Ammonia, produced via the Haber-Bosch process for more than 150 10⁶ t per year, is responsible of around 1.5% of the global greenhouse gas emissions. [1] It is a fundamental building-block for fertilizers and could represent a future H₂ carrier, but it is still dependent from fossil fuels. To find a delocalized electrochemical process complementary to Haber-Bosch could be a key solution to move towards a renewable-driven NH₃ production.

Nowadays, the lithium-mediated pathway represents the most promising solution in the N₂ reduction reaction challenging field, achieving the highest Faradaic efficiency and NH₃ production rate. [2], [3] Different strategies are under evaluation in literature, all exploiting the ability of this metal to bind N₂ even in standard conditions. They could be divided into continuous or step-by-step strategies. In the first, Li⁺ ions from the aprotic electrolyte are electrodeposited on the cathode, where N₂ is reduced and protonated into NH_3, directly and in the same environment. [4] In the second case, the electroreduction of N₂ at the cathode has been proposed, and the formation of an intermediate product containing fixated nitrogen is the key step. Only in a second separate step, this intermediate should be protonated into NH₃. To achieve the first step of N₂ activation, the exploitation of a Li-N₂ galvanic cell, inspired by lithium-air batteries, has been proposed in literature to optimize the process efficiency and allow the direct protonation with H₂O [5].

In both cases, is crucial to study the phenomena at the cathodic electrode-electrolyte interphase, as the aprotic electrolyte inevitably reacts on the active sites, forming a solid electrolyte interphase. This component of the system determines both the selectivity towards NH₃ formation and the stability of the process. Due to the dynamicity of this layer, a critical eye should be adopted for a correct electrochemical characterization and NH₃ quantification of the systems. Our laboratory is currently addressing these challenges within the SuN₂rise project, applying also statistical methods as the design of experiment to optimize the studied factor with a restricted number of experiments.

An overview of electrochemical and engineering-related crucial aspects will be presented in this contribution. In particular, the challenges related to the NH₃ quantification in highly concentrated aprotic electrolyte will be discussed, as well as the reliability of electrochemical characterization aimed to prove the N₂ electrochemical reduction at the cathode. The advantages and issue related to the strategy based on the Li-N₂ cell concept will be critically addressed, highlighting the precautions needed to avoid misleading result in presence of a metallic lithium anode.