Li‐Mediated Electrochemical Nitrogen Fixation: Key Advances and Future Perspectives

Abstract

The electrochemical nitrogen reduction reaction holds great potential for ammonia production using electricity generated from renewable energy sources and is sustainable. The low solubility of nitrogen in aqueous media, poor kinetics, and intrinsic competition by the hydrogen evolution reaction result in meager ammonia production rates. Attributing measured ammonia as a valid product, not an impurity, is challenging despite rigorous analytical experimentation. In this regard, Li‐mediated electrochemical nitrogen reduction is a proven method providing significant ammonia yields. Herein, fundamental advances and insights into the Li‐mediated strategy are summarized, emphasizing the role of lithium, reaction parameters, cell designs, and mechanistic evaluation. Challenges and perspectives are presented to highlight the prospects of this strategy as a continuous, stable, and modular approach toward sustainable ammonia production.

Ammonia synthesis from nitrogen and steam using electrochemical cells with a hydrogen-permeable membrane and Ru/Cs+/C catalysts

“…The NH 3 formation rate is thermodynamically limited by chemical equilibrium. Details of calculations for NH 3 equilibrium concentration are explained in our previous report, 25 and the individual calculation was performed using a freely provided software. 52,53 Calculating the rate of NH 3 formation on the basis of the theoretical chemical equilibrium, the attainment of chemical equilibrium for 30 wt%-Ru/Cs + (1.0)/VXC72R was derived as 84%, indicating that the rate of NH 3 formation was almost limited by the equilibrium.…”

“…This issue has been discussed in the previous papers. 23–25 This discrepancy may be due to the following reasons.…”

“…In our previous work, we observed a significant increase in cell voltage in the case of the hydrogen-permeable membrane electrochemical cell when the current density exceeded 30 mA cm −2 . 25 As explained in the experimental section, the anode was constructed using IrO 2 on Pt-plated Ti-sintered fibres, which differs from the Pt/Carbon-paper used in our previous report. 25 These modifications helped prevent anode corrosion by phosphate, allowing high-current-density operation up to 50 mA cm −2 .…”

“…25 As explained in the experimental section, the anode was constructed using IrO 2 on Pt-plated Ti-sintered fibres, which differs from the Pt/Carbon-paper used in our previous report. 25 These modifications helped prevent anode corrosion by phosphate, allowing high-current-density operation up to 50 mA cm −2 .…”

“…Electrochemical NH 3 synthesis via the electrochemical nitrogen reduction reaction (EC-NRR) at room-temperature has yielded only trace amounts of NH 3 in most cases, with precision in NH 3 detection being a concern. 19,20 While the Li-mediated EC-NRR appears to be a highly promising method, 21–25 it is thought to involve the use of metallic Li, an energy-dense substance much higher in energy content than H 2 , raising doubts about whether NH 3 can be obtained at voltages similar to that for water electrolysis. Moreover, there are numerous examples for synthesizing NH 3 using sacrificial reagents such as alcohols, and research cases that do not involve H 2 O and N 2 are also widely observed.…”