Electrochemically Regulated Hydrogen-Bonding Switches for Selective Ammonium Recovery from Wastewater

Recovering ammonium from wastewater is a promising strategy to mitigate nitrogen pollution and close the anthropogenic nitrogen cycle. Electrosorption offers a green recovery route but suffers from low selectivity and capacity in complex aqueous matrices. Herein, we report a phosphate-functionalized WO3 (PWO)-based Faradaic electrosorption (PWO-FES) platform for selective ammonium recovery through reversible hydrogen bonding-coupled intercalation. Phosphate functionalization introduces electron-rich oxygen sites that preferentially form directional N-H···O interactions with NH4+, resulting in stronger affinity than that for competing cations (K+, Na+, Ca2+ and Mg2+) with high selectivity coefficients of 9-25. When integrated into a continuous-flow module, the PWO-FES system recovers 89.9% of ammonium from actual swine wastewater over 8 cycles. The average energy consumption is only 4.7 kWh kg-1 N, with an average current efficiency of 81.1%. Over 100 h of consecutive operation, the system maintains 82.7-90.3% ammonium recovery with high stability. The recovered ammonium-rich sulfate fertilizer supports plant growth and nitrogen uptake in pot experiments at levels comparable to commercial ammonium sulfate. Life cycle assessment indicates the potential for reduced environmental burdens compared with conventional anaerobic-oxic treatment. This work demonstrates a robust, low-energy, and scalable platform for selective ammonium recovery and fertilizer production, advancing sustainable circular nitrogen management.