Nanostructural dimension and oxygen vacancy synergistically induced photoactivity across high surface area monodispersed AuNPs/ZnO nanorods heterojunction

Abstract

Inhibiting the electron-hole recombination by adequate surface modification is a significant challenge for developing highly efficient photoanodes. This report envisions a structural synergism between a surface oxygen vacancy and metal/semiconductor contact area to significantly boost up the charge separation and injection efficiency of ZnO nanorods (NRs) in photoelectrochemical (PEC) performance. A three-dimensional photoanode is designed by vertically aligning the ZnO NRs and tuned their dimension by varying the annealing temperature and time followed by their decoration with AuNPs. Different stages of heat treatment created high oxygen vacancy, which is a key factor in tailoring the PEC activity. The ZnO NRs-A offered 75.5% average contact area for hosting the 16 nm diameter AuNPs, whereas, the ZnO NRs-B delivered 47.8%. The ZnO NRs-B with high oxygen defects exhibits a similar photoactivity shown by large dimensional ZnO NRs-A. After decorating with AuNPs, the AuNPs/ZnO NRs-A delivered ~3-fold increases in photocurrent than AuNPs/ZnO NRs-B, suggesting the photoactivity enhancement is mainly contributed from the effective charge transfer across the heterojunction between the electron mediating AuNPs and ZnO NRs, which reduces the electron-hole pair recombination. Besides, having higher oxygen vacancies, the AuNPs/ZnO NRs-B exhibited substantial photoactivity similar with AuNPs/ZnO NRs-A. The comparison of the incident photon-to-current and the applied bias photon-to-current efficiencies of the AuNPs/ZnO NRs with the reported photoanodes further authenticated the enhanced PEC performance of AuNPs/ZnO NRs. This work opens up a potential approach to metal-semiconductor heterojunction design by reduction of electron-hole recombination in PEC water splitting and solar energy conversion applications. A three-dimensional (3-D) photoanode was designed based on vertically aligned ZnO nanorods followed by their homogeneous decoration with AuNPs and their defects versus metal/semiconductor heterojunction induced photoelectrochemical behavior was investigated. • The PEC performance of ZnO nanorods was improved by the decoration of AuNPs nanocomposite on SrTiO 3 substrate. • Different approaches were employed for tuning the dimension of ZnO NRs by varying the annealing temperature and time. • Decoration of AuNPs enhances the oxygen vacancy of ZnO NRs and hence the electron-hole pair recombination was evaded . • The ZnO NRs-B exhibited oxygen defects induced PEC performance than ZnO NRs-A in visible light region. • The AuNPs/ZnO NRs-A delivered plasmonic and metal/semiconductor contact area induced PEC performance .