Electrocatalytic Upcycling of Nitrate Wastewater into an Ammonia Fertilizer via an Electrified Membrane
Jianan Gao, Ning Shi, Yifan Li, Bo Jiang, Taha F. Marhaba, Wen Zhang
Abstract
Electrochemically upcycling wastewater nitrogen such as nitrate (NO3–) and nitrite (NO2–) into an ammonia fertilizer is a promising yet challenging research topic in resource recovery and wastewater treatment. This study presents an electrified membrane made of a CuO@Cu foam and a polytetrafluoroethylene (PTFE) membrane for reducing NO3– to ammonia (NH3) and upcycling NH3 into (NH4)2SO4, a liquid fertilizer for ready-use. A paired electrolysis process without external acid/base consumption was achieved under a partial current density of 63.8 ± 4.4 mA·cm–2 on the cathodic membrane, which removed 99.9% NO3– in the feed (150 mM NO3–) after a 5 h operation with an NH3 recovery rate of 99.5%. A recovery rate and energy consumption of 3100 ± 91 g-(NH4)2SO4·m–2·d–1 and 21.8 ± 3.8 kWh·kg–1-(NH4)2SO4, respectively, almost outcompete the industrial ammonia production cost in the Haber–Bosch process. Density functional theory (DFT) calculations unraveled that the in situ electrochemical conversion of Cu2+ into Cu1+ provides highly dynamic active species for NO3– reduction to NH3. This electrified membrane process was demonstrated to achieve synergistic nitrate decontamination and nutrient recovery with durable catalytic activity and stability.