Enhanced photocatalytic H2 evolution over covalent organic frameworks through an assembled NiS cocatalyst

Abstract

Covalent organic frameworks (COFs) have been investigated in the field of photocatalysts for H₂ evolution because of their crystalline structure and diversity. However, most of them need the help of noble metals as co-catalysts to realize a high hydrogen evolution. Herein, we chose typical COFs as a platform and constructed NiSX-BD (X: weight fraction of NiS) composites by assembling NiS at room temperature. The NiS nanoparticles are shown to tightly adhere to the COFs surface. Under visible light irradiation (wavelength > 420 nm), the optimized sample with 3 wt% NiS loading exhibits a photocatalytic H₂ evolution rate of 38.4 μmol h⁻¹ (3840 μmol h⁻¹ g⁻¹), which is about 120 folds higher than that of the pure TpBD-COF and better than TpBD-COF/Pt with the same Pt loading (3 wt%). NiS3-BD shows stable hydrogen evolution in at least six consecutive cycle tests totaling 18 h. Further investigation reveals that the loaded NiS can facilitate the transfer of photogenerated electrons from TpBD-COF to the co-catalyst, leading to efficient and high photocatalytic activity. Combining the significant feature of COFs, this study opens up a feasible avenue to boost the photocatalytic H₂ performance by constructing the synergetic effects between COFs and cost-effective material.