Pure hydrogen fuel is non-polluting. Current methods of extracting hydrogen, however, use energy derived from sources that pollute. Finding ways to use the sun's energy to split water to extract hydrogen would make for a truly clean energy source. Several research efforts are using materials engineered at the molecular scale to tap the sun as an energy source to extract hydrogen from water. Researchers from Pennsylvania State University have constructed a material made from titanium dioxide nanotubes that is 97 percent efficient at harvesting the ultraviolet portion of the sun's light and 6.8 percent efficient at extracting hydrogen from water....