Nanostructured PtxMy catalyst for PEMFC cells having a high activity and a moderate H2O2 production

Abstract

A method of manufacturing a catalyst for a Pt.sub.xM.sub.y-based PEMFC, M being a transition metal, including the steps of: depositing Pt.sub.xM.sub.y nanostructures on a support; annealing the nanostructures; depositing a Pt.sub.xM.sub.y layer at the surface of the nanostructures thus formed; and chemically leaching metal M. It also aims at the catalyst obtained with this method.

Claims

1. A method of manufacturing a catalyst for a Pt.sub.xM.sub.y-based PEMFC, M being a transition metal, comprising the steps of: depositing a first layer of Pt.sub.xM.sub.y nanostructures on a support; annealing the nanostructures; depositing a second Pt.sub.xM.sub.y layer at the surface of the nanostructures thus formed; and producing structured vacancies or cavities, having a size which does not exceed 6 Angstrms, at the surface of the second Pt.sub.xM.sub.y layer, by controlled chemical leaching of metal M.

2. The method of manufacturing a catalyst for a PEMFC of claim 1, wherein the support is a gas diffusion layer of the PEMFC.

3. The method of manufacturing a catalyst for a PEMFC of claim 2, wherein the gas diffusion layer has a thickness of 200 micrometers.

4. The method of manufacturing a catalyst for a PEMFC of claim 1, wherein the support is not a gas diffusion layer of the PEMFC, and wherein after annealing, the nanostructures are transferred onto the gas diffusion layer of the PEMFC.

5. The method of manufacturing a catalyst for a PEMFC of claim 1, wherein metal M is selected from the group consisting of Ni, Fe, Co, and Cr.

6. The method of manufacturing a catalyst for a PEMFC of claim 5, wherein the catalyst is formed with Pt.sub.3Ni.

7. The method of manufacturing a catalyst for a PEMFC of claim 1, wherein the deposition of nanostructures is performed by cathode sputtering.

8. The method of manufacturing a catalyst for a PEMFC of claim 1, wherein the anneal is performed at a temperature in a range of 600 C. to 1,200 C.

9. The method of manufacturing a catalyst for a PEMFC of claim 8, wherein the anneal is performed for a 1-hour duration.

10. The method of manufacturing a catalyst for a PEMFC of claim 1, wherein the deposition of the Pt.sub.xM.sub.y layer is performed by MOCVD.

11. The method of manufacturing a catalyst for a PEMFC of claim 10, wherein the MOCVD is performed by means of organometallic precursors of platinum and of the metal.

12. The method of manufacturing a catalyst for a PEMFC of claim 11, wherein the MOCVD is performed at a temperature in a range of 200 C. to 400 C.

13. The method of manufacturing a catalyst for a PEMFC of claim 12, wherein the MOCVD is performed at a temperature of 300 C.

14. The method of manufacturing a catalyst for a PEMFC of claim 1, wherein the chemical leaching of metal M is performed by immersion in a liquid electrolyte.

15. The method of manufacturing a catalyst for a PEMFC of claim 14, wherein the liquid electrolyte is H.sub.2SO.sub.4.

16. The method of manufacturing a catalyst for a PEMFC of claim 14, wherein the chemical leaching is performed for 1 hour.

17. A catalyst capable of being obtained by means of the method of claim 1, said catalyst comprising core/shell nanostructures made of Pt.sub.xM.sub.y covered with a Pt.sub.xM.sub.y layer comprising vacancies.

18. The catalyst of claim 17, wherein the vacancies have a size in the range from 2 to 6 Angstrms.

19. A PEMFC-type fuel cell comprising at least at one of its electrodes the catalyst of claim 17.

20. A method of improving the lifetime of a PEMFC-type fuel cell comprising using as a catalyst, at least at its cathode, the catalyst of claim 17.

21. A PEMFC-type fuel cell comprising as its cathode the catalyst of claim 17.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

(2) The foregoing features and advantages will now be discussed in the following non-limiting description of a specific embodiment, in relation with the accompanying drawings, among which:

(3) FIG. 1 shows the diagram of the operating principle of a PEMFC-type fuel cell.

(4) FIG. 2 shows the thermodynamic energy profile for the forming of H.sub.2O and H.sub.2O.sub.2 on a Pt.sub.3Ni(111) surface of Pt-skeleton type, determined from calculations using the density functional theory in periodic conditions. S5 shows the step of forming the hydroperoxyl (OOH), which is the surface precursor species for the forming of hydrogen peroxide H.sub.2O.sub.2.

(5) FIG. 3 shows the different steps implemented for the manufacturing of a nanostructured catalyst according to the invention: A/ anneal; B/ deposing the Pt.sub.3M layer by the MOCVD technique; C/ chemically leaching metal M.

(6) FIG. 4 shows the variation of the membrane conductivity along time for 2 different H.sub.2O.sub.2 production rates (100% and 50%, respectively).

DETAILED DESCRIPTION OF THE INVENTION

(7) Comparative experiments have been made in a PEMFC containing either: a membrane in the presence of a cathode with a Pt.sub.3Ni core/shell structure; or a membrane in the presence of a cathode with a nanostructured Pt.sub.3Ni catalyst according to the invention, in particular according to the method illustrated in FIG. 3.

(8) The results are shown in FIG. 4.

(9) In the first case, the membrane has a durability (80% loss of protonic conductivity) of approximately 1,000 hours in OCV conditions (Open Circuit Voltage: temperature=80 C.; relative humidity of the anode and of the cathode=80%; anode and cathode pressure: 1.5 bar; PtNi filling: 0.3 mg.Math.cm.sup.2 in the anode and 0.6 mg.Math.cm.sup.2 in the cathode; membrane thickness: 25 m; active surface area: 25 cm.sup.2).

(10) In the same conditions, the nanostructured Pt.sub.3Ni catalyst according to the invention enables to decrease by 50% the production of H.sub.2O.sub.2. Further, after 1,000 hours of operation, the membrane conductivity is approximately doubled, which extends by approximately 500 hours the cell lifetime (defined herein as the time required for the cell potential to become zero).