Approximately 150 million metric tons of ammonia is produced annually. A significant amount of the ammonia generated is used to make fertilizers, notably ammonium nitrate. Currently, the primary method of synthesizing ammonia involves the Haber Bosch process. The Haber Bosch process is based on the reaction between molecular nitrogen from the air and hydrogen derived from natural gas (methane). Such method is resource demanding and unsustainable. High pressures and temperatures are required to break the triple bond in molecular nitrogen, and natural gas must be burned to produce hydrogen. Therefore, industrial production of ammonia is responsible for about three percent, or 450 million metric tons, of global carbon dioxide emissions annually.
Researchers from the United States have developed a potentially more energy efficient method to synthesize ammonia using lithium. Density functional theory calculations suggest that lithium-based materials capable of carrying out this process. The strategy uses electricity to electrolyze lithium hydroxide to produce lithium metal, which can activate nitrogen at ambient conditions. The lithium metal is then exposed to a flowing nitrogen atmosphere to produce lithium nitride. In a hydrolysis reaction, the lithium nitride reacts with water—a source of hydrogen—to generate lithium hydroxide, completing the cycle.
“The fact that lithium binds nitrogen so strongly simply means that you pull down the barrier for nitrogen dissociation enough that you can do it at room temperature,” explains Jens Nørskov, who co-leads the research. “So if you can make lithium, then you can also make lithium nitride.”
This electrochemical ammonia production strategy has a current efficiency of 88.5% toward ammonia production. The researchers were pleased with the idea of powering ammonia synthesis using renewable energy; however, they acknowledged the challenges of replicating the results on an industrial scale. Cost analysis and input considerations reveal promise for the new process considering its advantages of using renewable resources and mitigating carbon dioxide emissions.
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Editor: Maria ‘Stefi’ Ticsa