Combining sunlight and wastewater nitrate to make the world's number 2 chemical

Researchers at UIC have created a sustainable electrochemical system that combines a solar cell with a well that holds a liquid solution. The liquid solution's nitrates are converted to ammonia when they are charged. Credit: Meenesh Singh/UIC
The University of Illinois Chicago engineers have developed a solar powered electrochemical reaction that uses wastewater to produce ammonia, the second most-produced chemical in this world. It also has a solar-to fuel efficiency of 10 times higher than any comparable technology.

Their results were published in Energy & Environmental Science. This is a leading journal for research on the intersection of energy delivery, environmental protections and energy delivery.

"This technology and our methodology have great potential to allow on-demand synthesizing fertilizers. This could have an enormous impact on the agricultural, energy, and efforts to reduce greenhouse gasses from fossil fuels," stated Meenesh Singh (assistant professor of chemical engineering, UIC College of Engineering).

Ammonia is a mixture of one and three hydrogen atoms. It is used in many fertilizers as well as manufactured products such plastics and pharmaceuticals. To make ammonia out of nitrogen, current methods require huge amounts heat. This heat is generated from burning fossil fuels. It breaks the strong bonds between the nitrogen atoms to allow them to bind to hydrogen. This century-old process is responsible for a significant portion of the world's greenhouse gas emissions. These gases are a major driver of climate change.

Singh and his associates had previously developed an environmentally friendly way to make ammonia. They did this by using an electrically-charged, catalyst-covered mesh screen with a water-based solution. The screen was only powered by a small amount of fossil fuel energy, but the result produced more hydrogen gas (80%) that ammonia (20%).

Researchers have now improved the concept and created a new method that uses groundwater contaminants like nitrate to provide nitrogen and sunlight to electrify this reaction. This system produces almost 100% ammonia and has virtually no hydrogen gas side effects. It requires no fossil fuels, produces no carbon dioxide, or other greenhouse gases and uses solar power to achieve an unparalleled solar-to-fuel efficiency (or STF) of 11%. This is 10 times higher than any other state of the art system to make ammonia.

The new method relies on a cobalt catalyst, which researchers describe in "Solar-Driven Elektrochemical Synthesis Of Ammonia Using Nitrate with 11% Solar to-Fuel Efficiency At Ambient Conditions."

Researchers at UIC describe their sustainable electrochemical process to convert wastewater nitrate into ammonia. Credit: Meenesh Singh/UIC

The researchers used computational theory to determine the best metal for the reaction. The team then experimented with cobalt, looking for ways to maximize its activity. Researchers found that a cobalt surface made from oxidation was the best for creating a selective reaction, which converts nearly all nitrate molecules into ammonia.

Singh stated that Singh was able to find an active, selective and stable catalyst in a solar-powered system, which is strong evidence that it is possible to sustainably synthesize ammonia on an industrial scale.

The reaction is carbon-neutral and good for the environment. However, if it is used in industry, it could also have a net-negative, positive effect on the environment.

"Using wastewater nitrate also means that we have to remove the contaminant form surface and groundwater. Singh explained that the process can be used to correct industrial waste and runoff water, and also to balance the nitrogen cycle. This is especially important for rural areas, which could suffer economic disadvantages or are most at risk from excessive nitrate exposure.

A high level of nitrate in drinking water has been linked to health conditions such as cancer, thyroid disease and low birth weight.

"We are all thrilled about this achievement and we won't stop there. "We are optimistic that we will soon be able to test a larger prototype," Singh said. Singh is currently working with municipalities, wastewater treatment centers and other industry professionals on further developing the system.

The UIC Office of Technology Management has filed a patent for this new process.

The paper's co-authors are Aditya Parajapati and Nishithan Kani of UIC, Joseph Gauthier from Texas Tech University and Jane Edgington and Linsey Seitz at Northwestern University. Isha Bordawekar, Warren Township High School, Windom Shields, Mitchell Shields, Worldwide Liquid Sunshine and Aayush Sing of Dow Inc.

Continue reading Researchers discover a new way to make ammonia that has a smaller carbon footprint

More information: Nishithan Kani et. al., Solar-driven electrochemical synthesis ammonia using nitrate at 11% solar-to fuel efficiency at ambient conditions. Energy & Environmental Science (2021). Information from the Journal: Energy & Environmental Science Nishithan Kani et. al., Solar-driven electrochemical synthesis ammonia using nitrate at 11% solar-to fuel efficiency at ambient conditions. (2021). DOI: 10.1039/D1EE01879E