Profs. Thomas E. Mallouk and W. Justin Youngblood at Penn State University have been working on a solar cell that can directly crack water into hydrogen and oxygen. Electrodes from the cells inserted into water can split the molecules. Unfortunately at this point the system is only about 0.3 percent efficient. The researchers are investigating a number of different catalysts to help stimulate the reaction. They are also looking at different dyes for the cell itself to improve the sensitivity to a larger portion of the light spectrum. Another issue is making the reaction self-sustaining. Currently much of the oxygen and hydrogen quickly recombines after splitting, limiting the amount of hydrogen that can be recovered. It's an interesting concept but clearly still a long way from being viable.