Well, things go this way: by combining hydrogen and oxygen, you get a reaction that releases heat, and produces water.
This with an efficiency < 1, as the laws of termodynamics clearly state.
If you get water, and want to separate it into oxygen and hydrogen again, to burn them, you must pump energy into the system. Again, the efficiency of the process is necessarily < 1, independently from the method used.
The result is that, to produce 1 kW of energy by "burning" sea water, you need MORE than 1 kW of energy to start with.
Hardly worth it.
Hydrogen is not available free in nature. It must first be produced. It's, as they say, an "energy carrier" (like batteries) rather than an energy source (like oil, or coal).
The only interesting thing in the whole process is electrolisis by radio wave instead than direct current applied to water.
That's about it.
But getting free energy from the sea? :jerkit:
Forget it.
If it was as the guy says, he'd invented a method of getting energy out of nowhere, and the perpetual motion, as you could burn sea water, obtaining again water and the energy to burn it again. Which is obviously impossible.
Either the guy is a cunning businessman who has devided a way to get financing for his researches out of the ecologist hysteria of these latest years, or one has to wonder how he spent the money which supposedly had to pay for his education... Surely not sea water. More probably high quality alcohol..

:foot:
