This invention relates to pt-WOx/C nano composite anode electrocatalyst for fuel cell application

BACKGROUND OF THE INVENTION:

Fuel cells are attractive power sources for both stationary and electric vehicle applications due to their high conversion efficiencies and low, pollution. Among the various types of fuel cells, the proton exchange membrane fuel cells (PEMFC) are the most suitable candidates for electric vehicles as they can be operated at low temperature of < 100 °C.

Basic element of fuel cell consists of polymer electrolyte membrane phase in contact with a porous anode and cathode on both sides.

The fuel (hydrogen) and oxidant (Oxygen) gas flow is provided through manifold plates placed at the backside of the anode and cathode, respectively, and generate electrical energy by the electrochemical oxidation of fuel and the electrochemical reduction of oxygen.

At anode side, proton (H+ ) will generate and mass transport through the membrane to the cathode side and combine with oxygen to generate water molecule as a by product.

In the anode, the following reaction (equ.l) takes place in the platinum catalytic layer of the anode and H+ ions are diffuses through the membrane

In the cathode, the following reaction takes place in the Platinum catalytic layer of the cathode. Protons combine with Oxygen and form water molecule as by-product (equ.2).

Platinum supported on carbon black is widely used as electrocatalysts in PEMFC. However, platinum is expensive and the world supply of platinum is limited. Therefore, improving the electrocatalytic activity of platinum with minimum loading level is important.

BRIEF DESCRIPTION OF THE DRAWINGS :

Fig -1 A flow chart diagram for the preparation method of the nano composite
electrocatalyst.
Fig-2 Performance Characteristics of a Single cell.
Fig-3 XRD pattern of the prepared catalyst.
Fig-4 SEM photograph of the prepared catalyst.
Fig-5 Typical Cyclic Voltammogram of the prepared catalyst.

DETAILED DESCRIPTION OF THE INVENTION:

PREPARATION OF THE CATALYST:

Refer Fig-1.
Calculated volume of Hydrogen hexa chloroplatinate (IV) aqueous solution is added to Vulcan XC-72R carbon black and mixed well.

The carbon slurry mixer is subjected to ultrasonic vibration for 45 minutes at room temperature.
pH of the slurry is adjusted to 9 by adding IN Sodium hydroxide solution and heated to 65°C ± 5°C.

Subsequently, 20 ml of 1% Sodium borohydride solution (reducing agent) is added drop by drop to the carbon slurry catalyst mixture with constant stirring.

Temperature is maintained at 65°C ± 5°C and allowed to react for one hour for the completion of reaction.

The resultant catalyst slurry is centrifuged and washed with distilled water till the final wash water pH to 7 - 8.

Calculated volume of Sodium tungstate aqueous solution is added to the washed slurry and the pH of the slurry is adjusted to < 0.5 by adding 5N Hydrochloric acid and the final slurry is heated to 65°C ± 5°C for one hour with constant stirring.

The treated catalyst slurry is centrifuged and washed to remove Sodium chloride and excess Sodium tungstate.

Finally, the thoroughly washed catalyst is dried at 110°C ± 5°C for 4 hours.

The prepared Pt-WOx /C (in which x is in the range of about 1 to 5) catalyst is characterized for Single cell evaluation (Figure-2) and the optimized catalyst further characterized for X-Ray Diffraction (Figure-3), Scanning Electron Microscope (Figure-4) and Cyclic Voltammetry (Figure-5).

The terms and expressions herein are of description and do not limit the scope and ambit of this invention.

We claim:

1. A method of preparation of carbon supported nano composite anode electrocatalyst
Pt-WOx /C (6:4 is the atomic % of Pt:W) comprising the steps of slurry making, ultrasonic mixing, reduction of precious metal with Sodium borohydride, washing , loading of Sodium tungstate solution , conversion of tungstate to tungstic acid by adjustment of pH (<0.5) and washing and drying.

2. A method as claimed in Claim 1 wherein the said calculated volume of 0.5 % to 2% Hydrogen hexa chloroplatinate (IV) aqueous solution.

3. A method as claimed in Claim 1 or .Claim 2 wherein the said quantity of Vulcan XC-72R carbon 0.45 to 0.50 g.
4. A method as claimed in anyone of the preceding Claims wherein the ultrasonic vibration is carried out for 30 to 60 minutes.

5. A method as claimed in anyone of the preceding Claims wherein the reaction time for the reduction of platinum solution using 0.5% to 1.5 % Sodium borohydride is 60 minutes ± 10 minutes.

6. A method as claimed in anyone of the preceding Claims wherein the addition of calculated amount of 1 % Sodium tungstate aqueous solution and further treated with 5N Hydrochloric acid to reduce the pH to <0.5.

7. A method as claimed in anyone of the preceding Claims wherein the washed slurry is dried at 110°C ± 10°C for 4 to 6 hours and prepared Pt-WOx /C nano composite electrocatalyst pulverized dry powder was characterized for Single cell evaluation and the optimized Pt-WOx /C catalyst further characterized for X-Ray Diffraction , Scanning Electron Microscope and Cyclic Voltammetry.

8. A method as claimed in anyone of the preceding claims wherein the electrode comprises an anode i.e., the electrode at which electrochemical oxidation of Hydrogen and / or a hydrogen-rich fuel (gas or liquid) is oxidized in-situ.

9. A method as claimed in anyone of the preceding claims wherein the atomic % of Pt:W are2:4, 4:6, 6:4 and 8:2

10. Carbon supported nano composite anode electrocatalyst Pt-WOx/C whenever manufacture by a method as claimed in any one of the preceding Claims