A new nanomaterial catalyst needs only light to convert ammonia into hydrogen, its developers have said.

Made of inexpensive raw materials, the catalyst was developed by a team from Rice University in Texas, Syzygy Plasmonics Inc., and Princeton University in New Jersey.

Liquid ammonia is easy to transport and packs a lot of energy, with one nitrogen and three hydrogen atoms per molecule. The new catalyst breaks those molecules into hydrogen gas, a clean-burning fuel, and nitrogen gas, the largest component of Earth’s atmosphere. Unlike traditional catalysts, it does not require heat. Instead, it harvests energy from light, either sunlight or energy-efficient LEDs.

Chemical producers spend billions of dollars each year on thermocatalysts, materials that speed up reactions under intense heating, the researchers said.

“Transition metals like iron are typically poor thermocatalysts,” said study co-author Naomi Halas from Rice. “This work shows they can be efficient plasmonic photocatalysts. It also demonstrates that photocatalysis can be efficiently performed with inexpensive LED photon sources.”

Fellow Rice co-author Peter Nordlander added: “This discovery paves the way for sustainable, low-cost hydrogen that could be produced locally rather than in massive, centralised plants.”

Following their 2011 discovery of plasmonic particles that give off short-lived, high-energy electrons called ‘hot carriers’, the team discovered in 2016 that hot-carrier generators could be married with catalytic particles to produce hybrid ‘antenna-reactors’, where one part harvests energy from light and the other part uses the energy to drive chemical reactions.

Halas, Nordlander, their students and collaborators worked for years to find non-precious metal alternatives for both the energy-harvesting and reaction-speeding halves of antenna reactors.

In their new study, the team showed that antenna-reactor particles made of copper and iron are highly efficient at converting ammonia. The copper captures energy from visible light.

Syzygy has licensed Rice’s antenna-reactor technology, and the study included scaled-up tests of the catalyst in the company’s commercially available, LED-powered reactors. In laboratory tests at Rice, the copper-iron catalysts had been illuminated with lasers, but the Syzygy tests showed the catalysts retained their efficiency under LED illumination and on a scale 500-times larger than the lab set-up.

“This is the first report in the scientific literature to show that photocatalysis with LEDs can produce gram-scale quantities of hydrogen gas from ammonia,” said Halas. “This opens the door to entirely replace precious metals in plasmonic photocatalysis.”

The research was published in Science.

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