Illustration showing how nano-sale artificial photosynthesis could be used to produce a carbon neutral and renewable fuel. To produce the fuel, nanotubes (blue) are seeded with cobalt oxide crystals. The cobalt oxide crystals are a photocatalyst that uses the energy in sunlight to split water (H2O) molecules. This frees up electrons and oxygen (O2) that then reacts with carbon dioxide (CO2) to produce methanol (CH3OF), the fuel.