Method for generating a shell of noble metal overlaid on a core of non-noble metal, and catalysts made thereby
An electrocatalyst is described. The electrocatalyst includes a core of a non-noble metal or non-noble metal alloy; and a continuous shell of a noble metal or noble metal alloy on the core, the continuous shell being at least two monolayers of the noble metal or noble metal alloy. Methods for making the electrocatalyst are also described.
1. A method of making an electrocatalyst comprising:
providing an initial mixture of a first solvent and reducing agent with a compound of a non-noble metal or a non-noble metal alloy;
heating the initial mixture to a temperature near a boiling point of the first solvent and reducing agent;
reducing the compound to form non-noble metal or non-noble metal alloy particles without a carbon support in the initial mixture;
cooling the initial mixture with the particles to a temperature less than near the boiling point of the first solvent and reducing agent;
adding a second mixture of a compound of a noble metal or noble metal alloy and a second solvent to the cooled initial mixture with the particles to form a combined mixture; and
reducing the compound of the noble metal or noble metal alloy in the combined mixture to the noble metal or noble metal alloy at the cooled temperature to form a continuous shell of the noble metal or noble metal alloy on the particles.
2. The method of claim 1 further comprising adding a dispersant to the initial mixture before heating the initial mixture.
3. The method of claim 1 further comprising heating the combined mixture with the continuous shell of the noble metal or noble metal alloy on the particles to form a continuous alloy shell of the noble metal or noble metal alloy and the non-noble metal or non-noble metal alloy on the particles.
4. The method of claim 1 wherein the first mixture is cooled to the temperature of less than 80° C.
5. The method of claim 1 wherein the compound of the non-noble metal or non-noble metal alloy is selected from salts, oxides, organometallic compounds, metal particles, or combinations thereof.
6. The method of claim 1 wherein the compound of the noble metal or noble metal alloy is selected from salts, oxides, organometallic compounds, metal particles, or combinations thereof.
7. The method of claim 1 wherein the first solvent and reducing agent or the second solvent is an alcohol.
8. The method of claim 1 wherein the first solvent and reducing agent or the second solvent is a glycol or polyol.
9. The method of claim 1 wherein the first solvent and reducing agent or the second solvent is a mixture of alcohols.
10. The method of claim 1 wherein the first solvent and reducing agent is a mixture of an organic solvent and a glycol or polyol.
11. The method of claim 1 further comprising adding a reducing agent to the second mixture.
12. The method of claim 1 wherein the shell has between two and about 50 monolayers of the noble metal or noble metal alloy.
13. The method of claim 1 wherein the noble metal or noble metal alloy is selected from Pt, Pd, Rh, Ir, Ru, Os, Au, Ag, Cu, or combinations thereof.