Research yields cheaper catalyst for hydrogen fuel production

May 5, 2011, 2:03 a.m.

Researchers at Stanford and the Technical University of Denmark (DTU) are bringing the dream of a green-powered world one step closer to reality.

Up to this point, scientists have encountered a practical hurdle in the production of clean hydrogen fuel: the lack of cheap and abundant catalysts that can expedite the generation of hydrogen and oxygen. Recent findings by chemical engineering professor Jens Norskov and his peers may effectively overcome this hurdle.

The concept of imitating plant photosynthesis in fuel production is not new. In fact, one feasible procedure today is to use a platinum catalyst in conjunction with a light-absorbing electrode to produce hydrogen fuel from sunlight and water.

But platinum is both expensive and scarce. According to Norskov and his team, a better option is molybdenum sulfide, a natural catalyst that is both cheap and abundant.

“Molybdenum sulfide is a good alternative,” Norskov said. “There are other catalysts that work but they’re based on platinum and similar materials, and they are too rare and too expensive for widespread use.”

Norskov and his peers hope to further develop a procedure called photo-electrochemical (PEC) water splitting. In this process, sunlight hits PEC cells and this absorbed energy is used to split water molecules into hydrogen and oxygen.

DTU researchers have created a device that harvests energy from sunlight — energy that is later used to power the conversion of single hydrogen ions into hydrogen gas. This latter process required a catalyst, which is where Norskov and his team came in.

“We have been studying catalysts and chemical processes for a long time but obviously one of the big challenges in that field is to find catalysts for making fuels from sunlight,” said Norskov, who is the professor of photon science at the SLAC National Accelerator Laboratory.

The Stanford researchers developed a theoretical method to examine catalyst behavior.

“We do calculations of the electronic structure of materials because that…determines all the properties of a material,” Norskov said.

As the Stanford researchers developed an “understanding of what is important a catalyst for hydrogen,” they were able to identify molybdenum sulfide as an inexpensive but effective catalyst.

These findings pave the way for future collaboration between Norskov’s research team and other scientists on the Farm and beyond. Thomas Jaramillo, assistant professor of chemical engineering, is one of these fortunate scientists. He has worked closely with Norskov over the years.

“In my research team, we are ultimately experimental,” Jaramillo said. “We can synthesize a lot of interesting materials and we have a lot of control over the composition of the material as well as the nanostructure of the material. We can work collaboratively [with Norskov] in that when we find interesting things in the lab, we can communicate that to him and his team.”

Norskov’s group, in turn, uses these findings to perform theoretical calculations and predictions.

“We’re in constant communication with one another and our output serve them as inputs and their outputs can serve as our inputs,” Jaramillo said.

Norskov, Jaramillo and their peers are adamant about continuing their research on energy efficient and clean fuels.

“You lose a lot of the energy from the sunlight in transferring that into a fuel, hydrogen for instance,” Norskov said.

Hydrogen is an attractive source of fuel because it is energy dense and serves as a relatively clean fuel. But PEC water splitting is not a surefire answer to the world’s energy needs yet, the researchers said.

“We would like to find catalysts and materials to absorb sunlight that are more efficient in doing it so we don’t lose a lot of energy and that is in the end that will make this competitive,” Norskov said.

“Let me stress: we’re not sure that there is a solution,” he said. “But we’re trying to get there.”

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