Enhancement of lithium-mediated ammonia synthesis by addition of oxygen

Abstract

Boosting ammonia with a little oxygen Ammonia synthesis from nitrogen for fertilizer production is highly energy intensive. Chemists are therefore exploring electrochemical approaches that could draw power from renewable sources while generating less waste. One promising cycle involves the reduction of lithium ions at an electrode, with the resultant metal in turn reducing nitrogen and regenerating the ions. Li et al . report the counterintuitive result that small quantities of oxygen could enhance the efficiency of this process, which they attribute to diffusional effects that limit excessive lithium reduction. —JSY

Oxygen-Enhanced Chemical Stability of Lithium-Mediated Electrochemical Ammonia Synthesis

“…Thus, the “real” amount of byproducts would be different than assumed here because of nonmeasurable inorganic species. We have seen and reported several inorganic phases before by XRD and XPS, 8 , 10 , 16 , 24 and they are reproducible.…”

“… 15 However, this is not the case; it has been reported recently by our group that small amounts of O 2 boost the LiMEAS. 16 It is very important to mention that the electrochemical reduction of the electrolyte on the negative electrode of LIB results in the formation of the solid electrolyte interphase (SEI), 12 which must be considered in LiMEAS as well. Both inorganic and organic components of this SEI are required for long-term performance if it is permeable for Li ions, thus protecting the highly reactive cathode against unwanted reductive side reactions.…”

“…It has been shown that 0.8 mol % of O 2 is an optimal amount for promotion of LiMEAS toward NH 3 with improved stability of the nonaqueous organic electrolyte based on THF. 8 , 16 …”

Recent advances in material design and reactor engineering for electrocatalytic ambient nitrogen fixation

“…It is generally believed that the LiNR process is carried out in three steps. 259 The first step is to reduce Li-ions in the electrolyte to active lithium metal via an electrochemical method. The formed metal Li then decomposes N 2 , and the surface N is finally reduced by a series of electron and proton transfer and reduced to NH 3 by a suitable proton source such as ethanol (EtOH).…”

Selectivity and Intrinsic Activity of Functionalized Cu Surfaces: Can the CO2 Reduction Reaction be Improved on Cu?

“…The modifier layer can be thought of as somewhat like a SEI (solid electrolyte interphase) layer for lithium-ion batteries 68 or for electrochemical ammonia synthesis in a Li-mediated system. [69][70][71] In both these systems, the SE allows transport of Li ions, but inhibits or limits transport of other species. Similarly, the modifier limits the passage of undesirable H2O while comparatively allowing the passage of desirable CO 2 .…”