Control of nanostructure and activity by alloying and/or segregation

1. A method of synthesizing Pt shell PtNi core particle comprising the steps of:

forming a reaction mixture comprising a nickel precursor, a reducing agent, and a surfactant comprising oleic acid, a platinum precursor, and a polar solvent;

reacting the reaction mixture at between 200° C. and 300° C. for at least 10 minutes, forming a PtNi nanocage solution;

isolating PtNi nanocages from the PtNi nanoparticle solution;

exposing the PtNi nanocages to oxygen;

forming nickel oxide by reaction of nickel of the PtNi nanocages with the oxygen;

exposing the nickel oxide PtNi nanocages to hydrogen and argon at a temperature of at least 400° C.; and

removing the nickel oxide from at least a portion of the PtNi nanocages.

2. The method of claim 1 , wherein isolation of the PtNi nanocages comprises:

sonicating the PtNi nanocages solution with substrate in chloroform solution;

adding hexane to the sonicated chloroform solution;

precipitating PtNi nanocages; and

collecting the PtNi nanocages by filtration.

3. The method of claim 1 , wherein exposing the PtNi nanocages to oxygen comprises exposure at a temperature of 150° C. to 400° C.

4. The method of claim 3 , wherein exposing the PtNi nanocages to oxygen comprises exposure at a temperature of 150° C. to 300° C.

5. The method of claim 3 , wherein exposing the PtNi nanocages is for 5-20 hours.

6. The method of claim 1 , wherein removing the nickel oxide is by acid leeching.

7. The method of claim 6 , wherein exposing to hydrogen and argon is concurrent with the removal of the nickel oxide by acid leeching.

8. The method of claim 6 , wherein the acid leaching is by exposure of an equal volume of acid to nanoparticle.

9. The method of claim 6 , wherein exposing the nickel oxide PtNi nanocages to hydrogen and argon is at a temperature between 400° C. and 600° C. for 1-4 hours.

10. A method of synthesizing Pt shell PtNi core nanoparticle comprising the steps of:

forming a reaction mixture comprising a nickel precursor, a reducing agent, and a surfactant comprising oleic acid, a platinum precursor, and a polar solvent;

reacting the reaction mixture at between 205° C. and 255° C. for at least 10 minutes forming a PtNi nanoparticle solution;

isolating PtNi nanoparticles from the PtNI nanoparticle solution;

exposing the PtNi nanoparticles to hydrogen and argon at a temperature of at least 400° C.;

exposing the PtNi nanoparticles to oxygen at a temperature of 150° C. to 400° C. for 5-20 hours;

forming nickel oxide on a surface of the PtNi nanoparticles by reaction of nickel of the PtNi nanoparticles with the oxygen; and

removing the nickel oxide from at a portion of the PtNi nanoparticles.

11. The method of claim 10 , wherein isolation of the PtNi nanoparticles comprises:

sonicating the PtNi nanoparticle solution with substrate in chloroform solution;

adding hexane to the sonicated chloroform solution;

precipitating PtNi nanoparticles; and

collecting the PtNi nanoparticles by filtration.

12. The method of claim 10 , wherein exposing the PtNi nanoparticles comprises exposure at a temperature of 150° C. to 300° C.

13. The method of claim 10 , wherein removing the nickel oxide is by acid leeching.

14. The method of claim 13 , wherein the acid leaching is by exposure of an equal volume of acid to nanoparticle.

15. The method of claim 13 , wherein the acid leaching is by exposure to HClO 4 .

16. The method of claim 6 , wherein exposing the nickel oxide PtNi nanoparticles to hydrogen and argon is at a temperature between 400° C. and 600° C. for 1-4 hours.

17. A method of synthesizing Pt shell PtNi core particle comprising the steps of:

forming a reaction mixture comprising a nickel precursor, a reducing agent, and a surfactant comprising oleic acid, a platinum precursor, and a polar solvent;

reacting the reaction mixture at between 200° C. and 300° C. for at least 10 minutes forming a PtNi particle solution comprising PtNi nanoparticles or PtNi nanocages;

isolating PtNi particles from the PtNI particle solution;

exposing the PtNi particles to oxygen;

forming nickel oxide by reaction of nickel of the PtNi particles with the oxygen; and

exposing the PtNi particles to hydrogen and argon at a temperature of at least 400° C.

18. The method of claim 17 , wherein the PtNi particles are nanocages and wherein the exposure to the hydrogen and argon is after the exposure to oxygen.

19. The method of claim 17 , wherein the PtNi particles are nanoparticles and wherein the exposure to the hydrogen and argon is before the exposure to oxygen.

20. The method of claim 17 , wherein exposing the PtNi particles to hydrogen and argon is at a temperature between 400° C. and 600° C. for 1-4 hours.