CdS/ZnS Co-Sensitized Hierarchical TiO₂Nanotree Array with Rutile/Anatase Junctions for Enhanced Photoelectrochemical Performance

Abstract

Hetero-structured TiO 2 nanotree arrays on flurine-doped tin oxide (FTO) substrates were deposited by a two-step hydrothermal method, CdS/ZnS core-shell quantum dots (CdS/ZnS QDs) were deposited by a successive ionic layer absorption and reaction (SILAR) process. The TiO 2 nanotree array is composed of a trunk-branch structure where the trunk is rutile TiO 2 nanorod array and the branch is anatase TiO 2 nanosheets standing on the trunk. Morphology, optical properties and photoelectrochemical (PEC) performances were investigated in detail. After the deposition of CdS/ZnS QDs, TiO 2 nanotree array photoanode shows much better PEC performance compared to TiO 2 nanorod array photoanode that sensitized nanotree array show a higher photocurrent desity (1.5 mA/cm 2 ) at 1.0 V and almost 2-fold current density (0.29 mA/cm 2 ) than sensitized nanorod array (1.0 mA/cm 2 and 0.15 mA/cm 2 ) in the measurement of linear sweep voltammetry (LSV) and transient photocurrent, respectively. This result is due to the enlarged surface specific area for more quantum dots loading, and also due to the rutile/anatase junctions formed on the boundary of trunks and branches, leading to an effective charge separating and transporting. It suggests that the hetero-structured TiO 2 nanotree array is very promising to be applied in highly efficient photoanodes for energy devices.In the past years, tremendous researches and developments in the area of synthesis and application of nanostructured titanium dioxide (nanorods, 1 nanosheets, 2 nanowires, 3 nanoflowers 4 and so on) have been reported. Titanium dioxide (TiO 2 ) as a n-type semiconductor is considered as one of the most promising and clean material in dyesensitized solar cells (DSSCs), 5,6 hydrogen production, 7,8 sensors 9-11 due to its long term stability, high photocatalytic activity, high chemical inertness, nontoxicity and low cost. 12-14 However, the absorption of TiO 2 in the full spectrum of solar energy is low because of its wide bandgap (∼3.2eV) and high recombination rate of photogenerated electron-hole pairs. There are several approaches to improve the PEC properties of TiO 2 such as doping, sensitizing and structure modifying.Recently, one dimensional (1D) TiO 2 like nanorods, nanowires and nanofibers 15 has drew much attention and been extensively synthesized by various chemical routes. This kind of anisotropic geometry with less grain bounderies and defects results in fast electron transportation and efficient quantum dots (QDs) loading. [16][17][18] However, bare 1D TiO 2 limits the light absorption and reaction contact area because of its small specific surface area which directly depresses the PEC properties of TiO 2 based photoanode. Thus, it is a decent approach to cover this shortage by designing and synthesizing hierarchical structures which can offer greatly enlarged specific surface area while providing a direct pathway for the rapid collection of photogenerated electrons. Shao et al. 19 reported that the solar cells made with forest-like TiO 2 hierarchical struc...

A Simplified Successive Ionic Layer Adsorption and Reaction (s-SILAR) Method for Growth of Porous BiVO4Thin Films for Photoelectrochemical Water Oxidation

“…Besides a few binary metal oxides (ZnO, Fe 2 O 3 , TiO 2 ), [24][25][26] the SILAR method is mainly used to synthesize metal sulfide and selenide (ZnS, CdS, PbS, SnS, CdSe, PbSe) thin films. [27][28][29][30][31][32][33][34][35][36][37] Most recently, the SILAR method has been used to prepare ternary metal oxides. 38,39 Since the monoclinic BiVO 4 is one of the most promising photoanodes, to develop a novel method to prepare this material will expand the photoanode synthesis library.…”

Fabrication and Growth Mechanism of Nanoleaf Sodium Titanate Coating on High-Purity Titanium Surface

“…Tremendous researches and developments in the Ti and titanium alloys have been a great deal of reported in recent years [1]. Due to desirable characteristics of mechanical properties and biocompatibility, Ti and its alloys are widely used as implants embedded in the human body [2].…”

“…The synthesis and application of nanostructured titanium oxide have made great strides over the past few years [8][9][10][11]. Furthermore, it has become of major interest for its wide variety of applications as n-type semiconductor [1] and electron transfer layer [12]. Several highly-oriented nanorod or nanotube arrays of ZnO or TiO 2 have extensively synthesized by various chemical routes [8][9][10][11].…”