EP-4735655-A1 - METHOD FOR CATALYST RECOVERY FROM CATALYST-COATED MEMBRANES

Abstract

A method for recycling anode and/or cathode catalyst from the catalyst coated membranes comprising proton exchange membrane, a continuous nonporous cross-linked polyelectrolyte multilayer coating comprising alternating layers of a polycation polymer and a polyanion polymer, an anode coating layer comprising anode catalyst particles, a cathode coating layer comprising cathode catalyst particles, and optionally a second continuous nonporous cross-linked polyelectrolyte multilayer coating between the second surface of the proton exchange membrane and the cathode coating layer. The cross-linked polyelectrolyte multilayer coating between the proton exchange membrane and the anode and/or cathode catalyst coating layer is dissolved in an aqueous solution with a pH of greater than 7. The catalyst coated membrane is delaminated, and the anode and/or cathode catalyst is recovered.

Inventors

• LIU, CHUNQING
• SHANG, ZHIHAO

Assignees

• UOP LLC

Dates

Publication Date

20260506

Application Date

20240809

Claims (1)

1. What is claimed is: 1. A method for recovering catalyst from a catalyst coated membrane (300) comprising: providing a catalyst coated membrane (300) comprising: a proton exchange membrane (305), the proton exchange membrane (305) having a first surface and a second surface; a first continuous nonporous cross-linked polyelectrolyte multilayer coating (310) on the first surface of the proton exchange membrane (305), the first continuous polyelectrolyte multilayer coating comprising alternating layers of a polycation polymer (315) and a polyanion polymer (320); an anode coating layer (325) comprising anode catalyst particles (330) on the continuous nonporous cross-linked polyelectrolyte multilayer coating (310) on the first surface of the proton exchange membrane (305); a cathode coating layer (335) comprising cathode catalyst particles (340) on the second surface of the proton exchange membrane (305); and optionally a second continuous nonporous cross-linked polyelectrolyte multilayer coating between the second surface of the proton exchange membrane (305) and the cathode coating layer (335); contacting the catalyst coated membrane (300) with an alkaline solution (420) and dissolving the first continuous nonporous cross-linked polyelectrolyte multilayer coating (310) or the first and the second continuous nonporous cross-linked polyelectrolyte multilayer coatings (310); and recovering the anode catalyst particles (330) or recovering both the anode catalyst particles (330) and the cathode catalyst particles (340) separately. 2. The method of claim 1 wherein contacting the catalyst coated membrane (300) with the alkaline solution (420) further comprises heating the catalyst coated membrane (300) and/or the alkaline solution (420), sonicating the catalyst coated membrane (300) and/or the alkaline solution (420), or heating and sonicating the catalyst coated membrane (300) and/or the alkaline solution (420). 3. The method of claim 2 wherein the catalyst coated membrane (300) is heated at a temperature in a range of 30°C to 150°C. 4. The method of any one of claims 1-2 wherein the alkaline solution (420) is added to an anode side of the catalyst coated membrane (300), or a cathode side of the catalyst coated membrane (300), or both the anode side and the cathode side of the catalyst coated membrane (300). 5. The method of any one of claims 1-2 wherein the anode catalyst particles (330) comprise a platinum group metal (PGM), a PGM supported on a different PGM support, a PGM supported on a non-PGM support, an alloy thereof, an oxide thereof, a carbide thereof, a phosphide thereof, or combinations thereof. 6. The method of any one of claims 1-2 wherein the anode catalyst particles (330) comprise iridium, iridium supported on a different PGM support, iridium supported on a non-PGM support, platinum, platinum supported on a non- PGM support, ruthenium, ruthenium supported on a non-PGM support, osmium, rhodium, palladium, tin, tungsten, vanadium, cobalt, silver, gold, copper, nickel, molybdenum, iron, chromium, alloys thereof, oxides thereof, carbides thereof, phosphides thereof, or combinations thereof. 7. The method of any one of claims 1-2 wherein the cathode catalyst particles (340) comprise a platinum group metal (PGM), a PGM supported on a non- PGM support, an alloy thereof, or combinations thereof. 8. The method of any one of claims 1-2 wherein the cathode catalyst particles (340) comprise platinum, platinum supported on a non-PGM support, ruthenium, ruthenium supported on a non-PGM support, osmium, rhodium, palladium, tin, tungsten, vanadium, cobalt, silver, gold, nickel, molybdenum, iron, copper, chromium, alloys thereof, carbides thereof, phosphides thereof, or combinations thereof. 9. The method of any one of claims 1-2 wherein the alkaline solution (420) comprises KOH, NaOH, LiOH, CsOH, KHCO 3 , K 2 CO 3 , LiHCO 3 , Li 2 CO 3 , NaHCO 3 , Na 2 CO 3 , or combinations thereof. 10. The method of any one of claims 1-2: wherein the proton exchange membrane (305) comprises a reinforced proton exchange membrane or a non-reinforced proton exchange membrane; or wherein the catalyst coated membrane (300) further comprises: a continuous nonporous hydrogen recombination catalyst coating layer (345) between the proton exchange membrane layer (305) and the first continuous nonporous cross-linked polyelectrolyte multilayer coating (310), wherein the continuous nonporous hydrogen recombination catalyst coating layer (310) comprises a mixture of a hydrogen recombination catalyst and a proton conducting ionomer, and optionally a radical scavenger; or combinations thereof.

Description

METHOD FOR CATALYST RECOVERY FROM CATALYST-COATED MEMBRANES STATEMENT OF PRIORITY [0001] This application claims priority to United States Patent Application Ser. No. 18/451,327, filed on August 17, 2023, the entirety of which is incorporated herein by reference. BACKGROUND [0002] Hydrogen as an energy vector for grid balancing or power-to-gas and power-to- liquid processes plays an important role in the path toward a low-carbon energy structure that is environmentally friendly. Water electrolysis produces high quality hydrogen by electrochemical splitting of water into hydrogen and oxygen; the reaction is given by Eq. 1 below. The water electrolysis process is an endothermic process and electricity is the energy source. Water electrolysis has zero carbon footprint when the process is operated by renewable power sources, such as wind, solar, or geothermal energy. The main water electrolysis technologies include alkaline electrolysis, proton exchange membrane (PEM) water electrolysis (PEM-WE as shown in Fig. 1), anion exchange membrane (AEM) water electrolysis (AEM-WE as shown in Fig. 2), and solid oxide water electrolysis. [0003] As shown in Fig.1, in a PEM-WE system 100, an anode 105 and a cathode 110 are separated by a solid PEM electrolyte 115, such as a sulfonated tetrafluoroethylene based cofluoropolymer sold under the trademark Nafion® by Chemours company. The anode and cathode catalysts typically comprise IrO2 and Pt, respectively. At the positively charged anode 105, pure water 120 is oxidized to produce oxygen gas 125, electrons (e-), and protons; the reaction is given by Eq. 2. The protons are transported from the anode 105 to the cathode 110 through the PEM 115 that conducts protons. At the negatively charged cathode 110, a reduction reaction takes place with electrons from the cathode 110 being given to protons to form hydrogen gas 130; the reaction is given by Eq.3. The PEM 115 not only conducts protons from the anode 105 to the cathode 110, but also separates the H2 gas 130 and O2 gas 125 produced in the water electrolysis reaction. PEM water electrolysis is one of the favorable methods for conversion of renewable energy to high purity hydrogen with the advantage of compact system design at high differential pressures, high current density, high efficiency, fast response, small footprint, lower temperature (20-90 oC) operation, and high purity oxygen byproduct. However, one of the major challenges for PEM water electrolysis is the high capital cost of the cell stack comprising expensive acid-tolerant stack hardware such as the Pt-coated Ti bipolar plates, expensive noble metal catalysts required for the electrodes, as well as the expensive PEM. [0004] Water electrolysis reaction∶ 2 H2O → 2 H2 + O2 (1) [0005] Oxidation reaction at anode for PEM-WE∶ 2 H2O → O2 + 4 H+ + 4 e (2) [0006] Reduction reaction at cathode for PEM-WE∶ 4 H+ + 4 e- → 2 H2 (3) [0007] In the PEM-WE and AEM-WE systems, several components are integrated to produce green H2, including current collector plates, bipolar plates (BPs), two porous transport layers (PTL), a three-layer membrane electrode assembly (MEA) or called catalyst-coated membrane (CCM) consisting of a membrane, an anode layer, and a cathode layer. Among the main components, CCM is the most important one as the electrochemical water electrolysis reaction occurs in the CCM. [0008] The anode in the CCM for an electrochemical cell coated on one surface of the membrane is the electrode at which the predominant reaction is oxidation (e.g., the water oxidation/oxygen evolution reaction electrode for a water electrolyzer). The cathode in the CCM for an electrochemical cell coated on the other surface of the membrane is the electrode at which the predominant reaction is reduction (e.g., the proton reduction/hydrogen evolution reaction electrode for a water electrolyzer). Both anode and cathode are key components in the CCM. Typically, unsupported or supported iridium (Ir) based scarce platinum group electrocatalysts are used for the oxygen evolution reaction (OER) on the anode and carbon supported platinum electrocatalyst (Pt/C) is used for the hydrogen evolution reaction (HER) on the cathode for PEM-WE. Both Ir and Pt based platinum group metal (PGM) catalyst are very expensive and scarce. Significant reduction of the PGM catalyst loading on the catalyst coating layer will be required with the increase of the GW-scale PEM-WE installation projects. Not only methods for reducing the loading of the PGM catalysts but also methods for recycling the PGM catalysts are important to the improved market penetration of PEM-WE technology for green H2 production. [0009] Significant advances are needed in finding cost-effective and sustainable PGM recovery methods for used CCMs. BRIEF DESCRIPTION OF THE DRAWINGS [00010] Fig.1 is an illustration of one embodiment of a PEMWE cell. [00011] Fig.2 is an illustration of one embodiment of a catalyst coated membrane of the present inv