Hydrogen
From RationalWiki
Hydrogen (H) is an element that is comprised of one (1) proton and one electron. At earth's surface conditions it forms a diatomic gas, which is colorless and odorless, but highly flammable. Up close it looks like this:
Hydrogen reacts violently with oxygen to form water, liberating a great deal of chemical energy in the process. See the Hindenberg disaster for an example of this.
Hydrogen nuclei at high enough temperatures and pressures react even more violently to form helium nuclei, liberating a very great deal of nuclear energy in the process. See the sun (but not with unprotected eyes) for an example of this.
[edit] The "hydrogen economy"
Numerous activists in both environmental and business circles have promoted the possibility of a "hydrogen economy", where the most abundant element in the universe becomes a universal fuel for pretty much any energy need. On its face it sounds good -- hydrogen burns to form water, which is not particularly polluting (except inasmuch as it's a notable greenhouse gas) -- but hydrogen economy activists forget one very important thing: while hydrogen is indeed abundant, there's very little free hydrogen on planet Earth.
The hydrogen economy thus becomes a thermodynamics problem -- in order to refine hydrogen (usually from water or methane), the fuel producer must use more energy to electrolyze the source compound than can be derived from burning the resulting hydrogen. While this can be acceptable if renewable resources such as solar power are used to run the electrolysis cells, it still means that earthbound hydrogen is good only for energy storage or transportation rather than as an energy source. In fact, hydrogen is no more an energy "source" than electricity is.
Translation: hydrogen cars may be practical if hydrogen is treated as a storage battery, but thinking that the "hydrogen economy" is a magic bullet that will solve our energy problems is nothing more than falling for an elaborate perpetual motion scheme.
