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.
The thing is that hydrogen has very limited utility as a fuel. Compressing it is as energy-intensive as producing it in the first place, and even compressed, it takes up a very large amount of volume. A pressure vessel identical in volume to a standard 15gal gas tank would hold less than 2.5 gge (gasoline gallon equivalents) of 700bar compressed hydrogen.
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).
