[ you really can’t extract any more energy from water than you add to it. It’s the law. ]
Unless the two gasses are separated easily.. and you burn them..
No, there is no unless.
Catalysts only reduce the amount of excess energy wasted in the conversion. You still need to put in all the energy that you want to extract as combustion heat, and then some. Repeating the contrary position again will not make it any more valid.