Tuning Polarization Fields in Zwitterionic Covalent Organic Frameworks for Efficient Photo-Assisted Rechargeable...

Covalent organic frameworks (COFs) with tunable topologies hold great promise for photoelectrochemical energy conversion. However, their inherently high structural symmetry and weak intramolecular polarization typically cause rapid charge recombination, thereby severely restricting their performance. Herein, we report two zwitterionic squaric acid (SQ)-based COFs featuring a twisted three-dimensional (3D) topology (SQ-COF-1) and a planar two-dimensional (2D) topology (SQ-COF-2) to achieve efficient charge separation. Density functional theory (DFT) calculations demonstrate that the symmetry-broken, 3D topology induces a larger dipole moment (3.367 vs. 1.916 debye) and a longer charge-transfer distance (0.797 vs. 0.181 Å) compared with 2D topology, which indicates the superior charge separation capability. Photoelectrochemical measurements further reveal that the twisted 3D architecture effectively suppresses electron-hole recombination, endowing SQ-COF-1 with a prolonged carrier lifetime and enhanced photocurrent response compared to planar SQ-COF-2. Leveraging these advantages, we present the first application of SQ-based zwitterionic COFs as photocathodes in photo-assisted zinc-air batteries, where SQ-COF-1 delivers an ultralow charge-discharge voltage gap of 0.03 V and an exceptional energy efficiency of 97.7% in virtue of the accelerated photoelectrochemical reaction kinetics. This work establishes topological engineering as a straightforward strategy to tailor local polarization fields in zwitterionic COFs for high-performance photoelectrochemical energy storage.