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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
11-Dec-13 ICAER'13 3
Fuel cell – Current status
*http://www.fuelcells.org.*http://www.eere.energy.gov.
Fuel cell cost –
electrodes represent
54 % of stack cost
11-Dec-13 ICAER'13 4
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
11-Dec-13 ICAER'13 5
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
11-Dec-13 ICAER'13 6
Electrodeposition
Coating DepositionElectrochemical
activation
1
2 3
Constant potential in
acidic electrolyte
containing Pd precursor
Potential cycling
in acidic medium
Methodology
11-Dec-13 ICAER'13 7
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
11-Dec-13 ICAER'13 8
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
Influence of precursor concentration
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
11-Dec-13 ICAER'13 9
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
11-Dec-13 ICAER'13 10
Influence of precursor concentration
Low Pd 2+
Concentration
High Pd 2+
Concentration
Substrate Substrate
11-Dec-13 ICAER'13 11
Ultra fine
nuclei Large
nuclei
Influence of precursor concentration
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.
11-Dec-13 ICAER'13 12
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
11-Dec-13 ICAER'13 14
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
11-Dec-13 ICAER'13 16
Formic acid oxidation
11-Dec-13 ICAER'13 17
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