Controlled synthesis of nanotubes and nanowires decorated with TiO2 nanocuboids with exposed highly reactive (111) facets to produce enhanced photoelectrochemical properties

Abstract

The ability to control the exposure of facets of a crystal has been garnering considerable attention due to the fascinating dependence of the physical properties of crystals on their shapes. Herein, a TiO₂WT photoelectrode decorated with anatase TiO₂ nanocuboids (TiO₂C₁₁₁WTs) displaying high-energy exposed (111) facets and quantum dot dimensions was prepared for the first time by using a TiCl₄ treatment process. F⁻ and NH₄⁺ were introduced together to limit the randomness of the TiCl₄ hydrolysates. We propose that both F⁻ and NH₄⁺ were necessary for controlling the exposure of the (111) facets. In comparison with TiO₂WT photoelectrodes decorated with either randomly deposited TiO₂ nanoparticles (non-facet) or with TiO₂ nanofilms or with TiO₂ nanocuboids displaying exposed {001} facets (denoted as TiO₂PWT, TiO₂FWT and TiO₂C₀₀₁WT photoelectrodes, respectively), the hybrid-structured TiO₂C₁₁₁WT photoelectrode achieved superior PEC performances, with J_sc and photoconversion efficiency values of 0.97 mA cm⁻² and 0.49%. This enhancement was attributed to the exposure of the highly active (111) facets and the increased specific surface area of TiO₂C₁₁₁WTs. Meanwhile, the photoactive (111) facets offered oxygen vacancies, resulting in an increase of donor density and the enhancement of PEC performances. These facets also promoted the adsorption of CdS QDs and hence further sensitization. The CdS/TiO₂C₁₁₁WTs achieved J_sc and photoconversion efficiency values of 3.95 mA cm⁻² and 2.05%, which were about twice those of CdS/TiO₂WTs.