Life‐Cycle‐Sustainable Capacitive Deionization Enabled by Organic Molecular Engineering for Selective Ammonium Capture

ABSTRACT

Selective ammonium (NH ₄ ⁺ ) recovery from complex wastewater streams remains a pivotal challenge in sustainable nitrogen management. Capacitive deionization (CDI) offers an energy‐efficient electrochemical route for ion separation, yet its practical application is constrained by the inherent trade‐off between NH ₄ ⁺ adsorption capacity and selectivity. Herein, we circumvent this fundamental limitation through the rational molecular engineering of an organic electroactive material, 1,4‐bis(1H‐imidazo[4,5‐b]phenazin‐2‐yl)benzene (IPB), which features extended electron delocalization and abundant C═N moieties for NH ₄ ⁺ ‐specific redox‐coupled capture. The resulting IPB‐based CDI prototype delivers a high NH ₄ ⁺ adsorption capacity of 267.23 mg g ⁻¹ and a fast rate of 62.51 mg g ⁻¹ min ⁻¹ , while sustaining remarkable selectivity in complex multi‐ion matrices, thereby effectively surpassing the conventional capacity‐selectivity trade‐off. Notably, CDI adsorption reduces wastewater NH ₄ ⁺ levels to below 3 mg L ⁻¹ and achieves 82.3% direct recovery as liquid fertilizer during CDI desorption, as demonstrated by isotope tracing experiments. The CDI process exhibits a low carbon footprint of only 4.66 × 10 ⁻² t CO ₂ ‐equivalent per tonne of NH ₄ ⁺ treated, underscoring its superior life‐cycle sustainability. Therefore, this work proposes a molecularly engineered organic electrode material for high‐performance wastewater remediation and circular nutrient recovery, paving the way toward carbon‐neutral electrochemical water treatment technologies.