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Alternative Fuels for Transportation
substantial advances in recent years, they still require significantly higher
amounts of precious metal catalyst than the direct-hydrogen PEFCs.
Another issue is to mitigate the problem of methanol crossover through
the membrane.
Hydrogen can also be produced electrolytically from water using renewable sources of energy that can reduce pollution and emission of greenhouse
gases (Hocevar and Summers 2008). Hydrogen can also be used in IC engines. But the efficiency of IC engines is quite low. Onboard storage of hydrogen, albeit being cost and volume intensive in relation to gasoline or diesel
tanks is much closer to automotive costs and performance figures. Fuel cells
have not had the advantage over combustion engines or batteries for a long
time in spite of the demonstration of various FCVs such as Allis–Chalmers
Fuel-Cell Tractor in 1959 and GM Electrovan in 1966 due to their limited
power-density. The advent of new electrolyte materials has offered the possibility for compact and lightweight fuel cells. Though the power density of
fuel cells has increased over the years, fuel cells remain heavier and bulkier
than conventional drivetrains. Accordingly, further technological developments focusing on additional size reduction and increased performance are
desired (Helmolt and Eberle 2007).
A fuel-cell running on hydrogen looks attractive as a long-term option
for passenger cars as it eliminates emissions on the tank-to-wheel path.
Hydrogen can be produced from many sources, and has attractive efficiencies. It is noteworthy that a fuel-cell reaches its highest efficiency at
part loads and there is little advantage against the ICE at full loads.
Interestingly, passenger vehicles are mostly operated at part loads, significantly below their rated power, such that the efficiency gain offered by
fuel cells could be maximum. It is noteworthy that at low-power output
even the fuel-cell system (FCS) efficiency drops as many of the balance of
plant units needed to be operated even at idle power. Accordingly, the
system has to be optimized for low-power consumption to capitalize on
the part load efficiency advantage of the fuel-cell. Performance at highpower density and efficiency in terms of high cell voltage has been the
mainstay of fuel-cell development. In recent years, these are complemented by other factors, namely lower cost at high volume production with
increased reliability and durability. The targets are derived from competing conventional automotive propulsion systems, which are designed
for 5500 h of operational lifetime at a cost of U.S. $50/kW, including fuel
storage.
Durability is a major issue for the fuel cell stacks, especially with thinner membranes and lower catalyst loadings for cost effectiveness. Among
the factors limiting the lifetime of PEFCs, chemical degradation has been
identified as a major problem. However, there has been remarkable progress
in system reliability owing to the continuous improvements in engineering
and operation of complete FCSs and vehicles.
Alternative Fuels for Transportation
substantial advances in recent years, they still require significantly higher
amounts of precious metal catalyst than the direct-hydrogen PEFCs.
Another issue is to mitigate the problem of methanol crossover through
the membrane.
Hydrogen can also be produced electrolytically from water using renewable sources of energy that can reduce pollution and emission of greenhouse
gases (Hocevar and Summers 2008). Hydrogen can also be used in IC engines. But the efficiency of IC engines is quite low. Onboard storage of hydrogen, albeit being cost and volume intensive in relation to gasoline or diesel
tanks is much closer to automotive costs and performance figures. Fuel cells
have not had the advantage over combustion engines or batteries for a long
time in spite of the demonstration of various FCVs such as Allis–Chalmers
Fuel-Cell Tractor in 1959 and GM Electrovan in 1966 due to their limited
power-density. The advent of new electrolyte materials has offered the possibility for compact and lightweight fuel cells. Though the power density of
fuel cells has increased over the years, fuel cells remain heavier and bulkier
than conventional drivetrains. Accordingly, further technological developments focusing on additional size reduction and increased performance are
desired (Helmolt and Eberle 2007).
A fuel-cell running on hydrogen looks attractive as a long-term option
for passenger cars as it eliminates emissions on the tank-to-wheel path.
Hydrogen can be produced from many sources, and has attractive efficiencies. It is noteworthy that a fuel-cell reaches its highest efficiency at
part loads and there is little advantage against the ICE at full loads.
Interestingly, passenger vehicles are mostly operated at part loads, significantly below their rated power, such that the efficiency gain offered by
fuel cells could be maximum. It is noteworthy that at low-power output
even the fuel-cell system (FCS) efficiency drops as many of the balance of
plant units needed to be operated even at idle power. Accordingly, the
system has to be optimized for low-power consumption to capitalize on
the part load efficiency advantage of the fuel-cell. Performance at highpower density and efficiency in terms of high cell voltage has been the
mainstay of fuel-cell development. In recent years, these are complemented by other factors, namely lower cost at high volume production with
increased reliability and durability. The targets are derived from competing conventional automotive propulsion systems, which are designed
for 5500 h of operational lifetime at a cost of U.S. $50/kW, including fuel
storage.
Durability is a major issue for the fuel cell stacks, especially with thinner membranes and lower catalyst loadings for cost effectiveness. Among
the factors limiting the lifetime of PEFCs, chemical degradation has been
identified as a major problem. However, there has been remarkable progress
in system reliability owing to the continuous improvements in engineering
and operation of complete FCSs and vehicles.