Phosphorized metal-organic framework with superior capacitive deionization performance

Metal-organic frameworks, especially zeolite imidazole framework-8 (ZIF-8), have gained attention in the capacitive seawater desalination (CDI) due to their ordered porous structure and high specific surface area. However, their poor electrical conductivity and limited electrochemical activity restrict their practical applications in desalination. Herein, P hetero-coordinated atoms are introduced to modify the local electronic structure of ZIF-8 via in situ phosphating. The incorporation of hetero-coordinated P atoms leads to the formation of P[sbnd]C bonds by substituting the sp² hybridized nitrogen atoms, which results in enhanced electron density, charge transfer efficiency, and pseudo-capacitive behavior. Bond nature alteration not only causes bond contract but also leads to core electrons entrapment and nonbonding lone pair electrons polarization, which improve the electrical conductivity to facilitate charge transfer and ion electro-sorption. As a result, P-doped ZIF-8 achieves an excellent desalination capacity of 35.95 mg g⁻¹ and a fast rate of 1.2 mg g⁻¹ min⁻¹ in 500 mg L⁻¹ NaCl solution at 1.2 V with a flow rate of 100 mL min⁻¹, outperforming that of ZIF-8 (16.44 mg g⁻¹). This work provides new insights into the relationship between local electronic structure and desalination performance, demonstrating that P doping is a feasible route to design high-performance MOF-based CDI electrodes.