"To make these devices more widely available, Nocera replaced the
platinum catalyst that produces hydrogen gas with a less-expensive
nickel-molybdenum-zinc compound. On the other side of the leaf, a cobalt
film generates oxygen gas. Nocera notes that all of these materials are
abundant on Earth, unlike the rare and expensive platinum, noble metal
oxides and semiconducting materials others have used."
Hydrogen and oxygen are what propel the space shuttle into orbit. It's a great clean fuel. If this really is possible cheaply enough it's a game changer for sure.