Nanoreactor Based on Cyclodextrin for Direct Electrocatalyzed Ammonia Synthesis

The high-efficiency transition metal-free electrocatalytic nitrate reduction reaction (NO3–RR) for ammonia synthesis has received more attention because of its green and environmentally friendly characteristics. Here, we report an efficient electrochemical NH3 synthesis directly from purely organic macrocyclic compounds α-, β-, and γ-cyclodextrins (CDs)-catalyzed transition metal-free electroreduction of nitrate under ambient conditions. In comparison with α-, and β-CDs, parent γ-CD presented uncommon catalytic performance with a relatively higher NH3 yield that can reach up to 2.28 mg h–1 cm–2 with a Faradaic efficiency (FE) of 63.2% at −0.9 V versus a reversible hydrogen electrode in alkaline medium, and the potassium ion-coordinated γ-CD complex can achieve a maximum NH3 production rate up to 4.66 mg h–1 cm–2 with an NH3 FE of 79.3%. Further comparison with permethyl-γ-CD, d-glucose, and poly(vinyl alcohol) for the NO3–RR indicated that the typical torus-shaped cyclic conformation and edge hydroxyl groups of parent CDs play important roles in the electrocatalytic process. The K+-mediated 3D γ-CD-K+ frameworks containing six CDs as nanoreactors greatly strengthen the enrichment effect of nitrate through hydrogen-bonding interaction and electrostatic interaction and promote the mass transfer, thus leading to the efficient NO3–RR in an alkaline electrolyte. This work provides a convenient, green, and economic method for high-performance NO3–RR, which has potential applications in the fields of environment, energy, and industry.