Evolution of rough-surface geometry and crystalline structures of aligned TiO2 nanotubes for photoelectrochemical water splitting

• Published in: Scientific reports Vol. 8; no. 1; pp. 1 - 11
• Main Authors: Zare, Maryam, Solaymani, Shahram, Shafiekhani, Azizollah, Kulesza, Slawomir, Ţălu, Ştefan, Bramowicz, Miroslaw
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 18.07.2018; Nature Publishing Group
• Subjects: 639/301/357; 639/925/357/1018; Diffraction; Fabrication; Fossil fuels; Humanities and Social Sciences; Hydrogen production; multidisciplinary; Nanotechnology; Nanotubes; Oxides; Renewable energy sources; Science; Science (multidisciplinary); Splitting; Titanium dioxide; X-ray diffraction
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-018-29247-3

Nowadays, increasing awareness of environment and fossil fuels protection stimulates intensive research on clean and renewable sources of energy. Production of hydrogen from water through solar-driven splitting reactions is one of the most promising approaches in the field of photoelectrochemistry (PEC). In this work we have fabricated well-aligned, highly-ordered, smooth-mouth TiO 2 nanotube arrays (TNAs) in a two-step anodization process of titanium foil, which were then used as photoelectrodes for PEC water splitting. It demonstrates for the first time correspondence between non-linear component characteristics of multiscale rough surface and crystalline structure of annealed TNAs measured at various fabrication stages and their photoelectrochemical response. The as-anodized TNAs with isotropic surface (deduced from AFM and SEM images) and largest figure of merit (according to their PEC performance) were annealed at 450 °C in air. Scale-invariant descriptors of the surface structure of the deposits involved: fractal dimension, corner frequency, roughness, size of nanostructures and their dominant habits. Moreover, X-ray diffraction data processed using the Rietveld method confirmed co-existence of various oxides, for example: TiO 2 in the form of anatase, TiO and Ti 3 O 5 phases in the TNAs under study pointing that previous well-established mechanisms of the TNA growth were to certain degree incomplete.