The origin of overpotential in lithium-mediated nitrogen reduction

Abstract

The verification of the lithium-mediated nitrogen reduction system in 2019 has led to an explosion in the literature focussing on improving the metrics of Faradaic efficiency, stability, and activity. However,...

Nonaqueous Li-Mediated Nitrogen Reduction: Taking Control of Potentials

“…In addition, this proof-of-concept can be applied to homemade coatings of LiFePO 4 commercial powders on metal wires that may be just as flexible as metal-based pseudoreference electrodes. , The second path is finding a way to directly correlate this measured potential to the reversible hydrogen electrode potential. Indeed, this reference potential is a standard both in aqueous and theoretical catalysis: knowing its relationship with measured potentials would enable quantification of the necessary electrochemical overpotential to drive the reaction, completing the picture given by the above analysis . In addition, H 2 oxidation is a likely counter electrode reaction for future N 2 reducing electrolyzers. , Therefore, it makes sense to measure voltage against that opposite reaction to have a more precise idea of the system’s energy efficiency.…”

“…Indeed, this reference potential is a standard both in aqueous and theoretical catalysis: knowing its relationship with measured potentials would enable quantification of the necessary electrochemical overpotential to drive the reaction, completing the picture given by the above analysis. 50 In addition, H 2 oxidation is a likely counter electrode reaction for future N 2 reducing electrolyzers. 38 , 39 Therefore, it makes sense to measure voltage against that opposite reaction to have a more precise idea of the system’s energy efficiency.…”

Water Increases the Faradaic Selectivity of Li-Mediated Nitrogen Reduction

“…Some reports propose that lithium nitride is directly protonated to ammonia, recycling the deposited lithium; ,, others propose that the layer of Li, or a mixed Li x N y H z layer, acts as an active surface for N 2 reduction. , In either case, nitrogen reduction must compete with hydrogen evolution and excessive lithium plating as parasitic side reactions; hence, there is a need to balance these competing reactions. Notably, the overpotentials for nitrogen reduction and hydrogen evolution are high due to the reaction operating at lithium-plating potential. ,,, …”

“…Notably, the overpotentials for nitrogen reduction and hydrogen evolution are high due to the reaction operating at lithiumplating potential. 4,6,10,11 We can understand lithium-mediated N 2 reduction by drawing insight from lithium-ion batteries: in both systems, a solid-electrolyte interphase (SEI) forms as a result of decomposition of electrolyte components at the highly reducing potentials. The SEI is an electrically insulating passivation layer which restricts further electrolyte degradation.…”

Water increases Faradaic selectivity of Li-mediated nitrogen reduction.

“…In either case, nitrogen reduction must compete with hydrogen evolution and excessive lithium plating as parasitic side reactions, hence there is a need to balance these competing reactions. Notably, the overpotentials for nitrogen reduction and hydrogen evolution are high due to the reaction operating at lithium-plating potential 4,6,10,11 .…”