Electrochemically Self-Doped TiO₂ Nanotube Arrays for Supercapacitors

Abstract

The application of highly ordered TiO 2 nanotube arrays (NTAs) for energy storage devices such as supercapacitors has been attractive and of great interest owing to their large surface area and greatly improved charge-transfer pathways compared to those of nonoriented structures. Modification of the semiconductor nature of TiO 2 is important for its application in constructing high-performance supercapacitors. Hence, the present study demonstrates a novel method involving fabrication of self-doped TiO 2 NTAs by a simple cathodic polarization treatment on the pristine TiO 2 NTAs to achieve improved conductivity and capacitive properties of TiO 2 . The self-doped TiO 2 NTAs at −1.4 V (vs SCE) exhibited 5 orders of magnitude improvement on carrier density and 39 times enhancement in capacitance compared to those of the pristine TiO 2 NTAs. Impedance analysis based on a proposed simplified transmission line model proved that the enhanced capacitive behavior of the self-doped TiO 2 NTAs was due to a decrease of charge-transport resistance through the solid material. Moreover, the MnO 2 species was introduced onto the TiO 2 NTAs by an impregnation−electrodeposition method, and the optimal specific capacitance achieved (1232 F g −1 ) clearly confirmed the suitability of self-doped TiO 2 NTAs as effective current collector materials for supercapacitors.

Black Titanium Dioxide Nanomaterials in Photocatalysis

“…When used as photocatalysts, the black TiO 2 exhibited the highest CO 2 reduction rate (11.9 μmol·g −1 h −1 for CH 4 and 23.5 μmol·g −1 h −1 for CO) (Figure 10(b)) [89]. The reported black TiO 2 nanomaterials with a nanotube morphology and an anatase phase are prepared by electrochemical reduction in ethylene glycol electrolytes [56,90,91]. However, it should be noted that electrochemically reduced black TiO 2 in ethylene glycol electrolytes was not stable [56,91], because glycerol has a higher viscosity making it difficult for the protons to insert into TiO 2 [91].…”

“…The reported black TiO 2 nanomaterials with a nanotube morphology and an anatase phase are prepared by electrochemical reduction in ethylene glycol electrolytes [56,90,91]. However, it should be noted that electrochemically reduced black TiO 2 in ethylene glycol electrolytes was not stable [56,91], because glycerol has a higher viscosity making it difficult for the protons to insert into TiO 2 [91]. It is worth noting that the electrochemically reduced black TiO 2 nanotubes were recently found unstable in air [17].…”

Photon Absorption Enhancement of TiO2 Nanotube Arrays Decorated with Aluminum Nanoparticles

“…These scholars came up with this idea under the inspiration of employing neutral electrolyte, while they also gather the huge aspect ration of nanotubes. The selected experimental neutral buffered electrolytes were NH4F/(NH4)2SO4 [97] and NaF/Na2SO4 [98]. Via the attempt of neutral electrolyte application to increase the growing rate, a relative low pH value was set up at the bottom of the nanotube; whereas in the opposite side, at the top or in the wall area of the nanotube, a relative high pH value effectively prevented the process of electrochemical dissolution.…”

Development of electrostatic supercapacitors by atomic layer deposition on nanoporous anodic aluminum oxides for energy harvesting applications

“…The outstanding properties exhibited by nanostructured materials are the key for the next generation of energy harvesting and storage devices. In order to accomplish with these objectives, the combination of patterned 3D nanostructures together with thin film deposition techniques are outstanding candidates to solve the high energy density storage problems, but without sacrifice the increasing power density requests [7][8][9][10][11][12][13][14][15][16]. In particular, one of the most promising applications of nanomaterials for energy storage technologies is aimed to the fabrication of electrostatic supercapacitors (ESCs) by taking advantage of the huge specific surface area of nanostructured substrates like patterned templates combined with novel thin film deposition techniques to achieve high capacitance values.…”

“…In particular, one of the most promising applications of nanomaterials for energy storage technologies is aimed to the fabrication of electrostatic supercapacitors (ESCs) by taking advantage of the huge specific surface area of nanostructured substrates like patterned templates combined with novel thin film deposition techniques to achieve high capacitance values. These engineered supercapacitors show a similar conductor-dielectric-conductor (CDC) structure to conventional electrostatic capacitors, which are constituted by two conductor (or semiconductor) electrodes and separated by an intermediate dielectric layer [5][6][7][17][18][19][20][21].…”