DENDRITIC METAL NANOSTRUCTURES FOR FUEL CELLS AND OTHER APPLICATIONS

Abstract

Embodiment of the present invention relate to dendrimers useful for application as catalysts, in particular as improved electrocatalysts for polymer electrolyte membrane fuel cells (PEM-FCs). Methods of preparing such catalysts are described. Examples include dendritic nanostructured metal catalysts, such as platinum and platinum-alloy catalysts.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B show TEM images of dendritic platinum nanosheets and commercial platinum black (respectively), used for the preparation of MEAs;

FIGS. 2A-2B show HAADF STEM images of dendritic platinum foam-like nanospheres used in preparation of the MEA;

FIG. 3 shows short-term durability tests at 0.5 V potentiostatic hold for 7 mg Pt/cm² loadings for dendritic nanospheres (curve 1), nanosheets (curve 2) and platinum black (curve 3);

FIG. 4 shows polarization curves before and after 75 hour potentiostatic tests on MEAs prepared with Pt nanosheets at time 0 (♦) and 75 h (⋄) and with Pt black at time 0 (▴) and 75 h (Δ) for loadings of 7 mg/cm²;

FIG. 5 shows short-term durability tests at 0.5 V potentiostatic hold for MEAs made with Pt nanospheres and Pt black;

FIGS. 6A-6B shows cyclic voltammagrams for Pt black and Pt nanosheets, respectively, where solid curves are at time 0 and the dashed curves are at 75 h;

FIG. 7 shows a comparison of CV features for Pt sheets (solid line) and Pt black (dashed line) before fuel cell test;

FIG. 8 shows cyclic voltammagrams for the 2 mg Pt/cm² MEAs for the Pt nanospheres before (gray line) and after (short dashed line) 75-hour aging, the circular Pt nanosheets before aging (long dashed line), and Pt black before aging (solid line);

FIGS. 9A-9D shows cross-section HAADF STEM images of the MEAs after a 75 h fuel cell tests, where FIGS. 9A and 9B show the dendritic platinum nanosheets and 9C and 9D show the platinum black;

FIG. 10 shows cross-section HAADF STEM images of the MEA made with platinum nanospheres after a 500 h fuel cell test; and

FIG. 11 illustrates a MEA using a catalyst according to an embodiment of the present invention.

Claims

1. A fuel cell, comprising: a first electrode;a second electrode; andan electrolyte located between the first electrode and the second electrode,wherein the first electrode includes an electron-conducting material and a catalyst, the catalyst comprising dendritic structures.

2. The fuel cell of claim 1, wherein the dendritic structures comprise platinum.

3. The fuel cell of claim 1, wherein the dendritic structures comprise a platinum alloy.

4. The fuel cell of claim 1, wherein the catalyst comprises a plurality of metal dendrimers.

5. The fuel cell of claim 4, wherein the metal dendrimers are partially fused together, the catalyst being a porous sheet including the dendritic structures.

6. The fuel cell of claim 4, wherein the metal dendrimers have a diameter, and the diameter is between approximately 1 nm and approximately 1000 nm.

7. The fuel cell of claim 6, wherein the diameter is between 1 nm and 500 nm.

8. The fuel cell of claim 4, wherein the metal dendrimers are generally spherical.

9. The fuel cell of claim 4, wherein the metal dendrimers are generally disk-shaped, having a disk thickness between approximately 1 nm and approximately 10 nm.

10. The fuel cell of claim 4, where at least some of the metal dendrimers have a single crystal structure.

11. The fuel cell of claim 1, where the electrolyte is a polymer electrolyte membrane.

12. A membrane-electrode assembly (MEA) comprising: a first electrode;a second electrode;an ion-conducting membrane located between the first electrode and the second electrode,the first electrode including dendritic nanostructures which act as an electrocatalyst during operation of the membrane-electrode assembly.

13. The membrane-electrode assembly of claim 12, wherein the dendritic nanostructures comprise a transition metal.

14. The membrane-electrode assembly of claim 12, wherein the catalyst comprises a plurality of metal dendrimers.

15. The membrane-electrode assembly of claim 14, wherein the first electrode comprises an electron-conducting material, at least some of the metal dendrimers being supported on the electron-conducting material.

16. The membrane-electrode assembly of claim 15, wherein the electron-conducting material includes graphitic carbon.

17. The membrane-electrode assembly of claim 12, wherein the ion-conducting membrane is a polymer electrolyte membrane.

18. A fuel cell including the membrane-electrode assembly of claim 12.