Combine Steam with Iodine Vapour at about 400-600C , 1 atm should do the trick.
I2 (g) + H2O (g) -> HI (g) + HIO (g)
2 HIO (g) -> 2 HI (g) + O2 (g)
2 HI (g) -> H2 (g) + I2 (g)
But you will have difficulty separating hydrogen, oxygen and iodine.
The beauty of electrolysis is that your products are already separated at formation. In fact, electrolysis isn't that bad. The efficiency of Electrolysis of Low Alkali Water with a Platinum Electrode is in fact 90% at 1 atm.