Solar-power photocatalysis—turning sunlight into energy—holds promise for sustainable and cost-efficient energy and chemical production. Advancing the technology, though, has been hindered by a lack of understanding of exactly how the process works. To that end, a team of Yale researchers has developed a technique that allows them to observe the sunlight-to-fuel conversion in real time, right down to the nanoscale. Specifically, they can see how the light-driven catalyst splits water into hydrogen and oxygen, and how electrons and holes move through the material.