A facile approach for photoelectrochemical performance enhancement of CdS QD-sensitized TiO2via decorating {001} facet-exposed nano-polyhedrons onto nanotubes

Abstract

In this study, we report a TiO₂ hybrid structure prepared by a facile route, wherein TiF₆²⁻ ion has been used as both the surfactant and titanium source. Single-crystalline TiO₂ nano-polyhedrons with exposed high active {001} facets were grown on a TiO₂ nanowire and nanotube (TWTs) films. This hybrid structure served as a model architecture for efficient photoelectrochemical (PEC) devices because it simultaneously offered a large contact area with the electrolyte and direct pathway for photoexcited electron collection. Under simulated sunlight illumination (AM 1.5 light at 100 mW cm⁻²), this hybrid structure exhibited a photocurrent density of 1.36 mA cm⁻² at 0 V vs. Ag/AgCl (J_SC) and photoconversion efficiency (η) of 0.81% at −0.51 V vs. Ag/AgCl, nearly 2.4 times higher than those of the bare TWTs. Morphology of the TiO₂ nano-polyhedrons in the hybrid structure was greatly influenced by the TiF₆²⁻ ion concentration, and a proper concentration was determined to be 2.5 mM. Moreover, the CdS QDs were sensitized onto the hybrid structure, and their J_SC and η reached 2.31 mA cm⁻² & 1.94%, respectively, 1.5 times higher than those of the CdS-sensitized bare TWTs. The TiO₂ nano-polyhedrons improved the efficiency via increasing the specific surface area of the electrode, thus facilitating hole transfer into the electrolyte. Moreover, the exposed high reactive {001} facets provided more effective area for the adsorption of CdS, leading to an enhanced photogeneration carrier density.