Influence of Na2WO4 and H2O2 concentration during electrodeposition on nanotubes of TiO2 to form hybrid TiO2-WO3 nanostrutures (Dataset)

Hybrid TiO2-WO3 nanostructures has been synthesized by electrochemical anodization under controlled hydrodynamic conditions followed by electrodeposition in the presence of different contents of Na2WO4 (5, 15 and25 mM) and H2O2 (20, 30 and 40 mM). The influence of the electrolyte used for electrodeposition on themorphology, crystalline structure and photoelectrochemical response for water splitting has been evaluatedthrough Field Emission Electronic Microscopy, High-Resolution Transmission Electron Microscopy, ConfocalRaman Spectroscopy, Grazing Incidence X Ray Diffraction and photocurrent versus potential measurements. Description of methods used for collection/generation of data: - Hybrid nanostructure synthesis To form the hybrid nanostructures a two-step method was followed,i.e.; first electrochemical anodization was carried out to create the TiO2nanotubes, and then WO3 was electrodeposited on the TiO2.First of all, titanium rods (8 mm in diameter) were subjected to asurface treatment, which consisted of abrading the surface of the samplewith sandpaper type SiC of different granulometry (220, 500 and 4000).Then, the titanium rod was cleaned in ethanol in an ultrasonic bath for 2min, rinsed with deionized water and dried with nitrogen. Finally, forthe electrochemical anodization, the titanium rod was coated withTeflon (to expose an area of 0.5 cm2 to the electrolyte) and immersed inthe anodization electrolyte. For anodization, titanium rods served as theworking electrode (anode) and a platinum foil (1 cm2) was used as thecathode. A potential difference between anode and cathode of 55 V wasapplied during 30 min and the titanium rod was connected to a rotatingdisk electrode (RDE) to establish hydrodynamic conditions of 3000 rpmduring anodization. The electrolyte used for anodization consisted of anethylene glycol based (EG) with 1 M of water and 0.05 M of ammoniumfluoride (NH4F).Once the sample was anodized, tungsten trioxide (WO3) was electrodepositedon the formed TiO2 nanotubes, in a three-electrode electrochemicalcell. A platinum foil was the counter electrode, a silver/silver chloride (Ag/AgCl, 3 M KCl) the reference electrode and the TiO2samples the working electrode. In order to optimize the electrodepositionprocess, different concentrations of Na2WO4 (5, 15, 25 mM) andH2O2 (20, 30, 40 mM) were used. The applied potential was fixed at- 0.44 VAg/AgCl for 150 s.After electrodeposition, the hybrid nanostructures were annealed inan oven to transform the amorphous structure into a crystalline one. Theannealing treatment was carried out for 2 h at 450 ◦C, using a heatingrate of 30 ◦C/min. - Characterization of the nanostructures To evaluate the crystalline structure of the samples a ConfocalRaman Microscope with a wavelength (λ) of 488mn (blue laser) wasused. Grazing Incidence X Ray Diffractometer measurements (GIXRD)were performed with a Bruker D8AVANCE diffractometer with Cu radiationoperating at 30 mA and 40 kV from 20◦ to 60◦ and a grazingincidence of 2◦. The morphology of the hybrid nanostructures was observed by a Field Emission ScanningElectron Microscope (FE-SEM). TEM Analysis of the TiO2-WO3 nanostructures was performed byHigh Resolution Transmission Electron Microscopy (HRTEM) with afield emission gun TECNAI G2 F20 microscope operated at 200 kV. In order to prepare the TEM samples, a piece of the TiO2-WO3 nanostructureswas deposited onto a holey-carbon film supported on a coppergrid. - Photoelectrochemical response tests Photoelectrochemical response of the nanostructures was carried outusing the samples as photoanodes with a solar simulator (AM 1.5 conditionsat 100 mW⋅cm-2) connected to a potentiostat. The electrochemicalcell consisted of three electrodes, using the TiO2-WO3photocatalyst as the working electrode (with an area of 0.26 cm2exposed to the electrolyte), an Ag/AgCl (3 M KCl) as the referenceelectrode, and a platinum foil as the counter electrode, immersed in theelectrolyte (H2SO4 0.1 M aqueous solution). The tests were carried outapplying different potential step pulses with and without light (intervalsof 60 mV in dark conditions and 20 mV with light), from an initial potentialof - 0.24 VAg/AgCl until 1 VAg/AgCl.