Freeze Drying as a Novel Approach to Improve Charge Transport in Titanium Dioxide Nanorod Arrays

Abstract

Ordered TiO2 nanostructure arrays, such as hydrothermal nanorod arrays (NRAs) and anodic nanotube arrays, have attracted great attention in solar cells, photocatalysis, and so on, mainly owing to their vertically aligned 1D architectures. However, the device performances are limited by their poor electronic properties, owing to the morphology collapse and surface adsorbates. In this work, a novel freeze‐drying technique has been used to post‐treat hydrothermal TiO2 NRAs. The freeze‐drying treatment not only leads to a well‐preserved nanoarray morphology, but also induces complete removal of adsorbed chlorine on the TiO2 surface. The light‐scattering feature and the energy band structure have thus changed after freeze drying as compared to common air drying. As a result, the charge transfer at the TiO2/electrolyte interface and the collection efficiency of photo‐excited electrons through the TiO2 NRAs are substantially improved, leading to the performance enhancement of model solar cells.

Long and Well-Separated TiO2 Nanowire Arrays Decorated with Au Nanoparticles for Visible-Light-Driven Photoelectrochemical Water Splitting

“…The architecture of the photoelectrode greatly influences the performance of PEC devices as it determines its surface area, charge transport, and collection capability. ,− Vertically aligned TiO 2 nanowire (NW) arrays is one of the ideal constructions for loading noble metal NPs due to their superiority on charge transport properties. − However, well-separated rutile TiO 2 NW arrays have been limited to lengths of about 3–4 μm, − and further increasing the length leads to fusion at their roots. ,− This, in turn, not only reduces the available surface area for noble metal NP loading but also decreases the charge transport properties, resulting in low utilization of the noble metal NPs. In the current study, we adopted a solvothermal method to fabricate long and well-separated single-crystal rutile TiO 2 NW arrays and then uniformly decorated the surface with Au NPs to form the Au-TiO 2 photoanode.…”

Length-independent charge transport of well-separated single-crystal TiO2 long nanowire arrays

“… 7 , 14 , 15 During the conventional bottom-up growth process, synthesis variations to increase the length generally result in the widening of the NWs and subsequent fusion at their roots. 16 – 18 This, in turn, reduces the aspect ratio, increases the structural disorder and reduces the charge transport; 19 , 20 experimental results shown in ESI Fig. S1 † indicate that the diffusion coefficient of bundled TiO 2 NWs is over one order of magnitude lower than that of well-separated ones.…”

Rational Design of Photoelectrodes with Rapid Charge Transport for Photoelectrochemical Applications

“…Zhong and coworkers used a freeze-drying technique to post-treat hydrothermally grown TiO 2 nanowire arrays. [139,140] They demonstrated that freeze-drying not only led to well-preserved nanoarray morphology but also resulted in the complete removal of adsorbed chlorine from the TiO 2 surface. They obtained a better electron collection coefficient on the treated nanowire arrays for use in solar cells.…”