5-µm-dip-coated Ni-YSZ layer (Meng et al. 2013). This
asymmetric dual-layer hollow fiber is comprised of dense
YSZ electrolyte layer supported on the porous cathode layer
of YSZ-LSM. Besides, an effort in broadening the
three-phase boundary length had been achieved through the
dual-layer MT-SOFC fabrication of cathode functional layer
LSM-YSZ sandwiched with LSM cathode layer (Meng et al.
2015). The main porous cathode layer usually will act as
current-collecting layer as well as site for oxygen reduction
process. Afterward, Panthi et al. (2017a, b) had carried out
an investigation with the purpose of lowering down the
co-sintering temperature as an attempt to avoid the chemical
reaction between cathode and electrolyte layer during the
co-sintering process. Co-sintering temperature can be lowering down till 1250–1300 °C with the help of sintering
additive, NiO and Fe 2 O 3 , and microcrystalline cellulose pore
former, adding into electrolyte and cathode, respectively
(Panthi et al. 2017a).
In many studies, the anode layer is made as the support
layer due to the fact that anode layer is the layer where the
oxidation of fuel takes place; thus, thicker anode layer may
be anticipated to give more area for the reaction to take place
yielding better performance. However due to the limitation
of material thermal expansion coefficient (TEC), the anode
layer is usually made with composition consisting of mixture
of electrolyte material and the anode material to ensure
stability of the layers during co-sintering of the dual layer.
This made the TEC of the anode and electrolyte layer to be
closed to each other, resulting in the opportunity of the two
layers to be fabricated together. Thus in co-extrusion of
dual-layer MT-SOFC, the electrolyte layer and anode layer
are usually co-extruded, co-sintered and coated with the
cathode layer. Omar et al. (2018) and Jamil et al. (2019)
fabricated dual-layer HF using almost similar method. Using
anode/electrolyte material of NiO-GDC/GDC, the ceramic
material was initially mixed with PESf polymer, dispersant,
and DMSO or NMP as solvent and were extruded through
spinnerets with water as the non-solvent phase to produce
dual-layer HF. The anode/electrolyte layer obtained was
found to range from 160 to 200 µm for anode and 30 to
60 µm for electrolyte.
Co-extrusion of triple-layer SOFC consisting of cathode,
electrolyte, and anode has garnered interest in recent years.
This method will further ease and reduce the fabrication step
compared to the co-extrusion of two layers. Jamil et al.
(2018) fabricated triple-layer HF in one single step consisting of anode, electrolyte, and cathode layers. The anode/
electrolyte/cathode that were made up of NiO-GDC/
GDC/LSCF-GDC employed similar phase inversion technique where the ceramic materials were mixed with solvent
NMP, polymer PESf, and dispersant to form initial suspension. The triple-layer HF was later heat-treated at 400 °C,
800 °C, and later sintered at 1450 °C for 8 h. By varying the
extrusion rate of anode/electrolyte/cathode to each
7/2/2 ml min
−1 is producing thickness of 234/13.5/40 µm
after co-sintering.
2.2 Proton Exchange Membrane Fuel Cells
Fuel cells generally create their names by electrolyte type
and responding substances. PEMFC is a type of fuel cell that
uses hydrogen as the fuel, oxygen as the oxidant and a type
of membrane that is only permissible to hydrogen ion or
proton. During PEMFC operation, the H 2 gas flows into the
fuel cell through the anode and is oxidized by the reaction at
catalyst site to form hydrogen ion. The hydrogen ion will
move from anode to the cathode layer through the electrolyte
membrane that is only permeable to hydrogen ion but not to
electron. Upon reaching the cathode, the hydrogen ion will
react with oxygen from air and electron to form water. The
electron flow externally from anode to cathode layer through
external circuit attached to the cell to generate electricity.
Chemical equation for the reaction is shown in equation
below.
Anode : H 2 ! 2H
þ
þ 2e
À
Cathode : 2H
þ
þ 1 = 2 O 2 þ 2e
À
! H 2 O
The electrodes layer in PEMFC (anode and cathode)
consists of catalyst layer (CL) that catalyzes the oxidation of
hydrogen or reduction of oxygen to produce water and gas
diffusion layer (GDL) that permit the diffusion of hydrogen
or oxygen into or water out of the CL and conduct electron
to complete the circuit. Illustration of PEMFC is shown in
Fig. 3 (Mehta and Cooper 2003; Wang et al. 2011).
The electrolyte membrane in the center of PEMFC is
considered to be the most significant element. Generally, the
electrolyte membrane should have strong affinity for proton
while being insulator to electron in order to be regarded as
material for membrane. Other criteria include durability,
resistance to chemical attack, and the state which needs to be
solid. The range of operating temperatures is an important
factor to consider when selecting membrane materials,
where common operation temperature of PEMFC ranges
from 30 to 200 °C.
Many distinct membranes exist and that are made from
distinct material types. The selection of materials used as
membrane depends on the physical and chemical properties
required to ensure effective membrane efficiency (Awang
et al. 2015; Mehta and Cooper 2003; Omar et al. 2018;
Wang et al. 2011). PEMFC membranes are categorized into
three primary classifications. These membranes are
perfluorinated compound, partially fluorinated compound,
and non-fluorinated. Besides these, however, we have other
membranes obtained from these main classifications or using
Solid Electrolyte Membranes for Low- and High-Temperature …
113
asymmetric dual-layer hollow fiber is comprised of dense
YSZ electrolyte layer supported on the porous cathode layer
of YSZ-LSM. Besides, an effort in broadening the
three-phase boundary length had been achieved through the
dual-layer MT-SOFC fabrication of cathode functional layer
LSM-YSZ sandwiched with LSM cathode layer (Meng et al.
2015). The main porous cathode layer usually will act as
current-collecting layer as well as site for oxygen reduction
process. Afterward, Panthi et al. (2017a, b) had carried out
an investigation with the purpose of lowering down the
co-sintering temperature as an attempt to avoid the chemical
reaction between cathode and electrolyte layer during the
co-sintering process. Co-sintering temperature can be lowering down till 1250–1300 °C with the help of sintering
additive, NiO and Fe 2 O 3 , and microcrystalline cellulose pore
former, adding into electrolyte and cathode, respectively
(Panthi et al. 2017a).
In many studies, the anode layer is made as the support
layer due to the fact that anode layer is the layer where the
oxidation of fuel takes place; thus, thicker anode layer may
be anticipated to give more area for the reaction to take place
yielding better performance. However due to the limitation
of material thermal expansion coefficient (TEC), the anode
layer is usually made with composition consisting of mixture
of electrolyte material and the anode material to ensure
stability of the layers during co-sintering of the dual layer.
This made the TEC of the anode and electrolyte layer to be
closed to each other, resulting in the opportunity of the two
layers to be fabricated together. Thus in co-extrusion of
dual-layer MT-SOFC, the electrolyte layer and anode layer
are usually co-extruded, co-sintered and coated with the
cathode layer. Omar et al. (2018) and Jamil et al. (2019)
fabricated dual-layer HF using almost similar method. Using
anode/electrolyte material of NiO-GDC/GDC, the ceramic
material was initially mixed with PESf polymer, dispersant,
and DMSO or NMP as solvent and were extruded through
spinnerets with water as the non-solvent phase to produce
dual-layer HF. The anode/electrolyte layer obtained was
found to range from 160 to 200 µm for anode and 30 to
60 µm for electrolyte.
Co-extrusion of triple-layer SOFC consisting of cathode,
electrolyte, and anode has garnered interest in recent years.
This method will further ease and reduce the fabrication step
compared to the co-extrusion of two layers. Jamil et al.
(2018) fabricated triple-layer HF in one single step consisting of anode, electrolyte, and cathode layers. The anode/
electrolyte/cathode that were made up of NiO-GDC/
GDC/LSCF-GDC employed similar phase inversion technique where the ceramic materials were mixed with solvent
NMP, polymer PESf, and dispersant to form initial suspension. The triple-layer HF was later heat-treated at 400 °C,
800 °C, and later sintered at 1450 °C for 8 h. By varying the
extrusion rate of anode/electrolyte/cathode to each
7/2/2 ml min
−1 is producing thickness of 234/13.5/40 µm
after co-sintering.
2.2 Proton Exchange Membrane Fuel Cells
Fuel cells generally create their names by electrolyte type
and responding substances. PEMFC is a type of fuel cell that
uses hydrogen as the fuel, oxygen as the oxidant and a type
of membrane that is only permissible to hydrogen ion or
proton. During PEMFC operation, the H 2 gas flows into the
fuel cell through the anode and is oxidized by the reaction at
catalyst site to form hydrogen ion. The hydrogen ion will
move from anode to the cathode layer through the electrolyte
membrane that is only permeable to hydrogen ion but not to
electron. Upon reaching the cathode, the hydrogen ion will
react with oxygen from air and electron to form water. The
electron flow externally from anode to cathode layer through
external circuit attached to the cell to generate electricity.
Chemical equation for the reaction is shown in equation
below.
Anode : H 2 ! 2H
þ
þ 2e
À
Cathode : 2H
þ
þ 1 = 2 O 2 þ 2e
À
! H 2 O
The electrodes layer in PEMFC (anode and cathode)
consists of catalyst layer (CL) that catalyzes the oxidation of
hydrogen or reduction of oxygen to produce water and gas
diffusion layer (GDL) that permit the diffusion of hydrogen
or oxygen into or water out of the CL and conduct electron
to complete the circuit. Illustration of PEMFC is shown in
Fig. 3 (Mehta and Cooper 2003; Wang et al. 2011).
The electrolyte membrane in the center of PEMFC is
considered to be the most significant element. Generally, the
electrolyte membrane should have strong affinity for proton
while being insulator to electron in order to be regarded as
material for membrane. Other criteria include durability,
resistance to chemical attack, and the state which needs to be
solid. The range of operating temperatures is an important
factor to consider when selecting membrane materials,
where common operation temperature of PEMFC ranges
from 30 to 200 °C.
Many distinct membranes exist and that are made from
distinct material types. The selection of materials used as
membrane depends on the physical and chemical properties
required to ensure effective membrane efficiency (Awang
et al. 2015; Mehta and Cooper 2003; Omar et al. 2018;
Wang et al. 2011). PEMFC membranes are categorized into
three primary classifications. These membranes are
perfluorinated compound, partially fluorinated compound,
and non-fluorinated. Besides these, however, we have other
membranes obtained from these main classifications or using
Solid Electrolyte Membranes for Low- and High-Temperature …
113