I was once excited about hydrogen powered cars as a green solution like many of you probably are. Hydrogen is the most abundant element in the universe and readily available here, no problem. It's also not expensive to produce. Hydrogen fuel cells work quite well. Iceland currently powers many buses in its transportation system using it (in fact the entire country is like a green experiment using all kinds of technologies like geothermal plants, etc).
But... the problem for the rest of the world is this:
We have a MASSIVE infrastructure of gas stations now that would all need to be converted to expend hydrogen and the cost would be staggering. Additionally, because hydrogen is the smallest element it readily escapes its enclosures unless sufficiently pressurized (it requires a ton of pressure). The hydrogen 'tanks' in cars have to be specially manufactured to be highly pressurized as well, to hold the fuel.
Well, that put a damper on things, however, something exciting that's emerging are ways to contain the hydrogen at 1 atmosphere (regular pressure). One research team discovered chicken feathers of all things have nano-pores that hydrogen readily will lodge within. Essentially, they heat the feathers up to condense the material into a fluff, if you will, and then that may be placed inside a tank to hold the hydrogen very cheaply. Chicken feathers are a very cheap commodity, obviously. In addition to that, carbon nanotubes can be used. It was not thought to be cost effective until recently. A chemical engineer in CA discovered that putting waste plastic bags (like grocery bags) into a small reactor and heating them up would produce pure nanotubes extremely cheaply. The exact technical specifications required are unknown to me, but it seems they don't need any special order (assuming the chicken feathers could be dumped into a tank, why not nanotubes?).