Bilayer electrified-membrane with pair-atom tin catalysts for near-complete conversion of low concentration nitrate to dinitrogen.

Discharge of wastewater containing nitrate (NO) disrupts aquatic ecosystems even at low concentrations. However, selective and rapid reduction of NO at low concentration to dinitrogen (N) is technically challenging. Here, we present an electrified membrane (EM) loaded with Sn pair-atom catalysts for highly efficient NO reduction to N in a single-pass electrofiltration. The pair-atom design facilitates coupling of adsorbed N intermediates on adjacent Sn atoms to enhance N selectivity, which is challenging with conventional fully-isolated single-atom catalyst design. The EM ensures sufficient exposure of the catalysts and intensifies the catalyst interaction with NO through mass transfer enhancement to provide more N intermediates for N coupling. We further develop a reduced titanium dioxide EM as the anode to generate free chlorines for fully oxidizing the residual ammonia (<1 mg-N L) to N. The sequential cathode-to-anode electrofiltration realizes near-complete removal of 10 mg-N L NO and ~100% N selectivity with a water resident time on the order of seconds. Our findings advance the single-atom catalyst design for NO reduction and provide a practical solution for NO contamination at low concentrations.