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Rephrased from Wikipedia:
1) Although the energy/weight of LH2 is around twice that of other fuels, its energy/volume is remarkably low. [This is problematic for passenger vehicles smaller than a bus.]
2) Note that LH2 liquifies near absolute zero. Therefore, it requires cryogenic storage technology such as special thermally insulated containers and requires special handling common to all cryogenic fuels. This is similar to, but more severe than liquid oxygen. Even with thermally insulated containers it is difficult to keep such a low temperature, and the hydrogen will gradually leak away (typically at a rate of 1% per day). It also shares many of the same safety issues as other forms of hydrogen, as well as being cold enough to liquefy (and possibly solidify) atmospheric oxygen which can be an explosion hazard.
