High performance electrolytic cell electrode/membrane structures and a process for preparing such electrode structures

• US 5,470,448 A
• Filed: 01/28/1994
• Issued: 11/28/1995
• Est. Priority Date: 01/28/1994
• Status: Expired due to Fees

• Current Assignee: United Technologies Corporation (Rtx Corporation)
• Original Assignee: United Technologies Corporation (Rtx Corporation)
• Inventors: Molter, Trent M., Critz, Kurt M.
• Primary Examiner(s): GORGOS, KATHRYN L
• Application Number:
  US08/188,487
• Time in Patent Office: 669 Days
• Field of Search: 204/252, 204/283, 204/290 R, 429/40, 429/42
• US Class Current: 204/252
• CPC Class Codes: C25B 9/23 comprising ion-exchange membranes in or on which electrode material is embedded
• CPC Class Codes: G01N 27/333 Ion-selective electrodes or membranes glass electrodes G01N27/36
• CPC Class Codes: H01M 2300/0082 Organic polymers
• CPC Class Codes: H01M 4/9008 Organic or organo-metallic compounds
• CPC Class Codes: H01M 4/9091 Unsupported catalytic particles; loose particulate catalytic materials, e.g. in fluidised state
• CPC Class Codes: H01M 4/928 Unsupported catalytic particles; loose particulate catalytic materials, e.g. in fluidised state
• CPC Class Codes: H01M 8/1004 characterised by membrane-electrode assemblies [MEA] H01M8/12 takes precedence
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

A high performance ionomer assisted electrolytic cell electrode structure is provided. Such structures operate effectively at catalyst loadings as low as 0.10 mg/cm² and demonstrate increased structural integrity without ionomer degradation. The inventive structure comprises a hydrated ion exchange membrane having a first surface and a second surface and at least one catalyst ionomer layer bonded to the first and/or second surface of the membrane that comprises hydrated and swollen ionomer solids bonded to discrete catalyst particles.

Claims

1. An improved ionomer assisted electrode structure for use in an electrolysis cell comprising an ion exchange membrane having a first surface and a catalyst ionomer layer bonded to said first surface of said membrane, wherein said improvement consists essentially of a hydrated ion exchange membrane having a first surface and a second surface and a first and optionally, a second pre-formed catalyst ionomer layer consisting essentially of hydrated and swollen ionomer solids bonded to discrete unsupported catalyst particles, wherein said first and said second catalyst ionomer layers each have a catalyst loading of at least 0.10 mg/cm², wherein said first catalyst ionomer layer is pressed and bonded to said first surface of said hydrated ion exchange membrane, and optionally, wherein said second catalyst ionomer layer is pressed and bonded to said second surface of said membrane.

5. The ionomer assisted electrode structure of claims 1 or 2 wherein said ionomer solids material is the same material forming said ion exchange membrane.

6. The ionomer assisted electrode structure of claim 5 wherein said ionomer solids are formed from a perfluoroionomer and wherein said ion exchange membrane is a perfluorinated ion exchange membrane.

7. The ionomer assisted electrode structure of claims 1 or 2 wherein said catalyst particles are platinum catalyst particles.

8. The ionomer assisted electrode structure of claims 1 or 2 wherein said electrode structure consists essentially of an ion exchange membrane having a first surface and a second surface, a first catalyst ionomer layer and a second catalyst ionomer layer, wherein said first catalyst ionomer layer is bonded to said first surface of said ion exchange membrane and wherein said second catalyst ionomer layer is bonded to said second surface of said ion exchange membrane.

2. An ionomer assisted electrode structure for use in an electrolysis cell which consists essentially of:

a. a hydrated ion exchange membrane having a first surface and a second surface; and

b. a first and optionally, a second pre-formed catalyst ionomer layer consisting essentially of hydrated and swollen ionomer solids bonded to discrete catalyst particles, wherein said first catalyst ionomer layer is pressed and bonded to said first surface of said hydrated ion exchange membrane, and optionally, wherein said second catalyst ionomer layer is pressed and bonded to said second surface of said membrane, wherein said ionomer assisted electrode structure is prepared according to a process comprising;

i. forming an aqueous solution comprising from about 0.10 to about 20% by weight swollen ionomer solids and from about 0.15 to about 30% by weight catalyst, based on the total weight of said aqueous solution;

ii. heating said solution to a temperature of from about 40°

C. to about 110°

C. until a dry powder residue remains;

iii. forming a solid paste comprising a quantity of said dry powder residue and a quantity of a fast drying or subliming agent;

iv. pressing said solid paste onto at least said first surface of said ion exchange membrane at a temperature of from about 121°

C. to about 232°

C. and at a pressure of from about 2.1 to about 27.6 MPa;

v. optionally repeating steps (i) through (iv) wherein said solid paste is pressed onto said second surface of said ion exchange membrane; and

finally

vi. rehydrating said ion exchange membrane and said swollen ionomer solids of said solid paste.

3. The ionomer assisted electrode structure of claim 2 wherein said first and said second catalyst ionomer layers each have a catalyst loading of at least 0.10 mg/cm².

4. The ionomer assisted electrode structure of claim 2 wherein said fast drying or subliming agent is dry ice.

9. An improved electrolysis cell, having an anode and a cathode and utilizing at least one improved ionomer assisted electrode structure, comprising an ion exchange membrane having a first surface and a catalyst ionomer layer bonded to said first surface of said membrane, wherein said improvement consists essentially of a hydrated ion exchange membrane having a first surface and a second surface and a first and optionally, a second pre-formed catalyst ionomer layer consisting essentially of hydrated and swollen ionomer solids bonded to discrete unsupported catalyst particles, wherein said first and said second catalyst ionomer layers each have a catalyst loading of at least 0.10 mg/cm², wherein said first catalyst ionomer layer is pressed and bonded to said first surface of said hydrated ion exchange membrane, and optionally, wherein said second catalyst ionomer layer is pressed and bonded to said second surface of said membrane.

10. An electrolysis cell, having an anode and a cathode, utilizing at least one ionomer assisted electrode structure as the anode or as the cathode, wherein said electrode structure consists essentially of:

a. a hydrated ion exchange membrane having a first surface and a second surface; and

b. a first and optionally, a second pre-formed catalyst ionomer layer consisting essentially of hydrated and swollen ionomer solids bonded to discrete catalyst particles, wherein said first catalyst ionomer layer is pressed and bonded to said first surface of said hydrated ion exchange membrane, and optionally, wherein said second catalyst ionomer layer is pressed and bonded to said second surface of said membrane,

wherein said ionomer assisted electrode structure is prepared according to a process comprising;

i. forming an aqueous solution comprising from about 0.10 to about 20% by weight swollen ionomer solids and from about 0.15 to about 30% by weight catalyst, based on the total weight of said aqueous solution;

ii. heating said solution to a temperature of from about 40°

C. to about 110°

C. until a dry powder residue remains;

iii. forming a solid paste comprising a quantity of said dry powder residue and a quantity of a fast drying or subliming agent;

iv. pressing said solid paste onto at least said first surface of said ion exchange membrane at a temperature of from about 121°

C. to about 232°

C. and at a pressure of from about 2.1 to about 27.6 MPa;

v. optionally repeating steps (i) through (iv) wherein said solid paste is pressed onto said second surface of said ion exchange membrane; and

finally

vi. rehydrating said ion exchange membrane and said swollen ionomer solids of said solid paste.

11. The electrolysis cell of claim 10 wherein said first and said second catalyst ionomer layers of said electrode structure each have a catalyst loading of at least 0.10 mg/cm².

12. The electrolysis cell of claim 10 wherein said fast drying or subliming agent is dry ice.

13. The electrolysis cell of claims 9 or 10 wherein said ionomer solids material of said electrode structure is the same material forming said ion exchange membrane of said electrode structure.

14. The electrolysis cell of claim 13 wherein said ionomer solids are formed from a perfluoroionomer and wherein said ion exchange membrane is a perfluorinated ion exchange membrane.

15. The electrolysis cell of claims 9 or 10 wherein said catalyst particles of said electrode structure are platinum catalyst particles.

16. The electrolysis cell of claims 9 or 10 wherein said electrode structure consists essentially of an ion exchange membrane having a first surface and a second surface, a first catalyst ionomer layer and a second catalyst ionomer layer, wherein said first catalyst ionomer layer is bonded to said first surface of said ion exchange membrane and wherein said second catalyst ionomer layer is bonded to said second surface of said ion exchange membrane.