Sulfur-Bridged Polymer Electrodes for Hybrid Capacitive Deionization: Ammonium Recovery and Multipollutant Removal

Abstract Pseudocapacitive electrode-based capacitive deionization (CDI) is a competitive water purification technology, yet organic electrodes are limited by insufficient redox activity and sluggish adsorption kinetics in practical use. A novel sulfur-bridged polymer (SPTCDA) was developed as the electrode for a hybrid CDI (HCDI) system to address efficient ammonium ion (NH4+) removal and recovery from industrial wastewater. Experimental characterizations and density functional theory calculations confirm that SPTCDA’s ladder-type conjugated structure, delocalized π-electron system, and structural flexibility synergistically boost conductivity, ion diffusion, and NH4+ affinity. The SPTCDA-HCDI system achieves a high NH4+ capacity of 190.87 mg g–1 at 1.6 V, a fast deammoniation rate (>18 mg g–1 min–1), low energy consumption (<60 kJ mol–1), and 91.5% capacity retention after 100 cycles. It also enables simultaneous removal of dyes and antibiotics, with the recovered ammonium solution reusable for irrigation. This sulfur-bridged polymer design provides a scalable route for high-performance electrochemical water treatment.