PEM water electrolysis hydrogen production membrane electrode and preparation method thereof

Abstract

The application discloses a PEM water electrolysis hydrogen production membrane electrode and a preparation method thereof, and relates to the technical field of water electrolysis hydrogen production. The PEM water electrolysis hydrogen production membrane electrode comprises a proton exchange membrane and cathode and anode catalyst layers located on both sides of the proton exchange membrane, wherein the cathode catalyst layer and the anode catalyst layer both comprise a catalyst, a perfluorosulfonic acid ionomer, a solvent and a perfluorosulfonic acid ionomer dispersion promoter; and the perfluorosulfonic acid ionomer dispersion promoter is at least one of dimethyl sulfoxide, tetrahydrofuran and N-methyl pyrrolidone. The PEM hydrogen production membrane electrode catalyst layer prepared by the application has the dispersion promoter of the ionomer added, the dispersion degree of the ionomer in the catalyst layer is increased, a good catalyst / ionomer microporous structure catalyst layer is constructed, the transmission resistance of the gas and water is reduced, and the performance of the membrane electrode is improved. The preparation method adopted by the application does not need special treatment process and equipment, is simple and fast in operation, and is easy to realize batch production.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of hydrogen production by water electrolysis, and particularly relates to a PEM water electrolysis hydrogen production membrane electrode and a preparation method thereof. BACKGROUND

[0002] The membrane electrode is a core component of a proton exchange membrane (PEM) water electrolysis hydrogen production electrolytic cell, is a reaction site of substances and an important flow channel. In the PEM water electrolysis reaction process, part of the water in the anode catalyst layer on the membrane electrode migrates to the cathode with protons, and the water exists in the cathode catalyst layer in a gaseous or gas-liquid coexisting manner. In the steady-state operation of the electrolytic cell, they must be discharged in time through the catalyst layer, and at the same time, the oxygen generated on the anode side and the hydrogen generated on the cathode side must also be discharged in time through the catalyst layer.

[0003] The ionomer, as the binder of the catalyst layer, mainly functions to immerse into the catalyst layer as a proton conductor, thereby expanding the catalytic reaction interface of the electrode to promote the transmission of protons in the micropores of the catalyst layer. In actual use, the dispersion degree of the ionomer particles in the catalyst layer directly affects the use performance of the membrane electrode.

[0004] The electrode reaction occurs in a three-phase zone where the ionomer, the catalyst and the reactants coexist. When the dispersion degree of the ionomer in the catalyst layer is low, part of the catalyst fails to be in complete contact with the ionomer, the surface of the catalyst has no proton channel and the ion conductivity is poor, so the part of the catalyst does not work, the utilization rate of the catalyst is low, the performance of the membrane electrode is relatively poor, and meanwhile, the poor dispersion degree of the ionomer causes the solid polymer electrolyte layer on the surface of the catalyst to thicken, resulting in that the electrode is hydrophilic and thus the electrode is flooded and inactivated. Moreover, the ionomer that is not completely dispersed is filled in the pores, increasing the resistance of gas and liquid transmission, directly leading to the difficulty in discharging the oxygen on the anode side and the hydrogen and water on the cathode side, and affecting the normal progress of the reaction.

[0005] The patent application with the publication number CN114899416A discloses a fuel cell catalyst layer and a preparation method thereof. The catalyst slurry I and the catalyst slurry II are alternately sprayed between layers to form a fuel cell catalyst layer with an interlayer structure; the catalyst slurry I comprises a catalyst, a perfluorosulfonic acid ionomer and a dispersant, wherein the total mass fraction of the catalyst and the perfluorosulfonic acid ionomer is 0.1-3%; the catalyst slurry II comprises a carbon material, a perfluorosulfonic acid ionomer and a solvent, wherein the total mass fraction of the carbon material and the perfluorosulfonic acid ionomer is 0.1-3%.

[0006] Patent application with publication number CN114899420A discloses a fuel cell catalyst layer and a preparation method thereof. The preparation method is: water-rich catalyst slurry and alcohol-rich catalyst slurry are alternately sprayed to form an interlayer structure of the fuel cell catalyst layer; the water-rich catalyst slurry and the alcohol-rich catalyst slurry both comprise a catalyst, a perfluorosulfonic acid ionomer, and a dispersant, the dispersant is a mixed solvent of water and a volatile alcohol; in the water-rich catalyst slurry, the mass percentage of the volatile alcohol in the dispersant is 5-30%; in the alcohol-rich catalyst slurry, the mass percentage of the volatile alcohol in the dispersant is 60-95%.

[0007] In the above prior art, the prepared membrane electrode is applied to a fuel cell, wherein the dispersant used refers to an alcohol solvent, which is mainly used for dispersing the catalyst to prevent random arrangement and stacking of the catalyst, and uniformity cannot be guaranteed.

[0008] In summary, there is an urgent need for a PEM water electrolysis hydrogen production membrane electrode with better performance and a preparation method thereof in the technical field of PEM water electrolysis hydrogen production. SUMMARY

[0009] In order to solve the problems in the prior art, the present application provides a PEM water electrolysis hydrogen production membrane electrode, which comprises a proton exchange membrane, a cathode catalyst layer and an anode catalyst layer coated on both sides of the proton exchange membrane, and the cathode catalyst layer and the anode catalyst layer are prepared from a catalyst, an ionomer, a solvent, and an ionomer dispersion promoter. The present application adds a dispersion promoter to the catalyst layer, which helps to disperse the ionomer particles, increases the dispersion degree, increases the activity of the catalyst, and at the same time reduces the transmission resistance of the catalyst layer to gas and water, and improves the performance of the membrane electrode.

[0010] The technical scheme of the present application is as follows:

[0011] The present application provides a PEM water electrolysis hydrogen production membrane electrode, which comprises a proton exchange membrane, a cathode catalyst layer and an anode catalyst layer coated on both sides of the proton exchange membrane, and the cathode catalyst layer and the anode catalyst layer are prepared from a catalyst, an ionomer, a solvent, and an ionomer dispersion promoter.

[0012] The ionomer dispersion promoter is at least one of dimethyl sulfoxide, tetrahydrofuran, and N-methyl pyrrolidone.

[0013] Preferably, the mass percentage of the ionomer dispersion promoter is 0.5wt%-10wt%.

[0014] Specifically, the catalyst is divided into an anode catalyst and a cathode catalyst.

[0015] The anode catalyst is iridium dioxide or carrier iridium dioxide, the content of iridium in the anode catalyst is 40wt%-90wt%, the mass ratio of the perfluorosulfonic acid ionomer dispersion promoter to the iridium in the catalyst is 1:1-20.

[0016] The cathode catalyst is a carbon-supported platinum catalyst, wherein the content of platinum in the catalyst is 20wt%-60wt%, and the mass ratio of the perfluorosulfonic acid ionomer dispersion promoter to the platinum in the catalyst is 1:1-10.

[0017] Based on the above technical solution, preferably, the perfluorosulfonic acid ionomer is a Nafion solution or a PFSA solution with a mass percentage of 5wt%-20wt%.

[0018] Based on the above technical solution, preferably, the solvent is a mixed solvent of an organic solvent and water, and the mass ratio of the organic solvent to water is 1-10:1.

[0019] Preferably, the organic solvent is at least one of n-propanol, isopropanol, ethylene glycol and ethanol.

[0020] The application also provides a preparation method of the PEM water electrolysis hydrogen production membrane electrode, comprising the following steps:

[0021] (1) mixing and uniformly dispersing the catalyst, the perfluorosulfonic acid ionomer, the solvent and the perfluorosulfonic acid ionomer dispersion promoter to obtain anode catalyst slurry and cathode catalyst slurry;

[0022] (2) spraying the anode catalyst slurry and the cathode catalyst slurry obtained in step (1) on both sides of the proton exchange membrane by using a spraying method to form an anode catalyst layer and a cathode catalyst layer;

[0023] (3) obtaining the PEM water electrolysis hydrogen production membrane electrode by a hot pressing process.

[0024] Specifically, in step (1), the dispersion is performed by ultrasonic dispersion and high-speed homogenizing stirring in sequence, wherein the ultrasonic dispersion time is 5-60 min, and the ultrasonic frequency is 20-70 kHz; the high-speed homogenizing stirring time is 10-60 min, and the rotating speed is 5000-20000 rpm.

[0025] Specifically, in step (2), the process parameters of the spraying method are as follows: the spraying flow is 0.5-5 mL / min, the spraying temperature is 90-130℃, and the nozzle pressure is 5-50 psi.

[0026] In step (3), the hot pressing process parameters are as follows: the hot pressing temperature is 110-160℃, the hot pressing time is 5-30 min, and the hot pressing pressure is 1-50 kg / cm 2 .

[0027] The preparation method further comprises removing the residual perfluorosulfonic acid ionomer dispersion promoter by protonation treatment; the process flow of the protonation treatment is: first, soaking in dilute sulfuric acid for water bath heating, the mass percentage of the dilute sulfuric acid is 1%wt-10%wt, the water bath temperature is 60-100℃, and the water bath time is 10-120min; then, soaking in distilled water for water bath heating and rinsing, the water bath temperature is 60-100℃, and the water bath time is 10-120min.

[0028] Compared with the prior art, the present application has the beneficial effects that:

[0029] (1) The PEM hydrogen production membrane electrode catalytic layer prepared by the present application has increased dispersity of the ionomer in the catalytic layer due to the addition of the dispersion promoter of the ionomer, thereby constructing a good and reasonable catalytic layer of catalyst / ionomer microporous structure, reducing the transmission resistance to the gas and water, and improving the performance of the membrane electrode.

[0030] (2) The preparation method adopted by the present application does not need special treatment process and equipment, is simple and fast in operation, and is easy to realize batch production. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The performance test curve of the catalytic layer prepared for Examples 1-3 and Comparative Examples 1-2 on the membrane electrode.

[0032] Figure 2 The durability test curve of the catalytic layer prepared for Examples 1-3 and Comparative Examples 1-2 on the membrane electrode. DETAILED DESCRIPTION

[0033] Example 1

[0034] The IrO2 catalyst 210mg with a mass percentage of 40% was placed in a 50mL beaker, then 5g of deionized water was removed to wet the catalyst, and then 10g of n-propanol, 5g of dimethyl sulfoxide solution with a mass fraction of 0.5% and 0.4g of Nafion solution with a mass fraction of 5% were added, respectively, and ultrasonic dispersion (70kHz) was carried out for 30min; after the end, the mixture was treated by high-speed stirring (10000rpm) for 30min, to obtain a mixed and uniform anode catalytic layer slurry.

[0035] Take 60 mg of 20% Pt / C catalyst in a 50 mL beaker, then take 2 g of deionized water to wet the catalyst, and then add 7 g of n-propanol, 1 g of 0.5% dimethyl sulfoxide solution, and 0.3 g of 5% Nafion solution, respectively, and ultrasonic (70 kHz) dispersion for 30 min; after the end, the mixture is treated by high-speed stirring (10000 rpm) for 30 min to obtain a uniformly mixed cathode catalyst layer slurry.

[0036] The uniformly dispersed anode and cathode catalyst slurries are directly sprayed onto the surface of the proton membrane using a direct spraying method to form thin anode and cathode catalyst layers on the membrane, and a required membrane electrode is obtained by hot pressing. The spraying process parameters are set as follows: nozzle flow rate 0.5 mL / min, temperature 100°C, and nozzle pressure 5 psi. The hot pressing process parameters are set as follows: temperature 110°C, time 30 min, and pressure 10 kg / cm 2 . The protonation process parameters are set as follows: 1% wt of dilute sulfuric acid heated in a 100°C water bath for 60 min, and 100°C distilled water bath heating and washing for 60 min. The platinum loading of the cathode catalyst layer is 0.3 mg / cm 2 , and the iridium loading of the anode catalyst layer is 2.0 mg / cm 2 .

[0037] Example 2

[0038] Take 140 mg of 60% IrO2 catalyst in a 50 mL beaker, then take 5 g of deionized water to wet the catalyst, and then add 10 g of n-propanol, 0.2 g of 5% tetrahydrofuran solution, and 0.2 g of 10% Nafion solution, respectively, and ultrasonic (70 kHz) dispersion for 30 min; after the end, the mixture is treated by high-speed stirring (10000 rpm) for 30 min to obtain a uniformly mixed anode catalyst layer slurry.

[0039] Take 60 mg of 20% Pt / C catalyst in a 50 mL beaker, then take 2 g of deionized water to wet the catalyst, and then add 7 g of n-propanol, 0.08 g of 5% tetrahydrofuran solution, and 0.15 g of 10% Nafion solution, respectively, and ultrasonic (70 kHz) dispersion for 30 min; after the end, the mixture is treated by high-speed stirring (10000 rpm) for 30 min to obtain a uniformly mixed cathode catalyst layer slurry.

[0040] The uniformly dispersed anode and cathode catalyst slurries are directly sprayed onto the surface of the proton exchange membrane using a direct spraying method to form thin anode and cathode catalyst layers on the membrane, and a required membrane electrode is obtained by hot pressing. The spraying process parameters are set as follows: nozzle flow rate 1.5 mL / min, temperature 110°C, and nozzle pressure 10 psi. The hot pressing process parameters are set as follows: temperature 140°C, time 20 min, and pressure 25 kg / cm 2 . The protonation process parameters are set as follows: 5% wt dilute sulfuric acid, 80°C water bath heating for 60 min, and 80°C distilled water bath heating for 60 min. The platinum loading of the cathode catalyst layer is 0.3 mg / cm 2 , and the iridium loading of the anode catalyst layer is 2.0 mg / cm 2 .

[0041] Example 3

[0042] 95 mg of an IrO2 catalyst with a mass percentage of 90% is placed in a 50 mL beaker, and then 5 g of deionized water is removed to wet the catalyst, and then 10 g of n-propanol, 0.1 g of a 10% N-methylpyrrolidone solution, and 0.1 g of a 20% Nafion solution are added, respectively, and ultrasonic dispersion (70 kHz) is performed for 30 min; after the end, the mixture is treated by high-speed stirring (10000 rpm) for 30 min to obtain a uniformly mixed anode catalyst layer slurry.

[0043] 20 mg of a Pt / C catalyst with a mass percentage of 60% is placed in a 50 mL beaker, and then 2 g of deionized water is removed to wet the catalyst, and then 7 g of n-propanol, 0.04 g of a 10% N-methylpyrrolidone solution, and 0.075 g of a 20% Nafion solution are added, respectively, and ultrasonic dispersion (70 kHz) is performed for 30 min; after the end, the mixture is treated by high-speed stirring (10000 rpm) for 30 min to obtain a uniformly mixed cathode catalyst layer slurry.

[0044] The uniformly dispersed anode and cathode catalyst slurries are directly sprayed onto the surface of the proton exchange membrane using a direct spraying method to form thin anode and cathode catalyst layers on the membrane, and a required membrane electrode is obtained by hot pressing. The spraying process parameters are set as follows: nozzle flow rate 2.0 mL / min, temperature 130°C, and nozzle pressure 20 psi. The hot pressing process parameters are set as follows: temperature 110°C, time 5 min, and pressure 50 kg / cm 2 . The protonation process parameters are set as follows: 10% wt dilute sulfuric acid, 60°C water bath heating for 120 min, and 60°C distilled water bath heating for 120 min. The platinum loading of the cathode catalyst layer is 0.3 mg / cm 2 , and the iridium loading of the anode catalyst layer is 2.0 mg / cm 2 .

[0045] Comparative Example 1

[0046] Take 100 mg of IrO2 catalyst with a mass percentage of 85% and place it in a 50 mL beaker, then take 5 g of deionized water to wet the catalyst, and then add 10 g of n-propanol and 0.4 g of a 5% by mass Nafion solution, respectively, and ultrasonic (70 kHz) disperse for 30 min; after the end, the mixture is treated by high-speed stirring (10000 rpm) for 30 min to obtain a mixed and uniform anode catalyst layer ink.

[0047] Take 30 mg of Pt / C catalyst with a mass percentage of 40% and place it in a 50 mL beaker, then take 2 g of deionized water to wet the catalyst, and then add 7 g of n-propanol and 0.3 g of a 5% by mass Nafion solution, respectively, and ultrasonic (70 kHz) disperse for 30 min; after the end, the mixture is treated by high-speed stirring (10000 rpm) for 30 min to obtain a mixed and uniform cathode catalyst layer ink.

[0048] The mixed and uniform anode and cathode catalyst slurries are directly sprayed onto the surface of the proton membrane using a direct spraying method to form a thin layer of anode and cathode catalyst layers on the membrane, and a hot-pressed membrane electrode is obtained. The spraying process parameters are set as follows: nozzle flow rate 1.0 mL / min, temperature 100°C, and nozzle pressure 5 psi. The hot-pressing process parameters are set as follows: temperature 110°C, time 30 min, and pressure 10 kg / cm 2 . The protonation process parameters are set as follows: 1% wt of dilute sulfuric acid heated in a 100°C water bath for 60 min, and 100°C distilled water bath heating and washing for 60 min. The platinum loading of the cathode catalyst layer is 0.3 mg / cm 2 , and the iridium loading of the anode catalyst layer is 2.0 mg / cm 2 .

[0049] Comparative Example 2

[0050] Mix 0.1 g of a 10% by mass dimethyl sulfoxide solution and 0.4 g of a 5% by mass Nafion solution in advance, and record as liquid A, and ultrasonic (70 kHz) disperse for 30 min.

[0051] Mix 0.04 g of a 10% by mass dimethyl sulfoxide solution and 0.3 g of a 5% by mass Nafion solution, and record as liquid B, and ultrasonic (70 kHz) disperse for 30 min.

[0052] Take 100 mg of 85% IrO2 catalyst in a 50 mL beaker, then take 5 g of deionized water to wet the catalyst, and then add 10 g of n-propanol and A liquid respectively, and ultrasonic (70 kHz) dispersion for 30 min; after the end, the mixture is treated by high-speed stirring (10000 rpm) for 30 min to obtain a uniformly mixed anode catalyst ink.

[0053] Take 30 mg of 40% Pt / C catalyst in a 50 mL beaker, then take 2 g of deionized water to wet the catalyst, and then add 7 g of n-propanol and B liquid respectively, and ultrasonic (70 kHz) dispersion for 30 min; after the end, the mixture is treated by high-speed stirring (10000 rpm) for 30 min to obtain a uniformly mixed cathode catalyst ink.

[0054] The uniformly dispersed anode and cathode catalyst slurries are directly sprayed onto the surface of the proton membrane using a direct spraying method to form a thin layer of anode and cathode catalyst layers on the membrane, and hot pressing is performed to obtain the required membrane electrode. The spraying process parameters are set as follows: nozzle flow rate 5 mL / min, temperature 130°C, and nozzle pressure 50 psi. The hot pressing process parameters are set as follows: temperature 140°C, time 5 min, and pressure 28 kg / cm 2 . The protonation process parameters are set as follows: 5% wt of dilute sulfuric acid heated in an 80°C water bath for 60 min, and then washed in an 80°C distilled water bath for 60 min. The platinum loading of the cathode catalyst layer is 0.3 mg / cm 2 , and the iridium loading of the anode catalyst layer is 2.0 mg / cm 2 .

[0055] Test Example 1

[0056] The membrane electrodes prepared in Examples 1-3 and Comparative Examples 1-2 are assembled into electrolytic cells, and performance tests and durability tests are performed under the same conditions, and the results are shown in Figure 1 and Figure 2 . The test conditions are as follows: electrolytic cell inlet water temperature 50°C, inlet water flow rate 0.5 L / min, and outlet gas normal pressure.

[0057] From Figure 1From the comparison of the performance test results of the membrane electrode prepared in Examples 1-3 and Comparative Example 1, it can be seen that after adding the ionomer dispersion promoter, the performance of the membrane electrode is obviously improved, which is mainly because the promoter promotes the dispersion effect of the ionomer in the catalyst layer, not only increases the effect of the catalyst, but also is beneficial to the discharge of gas and water. In terms of effect, dimethyl sulfoxide > tetrahydrofuran > N-methyl pyrrolidone. From the comparison of the performance test results of Example 1 and Comparative Example 2, it can be seen that the effect of mixing the dispersion promoter with the ionomer in advance is not as good as that of mixing all the catalyst slurry together, which may be that the ionomer is excessively dispersed, resulting in a decrease in the proton conduction ability of the ionomer during the subsequent preparation of the membrane electrode. The best use method of the ionomer dispersion promoter is to mix the catalyst, solvent and ionomer uniformly and then spray the catalyst layer.

[0058] From Figure 2 It can be seen that the voltage value of the membrane electrode prepared in Examples 1-3 and Comparative Example 2 is still very stable after 100h of testing, indicating that the durability test result is good, and the state of the catalyst layer is good. On the contrary, the voltage value of the membrane electrode prepared in Comparative Example 1 shows a gradually increasing trend, indicating that the durability test result is poor, which may be due to the excessive thickness of the dielectric layer, causing gas and liquid accumulation in the catalyst layer, forming a bubble effect, hindering the discharge of gas and liquid, and affecting the performance of the membrane electrode. Therefore, the addition of the dispersion promoter has a gain effect on the durability of the membrane electrode.

Claims

1. A PEM water electrolysis hydrogen production membrane electrode, comprising a proton exchange membrane and a cathode catalyst layer and an anode catalyst layer located on both sides of the proton exchange membrane, characterized in that: The cathode catalyst layer and the anode catalyst layer both include a catalyst, a perfluorosulfonic acid ionomer, a solvent, and a perfluorosulfonic acid ionomer dispersion promoter; The perfluorosulfonic acid ionomer dispersion promoter is at least one of dimethyl sulfoxide, tetrahydrofuran, and N-methylpyrrolidone; The catalyst is divided into an anode catalyst and a cathode catalyst; The anode catalyst is iridium dioxide or supported iridium dioxide, and the iridium content in the anode catalyst is 40%wt-90%wt; the mass ratio of the perfluorosulfonic acid ionomer dispersion promoter to the iridium in the catalyst is 1:1-20; The cathode catalyst is a carbon-supported platinum catalyst, wherein the platinum content in the catalyst is 20%wt-60%wt; the mass ratio of the perfluorosulfonic acid ionomer dispersion promoter to the platinum in the catalyst is 1:1-10; The solvent is a mixed solvent of an organic solvent and water, and the mass ratio of the organic solvent to water is 1-10:1; The organic solvent is at least one of n-propanol, isopropanol, ethylene glycol and ethanol; The preparation method of the PEM water electrolysis hydrogen production membrane electrode comprises the following steps: (1) mixing and uniformly dispersing a catalyst, a perfluorosulfonic acid ionomer, a solvent, and a perfluorosulfonic acid ionomer dispersion promoter to obtain an anode catalyst slurry and a cathode catalyst slurry; (2) spraying the anode catalyst slurry and cathode catalyst slurry obtained in step (1) on both sides of the proton exchange membrane to form an anode catalyst layer and a cathode catalyst layer; (3) The PEM water electrolysis hydrogen production membrane electrode is obtained through a hot pressing process.

2. The PEM water electrolysis hydrogen production membrane electrode according to claim 1, characterized in that The mass percentage of the ionomer dispersion promoter is 0.5%wt-10%wt.

3. The PEM water electrolysis hydrogen production membrane electrode according to claim 1, characterized in that The perfluorosulfonic acid ionomer is a Nafion solution with a mass percentage of 5%wt-20%wt.

4. The PEM water electrolysis hydrogen production membrane electrode according to claim 1, characterized in that The perfluorosulfonic acid ionomer is a PFSA solution with a mass percentage of 5%wt-20%wt.

5. The PEM water electrolysis hydrogen production membrane electrode according to claim 1, characterized in that: In step (1), the dispersion is carried out by ultrasonic dispersion and high-speed homogenization stirring in sequence, wherein the ultrasonic dispersion time is 5-60 min and the ultrasonic frequency is 20-70 kHz; the high-speed homogenization stirring time is 10-60 min and the rotation speed is 5000-20000 rpm.

6. The PEM water electrolysis hydrogen production membrane electrode according to claim 1, characterized in that: In step (2), the process parameters of the spraying method are as follows: spray flow rate is 0.5-5 mL / min, spray temperature is 90-130°C, and nozzle pressure is 5-50 psi; In step (3), the hot pressing process parameters are as follows: hot pressing temperature is 110-160°C, hot pressing time is 5-30min, hot pressing pressure is 1-50kg / cm 2 .

7. The PEM water electrolysis hydrogen production membrane electrode according to claim 1, characterized in that The method also includes removing residual perfluorosulfonic acid ionomer dispersion promoter by protonation treatment; the process flow of the protonation treatment is: first soaking in dilute sulfuric acid and heating in a water bath, the mass percentage of dilute sulfuric acid is 1%wt-10%wt, the water bath temperature is 60-100°C, and the water bath time is 10-120 minutes, and then soaking in distilled water and heating and rinsing in a water bath, the water bath temperature is 60-100°C, and the water bath time is 10-120 minutes.

Images