Rapid electrolyte development for ammonia synthesis through lithium chemical looping Parviz Hajiyev and Louis Dubrulle CEA LITEN, France Lately electrochemical ammonia synthesis has become very active research topic. Many different electrochemical research axes are being developed such as different electrocatalyst, aqueous and non-aqueous electrolytes, and different electrolyzer concepts. Most literature focuses on faradaic efficiency optimization; however, arguably one main challenge with electrochemical ammonia synthesis is very low synthesis rate. Which in practice limits the synthesis of enough ammonia molecules to characterize and analyze with acceptable experimental precision. Among different electrochemical ammonia synthesis approaches lithium based chemical looping approach is the most interesting. Particularly thanks to its high synthesis rate in hundreds nmol/cm 2 /s range recently reported by Hoang-Long Du et al. 1 as a successful improvement on early work of Akira Tsuneto et al 2 . The main interesting observation is that this particular performance improvement is mostly achieved by the development of a better electrolyte. This approach relies on electrochemical deposition of lithium on inert metal electrode such as copper or nickel in lithium rich electrolyte of an organic aprotic solvent (usually tetrahydrofuran). Under 10-20bar range nitrogen atmosphere, sufficient concentration of solubilized N 2 molecules are activated on the deposited lithium metal surface to form lithium nitride. Finally, the ethanol present in the electrolyte as a sacrificial proton source, protonates this nitride phase forming ammonia and liberating the lithium cation back in the electrolyte. Crucially, in this system, both nitride formation and its protonation are a chemical reaction while only lithium metal deposition is an electrochemical process. Hence, by choosing to start the ammonia synthesis from a commercial lithium metal, all the complexity associated with the electrochemical lithium deposition under 10-20 bar N 2 pressure can be avoided and rapid electrolyte development can be unlocked by using a simple pressure cell. We tested several different solvents, salts, concentrations and compared the quantity of the synthesized ammonia by uv-vis and nuclear magnetic resonance spectroscopy methods. A non-volatile solvent will have several major advantages over tetrahydrofuran for commercialization of this technology. Tetraethylene glycol dimethyl ether seems to outperform the tetrahydrofuran solvent with several different salt and concentration range. Finally, we compare these conclusions with the reproduction of improved ammonia synthesis in electrochemical pressure cell. References 1. Akira Tsuneto, Akihiko Kudo and Tadayoshi Sakata, Lithium-mediated electrochemical reduction of high pressure N 2 to NH 3 , Journal of Electroanalytical Chemistry 367 (1994) 183 2. Hoang-Long Du, Manjunath Chatti, Rebecca Y. Hodgetts, Pavel V. Cherepanov, Cuong K. Nguyen, Karolina Matuszek, Douglas R. MacFarlane, Alexandr N. Simonov, Electroreduction of nitrogen with almost 100% current-to-ammonia efficiency , Nature 609 (2022) 722
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