Inexpensive catalyst uses light energy to convert ammonia into hydrogen fuel – Zoo House News

Inexpensive catalyst uses light energy to convert ammonia into hydrogen fuel – Zoo House News

  • Science
  • November 26, 2022
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Rice University researchers have developed an important light-activated nanomaterial for the hydrogen economy. Using only cheap raw materials, a team from Rice’s Laboratory for Nanophotonics, Syzygy Plasmonics Inc. and Princeton University’s Andlinger Center for Energy and the Environment have developed a scalable catalyst that requires only the power of light to convert ammonia into clean-burning hydrogen fuel .

The research results are published online today in the journal Science.

The research follows government and industry investment to create infrastructure and markets for carbon-free liquid ammonia fuel that does not contribute to greenhouse warming. Liquid ammonia is easy to transport and full of energy, with one nitrogen and three hydrogen atoms per molecule. The new catalyst breaks these molecules down into hydrogen gas, a clean-burning fuel, and nitrogen gas, the largest component of the Earth’s atmosphere. And unlike traditional catalytic converters, it doesn’t require heat. Instead, it derives energy from light, either sunlight or low-power LEDs.

The rate of chemical reactions typically increases with temperature, and chemical manufacturers have taken advantage of this by applying heat on an industrial scale for more than a century. Burning fossil fuels to raise the temperature of large reaction vessels by hundreds or thousands of degrees results in a huge carbon footprint. Chemical manufacturers also spend billions of dollars each year on thermal catalysts – materials that do not react but accelerate reactions under high heat.

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

“This discovery paves the way for sustainable, low-cost hydrogen that could be produced locally rather than in huge centralized plants,” said Peter Nordlander, also a Rice co-author.

The best thermal catalysts are made from platinum and related noble metals such as palladium, rhodium, and ruthenium. Halas and Nordlander spent years developing light-activated, or plasmonic, metal nanoparticles. The best of these are also typically made with precious metals like silver and gold.

Following their 2011 discovery of plasmonic particles that emit short-lived, high-energy electrons called “hot carriers,” they discovered in 2016 that hot carrier generators could be married to catalytic particles to make hybrid “antenna reactors,” where one part harvested energy from light and the other part used the energy to power chemical reactions with surgical precision.

Halas, Nordlander, their students, and collaborators have worked for years to find base metal alternatives for both the energy-harvesting and reaction-accelerating halves of antenna reactors. The new study is a culmination of this work. In it, Halas, Nordlander, Rice alumnus Hossein Robatjazi, Princeton engineer and physical chemist Emily Carter, and others show that copper and iron antenna reactor particles are highly efficient at converting ammonia. The particles’ energy-harvesting copper piece captures energy from visible light.

“In the absence of light, the copper-iron catalyst showed about 300-fold lower reactivity than copper-ruthenium catalysts, which is not surprising since ruthenium is a better thermal catalyst for this reaction,” said Robatjazi, Ph.D. Graduate of Halas’ research group, who is now Chief Scientist at Syzygy Plasmonics in Houston. “Under illumination, the copper-iron showed efficiencies and reactivities similar and comparable to copper-ruthenium.

Syzygy licensed Rice’s antenna reactor technology and the study included large-scale testing of the catalyst in the company’s commercially available LED-powered reactors. In laboratory tests at Rice, the copper-iron catalysts were illuminated with lasers. The Syzygy tests showed that the catalysts maintained their efficiency under LED lighting and on a scale 500 times larger than in the laboratory setup.

“This is the first report in the scientific literature showing that photocatalysis with LEDs can produce gram-scale amounts of hydrogen gas from ammonia,” said Halas. “This opens the door to completely replacing noble metals in plasmonic photocatalysis.”

“Plasmonic antenna reactor photocatalysts are worth further investigation given their potential to significantly reduce carbon emissions from the chemical sector,” Carter added. “These results are of great motivation. They suggest that other combinations of abundant metals could likely be used as inexpensive catalysts for a variety of chemical reactions.”

Halas is the Stanley C. Moore Professor of Electrical and Computer Engineering at Rice and Professor of Chemistry, Bioengineering, Physics and Astronomy, and Materials Science and Nanotechnology. Nordlander is Rice’s Wiess Chair and Professor of Physics and Astronomy, and Professor of Electrical and Computer Engineering and Materials Science and Nanotechnology. Carter is Princeton’s Gerhard R. Andlinger Professor of Energy and the Environment at the Andlinger Center for Energy and the Environment, Senior Strategic Advisor in Sustainability Science at Princeton Plasma Physics Laboratory, and Professor of Mechanical and Aerospace Engineering and Applied and Computational Mathematics. Robatjazi is also an Associate Professor of Chemistry at Rice.

Halas and Nordlander are co-founders of Syzygy and hold an equity interest in the company.

The research was supported by the Welch Foundation (C-1220, C-1222), Air Force Office of Scientific Research (FA9550-15-1-0022), Syzygy Plasmonics, Department of Defense and Princeton University.

Other co-authors include Yigao Yuan, Jingyi Zhou, Aaron Bales, Lin Yuan, Minghe Lou, and Minhan Lou from Rice, Linan Zhou from Rice and South China University of Technology, Suman Khatiwada from Syzygy Plasmonics, and Junwei Lucas Bao from both Princeton and Boston College.

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