Thermal Ramping Rate during Annealing of TiO₂ Nanotubes Greatly Affects Performance of Photoanodes

Abstract

Herein, highly ordered TiO2 nanotube (NT) arrays on a Ti substrate is synthesized in a fluoride‐containing electrolyte, using the electrochemical anodization method, which yields amorphous oxide tubes. The effects of different thermal annealing profiles for the crystallization of the amorphous TiO2 NTs are studied. It is found that the temperature ramping rate has a significant impact on the magnitude of the resulting photocurrents (incident photon‐to‐current conversion efficiency [IPCE]) from the tubes. No appreciable changes are observed in the crystal structure and morphology of the TiO2 NTs for different annealing profiles (to a constant temperature of 450 °C). The electrochemical properties of the annealed TiO2 NTs are investigated using intensity‐modulated photocurrent spectroscopy (IMPS), open‐circuit potential decay, and Mott–Schottky analysis. The results clearly show that the annealing ramping rate of 1 °C s−1 leads to the highest IPCE performance. This beneficial effect can be ascribed to a most effective charge separation and electron transport (indicating the least amount of trapping states in the tubes). Therefore, the results suggest that controlling the annealing ramping rate is not only a key factor affecting the defect structure but also a powerful tool to tailor the physical properties, and photocurrent activity of TiO2 NTs.

Facile Approach of Direct Sulfidation of FTO to Form Vertically Aligned SnS2 Nanoflake Photoanodes for Efficient Photoelectrochemical Water Splitting

“…The optical band gaps were determined by the Kubelka–Munk equation using diffuse reflectance measurements and found to be 2.26 eV for all samples (Figure b). The latter is in line with literature values. ,− Figure a represents the DRS spectra of the S-0.5, S-1, and S-2 NF samples. As shown, all samples show reduced light reflection (Figure a spectra) as well as low light transmittance (Figure a, inset image), indicating strong absorption in the visible spectral range.…”

“…The area of SnS 2 NFs subjected to the irradiation was approximately 5 mm 2 . The IPCE value for each wavelength was obtained using eq where J ph is the photocurrent density (mA cm –2 ), P is the power density of incident light (W cm –2 ), h ν is the photon energy of the incident light (1240 eV nm –1 ), and λ is the wavelength of the light (nm).…”

CdS Decorated on Hierarchically Structured Single Crystal TiO2 Nanosheets for Enhanced Photoelectrochemical H2 Generation

“…The corresponding charge transport time (τ rs ) constants were calculated from the IMPS plot using Equation ( 4). [38] t rs ¼ ð2pf min Þ À 1 (…”

Photocorrosion of n‐ and p‐Type Semiconducting Oxide‐Covered Metals: Case Studies of Anodized Titanium and Copper

“…In general, processing routes greatly affect the structure and functional properties of TiO 2 . [64,65]…”