Water is a fairly common material in the Universe thanks to how much hydrogen and oxygen want to bond to form the molecule. When the elements do bond, energy is released and could be tapped to power man-made devices, but first we need the hydrogen and oxygen to bond. A common idea is to create systems that use solar energy to split water molecules, and researchers at Berkeley Lab have recently developed a new device for doing so.
This new device is actually a combination of nanowires made of silicon and titanium oxide. These materials are both semiconductors that react with light, but different parts of the spectrum. Silicon operates in the visible and infrared ranges, while titanium oxide reacts to ultraviolet light. When exposed to sunlight, the two materials also do different things as the silicon adds electrons to protons to produce hydrogen, and the titanium oxide pulls the oxygen out of water molecules. To improve performance, the titanium oxide nanowires are arranged like a forest on the larger silicon nanowire. This configuration increases the surface area to interact with water and helps capture sunlight.
Currently the device only achieves 0.12% solar-to-fuel conversion efficiency, which is not horrible, but does need to be increased for commercial use. Fortunately the researchers already know one way to optimize the system by matching the energy outputs of the silicon and titanium oxide.
Source: Berkeley Lab