Dipole engineering coupled with ionic framework design for high-performance seawater splitting over covalent organic frameworks

A dipole engineering strategy was employed to construct ionic redox TP-X-COFs . • By varying the alkyl chain length, the local electrostatic microenvironment of TP-X-COFs was finely modulated. • TP‑P‑COF gives 16.28 mmol g⁻¹ h⁻¹ H₂ in seawater (2.6 times that in water), the highest enhancement factor for COFs. • The strong Cl⁻ affinity of the ionic framework optimizes polarization and promotes seawater splitting. Covalent organic frameworks (COFs) are promising photocatalysts for hydrogen evolution, yet their rational design for efficient high-salinity seawater splitting remains a considerable challenge. Here, a dipole engineering method was proposed in the construction of ionic redox TP-X-COFs by systematically varying the alkyl-chain length. Among them, TP-P-COF with propyl linkers achieves an optimal balance between charge separation and migration, delivering a superior hydrogen evolution rate of 6.25 mmol·g⁻ 1 ·h⁻ 1 in pure water. Strikingly, it further exhibits an enhanced photocatalytic activity of 16.28 mmol·g⁻ 1 ·h⁻ 1 in natural seawater, a 2.6-fold increase that marks the highest boost factor reported for COF-based photocatalysts. Detailed experimental and theoretical analyses reveal that the moderate dipole moment of TP-P-COF facilitates efficient exciton dissociation and charge carrier migration. Critically, its ionic framework displays a strong affinity toward Cl⁻ (adsorption energy: −1.56 eV), generating pronounced regional polarization and further optimizing the local electrostatic microenvironment for enhanced seawater-splitting activity. This work demonstrates that dipole engineering, together with the rational utilization of ionic components in seawater, provides a powerful strategy for the rational design of high-performance COF photocatalysts tailored for working in saline environments. Download: Download high-res image (163KB) Download: Download full-size image