[FreeFull]

I have looked it up, and it seems the combustion of methane produces more energy than the combustion of hydrogen. Splitting water into hydrogen and oxygen won't be 100% efficient though, and neither will be turning heat into useful energy, so I don't know if you'll still be energy-positive in the end.

[sidek]

More realistic might be a long-term preparation scenario in which we send a first wave of robots to set up some solar panels and run them to store H2 and O2 for a couple of decades. We won't have gained energy necessarily, but we will have stored it in large enough amounts that early colonisation will have extra energy if it needs it.