Electrochemical doping of anatase TiO₂in organic electrolytes for high-performance supercapacitors and photocatalysts

Abstract

In this article, we report a facile electrochemical method to modify anatase TiO 2 by cathodically biasing TiO 2 in an ethylene glycol electrolyte. The resulting black TiO 2 is highly stable with a significantly narrower bandgap and higher electrical conductivity. Furthermore, largely improved photoconversion efficiency (increased from 48% to 72% in the visible region, and from nearly 0% to 7% in the UV region), photocatalytic efficiency, and charge-storage capability ($42 fold increase) are achieved for the treated TiO 2 .

Titanium Dioxide Nanotube Films for Electrochemical Supercapacitors: Biocompatibility and Operation in an Electrolyte Based on a Physiological Fluid

“…12 Films of TiO 2 nanotube arrays have particularly attracted attentions for the application in supercpacitors because of their high surface area and have been a subject of a number of studies. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] Based on the ideal capacitive response of TiO 2 (rectangular cyclic voltammetry curves) observed in some cases, researchers have previously assigned the storage mechanism in TiO 2 nanotube electrodes predominantly to the conventional electric double layer storage (see, for example, 17,23 ). Due to the low conductivity of TiO 2 and the amorphous nature of the anodized nanotubes, the capacitance of the pristine, as-anodized layer of TiO 2 nanotubes is quite low and, therefore, a number of approaches have been developed to improve the capacitance and rate capability of TiO 2 nanotube arrays via post-synthesis treatment and modification of its electronic conductivity, Ti 3+ /Ti 4+ ratio, hydrogenation and induction of oxygen vacancies.…”

Black Titanium Dioxide Nanomaterials in Photocatalysis

“…As shown in Figure 11, black TiO 2 nanotubes demonstrated the highest photocatalytic activity in rhodamine B degradation experiment, though the asanodized TiO 2 nanotubes were rich in oxygen vacancies [91]. [44].…”

“…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].…”

“…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].…”

“…In their study, a so-called "activation" step was adopted in order to obtain stable black TiO 2 nanotubes, where anodization was carried out in an ethylene glycol solution of 0.2 M HF and 0.12 M H 2 O 2 at 60 V for 30 s before the electrochemical reduction synthesis of black TiO 2 nanotubes at a cathodic voltage of −40 V for 680 s in an ethylene glycol solution of 0.27 wt.% NH 4 F [91]. The authors proposed the doping mechanism as follows:…”