Novel Co-Sintering Techniques for Fabricating Intermediate Temperature,
Metal Supported Solid Oxide Fuel Cells (IT-m-SOFCs)
S. H. Rahul
a
, Pantula K. P. Rupa
a
, Nirmal Panda
a
, Krishnamurty Balasubramanian
a
R. V. Kumar
b
and Venkatesan Venkata Krishnan
a
a
Non-Ferrous Materials Technology Development Center, Hyderabad, India
b
Department of Materials Science and Metallurgy, University of Cambridge,
Cambridge, U.K.
Metal supported SOFCs (m-SOFCs) offer the advantages of
inexpensive metal components as compared to the more expensive
rare earth materials, since the entire ceramic support layer is
replaced by ferritic steels, e.g., SS430L, AISI 441. However, with
sintering conditions for ceramic and metalliclayers being different,
it is difficult to sinter all the layers at one temperature to make a
fuel cell. In this work, a triple layered structure comprising porous
metal support (SS 430L), NiO + GDC (anode functional layer) and
GDC (electrolyte) was co-sintered at 950
o
C, with superimposed
high pressure (up to 180 bar, so far), with a soak time of 30
minutes at this temperature and pressure, to achieve densification
and interlayer bonding. An additional step of using plasma to
provide high heat flux to the electrolyte surface over a very short
time provides a good surface finish by enhancing sintering. Both
these methods have been applied for the first time for the
combined sintering of multiple layers. Preliminary runs have been
successful and the samples have been analyzed using SEM. Data
from SEM show the onset of sintering at temperatures as low as
960
o
C, at high pressures of up to 180 bar. Plasma ‘glazing’
experiments also demonstrate a temperature gradient of over 700
o
C
across the fuel cell element, and clearly observed densification of
NiO-GDC achieved over a 2 minute period of time.
Introduction
Typically, m-SOFCs have a porous ferritic type stainless steel substrate (1) that is
compatible with ceramic layers such as NiO-GDC and GDC, in terms of CTEs. However
for Intermediate Temperature m-SOFCs (IT-mSOFCs), operating in the 550-700
o
C range,
substrate options are many, and among them SS430L (1,2) is a very promising candidate
in terms of cost and oxidation resistance.
The principal challenges for sintering the individual layers lie in the fact that GDC
densification temperatures are usually about 1300
o
C or higher. This is despite the fact
that literature from Ceres Power reports a 1000
o
C sintering cycle for the GDC electrolyte,
deposited by Electrophoretic Deposition (3).To sinter the supported metallic layer at such
high temperatures (over 1200
o
C) is unadvisable due to diffusion of Fe and Cr from the
support structure to the anode functional layer and Ni to the support structure (3).
10.1149/05701.0857ecst ©The Electrochemical Society
ECS Transactions, 57 (1) 857-866 (2013)
857