It takes more energy to split H2O than it yields.
There were reports that the US Navy was working on this two years ago as a means of self fueling ships at sea by using seawater and carbon dioxide. There have been no further reports in the intervening two years that I know of. The problem then likely was that they didn’t have a fuel source to drive the process.
http://www.gizmag.com/jet-fuel-seawater/24287/
Except nobody mentioned that the nuclear powered aircraft carriers would generate the sort of power to convert salt water and CO2 to jet fuel. It would be expensive but cheaper than transporting jet fuel over the ocean.
I’m pretty sure you’re right. If I recall, The byproduct of burning hydrogen is H2O. So that would mean they would create a perpetual motion machine by making energy from water, which obviously is not possible.
“It takes more energy to split H2O than it yields”
So much for the Hydrogen powered cars. Same for ethonal.