This is a ball-and-stick model of the molecular structure of the solar-fuel catalyst developed at Caltech. Blue represents iron atoms; green is nickel; red is oxygen; white is hydrogen.

A team of scientists has begun to learn more about a catalyst needed to split water, a discovery that could potentially lead to the production of solar fuels.

Researchers from the California Institute of Technology had developed a water-splitting catalyst in 2014 comprised of layers of nickel and iron. The catalyst proved to be a mystery, with scientists largely unsure of how it worked. Many researchers hypothesized that the nickel layers were responsible for the water-splitting ability of the catalyst.

However, in a recent study, the researchers discovered that iron was the driver in splitting hydrogen from oxygen in water, not the previously believed nickel, a discovery that could yield economically viable solar fuels in the next few years.

“This will alert people worldwide that iron is particularly good for this kind of catalysis,” Harry Gray, Caltech's Arnold O. Beckman Professor of Chemistry, said in a statement. “I wouldn't be at all shocked if people start using these catalysts in commercial applications in four or five years.”

The researchers created an experimental setup that starved the catalyst of water.

“When you take away some of the water, the reaction slows down, and you are able to take a picture of what's happening during the reaction,” Bryan Hunter, PhD, a former fellow at the Resnick Institute and first author of the study, said in a statement.

The pictures taken revealed that in the active site of the catalyst—the specific location where water is broken down into oxygen—iron was performing the water-splitting reaction and not the nickel.

“Our experimentally supported mechanism is very different than what was proposed,” Hunter said. “Now we can start making changes to this material to improve it.”

The study was published in Joule.