diffusion layer. The electrode material is peeled off into pieces by impact. With dry ice, the electrode material becomes low temperature and becomes brittle, and the efficiency of peeling is improved. In addition, after the collision, the dry ice is vaporized and only the electrode material can be recovered. However, these are methods for processing the electrolyte membranes one by one, and are considered unsuitable for small MEA processing.

  On the other hand, it is considered that the method of immersing MEA in a liquid and promoting the peeling of the electrode material can be applied to a small MEA (see Patent Document 6 “Method for recovering electrolyte membrane of fuel cell and its device”). When the MEA is immersed in methanol or the like for about 10 minutes, the water in the electrolyte membrane is replaced with methanol and swells, and the joined product of the electrolyte membrane and the electrode dissolves, so that both can be easily separated. Thereafter, the separated electrolyte membrane is immersed in water and replaced with methanol, and then washed with hydrogen peroxide. However, it is pointed out that this method is difficult to reuse due to deformation of the electrolyte membrane and generation of wrinkles.

JP-A-11-288732 Special Table 2003-53964 JP 2004-190092 A JP 2005-235511 A JP 2006-95367 A JP-A-8-171922

  The MEA material recycling method according to the present invention is mainly intended for the recovery of both the fluoropolymer membrane and the PGM catalyst with a small fuel cell for mobile use in mind. Although it is a method according to the conventional method (Patent Document 6) for promoting the peeling of the material, a milder 25% or less ethanol aqueous solution is used for the organic solvent as the immersion medium, and the diffusion layer and the PGM are peeled off. By carrying out the above in two stages, it is an object to recover the platinum catalyst while recovering the platinum membrane without deformation and to enable reuse.

  [MEANS TO SOLVE THE PROBLEM] This invention is the material recycling method of MEA which collects the electrode agent particle | grains which consist of the carbon particle which carry | supported the platinum catalyst adhering to the electrolyte membrane, and electrolyte membrane from MEA of a fuel cell in order to solve the said subject, In the second stage, the diffusion layer is peeled off from the MEA electrolyte membrane by stirring and the electrode agent particles are collected together with the diffusion layer. In the second stage, the electrode agent particles are removed by ultrasonic irradiation from the MEA electrolyte membrane from which the diffusion layer has been peeled off. Provided is a MEA material recycling method characterized by peeling and collecting and collecting an electrolyte membrane.

  In the first stage treatment, the diffusion layer is preferably peeled off from the electrolyte membrane by stirring in an aqueous solution of ethanol of 25% or less or in water.

  In the second stage treatment, the electrode agent particles are preferably peeled off from the electrolyte membrane by ultrasonic irradiation in a 25% or less ethanol aqueous solution or water.

  [MEANS TO SOLVE THE PROBLEM] This invention is the material recycling method of MEA which collects the electrode agent particle | grains which consist of the carbon particle which carry | supported the platinum catalyst adhering to the electrolyte membrane, and electrolyte membrane from MEA of a fuel cell in order to solve the said subject, In the second stage, in a 25% or less ethanol aqueous solution or in water, the diffusion layer is peeled off from the electrolyte membrane by stirring to collect the electrode agent particles together with the diffusion layer. In the second stage, from the MEA electrolyte film from which the diffusion layer has been peeled off An MEA material recycling method is provided in which electrode agent particles are peeled off and collected from an electrolyte membrane by ultrasonic irradiation in an aqueous ethanol solution of 25% or less or in water.

  According to the MEA material recycling method according to the present invention, a milder 25% or less ethanol aqueous solution is used for the organic solvent as the immersion medium, and the diffusion layer and the PGM are peeled in two stages. While recovering the platinum catalyst, the electrolyte membrane (fluorine polymer membrane) can be recovered without deformation and can be reused.

  The best mode for carrying out the MEA material recycling method according to the present invention will be described below with reference to the drawings based on the embodiments.

  FIG. 1 is a plan view and a cross-sectional view showing an MEA 1 of a small fuel cell for a mobile device. A positive electrode 3 (including carbon particles and Pt—Ru) and a diffusion layer 4 are sequentially laminated on the surface of the electrolyte membrane 2, and a negative electrode 5 (including carbon particles and Pt) and a diffusion layer 6 are stacked on the back surface of the electrolyte membrane 2. Are sequentially stacked.

  The present invention is a method of individually collecting the positive and negative electrode materials 3 and 5 containing the platinum catalyst and the electrolyte membrane 2, and is characterized by the use of mild dilute ethanol. The electrode materials 3 and 5 are collected while minimizing deformation and deterioration.

(Ethanol concentration that minimizes deformation of electrolyte membrane)
In the method of the present invention, ethanol concentration is a very important requirement. Ethanol itself has low solubility and reactivity among organic solvents, but these were diluted with water to obtain a concentration at which deformation of the electrolyte membrane 2 was minimized.

  FIG. 2 shows the film thickness / height ratio when the electrolyte membrane 2 immersed in ethanol or water is immersed in water for 90 minutes, further dried, and untreated, and immersed for 5 minutes and 10 minutes. The electrolyte membrane 2 was not a perfect plane even when it was untreated, and the film thickness / height ratio was 1.75 (average value of 12 samples).

  On the other hand, when the electrolyte membrane 2 is immersed in water or 10% or 25% ethanol and then replaced with water and dried, the film thickness / height ratio is increased by about 5 times. 8 times to 10 times larger. That is, the degree of bending (deformation) is substantially constant with water and ethanol with a concentration of 25% or less.

  Moreover, the curved state of the electrolyte membrane 2 takes two forms as shown in FIG. The curve that occurs when the concentration of water and ethanol is 25% or less, as shown in FIG. 3 (b), is only gently rounded in one direction as when the paper is rolled up, and if it is pressed on a flat surface from above and below Easily return to the plane.

  On the other hand, when the ethanol concentration is 50% or more, as shown in FIG. 3C, the electrolyte membrane 2 is curved like a horseshoe over both axes of the XY single side. In this state, even if pressed against a flat surface from above and below, it does not return to a flat surface, and it is difficult to reuse it as the electrolyte membrane 2 even if there is no problem in the chemical function of the membrane itself.

  From the above results, in order to minimize the deformation of the electrolyte membrane 2, it is important to perform the treatment with water or ethanol concentration of 25% or less.

(Recycling process collection process)
Next, the recovery process of the MEA material recycling method according to the present invention will be described with reference to FIG.

(1) First stage processing (diffusion layer peeling) (see FIG. 6A)
In order to detach the electrode materials 3 and 5 by immersing the MEA in a solvent, it is necessary to first peel off the carbon paper as the diffusion layers 4 and 6. FIG. 4 shows the time required for the diffusion layers 4 and 6 to peel off under various peeling conditions.

  In the case of stirring alone, the diffusion layers 4 and 6 were slowly peeled off in water and required about 6 minutes, but 10% ethanol peeled off in about 50 seconds and 25% ethanol in about 20 seconds. On the other hand, even if ultrasonic waves are irradiated during stirring, there is almost no change compared to the case of stirring alone. Furthermore, when stirring was not performed and only ultrasonic waves were applied, the diffusion layers 4 and 6 did not peel even after 30 minutes with 10% ethanol.

  From the above results, separation of the diffusion layers 4 and 6 is realized by immersion with ethanol and shearing by high-speed stirring. In addition, although the ultrasonic wave does not become a hindrance to peeling even if it is irradiated simultaneously with stirring, it hardly brings about the peeling effect by itself.

  After the diffusion layers 4 and 6 are peeled, almost the same amount of PGM (platinum group metal) is attached to the surface of the electrolyte membrane 2 and the surfaces of the diffusion layers 4 and 6. The PGM adhered to the diffusion layers 4 and 6 may be recovered together with the diffusion layers 4 and 6.

(2) Second-stage treatment (peeling of electrode material and recovery of electrolyte membrane) (see FIGS. 6 (a) and (c))
As described above, after peeling off the diffusion layers 4 and 6, PGM (platinum group metal) is in a state where the same amount of PGM (platinum group metal) is attached to the surface of the electrolyte membrane 2 and the surfaces of the diffusion layers 4 and 6. The PGM adhering to the diffusion layers 4 and 6 may be recovered together with the diffusion layers 4 and 6, but for the reasons already described, the PGM adhering to the electrolyte membrane 2 is changed from the electrolyte membrane 2 to the electrode material 3 containing PGM, PGM cannot be recovered unless 5 is separated. Therefore, peeling of the electrode materials 3 and 5 is required.

  Peeling of the electrode materials 3 and 5 (PGM-supporting carbon particles) containing PGM is performed for 60 minutes in a 10% ethanol solution using the state in which the diffusion layers 4 and 6 are peeled off in the first stage treatment as a starting sample. (See FIG. 6A). As a result, the electrode materials 3 and 5 (PGM-supporting carbon particles) are recovered, and the electrolyte membrane 2 is recovered as the remaining electrode materials 3 and 5 are peeled off (see FIG. 6C).

  About the peeling state of the electrode materials 3 and 5 containing PGM, after peeling the electrode materials 3 and 5, the electrolyte membrane 2 is immersed in deionized water for 90 minutes and dried, and the total transmittance is measured by a transmission turbidimeter. Measured (FIG. 5). Since the electrolyte membrane 2 is almost transparent and the electrode materials 3 and 5 (PGM-supporting carbon particles) are black, the higher the transmittance is, the more the peeling of the electrode materials 3 and 5 is relatively advanced. In FIG. 5, “untreated” indicates a state immediately after the diffusion layers 4 and 6 are peeled in the first stage treatment.

  The tendency of PGM peeling is different from the case of the first-stage diffusion layers 4 and 6, and stirring <stirring + ultrasonic wave <ultrasonic wave. That is, in the peeling of the electrode materials 3 and 5, ultrasonic irradiation is more effective than stirring, and when both are used together, the effect of ultrasonic irradiation is hindered by stirring.

  When only ultrasonic irradiation was performed, PGM remaining on the electrolyte membrane 2 was 9.7%, and 90.3% PGM was recovered (see FIG. 6C). The particle diameters of the peeled electrode materials 3 and 5 (PGM-supporting carbon particles) are distributed between 30 μm and 150 μm, and can be easily separated and collected by a screen or flotation (FIG. 6C). reference).

  Moreover, as a result of comparing the IV characteristics of the MEA produced using the recovered electrolyte membrane 2 and the MEA using the new electrolyte membrane 2, it was confirmed that the MEA has the same performance as the MEA produced from the new one. did it.

  In addition, when manufacturing MEA from the regenerative electrolyte membrane 2, a new electrode agent (PGM catalyst) is applied, so that the PGM remaining in the electrolyte membrane 2 is a major obstacle except that the PGM content of the MEA slightly varies. It will not be.

  As described above, the best mode for carrying out the MEA material recycling method according to the present invention has been described based on the embodiments. However, the present invention is not limited to such embodiments, and is described in the claims. It goes without saying that there are various embodiments within the technical scope.

  Since the MEA material recycling method according to the present invention is configured as described above, it is particularly applicable to the recovery of both the electrolyte membrane and the PGM catalyst of a small fuel cell for mobile use.

It is a figure which shows the structure of the MEA sample which should be processed with the material recycling method of MEA which concerns on this invention. It is a figure required for description of the Example of this invention, and is a figure which shows the film thickness / height ratio after drying by the immersion conditions of MEA. It is a figure required for description of the Example of this invention, and is a figure which shows the shape change of the electrolyte membrane 2 by water immersion and ethanol immersion. It is a figure required for description of the Example of this invention, and is a figure which shows the time which peeling of a diffused layer requires. It is a figure required for description of the Example of this invention, and is a figure which shows the transmittance | permeability of the electrolyte membrane 2 after the process by an electrode material peeling method. It is a figure which shows the whole process of the collection | recovery process of the material recycling method of MEA which concerns on this invention.

Explanation of symbols

1 MEA
2 Electrolyte membrane 3 Positive electrode on surface 4 Diffusion layer 5 Negative electrode 6 Diffusion layer

Claims (4)

An MEA material recycling method for recovering electrode agent particles composed of carbon particles carrying a platinum catalyst attached to an electrolyte membrane and an electrolyte membrane from an MEA of a fuel cell,
In the first stage, the diffusion layer is peeled off from the MEA electrolyte membrane by stirring, and the electrode agent particles are collected together with the diffusion layer.
In the second step, the MEA material recycling method is characterized in that the electrode agent particles are peeled off and collected by ultrasonic irradiation from the MEA electrolyte membrane from which the diffusion layer has been peeled, and the electrolyte membrane is collected.   2. The MEA material recycling method according to claim 1, wherein in the first stage treatment, the diffusion layer is peeled off from the electrolyte membrane by stirring in an aqueous solution of ethanol of 25% or less or in water.   2. The MEA material recycling method according to claim 1, wherein in the second stage treatment, the electrode agent particles are peeled from the electrolyte membrane by ultrasonic irradiation in a 25% or less ethanol aqueous solution or in water. An MEA material recycling method for recovering electrode agent particles composed of carbon particles carrying a platinum catalyst attached to an electrolyte membrane and an electrolyte membrane from an MEA of a fuel cell,
In the first stage, the diffusion layer is peeled off from the electrolyte membrane by stirring in an aqueous ethanol solution of 25% or less or in water, and the electrode agent particles are recovered together with the diffusion layer.
In the second stage, the MEA material is characterized in that the electrode agent particles are peeled off from the electrolyte membrane by ultrasonic irradiation in an ethanol aqueous solution of 25% or less or in water from the MEA electrolyte membrane from which the diffusion layer has been peeled off. Recycling method.