Reactive Separations using a Cobalt Macrocycle Molecular Catalyst for Electrochemical Wastewater Refining of Nitrate to Ammonia

Enabling a sustainable food-energy-water nexus requires feeding a growing population while minimizing environmental impacts. Molecular catalysis of aqueous electrochemical nitrate reduction (NO₃RR) to ammonia can simultaneously reduce nitrogen pollution and electrify ammonia manufacturing. We focus on in this talk on Co(DIM), where DIM = 2,3-dimethyl-1,4,8,11-tetraazacyclotetradeca-1,3-diene, because it is the only water-soluble catalyst that has been reported to yield ammonia from NO₃RR with near full selectivity (&gt; 95%). A dearth of experimental investigations prevents the rational design and implementation of NO₃RR molecular platforms such as Co(DIM). From an electroanalysis standpoint, kinetic benchmarking of Co(DIM)-mediated NO₃RR would contextualize the performance of Co(DIM) relative to state-of-the-art molecular electrocatalysts and quantitatively facilitate optimization goals for next-generation NO₃RR molecular catalysts. Molecular catalysts remain underutilized in electrochemical water treatment because they require separation of catalyst, wastewater, and product.<br/><br/>In this talk, we cover three main areas related to the development and characterization of Co(DIM). First, we describe its integration into electrochemical stripping as a reactive separation configuration that facilitates energy-efficient ammonia recovery. Second, we interrogate the stability of Co(DIM) in real wastewaters and describe electrocatalyst-in-a-box as a novel reactor design that enables catalyst reuse and continuous ammonia recovery. Finally, we elucidate the mechanism of Co(DIM) activation and catalysis to guide rational design of reactive separations, including catalyst immobilization. Together, these results will guide the rational design of molecular catalysts and reactive separations to valorize wastewater nitrate to ammonia and other products.