Hydrogen gas that is created using solar energy to split water into
hydrogen and oxygen has the potential to be a cost-effective fuel source if
the efficiency of the catalysts used in the water-splitting process can be
By controlling the placement of key additives (dopant atoms) in an iron oxide
catalyst, researchers from the NIST Center for Nanoscale Science and Technology
have found that the final location of the dopants and the temperature at which
they are incorporated into the catalyst crystal lattice determine overall
catalytic performance in splitting water.
The iron oxide hematite is a promising catalyst for water
splitting because it is stable in water and absorbs a large portion of the solar
spectrum. It is also abundant in the earth’s crust, making it inexpensive.
Unfortunately, pure hematite has only modest catalytic activity, falling well
short of its predicted theoretical maximum efficiency. Incorporating dopants
such as tin atoms into hematite’s lattice improves performance, but it is a
challenge to accurately measure the dopant concentration, making it difficult
to understand and optimize their effects on catalyst performance.
Using thin films of hematite doped with tin, the researchers
produced highly active samples that enabled them to measure and characterize
the spatial distribution of dopants in the material and their role in
catalysis. The researchers determined that as a result of the sample
preparation protocol they followed, a dopant gradient extends from the
interface with the dopant source to the catalyst surface, where the measured
concentration is low compared with previous estimates from similarly prepared
Contrary to prior results, they found that only a small
dopant concentration is needed to improve catalytic activity. The researchers
believe this study creates a path for improving the rational design of
inexpensive catalysts for splitting water using solar energy.