Porous films of TiO2 and TiO2/WO3 were deposited onto transparent electrodes from aqueous suspensions with
polyethylene glycol, TiO2 particles and different amounts of tungistic acid. After annealing, crystalline samples were
obtained. The band gap energy, approximately 3.1 eV for TiO2, decreased from 2.9 to 2.7 eV for varying W/Ti molar
ratios from 3 to 12 %. The electrochemical properties were investigated in Na2SO4 aqueous solution; for the TiO2
electrode, the open circuit potential changed from 0.18 V in the dark to -0.25 V under irradiation from a solar simulator.
For hybrid TiO2/WO3 electrodes, the VOC values were almost independent of the WO3 content and corresponded to 0.3 V
in the dark and -0.1 V under irradiation; however, photocurrent and interfacial capacitance increased with a higher WO3
concentration. The electrodes were then used as photocatalysts for 17-α-etinylestradiol removal from water, and the
mixed TiO2/WO3 exhibited better performance for photocatalytic oxidation of estradiol than TiO2. Adding WO3
enhances the visible light harvesting and minimizes the charge recombination resulting in higher efficiency for solar
Fe-TiO2 particles were synthesized by sol-gel process from hydrolysis of titanium tetra-isopropoxide with nitric acid and
ferric nitrate aqueous solutions (relative Fe:Ti molar ratio ranging from 1 to 6 at %) followed by hydrothermal treatment.
Thin films were deposited onto conducting glass electrodes from a suspension with polyethylene glycol and heating at
450 °C for 30 min, which resulted in 1.5 μm thick transparent porous films. Crystalline samples, 93 % anatase and 7 %
brookite, were obtained. Increasing the iron amount, the crystallite size estimated from XRD patterns ranged from 18 to
11 nm and the color varied from slightly yellow to brown. The optical properties have also changed; the absorption edge
shifted towards longer wavelengths, with band gap energy decreasing from 3.0 to 2.7 eV. The films exhibited
photocatalytic activity for phenol degradation that indicates promising applications in solar energy conversion.
TiO2 and TiO2/WO3 porous films were deposited onto transparent conducting glass electrodes, resulting in uniform films
consisted of agglomerated particles with average diameters ranging from 50 to 200 nm; Ti, O and W atoms were
homogeneously distributed at the surface of hybrid film. Comparable electrochemical properties were observed in the
dark, with small capacitive currents and similar potentials for O2 and H2 evolution reactions in aqueous solution. Under
polychromatic irradiation, the hybrid film electrode, molar ratio WO3/TiO2 = 12 %, reveled higher photocurrent and
photocatalytic activity for oxidation of phenol and 17-α-ethinylestradiol. The visible light harvesting ability of hybrid
film, with band gap energy estimated as 2.3 eV, and the relative position of conduction and valence band edges that
inhibits charge recombination, should improve its photocatalytic activity for organic pollutant removal.
Alternative electrolytes for application in dye-sensitized TiO2 solar cells were investigated. The electrolytes were
prepared with NaI and I2 as redox couple in a matrix consisting of poly(ethylene oxide-co-diethyleneglycolglicidyl
methylether) and/or the ionic liquid N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide. Cyclic
Voltammetry and Electrochemical Impedance Spectroscopy revealed that, increasing the relative amount of ionic liquid
in the electrolytes, the impedance decreased and the ionic conductivity and the reversibility for the redox pair increased.
For solar cells assembled with the polymer electrolytes, the efficiency for energy conversion decreased with light
intensity, ranging from 3.2 to 1.4 % under 10 to 100 mW cm-2. Using the ionic liquid electrolyte, the efficiency was ca.
1.8 %, independent of irradiation. For hybrid electrolytes, the best performance, considering mechanical stability and
electrochemical properties, was achieved for an electrolyte consisting of 2:1 relative amount of polymer and ionic liquid.
Solar cells assembled with this hybrid electrolyte presented, under 100 mW cm-2, short-circuit current of 4.1 mA cm-2
and 1.4 % for overall efficiency (ca. 3.0 % under 10 mW cm-2).
The electrochemical and photocatalytic properties of a TiO2 film deposited on transparent electrodes were
investigated. Its electrochemical behavior was typical of an n-type semiconductor electrode. Its photocatalytic activity,
investigated for phenol degradation on an optical bench (area of 1 cm2, 5 mL of solution), revealed small currents (3 μA)
and poor total organic carbon (TOC) removal (5 %) when the electrode was biased at + 1.1 V in the dark for 3 h. Under
polychromatic irradiation, the electrode presented 25 μA of current and 12 % of phenol degradation. A better
performance was achieved for photoelectrocatalytic configuration, when the electrode was irradiated and biased with +
0.6 V. Experiments done under irradiation with a metallic vapor lamp using 9 cm2 electrodes and 10 mL of solution
revealed that heterogeneous photocatalysis configuration (HPC) resulted in 50 % of TOC removal, while 85 % was
achieved by the electro-assisted process (EHPC). Both the configurations exhibited pseudo-first order kinetics for phenol
degradation, but the rate constant was two times that of EHPC. The application of a potential bias to the TiO2 porous
electrode must enhance the photogenerated electron/hole separation, which minimize the charge recombination and
increases its photocatalytic activity towards organic pollutant degradation.
Dye sensitized TiO2 solar cells were assembled using rigid or flexible transparent electrodes (a conductive film deposited on glass or poly(ethylene terephthalate) as substrates and a polymer electrolyte based on (formula available in paper) and poly(epichlorohydrin-co-ethylene oxide). The cells were characterized by current-potential curves and electrochemical impedance spectroscopy under different light intensities. Under 100 mWcm-2 illumination, the rigid cell exhibited an open circuit potential VOC=0.75V, a short-circuit photocurrent ISC=2.5 mAcm-2 and an efficiency (eta) =0.9%; for the flexible cell, VOC=0.83V and (eta) and ISC were almost 10 times smaller. Under illumination, impedance spectra exhibited three semi-circles for the rigid cell. For the flexible cell the time constants were not well defined. In the dark, both systems presented very high impedance. The differences in the efficiency and the impedance spectra of both cells were compared and discussed.