Rice University researchers have engineered a key light-activated nanomaterial for the hydrogen economy. Using only inexpensive raw materials, a team from the Rice Laboratory for Nanophotonics, Syzygy Plasmonics Inc. and Princeton University’s Andlinger Center for Energy and the Environment has created a scalable catalyst that requires only the power of light to convert ammonia into clean-burning hydrogen fuel.
The research is published online today in the journal Science.
The research tracks government and industry investment to create infrastructure and markets for a 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 collects energy from light, either sunlight or stingy energy LEDs.
The rate of chemical reactions typically increases with temperature, and chemical producers have capitalized on this for over a century by applying heat on an industrial scale. Burning fossil fuels to raise the temperature of large reaction vessels by hundreds or thousands of degrees results in a huge carbon footprint. Chemical producers also spend billions of dollars each year on thermocatalysts—materials that do not react but speed up reactions under intense heating.
“Transition metals like iron are typically poor thermocatalysts,” said study co-author Naomi Halas of Ross. “This work shows that they can be efficient plasmonic photocatalysts. It also shows that photocatalysis can be performed efficiently with cheap LED photon sources.”
“This discovery paves the way for sustainable, low-cost hydrogen that can be produced locally rather than in massive centralized plants,” said Peter Nordlander, also co-author of Rice.
The best thermocatalysts are made of platinum and related precious metals such as palladium, rhodium and ruthenium. Halas and Nordlander spent years developing light-activated (plasmonic) metal nanoparticles. The best of these are also typically made with precious metals like 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 to catalytic particles to produce “ antenna-reactors” hybrids, where one. part harvested energy from light and the other part used the energy to drive chemical reactions with surgical precision.
Halas, Nordlander, their students and collaborators have worked for years to find non-precious metal alternatives both for energy harvesting and for the intermediates that speed up the reaction of the antenna reactors. The new study is the culmination of that work. In it, Halas, Nordlander, rice alumnus Hossein Robatjazi, Princeton engineer and physical chemist Emily Carter, and others show that the antenna-reactor particles made of copper and iron are very efficient to convert ammonia. The piece of copper particles, which collects energy, captures energy from visible light.
“In the absence of light, the copper-iron catalyst exhibited about 300 times less reactivity than copper-ruthenium catalysts, which is not surprising because ruthenium is a better thermocatalyst for this reaction,” said Robatjazi , Ph.D. an alumnus from Halas’ research group who is now chief scientist at Houston-based Syzygy Plasmonics. “Under illumination, copper-iron showed efficiencies and reactivity that were similar to and comparable to those of copper-ruthenium.
Syzygy licensed Rice’s antenna-reactor technology, and the study included scaled tests of the catalyst in the company’s commercially available, LED-powered reactors. In laboratory tests at Ross, the copper-iron catalysts were illuminated with lasers. Syzygy tests showed that the catalysts maintained their efficiency under LED illumination and on a scale 500 times larger than a laboratory setup.
“This is the first report in the scientific literature showing 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.”
“Given their potential to significantly reduce the carbon emissions of the chemical sector, plasmonic antenna-reactor photocatalysts are worthy of further study,” added Carter. “These results are a great motivator. They suggest that it is likely that other combinations of abundant metals can be used as cost-effective catalysts for a wide range of chemical reactions.”
Yigao Yuan et al, An Earth-abundant photocatalyst for H2 generation from NH3 with light-emitting diode illumination, Science (2022). DOI: 10.1126/science.abn5636. www.science.org/doi/10.1126/science.abn5636
Provided by Rice University
Citation: 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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