Method to prepare full monolayer of platinum on palladium based core nanoparticles

Patent metadata

Field	Value
Publication number	US-9246176-B2
Application number	US-201113983174-A
Country	US
Kind code	B2
Filing date	Feb 3, 2011
Priority date	Feb 3, 2011
Publication date	Jan 26, 2016
Grant date	Jan 26, 2016

Abstract

A method for forming catalytic nanoparticles includes forming core-shell catalytic nanoparticles and processing the core-shell catalytic nanoparticles. The core-shell catalytic nanoparticles have a palladium core enclosed by a platinum shell. The core-shell catalytic nanoparticles are processed to increase the percentage of the surface area of the core-shell catalytic nanoparticles covered by the platinum shell.

First claim

The invention claimed is:

1. A method for forming catalytic nanoparticles, the method comprising:
forming core-shell catalytic nanoparticles having a palladium core enclosed by a platinum shell; and
increasing a percentage of surface area of the core-shell catalytic nanoparticles covered by the platinum shell by further processing the core-shell catalytic nanoparticles,

wherein increasing the percentage of surface area of the core-shell catalytic nanoparticles covered by the platinum shell comprises A) or B):
A) storing the core-shell catalytic nanoparticles in a hydrogen environment to absorb hydrogen into the palladium core; and
depositing platinum atoms on the surface of the core-shell catalytic nanoparticles by reducing a platinum salt with the hydrogen absorbed into the palladium core; or

B) subjecting the core-shell catalytic nanoparticles to potential cycling before incorporating the core-shell catalytic nanoparticles into a catalyst layer of an electrochemical cell.

2. The method of claim 1 , wherein the platinum salt is a platinum(II) salt.

3. The method of claim 1 , wherein the platinum salt is selected from the group consisting of: potassium tetrachloroplatinate (K 2 PtCl 4 ), hydrogen hexachloroplatinate (H 2 PtCl 4 ), platinum (II) cyanide (Pt(CN) 2 ), platinum(II) chloride (PtCl 2 ), platinum(II) bromide (PtBr 2 ), and platinum(II) acetylacetonate (Pt(acac) 2 ).

4. The method of claim 1 , wherein depositing platinum atoms on the surface of the core-shell catalytic nanoparticles comprises:
exposing the core-shell catalytic nanoparticles to an inert atmosphere; and
mixing the core-shell catalytic nanoparticles with an aqueous solution containing the platinum salt.

5. The method of claim 1 , wherein the core-shell catalytic nanoparticles have a greater percentage of platinum by weight and a smaller percentage of palladium by weight after platinum atoms are deposited on the surface of the core-shell catalytic nanoparticles by reducing the platinum salt.

6. The method of claim 1 , wherein subjecting the core-shell catalytic nanoparticle to potential cycling comprises:
subjecting the core-shell catalytic nanoparticles to potential cycling between 0.65 volts and 1.0 volts.

7. The method of claim 1 , wherein subjecting the core-shell catalytic nanoparticle to potential cycling comprises:
subjecting the core-shell catalytic nanoparticles to at least about 50 potential cycles with at least about 5 seconds at each potential.

8. The method of claim 1 , wherein a mass activity of the core-shell catalytic nanoparticles is increased by at least about 20% after the potential cycling.

9. A method for forming a catalytic nanoparticle for use in an electrochemical cell, the method comprising:
depositing copper on a palladium nanoparticle core;
replacing the copper with a shell of platinum atoms to form a core-shell nanoparticle, the shell covering a portion of an exterior surface of the palladium nanoparticle core; and
reducing pinholes in the shell after replacing the copper so that platinum atoms cover a greater percentage of surface area of the core-shell nanoparticle,

wherein reducing pinholes in the shell comprises:
exposing the core-shell catalytic nanoparticle to a hydrogen environment; and
mixing the core-shell catalytic nanoparticle with an aqueous mixture containing a platinum salt after storing the core-shell catalytic nanoparticle in the hydrogen environment.

10. The method of claim 9 , wherein mixing the core-shell catalytic nanoparticle with an aqueous mixture comprises:
mixing the core-shell catalytic nanoparticle with an aqueous mixture containing a platinum salt in an inert environment.

11. The method of claim 10 , wherein the inert environment is selected from a nitrogen environment and an argon environment.

12. The method of claim 9 , wherein the platinum salt is a platinum(II) salt.

13. The method of claim 9 , wherein the platinum salt is selected from the group consisting of: potassium tetrachloroplatinate (K 2 PtCl 4 ), hydrogen hexachloroplatinate (H 2 PtCl 4 ), platinum (II) cyanide (Pt(CN) 2 ), platinum(II) chloride (PtCl 2 ), platinum(II) bromide (PtBr 2 ), and platinum(II) acetylacetonate (Pt(acac) 2 ).

14. The method of claim 9 , wherein after the step of reducing pinholes in the shell, the core-shell catalytic nanoparticle contains a greater weight percentage of platinum and a smaller weight percentage of palladium and copper compared to that before the step of reducing the pinholes.

15. The method of claim 9 , wherein reducing pinholes in the shell comprises:
subjecting the core-shell catalytic nanoparticle to potential cycling before incorporating the core-shell catalytic nanoparticle into a catalyst layer of an electrochemical cell.

16. The method of claim 15 , wherein subjecting the core-shell catalytic nanoparticle to potential cycling comprises:
subjecting the core-shell catalytic nanoparticle to potential cycling between 0.65 volts for about five seconds and 1.0 volt for about 5 seconds.

17. The method of claim 15 , wherein subjecting the core-shell catalytic nanoparticle to potential cycling comprises:
subjecting the core-shell catalytic nanoparticle to at least about 50 and less than about 5000 potential cycles.

18. The method of claim 15 , and further comprising:
recycling palladium that is leached from the palladium core nanoparticle during the potential cycling.

19. The method of claim 15 , wherein after the step of subjecting the core-shell catalytic nanoparticle to potential cycling, the mass activity of the core-shell catalytic nanoparticle is increased by 20% compared to that of the core-shell catalytic nanoparticle before the step of potential cycling.

Assignees

• Shao Minhua
• Audi Ag

Inventors

• Shao Minhua

Classifications

• Y02E60/50

  Fuel cells · CPC title

• H01M4/921

  Alloys or mixtures with metallic elements · CPC title

• B01J37/348

  Electrochemical processes, e.g. electrochemical deposition or anodisation · CPC title

• H01M4/92 Primary

  Metals of platinum group (H01M4/94 {, H01M4/9058} take precedence) · CPC title

• H01M4/8657

  layered · CPC title