ZIF-8 derived ZnO/TiO2 heterostructure with rich oxygen vacancies for promoting photoelectrochemical water splitting

Due to the serious recombination of electron-hole and weak photoresponse ability, achieving highly efficient photoelectrochemical (PEC) water splitting activity for TiO2 photoelectrode has become a key issue. In this paper, we reported a new method for preparing ZnO/TiO2 photoelectrodes by electrostatic adsorption from zeolitic imidazolate framework-8 (ZIF-8) as the precursor. ZIF-8 was combined with TiO2 nanorods (NRs) through electrostatic interaction and then calcined to obtain ZnO/TiO2 heterojunction photoelectrodes with abundant oxygen vacancies (Ovac). The introduced ZnO with Ovac provides a large number of active sites which enhanced the electrical conductivity and charges separation of ZnO/TiO2 photoelectrode. The optimal photocurrent density of ZnO/TiO2 photoelectrodes at 1.23 V versus (vs.) reversible hydrogen electrode (RHE) under illumination (100 mW/cm2) has reached 1.76 mA/cm2, almost 2.75 times that of the pure TiO2. Meanwhile, the incident photon-to-electron conversion efficiency (IPCE) of the best photoelectrode has increased to 58.2% at 390 nm, the charge injection (ηinjection) and separation (ηseparation) efficiency have reached to 93.53% and 51.62% (1.23 V vs. RHE), respectively.