Third Day Poster Session, 17 June 2010 - NanoTR-VI

Poster Session, Thursday, June 17
Theme F686 - N1123
Preparation of multi-layered Pt/Co cathodes for proton exchange membrane fuel cells (PEM) by
dc- magnetron sputtering
Oguz Kaan Ozdemir 1,2 , Ali Sems Ahsen 2 , Osman Ozturk 2 , Evelina Slavcheva 3
1 Yildiz Tech Univ, Dept Met & Mat Engn, Istanbul, Turkey
2 Nanotechnology Research Canter, Gebze Institute of Technology, Kocaeli, Turkey
3 Institute of Electrochemistry and Energy Systems-Bulgarian Academy of Sciences, Sofia, Bulgaria
Abstract- In order to investigate the effect of Co layers in the cathode electrode a series of unalloyed multilayer Pt/Co thin films were
deposited by dc magnetron sputtering upon a thin Ti sublayer sputtered on the top of a conductive micro porous carbon diffusion layer.
Proton exchange membrane (PEM) fuel cells are
promising power source due to their good energy
conversion efficiency and high power density of their fuel
sources [1]. Nevertheless, the achieved substantial
progresses in the PEM fuel cells are not broadly utilized
due to their cost and durability. Precious Pt catalyst is the
most important cost factor in the PEM fuel cells. Therefore,
many researches are focusing on the development of
compact unit and reducing the loads on the catalysts [2].
The Thin film deposition method of magnetron sputtering
(MS), which is widely used for integrated circuit
manufacturing, recently finds application as an alternative
catalyst preparation and electrode assembling technique.
This method allows deposition of thin compact films upon a
selected substrate material such as either gas diffusion layer
or Nafion, and ensures simplicity of the catalysts
preparation as well as improved stability, durability, and
utilization [3-5].
In our study, a series of unalloyed multilayer Pt/Co thin
films were deposited by dc magnetron sputtering upon a
thin Ti sublayer sputtered on the top of a conductive micro
porous carbon diffusion layer. In order to investigate the
effect of Co on the oxygen reduction reaction, different
compositions (70:30, 50:50, 30:70 Pt/Co atomic ratio) were
employed, while the amount of Pt was constant
(21 μg.cm -2 ). Each electrode was investigated using the
conventional electrochemical methods of cyclic
voltammetry and steady state polarization curves in 0.5M
H 2 SO 4 as well as a membrane electrode assembly, MEA,
cathode in a single hydrogen PEM fuel cell. The cyclic
voltammograms, CV, were used to calculate
the electrochemically active surface area, EASA, of the
electrode under study, applying the well established
procedure of integration the area under the hydrogen ads
orption / desorption peaks and using the value of 210
mC.cm -2 (the charge required for adsorption of hydrogen
monolayer on 1 cm 2 of smooth Pt electrode) as a correction
factor [6].
The electrocatalytic activity of Pt/Co films toward the
oxygen reduction was assessed applying the method of
linear sweep voltammetry, LSV, and Koutecky–Levich
plots. The rotation disc electrode, RDE, polarization curves
show characteristic behavior reported in the literature for
Oxygen Reduction reaction, ORR, on Pt in acid solutions
with a well distinguished region of kinetic mixed, and
diffusion limited reaction rate. Exchange current density, j o ,
is known to be a qualitative measure for the intrinsic
activity of the catalyst, and its calculation has been
explained elaborately in our previous study [7].
Table 1. EASA and Kinetic parameters.
Sample
Name
(Pt/Co)
EASA
(m 2 .gr -1 )
b
(V.dec -1 )
j o
ap
(A.cm -2 )
jo
(A.cm -2 )
70:30 28,789 -0,192 0,00426 1,48E-08
50:50 51,826 -0,181 0,00338 6,53E-09
30:70 52,461 -0,168 0,00557 1,06E-08
As show in Table 1, 30:70 Pt/Co atomic ratios has the
highest EASA. Moreover, its apparent exchange current
density is higher than other two samples, too. Figure 1
shows the polarization curves of a series of MEAs with
different Pt/Co atomic ratios.
E (V)
1
0,8
0,6
0,4
0,2
70:30
50:50
30:70
0 200 400 600 800 1000
J (mA.cm -2 )
As shown in Figure 1, among the three MEAs coated
with 70:30, 50:50, 30:70 cathode catalyst layer obtained by
sputter-deposition, consistent with the CV and RDE
analysis, the coated MEA with 30:70 Pt/Co atomic ratio
demonstrates the best cell performance. The polarization
curve shows a high current density of 974 mA.cm -2 at 0.4
V. Microstructure and electrochemical studies indicated
that the additional Co layers sputter-deposited in cathode
electrode might change the microstructure of the electrodemembrane
interface as well as vary charge transfer and
mass transport properties of MEAs [8].
This research has been carried out in the frame of the
project EVRENA-108M139.
*Corresponding author: 0Hoguz_kozdemir@hotmail.com
[1] R. O’Hayre at al., Journal of Power Sources 109, 483-493,
(2003).
[2] C.L. Chang et al., Surface & Coatings Technology, 201, 4442-
4446, (2006).
[3] W. Zhen-Bo at al., Int J Hydrogen Energy, 34, 4387-94,
(2009).
[4] H. Andrew at al., J Electrochem Soc, 149, A280-7, (2002).
[5] H. Kuo-Lin at al., J Power Sources, 156, 224-31, (2006).
[6] Bard AJ., Faulkner L., 2001. In: Electrochemical methods:
fundamentals and applications, (p. L849–57) , vol. 341. New
York: Wiley.
[7] O. Ozturt at al., International Journal of Hydrogen Energy, In
Press, (2010).
[8] Z. Tang at al., J Appl Electrochem, 39, 1821-1826, (2009).
6th Nanoscience and Nanotechnology Conference, zmir, 2010 756