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EP-4741519-A1 - METHOD OF RECOVERING VALUABLE RESOURCE

EP4741519A1EP 4741519 A1EP4741519 A1EP 4741519A1EP-4741519-A1

Abstract

A method of recovering a valuable resource from an electrochemical device including a catalyst of an oxide of a noble metal, includes: reducing the oxide while heating an object that has the catalyst; and applying a voltage to the object that is in contact with a solution containing at least one selected from the group consisting of ion species and chemical species which can form a complex with the noble metal, continuously increasing an absolute value of the voltage and then holding the value while periodically reversing a polarity of the voltage to perform an electrolytic reaction and dissolve the reduced noble metal in the solution as ions.

Inventors

  • KANAMURA, SHOHEI
  • YAGYU, Motoshige
  • OOMORI, TAKASHI

Assignees

  • Kabushiki Kaisha Toshiba
  • Toshiba Energy Systems & Solutions Corporation

Dates

Publication Date
20260513
Application Date
20250718

Claims (7)

  1. A method of recovering a valuable resource from an electrochemical device, the electrochemical device comprising a catalyst of an oxide of a noble metal, the method comprising: reducing the oxide while heating an object that has the catalyst; and applying a voltage to the object that is in contact with a solution containing at least one selected from the group consisting of ion species and chemical species which can form a complex with the noble metal, continuously increasing an absolute value of the voltage and then holding the value while periodically reversing a polarity of the voltage to perform an electrolytic reaction and dissolve the reduced noble metal in the solution as ions.
  2. The method according to claim 1, wherein the reducing the oxide is performed by a first method of supplying a solution containing a reducing agent and bringing the reducing agent into contact with the object, a second method of supplying a reducing gas and bringing the reducing gas into contact with the object, or a third method of bringing an electrolytic solution into contact with the object, applying a voltage to the object, and performing an electrolytic reaction without reversing a polarity of the voltage.
  3. The method according to claim 1, wherein the object has an electrode having the catalyst, and a polymer electrolyte membrane.
  4. The method according to claim 1, wherein the reducing the oxide is performed at a temperature equal to or higher than 100°C.
  5. The method according to claim 1, wherein the dissolving of the noble mental includes alternately repeating: a first period in which a value of the voltage is decreased linearly or curvilinearly from a first value to equal or lower than a second value that is lower than the first value and then held; and a second period in which the value of the voltage is increased linearly or curvilinearly from a third value the same as or different from the first value to equal to or higher than a fourth value that is higher than the third value and then held.
  6. The method according to claim 5, wherein a time necessary for the value of the voltage to reach the second value from the first value is 0.6 seconds or longer in the first period, and a time necessary for the value of the voltage to reach the fourth value from the third value is 0.6 seconds or longer in the second period.
  7. The method according to claim 1, wherein the catalyst contains at least one noble metal selected from the group consisting of platinum, iridium, ruthenium, rhodium, palladium, gold, and rhenium.

Description

FIELD Embodiments relate to a method of recovering a valuable resource. BACKGROUND As global transition to a carbon neutral society progresses, hydrogen is being focused on as an alternative to fossil energy. One of currently considered methods of utilizing hydrogen is a fuel cell, which obtains electric energy by making hydrogen and oxygen react electrochemically. Among the fuel cells, a polymer electrolyte fuel cell (PEFC), which uses a solid polymer membrane as an electrolyte and is operated at a temperature equal to or lower than 100°C, went on the market in 2009 as a household fuel cell cogeneration system (brand name: ENE FARM (registered trademark)). Further, the PEFC is also beginning to be installed in moving bodies such as a fuel cell vehicle (FCV), a forklift, a bus, and a truck, and demand for the PEFC is expected to increase further in the future. At the same time, a technology is being developed to produce a large amount of hydrogen to be used in the PEFC by electrolysis of water. There are various methods of water electrolysis, and mainly developed are high-temperature steam electrolysis using steam of several hundred degrees as a raw material and polymer electrolyte membrane (PEM)-type water electrolysis, which is operated at around a room temperature. A PEM-type water electrolysis device has characteristics such that high-temperature operation is unnecessary and that a configuration of the water electrolysis device is similar to that of the PEFC, thereby making development of cell easy, so that PEM-type water electrolysis devices of megawatt size are being introduced in countries throughout the world. The PEM-type water electrolysis device is constituted by components similar to those of the PEFC, and an electrolysis reaction proceeds in a membrane electrode assembly (MEA) constituted by an electrolyte membrane, an electrode catalyst, and a gas diffusion layer (GDL). In order to curtail energy at the time of electrolysis reaction, a noble metal element, which facilitates occurrence of a hydrogen evolution reaction and an oxygen evolution reaction, is usually used as the electrode catalyst. Currently, a cathode, where the hydrogen evolution reaction occurs, is formed by using platinum and an anode, where the oxygen evolution reaction occurs, is formed by using a catalyst containing iridium. For transition to a hydrogen society, introduction of the PEFC and the PEM-type water electrolysis device increases inevitably in order to realize a carbon-neutral society, and it is essential to secure valuable resources such as noble metal elements used in the aforementioned devices. Means for securing the noble metal elements include development of new mines, development of mining technology, and development of recycling technology. However, Japan depends on foreign countries to secure most of the noble metal elements such as platinum, ruthenium, and iridium, and cannot respond to situations such as a conflict and a battle for resources only by the development of mines or development of mining technology. Therefore, it is important to develop a technology to recover noble metal elements from devices which are already distributed in the world. REFERENCE Patent Document 1: Japanese Patent No. 1626036Patent Document 2: Japanese Patent No. 6652518Patent Document 3: Japanese Patent No. 6652454Patent Document 4: Japanese Patent No. 6109769Patent Document 5: Japanese Laid-open Patent Publication No. S63-270421Non-Patent Document 1: KOFUJI Yusuke et al., "CO2 Electrolysis Cell Operating at High Current Density for Power-to-Chemicals Co2 Utilization", Toshiba Review, Vol. 75, No. 6, p. 48-51 (November, 2020)Non-Patent Document 2: Mohammad Fathi Tovini et al., "Degradation Mechanism of an IrO2 Anode Co-Catalyst for Cell Voltage Reversal Mitigation under Transient Operation Conditions of a PEM Fuel Cell", J. Electrochem. Soc., 168, 064521 (2021) SUMMARY A problem to be solved by the present invention is to recover a valuable resource efficiently. A method of recovering a valuable resource from an electrochemical device including a catalyst of an oxide of a noble metal, includes: reducing the oxide while heating an object that has the catalyst; and applying a voltage to the object that is in contact with a solution containing at least one selected from the group consisting of ion species and chemical species which can form a complex with the noble metal, continuously increasing an absolute value of the voltage and then holding the value while periodically reversing a polarity of the voltage to perform an electrolytic reaction and dissolve the reduced noble metal in the solution as ions. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flowchart to explain an example of a method of recovering a valuable resource.FIG. 2 is a schematic view illustrating an example of an object from which a valuable resource is recovered.FIG. 3 is a graph illustrating a temporal variation of a voltage applied to an electrochemical device