Why not alcohol?
You seem more motivated by the "run out of energy" meme than the "pollution" meme, so why the hydrogen fixation? Alcohol is a renewable fuel that is much much much closer to reality than hydrogen.
My twin-turbo, tree-hugger's nightmare, Ferrari F50 actually burns a 60% alcohol fuel mix.
To be vaguely space related: the German V2 chose alcohol as a fuel largely because it could be domestically produced, as opposed to kerosene.
John Carmack
www.armadilloaerospace.com