Meanwhile, DMFC applications are mostly focused on
the small vehicles system since it can only generate a small
amount of power which make it not ideal for powering large
scale of applications. Anyhow, this DMFC system could
produce power for long period of time, which can supply up
to 25–5 W for 100 h of operations as long as having the fuel
supply. Like PEMFC, DMFC also mainly assists in the
transportation or vehicle industry technology. This technology has huge potential in competing with internal combustion engine vehicles (ICEVs) fuelled by fossil fuel in terms
of cost and performance as well as reducing global warming
issues (Shukla et al. 1998). Besides, it also can be implemented in military applications, man-portable tactical
equipment and battery chargers.
A company from Germany, Smart Fuel Cell Inc. had
developed a small unit of the DMFC system with power
supply of 15–150 W. Furthermore, electronic companies
like Toshiba Corporation, Sony, Samsung, and MTI had
stated their small development of DMFC system that applied
in particular portable electronics application and some
exhibits as prototypes (Narayan and Valdez 2008). In the
same papers, it also stated that 1 kW of the DMFC power
source had been designed and manufactured by Oorja Protonics Inc. called ad OorjaPacTM. This system works as a
battery charger for vehicles and grants about 20 kWh of
energy per six gallons of methanol, which provides sufficient
energy for a day operation. For all that, it yields about 20%
of fuel to electric efficiency. In fact, various of DMFC system had been introduced such as SFC Jenny (480 Wh),
EFOY 1600-M5 (4500 Wh), and EFOY 1600-M28
(25,200 Wh). Although the energy efficiency of the DMFC
system is relatively low, progress in the development of the
mobile DMFC at either the research or commercialization
scale has been continued to this day.
5 Potential and Future Direction
Due to the high operating temperature of SOFC that is in the
region of hydrocarbon reforming, common direction of
research now is aimed at utilizing readily available hydrocarbon fuel such as methane in natural gas and biogas,
propane, butane from butane canister and heavier hydrocarbon such as octane and kerosene from vehicle fuel. The
effort is made in finding reforming catalyst and fabricating
reforming layer on top of the anode to be used as internal
reformer or fixing external reformer to preprocess the fuel
(Sengodan et al. 2018). Metal oxide catalyst such as
Ni-Al 2 O 3 and Ru-CeO 2 with various doping is actively
research as internal reformer for SOFC. Other than that
metal–cermet also shows promising catalytic behavior for
direct oxidation of hydrocarbon fuel in the anode layer. This
enables the hydrocarbon to be used directly in the anode
layer with reforming layer (Mahato et al. 2015).
Another direction for SOFC research is into lowering the
operating temperature of the SOFC. As the function of
SOFC is mainly dictated by the ceramic electrolyte membrane that control the passing of O 2 -ion, finding O 2 -ceramic
material that operates at low temperature is actively done.
The current GDC operating at 500–800 °C classed as
intermediate temperature SOFC (IT-SOFC) was used electrolyte compared to YSZ operating at 800–1000 °C.
Nonetheless, GDC is also known to undergo reduction
reaction under reducing hydrogen environment, causing the
Ce(IV) to be reduced to Ce(III) which creates electron hole
in the GDC structure due to the mixture of Ce(IV)/Ce(III)
species. This made the GDC to obtain electronic conductivities, turning the material to MIEC which have electronic
current leakage in the electrolyte reducing the OCV and
power densities. This problem is currently researched to be
resolved by adding intermediate layer between the electrolyte and cathode to avoid contact with reducing gas and is
subject to under research. Apart from that other material
such from perovskite class such as La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3−d
(LSGM), and bismuth vanadate, BiVO 3 is also actively
research for application as IT-SOFC (Mahato et al. 2015).
The prospect of lowering the temperature of SOFC to 500 °
C is attractive due to the main challenge of finding material
compatible with high temperature. Lowering the temperature
of SOFC will allow better mechanical strength and compatibility among material such as anode, electrolyte, cathode,
and the interconnect.
Meanwhile, the development of electrolyte membrane
layer in PEMFC has managed to show remarkable
improvement over recent years. While the membrane layer
in PEMFC originally used commercial and high-cost Nafion
membrane, the development of other membrane as alternative had produced similar or better result. The practice of
doping of low-cost membrane such as PVA, sPAES, sPEEK,
and PBI with acid such as phosphoric acid has shown
increase in proton conductivities as well as hydration of the
membrane (Kim et al. 2015; Lade et al. 2017). Composite
membrane consisting of the mixture of the said polymer has
also been the further researched. Compositing membrane
will enable the combination of the best properties such as
mechanical and chemical strength, thermal stability and gas
tightness as well as lowering the cost. To enable this compositing, new fabrication method such as sputtering and
electrospunning should be further researched as well as this
enables the creation of layered electrolyte membrane.
High-temperature PEMFC (HT-PEMFC) that enables the
operation of PEMFC at higher than 120 °C has received
attention due to the fact the higher temperature will favor
better kinetics for the hydrogenation oxidation reaction,
Solid Electrolyte Membranes for Low- and High-Temperature …
121
the small vehicles system since it can only generate a small
amount of power which make it not ideal for powering large
scale of applications. Anyhow, this DMFC system could
produce power for long period of time, which can supply up
to 25–5 W for 100 h of operations as long as having the fuel
supply. Like PEMFC, DMFC also mainly assists in the
transportation or vehicle industry technology. This technology has huge potential in competing with internal combustion engine vehicles (ICEVs) fuelled by fossil fuel in terms
of cost and performance as well as reducing global warming
issues (Shukla et al. 1998). Besides, it also can be implemented in military applications, man-portable tactical
equipment and battery chargers.
A company from Germany, Smart Fuel Cell Inc. had
developed a small unit of the DMFC system with power
supply of 15–150 W. Furthermore, electronic companies
like Toshiba Corporation, Sony, Samsung, and MTI had
stated their small development of DMFC system that applied
in particular portable electronics application and some
exhibits as prototypes (Narayan and Valdez 2008). In the
same papers, it also stated that 1 kW of the DMFC power
source had been designed and manufactured by Oorja Protonics Inc. called ad OorjaPacTM. This system works as a
battery charger for vehicles and grants about 20 kWh of
energy per six gallons of methanol, which provides sufficient
energy for a day operation. For all that, it yields about 20%
of fuel to electric efficiency. In fact, various of DMFC system had been introduced such as SFC Jenny (480 Wh),
EFOY 1600-M5 (4500 Wh), and EFOY 1600-M28
(25,200 Wh). Although the energy efficiency of the DMFC
system is relatively low, progress in the development of the
mobile DMFC at either the research or commercialization
scale has been continued to this day.
5 Potential and Future Direction
Due to the high operating temperature of SOFC that is in the
region of hydrocarbon reforming, common direction of
research now is aimed at utilizing readily available hydrocarbon fuel such as methane in natural gas and biogas,
propane, butane from butane canister and heavier hydrocarbon such as octane and kerosene from vehicle fuel. The
effort is made in finding reforming catalyst and fabricating
reforming layer on top of the anode to be used as internal
reformer or fixing external reformer to preprocess the fuel
(Sengodan et al. 2018). Metal oxide catalyst such as
Ni-Al 2 O 3 and Ru-CeO 2 with various doping is actively
research as internal reformer for SOFC. Other than that
metal–cermet also shows promising catalytic behavior for
direct oxidation of hydrocarbon fuel in the anode layer. This
enables the hydrocarbon to be used directly in the anode
layer with reforming layer (Mahato et al. 2015).
Another direction for SOFC research is into lowering the
operating temperature of the SOFC. As the function of
SOFC is mainly dictated by the ceramic electrolyte membrane that control the passing of O 2 -ion, finding O 2 -ceramic
material that operates at low temperature is actively done.
The current GDC operating at 500–800 °C classed as
intermediate temperature SOFC (IT-SOFC) was used electrolyte compared to YSZ operating at 800–1000 °C.
Nonetheless, GDC is also known to undergo reduction
reaction under reducing hydrogen environment, causing the
Ce(IV) to be reduced to Ce(III) which creates electron hole
in the GDC structure due to the mixture of Ce(IV)/Ce(III)
species. This made the GDC to obtain electronic conductivities, turning the material to MIEC which have electronic
current leakage in the electrolyte reducing the OCV and
power densities. This problem is currently researched to be
resolved by adding intermediate layer between the electrolyte and cathode to avoid contact with reducing gas and is
subject to under research. Apart from that other material
such from perovskite class such as La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3−d
(LSGM), and bismuth vanadate, BiVO 3 is also actively
research for application as IT-SOFC (Mahato et al. 2015).
The prospect of lowering the temperature of SOFC to 500 °
C is attractive due to the main challenge of finding material
compatible with high temperature. Lowering the temperature
of SOFC will allow better mechanical strength and compatibility among material such as anode, electrolyte, cathode,
and the interconnect.
Meanwhile, the development of electrolyte membrane
layer in PEMFC has managed to show remarkable
improvement over recent years. While the membrane layer
in PEMFC originally used commercial and high-cost Nafion
membrane, the development of other membrane as alternative had produced similar or better result. The practice of
doping of low-cost membrane such as PVA, sPAES, sPEEK,
and PBI with acid such as phosphoric acid has shown
increase in proton conductivities as well as hydration of the
membrane (Kim et al. 2015; Lade et al. 2017). Composite
membrane consisting of the mixture of the said polymer has
also been the further researched. Compositing membrane
will enable the combination of the best properties such as
mechanical and chemical strength, thermal stability and gas
tightness as well as lowering the cost. To enable this compositing, new fabrication method such as sputtering and
electrospunning should be further researched as well as this
enables the creation of layered electrolyte membrane.
High-temperature PEMFC (HT-PEMFC) that enables the
operation of PEMFC at higher than 120 °C has received
attention due to the fact the higher temperature will favor
better kinetics for the hydrogenation oxidation reaction,
Solid Electrolyte Membranes for Low- and High-Temperature …
121