Ultra-thin dark amorphous TiOx hollow nanotubes for full spectrum solar energy harvesting and conversion

• Published in: Nano energy 2021-06, Vol.84, p.105872, Article 105872
• Main Authors: Liu, Youhai, Song, Haomin, Bei, Zongmin, Zhou, Lyu, Zhao, Chao, Ooi, Boon S., Gan, Qiaoqiang
• Format: Article
• Language: English
• Subjects: Atomic layer deposition; Dark TiOx; Photocatalysis; Photothermal effects; Ultra-thin films
• ISSN: 2211-2855
• DOI: 10.1016/j.nanoen.2021.105872

Dark titania (TiOx) have been widely used for solar energy harvesting and conversion applications due to its excellent light absorbing performance throughout the ultraviolet to near infrared wavelength band, low cost, and non-toxic nature. However, the synthesis methods of dark TiOx are usually complicated and time-consuming. Here we report a facile and rapid method to fabricate dark amorphous TiOx (am-TiOx) hollow nanotube arrays on nanoporous anodic alumina oxide (AAO) templates using atomic layer deposition. Systematic investigation was performed to demonstrate that Ti3+ and O- species in the am-TiOx ultra-thin films, as well as the spatial distribution of these am-TiOx ultra-thin films on the vertical side walls of AAO templates are two major mechanisms of the black color. Importantly, the film deposition took ~18 min only to produce the optimized ~4‐nm‐thick am-TiOx film. Representative applications were demonstrated using photocatalytic reduction of silver nitrate and photothermal solar vapor generation, revealing the potential of these ultra-thin dark am-TiOx/AAO structures for full spectrum solar energy harvesting and conversion. [Display omitted] •Dark amorphous TiOx (am-TiOx) were deposited on anodic aluminum oxide (AAO) templates using atomic layer deposition (ALD).•The atomically thick am-TiOx nanotubes show broadband strong optical absorption throughout the entire solar spectrum.•The darkness was introduced by three-dimensional structural features and high concentration of Ti3+ and O- species.•The optimized deposition of a 4-nm-thick film only took ~18 min to realize the full spectrum solar absorption spectrum.•Applications were demonstrated using photocatalytic reduction of silver nitrite and photothermal solar vapor generation.