NON-PLATINUM GROUP METAL ELECTROCATALYSTS USING METAL ORGANIC FRAMEWORK MATERIALS AND METHOD OF PREPARATION

• US 20120077667A1
• Filed: 09/27/2010
• Published: 03/29/2012
• Est. Priority Date: 09/27/2010
• Status: Active Grant

• Current Assignee: UChicago Argonne LLC
• Original Assignee: UChicago Argonne LLC
• Inventors: LIU, Di-Jia, Ma, Shengqian, Goenaga, Gabriel A.
• Granted Patent: US 8,835,343 B2
• Time in Patent Office: Days
• US Class Current: 502/101
• 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 31/18 containing nitrogen, phosphorus, arsenic or antimony as complexing atoms, e.g. in pyridine ligands, or in resonance therewith, e.g. in isocyanide ligands C=N-R or as complexed central atoms double metal cyanides B01J27/26; N-heterocyclic carbenes B01J31/2265
• CPC Class Codes: B01J 31/1805 the ligands containing nitrogen
• CPC Class Codes: H01M 2008/1095 Fuel cells with polymeric electrolytes
• CPC Class Codes: H01M 2250/20 Fuel cells in motive systems, e.g. vehicle, ship, plane
• CPC Class Codes: H01M 4/8605 Porous electrodes
• CPC Class Codes: H01M 4/8875 Methods for shaping the electrode into free-standing bodies, like sheets, films or grids, e.g. moulding, hot-pressing, casting without support, extrusion without support
• CPC Class Codes: H01M 4/8882 Heat treatment, e.g. drying, baking
• CPC Class Codes: H01M 4/9008 Organic or organo-metallic compounds
• CPC Class Codes: H01M 4/9041 Metals or alloys H01M4/92 takes precedence
• CPC Class Codes: H01M 8/10 Fuel cells with solid electrolytes
• CPC Class Codes: Y02E 60/50 Fuel cells
• CPC Class Codes: Y02T 90/40 Application of hydrogen technology to transportation, e.g. using fuel cells

Abstract

A method of preparing a nitrogen containing electrode catalyst by converting a high surface area metal-organic framework (MOF) material free of platinum group metals that includes a transition metal, an organic ligand, and an organic solvent via a high temperature thermal treatment to form catalytic active sites in the MOF. At least a portion of the contained organic solvent may be replaced with a nitrogen containing organic solvent or an organometallic compound or a transition metal salt to enhance catalytic performance. The electrode catalysts may be used in various electrochemical systems, including a proton exchange membrane fuel cell.

Claims

1. A method of preparing a high surface area electrode catalyst free of platinum group metals (PGM) for use in a fuel cell, comprising:

preparing a metal-organic framework (MOF) material having a plurality of pores and including a non-PGM first transition metal catalytic center, an organic ligand and a first organic solvent contained within a portion of the plurality of pores, comprising;

dissolving a first transition metal salt in a first organic solvent to form a metal salt solution, the transition metal salt includes the first transition metal which is selected from the group consisting of;

Co, Fe, Ni, Cr, Cu, Mn, Ta and W;

dissolving at least one multidentate ligand in the first organic solvent to form a ligand solution;

mixing a predetermined molar ratio of the metal salt solution and the ligand solution into a reaction mixture; and

forming the MOF material through chemical reaction and separating the MOF material from the reaction mixture as a precipitate;

substituting at least a portion of the contained first organic solvent with a second chemical moiety to enhance formation of electrocatalytic active sites in the MOF material; and

thermally treating the MOF material for a predetermined period within an environment at a thermal conversion temperature to form the high surface area electrode catalyst having a plurality of uniformly distributed electrocatalytic active sites.

2. The method of claim 1, wherein the first transition metal salt is selected from the group consisting of:

a nitrate, an acetate, and a chloride of the first transition metal.

3. The method of claim 1, wherein the second chemical moiety is dimensioned to infiltrate the plurality of pores and form a plurality of bimetallic electrocatalytic active sites, and wherein the second chemical moiety is one of an organometallic complex and a second metal salt.

4. The method of claim 3, wherein the at least one multidentate ligand comprises a plurality of nitrogen containing ligands selected from the group consisting of:

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

5. The method of claim 4, wherein the first organic solvent is selected from the group consisting of:

dimethylformamide (DMF), diethylormamide (DEF), dimethylacetamide (DMA), cynamide, and pyridine.

6. The method of claim 3, wherein organometallic compound is selected from the group consisting of:

ferrocene, cobaltocene, and Prussian blue; and

wherein the second metal salt is selected from the group consisting of;

a metal nitrate, a metal acetate, and a metal chloride.

7. The method of claim 1 further comprising dissolving at least one templating agent with the first organic solvent to form the ligand solution.

8. The method of claim 1, wherein the predetermined period is between about 60 minutes and about 90 minutes, and wherein the thermal conversion temperature is between about 700°

C. to about 800°

C.

9. The method of claim 8, wherein the environment comprises one of an inert carrier gas and a reductive carrier gas, wherein the inert carrier gas is selected from the group consisting Ar, He and N₂, and wherein the reductive carrier gas is selected from the group consisting of:

NH₃, pyridine, and acetonitrile.

10. The method of claim 1 further comprising subjecting the high surface area electrode catalyst to an acid washing process with an inorganic acid to remove a portion of the first transition metal from the MOF material, wherein the acid washing process improves the electrochemical activity of the high surface area electrode catalyst.

11. The method of claim 10 further comprising a secondary thermal treatment of the electrode catalyst in one of an inert carrier gas and a reductive carrier gas selected from the group consisting of:

NH₃, pyridine, and acetonitrile following the acid washing process.

12. A non-platinum group metal (PGM) electrode catalyst for use in a fuel cell, comprising:

a high surface area metal-organic framework (MOF) material having a plurality of pores, the MOF material including a non-PGM first transition metal capable of forming a catalytic center and selected from the group consisting of;

Co, Fe, Ni, Cr, Cu, Mn, Ta and W, a nitrogen containing organic multidentate ligand, and a first organic solvent contained within a portion of the plurality of pores, the first organic solvent capable of dissolving a precursor of the non-PGM first transition metal and a nitrogen containing organic multidentate ligand and a templating agent,

wherein at least the first transition metal, the multidentate ligand, and the contained first solvent are configured to react under a thermal treatment of the MOF material so to form a plurality of catalytic active sites uniformly distributed in the hence formed electrode catalyst.

13. The non-PGM electrode catalyst of claim 12, wherein at least a portion of the contained first solvent is replaced with one of:

a second organic solvent configured to react with the first transition metal; and

an organometallic compound or a metal salt, the organometallic compound and the metal salt containing a second transition metal configured to react with the multidentate ligand and configured to form a plurality of bimetallic catalytic active sites under the high temperature thermal treatment.

14. The non-PGM electrode catalyst of claim 13, wherein the organometallic compound is selected from the group consisting of:

ferrocene, cobaltocene, Prussian blue; and

wherein the metal salt is selected from the group consisting of;

a metal nitrate, a metal acetate, and a meal chloride.

15. A method of preparing a nitrogen containing electrode catalyst free of precious group metals (PGM), comprising:

synthesizing a metal-organic framework (MOF) electrode catalyst precursor, the MOF electrode catalyst precursor including a first non-PGM transition metal, a multidentate ligand, and a first organic solvent disposed within a plurality of uniformly distributed cavities in the MOF material;

substituting at least a portion of the first organic solvent disposed within the plurality of cavities with one of a nitrogen-containing organic solvent and a second non-PGM transition metal; and

thermally activating the MOF electrode catalyst precursor by an elevated temperature treatment to form a plurality of uniformly distributed electrocatalytic active sites.

16. The method of claim 15, wherein the second non-PGM transition metal is different from the first non-PGM transition metal.

17. The method of claim 16, wherein the multidentate ligand is a nitrogen-containing ligand selected from the group consisting of:

imidazolate, pyrazolate, piperazine, and tetrazolate.

18. The method of claim 15, wherein the nitrogen-containing organic solvent is selected from the group consisting of:

dimethylformamide (DMF), diethylormamide (DEF), dimethylacetamide (DMA), cynamide, and pyridine.

19. The method of claim 15 further comprising incorporating the electrode catalyst into a membrane electrode assembly of a proton exchange membrane fuel cell.

20. The method of claim 15 further including a post treatment process comprising:

washing the electrode catalyst in an inorganic acid to remove a portion of the first non-PGM transition metal; and

performing a secondary heat treatment on the electrode catalyst following the acid washing,

wherein the post treatment process enhances the catalytic activity of the electrode catalyst.