Li-Mediated Electrochemical Nitrogen Fixation: Key Advances and Future Perspectives.

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.

Metal-Sulfur Linkages Achieved by Organic Tethering of Ruthenium Nanocrystals for Enhanced Electrochemical Nitrogen Reduction.

Inspired by the metal-sulfur (M-S) linkages in the nitrogenase enzyme, here we show a surface modification strategy to modulate the electronic structure and improve the N2 availability on a catalytic surface, which suppresses the hydrogen evolution reaction (HER) and improves the rate of NH3 production. Ruthenium nanocrystals anchored on reduced graphene oxide (Ru/rGO) are modified with different aliphatic thiols to achieve M-S linkages. A high faradaic efficiency (11 %) with an improved NH3 yield (50 µg h-1 mg-1 ) is achieved at -0.1 V vs. RHE in acidic conditions by using dodecanethiol. DFT calculations reveal intermediate N2 adsorption and desorption of the product is achieved by electronic structure modification along with the suppression of the HER by surface modification. The modified catalyst shows excellent stability and recyclability for NH3 production, as confirmed by rigorous control experiments including 15 N isotope labeling experiments.

Synergistic bimetallic CoFe2O4 clusters supported on graphene for ambient electrocatalytic reduction of nitrogen to ammonia.

The energy-intensive nature, high level of CO2 emission and sophisticated infrastructure requirement hampered the utilization of the Haber-Bosch process as a green and decentralized system for NH3 production. The electrochemical N2 reduction reaction (NRR) provides a promising alternative to fix N2 under ambient conditions. Here, we report CoFe2O4 nanoclusters anchored on reduced graphene oxide for enhanced nitrogen reduction. In contrast to monometallic counterparts, this composite catalyst achieves a faradaic efficiency of 6.2% with a high rate of NH3 production of 4.2 × 10-11 mol s-1 cm-2 in 0.1 M Na2SO4 aqueous electrolyte. Amelioration of NRR performance could be attributed to the availability of different types of adsorption and active sites for N2 after the incorporation of Co in the Fe3O4 structure. Also, the homogeneous dispersion of nanoclusters on a 2D support can achieve higher active site density. This work provides a new category of binary metal oxides catalysts for NRR under ambient conditions.