To restore the natural nitrogen cycle (N-cycle), artificial N-cycle electrocatalysis with flexibility, sustainability, and compatibility can convert intermittent renewable energy (e.g., wind) to harmful or value-added chemicals with minimal carbon emissions. The background of such N-cycles, such as nitrogen fixation, ammonia oxidation, and nitrate reduction, is briefly introduced here. The discussion of emerging nanostructures in various conversion reactions is focused on the architecture/compositional design, electrochemical performances, reaction mechanisms, and instructive tests. Energy device advancements for achieving more functions as well as <i>in situ</i>/<i>operando</i> characterizations toward understanding key steps are also highlighted. Furthermore, some recently proposed reactions as well as less discussed C–N coupling reactions are also summarized. We classify inorganic nitrogen sources that convert to each other under an applied voltage into three types, namely, abundant nitrogen, toxic nitrate (nitrite), and nitrogen oxides, and useful compounds such as ammonia, hydrazine, and hydroxylamine, with the goal of providing more critical insights into strategies to facilitate the development of our circular nitrogen economy. 

https://www.sciopen.com/article_pdf/1531201054523838466.pdf

Recent advances in nanostructured heterogeneous catalysts for N-cycle electrocatalysis

Electrocatalytic nitrogen reduction reaction (NRR) is a promising approach for renewable NH3 production, while developing the NRR electrocatalysis systems with both high activity and selectivity remains a significant challenge. Herein, we combine catalyst and electrolyte engineering to achieve a high-efficiency NRR enabled by a Se-vacancy-rich WSe2-x catalyst in water-in-salt electrolyte (WISE). Extensive characterizations, theoretical calculations, and in situ X-ray photoelectron/Raman spectroscopy reveal that WISE ensures suppressed H2 evolution, improved N2 affinity on the catalyst surface, as well as an enhanced π-back-donation ability of active sites, thereby promoting both activity and selectivity for the NRR. As a result, an excellent faradaic efficiency of 62.5% and NH3 yield of 181.3 μg h-1 mg-1 is achieved with WSe2-x in 12 m LiClO4, which is among the highest NRR performances reported to date.

High-Efficiency N2 Electroreduction Enabled by Se-Vacancy-Rich WSe2-x in Water-in-Salt Electrolytes.

Nitrite reduction over Ag nanoarray electrocatalyst for ammonia synthesis.

B-doped MoS2 for nitrate electroreduction to ammonia.

Electrocatalytic nitrogen reduction reaction (NRR) is an appealing strategy for green ammonia synthesis. Despite tremendous efforts, current NRR performances of most catalysis systems remain far below the targets for practical applications. Herein, a highly active and selective NRR catalysis system is reported by using an Rh single-atom catalyst in water-in-salt electrolytes (WISE). The developed single-atomic Rh on MnO 2 (Rh 1 /MnO 2 ) catalyst in 9 m K 2 SO 4 presents a superior NH 3 yield of 271.8 μg h −1 mg −1 and Faradaic efficiency of 73.3%, far exceeding that in dilute electrolyte and representing one of the best NRR performances on record. Multiple operando XAS, in situ FTIR/Raman spectroscopic characterizations together with the theoretical calculations unravel that WISE enables Rh 1 /MnO 2 to exhibit suppressed H 2 evolution, increased N 2 enrichment on catalyst surface, and enhanced N 2 activation/hydrogenation on active Rh sites. A record-high NRR performance (271.8 μg h −1 mg −1 , 73.3%) was achieved over an Rh single-atom catalyst (Rh 1 /MnO 2 ) in water-in-salt electrolytes (WISE). Combined theoretical computations and operando/in situ spectroscopic characterizations revealed that WISE endowed Rh 1 /MnO 2 with suppressed H 2 evolution, increased N 2 enrichment on catalyst surface, and enhanced N 2 activation/hydrogenation on active Rh sites. • We combine catalyst and electrolyte engineering to achieve an ultra-efficiency nitrogen reduction reaction (NRR). • A record-high NH 3 yield of 271.8 μg h −1 mg −1 and FE of 73.3% is achieved in this new catalysis system. • Multiple operando characterizations and theoretical calculations are adopted to profoundly understand the NRR mechanism. 

Ultra-efficient N2 electroreduction achieved over a rhodium single-atom catalyst (Rh1/MnO2) in water-in-salt electrolyte

Electrochemical N2 fixation through nitrogen reduction reaction (NRR) is a promising way for sustainable NH3 synthesis, while exploring high-performing NRR catalysts lies at the heart of attaining high-efficiency NRR electrocatalysis....

Keung Y. Chu

Papers

Amorphization engineered VSe2-x nanosheets with abundant Se-vacancies for enhanced N2 electroreduction

High-Efficiency N2 Electroreduction Enabled by Se-Vacancy-Rich WSe2-x in Water-in-Salt Electrolytes.

Sulfur-deficient Bi2S3−x synergistically coupling Ti3C2Tx-MXene for boosting electrocatalytic N2 reduction

B-doped MoS2 for nitrate electroreduction to ammonia.

Ultra-efficient N2 electroreduction achieved over a rhodium single-atom catalyst (Rh1/MnO2) in water-in-salt electrolyte