A light-powered catalyst could hold the key to the hydrogen economy

A reaction cell tests copper-iron plasmonic photocatalysts for the production of hydrogen from ammonia. Credit: Brandon Martin/Rice University

Rice University researchers have engineered a light-activated nanomaterial key to the hydrogen economy. Using only inexpensive raw materials, a team from Rice’s Laboratory for Nanophotonics, Syzygy Plasmonics Inc. and Princeton University’s Andlinger Center for Energy and the Environment has created a scalable catalyst that needs 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 follows government and industry investments 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 contains a lot of energy, with one nitrogen atom and three hydrogen atoms per molecule. The new catalyst breaks these molecules into hydrogen gas, a clean-burning fuel, and nitrogen gas, the largest component of Earth’s atmosphere. And unlike traditional catalysts, it requires no heat. Instead, it harvests energy from light, sunlight, or energy-stingy LEDs.

The rate of chemical reactions generally increases with temperature, and chemical manufacturers have taken advantage of this for more than 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 manufacturers also spend billions of dollars each year on thermocatalysts, materials that do not react but further accelerate reactions under intense heating.

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

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

The best thermocatalysts are made from 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 from precious metals such as silver and gold.

Following their discovery in 2011 of short-lived high-energy electron-emitting plasmon particles called “hot carriers,” they discovered in 2016 that hot carrier generators could be married to catalytic particles to produce hybrid “antenna-reactors,” where one party harvested energy from light and the other party used the energy to drive chemical reactions with surgical precision.

Halas, Nordlander, their students and collaborators have worked for years to find base metal alternatives for both energy harvesting and reaction rate 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 antenna reactor particles made of copper and iron are highly efficient at converting ammonia . The piece of copper that collects particle energy captures the energy from visible light.

Rice's catalyst could hold the key to the hydrogen economy

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

β€œIn the absence of light, the copper-iron catalyst showed approximately 300 times lower reactivity than the copper-ruthenium catalysts, which is not surprising given that ruthenium is a better thermocatalyst for this reaction,” said Robatjazi, Ph.D. alumnus of Halas’ research team who is now chief scientist at Houston-based Syzygy Plasmonics. “Under illumination, the copper-iron exhibited similar and comparable efficiencies and reactivities as copper-ruthenium.

Syzygy licensed the antenna ballast technology from Rice, and the study included scale-up tests of the catalyst in the company’s commercially available LED-powered ballasts. In lab tests at Rice, the copper-iron catalysts were illuminated with lasers. Syzygy tests showed that the catalysts maintained their efficiency under LED illumination and at a scale 500 times larger than the lab setup.

Rice's catalyst could hold the key to the hydrogen economy

The photocatalytic platform used in the testing of copper-iron plasmonic photocatalysts for the production of hydrogen 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 complete substitution of precious metals in plasmon photocatalysis.”

“Given their potential to significantly reduce carbon emissions from the chemical sector, plasmonic antenna reactor photocatalysts deserve further study,” added Carter. “These findings are a big motivator. They suggest that other abundant metal combinations are likely to be used as inexpensive catalysts for a wide range of chemical reactions.”

More information:
Yigao Yuan et al, Earth Abundant Photocatalyst for Generation of H2 from NH3 under 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, Nov 24) Retrieved Nov 25, 2022 from https://phys.org/news/2022-11-light-powered-catalyst-key -hydrogen-economy.html

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