Jie Liang

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 in situ/operando 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.

Abstract NiCo 2 O 4 nanowire array on carbon cloth (NiCo 2 O 4 /CC) is proposed as a highly active electrocatalyst for ambient nitrate (NO 3 − ) reduction to ammonia (NH 3 ). In 0.1 m NaOH solution with 0.1 m NaNO 3 , such NiCo 2 O 4 /CC achieves a high Faradic efficiency of 99.0% and a large NH 3 yield up to 973.2 µmol h −1 cm −2 . The superior catalytic activity of NiCo 2 O 4 comes from its half‐metal feature and optimized adsorption energy due to the existence of Ni in the crystal structure. A Zn‐NO 3 − battery with NiCo 2 O 4 /CC cathode also shows a record‐high battery performance.

Industrial-scale ammonia (NH3) production mainly relies on the energy-intensive and environmentally unfriendly Haber-Bosch process. Such issue can be avoided by electrocatalytic N2 reduction which however suffers from limited current efficiency and NH3 yield. Herein, we demonstrate ambient NH3 production via electrochemical nitrite (NO2−) reduction catalyzed by a CoP nanoarray on titanium mesh (CoP NA/TM). When tested in 0.1 M PBS (pH = 7) containing 500 ppm NO2−, such CoP NA/TM is capable of affording a large NH3 yield of 2,260.7 ± 51.5 µg·h−1·cm−2 and a high Faradaic efficiency of 90.0 ± 2.3% at −0.2 V vs. a reversible hydrogen electrode. Density functional theory calculations reveal that the potential-determining step for NO2− reduction over CoP (112) is *NO2 → *NO2H.