Thapa Loknath, Retna Raj C
Functional Materials and Electrochemistry Lab, Department of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur, 721302, West Bengal, India.
ChemSusChem. 2023 Oct 20;16(20):e202300465. doi: 10.1002/cssc.202300465. Epub 2023 Aug 4.
The electrochemical activation of dinitrogen at ambient temperature and pressure for the synthesis of ammonia has drawn increasing attention. The faradaic efficiency (FE) as well as ammonia yield in the electrochemical synthesis is far from reaching the requirement of industrial-scale production. In aqueous electrolytes, the competing electron-consuming hydrogen evolution reaction (HER) and poor solubility of nitrogen are the two major bottlenecks. As the electrochemical reduction of nitrogen involves proton-coupled electron transfer reaction, rationally engineered electrolytes are required to boost FE and ammonia yield. In this Review, we comprehensively summarize various electrolyte engineering strategies to boost the FE in aqueous and non-aqueous medium and suggest possible approaches to further improve the performance. In aqueous medium, the performance can be improved by altering the electrolyte pH, transport velocity of protons, and water activity. Other strategies involve the use of hybrid and water-in-salt electrolytes, ionic liquids, and non-aqueous electrolytes. Existing aqueous electrolytes are not ideal for industrial-scale production. Suppression of HER and enhanced nitrogen solubility have been observed with hybrid and non-aqueous electrolytes. The engineered electrolytes are very promising though the electrochemical activation has several challenges. The outcome of lithium-mediated nitrogen reduction reaction with engineered non-aqueous electrolyte is highly encouraging.
在常温常压下通过电化学活化氮气合成氨已引起越来越多的关注。电化学合成中的法拉第效率（FE）以及氨产量远未达到工业规模生产的要求。在水性电解质中，竞争性的析氢反应（HER）消耗电子以及氮气的低溶解度是两个主要瓶颈。由于氮气的电化学还原涉及质子耦合电子转移反应，因此需要合理设计的电解质来提高FE和氨产量。在本综述中，我们全面总结了各种电解质工程策略，以提高水性和非水性介质中的FE，并提出进一步改善性能的可能方法。在水性介质中，可以通过改变电解质pH值、质子传输速度和水活性来提高性能。其他策略包括使用混合电解质和盐包水电解质、离子液体和非水性电解质。现有的水性电解质对于工业规模生产并不理想。在混合电解质和非水性电解质中观察到了对HER的抑制和氮气溶解度的提高。尽管电化学活化存在若干挑战，但设计的电解质非常有前景。锂介导的氮气还原反应与设计的非水性电解质的结果非常令人鼓舞。
