Electrocatalytic Upcycling of Nitrate Wastewater into an Ammonia Fertilizer via an Electrified Membrane.

Electrochemically upcycling wastewater nitrogen such as nitrate (NO 3 - ) and nitrite (NO 2 - ) 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 NO 3 - to ammonia (NH 3 ) and upcycling NH 3 into (NH 4 ) 2 SO 4 , 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% NO 3 - in the feed (150 mM NO 3 - ) after a 5 h operation with an NH 3 recovery rate of 99.5%. A recovery rate and energy consumption of 3100 ± 91 g-(NH 4 ) 2 SO 4 ·m -2 ·d -1 and 21.8 ± 3.8 kWh·kg -1 -(NH 4 ) 2 SO 4 , 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 Cu 2+ into Cu 1+ provides highly dynamic active species for NO 3 - reduction to NH 3 . This electrified membrane process was demonstrated to achieve synergistic nitrate decontamination and nutrient recovery with durable catalytic activity and stability.