Influence of the anatase/rutile ratio on the charge transport properties of TiO 2 -NTs arrays studied by dual wavelength opto-electrochemical impedance spectroscopy
Résumé
The modification of photo-generated charge transport properties in aligned titanium dioxide nanotubes
(TiO2-NTs) regarding the anatase/rutile ratio was studied by photo-electrochemical methods. TiO2-NTs
obtained by anodization were thermally treated under air flux at different temperatures to significantly
modify the proportion of TiO2 anatase and rutile phases in the tubular structure. Material characterisation
methods (XRD, SEM, UV-visible spectroscopy) were used to determine the characteristics of the different
TiO2-NT electrodes in terms of dimensions, proportion of each phase and optical properties. The solar to
chemical energy conversion efficiency of these electrodes during an oxidation process was investigated in
basic aqueous solution, using methanol as a sacrificial agent, by cyclic voltametry and Incident Photon to
Current conversion Efficiency (IPCE) measurements. TiO2-NTs with a high rutile content absorb photons
of higher wavelengths, but despite this red shifted optical band gap, they exhibit the lowest photoelectrochemical
conversion efficiency. To further investigate the transport properties in these
photoelectrodes, Intensity-Modulated Photocurrent Spectroscopy (IMPS) was used with two different
irradiation wavelengths to determine the transport and recombination properties of anatase and rutile
separately. The results obtained by this set of experiments indicate that the presence of the rutile at the
bottom of the nanotubes is the major factor limiting the photo-generated electron transfer.
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