Identification of Cu(111) as Superior Active Sites for Electrocatalytic NO Reduction to NH 3 with High Single-Pass Conversion Efficiency.

Opting for NO as an N source in electrocatalytic NH 3 synthesis presents an intriguing approach to tackle energy and environmental challenges. However, blindly pursuing high NH 3 synthesis rates and Faradaic efficiency (FE) while ignoring the NO conversion ratio could result in environmental problems. Herein, Cu nanosheets with exposed (111) surface is fabricated and exhibit a NO-to-NH 3 yield rate of 371.89 μmol cm -2  h -1 (flow cell) and the highest FE of 93.19±1.99 % (H-type cell). The NO conversion ratio is increased to the current highest value of 63.74 % combined with the development of the flow cell. Additionally, Crystal Orbital Hamilton Population (COHP) clearly reveals that the "σ-π* acceptance-donation" is the essence of the interaction between the Cu and NO as also supported by operando attenuated total reflection infrared spectroscopy (ATR-IRAS) in observing the key intermediate of NO - . This work not only achieves a milestone NO conversion ratio for electrocatalytic NO-to-NH 3 , but also proposes a new descriptor that utilizes orbital hybridization between molecules and metal centers to accurately identify the real active sites of catalysts.