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Alternative Fuels for Transportation
volume and manufacturing processes remain uncertain. For materials, for
example, polymer electrolyte membranes that are used in small quantities,
large production would be required. The cost of FCSs for mobile applications
at present is estimated to be $325/kW at a production level of 500,000 units
per year (Adamson 2008). U.S. DOE has set technical as well as cost targets
for mobile FCSs that have to be met in order to become competitive with
ICEVs. The direct hydrogen fuel-cell power system has to have 60% electric
efficiency at a cost of $45/kW by 2010 and $30/kW by 2015. Alternatively, a
reformer-based-fuel-cell-power system operating on clean hydrocarbon or
alcohol that meets emission standards has to have a 45% electric efficiency at
a cost of $45/kW by 2010 and $30/kW by 2015. The start-up time for a reformer-based system should be less than 30 s. The total cost consists of $5/kW for
the membrane, $5/kW for the electrodes, $10/kW for the MEA, and $10/kW
for the bipolar plates. For PEFCs, the challenge is catalyst cost reduction.
The search for nonplatinum catalysts has been on for more than 40 years.
At low temperatures and using hydrogen, platinum-based catalysts remain
most active (Arico et al. 2005). One could potentially use a greater amount
of a cheaper, less active catalyst, but the acidic environment of PEFCs rules
out non-noble metals at present (Gasteiger et al. 2005). Another option is to
reduce platinum loadings but this presents the problem of reducing catalyst durability (Zhang et al. 2006). The need for alternative catalysts is also
driven by the availability of platinum. Platinum catalysts in automobiles
already amount to approximately half of the platinum sold globally each
year (Loferski 2008). Unless breakthroughs are made, low-temperature fuel
cells will continue to require platinum catalysts in the foreseeable future.
However, the most critical issue is to reduce the amount of Pt loadings. An
average Pt loading is around 0.5 mg/cm 2 and the total amount of Pt used in
current 80 kW class stacks is estimated to be about 100–120 g. From the standpoint of cost and resource conservation, it is not possible to use this amount
of Pt in commercial vehicles. By comparison, the amount of Pt used in the
exhaust-gas after-treatment system for ICEVs is <10 g. To achieve a realistic
cost the amount of Pt used should be reduced to one-tenth of the present
level. However, there is currently no technology available for reducing the
amount of Pt loading to this extent. Innovative ideas for improving the performance of the electrode catalyst is therefore most desired.
One can expect continuous improvements and developments in conventional power trains. Engine downsizing and the hybridization of the power
trains will partly compensate for the low-load efficiency deficit of ICEVs.
As electric components have replaced many mechanical parts of the vehicle, hybridization combined with regenerative braking will bring increased
electrification of power trains. As many elements of the drivetrain and the
refueling infrastructure are new, there are still major improvements needed
for the FCVs to become competitive with ICEVs. Today, cost, range, and refueling parameters for FCVs are inferior to gasoline power trains. However,
these figures are better than advanced BEVs, and projections show that FCVs
Alternative Fuels for Transportation
volume and manufacturing processes remain uncertain. For materials, for
example, polymer electrolyte membranes that are used in small quantities,
large production would be required. The cost of FCSs for mobile applications
at present is estimated to be $325/kW at a production level of 500,000 units
per year (Adamson 2008). U.S. DOE has set technical as well as cost targets
for mobile FCSs that have to be met in order to become competitive with
ICEVs. The direct hydrogen fuel-cell power system has to have 60% electric
efficiency at a cost of $45/kW by 2010 and $30/kW by 2015. Alternatively, a
reformer-based-fuel-cell-power system operating on clean hydrocarbon or
alcohol that meets emission standards has to have a 45% electric efficiency at
a cost of $45/kW by 2010 and $30/kW by 2015. The start-up time for a reformer-based system should be less than 30 s. The total cost consists of $5/kW for
the membrane, $5/kW for the electrodes, $10/kW for the MEA, and $10/kW
for the bipolar plates. For PEFCs, the challenge is catalyst cost reduction.
The search for nonplatinum catalysts has been on for more than 40 years.
At low temperatures and using hydrogen, platinum-based catalysts remain
most active (Arico et al. 2005). One could potentially use a greater amount
of a cheaper, less active catalyst, but the acidic environment of PEFCs rules
out non-noble metals at present (Gasteiger et al. 2005). Another option is to
reduce platinum loadings but this presents the problem of reducing catalyst durability (Zhang et al. 2006). The need for alternative catalysts is also
driven by the availability of platinum. Platinum catalysts in automobiles
already amount to approximately half of the platinum sold globally each
year (Loferski 2008). Unless breakthroughs are made, low-temperature fuel
cells will continue to require platinum catalysts in the foreseeable future.
However, the most critical issue is to reduce the amount of Pt loadings. An
average Pt loading is around 0.5 mg/cm 2 and the total amount of Pt used in
current 80 kW class stacks is estimated to be about 100–120 g. From the standpoint of cost and resource conservation, it is not possible to use this amount
of Pt in commercial vehicles. By comparison, the amount of Pt used in the
exhaust-gas after-treatment system for ICEVs is <10 g. To achieve a realistic
cost the amount of Pt used should be reduced to one-tenth of the present
level. However, there is currently no technology available for reducing the
amount of Pt loading to this extent. Innovative ideas for improving the performance of the electrode catalyst is therefore most desired.
One can expect continuous improvements and developments in conventional power trains. Engine downsizing and the hybridization of the power
trains will partly compensate for the low-load efficiency deficit of ICEVs.
As electric components have replaced many mechanical parts of the vehicle, hybridization combined with regenerative braking will bring increased
electrification of power trains. As many elements of the drivetrain and the
refueling infrastructure are new, there are still major improvements needed
for the FCVs to become competitive with ICEVs. Today, cost, range, and refueling parameters for FCVs are inferior to gasoline power trains. However,
these figures are better than advanced BEVs, and projections show that FCVs