Abstract
AbstractIn this research, we investigate the effect of alkali metal cations including Li, Na and Cs in hydrothermal solution on the morphology, stability, and photoactivity of nanostructured TiO2 nanoflakes as a photoanode. The TiO2 nanoflakes are formed through hydrothermal treatment of Ti foil in 1.0 M LiOH, NaOH or CsOH at 100 °C for 3 h. By subsequent thermal reduction of the structure in an optimized Ar/H2 environment, conductive TiO2 nanoflakes were formed. The reduction treatment remarkably improves the photocurrent density of the TiO2 nanoflakes and has the highest impact on the sample treated in the NaOH alkali solution. For the nanoflakes produced in NaOH alkali solution, the bandgap is shifted to a lower value and the structure shows the most stable morphology after thermal treatment compared to nanoflakes formed in other alkali solutions. Such reduced hydrothermally treated nanoflakes formed in NaOH can generate a photocurrent density of approximately 1 mA/cm−2 vs. Ag/AgCl in 1.0 M KOH solution, which is six times higher than for pristine TiO2.
Highlights
Introduction positions forH2 and O2 generation from H2O.[2,3,4,5] pristine TiO2 as a photoanode suffers from ineffective utilization of solar light and has a low quantum efficiency due to its large bandgap, and intrinsic fast electron-hole recombination resulting in its poor electrical conductivity.[6,7,8,9]This clearly indicates that further improvement of its photoconversion efficiency is an important issue in terms of practical use and commercialization
F) after annealing at 500 °C. g) x-ray diffraction (XRD) diffraction patterns and h) Raman spectra of TiO2 nanoflake structures formed in different hydrothermal solutions after annealing at 500 °C for 3 h
We report a systematic investigation on the effect of different alkali metal hydroxides (LiOH, NaOH and CsOH) as hydrothermal solutions on the photoelectrochemical performance of TiO2 thin films
Summary
There are several reports on the self-doping of Ti3 + in a 1D TiO2 structure as an effective approach to enhance the electrical conductivity and photoactivity of TiO2.[23,24,25] In previous work, we showed that optimized post thermal treatment of TiO2 nanotubes in Ar/. To increase the conductivity of the hydrothermally treated nanoflakes for use as photoanodes, two reduction methods, namely thermal Ar/H2 and Ar/H2 plasma treatments were used. A drastic enhancement in photocurrent density is observed for the sample prepared in NaOH solution This could be ascribed to a shift of bandgap energy towards a lower value as well as preserving its morphology after thermal treatment as compared to samples hydrothermally treated in LiOH and CsOH solutions. F) after annealing at 500 °C (insets are their cross sections). g) XRD diffraction patterns and h) Raman spectra of TiO2 nanoflake structures formed in different hydrothermal solutions after annealing at 500 °C for 3 h
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