I'm currently looking for an efficient water splitting water catalyst for my Chemistry project. Titanium Dioxide is the popular one, as it's cheap and abundant. However, TiO2 is only most efficient when shined by UV light, not visible light ---> Which accounts for more than half of solar energy. Then, I stumbled upon Tin Oxide, which says here in this article: http://www.sciencedaily.com/releases/2014/04/140416172027.htm , that it's able facilitates a water-splitting reaction when exposed to visible light which does not activate TiO2. So my question is, When both Photocatalyst (Same amount) are placed under direct sunlight, which produces more Hydrogen in a given amount of time? And which one is more cost effective?