The Engineering of Pt/Carbon Catalyst Preparation for application on Proton

Exchange Fuel Cell Membrane (PEFCM)

By: Jaime O. RoblesMentored: John R. Regalbuto

Outline

• PROBLEM • OBJECTIVE• INTRODUCTION TO SCIENCE• KEY VARIABLE• POINT OF ZERO CHARGE EXPERIMENT• STRONG ELECTROSTATIC ADSORPTION

METHOD (WET IMPREGNATION)• STEM RESULTS AND EXAFS RESULST• CONCLUSION

Problem definition

• Determine the most efficient way to prepare high loadings of highly dispersed Pt on carbon catalysts.– Proposed method-strong electrostatic

adsorption (SEA)

Objective

• Identify the variables and conditions that will maximize the dispersion, and weight loading of Pt/Carbon catalyst to be used on PEFCM.

Proton Exchange Fuel Cell Membrane (PEFCM)

Key variables

• Point of zero charge:– Surface loading (m^2/L)– Surface area (m^2/g)– pH

• Method of impregnation of Pt onto carbon support-strong electrostatic adsorption:

– Pt concentration (ppm)– pH– Carbon support

Point of zero charge

• Why obtain point of zero charge?

– A characteristic of each carbon– Deciding factor for adsorption experiments– Obtain the pH at which the surface of carbon

is neutral

How do you conduct PZC experiments

( )grams

gramsm

mLm

AreaSurfaceVolumeLoadingSurfaceM carbon =

== 2

32

*][

_)(*)_(

1. Shift pH of eleven water samples using NaOH or HCL (ideal points 1,2,3,4,5,6,9,10,11,12,13)

2. Add carbon support to each sample, using equation below for calc.

3. Shake for an hour and measure pH

Electrostatic Illustration of PZC and results

OH2+

O-

pH<PZC

pH>PZC

OHPZC

K1

K2

•pH < PZC –SURFACEPROTONATED

•pH > PZC – SURFACE DEPROTONATED

0123456789

1011121314

0 2 4 6 8 10 12 14pH initial

pH fi

nal

KETJEN BLACK ED 300 J

Carbon Volume (m^3) SA (m^2/g) SL (m^2/L)g of

carbon needed

PZC

Ketjen Black EC

300 J0.05 795 10000 0.629 9.4

Ketjen Black EC

600 J0.05 1415 10000 0.353 9.5

Black Pearls 2000

0.05 1475 10000 0.339 9.5

Optimized Parameter for PZC surveys:

KETJEN BLACK ED 300 J

pH(initial)pH(final-1hr.

Contact1.06 1.061.97 2.073.05 7.724.01 8.904.89 9.445.86 9.519.12 9.84

10.18 10.2811.07 11.0611.88 11.8713.05 13.03

Revised Physical Adsorption graphic

OH2+

O-

OHPZC

K1

K2

[PtCl6]-2pH<PZC

pH>PZC

•CPA-anionic in solution•PTA-cationic in solution

[(NH3)4Pt]+2

Adsorption Results – via SEA

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

1.5 1.8 2.1 2.4 2.7 3 3.3 3.6 3.9

pH

Pt u

ptak

e ( µ µµµ

mol

/m2 )

EC300J

EC600J

Black Pearls

Umicore Ensaco 350

200ppm CPA

Carbon name Company Name Type Surface Area

(m^2/g) PZC SL (m^2/L)

Ketjen Black EC 300 J

Akzon Nobel cabon black 795 9.4 500

Ketjen Black EC 600 J

Akzon Nobel cabon black 1415 9.5 500

Black Pearls 2000

Cabot cabon black 1475 9.5 500

Specs:

Weight percent of Pt on Carbon

Weight percent of Pt on carbon

0

5

10

15

20

25

30

35

Ketjen Black EC 300J Ketjen Black EC 600J Black Pearls Ensaco 350

Carbon

Pt W

t%

Scanning Transmission Electron Microscope Results

• 30 wt% Pt/C • Average particle size: 10 – 20 Å

Ketjen Black EC 600JC S.A.= 1415 m^2/g

Extended X-ray Absorption Fine Structure-EXAFS

0.1

0.2

0 2 4 6

Mag

nitu

de o

f FT

[k3 *C

hi(k

)] R [Å]

Pt-Pt

Pt Higher Shells

Carbon: Timcal Timrex

•Large peak: Dry impregnating method

•Smaller peaks: Wet impregnating (Strong electrostatic adsorption method.)

EXAFS Fits Pt/CarbonJune 04

Sample Scatter CN R, Å DWF (x103)

Eo,eV

Est.Disp.

DI Pt-Pt 10.1 2.77 1.0 -1.6 0.2

WI Pt-Pt 4.7 2.74 1.0 -3.8 0.9

Conclusion

• Optimized conditions:– pH of 2.8– 200ppm conc. CPA– Large surface area black carbons– Strong electrostatic adsorption

Acknowledgments

• I would like to thank:– The National Science Foundation for funding

the program– Professor John R. Regalbuto– Dr. Jeff Miller, Michael Castorano, Xianghong

Hao, Mark Schreir, Rogelio Lopez