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Nanostructured platinum catalyst layer prepared by pulsedelectrodeposition for use in PEM fuel cells
N. Rajalakshmi*, K.S. Dhathathreyan
Centre for Fuel cell Technology, ARC-International, 120, Mambakkam Main Road, Medavakkam, Chennai 600 100, India
a r t i c l e i n f o
Article history:
Received 8 June 2007
Received in revised form
5 May 2008
Accepted 5 May 2008
Available online 20 September 2008
Keywords:
PEMFC
Pulsed electrodeposition
Platinum
Fuel cells
Catalyst layer
* Corresponding author.E-mail address: lakshmiraja2003@yahoo.
0360-3199/$ – see front matter ª 2008 Interndoi:10.1016/j.ijhydene.2008.05.100
a b s t r a c t
Nanostructured thin catalyst layer with uniform distribution of platinum particles on
a GDL useful for PEM fuel cell was obtained by preferential pulsed electrodeposition (PED)
from a dilute solution of chloroplatinic acid. A low platinum loading on the electrode was
obtained by PED method, without any loss in fuel cell performance compared with elec-
trodes prepared by conventional brush coating method. The electrodeposition was opti-
mized by varying the duty cycle and current density. The fuel cell performance was found
to be 350 mA/cm2 at an operating voltage of 0.6 V at 60 �C with hydrogen and air as reac-
tants at ambient pressure. The nanostructured thin catalyst layer showed a very less
ohmic resistance of 0.00076 mU/cm2.
ª 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights
reserved.
1. Introduction protons and electrons [3,4]. In the conventional method,
Fuel cells are receiving considerable attention as power
sources due to their high efficiency, modular nature and
environmental acceptability [1]. Polymer electrolyte
membrane fuel cells (PEMFC), being a low temperature fuel
cells have great potential for use in, stationary, transport and
portable applications. One of the challenges facing PEMFC
commercialization is to improve the utilization of platinum
within the catalyst layer that should ultimately reduce the
platinum loading in the electrodes [2]. Ideally all the platinum
in the catalyst layer should be active for the hydrogen oxida-
tion and oxygen reduction reactions in the fuel cell. For this to
happen the fuel and oxidant must react with the catalyst at
the electrolyte–catalyst interfacial region, which is a three-
phase reaction zone. Hence the electrode needs to be engi-
neered to allow fast access of the reactants into this zone and
the electrolyte/catalyst interface must be able to transfer both
com (N. Rajalakshmi).ational Association for H
platinum catalyst supported on carbon is mixed with ion-
omers and the resulting colloidal solution is pasted or sprayed
onto a porous carbon support layer like carbon paper or cloth.
In such cases most of the platinum particles are not accessible
to the reactants because they are deposited within the porous
structure of the carbon support and hence they do not take
part in the electrochemical reaction effectively [5]. Develop-
ment of improved electrodes with high utility of platinum is in
progress in many laboratories by way of improving the cata-
lyst ink composition, extending the wet area of catalytic
region by adding a semi hydrophobic carbon powder layer
between the substrate layer and the catalyst layer, sputter
deposition of the catalyst directly onto the surface of Nafion
bonded carbon paper, introducing novel electrodeposition
methods, etc. [6–10]. Among all the methods, electrodeposi-
tion of catalysts on the carbon substrate is promising in
increasing the utility of catalysts as it can control the growth
ydrogen Energy. Published by Elsevier Ltd. All rights reserved.
0 10 20 30 40 50 60-0.008
-0.006
-0.004
-0.002
0.000
0.002
0.004
0.006
0.008
0.010100mV 200 mV 300 mV 400 mV
Cu
rren
t (A
)
Time (secs)
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 3 ( 2 0 0 8 ) 5 6 7 2 – 5 6 7 7 5673
rate of particles and uniform deposition. Electrodeposition of
platinum by DC deposition, pulse deposition and by cyclic
voltammetry onto the carbon substrate of anode and cathode
of a PEMFC have been reported [11–13]. However, the ionomer
content, which is responsible for the proton network in the
catalyst layer, needs to be optimized along with the loading of
platinum, in order to enhance the performance. In this paper
we report our results on pulsed electrodeposition method of
preparing the polymer electrolyte membrane fuel cell elec-
trodes by optimizing the ionomer content. The duty cycle of
the applied pulse current also varied to get nanostructured
thin films of catalyst layers at the interface of electrolyte and
electrode. The fuel cell performance of the electrodes
prepared by pulsed electrodeposition and by conventional
method has also been presented in these studies.
Fig. 2 – Electrodeposition at various voltages.
2. Experimental
2.1. Preparation of carbon substrate layer forelectrodeposition
The catalyst layer of the electrodes for fuel cell is prepared by
pulsed electrodeposition on a carbon substrate paper from
Ballard Advanced Materials. The substrate layer of 30 cm2 area
was pretreated for electrodeposition consisting of three steps.
In the first step, the substrate layer was treated with hydro-
phobic agent and sintered at 350 �C for about 3 h. In the
second step, it was then coated with carbon powder and teflon
solution and sintered at 350 �C for about 3 h. In the third step,
the electrodes were coated with 5% Nafion solution. This
method paves way for reducing the platinum loading as well
to create a thin film of nanostructured platinum layer on the
treated carbon substrate layer.
2.2. Electrodeposition of nanostructured thin filmcatalyst layer
Pulsed electrodeposition has been selected to prepare the
catalyst layer for PEMFC electrodes due to its advantages
compared to DC electrodeposition in terms of controlled
particle size, adhesion with the substrate, uniformity of
deposition, etc. The pulsed electrodeposition method has
three independent variables to control the deposition namely
ton
V
toff
tcycle
t (sec)
Fig. 1 – Schematic of pulse electrodeposition.
ON time, OFF time and current density. The duty cycle is the
rate determining step for pulsed electrodeposition, in addition
to mass transport, because the properties of metal deposits
can be influenced by both ON time, during which the forma-
tion of nuclei and growth of existing crystal occur and OFF
time during which deposition of ions takes place. Hence in the
pulsed electrodeposition, the rate of nuclei formation
increases and the metal deposits become smaller. A typical
pulse electrodeposition schematic is shown in Fig. 1.
For pulsed electrodeposition of platinum, chloroplatinic
acid solution of 0.1 M mixed with dilute hydrochloric acid of
0.5 M is used as plating bath. The dilute solution of metal salts
is used based on the consideration of easily cleaning up the
residues of metal salts after deposition. A three electrode
system from Autolab Potentiostat/Galvanostal Model 30 has
been used as current generator for electrodeposition in
various steps of current. Pulses of current density ranging
from 1 mA cm�2 to 4 mA cm�2 current density, over a period of
pulse time ON ranging from 20 s to 50 s with OFF time ranging
from 50 s to 60 s, The duty cycle was found to lie in the range
50–20% for the electrodes of interest. The total amount of
charge is equal to 0.2–0.5 C cm�1 for various cases depending
on the current density and charging time. Several electrode-
position procedures like pulsed waveform, reverse waveform
and square waveform were tried to deposit platinum on the
0 50 100 150 200 250 3000.0
0.2
0.4
0.6
0.8
1.0 60 mA40 mA20 mA
Vo
ltag
e (V
)
Time (secs)
Fig. 3 – Effect of platinisation with respect to current.
0 50 100 150 200 250 300-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8 20mA30mA
Vo
latg
e (V
)
Time (secs)
Fig. 4 – Effect of square pulse for platinisation.
0 40 80 120 160 200 240 280 320-0.2
0.0
0.2
0.4
0.6
0.8
1.010s,50s20s,50s30s,50s50s,50s
Vo
ltag
e (V
)
Time (secs)
Fig. 6 – Platinisation with respect to duty cycle for a reverse
pulse.
0.10
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 3 ( 2 0 0 8 ) 5 6 7 2 – 5 6 7 75674
substrate layer. After each deposition, the electrode was
voltammetrically cycled in 0.5 M H2SO4 from �0.2 V to 1.2 V at
a scan rate of 50 mV/s in order to remove the chlorine ions
hidden in the electrodes, to activate the electrode electro-
chemically and to evaluate the electrochemical deposition.
From the hydrogen absorption peak at 0.05–0.1 V, the elec-
trochemical deposition can be estimated and the incom-
pletely platinised electrode was moved directly into the
deposition bath for further deposition. The catalyst layers of
the electrodes were subjected to structural microanalysis
using SEM and EDAX.
2.3. Electrode membrane assembly (EMA) fabricationand fuel cell testing
The EMAs were made by hot pressing the electrodes at 130 �C
for 2 min using a 1135 Nafion membrane and inserted
between two graphite blocks having serpentine flow field
channels for hydrogen and air. The assembly was tightened
between end plates and copper current collector with the help
of bolts and nuts and pinch implementation for uniform tor-
que. The polarization curves were obtained for the electro-
deposited fuel cell electrode using a custom built test bench
facility having provision for flow control of reactants using
0 50 100 150 200 250 300
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2 20mA 30mA
Vo
ltag
e (V
)
Time (secs)
Fig. 5 – Effect of reverse pulse for platinisation.
mass flow controller, calibrated bubble humidifiers with
temperature controllers, and a DC electronic load box.
3. Results and discussion
The deposition of Pt from chloroplatinic acid is described by
the following equations [14].
PtCl2�6 þ 2e / PtCl2�
4 þ 2Cl� (1)
PtCl2�4 þ 2e / Pt þ 4Cl� (2)
The formation of platinum particles on the electrodes
during the potential sweeps catalyses the reduction of
hydrogen ions to hydrogen atoms. The behaviour of current
versus potential is shown in Fig. 2 for the platinised electrode.
Another evidence for the platinisation of the electrode can be
seen from Fig. 3, where the potential of the electrode varies
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
20mA40mANaf coatedsubstrate layer30mA
cu
rren
t (A
)
voltage(V)
Fig. 7 – Half cell cyclic voltammogram for various
electrodes, Scanrate 50 mV/s.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 3 ( 2 0 0 8 ) 5 6 7 2 – 5 6 7 7 5675
from 0.52 Vto 0.93 V, showing the increase of deposition with
various pulsing current of 20–60 mA. The duty cycle was found
to be 50%.
Figs. 4 and 5 show how the pulse current can be activated
to get a higher voltage for deposition by reversing the potential
for a certain period at the same current density. The voltage
was found to be 0.75 V for a current of 30 mA, which increased
to 1.1 V, when the pulse is reversed for 50 s at 20 mA. It was
found that both peak current density and duty cycle control
the nucleation rate and the crystal growth. The optimum
conditions of pulse electrodeposition were found to be 100 ms
Fig. 8 – (a–c) SEM, EDAX of variou
of ON time and 400 ms of OFF time for a duty cycle of 20% in
the millisecond range. By the optimization of Nafion content
in the gas diffusion layer, the catalyst coating can be
controlled and a nanostructured catalyst layer can be
obtained, in order to obtain a required loading of catalyst with
nanoparticle size, as higher Nafion content leads to higher
potential for electrodeposition. Electrodeposition occurs only
when there is electrical contact leading to high utilization. If
deposit through Nafion, where there is ionic contact, thin
layers of deposition at high loadings and high dispersions can
be obtained. In addition, more Nafion content at the GDL
s pulse deposited electrodes.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 3 ( 2 0 0 8 ) 5 6 7 2 – 5 6 7 75676
increases the potential for electrodeposition, leading to higher
loading and higher particle size. Similarly at a particular
current pulse, the ON and OFF time has been varied to opti-
mize the duty cycle as shown in Fig. 6. It was found that at the
same current, the voltage increases to 0.82 V from 0.75 V,
when the pulse is switched off for 50 s.
Fig. 7 shows the cyclic voltammogram (CV) of the half cell
experiments, conducted with the help of electrodeposited
layer as working electrode in a 0.5 M H2SO4 acid. From the CV
we can see that the unplatinised diffusion layer and the
Nafion treated unplatinised layer do not show any hydrogen
absorption and only the platinised layer shows the hydrogen
absorption, which increases with pulse current and invariably
the voltage, and the deposition of platinum is more as seen by
the increase in limiting current to 0.08 A. The pulsed electro-
deposited catalyst layers were structurally analysed by SEM as
shown in Fig. 8a–c, and found that the platinum loading on the
carbon substrate varied from 36 wt% to 71 wt% depending on
the pulse current density and duty cycle. However, the atomic
percent shows the loading of platinum in the catalyst layer,
which varied between 3.5% and 13.5%. Fig. 8b shows the
uniform distribution of platinum particles (where the atomic
percent loading is 3.5%) compared to Fig. 8a and c, where the
platinum particles are seen as agglomerates. The particle size
was found to vary between 20 nm and 40 nm. The fuel cell
polarization curve at 60 �C (with humidified hydrogen and air)
is shown in Fig. 9, and it is compared with conventional
electrodes. Although the fuel cell performance in the activa-
tion region is almost the same compared to conventional
electrodes, the electrodes prepared by pulsed electrodeposi-
tion give a better performance in the ohmic region, which can
be attributed to the structure of the catalyst layer prepared by
the pulsed electrodeposition method compared to conven-
tional methods [15].
The polarization curves were fitted to the following equa-
tion
E ¼ Eo � b logðiÞ � cðRiÞ (3)
Where Eo, b and R are open circuit voltage, tafel slope and
resistance, respectively. It was found that the tafel slope was
0 100 200 300 400 500 600 700 8000.0
0.2
0.4
0.6
0.8
1.0 Pt/CPED
Vo
ltag
e(V
)
Current density (mA/cm2)
Fig. 9 – Fuel cell performance for H2/Air system at 60 8C,
ambient pressure, humidified reactants for conventional
and PED electrode.
18 and 47 mV/decade for the conventional and electro-
deposited electrode, respectively and the ohmic resistance
was found to be 0.0010 mU/cm2 and 0.00076 mU/cm2, respec-
tively. From the kinetic parameters obtained, one can see that
the ohmic resistance is very small compared to conventional
electrode, as the catalyst layer is very thin and having plat-
inum particles of nanostructure dimension. In conventional
electrodes although platinum particle size ranging from 3 nm
to 10 nm is being used, the real particle size in the electrode is
not the same as it gets agglomerated and the size increases
during catalyst ink preparation. But in the case of electro-
deposited catalyst layer, the particle size in the catalyst layer
is around 20 nm and the platinum loading is reduced by about
six times. In the conventional electrode 20% Pt/C is being used,
while for the electrodeposited catalyst layer 3.5% Pt is
observed, about six times reduction in catalyst requirement
with a better performance in the ohmic region due to their
low ohmic resistance. Further work is in progress to increase
the electrode area to 150 cm2 and optimize the pulse
conditions.
4. Conclusion
Nanostructured thin platinum catalyst layer for PEMFC elec-
trodes were obtained by preferential pulsed electrodeposition
with an optimized Nafion content, duty cycle and current
density. The nanostructured thin catalyst layer showed a very
less ohmic resistance of 0.00076 mU/cm2. The platinum
loading also was found to decrease by about six times
compared to conventional loading of platinum due to prefer-
ential pulsed electrodeposition during the optimization of
Nafion content. The fuel cell performance was found to be
350 mA/sq cm at 0.6 V.
Acknowledgement
The authors would like to thank Dr. G. Sundararajan, Director
(ARCI) for his support and encouragement and DST for
financial support. The authors would like to acknowledge
Dr. K. Ravichandra of ARCI, for his help in taking the SEM
pictures.
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