Ammonia produced using sunlight and wastewater nitrate

Scientists achieve solar-to-fuel efficiency that is 10 times better than any other current technologies

Paving way for what could be an on-demand fertilizer synthesizer, scientists at University of Illinois Chicago have developed a sustainable electrochemical device that is capable of producing ammonia from sunlight and wastewater nitrate at 10% more solar-to-fuel efficiency than any other system currently available to us.

Published in Energy & Environmental Science the study explains how the new solar-powered system is capable of eliminating the need for high-energy systems that not only are costly to run, but also produce substantial fraction of greenhouse gas emissions.

Improving upon a previously built system wherein the team produced more hydrogen gas (80%) than ammonia (20%), the new system produces nearly 100% ammonia with nearly zero hydrogen gas side reactions. Further the new system only uses nitrate from wastewater to supply nitrogen and sunlight to electrify the reaction.

Scientists say that the most important bit is that their system involves a reaction that requires fossil fuels and so produces no carbon dioxide or any other green house gases that are detrimental for Earth. Not only is the reaction itself carbon-neutral, which is good for the environment, but if the system is developed for industrial use, it may also have an almost net-negative, restorative effect on the environment.

Further use of solar power yields an unprecedented solar-to-fuel efficiency, or STF, of 11%, which is 10 times better than any other state-of-the-art system to produce ammonia (about 1% STF).

The new method hinges on a cobalt catalyst, which the researchers describe along with the new process in their paper, “Solar-Driven Electrochemical Synthesis of Ammonia using Nitrate with 11% Solar-to-Fuel Efficiency at Ambient Conditions.”

Cobalt is used in the system and that metal was decided by the team after first applying computational theory for selection and then different experimentation.

The researchers found that a rough cobalt surface derived from oxidation worked best to create a reaction that was selective, meaning it converted nearly all the nitrate molecules to ammonia.

The use of wastewater nitrate is an added advantage for it will allow removal of contaminant from surface and groundwater. This system effectively is able to help correct for industrial waste and runoff water and rebalance the nitrogen cycle in rural areas that are almost always at an economic disadvantage or are at a greater risk of exposure from excess nitrate in the ground. High exposure to nitrate through drinking water has been associated with health conditions like cancer, thyroid disease, preterm birth, and low birth weight.

A patent for the new process has been filed by the UIC Office of Technology Management.

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