Preparation of hollow Pt and Pt-alloy catalysts

1. A method for preparing hollow platinum or platinum-alloy catalysts, the method comprising:

forming a plurality of low-melting-point core metal nanoparticles in a non-aqueous solvent absent of oxygen;

depositing platinum or platinum-alloy onto the low-melting-point core metal nanoparticles to form a shell of platinum or platinum-alloy coating the low-melting-point core metal nanoparticles; and

removing the low-melting-point core metal nanoparticles from the platinum or platinum-alloy coated particles by melting to form a plurality of hollow platinum or platinum-alloy particles wherein a room-temperature-ionic liquid is used as a medium when depositing platinum or platinum-alloy onto the low-melting-point core metal nanoparticles or melting the low-melting-point core metal nanoparticles or annealing the shell to improve its catalytic activity.

2. The method of claim 1 wherein the low-melting-point core metal nanoparticles include a metal having a melting point less than about 400° C.

3. The method of claim 1 wherein the low-melting-point core metal nanoparticles include a low-melting-point metal selected from the group consisting of In, Ga, Ge, Sn, Sb, Tl, Pb, Bi, Zn, Cd, Hg, and combinations thereof.

4. The method of claim 1 wherein the low-melting-point core metal nanoparticles are formed by sputtering a metal into the non-aqueous solvent.

5. The method of claim 1 wherein the non-aqueous solvent includes a room-temperature-ionic liquid (RTIL).

6. The method of claim 1 wherein the low-melting-point core metal nanoparticles have an average diameter up to 500 nanometers.

7. The method of claim 1 wherein the low-melting-point core metal nanoparticles have an average diameter from about 0.5 to about 500 nanometers.

8. The method of claim 1 wherein the low-melting-point core metal nanoparticles have an average diameter from about 1 to about 100 nanometers.

9. The method of claim 1 wherein the non-aqueous solvent is a room temperature ionic liquid having cations and anions.

10. The method of claim 9 wherein the cations are selected from the group consisting of:

wherein R 1 , R 2 , and R 3 are each independently C 1-20 alkyl or C 2-20 alkyl ether.

11. The method of claim 10 wherein R 1 , R 2 , and R 3 are each independently methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, t-butyl, n-hexyl, n-octyl, n-decyl, n-C 16 H 33 , CH 3 OCH 2 —, and CH 3 OC 2 H 4 —.

12. The method of claim 9 wherein the anions are selected from the group consisting of [BF 4 ] − , [B(CN) 4 ] − , [CF 3 BF 3 ] − , [C 2 F 5 BF 3 ] − , [n-C 3 F 7 BF 3 ] − , [n- C 4 F 9 BF 3 ] − , [(C 2 F 5 ) 3 PF 3 ] − , [CF 3 CO 2 ] − , [CF 3 SO 3 ] − , [N(COCF 3 )(SO 2 CF 3 )]—, [N(SO 2 F) 2 ] − , [EtOSO 3 ]—, [N(CN) 2 ]—, [C(CN) 3 ]—, [SCN]—, [SeCN]—, [CuCl 2 ]—, [AlCl 4 ] − , [ZnCl 4 ] 2− , or [F(HF) 23 ]—.

13. The method of claim 9 wherein the room temperature ionic liquid is functionalized to prevent agglomeration.

14. The method of claim 1 wherein the hollow platinum or platinum-alloy particles are combined with a solvent, an ionomer, and an optional filler to form an ink composition.

15. The method of claim 14 wherein the ink composition is applied to a surface in a fuel cell component and then dried.

16. The method of claim 15 wherein the fuel cell component is an ion conducting layer or a gas diffusion layer.

17. The method of claim 1 wherein platinum or platinum-alloy is deposited onto the low-melting-point core metal nanoparticles by contacting the low-melting-point core metal nanoparticles with a platinum or a platinum-alloy precursor.

18. The method of claim 17 wherein the platinum-alloy precursor is selected from the group consisting of K 2 PtCl 6 , K 2 PtCl 4 , H 2 PtBr 4 , Pt(NO 3 ) 2 , Pt acetylacetonate, and combinations thereof.

19. The method of claim 18 wherein the platinum-alloy precursor is reduced to metal with a chemical reductant or by solvent decomposition.

20. The method of claim 1 wherein platinum or platinum-alloy is deposited onto the low-melting-point core metal nanoparticles by Galvanic displacement of metal in the low-melting-point core metal nanoparticles with platinum.

21. The method of claim 1 wherein the hollow platinum or platinum-alloy particles have an average from about 7 atomic layers to about 1.5 nm thick.