Ammonia (NH3) plays a vital role in global agriculture, chemical manufacturing, and emerging energy applications, including low-carbon fuels and power generation. However, conventional NH3 production via the Haber-Bosch process is highly energy-intensive, emitting approximately 2.4 tonnes of CO2 per tonne of NH3 and accounting for nearly 2% of global energy consumption. To meet net-zero climate targets, alternative pathways for sustainable, decentralized, and electrified ammonia synthesis are needed. Nitrate (NO3-), a widespread pollutant in agricultural runoff and industrial wastewater, presents a promising alternative nitrogen source. Electrochemical nitrate reduction (NO3RR) offers a route to simultaneously treat wastewater and produce ammonia in decentralized, renewable-powered systems, enabling integration with circular nitrogen management and clean energy infrastructure. However, nitrate-containing wastewaters vary widely in concentration and composition, posing significant challenges for selective separation and electrochemical conversion due to the presence of competing ions and contaminants.
In this work, we demonstrate an electricity-driven process that integrates concentration and conversion steps, enabling treatment of low-strength nitrate streams and accommodating variability in feed composition. First, we evaluate a range of electrocatalysts under conditions representative of real wastewater. These studies reveal key trade-offs between performance, durability, and cost, all of which inform the selection of a robust catalyst for continuous operation. Building on these insights, we validate an electrochemical reactor coupled with Donnan dialysis capable of achieving selective ammonia production, high ammonia recovery efficiency, and cost-effective operation. We also developed a techno-economic model derived through experimental validation that incorporates experimental performance metrics and operational constraints. This model is used to optimize component sizing, operating parameters, and reactor configurations under scenarios with intermittent renewable electricity and fluctuating nitrate availability. Ultimately, our integrated experimental and modeling approach provides a framework for deploying decentralized ammonia production systems that both valorize nitrogen-rich waste streams and reduce greenhouse gas emissions and nitrate pollution.
