Method for recovering noble metal catalyst in proton exchange membrane electrolysis of water

Abstract

The application provides a recovery method of noble metal catalyst in proton exchange membrane water electrolysis, and relates to the technical field of water electrolysis.The recovery method comprises the following steps: primary recovery: sequentially performing acid immersion activation, washing, drying and hot pressing on a membrane electrode to recover the membrane electrode;secondary recovery: sequentially performing dry stripping, wet stripping and grinding and crushing on the noble metal catalyst layer on the membrane electrode to obtain noble metal catalyst layer powder;mixing the noble metal catalyst layer powder, an ionomer and a solvent, and obtaining slurry after ball milling;sequentially performing coating and hot pressing on the slurry to recover the membrane electrode;tertiary recovery: sequentially performing ion exchange, precipitation and filtration after dissolving the noble metal catalyst layer powder in aqua regia to recover chloroiridic acid and chloroplatinic acid.The application provides a high-efficiency and accurate hierarchical recovery method of noble metal catalyst, solves the problem of resource bottleneck of platinum group metals in PEM water electrolysis, and provides a feasible path for efficient utilization of platinum group metals.

Description

Technical Field

[0001] The present invention relates to the technical field of water electrolysis, and in particular to a method for recovering a noble metal catalyst in proton exchange membrane water electrolysis. Background Art

[0002] Proton exchange membrane water electrolysis (PEMWE) hydrogen production is regarded as a promising clean energy conversion technology due to its high efficiency, low emissions and rapid start-up. In PEM water electrolysis, metallic iridium has good activity and stability under acidic conditions, and thus serves as a catalyst for the oxygen evolution reaction at the anode. Metallic platinum is used as a catalyst for the cathode due to its good hydrogen evolution activity. Both metallic iridium and metallic platinum belong to the platinum group metals. However, the further expansion and large-scale application of PEM water electrolysis production capacity are currently restricted by platinum group metals. According to platinum group metal market data statistics, the total demand for platinum group metals in 2023 will reach 236.6 tons, while the mineral supply will be only 180.1 tons. Among them, metallic iridium is a secondary mining metal and a by-product in the production of platinum (Pt) and palladium (Pd). The annual output is only 7 tons, which is 1 / 30 of the Pt output.

[0003] The imbalance between supply and demand of platinum group metals has limited the expansion of PEM electrolysis water production capacity and large-scale application, becoming a resource "bottleneck" for PEM electrolysis water. There are two ways to solve the "bottleneck" of insufficient platinum group metal resources in the large-scale layout of the PEM electrolysis water industry. One is to significantly reduce the loading of precious metal catalysts in PEM electrolysis water, and the other is to develop efficient precious metal catalyst recovery technology. Currently, a significant reduction in the loading of precious metal catalysts will result in a reduction in catalytic active sites and poor contact between the catalytic layer and the porous transport layer, resulting in poor durability. The further development and large-scale application of PEM electrolysis water are limited by the supply of platinum group metal resources. In the current situation where it is impossible to significantly reduce the catalyst loading in the short term, there is an urgent need to develop new and efficient recovery methods to solve the bottleneck of scarce platinum group metals in PEM electrolysis water.

[0004] There are few literature reports on the recovery methods of precious metal catalysts for PEM water electrolysis. The current industry recovery processes for precious metal catalysts use traditional pyrometallurgy and hydrometallurgy. Due to the high melting point of platinum group metals (for example, the melting point of metallic iridium is 2446°C), pyrometallurgical recovery requires high-temperature melting, which consumes a lot of energy and easily releases harmful gas HF during combustion, making it environmentally unsustainable. In hydrometallurgical recovery, recovery is mainly carried out through four main steps: pretreatment, dissolution, separation and purification, and precipitation. The wet method of precious metal recovery is lengthy, cumbersome, and has a low overall recovery rate. It also requires the use of a large amount of chemical reagents, polluting the environment, and has low economic efficiency and is unsustainable. In addition, in PEM water electrolysis, the recycling process of precious metals is as follows: the catalyst is synthesized from a precursor containing precious metal elements, the catalyst is mixed with a solvent and an ionomer to prepare a slurry, the slurry is coated as a catalytic layer, and finally hot-pressed to form a membrane electrode. After use, the prepared membrane electrode is directly recycled by wet and pyrometallurgical methods. Through the recycling process of precious metals, it can be found that the circulation cycle of precious metals in PEM electrolysis water is long, and the preparation cost of membrane electrodes is high and the time is long.

[0005] According to existing literature reports (Carmo M, Keeley GP, Holtz D, et al. PEM waterelectrolysis: Innovative approaches towards catalyst separation, recovery and recycling, International Journal of Hydrogen Energy (2019)), the membrane electrode is fixed in a homemade container and the catalytic layers on both sides of the cathode and anode are stripped to recover the catalyst by ultrasonic water circulation. Since the catalytic layer is stripped by ultrasound, the ultrasonic time and power depend on the thickness and area of ​​the catalytic layer. In addition, the membrane electrode needs to be fixed in a homemade reactor and the catalysts on both sides of the cathode and cathode are separated by a proton membrane. The precious metal catalyst on the damaged membrane electrode cannot be recovered by this method. Therefore, the currently reported membrane electrode recovery method is only suitable for the recovery of precious metal catalysts from a small area of ​​membrane electrode and is not suitable for large-scale, batch recovery of precious metal catalysts in membrane electrodes. In addition, this method requires high ultrasonic power and high energy consumption. At the same time, this method requires the recovery of precious metal catalysts from an intact membrane electrode and is not suitable for the recovery of precious metal catalysts from damaged membrane electrodes.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of the present invention is to provide an efficient and accurate "cascade recovery" method for precious metal catalysts to solve the bottleneck problem of platinum group metal resources in PEM electrolysis of water and provide a practical path for the efficient utilization of precious metals.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0009] The present invention provides a method for recovering a precious metal catalyst in proton exchange membrane (PEM) water electrolysis, the method comprising the following steps:

[0010] Primary recovery: The membrane electrode is acid-activated, washed, dried and hot-pressed in sequence to recover the membrane electrode;

[0011] Secondary recovery: The noble metal catalyst layers on the positive and negative sides of the membrane electrode are sequentially subjected to dry stripping, wet stripping, and pulverization to obtain noble metal catalyst layer powder; the noble metal catalyst layer powder, ionomer, and solvent are mixed and ball milled to obtain a slurry; the slurry is sequentially coated and hot pressed to recover the membrane electrode;

[0012] Three-stage recovery: The precious metal catalyst layer on the membrane electrode is sequentially subjected to dry stripping, wet stripping and crushing to obtain precious metal catalyst layer powder; after the precious metal catalyst layer powder is dissolved in aqua regia, ion exchange, precipitation and filtration are sequentially performed to recover chloroplatinic acid and chloroiridic acid.

[0013] Preferably, in the primary recycling, the membrane electrode is a used complete membrane electrode.

[0014] Preferably, the acid immersion activation is specifically: placing the membrane electrode in an acid solution for immersion.

[0015] Preferably, the acid solution used in the acid leaching activation is sulfuric acid and / or nitric acid.

[0016] Preferably, the concentration of the acid is 0.5-1.5M.

[0017] Preferably, the temperature of the acid leaching activation is 10 to 30° C., and the time of the acid leaching activation is 6 to 18 hours.

[0018] Preferably, in the primary recovery, the solvent used for washing is deionized water.

[0019] Preferably, the drying temperature is 60-80° C., and the drying time is 1-4 hours.

[0020] Preferably, the temperature of the hot pressing is 110-140° C., and the pressure of the hot pressing is 2-5 MPa.

[0021] Preferably, in the secondary recycling, the membrane electrode is a used and damaged membrane electrode and / or a membrane electrode that has failed after the primary recycling.

[0022] Preferably, the dry stripping is specifically as follows: firstly, the membrane electrode is fixed on the base of the stripping machine, and then a blade is installed on the stripping machine, and the blade is controlled to slide back and forth on the noble metal catalyst layer on the positive and negative sides of the membrane electrode.

[0023] Preferably, the wet stripping is specifically as follows: adding a water-alcohol solution to the surface of the membrane electrode after dry stripping, and while adding, controlling the blade to slide back and forth on the noble metal catalyst layers on the positive and negative sides of the membrane electrode until the noble metal catalyst layers on the positive and negative sides of the membrane electrode are completely stripped.

[0024] Preferably, the angle between the blade and the horizontal plane is 40-50°, preferably 45°.

[0025] Preferably, the moving speed of the blade in the reciprocating sliding is 5 to 20 mm / s, and the number of reciprocating sliding is 20 to 40 times.

[0026] Preferably, the alcohol in the hydroalcoholic solution comprises any one of methanol, ethanol, n-propanol, isopropanol, tert-butanol, ethylene glycol, propylene glycol or glycerol, or a combination of at least two thereof.

[0027] Preferably, the volume ratio of water to alcohol in the hydroalcoholic solution is (90-97):(3-10).

[0028] Preferably, in the secondary recovery, the pulverization is carried out in a grinding manner; wherein the particle size of the precious metal catalyst layer powder obtained after the pulverization is 50 to 400 nm.

[0029] Preferably, in the secondary recovery, the mass ratio of the noble metal catalyst layer powder, ionomer and solvent is 100:(5-20):(200-300).

[0030] Preferably, the solvent is n-propanol.

[0031] Preferably, the ionomer is perfluorosulfonic acid.

[0032] Preferably, in the secondary recovery, the coating amount of the slurry is 0.5-2 mL / cm 2 .

[0033] Preferably, the base material used in the coating includes any one of polytetrafluoroethylene, polyvinylidene fluoride or polychlorotrifluoroethylene.

[0034] Preferably, the temperature of the hot pressing is 110-140° C., and the pressure of the hot pressing is 2-5 MPa.

[0035] Preferably, in the three-stage recovery, the membrane electrode is a membrane electrode that has failed after the first-stage recovery and the second-stage recovery.

[0036] Preferably, the mass ratio of the noble metal catalyst layer powder to aqua regia is 1:(5-20).

[0037] Preferably, the dissolution temperature is 70-110° C., and the dissolution time is 6-12 hours.

[0038] Preferably, in the three-stage recovery, the ion exchange is specifically: adsorbing the aqua regia solution of the noble metal catalyst layer powder through an ion exchange resin, and then desorbing it through a desorption liquid to obtain an exchange liquid;

[0039] Preferably, the ion exchange resin comprises any one of Amberjet 4200Cl, Lewatit-MP-62 or Amberlite IRA-67.

[0040] Preferably, during the adsorption process, the resin concentration required to absorb each gram of precious metal is 2 to 10 g / L.

[0041] Preferably, the solute in the desorption solution includes any one of sodium hydroxide, sodium thiosulfate or thiourea, or a combination of at least two of them.

[0042] Preferably, during the desorption process, the concentration of the desorption liquid is 0.05 to 2 mol / L.

[0043] Preferably, in the three-stage recovery, the precipitation is specifically: adding a precipitant to the exchange liquid obtained by ion exchange to obtain a precipitate.

[0044] Preferably, the precipitant is ammonium chloride.

[0045] Preferably, the concentration of the precipitant is 5 to 25 g / L.

[0046] Preferably, the precipitation temperature is 25-40° C., and the precipitation time is 1-5 hours.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] (1) The present invention provides a precise and efficient cascade recovery method for the recycling of precious metal catalysts in PEM electrolysis water, which can effectively solve the bottleneck of the scarcity of platinum group metals in PEM electrolysis water;

[0049] (2) The present invention provides a technology for mechanically stripping the catalytic layer, which is suitable for large-scale, batch stripping and recovery of platinum group metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0051] Figure 1 The figure is a schematic flow chart of the primary recovery process in the method for recovering precious metal catalysts in PEM water electrolysis according to the present invention.

[0052] Figure 2 The figure is a schematic flow chart of the secondary recovery process in the method for recovering precious metal catalysts in PEM water electrolysis according to the present invention.

[0053] Figure 3 The figure is a schematic flow chart of the three-stage recovery process in the method for recovering precious metal catalysts in PEM water electrolysis according to the present invention.

[0054] Figure 4 Polarization curves before and after the first-level recovery provided in Example 1.

[0055] Figure 5 Polarization curves before and after primary recovery provided in Example 2.

[0056] Figure 6 Polarization curves before and after secondary recovery provided in Example 2.

[0057] Figure 7 Polarization curves before and after primary recovery provided in Example 3.

[0058] Figure 8 Polarization curves before and after secondary recovery provided in Example 3. DETAILED DESCRIPTION

[0059] Unless otherwise defined herein, scientific and technical terms used in conjunction with the present invention shall have the meanings commonly understood by those of ordinary skill in the art. The meaning and scope of the terms should be clear; however, in the event of any potential ambiguity, the definitions provided herein take precedence over any dictionary or external definitions. In this application, the use of "or" means "and / or" unless otherwise stated. In addition, the use of the term "including" and other forms is non-limiting.

[0060] It should be noted that the following description sets forth specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in a variety of other ways than those described herein, and those skilled in the art may make similar generalizations without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0061] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0062] As an optional embodiment of the present invention, the present invention provides a method for recovering a precious metal catalyst in PEM electrolysis of water, the recovery method comprising the following steps:

[0063] Primary recovery: The membrane electrode is acid-activated, washed, dried and hot-pressed in sequence to recover the membrane electrode (such as Figure 1 shown);

[0064] Secondary recovery: The noble metal catalyst layer on the positive and negative sides of the membrane electrode is sequentially subjected to dry stripping, wet stripping and crushing to obtain noble metal catalyst layer powder; the noble metal catalyst layer powder, ionomer and solvent are mixed and ball milled to obtain slurry; the slurry is sequentially coated and hot pressed to recover the membrane electrode (such as Figure 2 shown);

[0065] Three-stage recovery: The noble metal catalyst layer on the membrane electrode is sequentially subjected to dry stripping, wet stripping and crushing to obtain the noble metal catalyst layer powder; the noble metal catalyst layer powder is dissolved in aqua regia and sequentially subjected to ion exchange, precipitation and filtration to recover chloroplatinic acid and chloroiridic acid (such as Figure 3 shown).

[0066] It should be noted that the reason the present invention proposes "cascade recovery" is primarily based on two aspects: the PEM electrolyzer's platinum group metal circulation process and the utilization rate of precious metal catalysts. The main reasons for the performance degradation of PEM electrolyzers during operation are metal ion poisoning, catalyst degradation, and structural changes in the catalytic layer. Metal ion poisoning refers to the metal ions dissolved by equipment corrosion during storage or in the operating channel that poison the membrane electrode, causing the hydrogen ions on the perfluorosulfonate groups in the proton exchange membrane and ionomer to be replaced by metal ions. Since the metal ions migrate slowly under the action of the electric field, proton conduction is blocked, resulting in performance degradation. In addition, the migration of ionomers in the catalytic layer and the degradation and dissolution of catalysts cause changes in the catalytic layer structure, leading to performance degradation.

[0067] Based on the above two reasons, the present application first provides a primary recovery, that is, for the complete and non-broken used membrane electrode, the acid activation and hot pressing process steps are carried out to restore the approximate initial performance, and the platinum group metal (for example, it can be iridium element and / or platinum element) is recovered and used from the membrane electrode level. In addition, in the PEM electrolytic water, the catalyst in the catalyst layer is caused by agglomeration and ionomer wrapping, resulting in a reaction active dead zone, and the effective utilization rate of the catalyst is only about 20%. The present application conceives whether the remaining 80% or so of the catalyst in the used catalyst layer still has catalytic activity and can be reused until it is deactivated. Therefore, further, the present application provides a secondary recovery, for the membrane electrode which is broken due to unexpected circumstances or does not work for the first level recovery, the catalyst layer containing noble metal is peeled off, the slurry is reconfigured, the membrane electrode is prepared and used again, and the platinum group metal is recovered from the level of the catalyst layer. In particular, further, the present application cannot recover the platinum group metal for the first level and the second level, and the present application provides a third level to recover the platinum group metal from the noble metal catalyst, and the third level is mainly recovered by a wet method at present.

[0068] Therefore, based on the scarcity of platinum group metal resources in the PEM electrolytic water system and the imperfection of the existing recovery method, an economic and efficient recovery method of noble metal catalyst in the PEM electrolytic water is provided, which recovers the platinum group metal in the PEM electrolytic water from the levels of the membrane electrode, the catalyst layer and the catalyst, and implements precise recovery and efficient utilization of the platinum group metal.

[0069] As an optional embodiment of the present application, in the primary recovery, the membrane electrode is a used complete membrane electrode.

[0070] As an optional embodiment of the present application, in the primary recovery, the acid immersion activation is specifically that the membrane electrode is soaked in an acid solution.

[0071] As an optional embodiment of the present application, in the primary recovery, the acid solution used in the acid immersion activation is sulfuric acid and / or nitric acid, and preferably sulfuric acid.

[0072] As an optional embodiment of the present application, in the primary recovery, the concentration of the acid is 0.5-1.5M, for example, it can be 0.5M, 0.6M, 0.7M, 0.8M, 0.9M, 1.0M, 1.1M, 1.2M, 1.3M, 1.4M, 1.5M, etc.

[0073] As an optional embodiment of the present invention, in the primary recovery, the temperature of the acid leaching activation is 10 to 30°C, for example, 10°C, 15°C, 20°C, 25°C, 30°C, etc., and the time of the acid leaching activation is 6 to 18h, for example, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, etc.

[0074] As an optional embodiment of the present invention, in the primary recovery, the washing is specifically: immersing the membrane electrode after acid immersion activation in a solvent to remove excess acid on the surface.

[0075] As an optional embodiment of the present invention, in the primary recovery, the solvent used for washing is deionized water.

[0076] As an optional embodiment of the present invention, in the primary recovery, the drying temperature is 60-80°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C, etc., and the drying time is 1-4h, for example, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0077] As an optional embodiment of the present invention, in the primary recovery, the temperature of the hot pressing is 110-140°C, for example, it can be 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, etc., and the pressure of the hot pressing is 2-5MPa, for example, it can be 2MPa, 2.5MPa, 3MPa, 3.5MPa, 4MPa, 4.5MPa, 5MPa, etc.

[0078] As an optional embodiment of the present invention, the primary recovery specifically includes the following steps:

[0079] (A) Soak the used intact membrane electrode in acid solution;

[0080] (B) Soaking the membrane electrode in deionized water to remove excess acid on the surface;

[0081] (C) drying the soaked membrane electrode to remove excess water from the membrane electrode;

[0082] (D) The dried membrane electrode is re-hot pressed and the recovered membrane electrode is reused.

[0083] As an optional embodiment of the present invention, the hot pressing further includes assembly and / or electrochemical testing.

[0084] As an optional embodiment of the present invention, in the primary recovery, step (D) is followed by step (E): assembling the recovered membrane electrode and performing electrochemical testing.

[0085] As an optional embodiment of the present invention, in the secondary recovery, the membrane electrode is a used and damaged membrane electrode and / or a membrane electrode that has failed after the primary recovery.

[0086] As an optional embodiment of the present invention, in the secondary recovery, the dry stripping is specifically as follows: first, the membrane electrode is fixed on the base of the stripping machine, and then a blade is installed on the stripping machine, and the blade is controlled to slide back and forth on the precious metal catalyst layer on the positive and negative sides of the membrane electrode.

[0087] As an optional embodiment of the present invention, in the secondary recovery, the wet stripping is specifically: adding a water-alcohol solution to the surface of the membrane electrode after dry stripping, and while adding, controlling the blade to slide back and forth on the precious metal catalyst layer on the positive and negative sides of the membrane electrode until the precious metal catalyst layer on the membrane electrode is completely stripped.

[0088] As an optional embodiment of the present invention, in the secondary recovery, the angle between the blade and the horizontal plane is 40-50°, for example, it can be 40°, 42°, 44°, 46°, 48°, 50°, etc., preferably 45°.

[0089] As an optional embodiment of the present invention, in the secondary recovery, the movement speed of the blade in the reciprocating sliding is 5 to 20 mm / s, for example, it can be 5 mm / s, 6 mm / s, 8 mm / s, 10 mm / s, 12 mm / s, 14 mm / s, 16 mm / s, 18 mm / s, 20 mm / s, etc.

[0090] As an optional embodiment of the present invention, in the secondary recovery, the number of reciprocating sliding is 20 to 40 times, for example, 20 times, 25 times, 30 times, 35 times, 40 times, etc.

[0091] As an optional embodiment of the present invention, in the secondary recovery, the alcohol in the hydroalcoholic solution includes any one of methanol, ethanol, n-propanol, isopropanol, tert-butanol, ethylene glycol, propylene glycol or glycerol, or a combination of at least two thereof.

[0092] As an optional embodiment of the present invention, in the secondary recovery, the volume ratio of water to alcohol in the hydroalcohol solution is (90-97):(3-10);

[0093] Among them, "90-97" can be, for example, 90, 91, 92, 93, 94, 95, 96, 97, etc.;

[0094] Here, “3 to 10” can be, for example, 3, 4, 5, 6, 7, 8, 9, 10, etc.

[0095] As an optional embodiment of the present invention, in the secondary recovery, the pulverization is carried out by grinding; wherein the particle size of the precious metal catalyst layer powder obtained after the pulverization is 50 to 400 nm, for example, it can be 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, etc.

[0096] As an optional embodiment of the present invention, in the secondary recovery, the mass ratio of the noble metal catalyst layer powder, ionomer and solvent is 100:(5-20):(200-300);

[0097] Here, “5-20” can be, for example, 5, 10, 15, 20, etc.;

[0098] Here, “200-300” can be, for example, 200, 220, 240, 260, 280, 300, etc.

[0099] As an optional embodiment of the present invention, in the secondary recovery, the solvent in the slurry is n-propanol.

[0100] As an optional embodiment of the present invention, in the secondary recovery, the ionomer in the slurry is perfluorosulfonic acid.

[0101] As an optional embodiment of the present invention, in the secondary recovery, the grinding is ball milling.

[0102] As an optional embodiment of the present invention, in the secondary recovery, the coating amount of the slurry is 0.5 to 2 mL / cm 2 , for example, it can be 0.5mL / cm 2 , 0.6mL / cm 2 , 0.8mL / cm 2 , 1mL / cm 2 , 1.2mL / cm 2 , 1.4mL / cm 2 , 1.6mL / cm 2 , 1.8mL / cm 2 , 2mL / cm 2 wait.

[0103] As an optional embodiment of the present invention, the base material used in the coating in the secondary recycling includes any one of polytetrafluoroethylene, polyvinylidene fluoride or polychlorotrifluoroethylene.

[0104] As an optional embodiment of the present invention, in the secondary recovery, the temperature of the hot pressing is 110-140°C, for example, it can be 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, etc., and the pressure of the hot pressing is 2-5MPa, for example, it can be 2MPa, 2.5MPa, 3MPa, 3.5MPa, 4MPa, 4.5MPa, 5MPa, etc.

[0105] As an optional embodiment of the present invention, the secondary recovery specifically includes the following steps:

[0106] (A) Fixing the damaged membrane electrode or the membrane electrode that has failed in the first stage of recovery on the base of the stripping machine to prepare for the catalytic layer stripping;

[0107] (B) Install the scraper on the stripping machine, keep the scraper at a 45° angle to the plane, and control the blade to slide back and forth to strip the catalyst layer with poor surface bonding strength on the surface above the catalyst layer;

[0108] (C) until the blade can no longer peel off the lower catalyst layer, then the stripper starts to add the water-alcohol solution dropwise, while stripping with a scraper until the surface precious metal catalyst layer is completely stripped off;

[0109] (D) The stripped noble metal catalyst layer is ground and pulverized, and then ionomer and n-propanol are added, ball milled and mixed to prepare a slurry, which is then coated and hot-pressed to prepare a membrane electrode.

[0110] As an optional embodiment of the present invention, in the secondary recycling, the hot pressing further includes assembly and / or electrochemical testing.

[0111] As an optional embodiment of the present invention, in the secondary recovery, step (D) is followed by step (E): assembling the recovered membrane electrode and performing electrochemical testing.

[0112] As an optional embodiment of the present invention, in the three-stage recovery, the membrane electrode is a membrane electrode that has failed after the first-stage recovery and the second-stage recovery.

[0113] As an optional embodiment of the present invention, in the tertiary recovery, the method of preparing the precious metal catalyst layer powder is the same as the process of the secondary recovery.

[0114] As an optional embodiment of the present invention, in the three-stage recovery, the dry stripping is specifically as follows: first, the membrane electrode is fixed on the base of the stripping machine, and then a blade is installed on the stripping machine, and the blade is controlled to slide back and forth on the precious metal catalyst layer on the positive and negative sides of the membrane electrode.

[0115] As an optional embodiment of the present application, in the three-stage recycling, the wet stripping is specifically that: water-alcohol solution is added dropwise to the surface of the membrane electrode after dry stripping, and at the same time of dropwise adding, the blade slides back and forth on the noble metal catalytic layer on the cathode and anode sides of the membrane electrode until the noble metal catalytic layer on the cathode and anode sides of the membrane electrode is completely stripped.

[0116] As an optional embodiment of the present application, in the three-stage recycling, the angle between the blade and the horizontal plane is 40-50°, for example, it can be 40°, 42°, 44°, 46°, 48°, 50°, etc., and preferably 45°.

[0117] As an optional embodiment of the present application, in the three-stage recycling, the moving speed of the blade in the back-and-forth sliding is 5-20 mm / s, for example, it can be 5 mm / s, 6 mm / s, 8 mm / s, 10 mm / s, 12 mm / s, 14 mm / s, 16 mm / s, 18 mm / s, 20 mm / s, etc.

[0118] As an optional embodiment of the present application, in the three-stage recycling, the number of times of back-and-forth sliding is 20-40 times, for example, it can be 20 times, 25 times, 30 times, 35 times, 40 times, etc.

[0119] As an optional embodiment of the present application, in the three-stage recycling, the alcohol in the water-alcohol solution includes any one or a combination of at least two of methanol, ethanol, n-propanol, isopropanol, tert-butanol, ethylene glycol, propylene glycol, or glycerol.

[0120] As an optional embodiment of the present application, in the three-stage recycling, the volume ratio of water to alcohol in the water-alcohol solution is (90-97):(3-10);

[0121] Wherein, "90-97" can be 90, 91, 92, 93, 94, 95, 96, 97, etc.

[0122] Wherein, "3-10" can be 3, 4, 5, 6, 7, 8, 9, 10, etc.

[0123] As an optional embodiment of the present application, in the three-stage recycling, the pulverization adopts a grinding mode; wherein, the particle size of the noble metal catalytic layer powder obtained after pulverization is 50-400 nm, for example, it can be 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, etc.

[0124] As an optional embodiment of the present invention, in the three-stage recovery, the mass ratio of the precious metal catalyst layer powder to aqua regia is 1:(5-20), for example, it can be 1:5, 1:6, 1:8, 1:10, 1:12, 1:14, 1:16, 1:18, 1:20, etc.

[0125] As an optional embodiment of the present invention, in the three-stage recovery, the dissolution temperature is 70-110°C, for example, it can be 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, etc., and the dissolution time is 6-12h, for example, it can be 6h, 7h, 8h, 9h, 10h, 11h, 12h, etc.

[0126] As an optional embodiment of the present invention, in the three-stage recovery, the ion exchange is specifically: adsorbing the aqua regia solution of the noble metal catalyst layer powder through an ion exchange resin, and then desorbing it through a desorption liquid to obtain an exchange liquid.

[0127] As an optional embodiment of the present invention, in the tertiary recovery, the ion exchange resin includes any one of Amberjet 4200Cl, Lewatit-MP-62 or Amberlite IRA-67.

[0128] As an optional embodiment of the present invention, in the three-stage recovery, during the adsorption process, the resin concentration required to absorb each gram of precious metal is 2 to 10 g / L, for example, it can be 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L, etc.

[0129] As an optional embodiment of the present invention, in the tertiary recovery, the solute in the desorption liquid includes any one of sodium hydroxide, sodium thiosulfate or thiourea, or a combination of at least two of them.

[0130] As an optional embodiment of the present invention, in the three-stage recovery, during the desorption process, the concentration of the desorption liquid is 0.05 to 2 mol / L, for example, it can be 0.05 mol / L, 0.06 mol / L, 0.08 mol / L, 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, etc.

[0131] As an optional embodiment of the present invention, in the three-stage recovery, the precipitation is specifically: adding a precipitant to the exchange liquid obtained by ion exchange to obtain a precipitate.

[0132] As an optional embodiment of the present invention, in the three-stage recovery, the precipitant is ammonium chloride.

[0133] As an optional embodiment of the present invention, in the three-stage recovery, the concentration of the precipitant is 5 to 25 g / L, for example, it can be 5 g / L, 6 g / L, 8 g / L, 10 g / L, 12 g / L, 14 g / L, 16 g / L, 18 g / L, 20 g / L, 22 g / L, 25 g / L, etc.

[0134] As an optional embodiment of the present invention, in the three-stage recovery, the precipitation temperature is 25-40°C, for example, it can be 25°C, 26°C, 28°C, 30°C, 32°C, 34°C, 35°C, 36°C, 38°C, 40°C, etc., and the precipitation time is 1-5h, for example, it can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, etc.

[0135] As an optional embodiment of the present invention, the three-stage recovery specifically includes the following steps:

[0136] (A) When the precious metal catalyst cannot be recovered in the first and second stages, the precious metal catalyst layers on both the cathode and anode sides are peeled off, collected, crushed, and recovered by a wet method;

[0137] (B) The pulverized noble metal catalyst is dissolved by heating with aqua regia.

[0138] (C) The dissolved solution is separated and purified by ion exchange.

[0139] (D) Ammonium chloride is added to the solution for precipitation.

[0140] (E) The precipitate is filtered and recovered to obtain chloroplatinic acid and chloroiridic acid.

[0141] The present invention is further described below by way of examples. Unless otherwise specified, the materials in the examples were prepared according to existing methods or directly purchased from the market.

[0142] The calculation formulas for the recovery rates at various levels in the following examples and comparative examples are as follows:

[0143] The calculation formula of the primary recovery rate is shown in the following formula I:

[0144]

[0145] Among them, R1 represents the recovery rate of precious metals in primary recovery, M 10 Represents the mass of the membrane electrode before acid immersion activation, M 11 Represents the mass of the recovered membrane electrode.

[0146] The calculation formula for the dry recovery rate in secondary recovery is shown in Formula Ⅱ-1:

[0147]

[0148] Among them, R 2d Represents the recovery rate of PGMs from dry stripping in secondary recovery, M base Represents the mass of the membrane electrode substrate (excluding the platinum group metal catalyst layer), M 20 Represents the mass of the membrane electrode (containing the platinum group metal catalyst layer) before dry stripping, M 21 Represents the mass of the membrane electrode after dry stripping.

[0149] The calculation formula for the wet recovery rate in secondary recovery is shown in Formula II-2:

[0150]

[0151] Among them, R 2w Represents the recovery rate of platinum group metals from wet stripping in secondary recovery, M base Represents the mass of the membrane electrode substrate (excluding the precious metal catalyst layer), M 21 Represents the mass of the membrane electrode after dry stripping, M 22 Represents the mass of the membrane electrode after wet stripping.

[0152] The calculation formula for the total recovery rate of secondary recovery is shown in Formula II-3 below:

[0153]

[0154] Among them, R2 represents the total recovery rate of precious metals in secondary recycling.

[0155] The calculation formula for the leaching efficiency of the platinum group metal dissolution step in the tertiary recovery is shown in the following formula III-1:

[0156]

[0157] Among them, R 31 Represents the leaching efficiency of platinum group metals in tertiary recovery, m 30 represents the mass of the noble metal catalyst before the platinum group metal is dissolved, w 30 represents the mass fraction of platinum group metals in the noble metal catalyst, C 30 Represents the concentration of platinum group metals in the dissolved solution, V 30 Represents the volume of the dissolved solution.

[0158] The calculation formula for the recovery rate of the metal iridium separation and purification step in the tertiary recovery is shown in the following formula III-2:

[0159]

[0160] wherein R 3s represents the separation and purification efficiency of platinum group metals in the tertiary recovery, C 31 represents the concentration of platinum group metals in the stripping solution, V 31 represents the volume of the stripping solution.

[0161] wherein the recovery rate of the precipitation separation step of metal iridium in the tertiary recovery is calculated according to the following formula III-3:

[0162]

[0163] wherein R 3p represents the precipitation efficiency of platinum group metals in the tertiary recovery, m 31 represents the mass of chloroiridic acid or chloroplatinic acid after the precipitation separation, w 31 represents the mass fraction of iridium or platinum in the chloroiridic acid or chloroplatinic acid.

[0164] wherein the total recovery rate of metal iridium in the tertiary recovery is calculated according to the following formula III-4:

[0165] R3(%) = R 3l (% ) x R 3s (% ) x R 3p (% ) formula III-4

[0166] wherein R3represents the total recovery rate of noble metals in the tertiary recovery.

[0167] Example 1

[0168] The present embodiment provides a recovery method of noble metal catalysts in PEM electrolytic water, which comprises the following steps:

[0169] Primary recovery: recovering noble metals from the membrane electrode pair;

[0170] (A) A used complete membrane electrode (proton exchange membrane: Nafion membrane, catalytic layer: anode catalytic layer composed of IrO2catalyst and Nafion perfluorosulfonic acid ionomer, mass ratio 5:1; cathode catalytic layer composed of Pt / C catalyst and Nafion perfluorosulfonic acid ionomer, mass ratio 8:1) was activated by soaking in a 1M H2SO4aqueous solution at 25°C for 12h, to obtain an acid- soaked and activated membrane electrode;

[0171] (B) The acid-soaked and activated membrane electrode was soaked in deionized water at 25°C for 2h to remove excess acid on the surface, to obtain a washed membrane electrode;

[0172] (C) drying the washed membrane electrode at 60°C for 2h to remove the excess water from the membrane electrode, to obtain a dried membrane electrode;

[0173] (D) re-pressing the dried membrane electrode at 120°C under 2MPa pressure to recover the membrane electrode for reuse;

[0174] (E) assembling the recovered membrane electrode and performing electrochemical test.

[0175] Test result: the noble metal recovery rate on the first-stage membrane electrode was calculated to be 100%.

[0176] As shown in Figure 4 , comparing the performance difference between the membrane electrode before and after the first-stage recovery and the freshly prepared membrane electrode, it can be found that under the same current density, for example, 2A / cm 2 , the performance of the membrane electrode after the first-stage recovery recovered 100mV, only 20mV lower than that of the freshly prepared membrane electrode, and the used membrane electrode recovered 83% after the first-stage recovery.

[0177] Example 2

[0178] The present embodiment provides a method for recovering noble metal catalyst in PEM electrolysis water, which comprises the following steps:

[0179] (I) first-stage recovery: recovering noble metal from the membrane electrode;

[0180] (A) soaking the used complete membrane electrode (proton exchange membrane: Nafion membrane, catalytic layer: anode catalytic layer composed of IrO2 catalyst and Nafion perfluorosulfonic acid ionomer, mass ratio 5:1; cathode catalytic layer composed of Pt / C catalyst and Nafion perfluorosulfonic acid ionomer, mass ratio 8:1) in 1M H2SO4 aqueous solution at 25°C for 12h for activation treatment, to obtain an acid- soaked and activated membrane electrode;

[0181] (B) soaking the acid-soaked and activated membrane electrode in deionized water at 25°C for 2h to remove the excess acid on the surface, to obtain a washed membrane electrode;

[0182] (C) drying the washed membrane electrode at 60°C for 2h to remove the excess water from the membrane electrode, to obtain a dried membrane electrode;

[0183] (D) re-pressing the dried membrane electrode at 120°C under 2MPa pressure to recover the membrane electrode for reuse;

[0184] (E) assembling the recovered membrane electrode and performing electrochemical test.

[0185] Test results:

[0186] The calculation shows that the recovery rate of precious metals on the first-stage membrane electrode is 100%.

[0187] like Figure 5 As shown in the figure, the performance difference between the membrane electrode before and after the first stage recovery and the freshly prepared membrane electrode can be found at the same current density of 2A / cm 2 For example, the performance of the membrane electrode after the first level of recycling has only recovered 30mV, which is 90mV different from the freshly prepared membrane electrode. The performance of the used membrane electrode after the first level of recycling has only recovered 25%, and it cannot be used efficiently again, indicating that the membrane electrode after the first level of recycling has failed.

[0188] (II) Secondary recovery:

[0189] (A) Fixing the membrane electrode that has no effect in the first-stage recovery to the base of the stripping machine, preparing for the catalytic layer stripping;

[0190] (B) A scraper was installed on a homemade automatic stripping machine, maintained at a 45° angle to the plane, and the blade was controlled to slide back and forth (the blade's speed during the back-and-forth sliding was 10 mm / s, and the number of back-and-forth sliding cycles was 30) to strip the precious metal catalyst with poor surface adhesion on the upper surface of the catalytic layer;

[0191] (C) until the blade can no longer peel off the precious metal catalyst, then the stripper starts to add ethanol water solution (the volume ratio of water to alcohol is 97:3) while adding the solution (the rate of addition is 0.5 drops / s) while stripping with a scraper (the blade moves at a speed of 15 mm / s during the reciprocating sliding, and the number of reciprocating sliding is 20 times) until the precious metal catalyst layer on the surface is completely stripped off;

[0192] (D) After the stripped noble metal catalyst layer was ground to an average particle size of 150 nm, ionomer PFSA and n-propanol (wherein the mass ratio of the noble metal catalyst layer powder, ionomer and n-propanol was 100:5:200) were added and mixed by ball milling to obtain a slurry; the slurry was completely coated on a polytetrafluoroethylene substrate (1 mL / cm 2 ), and then re-hot-pressed at 120°C and 2MPa to recover the membrane electrode for reuse;

[0193] (E) The recovered membrane electrode was assembled and electrochemical testing was performed.

[0194] Test results:

[0195] The calculated recovery rates of precious metals on the second-stage membrane electrode are shown in Table 1 below:

[0196] Table 1

[0197]

[0198] like Figure 6 As shown in the figure, the performance difference between the membrane electrode before and after the second stage recovery and the freshly prepared membrane electrode can be found at the same current density of 2A / cm 2 For example, the performance of the membrane electrode after secondary recovery is similar to that of the freshly prepared membrane electrode, with a voltage difference of only 20mV. The catalyst recovered after the second stage can be used again.

[0199] Example 3

[0200] This embodiment provides a method for recovering a precious metal catalyst in PEM water electrolysis, the method comprising the following steps:

[0201] (I) Primary recovery: recovery of precious metals from membrane electrodes;

[0202] (A) A used intact membrane electrode (proton exchange membrane: Nafion membrane, catalytic layer: anode catalytic layer composed of IrO2 catalyst and Nafion perfluorosulfonic acid ionomer, mass ratio of 5:1; cathode catalytic layer composed of Pt / C catalyst and Nafion perfluorosulfonic acid ionomer, mass ratio of 8:1) was activated by immersion in a 1M H2SO4 aqueous solution at 25°C for 12 h to obtain an acid-activated membrane electrode.

[0203] (B) The membrane electrode after acid leaching activation was immersed in deionized water at 25°C for 2 h to remove excess acid on the surface, thereby obtaining a washed membrane electrode;

[0204] (C) drying the washed membrane electrode at 60° C. for 2 h to remove excess moisture from the membrane electrode to obtain a dry membrane electrode;

[0205] (D) re-hot pressing the dried membrane electrode at 120°C and a pressure of 2 MPa to recover the membrane electrode for reuse;

[0206] (E) The recovered membrane electrode was assembled and electrochemical testing was performed.

[0207] Test results:

[0208] The calculation shows that the recovery rate of precious metals on the first-stage membrane electrode is 100%.

[0209] like Figure 7 As shown in the figure, the performance difference between the membrane electrode before and after the first stage recovery and the freshly prepared membrane electrode can be found at the same current density of 2A / cm 2For example, the performance of the membrane electrode after the first level of recycling has only recovered 30mV, which is 90mV different from the freshly prepared membrane electrode. The performance of the used membrane electrode after the first level of recycling has only recovered 25%, and it cannot be used efficiently again, indicating that the membrane electrode after the first level of recycling has failed.

[0210] (II) Secondary recovery: recovery of precious metals from the catalytic layer;

[0211] (A) Fixing the membrane electrode that has no effect in the first-stage recovery to the base of the stripping machine, preparing for the catalytic layer stripping;

[0212] (B) A scraper was installed on a homemade automatic stripping machine, maintained at a 45° angle to the plane, and the blade was controlled to slide back and forth (the blade's speed during the back-and-forth sliding was 10 mm / s, and the number of back-and-forth sliding cycles was 30) to strip the precious metal catalyst with poor surface adhesion on the upper surface of the catalytic layer;

[0213] (C) until the blade can no longer peel off the precious metal catalyst, then the stripper starts to add ethanol water solution (the volume ratio of water to alcohol is 97:3) while adding the solution (the rate of addition is 0.5 drops / s) while stripping with a scraper (the blade moves at a speed of 15 mm / s during the reciprocating sliding, and the number of reciprocating sliding is 20 times) until the precious metal catalyst layer on the surface is completely stripped off;

[0214] (D) After the stripped noble metal catalyst layer was ground to an average particle size of 150 nm, ionomer PFSA and n-propanol were added (wherein the mass ratio of the noble metal catalyst layer powder, ionomer, and n-propanol was 100:5:200), and the mixture was ball-milled to obtain a slurry; the slurry was completely coated on a polytetrafluoroethylene substrate (1 mL / cm 2 ), and then re-hot-pressed at 120°C and 2MPa to recover the membrane electrode for reuse;

[0215] (E) The recovered membrane electrode was assembled and electrochemical testing was performed.

[0216] Test results:

[0217] The calculated recovery rates of precious metals on the second-stage membrane electrode are shown in Table 2 below:

[0218] Table 2

[0219]

[0220] like Figure 8 As shown in the figure, the performance difference between the membrane electrode after the second stage recovery and the freshly prepared membrane electrode can be found at the same current density of 2A / cm 2For example, the performance of the membrane electrode after secondary recovery was 20mV higher than that of the membrane electrode that failed in the first recovery, and was 70mV lower than that of the freshly prepared membrane electrode. After the secondary recovery process, the performance was only restored by 22%, and it could not be used efficiently again, indicating that the membrane electrode after the secondary recovery had failed.

[0221] (III) Tertiary recovery: recovery of precious metals from precious metal catalysts;

[0222] (A) The noble metal catalyst cannot be recovered in the first and second stages. The membrane electrode is fixed on the base of a stripping machine to prepare for stripping of the noble metal catalyst layer. A scraper is installed on the homemade automatic stripping machine, maintained at 45° to the plane, and the blade is controlled to slide back and forth (the blade moves at a speed of 10 mm / s during the back-and-forth sliding, and the number of times the blade slides back and forth is 30 times) to strip the noble metal catalyst with poor surface binding force on the surface above the catalyst layer. When the blade cannot strip the catalyst anymore, the stripping machine starts to drip an ethanol aqueous solution (the volume ratio of water to alcohol is 97:3) while dripping (the dripping rate is 0.5 drops / s) while stripping with a scraper (the blade moves at a speed of 15 mm / s during the back-and-forth sliding, and the number of times the blade slides back and forth is 20 times) until the noble metal catalyst layer on the surface is completely stripped. The stripped noble metal catalyst layer is ground and pulverized to an average particle size of 150 nm to obtain 10 g of pulverized iridium-containing catalyst and platinum-containing catalyst, respectively.

[0223] (B) adding 10 g of the crushed noble metal catalyst to 100 g of aqua regia, heating and dissolving at 100° C. for 6 h to obtain aqua regia solutions containing iridium and platinum catalyst layer powders, respectively;

[0224] (C) adsorbing the aqueous regia solutions containing the iridium and platinum catalyst layer powders respectively through an ion exchange resin (Amberjet 4200Cl resin, the resin concentration required to absorb each gram of precious metal is 8 g / L), and then desorbing the solution through a desorption solution (2 mol / L sodium hydroxide solution) to obtain exchange solutions;

[0225] (D) adding 5 g / L ammonium chloride to the exchange solution at 25° C., and allowing to stand for 2 hours for precipitation to obtain a solution containing a precipitate;

[0226] (E) filtering and drying the solution containing the precipitate to recover chloroiridic acid and chloroplatinic acid.

[0227] Test results:

[0228] The calculated recovery rates of precious metals on the second-stage membrane electrode are shown in Table 3 below:

[0229] Table 3

[0230]

[0231] Example 4

[0232] This embodiment provides an economical and efficient method for recovering precious metal catalysts in PEM water electrolysis, the recovery method comprising the following steps:

[0233] (I) Primary recovery: recovery of precious metals from membrane electrodes;

[0234] (A) A used intact membrane electrode (proton exchange membrane: Nafion membrane, catalytic layer: anode catalytic layer composed of IrO2 catalyst and Nafion perfluorosulfonic acid ionomer, mass ratio of 5:1; cathode catalytic layer composed of Pt / C catalyst and Nafion perfluorosulfonic acid ionomer, mass ratio of 8:1) was activated by immersion in 1M H2SO4 aqueous solution at 20°C for 12 h to obtain an acid-activated membrane electrode.

[0235] (B) Soaking the acid-activated membrane electrode in deionized water at 20°C for 3 h to remove excess acid on the surface, thereby obtaining a washed membrane electrode.

[0236] (C) drying the washed membrane electrode at 70° C. for 1 hour to remove excess moisture from the membrane electrode to obtain a dry membrane electrode;

[0237] (D) re-hot pressing the dried membrane electrode at 110°C and a pressure of 3 MPa to recover the membrane electrode for reuse;

[0238] (E) The recovered membrane electrode was assembled and electrochemical testing was performed.

[0239] Test results:

[0240] Calculations show that the recovery rate of precious metals on the first-stage membrane electrode is 100%, and the membrane electrode after the first-stage recovery has become ineffective.

[0241] (II) Secondary recovery: recovery of precious metals from the catalytic layer;

[0242] (A) Fixing the membrane electrode that has no effect in the first-stage recovery to the base of the stripping machine, preparing for the catalytic layer stripping;

[0243] (B) A scraper was installed on a homemade automatic stripping machine, maintained at a 45° angle to the plane, and the blade was controlled to slide back and forth (the blade's speed during the back-and-forth sliding was 15 mm / s, and the number of back-and-forth sliding cycles was 25) to strip the precious metal catalyst with poor surface adhesion on the upper surface of the catalytic layer;

[0244] (C) until the blade can no longer strip the precious metal catalyst, then the stripper begins to dropwise add n-propanol aqueous solution (water to alcohol volume ratio of 95:5), while adding dropwise (dropping rate of 1 drop / s) while stripping with a scraper (the blade moves at a speed of 13 mm / s during the reciprocating sliding, and the number of reciprocating sliding cycles is 30) until the precious metal catalyst layer on the surface is completely stripped;

[0245] (D) After the stripped noble metal catalyst layer was ground to an average particle size of 160 nm, ionomer PFSA and n-propanol were added (wherein the mass ratio of the noble metal catalyst layer powder, ionomer, and ethanol was 100:5:250), and the mixture was ball-milled to obtain a slurry; the slurry was completely coated on a polyvinylidene fluoride substrate (0.5 mL / cm 2 ), and then hot-pressed again at 110°C and 3MPa to recover the membrane electrode for reuse;

[0246] (E) The recovered membrane electrode was assembled and electrochemical testing was performed.

[0247] Test results:

[0248] The calculated recovery rates of precious metals on the second-stage membrane electrode are shown in Table 4 below:

[0249] Table 4

[0250]

[0251] And the membrane electrode after secondary recovery has become invalid.

[0252] (III) Tertiary recovery: recovery of precious metals from precious metal catalysts;

[0253] (A) The noble metal catalyst could not be recovered in the first and second stages, and the membrane electrode was fixed on the base of the stripping machine to prepare for stripping of the catalytic layer; a scraper was installed on the homemade automatic stripping machine, maintained at 45° to the plane, and the blade was controlled to slide back and forth (the blade moved at a speed of 12 mm / s during the back-and-forth sliding, and the number of times the blade slid back and forth was 28 times) to strip the catalyst with poor surface binding force on the surface above the catalytic layer; until the blade could no longer strip the catalyst, the stripping machine began to drip ethanol aqueous solution (the volume ratio of water to alcohol was 96:4), and the dripping speed was 2 drops / s while stripping with a scraper (the blade moved at a speed of 16 mm / s during the back-and-forth sliding, and the number of times the blade slid back and forth was 34 times) until the noble metal catalytic layer on the surface was completely stripped; the stripped noble metal catalytic layer was ground and pulverized to an average particle size of 120 nm to obtain 5 g of pulverized iridium-containing catalyst and platinum-containing catalyst, respectively;

[0254] (B) adding 5 g of the crushed catalyst to 50 g of aqua regia solution and heating and dissolving the mixture at 90° C. for 10 h to obtain aqua regia solutions containing iridium and platinum catalyst layer powders, respectively;

[0255] (C) adsorbing the aqueous regia solutions containing the iridium and platinum catalyst layer powders respectively by ion exchange resin (Lewatit-MP-62 resin, the resin concentration required to absorb each gram of precious metal is 4 g / L), and then desorbing the solution by desorption by a desorption solution (2 mol / L sodium thiosulfate solution) to obtain exchange solutions;

[0256] (D) adding 10 g / L ammonium chloride to the exchange solution at 30° C., and allowing to stand for 3 hours for precipitation to obtain a solution containing a precipitate;

[0257] (E) filtering and drying the solution containing the precipitate to recover chloroiridic acid and chloroplatinic acid.

[0258] Test results:

[0259] The calculated recovery rates of precious metals on the second-stage membrane electrode are shown in Table 5 below:

[0260] Table 5

[0261]

[0262] Example 5

[0263] This embodiment provides a method for recovering precious metal iridium from PEM electrolyzed water, the method comprising the following steps:

[0264] (I) Primary recovery: recovery of iridium from the membrane electrode;

[0265] (A) A used intact membrane electrode (proton exchange membrane: Nafion membrane, catalytic layer: anode catalytic layer composed of IrO2 catalyst and Nafion perfluorosulfonic acid ionomer, mass ratio of 5:1; cathode catalytic layer composed of Pt / C catalyst and Nafion perfluorosulfonic acid ionomer, mass ratio of 8:1) was activated by immersion in 1M H2SO4 aqueous solution at 35°C for 12 h to obtain an acid-activated membrane electrode.

[0266] (B) The membrane electrode after acid leaching activation was immersed in deionized water at 30°C for 5 h to remove excess acid on the surface, thereby obtaining a washed membrane electrode;

[0267] (C) drying the washed membrane electrode at 65°C for 4 hours to remove excess moisture from the membrane electrode to obtain a dry membrane electrode;

[0268] (D) re-hot pressing the dried membrane electrode at 113°C and 3 MPa to recover the membrane electrode for reuse;

[0269] (E) The recovered membrane electrode was assembled and electrochemical testing was performed.

[0270] Test results:

[0271] Calculations show that the recovery rate of precious metals on the first-stage membrane electrode is 100%, and the membrane electrode after the first-stage recovery has become ineffective.

[0272] (II) Secondary recovery: recovery of precious metals from the catalytic layer;

[0273] (A) Fixing the membrane electrode that has no effect in the first-stage recovery to the base of the stripping machine, preparing for the catalytic layer stripping;

[0274] (B) A scraper was installed on a homemade automatic stripping machine, held at a 45° angle to the plane, and the blade was controlled to slide back and forth (the blade's speed during the back-and-forth sliding was 19 mm / s, and the number of back-and-forth sliding cycles was 26) to strip the catalyst with poor surface adhesion on the upper surface of the catalytic layer;

[0275] (C) until the blade is unable to peel off the catalyst, then the stripper begins to drip ethylene glycol aqueous solution (water to alcohol volume ratio of 94:6), while adding the solution at a rate of 1.5 drops / s while stripping with a scraper (the blade moves at a speed of 22 mm / s during the reciprocating sliding, and the number of reciprocating sliding cycles is 33 times) until the surface precious metal catalyst layer is completely stripped off;

[0276] (D) After the stripped noble metal catalyst layer was ground to an average particle size of 90 nm, ionomer PFSA and n-propanol were added (wherein the mass ratio of the noble metal catalyst layer powder, ionomer, and isopropanol was 100:5:280); the slurry was completely coated on a polytrifluoroethylene substrate (1.2 mL / cm 2 ), and then re-hot-pressed at 125°C and 4MPa to recover the membrane electrode for reuse;

[0277] (E) The recovered membrane electrode was assembled and electrochemical testing was performed.

[0278] Test results:

[0279] The calculated recovery rates of precious metals on the second-stage membrane electrode are shown in Table 6 below:

[0280] Table 6

[0281]

[0282] And the membrane electrode after secondary recovery has become invalid.

[0283] (III) Tertiary recovery: recovery of precious metals from precious metal catalysts;

[0284] (A) The noble metal catalyst could not be recovered in the first and second stages, and the membrane electrode was fixed on the base of the stripping machine to prepare for stripping of the catalytic layer; a scraper was installed on the homemade automatic stripping machine, maintained at 45° to the plane, and the blade was controlled to slide back and forth (the speed of the blade in the back and forth sliding was 6.5 mm / s, and the number of back and forth sliding was 36 times) to strip the catalyst with poor surface binding force on the surface above the catalytic layer; until the blade could no longer strip the catalyst, the stripping machine began to drip ethanol aqueous solution (the volume ratio of water to alcohol was 92:8), and the dripping speed was 1.8 drops / s while stripping with a scraper (the speed of the blade in the back and forth sliding was 13 mm / s, and the number of back and forth sliding was 27 times) until the noble metal catalyst layer on the surface was completely stripped; the stripped noble metal catalyst layer was ground and pulverized to an average particle size of 140 nm to obtain 8 g of pulverized iridium-containing catalyst and platinum-containing catalyst, respectively;

[0285] (B) adding 8 g of the crushed catalyst to 80 g of aqua regia, heating and dissolving at 95° C. for 8 h to obtain aqua regia solutions containing iridium and platinum catalytic layer powders at 95° C.;

[0286] (C) adsorbing the aqueous regia solutions containing the iridium and platinum catalyst layer powders respectively by ion exchange resin (Lewatit-MP-62 resin, the resin concentration required to absorb each gram of precious metal is 8 g / L), and then desorbing the solution by desorption by a desorption solution (1.2 mol / L thiourea solution) to obtain exchange solutions;

[0287] (D) adding 12 g / L ammonium chloride to the exchange solution at 28° C., allowing the solution to stand for 3.5 hours for precipitation, and obtaining a solution containing a precipitate at 10° C.;

[0288] (E) filtering and drying the solution containing the precipitate to recover chloroiridic acid and chloroplatinic acid.

[0289] Test results:

[0290] The calculated recovery rates of precious metals on the second-stage membrane electrode are shown in Table 7 below:

[0291] Table 7

[0292]

[0293] In summary, the recycling method described in the application uses an automatic stripping machine and a specific angle blade to effectively strip the precious metal catalyst layer, improves the recycling rate of platinum group metals, and realizes efficient recovery and recycling of precious metal catalysts in PEM water electrolysis. In addition, the improved recycling method reduces environmental pollution, especially reducing the environmental burden brought by traditional fire and wet methods. Improving the recycling rate of platinum group metals helps the sustainable development and large-scale application of PEM water electrolysis technology.

[0294] The application improves the use rate of platinum group metals in PEM water electrolysis by classifying, grading and accurately recycling platinum group metals in different use conditions in PEM water electrolysis, effectively solving the problem of scarcity of platinum group metal resources in PEM water electrolysis. The first level recovery: for the used membrane electrode without damage, the precious metal is recovered through acid activation and hot pressing steps, and reused. The second level recovery is for damaged membrane electrodes or membrane electrodes that are ineffective in the first level recovery, stripping the unused precious metal catalyst from the membrane electrode, reconfiguring the slurry and preparing the membrane electrode for reuse. The third level recovery is for platinum group metals that cannot be recovered in the first and second levels, and the precious metal is recovered by wet method.

[0295] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the application, and not to limit them; although the application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the application.

Claims

1. A method for recovering precious metal catalysts in proton exchange membrane electrolysis of water, characterized in that: The recovery method comprises the following steps: Primary recycling: The used complete membrane electrode is acid-leached, activated, washed, dried and hot-pressed in sequence to recover the membrane electrode; determine whether the membrane electrode after the primary recycling treatment is invalid. If the membrane electrode after the primary recycling treatment is invalid, secondary recycling is carried out; Secondary recovery: The precious metal catalyst layers on the anode and cathode sides of the membrane electrode that has failed after primary recovery are sequentially subjected to dry stripping, wet stripping and pulverization to obtain precious metal catalyst layer powder; the precious metal catalyst layer powder, ionomer and solvent are mixed and ball milled to obtain a slurry; the slurry is sequentially coated and hot pressed to recover the membrane electrode; whether the membrane electrode after secondary recovery treatment has failed is determined. If the membrane electrode after secondary recovery treatment has failed, tertiary recovery is carried out; wherein, in the secondary recovery, the ionomer is perfluorosulfonic acid and the solvent is n-propanol; Tertiary recovery: Dry stripping, wet stripping, and pulverization are performed on the precious metal catalyst layer on the membrane electrode that has failed after primary and secondary recovery to obtain precious metal catalyst layer powder. The precious metal catalyst layer powder is dissolved in aqua regia and then subjected to ion exchange, precipitation, and filtration to recover chloroplatinic acid and chloroiridic acid. Among them, in the secondary recovery and tertiary recovery, the dry stripping method is specifically as follows: first, the membrane electrode is fixed on the base of the stripping machine, and then a blade is installed on the stripping machine, and the blade is controlled to slide back and forth on the noble metal catalyst layers on the positive and negative sides of the membrane electrode; the wet stripping method is specifically as follows: a water-alcohol solution is dripped onto the surface of the membrane electrode after the dry stripping, and while dripping, the blade is controlled to slide back and forth on the noble metal catalyst layers on the positive and negative sides of the membrane electrode until the noble metal catalyst layers on the positive and negative sides of the membrane electrode are completely stripped; Among them, in the three-stage recovery, the ion exchange is specifically: the aqueous regia solution of the precious metal catalyst layer powder is adsorbed by an ion exchange resin, and then desorbed by a desorption liquid to obtain an exchange liquid; the ion exchange resin includes any one of Amberjet 4200 Cl, Lewatit-MP-62 or Amberlite IRA-67; the solute in the desorption liquid includes any one of sodium hydroxide, sodium thiosulfate or thiourea, or a combination of at least two of them.

2. The method for recovering a noble metal catalyst in proton exchange membrane electrolysis water according to claim 1, wherein: The acid immersion activation specifically includes: placing the membrane electrode in an acid solution for immersion.

3. The method for recovering a noble metal catalyst in proton exchange membrane electrolysis water according to claim 2, wherein: The acid solution used in the acid leaching activation is sulfuric acid and / or nitric acid.

4. The method for recovering a noble metal catalyst in proton exchange membrane electrolysis water according to claim 3, wherein: The acid solution used in the acid leaching activation is sulfuric acid.

5. The method for recovering precious metal catalysts in proton exchange membrane electrolysis water according to claim 2, characterized in that: The concentration of the acid is 0.5-1.5 M.

6. The method for recovering precious metal catalysts in proton exchange membrane electrolysis water according to claim 5, characterized in that: The concentration of the acid was 1.0 M.

7. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, wherein: The temperature of the acid leaching activation is 10-30° C., and the time of the acid leaching activation is 6-18 h.

8. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, characterized in that: In the primary recovery, the solvent used for washing is deionized water.

9. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, wherein: In the primary recovery, the drying temperature is 60-80° C., and the drying time is 1-4 h.

10. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, wherein: In the primary recovery, the temperature of the hot pressing is 110-140° C., and the pressure of the hot pressing is 2-5 MPa.

11. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, characterized in that: In the secondary recovery, the angle between the blade and the horizontal plane is 40-50°.

12. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 11, characterized in that: In the secondary recovery, the angle between the blade and the horizontal plane is 45°.

13. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, wherein: In the secondary recovery, the blade moves at a speed of 5 to 20 mm / s in the reciprocating sliding motion, and the number of reciprocating sliding motions is 20 to 40 times.

14. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, characterized in that: In the secondary recovery, the alcohol in the hydroalcoholic solution includes any one of methanol, ethanol, n-propanol, isopropanol, tert-butanol, ethylene glycol, propylene glycol or glycerol, or a combination of at least two thereof.

15. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, characterized in that: In the secondary recovery, the volume ratio of water to alcohol in the hydroalcohol solution is (90-97):(3-10).

16. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, wherein: In the secondary recovery, the pulverization is carried out by grinding; wherein the particle size of the precious metal catalyst layer powder obtained after the pulverization is 50~400 nm.

17. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, characterized in that: In the secondary recovery, the mass ratio of the noble metal catalyst layer powder, ionomer and solvent is 100:(5-20):(200-300).

18. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, wherein: In the secondary recovery, the coating amount of the slurry is 0.5~2 mL / cm 2 .

19. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, characterized in that: In the secondary recycling, the base material used in the coating includes any one of polytetrafluoroethylene, polyvinylidene fluoride or polychlorotrifluoroethylene.

20. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, wherein: In the secondary recovery, the temperature of the hot pressing is 110-140° C., and the pressure of the hot pressing is 2-5 MPa.

21. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, characterized in that: In the three-stage recovery, the mass ratio of the noble metal catalyst layer powder to aqua regia is 1:(5-20).

22. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, wherein: In the three-stage recovery, the dissolution temperature is 70-110° C., and the dissolution time is 6-12 h.

23. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, wherein: During the adsorption process, the resin concentration required to absorb each gram of precious metal is 2-10 g / L.

24. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, wherein: During the desorption process, the concentration of the desorption liquid is 0.05-2 mol / L.

25. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, characterized in that: In the three-stage recovery, the precipitation is specifically: adding a precipitant to the exchange liquid obtained by ion exchange to obtain a precipitate.

26. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 25, characterized in that: The precipitant is ammonium chloride.

27. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 25, wherein: The concentration of the precipitant is 5-25 g / L.

28. The method for recovering precious metal catalysts in proton exchange membrane water electrolysis according to claim 1, wherein: The precipitation temperature is 25-40° C., and the precipitation time is 1-5 h.

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