158 volga

Improving the Dispersion of Electrodeposited

Palladium on Carbon Support

Volga Muthukumar, Kranthi Kumar Maniam, Raghuram Chetty

Department of Chemical Engineering

Indian Institute of Technology Madras, Chennai

International Conference on Advances in

Energy Research (ICAER’13)

11-Dec-13 ICAER'13 2

Outline

Introduction

Objective

Electrodeposition of palladium (Pd)

Influence of precursor concentration

Influence of catalyst support

Wood apple shell activated carbon (WASAC) as

support

Summary


Fuel cell – Current status

*http://www.fuelcells.org.*http://www.eere.energy.gov.

Fuel cell cost –

electrodes represent

54 % of stack cost


Electro

catalyst

Catalyst Support

Vulcan XC-R72

Alternative

Carbon from biomass

Wood apple carbon

Noble catalyst

Pt- limited availability, high cost

Alternative

Pd- low cost compared to Pt

Catalyst

Improvement in catalytic

dispersion

Increase active surface area

Decrease catalyst loading

Effective catalyst utilization


Electrodeposition

Formation of high purity catalyst

Ease in control of catalyst loading, shape and size

High growth rate at relatively low temperatures

Simple operation during MEA fabrication

Low-cost requirement without sacrificing its performance in fuel cell

Environment friendly

To increase the catalytic activity of Pd by improving the metal dispersion

on support material

To synthesize Pd nanoparticles using simple electrochemical deposition

Controlling the metal precursor concentration

Using a high surface area carbon support

To compare the activity of Pd supported electrocatalysts towards oxygen

reduction reaction (ORR) and formic acid oxidation.

Aim & Objective


Electrodeposition

Coating DepositionElectrochemical

activation

1

2 3

Constant potential in

acidic electrolyte

containing Pd precursor

Potential cycling

in acidic medium

Methodology


Graphite

Carbon Substrate

Catalyst

Electrochemical responses

Cyclic voltammetry (CV) – Formic acid oxidation

Linear sweep voltammetry (LSV) – ORR activity

Electrodeposition of Pd

Electrodeposition - Constant voltage technique

Schematic diagram of three

electrode setup


Chloride precursor

(PdCl2) in acidic medium

0.0 0.2 0.4 0.6 0.8 1.0 1.2-0.8

-0.6

-0.4

-0.2

0.0

0.2

Potential / V vs. RHE

Cyclic Voltammogram

Cu

rre

nt

de

nsi

ty /

mA

.cm

-2

0.6 V

Pd2+ Pd0

Deposition potential: 0.6 V


0.5mM 0.75mM 1mM

Lower precursor concentrations

o Most of the reduced metal atoms used for formation of nuclei

o Fast formation of ultra fine nuclei and subsequent slow crystal growth rate

On increasing the precursor concentration

o Formation of isolated and dispersed Pd nanoparticles


1.5mM 2 mM

On increasing precursor concentration, initial reduced metal atoms

increases and results in formation of large nuclei

1 mM precursor concentration - Well dispersed morphology of Pd

nanoparticles

Concentration >1 mM

o Aggregation of Pd

particles

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Low Pd 2+

Concentration

High Pd 2+

Concentration

Substrate Substrate

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Ultra fine

nuclei Large

nuclei


0.0 0.2 0.4 0.6 0.8 1.0 1.2

-5

-4

-3

-2

-1

0

Effect of precursor concentration

Potential, V vs RHEC

urr

en

t d

en

sity, m

A/c

m2

0. 5 mM

0.75 mM

1 mM

1.5 mM

2 mM

Deposition potential : 0.6 V

ORR peaks @ 5 mV s-1

Linear Sweep Voltammograms

ORR activity

Increasing trend in ORR activity

upto 1 mM precursor concentration.

Decline in reduction current beyond

1 mM concentration.

Pd particle aggregation beyond 1

mM concentration (SEM images)

decrease the activity and reduction

in metal utilization efficiency.

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Support - Wood Apple Shell Activated Carbon

(WASAC) prepared from wood apple shell

High surface area and comparable pore

volume to Vulcan XC-72R.

Rigid amorphous structure .

High porosity and good electronic

conductivity.

Alternative Carbon Support

*http://www.flowersofindia.net

11-Dec-13 ICAER'13 13

*Wood apple fruits

WASAC

Graphite electrodes with Wood Apple Shell Carbon (WASAC) as electrode.

SEM images - WASAC has a significant influence in improving dispersion of Pd

nanoparticles over Vulcan.

EDX image confirms deposition of Pd on carbon based support by

electrodeposition.

Vulcan WASAC EDX Image

Influence of Carbon Support

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0.0 0.2 0.4 0.6 0.8 1.0 1.2

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

Pd oxide

reduction

Pd oxide

formation

H adsorption

H desorption

Potential, V vs RHE

Cu

rre

nt d

en

sity, m

A/c

m2

(a)

(b)

Comparison of CV of Pd catalysts deposited in

nitrogen saturated 0.5 M H2SO4 at a scan rate of

50 mV s-1: (a) Vulcan and (b) WASAC.

Influence of Carbon Support

11-Dec-13 ICAER'13 15

0.0 0.2 0.4 0.6 0.8 1.0 1.2

-2.0

-1.6

-1.2

-0.8

-0.4

0.0

0.4

0

200

400

600

800

1000

1200

C

urr

ent density, m

A/c

m2

(a)

(b)

0.4 V

Potential, V vs RHEC

urr

en

t d

en

sity, m

A/c

m2

(a)

(b)

LSV of Pd catalysts deposited on (a)

Vulcan and (b) WASAC in oxygen

saturated 0.5 M H2SO4. Inset compares

the current densities taken at 0.5 V.

-0.15

0.00

0.15

0.30

0.45

0.0 0.2 0.4 0.6 0.8 1.0

-0.15

0.00

0.15

0.30

0.45

C

urr

en

t d

en

sity, m

A/c

m2

Wood apple carbon

(a)

Potential, V vs RHE

Vulcan

(b)

CV of Pd catalysts deposited on (a) WASAC and

(b) Vulcan support in nitrogen saturated 1 M

HCOOH in 0.5 M H2SO4 at a scan rate of 20 mV s-1

Pd deposited on WASC support

showed higher activity towards

HCOOH oxidation.

This phenomenon can be

attributed to

Improved dispersion of metal

nanoparticles

High ESA of the electrode

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Formic acid oxidation

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Type of

Carbon

Morphology of

Pd

Onset of Pd

Oxide

reduction (V)

Onset Potential

for ORR (V)

ESA

(cm2)

Current

density at

0.5 V

(μA /cm2)

Vulcan

Irregular

spherical

agglomerates

~ 0.75 ~ 0.70 0.123 16

WASAC

Dispersed

spherical

particles

~ 0.85 ~ 0.62 0.360 390

A positive shift in onset of Pd oxide reduction- weaken the chemical

adsorption energy with oxygen containing species.

Pd/WASAC showed a positive shift in onset potential and higher

current density values over that of Pd/ Vulcan.

Improved performance of WASAC

supported Pd

11-Dec-13 ICAER'13 18

Conclusions

Electrodeposition of Pd on an electrochemically activated carbon based

substrates was carried out using constant voltage technique.

The effect of precursor concentration and support was studied in relation

to the dispersion of Pd.

Well dispersed Pd nanoparticles were formed upto a precursor

concentration of 1 mM and aggregates beyond1 mM.

WASAC supported Pd showed better dispersion and hence showed

higher formic acid and ORR activity than Vulcan supported Pd.

11-Dec-13 ICAER'13 19

Future Work

Rotating Disc Electrode studies.

To perform stability test.

To test the performance of Pd/WASAC in a single direct methanol

fuel cell (DMFC) and formic acid fuel cell (FAFC).

Our Research Group

11-Dec-13 ICAER'13 20