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

Conversion of NO₃^- to NH₃ proceeds stepwise in natural system under two different enzymes involving intermediate NO₂^-. Artificial electro-driven NO₃^- 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 NO₃^--to-NO₂^--to-NH₃ for the first time. TpBpy-Cu₂Co₄ exhibits a significantly improved performance, with an enhancement factor of 1.4-2 compared to monometallic TpBpy-M. The NH₃ yield rate achieves 25.6 mg h^-1 mg_cat.^-1 at -0.55 V vs RHE over TpBpy-Cu₂Co₄, 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 *NO₃-to-*NO₃H 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.