Titanium Dioxide Electrodes Research Articles

Adsorption of human serum albumin on electrochemical titanium dioxide electrodes: Protein–oxide surface interaction effects studied by electrochemical techniques

The adsorption of Human Serum Albumin (HSA) on a semiconductor TiO 2 electrochemical oxide was investigated using Cyclic Voltammetry ( CV), Capacity–Potential curves ( C– E) and time-resolved techniques as a function of electrode potential and protein concentration. The presence of HSA adsorbed on the electrode surface modifies the voltamperometric behavior of the hydrogen evolution reaction ( her) and also produces a major modification in the diffusional layer thickness of the H + ions. The adsorbed amounts of HSA were analyzed throughout different adsorption isotherms. The experimental data were modeled with a modified Langmuir type isotherm, considering a weak chemisorption on a surface with heterogeneity in site-energy distribution with some degree of attractive lateral interactions between the adsorbed protein molecules. The effect of the adsorption potential ( E ads ) was investigated polarizing the electrode at −0.70, −0.50 and −0.08 V vs. SCE. The capacity response obtained from the different impedance experiments was determined by the space charge region in the semiconductor. It was possible to correlate processes produced by the protein adsorption on the surface (occurring in the electrolyte side of the interface) with changes in the semiconductor properties of the TiO 2 (in the oxide side of the interface). The adsorption of HSA produces an increase in donor concentration ( N D ) of the semiconductor and a shift of the E fb to more negative values. These effects are more pronounced with an increase in the protein concentration. The relative change in N D is lower and the change in E fb is higher when the adsorption occurs at less negative applied potentials. Adsorption kinetics and thermodynamic parameters were calculated for a wide protein concentration range.

Laser annealed composite titanium dioxide electrodes for dye-sensitized solar cells on glass and plastics

We report a rapid and low temperature process for fabricating composite TiO2 electrodes for dye-sensitized solar cells on glass and plastics by in tandem spray deposition and laser annealing. A homogenized KrF excimer laser beam (248 nm) was used to layer-by-layer anneal spray deposited TiO2 nanoparticles. The produced TiO2 film is crack free and contains small particles (30 nm) mixed with different fractions of larger particles (100–200 nm) controlled by the applied laser fluence. Laser annealed double-layered structure is demonstrated for both doctor-blade deposited and spray-deposited electrodes and performance enhancement can be observed. The highest demonstrated all-laser-annealed cells utilizing ruthenium dye and liquid electrolyte showed power conversion efficiency of ∼3.8% under simulated illumination of 100 mW/cm2.

Experimental Demonstration of the Mechanism of Light Harvesting Enhancement in Photonic-Crystal-Based Dye-Sensitized Solar Cells

Herein, we report an experimental analysis of the photogenerated current of very thin and uniform dye-sensitized nanocrytalline titanium oxide (nc-TiO2) electrodes coupled to high-quality one-dimensional photonic crystals. The effect of well-defined optical absorption resonances are detected both in optical spectroscopy and photogenerated current experiments, a clear correspondence between them being established. Our study demonstrates that light trapping within absorbing electrodes is responsible for the absorption enhancement that has previously been reported and unveils the mechanism behind it. We prove that this effect improves significantly the power conversion efficiency of very thin electrodes.

Charge recombination studies in conformally coated trifluoroacetate/TiO2 modified dye sensitized solar cells (DSSC)

We report the preparation of conformational coatings of the titania electrode by trifluoroacetic acid (TFA) and its influence on the efficiency of dye sensitised solar cells. We have observed that the TFA creates a hydrophobic barrier on the titania surface preventing direct contact with the electrolyte. Interestingly, when N719 is used as sensitiser, the presence of TFA accelerates the recombination reactions between photo-injected electrons at the TiO2 and the oxidised electrolyte.

Pyrococcus furiosus-immobilized anodized tubular titania cathode in a hydrogen production system

Anodized tubular titania (TiO 2) electrodes (ATTEs) are prepared and used as both the photoanode and the cathode substrate in a photoelectrochemical system designed to split water into hydrogen with the assistance of an enzyme and an external bias of 1.5 V. In particular, the ATTE used as the cathode substrate for the immobilization of the enzyme is prepared by two methods—adsorption and crosslinking. Results show that the optimized amount of enzyme is 10.98 units for the slurried enzyme, 3.66 units for the adsorbed one and 7.32 units for the crosslinked one, and the corresponding hydrogen evolution rates are 33.04, 148.58 and 234.88 μmol h −1, respectively. The immobilized enzyme, specifically the chemically crosslinked one, seems to be much superior to the slurried enzyme, due to the enhanced charge-transfer process that is caused by the lower electrical resistance between the enzyme and the ATTE. This results in a greater number of accepted electrons and a larger amount of enzymes able to deal with the electrons.

Inverted type bulk-heterojunction organic solar cell using electrodeposited titanium oxide thin films as electron collector electrode

We developed an inverted type bulk-heterojunction organic solar cell with 1 cm 2 active area using a fluorine-doped tin oxide/electrodeposited amorphous (TiO x ) or anatase (TiO 2) titanium oxide electrode instead of the low work-functional electrode such as Al. The cell with TiO 2 showed the power conversion efficiency ( η) of 2.5% by irradiating AM 1.5–100 mW cm − 2 simulated sunlight. While, the performance of the cell with TiO x was almost maintained in an ambient atmosphere under continuous light irradiation of 10 h, although slightly small initial η value of 2.1% was observed.

Performance & Application based on Graphite/Activated Carbon with Titanium Dioxide Electrode for Electrochemical Capacitor

The capacitive properties of activated carbon electrodes with CNT coated titanium oxide composite electrode were investigated in PC containing TEABF4 or LiPF6 by galvanostatic charge/discharge and electrochemical impedance spectroscopy. The composite electrode showed relatively good electrochemical behaviors better than activated carbon electrode. During cycling, the composite electrode presented 275 mF/cm2 of specific capacitance in TEABF4/PC and reduced resistance.

Characterization of tungsten–titanium oxide electrode for electrochromic applications

Titanium oxide films are of critical importance for the electrochromic device technology. The substrate, a conductive glass being coated with indium tin oxide (ITO) thin films, was deposited tungsten and titanium oxide by pulsed co-sputtering deposition system. The film thickness increased with the ion beam power. However, the slope of the curve of thickness against power at an ion beam power of less than 300W was greater than that at a power of 400 or 500W. A high ion beam power resulted produced a crystalline structure, as revealed by X-ray diffraction (XRD). Moreover, increasing the ion beam power resulted in the high Li-ions transport. The electrochromic behavior was optimal at an ion beam power of 200W.

Performance & Application based on Graphite/Activated Carbon with Titanium Dioxide Electrode for Electrochemical Capacitor

not Available.

Highly durable inverted-type organic solar cell using amorphous titanium oxide as electron collection electrode inserted between ITO and organic layer

An indium tin oxide/titanium oxide/[6,6]-phenyl C 61 butyric acid methyl ester:regioregular poly(3-hexylthiophene)/poly(3,4-ethylenedioxylenethiophene):poly(4-styrene sulfonic acid)/Au type organic solar cell (ITO/TiO x /PCBM:P3HT/PEDOT:PSS/Au) with 1 cm 2 active area, which is called “inverted-type solar cell”, was developed using an ITO/amorphous titanium oxide (TiO x ) electrode prepared by a sol–gel technique instead of a low functional electrode such as Al. The power conversion efficiency ( η) of 2.47% was obtained by irradiating AM 1.5G-100 mW cm −2 simulated sunlight. We found that a photoconduction of TiO x by irradiating UV light containing slightly in the simulated sunlight was required to drive this solar cell. The device durability in an ambient atmosphere was maintained for more than 20 h under continuous light irradiation. Further, when the air-stable device was covered by a glass plate with a water getter sheet which was coated by an epoxy-UV resin as sealing material, the durability was still higher and over 96% of relative efficiency was observed even after continuous light irradiation for 120 h.

Photoanodic and cathodic role of anodized tubular titania in light-sensitized enzymatic hydrogen production

An anodized tubular titania (TiO 2) electrode (ATTE) is prepared and utilized as both a photoanode and a cathode in a photoelectrochemical system designed to split water into hydrogen (for use in fuel cells) with the assistance of a hydrogenase enzyme and an external bias of 1.5 V. In particular, the cathodic ATTE acts as a substrate for the immobilization of the enzyme due to its large surface area that results from the tubular oxides. The optimum molar concentration of KOH in anode and cathode compartments is 1.0 M and the optimum amount of enzyme for the cathode is ca. 3.66 units per geometrical unit area (1 cm × 1 cm) of the cathodic ATTE. After exposure to air for three weeks, the enzyme shows a hydrogen evolution rate that is 85.8% of that of an argon-purged enzyme. The rate of hydrogen evolution is increased from ca. 65 (in a slurry system) to more than 140 μmol cm −2 h −1, even after eliminating the electron relay (methyl viologen) and costly platinum counter electrode.

Photochromism and Electrochemistry of a Dithienylcyclopentene Electroactive Polymer

A bifunctional substituted dithienylcyclopentene photochromic switch bearing electropolymerisable methoxystyryl units, which enable immobilization of the photochromic unit on conducting substrates, is reported. The spectroscopic, electrochemical, and photochemical properties of a monomer in solution are compared with those of the polymer formed through oxidative electropolymerization. The electroactive polymer films prepared on gold, platinum, glassy carbon, and indium titanium oxide (ITO) electrodes were characterized by cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The thickness of the films formed is found to be limited to several monolayer equivalents. The photochromic properties and stability of the polymer films have been investigated by UV/vis spectroscopy, electrochemistry, and XPS. Although the films are electrochemically and photochemically stable, their mechanical stability with respect to adhesion to the electrode was found to be sensitive to both the solvent and the electrode material employed, with more apolar solvents, glassy carbon, and ITO electrodes providing good adhesion of the polymer film. The polymer film is formed consistently as a thin film and can be switched both optically and electrochemically between the open and closed state of the photochromic dithienylethene moiety.

Method to Increase the Surface Area of Titania Films and Its Effects on the Performance of Dye-Sensitized Solar Cells

We report a method to increase the surface area of the titania films used as the anodes of dye-sensitized solar cells (DSSCs) by applying additional titania-coating. The modification was achieved by spin-coating a coating solution that contained a surfactant with a titania source onto the titania electrodes, followed by calcination. Previous similar attempts without a surfactant all reported decreased surface areas. We fabricated DSSCs by using the modified titania films as the anode and measured their performances. The increased surface area increased the amount of adsorbed dyes, which resulted in increased current densities. At the same time, the titania-coating increased both the open-circuit voltage and the current density by reducing the charge-recombination rates of the injected electrons, similar to the results of literatures. Therefore, our method shows an additional mechanism to increase the current density of DSSCs in addition to the other mechanisms of surface modifications with titania-coatings.

Enhanced photoelectrochemical method for linear DNA hybridization detection using Au-nanopaticle labeled DNA as probe onto titanium dioxide electrode

A photoelectrochemical method was proposed to detect DNA hybridization using Au nanoparticle modified DNA as one probe on TiO2 substrate, in which the TiO2 substrate was used not only as DNA anchors but also as the signal transducers. Hybridization between the probe and the target DNA oligonucleotides was confirmed by the decreased photocurrent of the TiO2 electrode. Compared with non-label probe, Au nanoparticles enhanced the photocurrent shifts after the hybridization. The photocurrent decreased with increasing the concentration of target DNA, indicating that this method could be used for quantitative measurements, and the discrimination of the complementary from mismatched DNA. Furthermore, the hybridization binding constant was obtained and photocurrent generation mechanism was discussed. The major advantages of this photochemical method are speed, simplicity and excellent specificity. This method provides a platform for studying a wide variety of biological processes using photoelectrochemical method.

Optical waveguide spectroscopy study of the transport and binding of cytochrome c in mesoporous titanium dioxide electrodes.

The increasing interest in using nanoporous and mesoporous films for a range of applications including sensors and solar cells has created a concomitant demand for the development of analytical methodologies to study the films in situ. Especially important is the ability to quantify the filling of such films with guest molecules, be they dyes or proteins. In this paper we have demonstrated a simple methodology for the highly sensitive monitoring of nanoporous titania films as protein is both adsorbed in, and removed from the film matrix: optical waveguide mode spectroscopy. Porous titania films of thickness between 0.5 and 1.5 μm were created on gold slides by the deposition of a colloidal suspension of titanium dioxide nanoparticles with a phytate binder. Absorption of cytochrome c into the highly porous titanium structure was followed by both optical waveguide spectroscopy (OWS) and electrochemistry. OWS showed that saturation occurred when 27% of the pore volume was filled with cytochrome c and initial diffusion coefficients of 10−17 m2 s−1 were measured for cytochrome c within the pores. Electrochemical measurements displayed good agreement with OWS measurements and showed that the protein permeated all the way through the porous film to the gold substrate. The results further demonstrate that the OWS method is more than two orders of magnitude more sensitive than classical electrochemical methods conventionally used to study such systems, and is not dependent on having a redox-active adsorbate.

Spectral Response of Opal-Based Dye-Sensitized Solar Cells

Herein we present an experimental study of the spectral dependence of the photogenerated current of opal-based solar cells. We analyze the incident photon-to-current conversion efficiency (IPCE) for dye-sensitized solar cells in which colloidal crystals are introduced in different configurations. We prove that a dye-sensitized nanocrystalline titanium oxide electrode moulded in the shape of an inverse opal shows a decrease of efficiency for the spectral region in which a photonic stop band opens up. Contrarily, when a standard thin film of disordered titania nanocrystallites is coupled to an inverse opal, the mirror effect of the photonic crystal at band gap frequencies increases the light harvesting efficiency of the cell and thus the IPCE. This effect is further demonstrated by coupling an inverse opal multilayer to a homogeneous electrode, with two well-defined spectral ranges of increased photogenerated current being detected.

Enhanced Photoconductivity in Thin‐Film Semiconductors Optically Coupled to Photonic Crystals

Photonic crystals (PCs) are a remarkable class of materials wherein the periodicity of the index of refraction can be engineered to obtain unprecedented optical properties that have no parallels in other materials. Some interesting optical phenomena inherent to PCs include second harmonic generation, the superprism effect, photonic bandgaps (PBGs), and “slow photons”. It is also possible to achieve light localization within PCs by introducing defects by design that disrupt the periodicity of the index of refraction, allowing the creation of localized photon modes having frequencies that lie within the PBG of the PC. The ability of defect modes in PCs to confine photons is expected to provide the infrastructure for optical circuits. Moreover, lossless light propagation along PBG waveguides with coupling to quantum dots or optical cavities could provide new avenues for quantum information processing. Considering that an ideal crystal is a periodic structure extending to infinity in all directions, the planar surface of a PC can actually be regarded as a 2D crystal defect. Accordingly, it is interesting to note that as in the case of defects introduced into the bulk of a PC, light can also be localized at the PC surface. For instance, it has been known for quite some time that light can propagate in localized modes along the surface of a periodically layered medium, which effectively acts a 1D PC. Recently, Miguez and co-workers have investigated photon surface resonant modes in thin films coupled to PCs. One structure studied in this work has been fabricated by depositing a homogeneous silica layer on top of a silica inverse colloidal crystal. The results of the study indicate that upon illumination of this layer of silica with normally incident light at certain frequencies within the bandgap of the PC, the electromagnetic field near the PC/film interface is amplified with respect to the electromagnetic fields in the surrounding regions. This phenomenon arises from partial light localization at the modified PC surface, which behaves as an optical dopant or defect. Structures similar to those studied by Miguez and co-workers have been used to enhance the efficiency of Gratzel cells comprising dye-sensitized titania electrodes shaped as PCs. The observed improvements were initially attributed to slow photons propagating through the PC structure; however, it has subsequently been pointed out that this hypothesis does not account for all of the observed results and that the improvements arise primarily from light localization at the surface of the structure. The objective of the research reported herein is two-fold. The first objective is to demonstrate that the photoconductivity of a semiconductor film can be amplified by optically coupling the film to a PC surface. Indeed, in this construct, the film does not itself need to be periodically structured. The second objective is to show that the photoconductivity enhancement attainable from surface resonant modes in thin films coupled to PC surfaces is greater than the enhancement that can be achieved by depositing a perfect mirror (PM) onto the backside of this film. To address the first objective, we have compared the measured quantum efficiencies (QEs) of a thin hydrogenated amorphous silicon (a-Si:H) film deposited on a glass substrate for two different structures. One structure is the film–PC construct shown in Figure 1a, wherein an opaline PC is deposited onto the backside of a thin a-Si:H film, whereas the secC O M M U N IC A IO N

Increase of the Efficiency of Quasi‐Solid State Dye‐Sensitized Solar Cells by a Synergy between Titania Nanocrystallites of Two Distinct Nanoparticle Sizes

Nanocrystalline titanium dioxide electrodes are standard choice for the construction of Dye-sensitized Solar Cells (DSC). Nanocrystallinity, small number of defect sites, optimized electrical conduct between nanoparticles and sufficient active surface area are crucial factors, which determine the quality of the electrodes and, subsequently, the overall efficiency of the cell. The maximum efficiency of DSC ever reported was around 10.4 % and referred to cells based on a liquid electrolyte and on non-transparent Light-Scattering Electrodes (LSE) of 18 m thickness. For several years, we have made efforts to reach comparable cell efficiencies with DSC’s employing thinner transparent TiO2 electrodes by optimizing the synthesis and deposition procedures. The motive of these efforts is related with the prospect of utilizing such transparent cells as photovoltaic windows. LSEs do not offer this possibility but, instead, they entrap light and result in higher cell efficiencies. In order for Transparent Electrodes (TE) to reach performance of LSE, it is necessary that the former are deposited with optimized parameters: good quality nanocrystals without defects, compact enough films to allow sufficient electric contact between nanoparticles and sufficient mesoporosity to allow dye-sensitizer and electrolyte filling. We have achieved this goal by synthesizing titania through the sol-gel procedure in the presence of surfactant templates under ambient conditions. Spatially isolated self-organized entities seem to encourage formation of good quality nanosrystalline particles. For example, reverse micelles dispersed in an organic solvent, originally used to synthesize CdS nanocrystals proved excellent templates for TiO2 nanocrystals as well. However, reverse micelles are rather costly and less environmentally friendly systems. It has been found that simpler systems can offer similar results and more handy experimental procedures. Thus organic acid solvolysis of titanium isopropoxide in the presence of the non-ionic surfactant Triton X-100 (polyoxyethylene-(10) isooctylphenyl ether), can assist nanocrystalline anatase deposition with nanoparticle size of around 12 nm and active surface area around 110 m g. About 2 lm thick TE were made by subsequent layer deposition by dipping under ambient conditions. Organic acid solvolysis in the absence of water has the advantage of slow sol-gel evolution that allows surfactant assembling and shell formation around titania core. The choice of this route was rewarding. Indeed, as it has been previously reported, such electrodes gave DSCs with efficiency > 9 %, i.e., not far from the reported maximum. The DSC of ref. [4] was a non-optimized cell employing cis-bis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)-ruthenium(II) [abbreviated RuL2(NCS)2] as dye sensitizer and I3 /I in acetonitrile as liquid redox electrolyte. When the same electrodes were used to construct quasi-solid state DSCs, where the redox couple I3 /I was incorporated into a sol-gel nanocomposite organic-inorganic gel, efficiency dropped but it was still at satisfactory levels of 5.3 %. This efficiency decrease was due to current decrease, which in turn was due to lower ionic mobility in the gel. Gel electrolytes based on nanocomposite organic-inorganic materials is our approach to ensure cell stability and avoidance of electrolyte leakage. In the present work we are testing an alternative method of titania deposition, in which we try to further increase cell efficiency by producing LSEs, using new organic templates or combined templating methods. It will be seen that indeed LSEs do increase cell efficiency by an important percentage, however, this increase should be appreciated by also taking into account the disadvantages related with the loss of transparency. The cell described in the following paragraphs is made by using a titania electrode that consists of two layers: a rough nanocrystalline titania film making a light-scattering layer and a compact nanocrystalline titania layer filling the voids and standing on the top of the lower layer. As a matter of fact, the deposition of the second layer did not produce a separate stratum and did not increase the thickness of the film but it was accommodated within the voids and the pores of the first layer. The assembly made a LSE. The efficiency of this cell climbed to 6.9 %, a value that is more than 20 % higher than that of the corresponding cell employing a single transparent layer. This efficiency is very high, if we take into account the fact that it concerns a solid-state device. Another interesting feature of this cell is the employment of a silicabased nanocomposite organic-inorganic gel as host for the I3 / C O M M U N IC A TI O N

Superior Electrocatalysis of Spin-coated Titanium Oxide Electrodes for the Electrochemical Ozone Production

Abstract A cheap spin-coated Si/TiOx/Pt/TiOx electrode is fabricated and proved to possess an excellent catalysis for ozone electrogeneration. A high current efficiency of 2.5% was obtained at 33 mA cm−2 in 10 mM HClO4 at room temperature.

Application of Anodic Titanium Oxide to Dye-Sensitized Solar Cells

Dye-sensitized solar cells were fabricated using anodized titanium oxide. An aqueous solution of 0.5 wt % HF was used for the electrolyte and platinum plate was used for the counter electrode in the anodizing process at a voltage of 20 V. We obtained well-arranged titanium oxide nanotubes with diameters of 80-150 nm. The anodic titanium was coated with the dye (Ruthenium 535 bis-TBA). A dye-sensitized solar cell was fabricated with lodolyte PMI-50 (Solaronix™) as the electrolyte and a Pt (200 nm)/ Ti (50 nm)/ glass substrate as the counter electrode. The short circuit current (I SC ), open circuit voltage (V oc ), fill factor (FF) and energy conversion efficiency of this cell were 0.54 mA/cm 2 , 0.103 V, 39 % and 0.0022%, respectively. When a current density of 2.0x10 -3 mA/cm 2 was applied to the titanium oxide electrode, the I sc , V oc , FF and energy conversion efficiency were 0.24 mA/cm 2 , 0.675 V, 30 % and 0.050 %, respectively. When the cells were coated with the dye and current was applied, the I sc , V oc , FF and energy conversion efficiency were 0.88 mA/cm 2 , 0.54 V, 24 % and 0.11 %, respectively.