Surface modification of highly ordered TiO2 nanotube arrays for efficient photoelectrocatalytic water splitting

Abstract

An efficient visible-light-sensitive heterostructure photoanode of CdS nanoparticles/ZnO shell/TiO2 nanotube (CdS/ZnO–TiNT) arrays were investigated for solar water splitting. Highly ordered arrays of TiNT were grown vertically on Ti foil by electrochemical anodization. Both aqueous solution routes were used in turn to coat a thin recombination barrier of ZnO shell and narrow band gap CdS nanoparticles to the surface of the TiNT arrays. As a result of strong absorption within solar spectrum and effective suppression of electron-hole pair recombination in CdS/ZnO–TiNT arrays, a significant improvement in solar-to-hydrogen conversion efficiency from 0.39% to 1.30% was obtained.

Hydrogen generation from photoelectrochemical water splitting based on nanomaterials

“…The primary reason is their unique physical and chemical properties compared to bulk materials as well as their potential applications in various technologies including energy conversion. Photoelectrodes based on nanostructured semiconductor materials have been explored for a number of systems, usually single-component nanomaterials such as CdS [79], Bi 2 S 3 [22], Sb 2 S 3 [23], WO 3 [24][25][26][27][28][29][30], ZnO [31][32][33], Fe 2 O 3 [34][35][36], and, more commonly, TiO 2 [13,[37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52]. Nanomaterials including zerodimensional (0D) nanocrystals and one-dimensional (1D) nanorods and nanotubes offer some potential advantages over their bulk counterparts for photoelectrodes in PEC.…”

“…This general concept of using 1D nanostructures for PEC photoelectrodes has been further extended to nanotubes [44,46,48,50,[63][64][65][66][67][68][69][70][71][72]. In comparison to nanorods or nanowires, nanotubes exhibit less material for light absorption but higher surface area for redox reactions.…”

“…Various studies have shown improved visible-light photoactivity with coupled semiconductors with different band gaps, e.g. TiO 2 /CdS [44,64,71,[98][99][100][101], TiO 2 /CdSe [102], TiO 2 /Si [45,51], ZnO/CdS [103], ZnS/CdS [104], SnO 2 /TiO 2 [105], SnO 2 /ZnO [106], and SnO 2 /CdSe [107]. These heterogeneous nanostructures are typically composed of two semiconductors, one with a wide band gap and another with a smaller band gap.…”

“…In addition, the coupling between 1D metal oxide nanostructures with 0D narrow band gap semiconductor photosensitizers such as CdS and CdSe nanoparticles or quantum dots (QDs) for water splitting has attracted much attention lately [44,64,113]. Similar to dye sensitization, quantum dot sensitized nanostructured photoanodes enable light absorption in the visible region of interest and effective transportation of excited electrons.…”

Research Update: Strategies for efficient photoelectrochemical water splitting using metal oxide photoanodes

“…In situ cadmium chalcogenide QD formations by electrodeposition, chemical bath deposition or successive ionic layer adsorption, and reaction routes on various nanostructure arrays (e.g., nanotubes, nanowires, nanorods, and inverse opal) of TiO 2 , 91,92 ZnO,93,94 or TiO 2 /ZnO (core/shell) 95 for PEC photoanodes have been reported. Visible light absorption of the QDs and type-II band edge configuration promoting spatial separation of photogenerated carriers could significantly enhance PEC water oxidation efficiencies under simulated sunlight.…”