Engineering Mass Transport for Scalable Acidic Nitrate‐to‐Ammonia Electrolysis in a Continuous Flow Reactor

The electrochemical reduction of nitrate to ammonia () presents a sustainable pathway to valorize nitrate‐contaminated wastewater while enabling decentralized ammonia production. Despite promising advances in catalyst development, most studies rely on batch‐type or single‐pass electrochemical cells, which are often encompassed by high mass‐transfer resistances or noncontinuous operation, hindering scalability and process control. In this work, we investigate nitrate reduction in a temperature‐controlled, continuous‐flow feed‐and‐bleed reactor equipped with a copper foam cathode, designed to decouple conversion and mass transfer, which enables high reaction rates at high conversion. At low current densities (), Faraday efficiencies (FE) toward reached up to 94%, with minimal and formation at steady‐state concentrations below . Increasing flow rates improved mass transport and suppressed the hydrogen evolution reaction, but also increased the loss of intermediates to the bulk. Analysis of steady‐state nitrate concentrations and partial currents confirmed that the process is limited by mass transport under high current conditions. Increasing the recirculation flow rate proved essential to sustain a high FE at industrially relevant conditions and low reactant concentrations.