An in situ reconstructed CuOx–BTA heterointerface enables stable and selective nitrate electroreduction to ammonia

The electrocatalytic nitrate reduction reaction (NitrRR) to ammonia offers a sustainable approach for wastewater treatment and value-added chemical synthesis. However, its practical application is hindered by sluggish kinetics and low selectivity, stemming from complex proton–electron transfer processes. Herein, we report an in situ electrochemical reconstruction strategy to construct a CuOx–BTA heterojunction catalyst, where CuOx species are controllably derived from a Cu-based metal–organic framework (Cu–BTA) precursor. The engineered interface induces strong interfacial charge transfer from CuOx to BTA, promoting electron localization on Cu active sites and optimizing the adsorption energy of key intermediates. These structural and electronic features establish a dual-functional synergy: Cu0 sites catalyze the critical conversion of NO3− to NO2−, while Cu+ sites facilitate the subsequent reduction of NO2− to NH3. Meanwhile, the BTA ligand enhances NO3− activation and water dissociation, providing abundant *H intermediates for NH3 formation. Benefiting from this cooperative mechanism, the catalyst achieves a remarkable NH3 faradaic efficiency of 99.2% at −0.68 V vs. RHE and maintains stable performance for over 100 hours, significantly outperforming individual components (Cu–BTA, CuNPs and Cu2O). This study demonstrates the potential of electrochemical reconstruction-driven interface engineering for the rational design of high-performance cascade NitrRR catalysts.