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Researchers create green fuel by flipping a light switch


Researchers create green fuel by flipping a light switch

Calculations for the project were performed at Princeton’s Center for High Performance Computing Research. Credit: Denise Applewhite, Princeton University Communications Office

Researchers at Princeton and Rice universities have combined iron, copper and a simple LED to demonstrate a low-cost technique that could be the key to delivering hydrogen, an energy-rich fuel without carbon pollution.

Researchers used advanced experiments and calculations to develop a technique that uses nanotechnology to separate hydrogen from liquid ammoniaa process that has so far been costly and energy-intensive.

In an article published online November 24 in the journal Science, the researchers describe how they used light from a standard LED to crack ammonia without the high temperatures or expensive elements typically required by this chemical. The technique overcomes an important hurdle to realizing hydrogen’s potential as a clean, low-emission fuel that can help meet energy needs without exacerbating climate change.

“We hear a lot about hydrogen being the ultimate clean fuel, if only it were less expensive, easier to store and obtain,” said Naomi Halas, a professor at Rice University and one of the study’s lead authors. out for use”. “This result demonstrates that we are moving fast towards that goal, with a new, affordable way to release hydrogen on demand from a practical hydrogen storage vehicle using earth-abundant materials and technological breakthrough of solid-state lighting.”

Hydrogen offers many advantages as a green fuel including high energy density and zero carbon pollution. It is also commonly used in industry, for example for the production of fertilizers, foodstuffs and metals. But pure hydrogen is expensive to compress and transport and difficult to store for long periods of time. In recent years, scientists have sought to use chemical intermediates to transport and store hydrogen. One of the most promising hydrogen carriers is ammonia3), consisting of three hydrogen atoms and one nitrogen atom. Unlike pure hydrogen gas (H2), liquid ammoniaAlthough dangerous, there are systems in place for safe transport and storage.

“This discovery paves the way for low-cost, sustainable hydrogen that can be produced locally rather than in large-scale centralized plants,” said. Peter Nordlandera professor at Rice and another lead author.

A persistent problem for proponents is that cracking ammonia into hydrogen and nitrogen often requires high temperatures to drive the reaction. conversion system may require temperature above 400 degrees Celsius (732 degrees Fahrenheit). That requires a lot of energy to convert ammonia, as well as special equipment to process the operation.

Researchers led by Halas and Nordlander at Rice University, and Emily Carter, Gerhard R. Andlinger Professor of Energy and Environment and Professor of Mechanical and Aerospace Engineering and Applied and Computational Mathematics at Princeton, wanted to modify the separation process to make ammonia a more sustainable and economically viable carrier for hydrogen fuel. Using ammonia as a hydrogen carrier has attracted considerable research interest because of its potential to promote the hydrogen economy, as a recent reviews by the American Chemical Society.

Regular industrial activity cracking ammonia at high temperatures use a variety of materials as catalysts, which are materials that accelerate chemical reactions without being changed by the reaction. Previous research has demonstrated that it is possible to reduce the reaction temperature by using a ruthenium catalyst. But ruthenium, a metal of the platinum group, is very expensive. The researchers believe they can use nanotechnology to enable the use of cheaper elements such as copper and iron as catalysts instead.

The researchers also wanted to address the energy costs of ammonia cracking. Current methods use a lot of heat to break the chemical bonds that hold the ammonia molecules together. The researchers believe they can harness light to sever chemical bonds like a scalpel instead of using heat to break them like a hammer. To do so, they turned to nanotechnology, along with a much cheaper catalyst containing iron and copper.

The combination of nanotechnology’s microscopic metal structure and light is a relatively new field known as plasmons. By shining light onto structures smaller than one wavelength of light, engineers can manipulate light waves in unusual and specific ways. In this case, the Rice team wanted to use this engineered light to excite electrons in metal nanoparticles as a way to split ammonia into its hydrogen and nitrogen components without the need for high temperatures. Because plasmonics requires some kind of metal, such as copper, silver or gold, the researchers added iron to the copper before creating the small structures. When completed, the copper structures act as antennas to direct the light from the LEDs to excite the electrons to higher energies, while the iron atoms embedded in the copper act as catalysts to accelerate the reaction done by excited electrons.

The researchers created the structures and conducted experiments in the laboratories at Rice. They can adjust many variables around the response such as pressure, light intensity, and wavelength of light. But calibrating the exact parameters is difficult. To investigate how these variables affect responses, the researchers worked with lead author Carter, who specializes in detailed studies of reactions at the molecular level. Using Princeton’s high-performance computing system, Terascale Infrastructure for Breakthrough Research in Engineering and Science (TIGRESS), Carter and her postdoctoral fellow, Junwei Lucas Bao, ran the reacts through her specialized quantum mechanical simulator, which is uniquely capable of studying excited electron catalysis. The molecular interactions of such reactions are incredibly complex, but Carter and her fellow researchers can use the simulator to understand what variables need to be adjusted to continue the reaction.

Carter, who also holds appointments at Princeton’s Andlinger Center for Energy and the Environment, for applied and computational mathematics, and at the Princeton Plasma Physics Laboratory, said: “With quantum mechanical simulations we can determine rate-limiting reaction steps. “These are the bottlenecks.”

By refining the process, and using the atomic-scale insights Carter and her team provided, the Rice team was able to consistently extract hydrogen from ammonia using only light. from energy-saving LEDs at room temperature without the need for additional heating. The process is scalable, the researchers say. In further research, they plan to investigate other possible catalysts to increase process efficiency and reduce costs.

Carter, who is also chair of the National Academies’ committee on carbon use, said the next important step would be to reduce the cost and carbon pollution associated with creating the ammonia that starts the transport cycle. Currently, most ammonia is generated at high temperature and pressure to use fossil fuels. This process is both energy intensive and polluting. Carter said many researchers are working to develop green techniques to produce ammonia.

“Hydrogen is widely used in industry and will be used more and more as a fuel as the world seeks to decarbonize its energy sources,” she said. “However, today it is mainly produced unsustainably from natural gas—which produces carbon dioxide emissions—and is difficult to transport and store. Hydrogen needs to be sustainably produced and transported where it is needed. If carbon-free ammonia can be produced, for example by electrolytic denitrification with decarbonization, it can be transported, stored and can serve as a source of green hydrogen on demand by usage of LED-illuminated copper-iron photocatalysts is reported here.”

The article, “Earth-abundant photocatalysts for generating H2 from NH3 with light-emitting diode illumination,” was published in the November 25 issue of the journal Science. In addition to Carter, Halas and Nordlander, co-authors include Hossein Robatjazi, who received his PhD at Rice and is now Syzygy Plasmonics’ chief scientist; Junwei Lucas Bao, now a professor at Boston University; Yigao Yuan, Jingyi Zhou, Aaron Bales, Lin Yuan, Minghe Lou and Minhhan Lou of Rice University; Linan Zhou of both Rice and South China University of Technology, and Suman Khatiwada of Syzygy Plasmonics.

More information:
Yigao Yuan et al, Earth-abundant photocatalyst for generating H2 from NH3 with light-emitting diode illumination, Science (2022). DOI: 10.1126/science.abn5636. www.science.org/doi/10.1126/science.abn5636

quote: Researchers make green fuel by flipping a light switch (2022, November 25) retrieved November 25, 2022 from https://techxplore.com/news/2022-11-green- fuel-flip.html

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