Ionize Hydrogen and Oxygen Gas in Electrolytic Cell?
Since the monatomic hydrogen and oxygen have combined, respectively, in H2 and O2 gases, those molecular bonds must be broken in order to get them to recombine as water and produce electricity. That is precisely what a fuel cell does. You can lease a hydrogen fuel cell powered Hyundai Tucson, if you're close to H2 filling stations, and Iceland is looking into setting up a hydrothermal-powered H2 fuel station system.