Tianxiang Hang, Ruijie Che, Ciyang Zhang, Jun Chen, Fubin Pei, Mingzhu Xia, Wu Lei
The combination of enlarged electrochemical active areas and directed electron transport toward catalytically active sites holds great potential for enhancing the overall performance of artificial photoelectrochemical (PEC) hydrogen production. Herein, we present an alkyl-linked heterostructure constructed from TiO2 nanorod arrays and a covalent organic framework, combined with a metal-organic-framework-on-covalent-organic-framework (MOF-on-COF) assembly strategy (TiO2@COF-2@NH2-MIL-125), for the PEC water splitting reaction. Upon light irradiation, the photoinduced charge carriers generated in COF can directionally migrate across the interface along the alkyl chains and amino group to the active sites of the TiO2 and MOF, while the remaining holes are consumed by water oxidation, thereby enhancing the spatial separation and utilization efficiency of electron-hole (e-h+) pairs. Benefiting from the clever construction of the porous MOF-on-COF featuring a high specific surface area, the electrochemically active surface area of the photoanode was greatly increased. The differential charge density analysis offers compelling evidence for the presence of a dual type-II band alignment and extremely rapid charge transfer kinetics in the TiO2@COF-2@NH2-MIL-125 heterojunction. Consequently, TiO2@COF-2@NH2-MIL-125 provides remarkably superior photocurrent density (2.85 mA·cm-2 at 1.23 V vs. reversible hydrogen electrode, RHE) among the TiO2@COF-2 and pristine TiO2. This work provides a new sight in integrating MOF and COF epitaxial growth for enhancing PEC applications of TiO2 based hybrid materials.