electrolyte to be co-fabricated together, reducing the time
and step of fabrications. This is usually can be achieved by
fabrication of anode and electrolyte layer together, or the
recent technique: cathode–electrolyte–anode triple layer.
Currently SOFC is investigated to be used not only with H 2
fuel, but also the hydrocarbons such as methane, butane, and
alcohol such as ethanol and butanol as well as biogas. The
variation of the fuel source is made possible due to the fact
that high operating temperature of SOFC actually encompasses the working temperature of steam reforming process
together with some modification in anode layer. The modification can be either (1) allowed anode to directly catalyze
oxidation of fuel or (2) by adding material that performs
reforming process in the anode, or (3) by joining the
reforming layer onto the anode. This modification was
achieved by using metal or metal layer alloy or usage of
other ceramic material with fluorite and perovskite structure.
A tubular SOFC had been developed since the late 1950s
by the Westinghouse Electric Corporation (Stambouli and
Traversa 2002). Commonly, plastic mass-ram extrusion
technique via a die with desired dimensions will be applied
in the fabrication of tubular SOFC. This technique will
involve the mixing of support materials with the binder and
solvent in order to form a viscous paste. The paste is then
extruded through the die forming with the support tube, and
it then followed up by drying and firing that tubular membrane. As in 2004, a tubular anode-supported SOFC manages to be produced via the plastic mass extrusion method
assisted with vacuum dip-coating and painting (Du and
Sammes 2004). 300 MPa of Ni-YSZ tube with 10–50 µm
gastight YSZ layer was obtained in this work. Apart of that,
thermal spraying technique is also being employed in the
development of tubular SOFC. For example, Ni–Al 2 O 3
cermet-supported tubular SOFC had been produced by using
this technique in the study conducted by Li et al. (2006).
800 µm of porous Ni–Al 2 O 3 supporting tube was successfully developed together with 25 µm of NiO-4.5YSZ, anode
layer deposited on supporting tube via an atmospheric
plasma spraying method.
Micro-tubular SOFC (MT-SOFC) can be fabricated using
ram extrusion or co-extrusion coupled with phase inversion
process, whereby the electrode or electrolyte is mixed with
polymer material together with its solvent to form suspension. For co-extrusion phase inversion process, the suspension then can be extruded through tubular opening (called
spinnerets) into non-solvent at which the polymer will form
hollow fiber (HF) with the electrode or electrolyte material in
it. MT-SOFC fabricated using this method usually requires
one layer to act of support at which the layer will hold the
highest mechanical strength or the layer will be fabricated to
have the highest thickness to provide the required mechanical strength. The layer may consist of cathode-, electrolyte-,
or anode-supported solid oxide fuel cell. The support layer
may be extruded first followed by sintering at which other
layer will be deposited onto the support, or the support layer
will be extruded together to form dual-layer or even
triple-layer HF.
Example of anode-supported MT-SOFC was done by
Azzolini et al. (2015) using ram extrusion process. The
initial anode materials of GDC, CuO or Cu 2 O, and LiNO 3
were mixed with hydroxypropyl methylcellulose and water
to form paste which were later extruded and dried. The
electrolyte GDC later was deposited onto the electrolyte
using dip-coating method followed by sintering and deposition of cathode LSCF using the dip-coating method as
well. However, there is no mention of thickness of the anode
layer obtained in this study. Sumi et al. (2015, 2017) also
investigated anode-supported MT-SOFC by fabricating the
anode layer using ram extrusion. Mixture of 60% NiO and
40% GDC with binder acrylic resin, water, and cellulose was
extruded using piston cylinder to form the micro-tube followed by air drying. The YSZ electrolyte layer was later
dip-coated onto the anode, followed by brush painting of
LSCF onto the electrolyte layer. Using this method, anode,
electrolyte, and cathode thickness of 640, 10, and 20 lm
were each obtained.
Recent research on extrusion of electrolyte layer for
electrolyte-supported SOFC using phase inversion was carried by Rabuni et al. (2018). The initial YSZ material was
mixed with N-methyl-2-pyrrolidone (NMP), dispersant and
polyethersulfone (PESf), and extruded into microtubular
form. The process produces electrolyte with two different
layers, dense thick outer layer of approximately 10 µm and
micro-channel/porous layer. The anodic material of Cu and
CeO 2 was deposited onto the porous layer using wet
impregnation technique where precursor aqueous metal
nitrate was deposited followed by sintering at 1450 °C and
reduction by H 2 . Cathode layer of LSM was brush painted
onto the electrolyte using mixture of LSM and ethylene
glycol followed by sintering at 1200 °C to form complete
cell. In other study, Meng et al. (2014) fabricated dual-layer
HF to produce NiO and YSZ layer for electrolyte-supported
SOFC. The precursor ceramic layer of NiO and YSZ was
mixed with PESf, dispersant and NMP and co-extruded
together, followed by sintering at 1450 °C to obtain dense
structure with thickness of 32 and 210 lm each for anode
and electrolyte layer.
Cathode-supported MT-SOFC is being a preference to the
researchers in this area due to the reason of good stability
control during redox cycles. This reliable stability comes
from the cathode-supported configuration itself where thinner anode would reduce the detrimental effect due to the
expansion and contraction of Ni particles within the anode
layer that may lead to the re-oxidation of Ni back to NiO.
Dual-layer YSZ/YSZ-LSM of cathode-supported MT-SOFC
well-developed via co-spinning/so-sintering technique with
112
S. M. Jamil et al.
and step of fabrications. This is usually can be achieved by
fabrication of anode and electrolyte layer together, or the
recent technique: cathode–electrolyte–anode triple layer.
Currently SOFC is investigated to be used not only with H 2
fuel, but also the hydrocarbons such as methane, butane, and
alcohol such as ethanol and butanol as well as biogas. The
variation of the fuel source is made possible due to the fact
that high operating temperature of SOFC actually encompasses the working temperature of steam reforming process
together with some modification in anode layer. The modification can be either (1) allowed anode to directly catalyze
oxidation of fuel or (2) by adding material that performs
reforming process in the anode, or (3) by joining the
reforming layer onto the anode. This modification was
achieved by using metal or metal layer alloy or usage of
other ceramic material with fluorite and perovskite structure.
A tubular SOFC had been developed since the late 1950s
by the Westinghouse Electric Corporation (Stambouli and
Traversa 2002). Commonly, plastic mass-ram extrusion
technique via a die with desired dimensions will be applied
in the fabrication of tubular SOFC. This technique will
involve the mixing of support materials with the binder and
solvent in order to form a viscous paste. The paste is then
extruded through the die forming with the support tube, and
it then followed up by drying and firing that tubular membrane. As in 2004, a tubular anode-supported SOFC manages to be produced via the plastic mass extrusion method
assisted with vacuum dip-coating and painting (Du and
Sammes 2004). 300 MPa of Ni-YSZ tube with 10–50 µm
gastight YSZ layer was obtained in this work. Apart of that,
thermal spraying technique is also being employed in the
development of tubular SOFC. For example, Ni–Al 2 O 3
cermet-supported tubular SOFC had been produced by using
this technique in the study conducted by Li et al. (2006).
800 µm of porous Ni–Al 2 O 3 supporting tube was successfully developed together with 25 µm of NiO-4.5YSZ, anode
layer deposited on supporting tube via an atmospheric
plasma spraying method.
Micro-tubular SOFC (MT-SOFC) can be fabricated using
ram extrusion or co-extrusion coupled with phase inversion
process, whereby the electrode or electrolyte is mixed with
polymer material together with its solvent to form suspension. For co-extrusion phase inversion process, the suspension then can be extruded through tubular opening (called
spinnerets) into non-solvent at which the polymer will form
hollow fiber (HF) with the electrode or electrolyte material in
it. MT-SOFC fabricated using this method usually requires
one layer to act of support at which the layer will hold the
highest mechanical strength or the layer will be fabricated to
have the highest thickness to provide the required mechanical strength. The layer may consist of cathode-, electrolyte-,
or anode-supported solid oxide fuel cell. The support layer
may be extruded first followed by sintering at which other
layer will be deposited onto the support, or the support layer
will be extruded together to form dual-layer or even
triple-layer HF.
Example of anode-supported MT-SOFC was done by
Azzolini et al. (2015) using ram extrusion process. The
initial anode materials of GDC, CuO or Cu 2 O, and LiNO 3
were mixed with hydroxypropyl methylcellulose and water
to form paste which were later extruded and dried. The
electrolyte GDC later was deposited onto the electrolyte
using dip-coating method followed by sintering and deposition of cathode LSCF using the dip-coating method as
well. However, there is no mention of thickness of the anode
layer obtained in this study. Sumi et al. (2015, 2017) also
investigated anode-supported MT-SOFC by fabricating the
anode layer using ram extrusion. Mixture of 60% NiO and
40% GDC with binder acrylic resin, water, and cellulose was
extruded using piston cylinder to form the micro-tube followed by air drying. The YSZ electrolyte layer was later
dip-coated onto the anode, followed by brush painting of
LSCF onto the electrolyte layer. Using this method, anode,
electrolyte, and cathode thickness of 640, 10, and 20 lm
were each obtained.
Recent research on extrusion of electrolyte layer for
electrolyte-supported SOFC using phase inversion was carried by Rabuni et al. (2018). The initial YSZ material was
mixed with N-methyl-2-pyrrolidone (NMP), dispersant and
polyethersulfone (PESf), and extruded into microtubular
form. The process produces electrolyte with two different
layers, dense thick outer layer of approximately 10 µm and
micro-channel/porous layer. The anodic material of Cu and
CeO 2 was deposited onto the porous layer using wet
impregnation technique where precursor aqueous metal
nitrate was deposited followed by sintering at 1450 °C and
reduction by H 2 . Cathode layer of LSM was brush painted
onto the electrolyte using mixture of LSM and ethylene
glycol followed by sintering at 1200 °C to form complete
cell. In other study, Meng et al. (2014) fabricated dual-layer
HF to produce NiO and YSZ layer for electrolyte-supported
SOFC. The precursor ceramic layer of NiO and YSZ was
mixed with PESf, dispersant and NMP and co-extruded
together, followed by sintering at 1450 °C to obtain dense
structure with thickness of 32 and 210 lm each for anode
and electrolyte layer.
Cathode-supported MT-SOFC is being a preference to the
researchers in this area due to the reason of good stability
control during redox cycles. This reliable stability comes
from the cathode-supported configuration itself where thinner anode would reduce the detrimental effect due to the
expansion and contraction of Ni particles within the anode
layer that may lead to the re-oxidation of Ni back to NiO.
Dual-layer YSZ/YSZ-LSM of cathode-supported MT-SOFC
well-developed via co-spinning/so-sintering technique with
112
S. M. Jamil et al.