I'm not sure of any generators that would be effective at colder than antarctic temps for use with hydro... I mean, most complex materials will become brittle and shatter. It's not a problem anyone I'm aware of is really trying to solve.
I think for a "titanothermal" system, you use the right density hydrocarbon as the working fluid in the "boiler", and 3-D print the components out of H2O :-)
Except water ice isn't a very good heat conductor, so the evaporator / condenser might have to be something else. Ice could be used for other parts, though.
