Immobilization of Single Ni Sites and Separated Pd Clusters in Covalent Organic Framework for Enhanced Electrochemical Reduction of Nitrite to Ammonia

The electrochemical reduction of nitrite (NO 2 – ) to ammonia (NH 3 ) offers a promising strategy for simultaneously purifying wastewater and producing value-added chemicals. The metal active site struggles to simultaneously optimize the adsorption strengths of NO 2 – and H*, resulting in a mismatch between the kinetics of intermediate activation and hydrogenation. In this work, we construct a composite catalyst of NiSS-COF/Pd ICs, which enhances the catalytic performance by precisely incorporating nickel single sites (NiSS) and Pd metal-isolated clusters (Pd ICs) into covalent organic frameworks. Thus, NiSS-COF/Pd ICs exhibit an NH 3 production rate of 20.9 mg h –1 mg cat –1 and a high NH 3 Faradaic efficiency of 95.5% at −1.0 V (vs RHE). With −1.3 V applied, NiSS-COF/Pd ICs yielded 35.3 mg h –1 mg cat –1 NH 3, the turnover number reached 58421, and the turnover frequency was 3436.8 h –1 per Ni. The NiSS tunes electronic structures to boost NO 2 – adsorption, while Pd ICs generate H* via these H* migrate to Ni sites, facilitating rapid hydrogenation and synergistic catalysis. As a result, the NiSS-COF/Pd ICs catalyst enables efficient electrochemical conversion of NO 2 – to NH 3, delivering high Faradaic efficiency and enhanced NH 3 production. Overall, this work presents a novel design strategy for developing synergistic catalytic systems that integrate single sites with metal-isolated clusters.