New Insights into the Electron-Collection Efficiency Improvement of CdS-Sensitized TiO2 Nanorod Photoelectrodes by Interfacial Seed Layer Mediation

Titanium dioxide (TiO2) nanorods (NRs) are widely used as photoanodes in photoelectrochemical (PEC) solar fuel production because of their remarkable photo-activity and stability. In addition, TiO2 NR electrode materials can be decorated with active CdS quantum dots (QDs) to Sue light expand the sunlight photon capture. The overall photoelectric conversion efficiency for TiO2 NR or QD-sensitized TiO2 NR electrode materials in PEC is typically dominated by their interfacial electron transfer (ET) properties. To understand the key factors affecting the ET, the anatase TiO2 seed layer was added into the interface between the rutile TiO2 NRs and fluorine-doped tin oxide (FTO) substrate. This seed layer enhanced the photocatalytic performance of both the TiO2 NR and CdS QD-sensitized TiO2 NR photoanodes in PEC. Time-resolved photoluminescence spectroscopy and PEC analyses, including Mott-Schottky, electrochemical impedance spectroscopy, and photovoltage (V-ph) measurements, were used to study the charge-carrier dynamics at the interfaces between the FTO, TiO2, and CdS QD. Analysis of the results showed that band alignment at the anatase/rutile junction between the TiO2 and FTO promoted electron-collection efficiency (e(EC)) at the FTO/TiO2 interface and ET rate constant (k(ET)) at the TiO2/CdS QD interface. Furthermore, 34% enhancement of the efficiency in hydrogen (H-2) generation demonstrated the potential of the TiO2 seed-layer-mediated TiO2/CdS QD NR photoanode in the application of PEC solar fuel production. The current work represents new insights into the mechanism of ET in TiO2 and TiO2/CdS QD NR, which is very useful for the development of photoelectrode materials in solar energy conversions.