A copper-Zeolitic Imidazolate framework@cobalt-Bipyridine covalent organic framework Heterostructure for efficient tandem catalysis of nitrate Electroreduction to Ammonia.

The electrochemical nitrate reduction reaction (NORR) has gained prominence as a promising strategy for sustainable ammonia (NH) synthesis and the treatment of nitrate-polluted wastewater. A significant hurdle in this process is the multi-step proton-coupled electron transfer mechanism inherent to NORR, which creates kinetic obstacles to achieving efficient NH generation. Although copper-based electrocatalysts are widely studied for their ability to adsorb NO, their effectiveness is hindered by the buildup of nitrite (NO) intermediates. This issue arises from the weak binding affinity of NO and sluggish HO dissociation kinetics, which limit the production of reactive *H species necessary for subsequent hydrogenation, resulting in suboptimal NH production Faradaic efficiency (FE) and yield rates. To address these challenges, a tandem catalyst was engineered by combining a Cu-coordinated zeolite imidazolate framework (Cu-ZIF) with a Co-coordinated bipyridine-based covalent organic framework (Co-TpBpy-COF) for NORR. In this design, Cu-ZIF acts as a selective adsorbent and activator of NO, facilitating its conversion to NO, while Co-TpBpy-COF enhances HO activation, producing *H species and promoting the hydrogenation of NO to NH. As a result, in a 1 M NaOH +0.1 M NO electrolyte, the Cu-ZIF@Co-TpBpy-COF heterostructure delivers an outstanding FE of 99.2 % and an NH yield rate of 8.6 mg h mg at -0.5 V versus reversible hydrogen electrode (vs. RHE), surpassing the performance of leading Cu-based electrocatalysts.