JP2008146985A - Manufacturing method of regenerated electrolyte membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a regenerated electrolyte membrane capable of providing a regenerated electrolyte membrane formed by suppressing deterioration to the utmost extent in regeneration. <P>SOLUTION: This manufacturing method of a regenerated electrolyte membrane has a catalyst electrolyte layer-electrolyte membrane separation process of separating a catalyst electrolyte layer 3 from an electrolyte membrane by arranging a membrane-electrode assembly 1 with moisture included therein in a thermal cycle environment across 0°C. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a regenerative electrolyte membrane capable of obtaining a regenerative electrolyte membrane in a state in which deterioration is suppressed to the maximum during regeneration.

  A fuel cell uses a membrane electrode composite to generate electric energy generated by an electrochemical reaction in a membrane electrode assembly (MEA) comprising an electrolyte and electrodes (anode and cathode) disposed on both sides of the electrolyte. It is taken out to the outside through separators disposed on both sides of the body. Among fuel cells, solid polymer fuel cells (hereinafter sometimes simply referred to as fuel cells) used in household cogeneration systems and automobiles can be operated in a low temperature region. In addition, since it exhibits high energy conversion efficiency, has a short start-up time, and has a small and lightweight system, it has attracted attention as an optimal power source for electric vehicles and portable power supplies.

  A unit cell, which is the minimum power generation unit of a solid polymer electrolyte fuel cell, generally comprises a membrane electrode assembly in which catalyst electrode layers (anode side catalyst electrode layer and cathode side catalyst electrode layer) are bonded to both sides of a solid electrolyte membrane. A gas diffusion layer is disposed on both sides of the membrane electrode assembly. Furthermore, a separator having a gas flow path is disposed outside thereof, and the fuel gas and the oxidant gas supplied to the catalyst electrode layer of the membrane electrode composite are passed through the gas diffusion layer, It works to transmit the current obtained by power generation to the outside.

  Here, the electrolyte membrane functions as a proton transfer medium and a hydrogen gas or oxygen gas diaphragm. Therefore, high proton conductivity, strength, and chemical stability are required for the electrolyte membrane. At present, as a membrane material having such a function, for example, “Nafion (trade name)” manufactured by DuPont, USA. Fluorine-containing polymers having a sulfonic acid group such as perfluorosulfonic acid polymer represented by “Flemion (trade name)” manufactured by Asahi Glass Co., Ltd. are used.

  Further, as a catalyst for the catalyst electrode layer, a catalyst in which a noble metal such as platinum is supported on a carrier having electron conductivity such as carbon is generally used. A proton conductive polymer electrolyte is used for the purpose of mediating proton transfer onto the catalyst carried by the catalyst electrode layer and increasing the utilization efficiency of the catalyst. Fluorine-containing polymers having a sulfonic acid group such as the same perfluorosulfonic acid polymer can be used. The fluorine-containing polymer having a sulfonic acid group can also serve as a binder for the catalyst of the catalyst electrode layer or as a binder for improving the adhesion between the electrolyte membrane and the catalyst electrode layer.

  Thus, in a polymer electrolyte fuel cell, a fluorine-containing polymer or a noble metal is often used as a constituent material. A fluorine-containing polymer having a sulfonic acid group such as a perfluorosulfonic acid polymer used as an electrolyte membrane is an extremely expensive material and has a great influence on the environment. Moreover, platinum etc. which are the catalysts in a catalyst electrode layer are also expensive. Therefore, in order to commercialize fuel cells at low cost in a resource-saving manner, it is important to recycle, that is, reuse, the electrolyte membranes in these membrane electrode composites and the noble metals in the catalyst electrode layer. One of the challenges.

  For example, in Patent Document 1, a proton conductive solid polymer that joins an electrolyte membrane and a catalyst electrode layer by expanding the electrolyte membrane by immersing the membrane electrode assembly in methanol and replacing water in the electrolyte membrane with methanol. Disclosed is a method of dissolving a cured product of a solution and reducing the adhesive force at the interface between the electrolyte membrane and the catalyst electrode layer to peel off the catalyst electrode layer and recovering the electrolyte membrane, that is, a method of obtaining a regenerated electrolyte membrane. . However, when an organic solvent such as methanol is used, the components of the electrolyte membrane are eluted and the electrolyte membrane is deteriorated, so that the chemical and mechanical strength of the recovered electrolyte membrane (regenerated electrolyte membrane) is reduced. There was a problem that. Patent Document 2 discloses a method of recovering an electrolyte membrane by freezing the membrane electrode assembly containing water in a stressed state and applying external stress (a method for producing a regenerated electrolyte membrane). In this case, it is necessary to go through a step of applying external stress, and the electrolyte membrane itself may be deteriorated by the external stress.

JP-A-8-171922 JP 2005-289001 A

  The present invention has been made in view of the above-mentioned problems, and has as its main object to provide a method for producing a regenerative electrolyte membrane capable of obtaining a regenerative electrolyte membrane that suppresses deterioration during regeneration to the maximum extent. is there.

  In order to achieve the above object, in the present invention, a catalyst electrode layer / electrolyte membrane separation in which the catalyst electrode layer is separated from the electrolyte membrane by placing the hydrated membrane electrode composite in a cold cycle environment over 0 ° C. There is provided a method for producing a regenerative electrolyte membrane characterized by comprising steps.

  According to the present invention, through the above steps, the catalyst electrode layer can be separated from the electrolyte membrane with almost no deterioration of the electrolyte membrane, and a regenerated electrolyte membrane that suppresses deterioration during regeneration to the maximum is obtained. Has the advantage of being able to

  Moreover, in the said invention, it is preferable that the temperature-fall rate of the said cooling-heat cycle is a speed | rate which the water in a membrane electrode assembly stays in the interface of a catalyst electrode layer and an electrolyte membrane during temperature fall. If the temperature lowering rate is as described above, water remains at the interface between the catalyst electrode layer and the electrolyte membrane in the membrane electrode assembly. For this reason, the separation of the catalyst electrode layer from the electrolyte membrane due to the volume expansion caused by the change in the state of water accompanying the cooling cycle over 0 ° C. can be performed satisfactorily, and a desired regenerated electrolyte membrane with suppressed deterioration can be obtained. Because.

  In this invention, there exists an effect that the reproduction | regeneration electrolyte membrane which suppressed the deterioration at the time of reproduction | regeneration to the maximum can be obtained.

  The method for producing the regenerative electrolyte membrane of the present invention will be described in detail below.

  The method for producing a regenerative electrolyte membrane according to the present invention comprises a catalyst electrode layer / electrolyte membrane separation step of separating the catalyst electrode layer from the electrolyte membrane by placing the water-containing membrane electrode composite in a cold cycle environment over 0 ° C. It is characterized by having.

  According to the present invention, the catalyst electrode layer can be separated from the electrolyte membrane through the above steps with almost no deterioration of the electrolyte membrane, and a regenerated electrolyte membrane that suppresses deterioration during regeneration to the maximum can be obtained. It has the advantage of being able to.

The method for producing a regenerative electrolyte membrane of the present invention is not particularly limited as long as it has at least the catalyst electrode layer / electrolyte membrane separation step, and may have other steps.
Hereinafter, each process in the manufacturing method of the reproduction | regeneration electrolyte membrane of this invention is demonstrated in detail.

1. Catalyst electrode layer / electrolyte membrane separation step The catalyst electrode layer / electrolyte membrane separation step in the present invention will be described. The catalyst electrode layer / electrolyte membrane separation step of the present invention is a water-containing membrane electrode assembly 1 as shown in FIG. 1 in which an electrolyte membrane 2 is arranged at the center and sandwiched between catalyst electrode layers 3. In this process, the catalyst electrode layer 3 is separated from the electrolyte membrane 2 by being placed in a cold cycle environment over 0 ° C.

  In this step, the above-described cooling cycle over 0 ° C. means a predetermined temperature higher than 0 ° C. (hereinafter sometimes referred to as a high temperature side holding temperature) and a predetermined temperature of 0 ° C. or lower across 0 ° C. This is a cooling cycle that is performed by raising and lowering the temperature within a temperature range (hereinafter, sometimes referred to as a low temperature holding temperature). Specifically, a method of raising or lowering the temperature in a constant temperature bath can be used.

  Through this step, the catalyst electrode layer can be separated from the electrolyte membrane with almost no deterioration of the electrolyte membrane, and a regenerated electrolyte membrane with suppressed deterioration can be obtained. This can be presumed to be due to the following reason. FIG. 2 is a schematic view showing an example of a separation mechanism of the catalyst electrode layer and the electrolyte membrane by the cooling cycle in this step. FIG. 2 shows the electrolyte membrane 2 and the catalyst electrode layer 3 that is either the anode-side catalyst electrode layer or the cathode-side catalyst electrode layer. From a state (FIG. 2 (a)) in which water 4 is included in a saturated state at a predetermined temperature higher than 0 ° C. such as room temperature (high temperature side holding temperature) (FIG. 2 (a)), a predetermined temperature (low temperature) below 0 ° C. When the temperature is gradually lowered to the (side holding temperature), first, the temperature of the membrane electrode assembly is cooled from the catalyst electrode layer 3 side, so that ice 5 is generated in the catalyst electrode layer 3 (FIG. 2). (B)). Thereafter, when the temperature is further lowered, the amount of water that can be contained in the electrolyte membrane 2 varies depending on the temperature. That is, as the temperature decreases, the amount of water that can be contained in the electrolyte membrane 2 (water content) decreases. As the temperature decreases, the water 4 oozes out from the electrolyte membrane 2 toward the catalyst electrode layer 3 side. Then, water accumulates in the vicinity of the interface between the electrolyte membrane 2 and the catalyst electrode layer 3 (FIG. 2C). When further cooling is performed, there is a gap at the interface, where water 4 freezes and ice 5 grows (FIG. 2 (d)). As the ice 5 grows, volume expansion occurs, so that a crack is generated at the interface between the electrolyte membrane 2 and the catalyst electrode layer 3. By repeating such a cooling / heating cycle over 0 ° C. a predetermined number of times, the catalyst electrode layer 3 is peeled off from the electrolyte membrane 2 and can be separated. Thereafter, a regenerated electrolyte membrane can be obtained by washing with water or the like. As described above, the catalyst electrode layer can be separated from the electrolyte membrane without substantially deteriorating the electrolyte membrane by placing the hydrated membrane electrode assembly in such a thermal cycle environment over 0 ° C. .

  In this step, the cooling rate when the temperature is lowered from the high temperature holding temperature to the low temperature holding temperature is such that the water in the membrane electrode assembly stays at the interface between the catalyst electrode layer and the electrolyte membrane during the temperature drop. It is preferably a speed, specifically 1.0 ° C./min or more, more preferably 5.0 ° C./min or more, and particularly preferably in the range of 5.0 to 10.0 ° C./min. When the rate of temperature decrease is smaller than the above range, that is, when the rate of temperature decrease becomes slower, water does not stay at the interface between the catalyst electrode layer and the electrolyte membrane in the membrane electrode assembly, and water is discharged outside the membrane electrode assembly. Will be discharged. For this reason, the separation of the catalyst electrode layer due to the volume expansion caused by the water state change accompanying the cooling cycle over 0 ° C. is hindered, and there is a possibility that the catalyst electrode layer does not peel and the desired regenerated electrolyte membrane cannot be obtained. is there.

  Further, in this step, the rate of temperature rise when raising the temperature from the low temperature side holding temperature to the high temperature side holding temperature is as follows. There is no particular limitation as long as the ice in the electrode complex is melted and sufficiently water, and is not particularly limited, but is specifically within the range of 1.0 to 20.0 ° C./min. It is preferably in the range of 0 to 10.0 ° C./min, particularly in the range of 5.0 to 10.0 ° C./min.

  Moreover, the high temperature side holding temperature in the above-mentioned cooling cycle over 0 ° C. may be a temperature higher than 0 ° C., but it is preferably in the range of 10 to 90 ° C., particularly in the range of 40 to 80 ° C. . If the high temperature side holding temperature is too high, the membrane electrode assembly may be melted or deteriorated. Moreover, if the above-mentioned high temperature side holding temperature is too low, the ice in the membrane electrode assembly may be melted and not sufficiently converted to water, which is caused by the volume expansion caused by the water state change accompanying the cooling cycle over 0 ° C. This is because separation of the catalyst electrode layer is hindered, and there is a possibility that a desired regenerated electrolyte membrane with suppressed deterioration cannot be obtained.

  The holding time at the high temperature holding temperature is preferably held at the high temperature holding temperature until the ice in the membrane electrode assembly melts and becomes sufficiently water, specifically 0.1 hour or more. In particular, it is preferably within a range of 0.1 to 6 hours, particularly preferably within a range of 0.5 to 2 hours.

  The low temperature side holding temperature in the above-described cooling cycle over 0 ° C. may be a temperature of 0 ° C. or less, but is particularly in the range of −1 to −40 ° C., particularly in the range of −10 to −30 ° C. It is preferable. If the low temperature side holding temperature is too low, the membrane electrode assembly may be deteriorated. In addition, if the low temperature holding temperature is too high, the water in the membrane electrode assembly may freeze and not become enough ice, and the volume expansion caused by the water state change accompanying the cooling cycle over 0 ° C. This is because the separation of the catalyst electrode layer due to the formation is hindered, and there is a possibility that a desired regenerated electrolyte membrane with suppressed deterioration cannot be obtained.

  The holding time at the low-temperature holding temperature is preferably held at the low-temperature holding temperature until the water in the membrane electrode assembly freezes and becomes sufficiently ice, specifically 0.5 hours or more. It is preferably within a range of 0.5 to 6 hours, particularly preferably within a range of 0.5 to 2 hours.

  The number of repetitions of the above-mentioned cooling cycle over 0 ° C. is one cooling cycle in which the temperature is lowered and held at the low temperature holding temperature for a predetermined time, and then further raised to the high temperature holding temperature and held for a predetermined time. When it is (1 cycle), specifically, it is preferably 1 or more times, more preferably 1 to 50 times, particularly preferably 1 to 20 times.

  In this step, after the above cooling cycle is repeated a predetermined number of times, the electrolyte membrane and the catalyst electrode layer are separated by washing with water or the like, whereby a regenerated electrolyte membrane can be obtained. Specifically, a method of separating the electrolyte membrane and the catalyst electrode layer by washing with ultrasonic waves in water and the like can be mentioned.

In this step, it is preferable to carry out a cooling cycle so that the water in the membrane electrode assembly containing water does not evaporate. Specifically, a method of performing a cooling / heating cycle in a sealed state or the like in a sealed state can be used. Alternatively, a method in which the humidity around the membrane electrode assembly is sufficiently high to the extent that the water in the membrane electrode assembly does not evaporate, and a cooling cycle is performed may be used.
This is because the water in the membrane electrode composite will evaporate in the thermostatic bath if the membrane electrode composite containing water in this step is subjected to the above-described cooling cycle conditions of the catalyst electrode layer / electrolyte membrane separation step. there is a possibility. When the membrane electrode composite is in a state where there is not enough moisture by such evaporation, the catalyst electrode layer in the catalyst electrode layer due to the volume expansion caused by the state change of water accompanying the cooling cycle over 0 ° C., and the catalyst electrode Cracks are less likely to occur at the interface between the layer and the electrolyte membrane. For this reason, it is because there exists a possibility that a catalyst electrode layer cannot be favorably isolate | separated from an electrolyte membrane, and a desired reproduction | regeneration electrolyte membrane cannot be obtained even when it is in a cold-heat cycle environment.

2. Other Steps In the present invention, (1) a pretreatment step and (2) a posttreatment step can be performed before and after the catalyst electrode layer / electrolyte membrane separation step.
(1) Pretreatment process First, the above pretreatment process will be described. The method for producing a regenerative electrolyte membrane of the present invention can perform a pretreatment step before the catalyst electrode layer / electrolyte membrane separation step. Examples of the pretreatment step include (a) membrane electrode assembly recovery step, ( b) Membrane electrode composite water-containing step and the like. Hereinafter, each step will be described in detail.

(A) Membrane electrode composite recovery step The membrane electrode composite recovery step will be described. The membrane electrode assembly recovery step is a step of recovering the membrane electrode assembly from the fuel cell after power generation. FIG. 3 is a schematic sectional view showing an example of the configuration of a general fuel cell. As shown in FIG. 3, in the fuel cell 6, the solid electrolyte membrane 2 is sandwiched by the catalyst electrode layer 3, and a gas is further provided outside the membrane electrode assembly 1 composed of the solid electrolyte membrane 2 and the catalyst electrode layer 3. A diffusion layer 7 and a separator 8 are disposed. In order to recover the membrane electrode assembly 1, first, the separator 8 is removed from the fuel cell 6. For example, the clamping bolts and the like are pulled out from the fuel cell 6 that has been used or is recycled for reasons such as defects, and the separator 8 is removed. Thereafter, the membrane electrode assembly 1 can be obtained by separating the gas diffusion layer 7. The gas diffusion layer 7 can be relatively easily separated from the interface between the catalyst electrode layer 3 and the gas diffusion layer 7 or from the inside of the catalyst electrode layer 3. For example, the catalyst electrode layer 3 and the gas diffusion layer can be separated with a slicer or the like. Alternatively, the gas diffusion layer 7 may be separated by slicing the interface with the gas.

(B) Membrane electrode composite water-containing step Next, the membrane electrode composite water-containing step will be described. The membrane electrode composite water-containing step is a step of containing the membrane electrode composite recovered in the membrane electrode composite recovery step. The method of hydrating is not particularly limited as long as it can be hydrated in the membrane electrode assembly. For example, until the water in the membrane electrode assembly is saturated by immersing in pure water at room temperature. For example, a method of leaving it to stand.

(2) Post-processing step Next, the post-processing step will be described. The method for producing a regenerative electrolyte membrane of the present invention can perform a post-treatment step after the catalyst electrode layer / electrolyte membrane separation step. Examples of such a post-treatment process include (a) a drying process, (b) a contamination removal process, and (c) a precious metal recovery process. Hereinafter, each step will be described in detail.

(A) Drying step This step is a step of drying the regenerated electrolyte membrane and the like obtained in the catalyst electrode layer / electrolyte membrane separation step. Examples of this step include a method of completely drying by leaving at room temperature and a method of drying by performing a heat treatment in a drying chamber or the like. In the case of drying by the above heat treatment, it is preferable that the temperature is typically 0 ° C. or higher, particularly 20 to 100 ° C., particularly 40 to 80 ° C.

(B) Contamination Removal Step Next, the contamination removal step will be described. The contamination removal step is a step of performing a treatment for removing contamination in the regenerated electrolyte membrane obtained in the catalyst electrode layer / electrolyte membrane separation step. Specifically, hydrogen peroxide treatment for removing organic substances in the regenerative electrolyte membrane, sulfuric acid treatment for removing metal ions and the like in the regenerative electrolyte membrane, and the like can be mentioned.

(C) Noble metal recovery step This step is a step of recovering the noble metal and the like in the catalyst electrode layer obtained when the electrolyte membrane is separated in the catalyst electrode layer / electrolyte membrane separation step. Specific methods for recovering catalytic noble metals such as platinum from the catalyst electrode layer include conventional metal recovery methods such as the combustion method, aqua regia dissolution method, alkali melting method, sulfuric acid dissolution method, and the separated catalyst electrode layer. A method of reusing as a catalyst for a fuel cell can be applied by stirring the powder in water and then collecting it by filtration or the like. Further, the catalyst electrode layer obtained upon separation may be dehydrated as it is, dissolved in an organic solvent, and reused as electrode ink.

3. Uses Although there is no particular limitation on the use of the regenerated electrolyte membrane obtained by the regenerated electrolyte membrane manufacturing method of the present invention that suppresses deterioration during regeneration as much as possible, for example, a membrane electrode of an automobile fuel cell It can be used as an electrolyte membrane of a composite.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be described in more detail with reference to examples.

[Example]
(Membrane electrode composite recovery process)
The cell module (separator, gas diffusion layer, membrane electrode assembly integrated structure) was taken out from the fuel cell stack, and the clamping bolt was pulled out to separate the separator. Thereafter, the gas diffusion layer was peeled off and separated to obtain a membrane electrode assembly.
(Membrane electrode composite hydrous process)
Next, the membrane electrode composite obtained in the membrane electrode composite recovery step was immersed in a polyethylene zipper bag containing water for 30 minutes until the water in the membrane electrode composite became saturated. Thereafter, the membrane electrode assembly was sealed in order to retain moisture.

(Catalyst electrode layer / electrolyte membrane separation process)
The membrane electrode composite was hydrated in the water-containing step until it was saturated, sealed in a bag, and sealed. The membrane electrode composite was placed in a constant temperature bath in a cold cycle environment over 0 ° C. The conditions for the cooling / heating cycle were a cooling / heating cycle in which the temperature was lowered from 60 ° C. in 2 hours and held at −40 ° C. for 1 hour, and further raised to 60 ° C. in 2 hours and held for 1 hour. With this as one cycle, the cooling / heating cycle under these conditions was repeated 10 times (10 cycles). The membrane electrode assembly after the cooling / heating cycle was taken out from the sealed bag and washed with water to remove the catalyst electrode layer adhering to the electrolyte membrane surface from the electrolyte membrane. Then, it dried by performing heat processing in a drying chamber, and obtained the reproduction | regeneration electrolyte membrane.

[Comparative example]
(Membrane electrode composite recovery process)
The cell module (separator, gas diffusion layer, membrane electrode assembly integrated structure) was taken out from the fuel cell stack, and the clamping bolt was pulled out to separate the separator. Thereafter, the gas diffusion layer was peeled off and separated to obtain a membrane electrode assembly.

(Catalyst electrode layer / electrolyte membrane separation process)
Next, the catalyst electrode layer was scraped off from the membrane electrode assembly using gauze sufficiently immersed in ethanol. Then, the foreign material etc. of the electrolyte membrane were removed by washing with water, and dried by performing a heat treatment in a drying chamber to obtain a regenerated electrolyte membrane.

[Evaluation]
The surfaces of the regenerated electrolyte membranes obtained in the examples and comparative examples were observed with a scanning electron microscope (SEM). The measurement conditions are as follows.
Acceleration voltage: 5 kV
Emission current: 10μA
The result of SEM observation is shown in FIG. 4A is an SEM photograph of the example, and FIG. 4B is an SEM photograph of the comparative example. As shown in FIG. 4 (a), the surface of the regenerated electrolyte membrane obtained in the example had few remaining catalyst electrode layers and few surface scratches. On the other hand, as shown in FIG. 4B, the surface of the regenerated electrolyte membrane obtained in the comparative example had many remaining catalyst electrode layers, and many scratches on the surface were observed. It was speculated that this was mainly due to the fact that the components of the electrolyte membrane were eluted and deteriorated by the ethanol used in the comparative example.

  From the above results, in the examples, when the membrane electrode assembly is below freezing in a water-containing state, water in the catalyst electrode layer and at the interface between the catalyst electrode layer and the electrolyte membrane is frozen. Along with this, volume expansion occurs, and a crack occurs at the interface between the catalyst electrode layer and the electrolyte membrane. By repeating such a heat cycle over 0 ° C., the catalyst electrode layer can be separated from the electrolyte membrane with almost no deterioration of the electrolyte membrane, and a regenerated electrolyte membrane with suppressed deterioration can be obtained.

It is a schematic sectional drawing which shows an example of a structure of a membrane electrode assembly. It is the schematic diagram which showed an example of the separation mechanism of the catalyst electrode layer and electrolyte membrane of this invention. It is a schematic sectional drawing which shows an example of a structure of a fuel cell. It is a SEM photograph of the surface of the regenerated electrolyte membrane after catalyst electrode layer separation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Membrane electrode complex 2 ... Solid electrolyte membrane 3 ... Catalyst electrode layer 4 ... Water 5 ... Ice 6 ... Fuel cell 7 ... Gas diffusion layer 8 ... Separator

Claims (2)

  Production of a regenerative electrolyte membrane characterized by having a catalyst electrode layer / electrolyte membrane separation step of separating the catalyst electrode layer from the electrolyte membrane by placing the water-containing membrane electrode composite in a cold cycle environment over 0 ° C. Method.   2. The regenerative electrolyte membrane according to claim 1, wherein the temperature decrease rate of the cooling cycle is such a rate that water in the membrane electrode assembly stays at the interface between the catalyst electrode layer and the electrolyte membrane during the temperature decrease. Production method.

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