LASER INDUCED PT CATALYST MATERIALS

Abstract

A method of forming a platinum on carbon (Pt/C) catalyst, comprising the steps of: impregnating a carbon substrate made of carbon materials with an aqueous Pt ion containing solution; drying the impregnated substrate; and scribing the surface of the substrate in-situ with a laser beam by moving the beam over the surface in order to vaporize the carbon materials and redeposited them as nano sized carbon particles onto the carbon substrate. As a result, the heat generated in situ from the laser process reduces Pt salt particles dispersed on the surface into Pt (0). This avoids the slurry preparation, tape casting and drying procedure of the prior art and results in reduced manufacturing times and a better product.

Claims

1. A method of forming a platinum on carbon (Pt/C) catalyst, comprising the steps of: impregnating a carbon substrate made of carbon materials with a Pt ion containing solution; drying the impregnated substrate; scribing the surface of the substrate with a laser beam by moving the beam over the surface in order to vaporize the carbon materials and redeposited them as nano sized carbon particles onto the carbon substrate; whereby the heat generated in situ from the laser process reduces Pt salt particles dispersed on the surface into Pt (0).

2. The method of forming platinum on carbon (Pt/C) catalyst according to claim 1 wherein the carbon substrate is carbon paper.

3. The method of forming platinum on carbon (Pt/C) catalyst according to claim 1 wherein the step of impregnating involves spraying or soaking.

4. The method of forming platinum on carbon (Pt/C) catalyst according to claim 1 wherein the Pt ion containing solution includes 0.1 mM to 100 mM of PtCl.sub.4, H.sub.2PtCl.sub.6, or H.sub.2Pt(OH).sub.6 in deionized water or ethanol or isopropanol.

5. The method of forming platinum on carbon (Pt/C) catalyst according to claim 1 wherein the drying step is carried out in an oven which could be under vacuum, N.sub.2 or Ar or other inert gas protection.

6. The method of forming platinum on carbon (Pt/C) catalyst according to claim 1 wherein the laser beam has a wavelength of 300-700 nm.

7. The method of forming platinum on carbon (Pt/C) catalyst according to claim 6 wherein the laser beam has a wavelength of 455 nm.

8. The method of forming platinum on carbon (Pt/C) catalyst according to claim 1 wherein a laser forming the laser beam has its power, sweeping frequency and pulsation adjusted to obtain different Pt oxidation states and particle morphology.

9. A carbon substrate with loaded Pt made according to the method of claim 1.

10. The carbon substrate of claim 9 used directly as an electrode of a fuel cell.

11. The carbon substrate of claim 9 used directly as a membrane in a catalytic converter of an automobile.

12. A method of forming a platinum on carbon (Pt/C) catalyst, comprising the steps of: preparing a 50 mM H.sub.2PtCl.sub.6 solution; spraying the prepared solution onto a piece of carbon cloth; after spraying, leaving the carbon cloth to dry in air overnight; laser treating the dried carbon cloth with a linear heat density of 0.17 J/mm to reduce Pt.sup.4+ into Pt.

13. A method of forming a platinum on carbon (Pt/C) catalyst, comprising the steps of: preparing a 50 mM PtCl.sub.4 solution; sprayed the solution onto a piece of carbon cloth; immediately after spraying, transferring the carbon cloth into a vacuum oven; drying the cloth in the oven for about 4 hours at about 60? C.; and laser treating the dried carbon cloth with a linear heat density of 0.17 J/mm to reduce Pt.sup.4+ into Pt.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] This 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.

[0013] The foregoing and other objects and advantages of the present invention will become more apparent when considered in connection with the following detailed description and appended drawings in which like designations denote like elements in the various views, and wherein:

[0014] FIG. 1A is a photograph of a main body of a laser placed in a laser protection box in which the Pt catalyst is created and FIG. 1B is a diagram of a laser scribing procedure on a carbon substrate according to the present invention;

[0015] FIG. 2A is a graph of a survey X-ray photoelectron spectroscopy (XPS) scan of reduced Pt on a carbon cloth, FIG. 2B is a high-resolution X-ray XPS of Pt 4f.sub.7/2 and 4f.sub.5/2 peaks and FIG. 2C shows the Pt binding energies of Pt metal, Pt(II) and Pt(IV);

[0016] FIG. 3A is a high-resolution Pt XPS scan indicating the metallic state of Pt deposited on a graphite fiber and FIG. 3B is a scanning electron microscope-energy-dispersive spectroscopy (SEM-EDS) scan of C, O, Cl and Pt on a laser treated graphite fiber which indicates the Pt metal deposition in micro size; and

[0017] FIG. 4 is an SEM-EDS scan of C, O, Cl and Pt on a laser treated graphite fiber, which indicates the Pt metal deposition in micro size.

DETAILED DESCRIPTION OF THE INVENTION

[0018] Pt has been known as a good catalyst candidate for many reactions that involve gaseous chemicals, such as an oxygen reduction reaction and a hydrogen oxidation reaction, due to its excellent reactivity and adequate bonding energy to gaseous chemicals.

[0019] A carbon substrate used in the present invention can be carbon paper as shown in illustration 10 and photograph 11 of FIG. 1B. In some embodiments, aqueous Pt ion containing solution (0.1 mM to 100 mM of PtCl.sub.4, H.sub.2PtCl.sub.6, H.sub.2Pt(OH).sub.6) is used to impregnate carbon substrates through spraying or soaking as shown in illustration 12.

[0020] After being dried in a vacuum oven or under N.sub.2, Ar or other inert gas atmospheres (or not being dried) as shown in illustration 14 of FIG. 1B, the carbon paper is placed properly under the laser beam device as shown in FIG. 1A. The laser beam device, which may project a 455 nm blue light, is operated to scribe on the carbon cloth as shown in illustration 16 and photograph 17 of FIG. 1B. This process vaporizes the carbon materials and redeposits them as nano sized carbon particles onto the carbon substrate, as in the survey X-ray photoelectron spectroscopy (XPS) scan in FIGS. 2A-2C. Simultaneously, the heat generated in situ from the laser process reduces Pt salt particles dispersed on the surface into Pt (0). In effect, the laser scribing process reduces the Pt.sup.4+ to Pt.sup.2+ at 300-320? C. and Pt.sup.2+ to Pt (0) at 375-510? C. This has been confirmed with XPS scans. The laser beam power, sweeping frequency and pulsation can be adjusted to obtain different Pt oxidation states and particle morphology.

[0021] FIG. 2A shows the survey XPS scan of reduced Pt on the carbon cloth. FIG. 2B is an expanded graph of the Pt 4f.sub.5/2 and Pt 4f.sub.7/2 peaks from FIG. 2A showing that the peaks usually have a separation of 3.3 eV. The table of FIG. 2C shows the chemical state and binding energy Pt 4f.sub.7/2 of Pt metal, PtO and PtO.sub.2.

[0022] A first example was created by preparing a 50 mM H.sub.2PtCl.sub.6 solution and sprayed it onto a piece of carbon cloth. After spraying, the carbon cloth was left to dry in air overnight. Then the dried carbon cloth was laser treated with a linear heat density of 0.17 J/mm to reduce Pt.sup.4+ into Pt. The XPS scan result (FIG. 3A) shows the successful reduction of Pt.sup.4+ to Pt, while the SEM-EDS scan result (FIG. 3B) shows the Pt deposited on the carbon fibre in 1-2 ?m size.

[0023] A second example was created by preparing a 50 mM PtCl.sub.4 solution and sprayed it onto a piece of carbon cloth. Immediately after the spraying, the carbon cloth was transferred into a vacuum oven and dried for 4 hours at 60? C. Then the dried carbon cloth was laser treated with a linear heat density of 0.17 J/mm to reduce Pt.sup.4+ into Pt. The XPS result (FIG. 4) shows the successful reduction of Pt.sup.4+ to Pt and the SEM result shows the Pt deposited on the carbon fibre in 1-2 ?m size.

[0024] The mentioned carbon paper with the loaded Pt can then be directly used as an electrode in a fuel cell or a membrane in a catalytic converter of an automobile.

[0025] In general, the present invention involves in-situ inducement of the growth of Pt or other metallic particles on carbon paper, which can later be assembled directly into an electrode for further use or testing. The laser process of the present invention allows for direct deposition of Pt catalyst on the electrode without the adoption of the whole slurry preparation, tape casting and drying procedure of the prior art.

[0026] While the invention is explained in relation to certain embodiments, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications.