Electrolyzing water would also give hydrogen which would make the transpiration of materials easier. I’m guessing that it would require a large amount of electricity to get enough hydrogen/oxygen from the water (they really would need a miniature nuclear reactor).

Edit: for my last comment (which I can’t edit now) I meant to say that hydrogen has a high energy content by mass but not by volume. So 1kg of the stuff has a huge amount of energy but also takes up a lot of physical space.