Technology Status of Hydrogen Road Vehicles

The most abundant and accessible hydrogen-dense feedstocks are water, coal, oil and natural gas.
.......
Of course, fossil fuel hydrogen is not a clean, renewable resource. Most of the hydrogen research community
agrees that eventually hydrogen should be produced from water. Nevertheless it may be easiest to sustain a
transition to hydrogen by expanding commercially-available, relatively inexpensive production processes, such
as the manufacture of H 2 from coal for many decades, environmental considerations aside......
.......
Hydrogen also can be produced from the gasification of biomass....
However the biomass resource base, although renewable, is many times smaller than the coal resource base.
.......
For simplicity, this paper considers only the most abundant hydrogen feedstocks: coal to represent a low-cost
base in the near-to-medium term, and solar water electrolysis as a low-environmental impact case in the longer
term.
.......
Water can be decomposed thermally at temperatures above 2500 K.....(but) many researchers do not think
thermochemical production is very promising, and favor electrolytic and photolytic water-splitting techniques
instead..... In my analysis, I consider water electrolysis only...
Non-fossil feedstocks should be used....of these, solar energy and nuclear energy are available in the long
term.....; this cost analysis examines solar hydrogen.
3. Hydrogen Distribution
Typically, hydrogen would be transported from the site of production to end users as a gas, via pipeline.
Ideally, the current natural gas system would be used for at least the initial stages of a transition to hydrogen.
However, pure hydrogen reacts at the surface of certain pipeline steels, embrittling them and accelerating the
growth of fatigue cracks.....(but) compounds can be added to hydrogen to inhibit embrittlement, (but) none
is safe, inexpensive and effective. Otherwise, dedicated pipelines would have to be built.
.......
Hydrogen also could be shipped in liquid form, in 49 000 l tank trucks, 132 000 l rail cars, or, for short
distances, in vacuum-jacketed pipelines.
4. Vehicular Fuel Storage and Refueling
Hydrogen may be stored on board a vehicle as a gas bound with certain metals, as a liquid in cryogenic
containers, or as highly compressed gas (690 bar) in ultra-high-pressure vessels. Other forms of hydrogen
storage, such as glass microspheres, cryoadsorbents, and liquid hydrides, are discussed in the literature...
.......
The metals most used in hydrides are iron, magnesium, nickel, manganese and titanium. Vehicular hydride
storage systems are usually long thin hollow cylinders, tightly bundled, and pressurized with hydrogen to
about 34 bar. When the vessel is charged, a good deal of heat is released... and during discharge the reaction
is reversed and heat is required.
.......
The most serious shortcoming of hydrides is their low mass and volumetric energy density...The low mass
density of most hydrides means that hydride vehicles are much heavier and less efficient than comparable
gasoline or LH 2 vehicles, and are limited by storage weight to about a 150-300 km range.
.......
Hydrides are susceptible to contamination by impurities in the hydrogen gas.....(and) a 99.999% purity is
necessary to insure that hydrides have relatively long lives.
.......
42