is the lightest gas (and element) in the universe, and a potentially
important fuel both in internal combustion engines and fuel
cells, both of which can power low or zero-emission vehicles.
The interest in hydrogen as an alternative transportation
fuel stems from its clean-burning qualities, its ability to
be produced domestically, and the potential of fuel-cell vehicles
for high efficiency (two to three times more efficient than
The energy in 1 kg (2.2 lb) of hydrogen gas is about the same
as the energy in 1 gallon of gasoline. A light-duty fuel cell
vehicle must store 5-13 kg (11-29 lb) of hydrogen to enable
an adequate driving range of 300 miles or more. Because hydrogen
has a low volumetric energy density (a small amount of energy
by volume compared with fuels such as gasoline), storing this
much hydrogen on a vehicle using currently available technology
would require a very large tank — larger than the trunk of
a typical car. Advanced technologies are needed to reduce
the required storage space and weight. Storage technologies
under development include high-pressure tanks with gaseous
hydrogen compressed at up to 10,000 pounds per square inch,
cryogenic liquid hydrogen cooled to (-253°C (-423°F) in insulated
tanks, and chemical bonding of hydrogen with another material
(such as metal hydrides).
Natural gas can be blended with hydrogen to make hydrogen/natural
gas blends (HCNG). Vehicles fueled with HCNG represent a first
step toward the hydrogen-based transportation of the future.
HCNG vehicles offer the potential for immediate emissions
benefits, such as a reduction in nitrogen oxides emissions.
At the same time, they can pave the way for a transition to
fuel-cell vehicles by building early demand for hydrogen infrastructure.
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