A NiO/TiO₂ junction electrode constructed using self-organized TiO₂ nanotube arrays for highly efficient photoelectrocatalytic visible light activations

Abstract

One dimensional (1D), self-organized TiO2 nanotube arrays are known to have excellent charge transport properties and a NiO/TiO2 junction is efficient in separating electron–hole pairs. This paper describes the synthesis of a NiO/TiO2 junction electrode constructed using self-organized TiO2 nanotube arrays combining the above two properties. The self-organized TiO2 nanotube arrays used in this study were prepared by anodizing titanium films, which resulted in closely packed n-type TiO2 tubes with an inner pore diameter of 60–90 nm, a wall thickness of approximately 15 nm and a length of 600 nm. The NiO/TiO2 junction was synthesized by electroless plating and annealing which resulted in TiO2 nanotube arrays coated with a layer (about 200 nm in thickness) of NiO particles (20–40 nm). The resulting NiO/TiO2 junction electrode enabled us to obtain an enhanced photocurrent (3.05 mA cm−2) as compared with a TiO2 electrode based on TiO2 nanotube arrays (0.92 mA cm−2) under AM 1.5 G (100 mw cm−2) at a bias of 0.65 V.

Enhanced Photocatalytic Activity in p-NiO Grafted n-TiO2 Porous Coatings

“…5(c), the Ti 2p 3/2 peak is deconvoluted into two distinct peaks at binding energies of 458.89 (peak A) and 456.57 (peak B) eV. These peaks represent titanium in Ni x Ti y O z and TiO 2 compounds, respectively [27,40] .…”

Amphiphilic and photocatalytic behaviors of TiO2 nanotube arrays on Ti prepared via electrochemical oxidation

“…Some researchers used a three-electrode electrochemical cell for the anodic oxidation [22,29]. But a two-electrode electrochemical cell was also found to have produced good quality titania nanotubes [23,26,27]. In this electrochemical experiment, anodic oxidation was performed in a simpler twoelectrode cell at room temperature.…”

“…The distance between the two electrodes was about 40 mm. The operation voltage was 20.0 V and the processing time was 2 h. Other researchers have also used these conditions [27,34]. After anodic oxidation, the samples were washed by immersion in de-ionized water and air-dried.…”

“…Among these, the electrochemical method, as introduced by Zwilling et al in 1999 [19], is simplest. This method has caught more attention recently [20][21][22][23][24][25][26][27][28][29]. Basically, TiO 2 NTs grow on the surface of the anode of Ti foils or thin sheets.…”

“…Several kinds of inorganic or organic solutions containing F − ions can be used as electrolytes. For example, H 2 SO 4 /HF [20,21], H 3 PO 4 /HF [22], ethylene glycol/HF [23], glycerol/NH 4 F [24,25], ethylene glycol/NH 4 F [10,24,26], NaH 2 SO 4 /HF [27,28], and Na 2 SO 4 /NaF [29] have been used before. In this method, the size of the TiO 2 NTs can be controlled by adjusting electrochemical processing parameters [23,24].…”