by Emil Morhardt
Photosynthesis converts CO2 and water to sugar (glucose). In the normal course of things we get fuel from the glucose by letting yeast ferment it in a water mix to not much more than 16% ethanol, then get rid of the water by distillation or some other energy-intensive process, exactly the same process as producing vodka or whisky (see picture). An intriguing possibility is to bypass the fermentation/distillation stage entirely and produce fuel directly from a sugar solution using only light—a form of artificial photosynthesis. Amao et al. (2014) at Osaka University seem to have pulled that off by using only visible light, glucose, and CO2, plus some catalysts, to produce both hydrogen and formic acid directly. The formic acid is particularly interesting because it is a liquid, but can be converted enzymatically to hydrogen when needed, thus providing a high density storage and transportation medium that is much easier to manage than hydrogen.
Amao, Y., Takahara, S., Sakai, Y., 2014. Visible-light induced hydrogen and formic acid production from biomass and carbon dioxide with enzymatic and artificial photosynthesis system. International Journal of Hydrogen Energy. http://bit.ly/1k4ZE8l