I read a long drawn out debate on a Toyota forum regarding all aspects of the chemistry and thermodynamics of this system and the final conclusion is that it simply wouldn't work. You can't get more energy from water (already fully oxidized) than what you put in. Even if you were to break water into hydrogen and oxygen, it would take more energy to produce browns gas from water than the energy that the browns gas would provide.

Some guy on there says he's going to try it and get back to us. That was about a month ago and we haven't heard from him since.

Edit:
There is only one way I can think of, which is currently in practice, of breaking water into hydrogen and oxygen for any viable source of energy and that is the use of nuclear power during off peak hours to split water. It still takes more energy to do it than energy it provides, but in the case of a nuclear reactor where you can't slow the reaction much, you might as well use the available energy for something during off peak energy use hours. That's about the only useful way to use this technology that I can think of.