Fine tuning dual active sites in modulating cascade electrocatalytic nitrate reduction over covalent organic framework.

Conversion of NO to NH proceeds stepwise in natural system under two different enzymes involving intermediate NO. Artificial electro-driven NO reduction also faces the obstacle of low faradaic efficiency due to insufficient utilization of this intermediate. Herein, we demonstrate a bimetallic COF-based electrocatalyst for the cascade catalysis of NO-to-NO-to-NH for the first time. TpBpy-CuCo exhibits a significantly improved performance, with an enhancement factor of 1.4-2 compared to monometallic TpBpy-M. The NH yield rate achieves 25.6 mg h mg at -0.55 V vs RHE over TpBpy-CuCo, together with excellent faradaic efficiency (93.4 %). This achievement demonstrates cascade catalysis between Co and Cu units, and their distinct roles are investigated through electrochemical experiments and theory calculations. In electrocatalytic process, Cu site facilities *NO-to-*NOH step, while the Co site significantly decreases the energy barrier of *NHOH-to-*NH. The present work provides a valuable inspiration in designing efficient catalysts for cascade reaction.