TiO2 Nanotubes Architectures for Solar Energy Conversion

Abstract

Electromagnetic light from the Sun is the largest source, and the cleanest energy available to us; extensive efforts have been dedicated to developing science and engineering solutions in order to avoid the use of fossil fuels. Solar energy transforms photons into electricity via the photovoltaic effect, generating about 20 GW of energy in the USA in 2020, sufficient to power about 17 million households. However, sunlight is erratic, and technologies to store electric energy storage are unwieldy and relatively expensive. A better solution to store energy and to deliver this energy on demand is storage in chemical bonds: synthesizing fuels such as H2, methane, ethanol, and other chemical species. In this review paper we focus on titania (TiO2) nanotubes grown through electrochemical anodization and various modifications made to them to enhance conversion efficiency; these semiconductors will be used to implement the synthesis of H2 through water splitting. This document reviews selected research efforts on TiO2 that are ongoing in our group in the context of the current efforts worldwide. In addition, this manuscript is enriched by discussing the latest novelties in this field.

Improvements in the Magnesium Ion Transport Properties of Graphene/CNT‐Wrapped TiO2‐B Nanoflowers by Nickel Doping

“…For many years, TiO 2 has been widely used in solar cells, in photocatalysis, and in lithiumion batteries. [22][23][24][25][26] There are many different crystalline forms of TiO 2 (such as anatase, rutile, and bronze), but anatase and rutile TiO 2 are considered to be the most promising materials for solar cells and photocatalysts. More and more studies have found that when TiO 2 is used as rechargeable battery electrode material, it has better electrochemical cycle stability because of its small volume expansion and stable structure.…”

The Impact of Side-Selective Laser Tailoring of Titania Nanotubes on Changes in Photoelectrocatalytic Activity

“…The process upscaling requires several optimization steps, and the elaborated route can only be performed at the laboratory scale and cannot be carried out on only a specific part of the substrate. In contrast to these limitations, laser technology offers rapid and easily scalable processing based on the interaction between the coherent, intense light of a particular wavelength with the material [ 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ]. Additionally, the selection of the laser fluence and the environment in which the process is carried out (vacuum, ambient atmosphere, or ever water) can also be included into the group of important parameters affecting the final product [ 39 , 40 ] (see Table 1 ).…”

“…As can be seen, the modification of TiO 2 NTs with laser radiation can be implemented using several different lasers which emit wavelengths from almost the whole spectrum. In most cases, the process leads to an amorphous-to-crystalline phase transition with a multi-fold increase in the measured photocurrent as well as a general enhancement of catalytic activity [ 35 , 40 , 41 , 42 , 43 ]. However, several drawbacks of the used treatment were also described.…”

“…However, several drawbacks of the used treatment were also described. In the work of Xu and Zangari [ 35 ], after increasing the laser fluence above 0.3 J/cm 2 , the amount of photoinduced charge carriers dropped significantly, resulting in a final decrease in the activity of the samples. Moreover, both Xu et al [ 40 ] and Wawrzyniak et al [ 43 ] observed an increment of formed structural defects, leading to a decrease in activity.…”

Structural Regulation and Growth Mechanism of 3D-TiO2 Nanotubes

“…5 Anodic oxidation is a relatively simple and low-cost method that can obtain TiO 2 nanotubes with controllable geometry and self-organization under specific anodic oxidation conditions. TiO 2 nanotubes prepared through anodic oxidation have been widely used in photocatalysis, [6][7][8][9] solar cells, [10][11][12] sensors, [13][14][15] and biomedicine 16,17 owing to their remarkable photoelectrochemical properties and semiconducting properties.…”