Precious metal recovery method and precious metal recovery device

Abstract

To provide a method for recovering a precious metal and a device for recovering a precious metal capable of facilitating dissolution and recovery of a precious metal embedded in a solid polymer membrane of a membrane electrode junction when recovering the precious metal included in a fuel cell and a water electrolysis device to improve the recovery efficiency of the precious metal.SOLUTION: The method for recovering a precious metal from a fuel cell or a water electrolysis device has a cooling step for cooling a membrane electrode junction of the fuel cell or water electrolysis device to a temperature below the freezing point at which water included in the membrane electrode junction is frozen, a solution supply step for supplying a solution and bringing the solution in contact with the membrane electrode junction, a precious metal dissolving step for dissolving a precious metal included in a cathode and anode into the solution by applying a voltage to the membrane electrode junction in contact with the solution.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to a precious metal recovery method and a precious metal recovery apparatus. [Background technology]

[0002] Hydrogen is attracting attention as an energy source for the establishment of a sustainable society, and there is an increasing need for hydrogen production equipment and fuel cells that use water electrolysis to produce hydrogen. In particular, water electrolysis equipment (Polymer Electrolyte Electrolysis Cell: PEEC) and polymer electrolyte fuel cells (Polymer Electrolyte Fuel Cell: PEFC) that use a polymer electrolyte membrane (Polymer Electrolyte Membrane: PEM) are undergoing demonstration tests with a view to their widespread use, mainly in Europe. These devices use precious metals such as platinum as catalysts, and recycling of these metals is essential for the establishment of a sustainable society in the future.

[0003] The following techniques are known as techniques for recovering precious metals from such fuel cells and water electrolysis devices (hydrogen production devices). For example, Patent Document 1 proposes a technique for promoting the dissolution of precious metals by alternately applying an oxidation potential and a reduction potential to a fuel cell filled with a dissolution solution, and Patent Document 2 proposes making the dissolution solution coexist with an anion exchange resin to recover complex-ionized precious metals. Patent Document 3 also refers to the location at which the dissolution solution is supplied to the fuel cell housing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6109769 [Patent Document 2] Patent No. 6652454 [Patent Document 3] Patent No. 6652518 [Non-patent literature]

[0005] [Non-Patent Document 1] Transactions of the Japan Society of Mechanical Engineers (Series B), Vol. 77, No. 776, Characteristics of Performance Degradation and Major Material Functionality Degradation Caused by Repeated Start-up at Subzero Temperatures in Polymer Electrolyte Fuel Cell Electrodes, Mitsuru Onoda et al. Summary of the Invention [Problem to be solved by the invention]

[0006] Although these prior art technologies can be used to recover precious metals from fuel cells and water electrolysis devices, there is a need to further improve the efficiency of precious metal recovery in order to eliminate the imbalance in the supply and demand of precious metals caused by the rapid increase in demand for fuel cells and water electrolysis devices.

[0007] The precious metals used in polymer electrolyte fuel cells and water electrolysis devices are incorporated into the devices in the form of a membrane electrode assembly (MEA), and are used in a state where a part of the precious metal is embedded in the polymer electrolyte membrane. In the conventional technology described above, dissolution begins at the part where the dissolving solution and the precious metal come into contact, so it takes a lot of time and energy to recover the precious metal embedded in the polymer electrolyte membrane, which is difficult to come into contact with the dissolving solution.

[0008] The present invention has been made in consideration of the above-mentioned conventional circumstances, and has an object to provide a precious metal recovery method and apparatus that can easily dissolve and recover precious metals embedded in a solid polymer membrane of a membrane electrode assembly and improve the efficiency of precious metal recovery when recovering precious metals contained in fuel cells and water electrolysis systems. [Means for solving the problem]

[0009] A precious metal recovery method of an embodiment is a precious metal recovery method for recovering precious metals from a fuel cell or a water electrolysis device, and includes a cooling step of cooling a membrane electrode assembly of the fuel cell or the water electrolysis device to a temperature below the freezing point at which moisture contained in the membrane electrode assembly freezes, a dissolution solution supplying step of supplying a dissolution solution and bringing the membrane electrode assembly into contact with the dissolution solution, and a precious metal dissolving step of applying a voltage to the membrane electrode assembly in contact with the dissolution solution to dissolve the precious metals contained in the cathode and the anode in the dissolution solution.

[0010] The precious metal recovery device of one embodiment is a precious metal recovery device that recovers precious metals from a fuel cell or a water electrolysis device, and includes: a cooling means that cools a membrane electrode assembly of the fuel cell or water electrolysis device to a temperature below the freezing point at which water contained in the membrane electrode assembly freezes; a dissolving solution supplying means that supplies a dissolving solution and brings the dissolving solution into contact with the membrane electrode assembly; and a precious metal dissolving means that applies a voltage to the membrane electrode assembly in contact with the dissolving solution to dissolve the precious metals contained in the cathode and the anode into the dissolving solution. Effect of the Invention

[0011] According to an embodiment of the present invention, it is possible to provide a precious metal recovery method and a precious metal recovery apparatus that can easily dissolve and recover the precious metal embedded in the solid polymer membrane of a membrane electrode assembly when recovering the precious metal contained in a fuel cell and a water electrolysis device, and can improve the precious metal recovery efficiency. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a general polymer electrolyte fuel cell and a general water electrolysis device. [Diagram 2] FIG. 1 is a schematic diagram showing the configuration of a general membrane electrode assembly (MEA). [Diagram 3] FIG. 2 is a schematic diagram showing the microstructure of a membrane electrode assembly (MEA). [Figure 4] FIG. 1 is a block diagram showing a configuration of a first embodiment. [Diagram 5] FIG. 2 is a flow diagram showing the steps of the first embodiment. [Figure 6] FIG. 13 is a block diagram showing a configuration of a second embodiment. [Figure 7] FIG. 11 is a flow diagram showing the steps of a second embodiment. [Figure 8] FIG. 13 is a block diagram showing a configuration of a third embodiment. [Figure 9] FIG. 11 is a flow diagram showing the steps of a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, a precious metal recovery method and a precious metal recovery device according to an embodiment will be described with reference to the drawings.

[0014] First, we will explain the basic structure of the membrane electrode assembly (MEA) that constitutes the fuel cell (PEFC) and water electrolysis device (PEEC), and the issues involved in recovering precious metals from them. The basic structure of the fuel cell and water electrolysis device is shown in Figure 1.

[0015] A water electrolysis device is a device that converts water into hydrogen and oxygen by electrolyzing the water through a solid polymer electrolyte, and a fuel cell is a device that obtains electricity by utilizing the reverse reaction of the water electrolysis device. As shown in Fig. 1, a fuel cell and a water electrolysis device are structured so that reactants are supplied from reactant supply ports 2a, 2b that supply raw materials to a membrane electrode assembly (MEA) 1, and products are discharged from product discharge ports 3a, 3b. The membrane electrode assembly (MEA) 1 has an anode and a cathode, and the fuel cell or water electrolysis device is connected to electrical contacts (anode terminal and cathode terminal) 4a, 4b for electrical connection between the inside and outside of the fuel cell or water electrolysis device.

[0016] In the case of a water electrolysis device, water is supplied from reactant supply ports 2a and 2b, electricity is supplied via electrical contacts 4a and 4b, hydrogen is discharged from product outlet 3a or 3b, and oxygen is discharged from the remaining product outlet 3b or 3a together with unreacted water. In the case of a fuel cell, hydrogen is supplied from reactant supply port 2a or 2b, and air is supplied from the remaining reactant supply port 2b or 2a, electricity is taken out via electrical contacts 4a and 4b, and unreacted hydrogen, oxygen, and generated water are discharged from product outlet 3a and 3b.

[0017] As explained above using Figure 1, a fuel cell and a water electrolysis device have the same basic configuration, and their functions change depending on whether or not they are supplied with materials and electricity from reactant supply ports 2a, 2b. Due to these characteristics, for simplicity, the following explanation will focus on a fuel cell.

[0018] Next, the configuration of a typical membrane electrode assembly will be described with reference to FIG.

[0019] As shown in FIG. 2, the membrane electrode assembly 1 comprises diffusion layers 11a, 11b for efficiently bringing the reactants into contact with the catalyst and simultaneously transferring electrons, catalyst layers 12a, 12b for promoting the bonding reaction between hydrogen and oxygen, and an electrolyte membrane 13 for ensuring the movement of protons while preventing mixing of hydrogen and oxygen. The structure is such that the electrolyte membrane 13 is sandwiched between catalyst layers 12a, 12b and is further sandwiched between diffusion layers 11a, 11b from the outside of the catalyst layers 12a, 12b, and the reactants or products flow through the diffusion layers 11a, 11b and their outside.

[0020] The state of the catalyst layer 12 and the electrolyte membrane 13 in the membrane electrode assembly 1 will be further described with reference to Fig. 3. The catalyst layer 12 has a structure including a precious metal 121 that is the starting point of the catalytic reaction, a catalyst support 122 that widely disperses the precious metal 121 in order to use the precious metal 121 efficiently, and an ionomer layer 123 that fixes the electrolyte membrane 13 to the catalyst support 122 and the precious metal 121. As shown in the figure, a part of the precious metal 121 contained in the catalyst layer 12 is incorporated into the ionomer layer 123, although there are differences between products, manufacturing processes, and lots.

[0021] As described above, the precious metal 121 contained in the catalyst layer 12 in the fuel cell or water electrolysis device is partially embedded in the ionomer layer 123 or the electrolyte membrane 13, and therefore there are areas where recovery of the precious metal is difficult, which is a factor in reducing the efficiency of precious metal recovery.

[0022] Next, embodiments will be described. The method for recovering precious metals according to the present embodiment is a method for recovering precious metals contained in a membrane electrode assembly 1 constituting a fuel cell or a water electrolysis device. First, a first embodiment will be described with reference to Figs. 4 and 5.

[0023] Fig. 4 shows the configuration of a precious metal recovery apparatus 400 of the first embodiment. As shown in Fig. 4, the precious metal recovery apparatus 400 includes a cooling means 401 for cooling the membrane electrode assembly 1 of a fuel cell or a water electrolysis apparatus to a temperature below the freezing point at which the moisture contained in the membrane electrode assembly 1 freezes, a dissolving solution supplying means 402 for supplying a dissolving solution and bringing the dissolving solution into contact with the membrane electrode assembly, a precious metal dissolving means 403 for applying a voltage to the membrane electrode assembly in contact with the dissolving solution to dissolve the precious metal contained in the cathode and the anode in the dissolving solution, and a dissolving solution recovering means 404 for recovering the dissolving solution containing the precious metal.

[0024] In the precious metal recovery apparatus 400 shown in FIG. 4, the cooling means 401 has a storage section 401a that stores a fuel cell or water electrolysis device having a membrane electrode assembly 1, and cools the entire fuel cell or water electrolysis device inside this storage section 401a to cool the membrane electrode assembly 1 therein. The dissolving solution supplying means 402 supplies a dissolving solution to the inside of the fuel cell or water electrolysis device that has been transported outside the storage section 401a after completing the cooling and placed at room temperature, and supplies the dissolving solution to the membrane electrode assembly 1. Then, the precious metal dissolving means 403 applies electricity to the membrane electrode assembly 1 in this state to dissolve the precious metal in the dissolving solution. The dissolving solution recovery means 404 discharges the dissolving solution containing the precious metal from the fuel cell or water electrolysis device and recovers it.

[0025] 5 shows an outline of the steps of the precious metal recovery method of the first embodiment. In this first embodiment, first, a cooling step 501 is performed in which the fuel cell or water electrolysis device is cooled to below the freezing point. This cooling step 501 is a step of bringing the membrane electrode assembly of the fuel cell or water electrolysis device to a temperature below the freezing point, that is, a temperature below the freezing point at which the water inside the polymer membrane in the membrane electrode assembly, where the freezing point depression occurs due to the interaction with the polymer membrane, freezes. In this case, the specific temperature is, for example, preferably -20°C or lower, and more preferably -30°C or lower.

[0026] In the cooling step 501, it is preferable to perform cooling for a predetermined cooling time that can sufficiently freeze the moisture inside the polymer membrane in the membrane electrode assembly. For this reason, it is determined (502) whether cooling for the predetermined cooling time has been performed, and cooling is continued for the predetermined cooling time. This predetermined cooling time is preferably, for example, about several hours. In the case of the precious metal recovery device 400 shown in FIG. 4, when the cooling step is completed, the fuel cell or water electrolysis device is taken out of the accommodation section 401a of the cooling means 401 and placed at room temperature.

[0027] Next, a dissolution liquid supplying step 503 is performed. The dissolution liquid supplying step 503 is a step of supplying an acidic dissolution liquid L containing halogen ions such as chloride ions into the fuel cell or water electrolysis device, and bringing the membrane electrode assembly into sufficient contact with the dissolution liquid L. The site for supplying the dissolution liquid L to the fuel cell or water electrolysis device is not particularly limited as long as the membrane electrode assembly can be brought into contact with the dissolution liquid L, but it is preferable to use any one of the reactant supply ports 2a, 2b or the product discharge ports 3a, 3b shown in FIG. 1.

[0028] Next, a precious metal dissolving step 504 is carried out. This precious metal dissolving step 504 is a step in which a current is applied to a membrane electrode assembly in a fuel cell or a water electrolysis device filled with a dissolving solution L to promote dissolution of the precious metal, and it is preferable that the voltage of the current applied at this time is periodically changed. Furthermore, during the precious metal dissolving step 504, it is also possible to carry out the step while appropriately replacing or circulating the dissolving solution L.

[0029] Next, a solution recovery step 505 is performed. This solution recovery step 505 is a step of discharging the solution containing the precious metal dissolved from the membrane electrode assembly as described above from within the fuel cell or water electrolysis device and recovering it.

[0030] According to this embodiment having the above configuration, in the cooling step 501, the moisture in the polymer membrane contained in the membrane electrode assembly in the fuel cell or water electrolysis device is frozen, which causes cracks in the polymer membrane and increases the exposed area of ​​the precious metal. This makes it easier for the dissolving solution to come into contact with the precious metal in the dissolving solution supplying step 503 and the precious metal dissolving step 504, thereby improving the efficiency of precious metal recovery.

[0031] Next, a second embodiment will be described with reference to Figures 6 and 7. Figure 6 shows the configuration of a precious metal recovery apparatus 600 of the second embodiment. As shown in Figure 6, the precious metal recovery apparatus 600 includes, in addition to the precious metal recovery apparatus 400 of the first embodiment shown in Figure 4, an operating means 405 that supplies hydrogen gas and air to the membrane electrode assembly in a cooled environment to operate it as a fuel cell. Note that the configuration of other parts is similar to that of the precious metal recovery apparatus 400 of the first embodiment shown in Figure 4, so that the same reference numerals are used for corresponding parts and duplicated explanations will be omitted.

[0032] Fig. 7 shows an outline of the process of the second embodiment, in which a cooling operation process 701 is performed instead of the cooling process 501 in the first embodiment shown in Fig. 5. The other processes, i.e., the dissolving solution supply process 503, the precious metal dissolving process 504, and the dissolving solution recovery process 505, are the same as those in the first embodiment shown in Fig. 5.

[0033] The cooling operation step 701 is a step of operating the membrane electrode assembly as a fuel cell below freezing point, and the specific temperature in this case is, for example, preferably -20°C or lower, and more preferably -30°C or lower. It is known that operating the membrane electrode assembly as a fuel cell below freezing point promotes decomposition of the polymer membrane (see, for example, Non-Patent Document 1), and promotes exposure of the precious metal embedded in the polymer membrane due to fine cracks caused by decomposition of the polymer membrane caused by fuel cell operation below freezing point. This cooling operation step 701 is also performed for a predetermined time, similar to the cooling step 501.

[0034] According to the second embodiment, by operating the membrane electrode assembly below the freezing point, cracks are generated due to the freezing of water in the polymer membrane, and in addition, the exposed area of ​​the precious metal increases due to cracks caused by decomposition of the polymer membrane. This makes it easier for the dissolving solution and the precious metal to come into contact with each other in the dissolving solution supplying step 503 and the precious metal dissolving step 504, thereby improving the efficiency of precious metal recovery.

[0035] Next, a third embodiment will be described with reference to Figs. 8 and 9. Fig. 8 shows the configuration of a precious metal recovery apparatus 800 of the third embodiment. As shown in Fig. 8, the precious metal recovery apparatus 800 has a dissolving solution supplying means 802 having an electrolytic cell 801, instead of the dissolving solution supplying means 402 of the precious metal recovery apparatus 400 of the first embodiment shown in Fig. 4, and does not have a configuration corresponding to the dissolving solution recovery means 404. The membrane electrode assembly 1 taken out from a fuel cell or a water electrolysis device is immersed in the electrolytic cell 801. A counter electrode 801a is provided in the electrolytic cell 801, which faces the membrane electrode assembly 1 and to which a voltage is applied between them. Note that the configuration of other parts is the same as that of the precious metal recovery apparatus 400 of the first embodiment shown in Fig. 4, so that the corresponding parts are given the same reference numerals and a duplicated description is omitted.

[0036] FIG. 9 shows an outline of the process of the third embodiment. In this third embodiment, subsequent steps after the cooling step 501 are performed, which include a removal step 903 of removing the membrane electrode assembly 1 from the fuel cell or the water electrolysis apparatus, a membrane electrode assembly attachment step 904 of attaching the membrane electrode assembly 1 to an electrolytic cell 801, and a precious metal dissolving step 905 of passing an electric current through the membrane electrode assembly 1 attached to the electrolytic cell 801 to dissolve the precious metal.

[0037] The removal step 903 is a step of removing the membrane electrode assembly 1 from the fuel cell or water electrolysis device. The method of removal is not particularly limited, and removal can be performed by a general procedure. The membrane electrode assembly attachment step 904 is a step of attaching the membrane electrode assembly 1 to an electrolytic cell 801 that is energized from an external power source of the precious metal dissolving means 403 and in which the membrane electrode assembly 1 and the counter electrode 801a are electrically connected by a dissolving liquid L. The electrolytic cell 801 used should not be corroded by the dissolving liquid L, and should be capable of appropriately controlling the voltage between the membrane electrode assembly 1 and the counter electrode 801a after attachment, and a general electrolytic cell 801 can be used.

[0038] In addition, the second embodiment having the cooling operation step 701 described using Figures 6 and 7 can also be made into a similar embodiment by removing the membrane electrode assembly 1 after the cooling operation step 701 as in the third embodiment shown in Figures 8 and 9.

[0039] According to this embodiment, even if the dissolving solution reacts with the housings of the fuel cell and the water electrolysis device and the dissolving solution cannot be supplied to the fuel cell and the water electrolysis device, it can be applied by removing the membrane electrode assembly 1 from the housing. Also, in the third embodiment, by freezing the moisture in the polymer membrane contained in the membrane electrode assembly 1, cracks are generated in the polymer membrane and the exposed area of ​​the precious metal increases, which makes it easier for the dissolving solution to come into contact with the precious metal, improving the efficiency of precious metal recovery.

[0040] As described above, according to each embodiment, it is possible to provide a method for recovering precious metals that can efficiently recover precious metals from a membrane electrode assembly of a fuel cell or a water electrolysis device.

[0041] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0042] 1...membrane electrode assembly (MEA), 2a, 2b...reactant supply port, 3a, 3b...product discharge port, 4a, 4b...electrical contacts, 11a, 11b...diffusion layer, 12a, 12b...catalyst layer, 13...polymer membrane, 121...precious metal, 122...catalyst support, 123...ionomer layer, 401...cooling means, 401a...container, 402...dissolving solution supply means, 403...precious metal dissolving means, 404...dissolving solution recovery means, 405...operating means, 801...electrolytic cell, 801a...counter electrode, 802...dissolving solution supply means, 400, 600, 800...precious metal recovery device.

Claims

1. A method for recovering precious metals from a fuel cell or a water electrolysis device, comprising the steps of: a cooling step of cooling the membrane electrode assembly of the fuel cell or water electrolysis device to a temperature below the freezing point at which moisture contained in the membrane electrode assembly freezes; a solution supplying step of supplying a solution to bring the solution into contact with the membrane electrode assembly; a precious metal dissolving step of applying a voltage to the membrane electrode assembly in contact with the dissolving solution to dissolve the precious metal contained in the cathode and the anode in the dissolving solution; A method for recovering precious metals comprising the steps of:

2. The precious metal recovery method according to claim 1, In the cooling step, the fuel cell or the water electrolysis apparatus including the membrane electrode assembly is cooled as a whole, In the dissolution solution supplying step, the dissolution solution is supplied to a reactant supply port for supplying a raw material or a product discharge port for discharging a product during use of the fuel cell or the water electrolysis device, and the dissolution solution is brought into contact with the membrane electrode assembly; In the noble metal dissolving step, a voltage is applied to the membrane electrode assembly in contact with the dissolving solution via a cathode terminal electrically connected to the cathode of the membrane electrode assembly and an anode terminal electrically connected to the anode of the membrane electrode assembly, The precious metal recovery method further comprises a solution recovery step of recovering the solution containing the precious metal from the reactant supply port or the product discharge port.

3. The precious metal recovery method according to claim 1, a removal step of removing the membrane electrode assembly from the fuel cell or water electrolysis device, In the dissolving solution supplying step, the removed membrane electrode assembly is immersed in the dissolving solution. A method for recovering precious metals.

4. The precious metal recovery method according to any one of claims 1 to 3, In the cooling step, hydrogen and air are supplied to the membrane electrode assembly in the state where the membrane electrode assembly is cooled to the subzero temperature, and the membrane electrode assembly is operated as a fuel cell. A method for recovering precious metals.

5. A precious metal recovery device for recovering precious metals from a fuel cell or a water electrolysis device, comprising: a cooling means for cooling the membrane electrode assembly of the fuel cell or water electrolysis device to a temperature below the freezing point at which moisture contained in the membrane electrode assembly freezes; a dissolution liquid supplying means for supplying a dissolution liquid to bring the dissolution liquid into contact with the membrane electrode assembly; a precious metal dissolving means for applying a voltage to the membrane electrode assembly in contact with the dissolving solution to dissolve the precious metal contained in the cathode and the anode in the dissolving solution; A precious metal recovery device comprising:

6. The precious metal recovery apparatus according to claim 5, The precious metal recovery apparatus further comprises an operating means for supplying hydrogen and air to the membrane electrode assembly in the subfreezing state, thereby operating the assembly as a fuel cell.

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