Enhancing photocatalytic performance of covalent organic frameworks via ionic polarization
Jiahe Zhang, Xiaoning Li, Haijun Hu, Hongwei Huang, Hui Li, Xiaodong Sun, Tianyi Ma
Abstract
Covalent organic frameworks have emerged as a thriving family in the realm of photocatalysis recently, yet with concerns about their high exciton dissociation energy and sluggish charge transfer. Herein, a strategy to enhance the built-in electric field of series β-keto-enamine-based covalent organic frameworks by ionic polarization method is proposed. The ionic polarization is achieved through a distinctive post-synthetic quaternization reaction which can endow the covalent organic frameworks with separated charge centers comprising cationic skeleton and iodide counter-anions. The stronger built-in electric field generated between their cationic framework and iodide anions promotes charge transfer and exciton dissociation efficiency. Moreover, the introduced iodide anions not only serve as reaction centers with lowered H* formation energy barrier, but also act as electron extractant suppressing the recombination of electron-hole pairs. Therefore, the photocatalytic performance of the covalent organic frameworks shows notable improvement, among which the CH3I-TpPa-1 can deliver an high H2 production rate up to 9.21 mmol g−1 h−1 without any co-catalysts, representing a 42-fold increase compared to TpPa-1, being comparable to or possibly exceeding the current covalent organic framework photocatalysts with the addition of Pt co-catalysts. Covalent organic frameworks (COFs) show great promise in photocatalysis but are limited by slow charge transfer. Here, the authors report a strategy to enhance the built-in electric field of COFs via ionic polarization, resulting in a hydrogen evolution rate of 9.21 mmol g-¹ h-¹ without Pt co-catalysts.