Platinum- and platinum alloy-coated palladium and palladium alloy particles and uses thereof
The present invention relates to particle and nanoparticle composites useful as oxygen-reduction electrocatalysts. The particle composites are composed of a palladium or palladium-alloy particle or nanoparticle substrate coated with an atomic submonolayer, monolayer, bilayer, or trilayer of zerovalent platinum atoms. The invention also relates to a catalyst and a fuel cell containing the particle or nanoparticle composites of the invention. The invention additionally includes methods for oxygen reduction and production of electrical energy by using the particle and nanoparticle composites of the invention.
1. A particle composite comprising a palladium-alloy particle coated with a layer selected from the group consisting of an atomic submonolayer, monolayer, bilayer, or trilayer of zerovalent platinum atoms, or a combination thereof, wherein said palladium-alloy does not include platinum.
2. A particle composite according to claim 1 , wherein said palladium-alloy particle is a palladium-alloy nanoparticle.
3. A particle composite according to claim 2 , wherein said palladium-alloy nanoparticle is comprised of a homogeneous combination of palladium and an alloying metal.
4. A particle composite according to claim 3 , wherein the alloying metal is a transition metal.
5. A particle composite according to claim 4 , wherein the transition metal is a 3d transition metal.
6. A particle composite according to claim 4 , wherein the transition metal is iron, cobalt, nickel, gold, or a combination thereof.
7. A particle composite according to claim 2 , wherein said palladium-alloy nanoparticle is comprised of a heterogeneous combination of palladium and an alloying metal.
8. A particle composite according to claim 7 , wherein said heterogeneous combination is comprised of an inner core of alloying metal coated with a layer of palladium.
9. A particle composite comprising:
a palladium or palladium-alloy particle coated with a layer selected from the group consisting of an atomic submonolayer, monolayer, bilayer, or trilayer of zerovalent platinum atoms, or a combination thereof, wherein said palladium-alloy does not include platinum; and
metal-bonding ligands or surfactants on said surface layer of zerovalent platinum.
10. A particle composite according to claim 2 , wherein the palladium-alloy nanoparticle has a size of about three to ten nanometers.
11. A particle composite comprising:
a palladium or palladium-alloy particle coated with a layer selected from the group consisting of an atomic submonolayer, monolayer, bilayer, or trilayer of zerovalent platinum atoms, or a combination thereof, wherein said palladium-alloy does not include platinum; and
wherein the palladium or palladium-alloy nanoparticle has a size of about five nanometers.
12. A particle composite, comprising:
a palladium or palladium-alloy particle coated with a layer selected from the group consisting of an atomic submonolayer, monolayer, bilayer, or trilayer of zerovalent platinum atoms, or a combination thereof, wherein said palladium-alloy does not include platinum; and
wherein the palladium or palladium-alloy particle is coated with an atomic submonolayer of zerovalent platinum atoms.
13. A particle composite according to claim 12 , wherein the atomic submonolayer of zerovalent platinum atoms is co-deposited with a submonolayer of a metal other than platinum to form a platinum-metal alloy monolayer.
14. A particle composite according to claim 13 , wherein the metal other than platinum is a transition metal.
15. A particle composite according to claim 14 , wherein the transition metal is Ir, Ru, Os, or Re.
16. A particle composite according to claim 15 , wherein said platinum-metal alloy monolayer is according to the formula Ir 0.2 Pt 0.8 .
17. A particle composite according to claim 15 , wherein said platinum-metal alloy monolayer is according to the formula Ru 0.2 Pt 0.8 .
18. A particle composite according to claim 15 , wherein said platinum-metal alloy monolayer is according to the formula Os 0.2 Pt 0.8 .
19. A particle composite according to claim 15 , wherein said platinum-metal alloy monolayer is according to the formula Re 0.2 Pt 0.8 .
20. A suspension or dispersion comprising a particle composite suspended or dispersed in a liquid phase, wherein said particle composite comprises a palladium or palladium-alloy particle coated with a layer selected from the group consisting of an atomic submonolayer, monolayer, bilayer, or trilayer of zerovalent platinum atoms, or a combination thereof, wherein said palladium-alloy does not include platinum.
21. A catalyst comprising a particle composite comprising a palladium or palladium-alloy particle coated with a layer selected from the group consisting of an atomic submonolayer, monolayer, bilayer, or trilayer of zerovalent platinum atoms, or a combination thereof, wherein said palladium-alloy does not include platinum, wherein said particle composite is bound to a support.
22. A catalyst according to claim 21 , wherein the support is electrically conductive.
23. A catalyst according to claim 22 , wherein the support is carbon black, graphitized carbon, graphite, or activated carbon.
24. A method for reducing oxygen gas, the method comprising contacting a nanoparticle composite comprising a palladium or palladium-alloy nanoparticle coated with a layer selected from the group consisting of an atomic submonolayer, monolayer, bilayer, or trilayer of zerovalent platinum atoms, or a combination thereof, wherein said palladium-alloy does not include platinum, with oxygen gas.