A light-powered catalyst could be key for hydrogen economy

The Rice lab's catalyst could be key to the hydrogen economy

Reaction cell testing copper-iron plasmonic photocatalysts for hydrogen production from ammonia. Credit: Brandon Martin / Rice University

Rice University researchers have developed a key nanomaterial for light in the hydrogen economy. Using only inexpensive materials, a team from Rice’s Nanophotonics Laboratory, Syzygy Plasmonics Inc. and Princeton University’s Andlinger Center for Energy and the Environment developed a scalable catalyst that requires only light energy to convert ammonia into clean hydrogen fuel.

The research is 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 will not contribute to greenhouse warming. 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. And unlike traditional catalysts, it does not require heat. Instead, it harvests energy from light, whether it’s sunlight or powerful LEDs.

The rate of chemical reactions generally increases with temperature, and chemical manufacturers have capitalized on this for over a century by applying heat on an industrial scale. Burning fossil fuels to raise the temperature of large reactor vessels by hundreds or thousands of degrees leads to a large carbon footprint. Chemical manufacturers also spend billions of dollars each year on thermocatalysts—materials that are inactive but react at an increased rate under high temperatures.

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

“This discovery opens up a sustainable, low-cost way for hydrogen to be produced locally instead of large, centralized plants,” said Peter Nodlander, co-author of Rice.

The best thermocatalysts are made of platinum and the related precious metals palladium, rhodium and ruthenium. Halas and Nordlander spent years developing light-activated (plasmonic) metal nanoparticles. The best of these are usually made of precious metals such as silver and gold.

Following their discovery in 2011 of plasmonic particles that emit short-lived, high-energy electrons called “hot carriers,” they discovered in 2016 that hot carrier generators can be coupled with catalytic particles to produce hybrid “antenna-reactors,” in which one part harvested energy from light and another part used energy to conduct chemicals with surgical precision.

Halas, Nordlander, their students and collaborators have worked for years to find alternatives to non-precious metals in both halves of the energy harvest and the response speed of the antenna. The new study is the culmination of this work. In it, Halas, Nordlander, Rice alumnus Hossein Robatjazi, Princeton engineer and physical chemist Emily Carter, and others show that antenna-reactor components made of copper and steel are very efficient in converting the -ammonia. Copper, an energy-harvesting piece of particles captures energy from visible light.

The Rice lab's catalyst could be key to the hydrogen economy

Reaction cell (left) and photocatalytic platform (right) used in tests of copper-iron plasmonic photocatalysts for hydrogen production from ammonia at Syzygy Plasmonics in Houston. All the energy for the catalysis reaction comes from LEDs that produce light with a wavelength of 470 nanometers. Credit: Syzygy Plasmonics, Inc.

“In the absence of light, the copper-iron catalyst showed about 300 times lower reactivity than the copper-ruthenium catalysts, which is not surprising since ruthenium is the best thermocatalyst for the reaction,” said Robatjazi, Ph.D. . an alumnus from Halas’ research group who is now chief scientist at Houston-based Syzygy Plasmonics. “Under the light, copper-iron showed the same performance and reactivity as copper-ruthenium.

Syzygy has licensed Rice’s antenna-reactor technology, and the study includes proposed tests of the catalyst in the company’s commercially available, LED-powered reactors. In laboratory experiments at Rice, copper-iron catalysts were illuminated with lasers. Syzygy’s tests showed that the catalysts maintain their performance under LED light and a scale of 500 times greater than the laboratory setting.

The Rice lab's catalyst could be key to the hydrogen economy

A photocatalytic platform used in experiments with copper-iron plasmonic photocatalysts for hydrogen production from ammonia. Credit: Brandon Martin / Rice University

“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 completely replace precious metals in plasmonic photocatalysis.”

“Because of their ability to significantly reduce the carbon emissions of the chemical sector, plasmonic antenna-reactor photocatalysts are suitable for further study,” added Carter. “These results are very encouraging. They suggest the possibility that many other metal compounds can be used as inexpensive tools for many types of chemistry.”

More information:
Yigao Yuan et al, Ground-based photocatalyst for generation of H2 from NH3 with light emitting diode, Science (2022). DOI: 10.1126/science.abn5636. www.science.org/doi/10.1126/science.abn5636

Provided by Rice University

Quote: Light-powered catalyst could be key to hydrogen economy (2022, November 24) Retrieved November 24, 2022 from https://phys.org/news/2022-11-light-powered-catalyst-key-hydrogen-economy .html

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