Splitting water into hydrogen provides a means of harvesting the hydrogen for fuel. This image depicts the water-splitting process in a light-sensitive electrode material (BiVO4), which UChicago and University of Wisconsin researchers investigated in an experimental and computational study.An inexpensive method for generating clean fuel is the modern-day equivalent of the philosopher's stone. One compelling idea is to use solar energy to split water into its constituent hydrogen and oxygen and then harvest the hydrogen for use as fuel. But splitting water efficiently turns out to be not so easy.