Or, you know, you could just use the electricity to convert water to hydrogen (itself a usable fuel). How much of the energy required for this reaction is actually coming from the carbon / atmosphere? I would guess very little.
There are all sorts of storage media under development to get around this hydrogen volumetric density problem, but none are much closer to market than this butanol project. At the very least, an existing vehicle fleet would require significant engine modifications to run on hydrogen (not to mention fuel storage and delivery system modifications).