Photoelectrochemical study of ZnO nanowires (Dataset)

ZnO nanowires with high aspect ratio were obtained by fast and simple electrochemical anodization.Morphological and photoelectrochemical characteristics of the synthesized ZnO nanowireswere evaluated by using different techniques: high resolution transmission electron microscopy, X-rayphotoelectron spectroscopy, UV–VIS spectroscopy and Mott-Schottky analysis. Description of methods used for collection/generation of data: - Synthesis ZnO nanowires were formed by electrochemicalanodization in a 2-electrode cell with a zinc rod (99,999% purity, 8 mm)anode and a platinum foil cathode. A ZnOcompact layer was fabricated for comparison by etching the zinc rod in asolution of 5% HCl for 30 s. Previously to anodization, the zinc rodsurface was polished with 240–4000 SiC papers to achieve a mirrorfinish. Next, the degreasing of the samples was carried out by sonicationin ethanol for 2 min. Then, the electrodes were rinsed with distilledwater, dried in an air stream and covered with Teflon to just expose thetop surface (0.5 cm2) to the electrolyte. Anodization was performed in a50 mM NaHCO3 aqueous electrolyte containing 10 v/v % ethanol at 10 Vfor 10 min at room temperature. During the process, current densityversus time was recorded. Once the ZnO nanostructures wereformed on top of the Zn rods, thin slices (4–5 mm in height) were cutfrom these rods by using a cutting machine. Nanostructures were protectedlest they undergo damage during this process. Finally, thermalannealing of the as-prepared samples was carried out at 300 ◦C for 1 h inair atmosphere. - Morphological characterization Morphological characterization of the nanostructureswas carried out by Transmission Electron Microscopy(TEM) and high resolution TEM (HRTEM). The equipment used is a FEIField Emission Gun (FEG) TECNAI G2 F20 S-TWIN microscopy workingat 200 kV. - Structural characterization The chemical states of the ZnO nanowires were analyzed by means of X-rayphotoelectron spectroscopy (XPS, K-ALPHA, Thermo Scientific). Al–K_radiation (1486.6 eV) monochromatized by a twin crystal monochromatorproviding a focused X-ray spot at 3 mA × 12 kV wasemployed to collect the spectra. The alpha hemispherical analyzeroperated in the constant energy mode by using 200 eV in a survey scanpassing energies for the whole energy band measurements and 50 eV in anarrow scan for the elements. The experimental backgrounds were approximated byusing a smart background function and the surface elemental compositionwas calculated from the background-substracted peak areas. Thesystem flood gun yielding from a single source low energy electrons andlow energy argon ions provided the charge compensation. In the processingof the data from the XPS spectra, the values of the binding energy(BE) were referenced to the carbon (C 1s) peak at 284.5 eV. The sampleswere also characterized by UV–vis diffuse reflectance. UV-Vis. spectroscopy measurements of the samples were carried out within the200–850 nm range using a Shimadzu spectrometer model UV-1800. Thespectra shown has been obtained from that of the untreated ZnO sample(ZnO over the Zn support) extracting the signal of the Zn support. Thevalue of the band gap, Eg, was obtained by extrapolating the linear fittedregion at [F(R(∞))hυ]2 = 0 in the plot of [F(R(∞)) hυ]2 versus hυ. - Electrochemical and photoelectrochemical characterization Mott-Schottky (MS) analysis: All these experiments took place in athree-electrode configuration cell with a 0.24 M Na2S and 0.35 M Na2SO3 aqueous solution as electrolyte. The zinc oxide samples were used as the photoanodes (with 0.26 cm2 of exposed effective area), aplatinum foil (1 cm2) as the cathode and an Ag/AgCl electrode as thereference electrode. The electrodes were immersed in the electrolyte andconnected to a potentiostat (Autolab). Simulated sunlight conditionswere carried out using AM 1.5 illumination (100 mW/cm2).Mott-Schottky analyses in dark and illumination conditionswere carried out by sweeping the potential from - 1.0 to - 0.2 V, with anamplitude signal of 0.01 V at a frequency value of 5 kHz.