Herein, both plasmonic sensitizer and electron relay are integrated into ZnO/Au/CdS sandwich nanotube array (NTA) to construct a novel photoanode for efficient solar-to-hydrogen conversion via photoelectrochemical (PEC) cell. Under bias-free simulated solar light illumination, a photocurrent of the ZnO/Au/CdS sandwich NTA photoanode is up to 6.5 mA/cm(2), 24 times that of ZnO, and 14 times that of ZnO/Au NTA photoanodes, respectively. Furthermore, the highest solar-to-hydrogen efficiency of the ZnO/Au/CdS sandwich NTA photoanode is 3.2% at 0.72 eV vs. RHE, 23 times as high as that of ZnO/Au and 80-folds that of the pure ZnO NTA photoanodes, respectively. The PEC and photoluminescence measurements experimentally demonstrate that the Aunanoparticles not only serve as plasmonic sensitizer to efficiently transfer the electrons from the defect level of ZnO to its conduction band via resonance coupling action of the plasmon and defect energy emission, but also serve as electron relay to transfer the electrons from the conduction band of CdS to that of ZnO, enabling the ZnO/Au/CdS sandwich NTAs to achieve greatly enhanced PEC water splitting activity. This work offers a new strategy for integrating both plasmonic sensitizer and electron relay into a photoanode for efficient conversion of solar energy to chemical energy. (c) 2020 Elsevier Ltd. All rights reserved.