Different strategies in the lithium-mediated nitrogen reduction reaction into ammonia: classification of present achievements and future possibilities Anna Mangini , Lucia Fagiolari, Julia Amici, Carlotta Francia, Silvia Bodoardo, Federico Bella Politecnico di Torino, Italy The lithium-mediated (Li-m) nitrogen reduction reaction (NRR) represents the most promising electrochemical process for renewable-driven and delocalized NH 3 production. Finding a complementary pathway to the Haber- Bosh (HB) process allows a step forward to the net-zero carbon emission policy, essential to contrast the climate crisis. Indeed, HB causes a global average of 2.86 tons of CO 2 emitted per ton of NH 3 1 . The reducing power of lithium has been applied in different strategies; it is possible to distinguish between continuous processes and step-by-step systems. In the first case, N 2 is reduced simultaneously to the protonation into NH 3 , while, in the second option, the Li nitridation is conducted in the absence of H + to avoid the competitive hydrogen evolution reaction (HER). Among the continuous processes, the most promising one employed a batch cell at 20 bar of N 2 with a fluorinated Li salt in tetrahydrofuran and with ethanol addition as the proton donor. Indeed, these systems reached a Faradaic efficiency approaching 100% 2 , as well as a commercially relevant ammonia production rate of 153.28 μg/h*cm 2 at a current density of 1 A/cm 2 geo 3 . The step-by-step technology presents the intrinsic advantage of water exploitation as the proton donor in a separate environment and or time of the process, ensuring greater stability. Therefore, this pathway avoids organic molecule degradation, as well as H 2 feedstock need and consumption 4 . Moreover, the Li–N 2 reaction in a completely aprotic environment could maximize Li exploitation, enhancing scalability. Indeed, Li reduction, essential for the mediator recirculation, is the most energy-requiring step 4 . Li nitridation has been studied both in a direct thermochemical reaction 4 and with promising Li–N 2 galvanic cells 5 . In similarity with metallic Li–gaseous batteries (e.g. Li-O 2 devices), Li-N 2 devices have been recently tested both for NH 3 production and for energy storage. Even if this technology is still in its infancy, a proof-of-concept of Li 3 N formation has been verified 5 . This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 948769, project title: SuN 2 rise). References
1. G. Soloveichik, Nat. Catal ., 2019, 2 , 377–380. 2. H. L. Du et al. , Nature , 2022, 609 , 7928, 722–727. 3. S. Li et al. , Joule , 2022, 6 , 9, 2083–2101. 4. J. M. McEnaney et al. , Energy Environ. Sci. , 2017, 10 , 7, 1621–1630. 5. J. Islam et al. , Energy Storage Mater., 2023, 54 , 98–119.
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