A copper-Zeolitic Imidazolate framework@cobalt-Bipyridine covalent organic framework Heterostructure for efficient...

The electrochemical nitrate reduction reaction (NO₃RR) has gained prominence as a promising strategy for sustainable ammonia (NH₃) 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 NO₃RR, which creates kinetic obstacles to achieving efficient NH₃ generation. Although copper-based electrocatalysts are widely studied for their ability to adsorb NO₃^-, their effectiveness is hindered by the buildup of nitrite (NO₂^-) intermediates. This issue arises from the weak binding affinity of NO₂^- and sluggish H₂O dissociation kinetics, which limit the production of reactive *H species necessary for subsequent hydrogenation, resulting in suboptimal NH₃ production Faradaic efficiency (FE_NH3) 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 NO₃RR. In this design, Cu-ZIF acts as a selective adsorbent and activator of NO₃^-, facilitating its conversion to NO₂^-, while Co-TpBpy-COF enhances H₂O activation, producing *H species and promoting the hydrogenation of NO₂^- to NH₃. As a result, in a 1 M NaOH +0.1 M NO₃^- electrolyte, the Cu-ZIF@Co-TpBpy-COF heterostructure delivers an outstanding FE_NH3 of 99.2 % and an NH₃ yield rate of 8.6 mg h^-1 mg_cat^-1 at -0.5 V versus reversible hydrogen electrode (vs. RHE), surpassing the performance of leading Cu-based electrocatalysts.