Li-mediated N2 reduction reaction into NH3: recent outcomes and the SuN2rise Li-N2 cells concept

Operating in severe conditions (at least 450 °C and, in particular, 200 atm), the Haber-Bosh (HB) process is responsible of around 1.44% of the global greenhouse gas emissions. To find a renewable-driven and delocalized electrochemical process complementary to HB for NH3 production could be a key solution for our society that is facing climate change crisis and is demographically growing. The Li mediated (Li-m) pathway represents the most promising solution: thanks to the unique reducing power of this alkali metal, electrochemical cell with Li salt in aprotic environment achieves the highest Faradic efficiency (FE) in the N2 reduction reaction (NRR) research field. Different systems have been evaluated in literature for Li-m NRR, both in a continuous process in presence of a proton donor as ethanol and in a step-by-step system, to conduct Li nitridation in absence of H+ and avoid the competitive hydrogen evolution reaction (HER). In comparison with Li-m NRR continuous systems, the step-by-step technology could alternate H2O presence, as proton donor, with the electrochemical reaction. The system degradation, the proton donor consumption and HER could be avoided. Moreover, the Li-N2 reaction in a completely aprotic environment could maximize Li exploitation. This technology could enhance scalability, since the Li reduction, essential for its recirculation, is the more energy requiring step. The promising Li-N2 cells have been recently tested both for ammonia production and as energy storage devices, in similarity with metallic Li-gaseous batteries (e.g. Li-O2 devices); even if this technology is still in its infancy, a proof-of-concept of NH3 formation has been verified and our laboratory is currently addressing this challenge within the SuN2rise project.