Improving the Photoelectrochemical Response of TiO₂Nanotubes upon Decoration with Quantum-Sized Anatase Nanowires

Abstract

TiO2 nanotubes (NTs) have been widely used for a number of applications including solar cells, photo(electro)chromic devices, and photocatalysis. Their quasi-one-dimensional morphology has the advantage of a fast electron transport although they have a relatively reduced interfacial area compared with nanoparticulate films. In this study, vertically oriented, smooth TiO2 NT arrays fabricated by anodization are decorated with ultrathin anatase nanowires (NWs). This facile modification, performed by chemical bath deposition, allows to create an advantageous self-organized structure that exhibits remarkable properties. On one hand, the huge increase in the electroactive interfacial area induces an improvement by 1 order of magnitude in the charge accumulation capacity. On the other hand, the modified NT arrays display larger photocurrents for water and oxalic acid oxidation than bare NTs. Their particular morphology enables a fast transfer of photogenerated holes but also efficient mass and electron transport. The importance of a proper band energy alignment for electron transfer from the NWs to the NTs is evidenced by comparing the behavior of these electrodes with that of NTs modified with rutile NWs. The NT-NW self-organized architecture allows for a precise design and control of the interfacial surface area, providing a material with particularly attractive properties for the applications mentioned above.

Preparation of multiple-doped TiO2 nanotube arrays with nitrogen, carbon and nickel with enhanced visible light photoelectrochemical activity via single-step anodization

“…1. 4 ] respectively, followed by a heat-treatment at 500 C for 2.5 h. In all cases, it is observed that the nanotubes are open at the top end and closed at the bottom (corresponding to the barrier layer), similar to the case of pore formation of Al [45]. The nanotube arrays grown on the very top of the substrate show a thin, less ordered initiation phase but almost every tube grows straight and highly ordered.…”

“…The Ti disk with an active anode area 3 cm 2 was kept between a set of O-rings in the sample holder and a copper wire was connected to both anode and cathode as the electrical contact. The anodization was performed in an ethylene glycol based electrolyte consisting of NH 4 4 ] (0.008, 0.015, 0.028,0.045, 0.07wt %). After anodization, the obtained nanotube electrodes were i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 5 ) 1 e1 4 rinsed immediately with ultra pure water for a couple of minutes to avoid dissolution of the TNAs, and then dried in an air stream.…”

“…The nanotube arrays grown on the very top of the substrate show a thin, less ordered initiation phase but almost every tube grows straight and highly ordered. The average inner diameter for doped and undoped TiO2 nanotubes is about 75 ± 7 nm which indicates that the process of NieCeN doping does not destroy the tubular 4 ]. Solution pH considered as a determining factor in the preparation of doped nanotube arrays [38].…”

Recent progress in enhancing solar-to-hydrogen efficiency

“…One of the approaches to addressing this problem is to control the photocatalyst structure to maximize photon absorption and minimize the distance charge carriers travel before reaching the surface. Typical photoelectrode designs include mesoporous nanostructures [167], one-dimensional (1D) nanostructures (nanowire [168,169], nanotube [170], nanorod [171]), thin films [172], as well as 3D hierarchical nanostructures [173e177].…”

“…Decorating TiO 2 nanotube with quantum-sized anatase nanowires induces great enhancement of interfacial area of the tubular structure. In addition, the band alignment of anatase and rutile TiO 2 promotes the charge carrier separation and transfer [170]. BiVO 4 has a bandgap of 2.4 eV and is a promising photocatalytic material candidate.…”