It's hard to beat the energy density of gasoline. Batteries don't come anywhere close, which is why nobody likes to use them for anything. But what if we could just take electrical energy and turn it into gasoline, and what if the only other ingredient we needed to do this was evil carbon dioxide, how awesome would that be? Liquid electricity: we can do it.
There's nothing wrong with electricity, per se. The problem with it is that we don't have a very good way of storing it. The energy density of a fully charged lithium-ion battery is about 0.75 MJ per kilogram. The energy density of gasoline is better than 47 MJ per kilogram. Furthermore, when you use up the energy in gasoline, you're not hauling the gasoline around anymore, whereas a lithium-ion battery with zero energy in it doesn't weigh any less than a lithium-ion battery that's charged up.
Clearly, liquid fuel is awesome, it's just unfortunate that it's so dirty to produce and use. Researchers at the UCLA Henry Samueli School of Engineering and Applied Science have managed to come up with a way to convert electricity directly into a liquid fuel, using only engineered microbes (which work for free) and carbon dioxide (which we have too much of anyway). The microbes were intelligently designed to perform the second half of photosynthesis: they can turn carbon into sugar (in the form of alcoholic biofuel).
The clever bit that UCLA managed to do was to entirely separate out the first half of photosynthesis, the half involving light. Instead of trying to reinvent the plant, they let conventional solar cells use light to generate electricity, and that electricity powers a process that makes formic acid. Then, the formic acid is fed to the microbes along with CO2, and out comes liquid fuel. When considering the overall system, the only energy input is electricity (from the sun), and the only carbon input is CO2, just like a plant. Doesn't get much better than that. This process isn't just renewable, it also temporarily fixes carbon out of the atmosphere, which makes the whole thing at least eco-neutral, if not eco-friendly.
The other big advantage to all this (besides the inherent eco-friendliness of reusing CO2), is that no massive infrastructure changes would be required to bodily transition from fossil fuels to carbon-neutral fuels. You'd still have a car with a gas engine, and you'd still go to the gas station to refuel, but you'd be effectively burning liquid electricity with a zero net output of carbon. At this point, the UCLA researchers have proven that their process works, and they're looking to scale things up to microbial bioreactors that can output enough fuel to make liquid electricity commercially viable.