Nafion
® -based membranes by adding inorganic compounds
(SiO 2 , silans, Zr, MoPh-a, etc.) and acid-based composites
(polyaryl) reduces methanol crossover but does not reduce
costs. Hydrocarbon membranes are cheaper for DMFC than
Nafion
® membranes and are more technically efficient. They
have reduced methanol crossover and greater conductivity
and stability. Hydrocarbon and composite fluorinated
membranes presently exhibit the greatest potential for lowcost membranes with low permeability of methanol and high
durability (Jörissen et al. 2002). Some of these membranes
are already starting to impact the market for mobile fuel
cells.
3 Performance Evaluation of Fuel Cells
Involving Membrane Applications
3.1 Performance of Solid Oxide Fuel Cell
Performance evaluation of fuel cells is done in-situ under
operating condition or ex-situ which is not under operating
condition. Common in-situ measurement involves measuring the open-circuit voltage (OCV) and power density under
operating condition and ex-situ by measuring the cell
impedance using electrochemical impedance spectroscopy
(EIS). Measurement of OCV for SOFC is usually accompanied by the measurement of current generated shown in I–
V or I–P diagram. Since the recent interest of utilizing SOFC
with hydrocarbon fueled has gained interest, performance of
SOFC operating under hydrocarbon fueled is usually done in
comparison with performance using H 2 fuel. However, the
performance of SOFC running on H 2 fuel is still generally
better compared to cell running on hydrocarbon fuel such as
CH 4 as given in Table 1.
From the latest literature finding, there are not much
differences in cell performance between planar and tubular
membrane SOFC. However as described earlier,
micro-tubular form offers advantages in terms of the fabrication step and the void of need to design for interconnect.
The electrolyte layer which is the most important layer
functions optimally at different temperature depending on
the material. Current use of YSZ which is considered as
high-temperature SOFC (HT-SOFC) with operating temperature ranging from, 800 to 1000 °C received the same
interest as GDC electrolyte, which considered as intermediate temperature SOFC (IT-SOFC) with operating temperature ranging from 500 to 800 °C. IT-SOFC hs higher ionic
conductivity at lower working temperature compared to
HT-SOFC but the tendency for cerium oxide to form Ce
4+ /
Ce
3+ species in reducing environment resulted in undesired
electronic conductivity that cause current leakage, hence
lowering the performance of the cell.
Electrochemical impedance spectroscopy (EIS) has
become major tool to characterize and test fuel cells. Electrical impedance (usually denoted by Z) similar to electrical
resistance (R) is a measurement of the circuit resistance to
electrical flow when electrical potential is applied across the
circuit. However unlike resistance, impedance measurement
also concerns the phase shift of the current flowing when AC
potential is applied. This phase shift is the characteristics of
resistor–capacitor circuit (RC circuit) which is be used to
model the layer of the fuel cell in the form of equivalent
electrical circuit. Electrochemical impedance is measure by
applying AC potential across the membrane at various frequencies, and the resultant impedance is measured and
expressed in complex form consisting of real and imaginary
part called Nyquist plot as illustrated in Fig. 5. The data
from Nyquist plot then will be fitted into mathematical
model to find equivalent electrical circuit consisting of
electrical elements of resistor, inductor, and capacitor. EIS
interpretation correlates to the cell characterization due to the
fact that certain process works like electrical components
(Pivac and Barbir 2016).
From literatures, most of studies on SOFC performance
also include EIS as part of result reporting to not only show
the resistance value of the cell, but also investigated the
effect of modification of electrode or electrolyte on the EIS
and the postulated microscopic change associated with the
change. Effect of metal and metal alloy layer on the ohmic
and polarization resistance change has been investigated by
Meng et al. (2014), Yan et al. (2016), Wu et al. (2016), Jamil
et al. (2019), Lee et al. (2016) and Harris et al. (2017). EIS is
also used to investigate degradation at the anode by carbon
deposition associated with the utilization of hydrocarbon
fuel by Sarruf et al. (2017), Panthi et al. (2017b), Omar et al.
(2018) and Akdeniz et al. (2016) where the utilization of
methane fuel was shown to cause increase in ohmic resistance of the cell.
Modification of traditional anode layer of Ni-YSZ to
enable SOFC to be able to be used with varieties of fuel
seems to be the current direction of recent research. Since
Ni-YSZ suffers from performance degradation due to carbon
deposition when used with hydrocarbon fuel, anode modification through the insertion of ceria, metal alloy or used of
fluorite or perovskite material to act as oxidation catalyst has
been extensively studied. Insertion of ceria and copper metal
in anode-supported MT-SOFC using YSZ electrolyte was
studied by Meng et al. (2014) and Rabuni et al. (2018). The
former anode composition containing YSZ, Ni, CeO 2 , and
Cu obtained increased the performance from H 2 and CH 4
fuel (0 0.15 and 0.25 W cm
−2 , respectively) while later
study, lacking Ni managed to obtain 0.55 and 0.16 W cm
−2
each for H 2 and CH 4 fueled. The results contradicted each
other but may also indicate the importance of Ni even in
116
S. M. Jamil et al.
® -based membranes by adding inorganic compounds
(SiO 2 , silans, Zr, MoPh-a, etc.) and acid-based composites
(polyaryl) reduces methanol crossover but does not reduce
costs. Hydrocarbon membranes are cheaper for DMFC than
Nafion
® membranes and are more technically efficient. They
have reduced methanol crossover and greater conductivity
and stability. Hydrocarbon and composite fluorinated
membranes presently exhibit the greatest potential for lowcost membranes with low permeability of methanol and high
durability (Jörissen et al. 2002). Some of these membranes
are already starting to impact the market for mobile fuel
cells.
3 Performance Evaluation of Fuel Cells
Involving Membrane Applications
3.1 Performance of Solid Oxide Fuel Cell
Performance evaluation of fuel cells is done in-situ under
operating condition or ex-situ which is not under operating
condition. Common in-situ measurement involves measuring the open-circuit voltage (OCV) and power density under
operating condition and ex-situ by measuring the cell
impedance using electrochemical impedance spectroscopy
(EIS). Measurement of OCV for SOFC is usually accompanied by the measurement of current generated shown in I–
V or I–P diagram. Since the recent interest of utilizing SOFC
with hydrocarbon fueled has gained interest, performance of
SOFC operating under hydrocarbon fueled is usually done in
comparison with performance using H 2 fuel. However, the
performance of SOFC running on H 2 fuel is still generally
better compared to cell running on hydrocarbon fuel such as
CH 4 as given in Table 1.
From the latest literature finding, there are not much
differences in cell performance between planar and tubular
membrane SOFC. However as described earlier,
micro-tubular form offers advantages in terms of the fabrication step and the void of need to design for interconnect.
The electrolyte layer which is the most important layer
functions optimally at different temperature depending on
the material. Current use of YSZ which is considered as
high-temperature SOFC (HT-SOFC) with operating temperature ranging from, 800 to 1000 °C received the same
interest as GDC electrolyte, which considered as intermediate temperature SOFC (IT-SOFC) with operating temperature ranging from 500 to 800 °C. IT-SOFC hs higher ionic
conductivity at lower working temperature compared to
HT-SOFC but the tendency for cerium oxide to form Ce
4+ /
Ce
3+ species in reducing environment resulted in undesired
electronic conductivity that cause current leakage, hence
lowering the performance of the cell.
Electrochemical impedance spectroscopy (EIS) has
become major tool to characterize and test fuel cells. Electrical impedance (usually denoted by Z) similar to electrical
resistance (R) is a measurement of the circuit resistance to
electrical flow when electrical potential is applied across the
circuit. However unlike resistance, impedance measurement
also concerns the phase shift of the current flowing when AC
potential is applied. This phase shift is the characteristics of
resistor–capacitor circuit (RC circuit) which is be used to
model the layer of the fuel cell in the form of equivalent
electrical circuit. Electrochemical impedance is measure by
applying AC potential across the membrane at various frequencies, and the resultant impedance is measured and
expressed in complex form consisting of real and imaginary
part called Nyquist plot as illustrated in Fig. 5. The data
from Nyquist plot then will be fitted into mathematical
model to find equivalent electrical circuit consisting of
electrical elements of resistor, inductor, and capacitor. EIS
interpretation correlates to the cell characterization due to the
fact that certain process works like electrical components
(Pivac and Barbir 2016).
From literatures, most of studies on SOFC performance
also include EIS as part of result reporting to not only show
the resistance value of the cell, but also investigated the
effect of modification of electrode or electrolyte on the EIS
and the postulated microscopic change associated with the
change. Effect of metal and metal alloy layer on the ohmic
and polarization resistance change has been investigated by
Meng et al. (2014), Yan et al. (2016), Wu et al. (2016), Jamil
et al. (2019), Lee et al. (2016) and Harris et al. (2017). EIS is
also used to investigate degradation at the anode by carbon
deposition associated with the utilization of hydrocarbon
fuel by Sarruf et al. (2017), Panthi et al. (2017b), Omar et al.
(2018) and Akdeniz et al. (2016) where the utilization of
methane fuel was shown to cause increase in ohmic resistance of the cell.
Modification of traditional anode layer of Ni-YSZ to
enable SOFC to be able to be used with varieties of fuel
seems to be the current direction of recent research. Since
Ni-YSZ suffers from performance degradation due to carbon
deposition when used with hydrocarbon fuel, anode modification through the insertion of ceria, metal alloy or used of
fluorite or perovskite material to act as oxidation catalyst has
been extensively studied. Insertion of ceria and copper metal
in anode-supported MT-SOFC using YSZ electrolyte was
studied by Meng et al. (2014) and Rabuni et al. (2018). The
former anode composition containing YSZ, Ni, CeO 2 , and
Cu obtained increased the performance from H 2 and CH 4
fuel (0 0.15 and 0.25 W cm
−2 , respectively) while later
study, lacking Ni managed to obtain 0.55 and 0.16 W cm
−2
each for H 2 and CH 4 fueled. The results contradicted each
other but may also indicate the importance of Ni even in
116
S. M. Jamil et al.