Non-platinum group metal electrocatalysts using metal organic framework materials and method of preparation
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 an alkaline fuel cell.
1. A method of preparing a high surface area electrode catalyst free of platinum group metals (PGM) for use in a fuel cell, comprising:
mixing a metal oxide secondary building unit, a nitrogen-containing organic ligand, and transition metal complex to form a uniform, solid mixture;
applying a first heat treatment to the uniform solid mixture sufficient to melt the organic ligand;
reacting the organic ligand with the metal oxide secondary building unit and the transition metal complex to form a metal organic framework (“MOF”), wherein the MOF includes nitrogen from the nitrogen-containing organic ligand and a metal from the metal oxide secondary building unit;
applying a second heat treatment, converting organic components of the MOF to a carbonaceous material; and
forming a catalytically active site by reacting the transition metal in the MOF with nitrogen in the MOF.
2. The method of claim 1 , wherein mixing comprises mechanically mixing solid metal oxide secondary building unit, solid nitrogen-containing organic ligand, and solid transition metal complex.
3. The method of claim 1 , wherein the metal oxide secondary building unit is zinc oxide.
4. The method of claim 1 , further including a post-treatment after the second heat treatment comprising modifying the catalyst to enhance catalytic activity.
5. The method of claim 4 , wherein the post-treatment includes a third heat treatment.
6. The method of claim 5 , further comprises the third heat treatment applied in the presence of a nitrogen-containing gas.
7. The method of claim 1 , wherein the transition metal complex is selected from the group consisting of a transition metal salt and an organometallic compound.
8. The method of claim 7 , wherein the organometallic compound is selected from the group consisting of: iron phthalocyanine, iron porphyrine, phenanthroline iron perchlorate, cobalt phthalocyanine, cobalt porphyrine, cobalt phenanthroline, nickel phthalocyanine, nickel porphyrine, nickel phenanthroline, chromium phthalocyanine, chromium porphyrine, copper phthalocyanine, copper porphyrine, manganese phthalocyanine, manganese porphyrine.
9. The method of claim 7 , wherein the transition metal salt is selected from the group consisting of: a metal nitrate, a metal acetate, and a metal chloride including iron nitrate, iron acetate, iron chloride, cobalt nitrate, cobalt acetate, cobalt chloride, nickel nitrate, nickel acetate, nickel chloride, chromium nitrate, chromium acetate, chromium chloride, copper nitrate, copper acetate, copper chloride, manganese nitrate, manganese acetate, manganese chloride.
10. The method of claim 3 , wherein the nitrogen containing organic ligand selected from the group consisting of: imidazolate, pyrazolate, piperazine, tetrazolate, and combinations thereof.
11. The method of claim 1 , wherein the first heat treatment is applied for a first predetermined period of between about 60 minutes and about 20 hours.
12. The method of claim 1 , wherein the second heat treatment is applied for a second predetermined period of between about 30 minutes and about 90 minutes.
13. 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.