Nitrogen Electrocatalysis: Electrolyte Engineering Strategies to Boost Faradaic Efficiency

Abstract

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.

Theoretical Insight into the Special Synergy of Bimetallic Site in Co/MoC Catalyst to Promote N2‐to‐NH3 Conversion

“…Above results show that N 2 molecule can be activated on both pristine and Co-supported α-MoC(001) surfaces, and there are two typical pathways, the dissociative and associative mecha-nisms for the thermal conversion of activated N 2 into NH 3 . 10 For the dissociative mechanism, the N � N bond of N 2 molecule firstly undergoes a cleavage and leaves two adsorbed N atoms on the surface of catalyst. While in the associative pathway, the N � N bond does not broken until N 2 * is hydrogenated to NNH* species.…”

“…[6][7][8] Considering the energy and environmental costs, it is highly desirable to find an efficient catalyst as an alternative to the traditional ammonia synthesis process and develop environmentally friendly ammonia synthesis. [9,10] For the nitrogen reduction reaction (NRR), it has been demonstrated that the electron-feeding capacity of the catalysts plays an important role in the redox mechanism of N 2 activation. [11,12] It is well known that ammonia synthesis over Fe and Ru metal surfaces is regarded as classical examples for NRR, in which N 2 activation is shown to be a direct N�N cleavage process.…”

Development of Structure–Property Relationships for Ammonium Transport through Charged Organogels

“…Electrochemical nitrogen reduction reacts nitrogen gas with protons and electrons generated by splitting water in the electrochemical cell, and the electricity could come from renewable sources, thereby allowing for low temperature and ambient operation. However, these methods generally suffer from a large overpotential [ 13 ], low faradaic efficiencies [ 14 ], and poor selectivity [ 15 ] for ammonia production, so many efforts are focused on designing robust electrocatalysts to improve the faradaic efficiency of the NRR [ 16 , 17 , 18 ]. One area that has received relatively little attention has been the development of tailored membranes for NRR cells.…”