Boosting photocatalytic hydrogen evolution enabled by SiO2-supporting chiral covalent organic frameworks with parallel stacking sequence

Abstract

Two-dimensional covalent organic frameworks (2D COFs) feature extended π-conjugation and ordered stacking sequence, showing great promise for high-performance photocatalysis. Periodic atomic frameworks of 2D COFs facilitate the in-plane photogenerated charge transfer, but the precise ordered alignment is limited due to the non-covalent π-stacking of COF layers, accordingly hindering out-of-plane transfer kinetics. Herein, we address a chiral induction method to construct a parallelly superimposed stacking chiral COF ultrathin shell on the support of SiO₂ microsphere. Compared to the achiral COF analogues, the chiral COF shell with the parallel AA-stacking structure is more conducive to enhance the built-in electric field and accumulates photogenerated electrons for the rapid migration, thereby affording superior photocatalytic performance in hydrogen evolution from water splitting. Taking the simplest ketoenamine-linked chiral COF as a shell of SiO₂ particle, the resulting composite exhibits an impressive hydrogen evolution rate of 107.1 mmol g^–1 h^–1 along with the apparent quantum efficiency of 14.31% at 475 nm. Furthermore, the composite photocatalysts could be fabricated into a film device, displaying a remarkable photocatalytic performance of 178.0 mmol m^–2 h^–1 for hydrogen evolution. Our work underpins the surface engineering of organic photocatalysts and illustrates the significance of COF stacking structures in regulating electronic properties.