SYNTHESIS OF ELECTROCATALYSTS USING METAL-ORGANIC FRAMEWORK MATERIALS

• US 20130273461A1
• Filed: 04/11/2012
• Published: 10/17/2013
• Est. Priority Date: 04/11/2012
• Status: Active Grant

• Current Assignee: UChicago Argonne LLC
• Original Assignee: UChicago Argonne LLC
• Inventors: LIU, Di-Jia, ZHAO, Dan
• Granted Patent: US 10,326,145 B2
• Time in Patent Office: Days
• US Class Current: 429/535
• CPC Class Codes: B01J 2531/26 Zinc
• CPC Class Codes: B01J 2531/842 Iron
• CPC Class Codes: B01J 2531/845 Cobalt
• CPC Class Codes: B01J 2531/847 Nickel
• CPC Class Codes: B01J 31/1691 Coordination polymers, e.g. metal-organic frameworks [MOF] preparation of metal complexes containing carboxylic acid moieties C07C51/418; MOF's per se C07F
• CPC Class Codes: B01J 31/181 Cyclic ligands, including e.g. non-condensed polycyclic ligands, comprising at least one complexing nitrogen atom as ring member, e.g. pyridine
• CPC Class Codes: H01M 2008/1095 Fuel cells with polymeric electrolytes
• CPC Class Codes: H01M 4/9008 Organic or organo-metallic compounds
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

Methods and compositions for use in the preparation of MOF-based non-PGM electrocatalysts including combining transition metal compounds with organic ligands and secondary building units to create a solid mixture, heating the solid mixture to form a MOF through a solid-state reaction, optionally heating the MOF to convert it to an electrocatalyst via pyrolysis, and optionally post-treating. The electrode catalysts may be used in various electrochemical systems, including a proton exchange membrane fuel cell.

Claims

1. A method of synthesis of a non-platinum group metal (PGM) catalyst for use in an oxygen reduction reaction (ORR) process, said method comprising the steps of

combining at least one organic ligand, a secondary building unit, and at least one transition metal compound into a solid mixture substantially solvent-free;

heating the solid mixture to a temperature and for a duration sufficient to form a metal-organic framework (MOF) through a solid-state reaction; and

forming MOF crystallites;

wherein the step of combining takes place in a single vessel.

2. The method of claim 1, further comprising the step of converting the MOF to an electro-catalyst via pyrolysis at high temperature.

3. The method of claim 1, wherein the method does not comprise the step of separating the MOF from the other reaction components.

4. The method of claim 1, wherein the at least one transition metal is incorporated into the MOF either as part of the framework or as a uniformly distributed additive during the synthesis.

5. The method of claim 1, wherein the MOF contains at least two different transition metals.

6. The method of claim 5, wherein the step of combining comprises mixing a first transition metal salt or metal oxide with the organic ligand in a desired stoichiometrical ratio for the formation of the MOF, and adding a second transition metal salt or complex.

7. The method of claim 5, wherein the step of adding the at least two different transition metals is followed by the step of uniformly mixing the solid mixture through mechanical means prior to subjecting the solid mixture to heat treatment.

8. The method of claim 2, wherein the solid-state reaction step and the pyrolysis step are performed in tandem without a step of cooling in between the solid-state reaction step and the pyrolysis step.

9. The method of claim 1, wherein the at least one organic ligand comprises a plurality of nitrogen containing ligands selected from the group consisting of:

imidazolate, pyrazolate, piperazine, tetrazolate, and combinations thereof.

10. The method of claim 5, wherein the first transition metal is in the zinc salt or zinc oxide form.

11. The method of claim 5, wherein the second transition metal is selected from the group consisting of the salt or organometallic complex form of iron, cobalt, copper, or nickel.

12. The method of claim 1, further comprising the step of processing the heat-treated MOF to further enhance catalytic activity, said processing comprising acid wash, ball milling, and/or thermal treatment in inert gas or in the presence of ammonia.

13. The method of claim 2 further comprising incorporating the electro-catalyst into a membrane electrode assembly of a proton exchange membrane fuel cell.

14. A composition for use in synthesis of a non-PGM catalyst according to claim 1, said composition comprising at least two transition metal compounds and at least one organic ligand compound.

15. The composition of claim 14, wherein the at least one organic ligand comprises a plurality of nitrogen containing ligands selected from the group consisting of:

imidazolate, pyrazolate, piperazine, tetrazolate, and combinations thereof.

16. The composition of claim 14, wherein the first transition metal is in the zinc salt or zinc oxide form.

17. The composition of claim 14, wherein the second transition metal is selected from the group consisting of the salt or organometallic complex form of iron, cobalt, copper, or nickel.

18. The composition of claim 14, wherein the molecular ratio between the first transition metal compound to the organic ligand is stoichiometrically equivalent to that in the MOF framework, and the concentration of the second transition metal compound is independent.

19. The composition of claim 14, wherein the molecular ratio of the sum of first and second transition metals to the organic ligand is stoichiometrically equivalent to that for the formation of mixed MOF frameworks.

20. A non-PGM catalyst for use in an ORR process, the catalyst comprising:

a metal-organic framework comprising;

at least one transition metal;

at least one organic ligand; and

a secondary building unit;

wherein the metal-organic framework is formed in a reaction that is substantially solvent-free.