Method for recovering noble metal catalyst in proton exchange membrane electrolyzed water

Abstract

The invention provides a method for recovering a noble metal catalyst in proton exchange membrane electrolyzed water, and relates to the technical field of electrolyzed water. The recovery method comprises the following steps: primary recovery: sequentially carrying out acid leaching activation, washing, drying and hot pressing on a membrane electrode, and recovering to obtain the membrane electrode; secondary recovery: sequentially performing dry stripping, wet stripping and grinding 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 carrying out ball milling to obtain slurry; coating and hot-pressing the slurry in sequence, and recovering to obtain a membrane electrode; and third-stage recovery: dissolving the noble metal catalyst layer powder in aqua regia, sequentially carrying out ion exchange, precipitation and filtration, and recovering to obtain chloroiridic acid and chloroplatinic acid. The efficient and accurate stepped recovery method of the noble metal catalyst is provided, the problem of the bottleneck of platinum group metal resources in the PEM electrolyzed water is solved, and a feasible path is provided for efficient utilization of the platinum group metal.

Description

Technical Field

[0001] The 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, iridium metal is used as a catalyst for the anode oxygen evolution reaction due to its good activity and stability under acidic conditions. Platinum metal is used as a cathode catalyst due to its good hydrogen evolution activity. Both iridium metal and platinum metal belong to the platinum group metals. However, the further expansion and large-scale application of PEM water electrolysis 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, iridium metal 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 water electrolysis capacity and its large-scale application, and has become a resource "bottleneck" for PEM water electrolysis. There are two ways to solve the "bottleneck" of insufficient platinum group metal resources in the large-scale layout of the PEM water electrolysis industry. One is to significantly reduce the loading of precious metal catalysts in PEM water electrolysis, and the other is to develop efficient precious metal catalyst recovery technology. At present, 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 water electrolysis are limited by the supply of platinum group metal resources. In the current situation where the catalyst loading cannot be significantly reduced in the short term, it is urgent to develop new and efficient recovery methods to solve the bottleneck of scarce platinum group metals in PEM water electrolysis.

[0004] There are few literature reports on the recovery methods of precious metal catalysts in PEM water electrolysis. The current industry uses traditional pyrometallurgy and hydrometallurgy for the recovery of precious metal catalysts. Due to the high melting point of platinum group metals (for example, the melting point of metal iridium is 2446°C), they need to be melted at high temperatures in pyrometallurgical recovery, which consumes a lot of energy and easily releases harmful gas HF during combustion, which is not environmentally sustainable. In hydrometallurgical recovery, recovery is mainly carried out through four main steps: pretreatment, dissolution, separation and purification, and precipitation. The wet recovery of precious metals has lengthy steps, cumbersome operations, low total recovery rate, and requires the use of a large amount of chemical reagents, which pollutes the environment, has low economic efficiency, and is not sustainable. In addition, in PEM water electrolysis, the recycling process of precious metals is: synthesizing a catalyst from a precursor containing precious metal elements, mixing the catalyst with a solvent and an ionomer to prepare a slurry, coating the slurry as a catalytic layer, and finally hot pressing to form a membrane electrode. The prepared membrane electrode is directly recycled by wet and pyrometallurgical recovery after use. Through the recycling process of precious metals, it can be found that the circulation period 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 water electrolysis: 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 catalyst layer on both sides of the positive and negative sides is stripped by ultrasonic water circulation to recover the catalyst. Since the catalyst layer is stripped by ultrasound, the ultrasonic time and power depend on the thickness and area of ​​the catalyst layer. In addition, the membrane electrode needs to be fixed in a homemade reactor, and the catalysts on both sides of the positive and negative sides are isolated by a proton membrane. The precious metal catalyst on the damaged membrane electrode cannot be recovered by this method. Therefore, the membrane electrode recovery method currently reported is only suitable for the recovery of precious metal catalysts from a small area of ​​membrane electrode, and cannot be used 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 needs to recover precious metal catalysts from intact membrane electrodes, which is not suitable for the recovery of precious metal catalysts in 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 particularly adopted:

[0009] The present invention provides a method for recovering a noble 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: dry-stripping, wet-stripping and crushing the precious metal catalyst layer on both sides of the membrane electrode in turn to obtain precious metal catalyst layer powder; mixing the precious metal catalyst layer powder, ionomer and solvent, and obtaining slurry after ball milling; coating and hot pressing the slurry in turn 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 recovery, 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 damaged membrane electrode and / or a membrane electrode that has failed after 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: a water-alcohol solution is dripped onto the surface of the membrane electrode after dry stripping, and while dripping, a 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.

[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 the 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, the ionomer and the 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 primary recovery and the secondary 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 0.05-2 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 an accurate and efficient cascade recovery method for the recovery and utilization 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 implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

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

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

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

[0054] Figure 4 This is a polarization curve diagram before and after the first-level recovery provided in Example 1.

[0055] Figure 5 This is a polarization curve diagram before and after the first-level recovery provided in Example 2.

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

[0057] Figure 7 This is a polarization curve diagram before and after the first-level 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 case of any potential ambiguity, the definitions provided herein take precedence over any dictionary or external definitions. In this application, unless otherwise stated, the use of "or" means "and / or". In addition, the use of the term "including" and other forms is non-limiting.

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

[0061] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work 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 a 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 (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 why the present invention proposes "cascade recovery" is mainly based on two aspects: the PEM electrolyzer platinum group metal circulation process and the utilization rate of precious metal catalysts. The main reasons for the performance degradation of the PEM electrolyzer 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 the storage process of the membrane electrode or in the operating channel, which poison the membrane electrode, causing the hydrogen ions on the perfluorosulfonate groups in the proton exchange membrane and the ionomer to be replaced by metal ions. Since the metal ions migrate slowly under the action of the electric field, proton conduction is blocked and performance declines. In addition, the migration of the ionomer in the catalytic layer and the degradation and dissolution of the catalyst cause changes in the catalytic layer structure, resulting in performance decline.

[0067] Based on the above two reasons, the present invention first provides a primary recovery, that is, for a complete and undamaged used membrane electrode, acid activation and hot pressing and other process steps are performed to restore its performance close to the initial level, so as to realize the recovery and use of platinum group metals (for example, iridium and / or platinum) from the membrane electrode layer. In addition, in PEM electrolysis of water, the catalyst in the catalytic layer causes a dead zone of reactive activity due to agglomeration and ionomer wrapping, and the effective utilization rate of the catalyst is only about 20%. The present invention contemplates whether the remaining 80% of the catalyst in the used catalytic layer still has catalytic activity and can be reused until it is inactivated. Therefore, the present invention further provides a secondary recovery. For a membrane electrode that is damaged due to an accident or the first-level recovery is ineffective, the catalytic layer containing precious metals is peeled off, the slurry is reconfigured, and the membrane electrode is prepared for reuse, so as to realize the recovery of platinum group metals from the catalytic layer. In particular, the present invention further provides a third-level recovery of platinum group metals from precious metal catalysts for the first and second levels that cannot recover platinum group metals. At present, the third level is mainly recovered by wet method.

[0068] Therefore, based on the scarcity of platinum group metal resources in PEM water electrolysis systems and the imperfection of existing recovery methods, an economical and efficient recovery method for precious metal catalysts in PEM water electrolysis is provided. This method performs "step-by-step recovery" of platinum group metals in PEM water electrolysis, starting from the three levels of membrane electrode, catalytic layer, and catalyst, to implement accurate recovery and efficient utilization of platinum group metals.

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

[0070] As an optional embodiment of the present invention, in the primary recovery, the acid immersion activation is specifically: placing the membrane electrode in an acid solution for immersion.

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

[0072] As an optional embodiment of the present invention, 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 10-30°C, for example, it can be 10°C, 15°C, 20°C, 25°C, 30°C, etc., and the time of the acid leaching activation is 6-18h, for example, it can be 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 an 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 hot-pressed again, 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) further includes step (E): assembling the recovered membrane electrode and performing electrochemical testing.

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

[0086] As an optional embodiment of the present invention, in the secondary recovery, 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 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: dripping a water-alcohol solution onto the surface of the membrane electrode after dry stripping, and while dripping, 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 off.

[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 hydroalcohol 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, “3-10” 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 in a grinding manner; 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, the ionomer and the 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 0.5-2 mL / cm 2 , for example, it can be 0.5 mL / 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 substrate of the stripping machine to prepare for the catalytic layer stripping;

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

[0108] (C) until the blade can no longer peel off the lower catalyst layer, then the stripping machine starts to drip the water-alcohol solution, and the scraper is used to peel off while dripping, until the surface precious metal catalyst layer is completely peeled off;

[0109] (D) The stripped precious 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) further includes 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 primary recovery and the secondary 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: 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 precious metal catalyst layer on the positive and negative sides of the membrane electrode.

[0115] As an optional embodiment of the present invention, in the three-stage recovery, the wet stripping is specifically: dripping a water-alcohol solution onto the surface of the membrane electrode after dry stripping, and while dripping, 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 positive and negative sides of the membrane electrode is completely stripped.

[0116] As an optional embodiment of the present invention, in the three-stage 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°.

[0117] As an optional embodiment of the present invention, in the three-stage 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.

[0118] As an optional embodiment of the present invention, in the three-stage recovery, the number of reciprocating sliding is 20 to 40 times, for example, 20 times, 25 times, 30 times, 35 times, 40 times, etc.

[0119] As an optional embodiment of the present invention, in the tertiary recovery, the alcohol in the hydroalcohol 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.

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

[0121] Among them, "90-97" can be, for example, 90, 91, 92, 93, 94, 95, 96, 97, etc.;

[0122] Here, “3-10” can be, for example, 3, 4, 5, 6, 7, 8, 9, 10, etc.

[0123] As an optional embodiment of the present invention, in the three-stage 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, 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 precious metal catalyst layer powder by an ion exchange resin, and then desorbing it by 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 Amberjet4200Cl, 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 solution 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 0.05-2 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 positive and negative sides are peeled off, collected, crushed, and recovered by a wet method;

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

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

[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 are 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 embodiments and comparative examples are as follows:

[0143] Among them, 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] Among them, the calculation formula of dry recovery rate in secondary recovery is shown in the following 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] Among them, the calculation formula for the wet recovery rate in secondary recovery is shown in the following 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] Among them, the calculation formula for the total recovery rate of secondary recovery is shown in the following formula II-3:

[0153]

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

[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 precious 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 three-stage recovery is shown in the following formula III-2:

[0159]

[0160] Among them, 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 desorption solution, V 31 Represents the volume of the desorption liquid.

[0161] The calculation formula for the recovery rate of the metal iridium precipitation separation step in the three-stage recovery is shown in the following formula III-3:

[0162]

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

[0164] Among them, the calculation formula for the total recovery rate of metal iridium in the tertiary recovery is shown in the following formula III-4:

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

[0166] Among them, R3 represents the total recovery rate of precious metals in tertiary recycling.

[0167] Example 1

[0168] This embodiment provides a method for recovering a precious metal catalyst in PEM electrolysis of water, the method comprising the following steps:

[0169] Primary recovery: recovery of precious metals from membrane electrodes;

[0170] (A) A used complete membrane electrode (proton exchange membrane: Nafion membrane, catalyst layer: anode catalyst layer composed of IrO2 catalyst and Nafion perfluorosulfonic acid ionomer, the mass ratio of the two is 5:1; cathode catalyst layer composed of Pt / C catalyst and Nafion perfluorosulfonic acid ionomer, the mass ratio of the two is 8:1) was immersed in a 1M H2SO4 aqueous solution at 25°C for 12 h for activation treatment to obtain an acid-activated membrane electrode;

[0171] (B) Soaking the membrane electrode activated by acid immersion in deionized water at 25°C for 2 hours to remove excess acid on the surface, thereby obtaining a washed membrane electrode;

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

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

[0174] (E) The recovered membrane electrode was assembled and electrochemically tested.

[0175] Test results: The recovery rate of precious metals on the first-stage membrane electrode was calculated to be 100%.

[0176] like Figure 4 As shown in the figure, by comparing the performance differences between the membrane electrode before and after the first stage of recovery and the freshly prepared membrane electrode, it can be found that at the same current density, at 2A / cm 2 For example, the performance of the membrane electrode after primary recycling recovered 100mV, which was only 20mV lower than that of the freshly prepared membrane electrode. The performance of the used membrane electrode recovered 83% after primary recycling.

[0177] Example 2

[0178] This embodiment provides a method for recovering a precious metal catalyst in PEM electrolysis of water, the method comprising the following steps:

[0179] (I) Primary recovery: recovery of precious metals from membrane electrodes;

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

[0181] (B) Soaking the membrane electrode activated by acid immersion in deionized water at 25°C for 2 hours to remove excess acid on the surface, thereby obtaining a washed membrane electrode;

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

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

[0184] (E) The recovered membrane electrode was assembled and electrochemically tested.

[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, by comparing the performance differences between the membrane electrode before and after the first stage of recovery and the freshly prepared membrane electrode, it can be found that at the same current density, at 2A / cm 2 For example, the performance of the membrane electrode after the first-level recycling only recovered 30mV, which is 90mV different from the freshly prepared membrane electrode. The performance of the used membrane electrode after the first-level recycling process only recovered 25%, and it could not be used efficiently again, indicating that the membrane electrode after the first-level recycling has failed.

[0188] (II) Secondary recovery:

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

[0190] (B) Installing a scraper on a homemade automatic stripping machine, keeping it at 45° to the plane, and controlling the blade to slide back and forth (the blade's moving speed in the back and forth sliding is 10 mm / s, and the number of back and forth sliding is 30 times), to strip the precious metal catalyst with poor surface bonding force on the surface above the catalyst layer;

[0191] (C) until the blade can no longer strip the precious metal catalyst, then the stripping machine starts to drip ethanol aqueous solution (the volume ratio of water to alcohol is 97:3), while dripping (the dripping speed is 0.5 drops / s) and stripping with a scraper (the movement speed of the blade in the reciprocating sliding is 15 mm / s, and the number of reciprocating sliding is 20 times), until the precious metal catalyst layer on the surface is completely stripped;

[0192] (D) After the stripped precious metal catalyst layer is ground to an average particle size of 150 nm, ionomer PFSA and n-propanol (wherein the mass ratio of the precious metal catalyst layer powder, ionomer and n-propanol is 100:5:200) are added and mixed by ball milling to obtain a slurry; the slurry is 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 electrochemically tested.

[0194] Test results:

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

[0196] Table 1

[0197]

[0198] like Figure 6 As shown in the figure, by comparing the performance differences between the membrane electrode before and after the second stage recovery and the freshly prepared membrane electrode, it can be found that at the same current density, at 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 electrolysis of water, the method comprising the following steps:

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

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

[0203] (B) Soaking the membrane electrode activated by acid immersion in deionized water at 25°C for 2 hours 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 water 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 electrochemically tested.

[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, by comparing the performance differences between the membrane electrode before and after the first stage of recovery and the freshly prepared membrane electrode, it can be found that at the same current density, at 2A / cm 2For example, the performance of the membrane electrode after the first-level recycling only recovered 30mV, which is 90mV different from the freshly prepared membrane electrode. The performance of the used membrane electrode after the first-level recycling process only recovered 25%, and it could not be used efficiently again, indicating that the membrane electrode after the first-level recycling has failed.

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

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

[0212] (B) Installing a scraper on a homemade automatic stripping machine, keeping it at 45° to the plane, and controlling the blade to slide back and forth (the blade's moving speed in the back and forth sliding is 10 mm / s, and the number of back and forth sliding is 30 times), to strip the precious metal catalyst with poor surface bonding force on the surface above the catalyst layer;

[0213] (C) until the blade can no longer strip the precious metal catalyst, then the stripping machine starts to drip ethanol aqueous solution (the volume ratio of water to alcohol is 97:3), while dripping (the dripping speed is 0.5 drops / s) and stripping with a scraper (the movement speed of the blade in the reciprocating sliding is 15 mm / s, and the number of reciprocating sliding is 20 times), until the precious metal catalyst layer on the surface is completely stripped;

[0214] (D) After the stripped precious metal catalyst layer is ground to an average particle size of 150 nm, ionomer PFSA and n-propanol are added (wherein the mass ratio of the precious metal catalyst layer powder, ionomer and n-propanol is 100:5:200), and a slurry is obtained after ball milling; the slurry is 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 electrochemically tested.

[0216] Test results:

[0217] The calculated recovery rate of precious metals on the second-stage membrane electrode is 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 that at the same current density, the recovery rate is 2A / cm 2For example, the performance of the membrane electrode after secondary recovery was 20mV higher than that of the failed membrane electrode after primary recovery, and was 70mV lower than that of the freshly prepared membrane electrode. After secondary recovery, the performance was only restored by 22%, and it could not be used efficiently again, indicating that the membrane electrode after 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, and the membrane electrode is fixed on the base of the stripping machine to prepare for stripping of the noble metal catalyst layer; a scraper is installed on the homemade automatic stripping machine, and the angle is kept at 45° to the plane, and the blade is controlled to slide back and forth (the speed of the blade in the reciprocating sliding is 10 mm / s, and the number of reciprocating sliding is 30 times) to strip the noble metal catalyst with poor surface binding force on the surface above the catalyst layer; until the blade cannot strip the catalyst, the stripping machine starts to drip ethanol aqueous solution (the volume ratio of water to alcohol is 97:3), and the scraper is used to strip while dripping (the dripping speed is 0.5 drops / s) (the speed of the blade in the reciprocating sliding is 15 mm / s, and the number of reciprocating sliding is 20 times) until the noble metal catalyst layer on the surface is completely stripped; the stripped noble metal catalyst layer is ground and crushed to an average particle size of 150 nm to obtain 10 g of crushed 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 solution containing iridium and platinum catalyst layer powders respectively through ion exchange resin (Amberjet 4200Cl resin, the resin concentration required to absorb each gram of precious metal is 8 g / L), and then desorbing through desorption liquid (2 mol / L sodium hydroxide solution) to obtain exchange liquid;

[0225] (D) adding 5 g / L ammonium chloride to the exchange solution at 25° C., standing for 2 hours for precipitation, and obtaining 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 rate of precious metals on the second-stage membrane electrode is 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 complete membrane electrode (proton exchange membrane: Nafion membrane, catalyst layer: anode catalyst layer composed of IrO2 catalyst and Nafion perfluorosulfonic acid ionomer, the mass ratio of the two is 5:1; cathode catalyst layer composed of Pt / C catalyst and Nafion perfluorosulfonic acid ionomer, the mass ratio of the two is 8:1) was immersed in a 1M H2SO4 aqueous solution at 20°C for 12 h for activation treatment to obtain an acid-activated membrane electrode;

[0235] (B) Soaking the membrane electrode activated by acid immersion in deionized water at 20°C for 3 hours 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 water 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 electrochemically tested.

[0239] Test results:

[0240] The calculation shows 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 invalid.

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

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

[0243] (B) Installing a scraper on a homemade automatic stripping machine, keeping it at 45° to the plane, and controlling the blade to slide back and forth (the blade's moving speed in the back and forth sliding is 15 mm / s, and the number of back and forth sliding is 25 times), to strip the precious metal catalyst with poor surface bonding force on the surface above the catalyst layer;

[0244] (C) until the blade can no longer strip the precious metal catalyst, then the stripping machine starts to drip an aqueous solution of n-propanol (the volume ratio of water to alcohol is 95:5), while dripping (the dripping speed is 1 drop / s) and stripping with a scraper (the movement speed of the blade in the reciprocating sliding is 13 mm / s, and the number of reciprocating sliding is 30 times) until the precious metal catalyst layer on the surface is completely stripped;

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

[0246] (E) The recovered membrane electrode was assembled and electrochemically tested.

[0247] Test results:

[0248] The calculated recovery rate of precious metals on the second-stage membrane electrode is 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 cannot be recovered in the first and second stages, and the membrane electrode is fixed on the base of the stripping machine to prepare for stripping of the catalyst layer; a scraper is installed on the homemade automatic stripping machine, and the angle is kept at 45° to the plane, and the blade is controlled to slide back and forth (the speed of the blade in the reciprocating sliding is 12 mm / s, and the number of reciprocating sliding is 28 times) to strip the catalyst with poor surface bonding force on the surface above the catalyst layer; until the blade cannot strip the catalyst, the stripping machine starts to drip ethanol aqueous solution (the volume ratio of water to alcohol is 96:4), and the scraper is used to strip while dripping (the dripping speed is 2 drops / s) (the speed of the blade in the reciprocating sliding is 16 mm / s, and the number of reciprocating sliding is 34 times) until the noble metal catalyst layer on the surface is completely stripped; the stripped noble metal catalyst layer is ground and crushed to an average particle size of 120 nm, and 5 g of crushed iridium-containing catalyst and platinum-containing catalyst are obtained respectively;

[0254] (B) adding 5 g of the crushed catalyst to 50 g of aqua regia, heating and dissolving 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 solution containing iridium and platinum catalyst layer powders respectively through 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 through desorption liquid (2 mol / L sodium thiosulfate solution) to obtain exchange liquid;

[0256] (D) adding 10 g / L ammonium chloride to the exchange solution at 30° C. and standing 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 rate of precious metals on the second-stage membrane electrode is shown in Table 5 below:

[0260] Table 5

[0261]

[0262] Example 5

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

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

[0265] (A) A used complete membrane electrode (proton exchange membrane: Nafion membrane, catalyst layer: anode catalyst layer composed of IrO2 catalyst and Nafion perfluorosulfonic acid ionomer, the mass ratio of the two is 5:1; cathode catalyst layer composed of Pt / C catalyst and Nafion perfluorosulfonic acid ionomer, the mass ratio of the two is 8:1) was immersed in a 1M H2SO4 aqueous solution at 35°C for 12 h for activation treatment to obtain an acid-activated membrane electrode;

[0266] (B) Soaking the membrane electrode activated by acid immersion in deionized water at 30°C for 5 hours 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 h to remove excess water 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 electrochemically tested.

[0270] Test results:

[0271] The calculation shows 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 invalid.

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

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

[0274] (B) Installing a scraper on a homemade automatic stripping machine, keeping it at 45° to the plane, and controlling the blade to slide back and forth (the blade's moving speed in the back and forth sliding is 19 mm / s, and the number of back and forth sliding is 26 times), to strip the catalyst with poor surface bonding strength on the surface above the catalyst layer;

[0275] (C) until the blade can no longer strip the catalyst, then the stripper starts to drip ethylene glycol aqueous solution (the volume ratio of water to alcohol is 94:6), while dripping (the dripping speed is 1.5 drops / s) and stripping with a scraper (the movement speed of the blade in the reciprocating sliding is 22 mm / s, and the number of reciprocating sliding is 33 times) until the precious metal catalyst layer on the surface is completely stripped;

[0276] (D) After the stripped precious metal catalyst layer is ground to an average particle size of 90 nm, ionomer PFSA and n-propanol are added (wherein the mass ratio of the precious metal catalyst layer powder, ionomer and isopropanol is 100:5:280); the slurry is 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 electrochemically tested.

[0278] Test results:

[0279] The calculated recovery rate of precious metals on the second-stage membrane electrode is 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 cannot be recovered in the first and second stages, and the membrane electrode is fixed on the base of the stripping machine to prepare for stripping of the 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 6.5 mm / s in the reciprocating sliding, and the number of times in the reciprocating sliding is 36 times) to strip the catalyst with poor surface bonding force on the surface above the catalyst layer; until the blade cannot strip the catalyst, the stripping machine starts to drip ethanol aqueous solution (the volume ratio of water to alcohol is 92:8), dripping (the dripping speed is 1.8 drops / s) while stripping with a scraper (the blade moves at a speed of 13 mm / s in the reciprocating sliding, and the number of times in the reciprocating sliding is 27 times) until the noble metal catalyst layer on the surface is completely stripped; the stripped noble metal catalyst layer is ground and crushed to an average particle size of 140 nm, and 8 g of crushed iridium-containing catalyst and platinum-containing catalyst are obtained 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 catalyst layer powders at 95° C.;

[0286] (C) adsorbing the aqueous regia solution containing iridium and platinum catalyst layer powders respectively through 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 through desorption liquid (1.2 mol / L thiourea solution) to obtain exchange liquid;

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

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

[0289] Test results:

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

[0291] Table 7

[0292]

[0293] In summary, the recovery method of the present invention uses an automatic stripping machine and a blade with a specific angle to effectively strip the precious metal catalyst layer, improve the recycling rate of platinum group metals, and achieve efficient recovery and recycling of precious metal catalysts in PEM electrolysis water. In addition, the improved recovery method reduces environmental pollution, especially reduces the environmental burden caused by traditional pyrolysis and hydrolysis. Improving the recycling rate of platinum group metals is conducive to the sustainable development and large-scale application of PEM electrolysis water technology.

[0294] The present invention improves the utilization rate of platinum group metals in PEM electrolysis water by classifying, gradient and precision recovery of platinum group metals in different usage situations, and effectively solves the problem of scarce platinum group metal resources in PEM electrolysis water. Among them, the first-level recovery: for undamaged used membrane electrodes, precious metals are recovered through acid activation and hot pressing and other steps, and reused. The second-level recovery is for damaged membrane electrodes or membrane electrodes that are ineffective in the first-level recovery. The ineffectively utilized precious metal catalyst is stripped from the membrane electrode, and the slurry is reconfigured and prepared as a 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 metals are recovered by a wet method.

[0295] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

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 recovery: The membrane electrode is acid-activated, washed, dried and hot-pressed in sequence to recover the membrane electrode; Secondary recovery: dry-stripping, wet-stripping and crushing the precious metal catalyst layer on both sides of the membrane electrode in turn to obtain precious metal catalyst layer powder; mixing the precious metal catalyst layer powder, ionomer and solvent, and obtaining slurry after ball milling; coating and hot pressing the slurry in turn to recover the membrane electrode; 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.

2. The method for recovering precious metal catalysts in proton exchange membrane electrolysis water according to claim 1, characterized in that: In the primary recycling, the membrane electrode is a used complete membrane electrode; Preferably, the acid immersion activation specifically comprises: placing the membrane electrode in an acid solution for immersion; Preferably, the acid solution used for the acid leaching activation is sulfuric acid and / or nitric acid, preferably sulfuric acid; Preferably, the concentration of the acid is 0.5 to 1.5 M, preferably 1.0 M; 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.

3. The method for recovering precious metal catalysts in proton exchange membrane electrolysis water according to claim 1, characterized in that: In the primary recovery, the solvent used for washing is deionized water; Preferably, the drying temperature is 60-80°C, and the drying time is 1-4h; Preferably, the temperature of the hot pressing is 110-140° C., and the pressure of the hot pressing is 2-5 MPa.

4. The method for recovering precious metal catalysts in proton exchange membrane electrolysis water according to claim 1, characterized in that: In the secondary recycling, the membrane electrode is a used damaged membrane electrode and / or a membrane electrode that has failed after primary recycling; 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; Preferably, the wet stripping is specifically as follows: dripping a water-alcohol solution onto the surface of the membrane electrode after dry stripping, and while dripping, controlling the blade to slide back and forth on the noble metal catalyst layers on both sides of the membrane electrode until the noble metal catalyst layers on both sides of the membrane electrode are completely stripped; Preferably, the angle between the blade and the horizontal plane is 40-50°, preferably 45°; Preferably, the blade moves at a speed of 5 to 20 mm / s during reciprocating sliding, and the number of reciprocating sliding is 20 to 40 times; 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; Preferably, the volume ratio of water to alcohol in the hydroalcoholic solution is (90-97):(3-10).

5. The method for recovering precious metal catalysts in proton exchange membrane electrolysis water according to claim 1, characterized in that: 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.

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

7. The method for recovering precious metal catalysts in proton exchange membrane electrolysis water according to claim 1, characterized in that: In the secondary recovery, the coating amount of the slurry is 0.5-2 mL / cm 2 ; Preferably, the base material used in the coating includes any one of polytetrafluoroethylene, polyvinylidene fluoride or polychlorotrifluoroethylene; Preferably, the temperature of the hot pressing is 110-140° C., and the pressure of the hot pressing is 2-5 MPa.

8. The method for recovering precious metal catalysts in proton exchange membrane electrolysis water according to claim 1, characterized in that: In the three-stage recycling, the membrane electrode is a membrane electrode that has failed after the first-stage recycling and the second-stage recycling; Preferably, the mass ratio of the noble metal catalyst layer powder to aqua regia is 1:(5-20); Preferably, the dissolution temperature is 70-110° C., and the dissolution time is 6-12 hours.

9. The method for recovering precious metal catalysts in proton exchange membrane electrolysis water according to claim 1, characterized in that: 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; Preferably, the ion exchange resin comprises any one of Amberjet 4200Cl, Lewatit-MP-62 or Amberlite IRA-67; Preferably, during the adsorption process, the resin concentration required to absorb each gram of precious metal is 2 to 10 g / L; Preferably, the solute in the desorption solution includes any one of sodium hydroxide, sodium thiosulfate or thiourea or a combination of at least two thereof; Preferably, during the desorption process, the concentration of the desorption liquid is 0.05-2 mol / L.

10. The method for recovering precious metal catalysts in proton exchange membrane electrolysis water according to claim 1, characterized in that: In the three-stage recovery, the precipitation is specifically: adding a precipitant to the exchange solution obtained by ion exchange to obtain a precipitate; Preferably, the precipitant is ammonium chloride; Preferably, the concentration of the precipitant is 5 to 25 g / L; Preferably, the precipitation temperature is 25-40° C., and the precipitation time is 1-5 hours.

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