We’ve described this before, with the key word you need for the search being ’electrolysis’.
By the way, electrolysis is the main method by which it is proposed to get H2 for the 'hydrogen economy'. The problem of course is that the electrolysis always requires more energy input than can be recovered from burning the H2. (That's a law of physics, not an engineering problem.) The energy source would probably be nuclear reactors, although solar energy and other sources are also possible. Some H2 is available directly from fossil fuels, but it carries only a fraction of the energy that could be obtained from burning the entire fuel.
In other words, hydrogen is not an energy source because we don't have any significant amount available except as water, which is hydrogen that's already been burned. Hydrogen may be a nice way to carry energy around, but we still have to get that energy somewhere.Mike
(published on 10/22/2007)