Researchers at Princeton and Rice universities have combined iron, copper, and a simple LED light to demonstrate a low-cost method that could be the key to producing hydrogen, a fuel that fuses consumes a lot of energy and carbon pollution.
Researchers have used experiments and advanced calculations to develop a technique that uses nanotechnology to separate hydrogen from liquid ammonia, a process that has so far been more energy-intensive.
In an article published online in the journal Science, the researchers explain how they used light from a standard LED to break down ammonia without the need for high temperatures or expensive equipment that such chemistry often requires. Technology is overcoming a major challenge in realizing the potential of hydrogen as a low-cost clean fuel that can help meet energy demands without causing climate change.
“We hear a lot about hydrogen being the cleanest fuel, if not cheaper and easier to store and bring back for use,” said Naomi Halas, a professor at Rice University and one of the main authors of the study. “This result shows that we are moving quickly towards that goal, with a new and easy way to release hydrogen on demand from a reliable hydrogen storage device that uses the world’s most valuable materials and technological advancement of solid lighting.”
Hydrogen offers many advantages as a green fuel with high energy density and no carbon pollution. It is used everywhere in industry, for example in the production of fertilizers, food, and metals. But pure hydrogen is expensive to 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 best hydrogen carriers is ammonia (NH3), contains three hydrogen atoms and one nitrogen atom. Unlike pure hydrogen gas (H2), ammonia water, although it is dangerous, there are systems for its transportation and storage.
“This discovery paves the way for sustainable, low-cost hydrogen that can be produced locally rather than in large, centralized plants,” said Peter Nordlander, a professor at Rice and one of the co-authors.
Another sticking point for proponents is that splitting ammonia into hydrogen and nitrogen often requires high temperatures to effect the reaction. Conversion systems can require temperatures above 400 degrees Celsius (732 degrees Fahrenheit). It requires a lot of energy to convert ammonia, and special equipment to keep the job.
The researchers led by Halas and Nordlander at Rice University, and Emily Carter, the Gerhard R. Andlinger Professor in Energy and the Environment and Professor of Mechanical and Aerospace Engineering and Applied and Computational Mathematics at Princeton, wants to change the separation process to produce ammonia and better transport hydrogen fuels. The use of ammonia as a hydrogen carrier has attracted much research interest due to its ability to drive the hydrogen economy, according to a recent report by the American Chemical Society.
Industrial processes often destroy ammonia at high temperatures using various substances such as catalysts, which accelerate the chemical reaction without being changed by the reaction. Previous studies have shown that the reaction temperature can be lowered by using a ruthenium catalyst. But ruthenium, a metal in the platinum group, is expensive. The researchers thought they could use nanotechnology to allow small elements such as copper and iron to be used as catalysts.
The researchers also wanted to fix the energy cost of breaking down ammonia. Current methods use high heat to break down the chemical bonds that hold ammonia molecules together. The researchers thought they could use light to cut chemical bonds like a scalpel instead of using heat to break them up like a hammer. To do so, they turned to nanotechnology, with a catalyst that contains less iron and copper.
The combination of small and light metal structures of nanotechnology is a new field called plasmonics. By shining light into structures smaller than the wavelength of light, engineers can manipulate light waves in different and specific ways. In this case, the Rice team wanted to use this engineering light to stimulate electrons in metal nanoparticles as a way to separate ammonia into its hydrogen and nitrogen without of extreme heat. Because plasmonics requires certain metals, such as copper, silver, and gold, researchers have added iron to copper before making tiny structures. When finished, the copper structures act like antennas to convert the light from the LED to generate electrons at high energy, while the iron particles embedded in the copper act as catalysts to accelerate in the reaction carried by excited electrons.
Researchers have built structures and conducted experiments in laboratories at Rice. They are able to change the various factors related to the effect such as pressure, light intensity and wavelength. But calibrating the correct parameters is difficult. To investigate the impact of these differences in response, 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, the Terascale Infrastructure for Groundbreaking Research in Engineering and Science (TIGRESS), Carter and his postdoctoral fellow, Junwei Lucas Bao, ran the results through his quantum simulator. Special mechanics can study the catalysis excited electron. The interaction of those variables is very complex, but Carter and his research colleagues can use the simulator to understand the variables that need to be adjusted to maximize the effect.
“With quantum mechanics simulations, we can determine which reaction steps are limiting,” said Carter, who holds appointments at Princeton’s Andlinger Center for Energy and the Environment, in applied mathematics and computing, and at the Princeton Plasma Physics Laboratory. “These are rubbish.”
By successfully adapting the process, while using the atomic-scale knowledge Carter and his team provided, the Rice group was able to continuously extract hydrogen from ammonia using only lights from energy-efficient LEDs at room temperature without heating. Researchers say the process is scalable. In further research, they plan to investigate other catalysts with a view to increasing the process and reducing the cost.
Carter, who chairs the National Academies’ committee on carbon emissions, said the effort to reduce the costs and carbon pollution associated with manufacturing is critical. ammonia to start the cycle. Currently, most ammonia is produced at high temperatures and pressures using fossil fuels. The process is laborious and messy. Carter said many researchers are working to develop greener technologies for ammonia production as well.
“Hydrogen is widely used in industry and is increasingly being used as a fuel as the world seeks to decarbonize its energy sources,” he said. “However, today it is not produced from natural gas – it creates carbon emissions – and is difficult to transport and store. Hydrogen must be produced and transported where it is needed. If it can be done carbon-free ammonia, for example through the electrolytic reduction of nitrogen using decarbonized electricity, can be transported, stored, and may become a source of green hydrogen using iron-copper photocatalysts are presented here.