TiO2-Au-Cu2O Photocathodes: Au-Mediated Z-Scheme Charge Transfer for Efficient Solar-Driven Photoelectrochemical Reduction

An Au-mediated Cu 2 O-based Z-scheme heterostructure system is demonstrated for use as efficient photocathodes in photoelectrochemical (PEC) reduction. The samples are prepared by electrodepositing a Cu 2 O layer on the surface of Au particle-coated TiO 2 nanorods. For TiO 2 -Au-Cu 2 O, the embedded Au particles function as a charge transfer mediator to enhance the electron transportation from the conduction band of TiO 2 to the valence band of Cu 2 O. Such a vectorial charge transfer leads to the concentration of electrons at the conduction band of Cu 2 O and the collection of holes at the valence band of TiO 2, providing TiO 2 -Au-Cu 2 O with substantially high redox abilities for reduction applications. Time-resolved photoluminescence spectra and electrochemical impedance spectroscopy analysis suggest that interfacial charge transfer is significantly improved because of the Au-mediated Z-scheme charge transfer mechanism. By virtue of the high redox ability and improved interfacial charge transfer, TiO 2 -Au-Cu 2 O performs much better as a photocathode in H 2 production and CO 2 reduction than pure Cu 2 O and binary TiO 2 -supported Cu 2 O do. Remarkably, the photocurrent density of TiO 2 -Au-Cu 2 O toward PEC CO 2 reduction can reach as high as −1.82 mA/cm 2 at +0.11 V vs RHE. The incident photon-to-current conversion efficiency data manifest that TiO 2 -Au-Cu 2 O surpasses both pure Cu 2 O and binary TiO 2 -supported Cu 2 O in PEC reduction across the whole photoactive region. The current study paves a valuable approach of devising Z-scheme photocathode for the construction of sophisticated artificial photosynthesis systems capable of solar-to-fuel conversion.