Ammonia (NH₃) is a promising energy vector for the storage and utilization of renewable energies. Artificially synthesizing NH₃ from its elements requires harsh reaction conditions (400-500 °C, 10-30 MPa) because N₂ is inert and nonpolar with a strong N≡N bond. The synthesis of NH₃ under mild conditions is still challenging.

Recently, Assoc. Profs. CAO Hujun, GAO Wenbo and their collaborators from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) have proposed a new process for ammonia synthesis using Li₂NH as an N carrier via the method of electrodriven chemical looping.

This study was published in ACS Energy Letters on Feb. 23.

The researchers carried out this electrodriven chemical looping ammonia synthesis (ECLAS) in a LiCl-NaCl-KCl eutectic electrolytic cell using a nickel foam as electrode.

Electric energy input not only improved the hydrogenation rate of Li₂NH, but also promoted the nitrogen fixation reaction of LiH. In addition, the average ammonia production rate of this ECLAS process was nearly eight times higher than that of the thermal-driven CLAS process.

They found that the process contained two electrochemical reactions, one was the nitridation of LiH to form Li₂NH, and the other was the hydrogenation of Li₂NH to produce ammonia and regenerate LiH. This was different from the reported Li₃N-mediated electrochemical ammonia synthesis process, which included three-step reactions: Li ion was reduced to Li, Li fixed dinitrogen to form Li₃N, and Li₃N was then protonated to produce ammonia and Li⁺.

"This ECLAS process has a low theoretical operating voltage than the Li₃N-mediated electrochemical ammonia synthesis process, and it could work under as low voltages as 2.0 V," said CAO.