E-Mail IMAGE: An illustration combines two possible types of surface layers for a catalyst that performs the water-splitting reaction, the first step in making hydrogen fuel. The gray surface, top, is lanthanum... view more Credit: CUBE3D Graphic Scientists crafting a nickel-based catalyst used in making hydrogen fuel built it one atomic layer at a time to gain full control over its chemical properties. But the finished material didn't behave as they expected: As one version of the catalyst went about its work, the top-most layer of atoms rearranged to form a new pattern, as if the square tiles that cover a floor had suddenly changed to hexagons.