By intensely focusing the suns rays on a rare earth oxide, researchers have discovered a reactor that could produce fuel from water.
The reactor hits ceric oxide with an intense blast of focused sun, which heats up the material enough that it starts to shed the oxygen from its lattice. The material then merrily strips the oxygen from either water or carbon dioxide if they're nearby, leaving hydrogen or carbon monoxide — which can be combined to form hydrocarbon fuels using further catalysts.
Still in its early stages, the reactor demonstrates a sun-to-fuel efficiency of 0.7%-0.8%, but according to researchers these are "largely limited by the system scale and design rather than by chemistry." The major advantage to this technology would be that it creates a form a fuel that is energy-dense, and easily stored and transported. The reactor was put through its paces 500 times without interruption, and the oxygen and hydrogen production rates remained constant after a spike in the first 100.
Research published in Science