Photoelectrochemical Analysis of Anion-Doped TiO[sub 2] Colloidal and Powder Thin-Film Electrodes (original) (raw)
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Journal of Alloys and Compounds, 2017
Nanocomposite TiO 2 powders were prepared via hydrothermal route using titanium(IV) butoxide as starting material at different pH media. In particular, three alkaline media composed of ammonium carbonate, ammonium bicarbonate and urea were used as modulators of the TiO 2 nanostructure. Besides, sulfuric acid was also used succeeding an acidic environment for the growth of TiO 2 nanoparticles. The structural properties of powders made either in acidic or alkaline environment were examined with microscopy techniques (FE-SEM), X-ray diffraction patterns (XRD), porosimetry (BET) and FTIR spectroscopy. TiO 2 films were fabricated by suitably modifying the synthesized powders in the form of easily handled pastes. The powders were evaluated to their photoconductivity properties while films were sensitized with N719 ruthenium dye and employed as photoanodes in quasi-solid state dye sensitized solar cells (DSSCs). The cells were characterized in terms of their electrical and electrochemical characteristics using impedance spectroscopy. The overall performance of the solar cells employing TiO 2 films prepared in acidic or alkaline environment was higher than that recorded for commercially obtained TiO 2 powder (Degussa-P25) with a maximum difference of 16% in the case of TiO 2 made in acidic environment.
Nanocrystalline Titanium Oxide Electrodes for Photovoltaic Applications
Journal of the American Ceramic Society, 2005
During the past five years, we have developed in our laboratory a new type of solar cell that is based on a photoelectrochemical process. The light absorption is performed by a monolayer of dye (i.e., a Ruthenium complex) that is adsorbed chemically at the surface of a semiconductor (i.e., titanium oxide (TiO 2 )). When excited by a photon, the dye has the ability to transfer an electron to the semiconductor. The electric field that is inside the material allows extraction of the electron, and the positive charge is transferred from the dye to a redox mediator that is present in solution. A respectable photovoltaic efficiency (i.e., 10%) is obtained by the use of mesoporous, nanostructured films of anatase particles. We will show how the TiO 2 electrode microstructure influences the photovoltaic response of the cell. More specifically, we will focus on how processing parameters such as precursor chemistry, temperature for hydrothermal growth, binder addition, and sintering conditions influence the film porosity, pore-size distribution, light scattering, and electron percolation and consequently affect the solar-cell efficiency.
Photochemical and Photoelectrochemical Behavior of a Novel TiO[sub 2]∕Ni(OH)[sub 2] Electrode
Journal of The Electrochemical Society, 1998
Transparent Ni(OH)2 films were electrochemically deposited onto Ti02 layers which had been formed on conductive glass. This optically transparent composite electrode exhibited strong, reversible photochromic and electrochromic properties when either illuminated by a 75 W Xe lamp at open circuit or anodically polarized in 1.0 M aqueous NaOH electrolyte. The extent of electrode darkening depended on the intensity of UV light, exposure time, and applied potential. Electrochemical and optical-absorption measurements indicated that UV-photogenerated holes in the Ti02 valence band recombined with electrons from the electrochromic Ni(OH)2 layer; which consequently oxidized the Ni(OH)2 to NiOOH and darkened the composite electrode. Because the darkening process occurred only on the specific electrode areas which were exposed to light, nonuniform illumination produced a patterned optical state of the electrode. Infroduction The NiOOH-Ni(OH)2 electrode is under consideration for use in electrochromic devices,'5 which are being developed for architecture, aerospace, and vehicle applications. The transparency change from clear to opaque (black) that accompanies the Ni2 to Ni3* oxidation reaction represents an advantage over electrochromic oxides which are strongly colored. Although significant knowledge about the electrochemical behavior of NiOOH-Ni(OH), films has arisen from
Russian Journal of Electrochemistry, 2013
Photoelectric parameters of dye sensitized solar cells (DSSC) based on nanocrystaline titanium dioxide synthesized by several methods are studied. The lifetime of charge carriers (electrons) is shown to be 10 ms for DSSC with anodes of TiO 2 synthesized by hydrolysis of ammonium dihydroxodilactatotitanate(IV) (DLTA) and about 7 ms for anodes of commercial titanium dioxide (AEROXIDE ® , TiO 2 , P 25, Evonik), which points to the lower recombination losses for anodes of DLTA. The transition times for both cell versions are close to one another and equal to 10 ms; under these conditions, the diffusion coefficient of electrons is assessed to be ca. 10 -5 cm 2 s -1 . The comparable transition times and lifetimes of electrons in DSSCs under study suggest that a part of photogenerated electrons is lost at the diffusion to the conducting substrate.
Synthesis, characterization and activity of photocatalytic sol–gel TiO 2 powders and electrodes
Applied Catalysis B-environmental, 2009
The efficiency of photoelectrocatalytic processes is strongly influenced by the electrode type and synthesis procedure. This work reports the sol-gel synthesis and characterization of TiO 2 and Fe-doped TiO 2 powders and electrodes as a function of pH and preparation temperatures and the correlation of their photoelectrochemical properties with their activity for azo dye decolourization. pH is shown to be the variable that most influences the formation of the TiO 2 crystalline phases, the photocurrents of the electrodes, and consequently their photocatalytic activity.
Highly active nanocrystalline TiO 2 photoelectrodes
Nanotechnology, 2008
A simple method for the fabrication of highly photoactive nanocrystalline two-layer TiO 2 electrodes for solar cell applications is presented. Diluted titanium acetylacetonate has been used as a precursor for covering SnO 2 :F (FTO) films with dense packed TiO 2 nanocrystallites. The nanoporous thick TiO 2 film follows the dense packed thin TiO 2 film as a second layer. For the latter, amorphous TiO 2 nanoparticles have been successfully synthesized by a sol-gel technique in an acidic environment with pH < 1 and hydrothermal growth at a temperature of 200 • C. The acidic nanoparticle gel was neutralized by basic ammonia and a TiO 2 gel of pH 5 was obtained; this pH value is higher than the recently reported value of 3.1 (Park et al 2005 Adv. Mater. 17 2349-53). Highly interconnected, nanoporous, transparent and active TiO 2 films have been fabricated from the pH 5 gel. SEM, AFM and XRD analyses have been carried out for investigation of the crystal structure and the size of nanoparticles as well as the surface morphology of the films. Investigation of the photocurrent-voltage characteristics has shown improvement in cell performance along with the modification of the surface morphology, depending on pH of the TiO 2 gel. Increasing the pH of the gel from 2.1 to 5 enhanced the overall conversion efficiency of the dye-sensitized solar cells by approximately 30%. An energy conversion efficiency of 8.83% has been achieved for the cell (AM1.5, 100 mWcm −2 simulated sunlight) compared to 6.61% efficiency in the absence of ammonia in the TiO 2 gel.
A working electrode in dye-sensitized solar cells was fabricated using T1O2 colloidal sol prepared from titanium isopropoxide used as a starting material by applying the sol-gel method. The effect of aging times and temperatures on physical and chemical properties of TiO2 sol particles was systematically investigated. Results showed that the crystallinity and average particle size of TiO2 colloidal sol can be successfully controlled by the adjustment of aging time and temperature. The conversion efficiency of the repetitive dry coating films fabricated using the dried TiO2 colloidal sol particles and hydroxypropyl cellulose binder (15%) was 10.31% with a high transparency.
Electrochemical Properties of TiO2 Electrode Prepared by Various Methods
Procedia Engineering, 2012
Thin transparent TiO 2 layers were created on the conductive ITO glass by means of the templated sol-gel technique and by the subsequent calcination at 450˚ C. The sol-gel method using molecular templating is based on a chemical process utilizing hydrolysis and polycondesation of metal alkoxides in the core of reverse micelles which allows a production of uniform particles in layers. The sol-gel method was chosen by reason of the sol-gel layers electrodes are transparent and possess very stabile surface. For the preparation of the thin sol-gel TiO 2 films, numerous deposition techniques were applied. This contribution is focused on the study of structural and photo-electrochemical properties of the sol-gel nanostructured layers deposited by two various techniques (a dip-coating and an inkjet printing). The sol's viscosity, concentration, solvent volatility, speed of pulling etc. may influence the final structural properties of layers, such as film thickness, nanoparticles size and surface morphology. The surface properties were determined by XRD, Raman, SEM, AFM and UV-Vis analyses. Photo-induced electrochemical properties were measured by potentiodynamic methods in the three-compartment electrochemical cell. This Pyrex cell contained supporting electrolyte (0.1M Na 2 SO 4 ) and the TiO 2 /ITO electrode was used as a working electrode. As an UV source the polychromatic mercury lamp was employed and the wavelength of the incident light was focused by an interference filter on 365 nm.
Microporous and Mesoporous Materials, 2008
Hybrid films of TiO 2 and benzoquinone, its derivative 2-methyl-benzoquinone or the dye 2,9,16,23-tetrasulfophthalocyaninatonickel(II) were prepared by anodic electrodeposition from titanium alkoxide solutions. Calcination of the films at 450°C led to removal of the organics and the formation of crystalline and highly porous TiO 2 films as seen in XRD and Kr adsorption measurements, respectively. In dye-sensitized solar cells the films achieved an overall light-to-electricity conversion efficiency of 0.8% despite a low film thickness of 0.55 lm. In the photocatalytic decomposition of methylene blue the films showed photonic efficiencies of up to 0.09% for film thicknesses around 0.5 lm, which is much higher than those of comparable TiO 2 films prepared by sol-gel method.
Photoelectrochemical cells based on dye sensitized colloidal TiO2 layers
Solar Energy Materials and Solar Cells, 1993
A new, low cost solar cell -based on work done by Professor Gr~itzel -was evaluated for power generation applications. The main effort at ABB was directed towards the development of cells with high efficiencies and towards the development of production methods for the electrodes. Using optimized electrodes made by screen-printing techniques, an efficiency of 9.4% could be obtained for small electrodes (0.5 cm2). Lifetimes of more than 10 months without degradation could be achieved at the EPF Lausanne using this type of cell.