Nanocrystalline Electrodes Research Articles

Carbon Doped Nano-Crystalline TiO<sub>2</sub> Photo-Active Thin Film for Solid State Photochemical Solar Cells

Carbon doped titanium dioxide (C-TiO2) is considered as a promising photocatalytic material due to its optical absorption extended in the visible region compared to pure TiO2. However, in the field of photovoltaic’s, use of C-doped nano-crystalline titanium dioxide (C-TiO2) electrodes for light absorption has been considered to be unnecessary so far. In this context, we report here on the use of C-TiO2 nano-crystalline electrodes in photochemical solar cells devices (PCSC). Carbon doping has reduced the band gap of TiO2 to 2.41 eV and 2.25 eV with increase in the doping extent for the 9 mM C-TiO2 and 45 mM C-TiO2 respectively. The C-TiO2 electrodes were first used as photo electrodes for solar cells, exhibiting JSC of 1.34651 mA/cm2, VOC 0.683 V, FF 50.23% and η 0.46%. for the 9 mM C-TiO2 and exhibiting JSC of 1.34651 mA/cm2, VOC 0.815 V, FF 54.3% and η 0.59% for the 45 mM C-TiO2. The fabricated solar cell devices have shown an increase in VOC of up to 0.815 V, which is higher than that of 0.7 V for dye sensitized solar cells. The doping of carbon in TiO2 lattice was closely studied by SEM, XRD, RS and UV-Vis spectroscopy.

Ex Situ CdSe Quantum Dot-Sensitized Solar Cells Employing Inorganic Ligand Exchange To Boost Efficiency

We present an effective way to boost the as-synthesized CdSe quantum dot-sensitized solar cells (QDSSCs) performance by introducing an inorganic ligand exchange strategy into this traditional system. Inorganic ligand exchange, to the best of our knowledge, is designed for the first time for CdSe-based QDSSCs, and it features low-cost, easy operation, and repeatable process. The route involves the direct deposition of the CdSe quantum dots (QDs), which were initially capped with trioctylphosphine (TOP) ligands onto mesoporous TiO2 nanocrystalline electrodes and followed by a post-treatment of the sensitized photoanode films with sulfur ions (S2–) solution. Here, changes in surface chemical status of CdSe QDs during the inorganic ligand exchange process and the influence of ligand exchange on the electron’s ultralfast transfer between nanoparticles were investigated through XPS and femtosecond transient grating techniques, respectively. With the inorganic ligand passivated CdSe QDs, the QDSSCs exhibited a power conversion efficiency of 3.17% (AM1.5G, 100 mW/cm2), 65% higher than that of the organic ligands capped QDSSCs.

Cycling behaviour of sponge-like nanostructured ZnO as thin-film Li-ion battery anodes

Single phase wurtzitic porous ZnO thin films are obtained by a simple two-step method, involving the sputtering deposition of a sponge-like metallic Zn layer, followed by a moderately low temperature treatment for the complete zinc oxidation. Thanks to its 3D nanostructuration, the superimposition of small branches able to grow in length almost isotropically and forming a complex topography, sponge-like ZnO can combine the fast transport properties of one dimensional material and the high surface area usually provided by nanocrystalline electrodes. When galvanostatically tested in lithium cell, after the initial decay, it can provide an almost stable specific capacity higher than 50μAhcm−2 after prolonged cycling at estimated 0.7C, with very high Coulombic efficiency.

Use of boron-doped diamond electrode pre-treated cathodically for the determination of trace metals in honey by differential pulse voltammetry

In this work, a methodology for the determination of Cu(II), Pb(II), Cd(II) and Zn(II) in honey by differential pulse anodic stripping voltammetry (DPASV) on a nano crystalline boron-doped diamond electrode (BDD) is proposed. A 33 Box-Behnken Design, 32 Factorial Design and Principal Components Analysis (PCA) were performed to optimise the electrochemical conditions. According to the response surfaces obtained, it was stipulated for Zn analysis a pH of 4, Ed of −1.50 V and td of 240 s. For simultaneous analysis of Cu, Pb and Cd a pH of 1, Ed of −0.95 V and td of 240 s was used. Detection limits of 0.37, 0.40, 1.28 and 0.16 μg L−1 were found for Cu, Pb, Cd and Zn, respectively. The analyte concentration ranged between 0.242 and 1.38 mg L−1 for Cu, 0.129 and 0.918 mg L−1 for Pb and 0.819 and 2.492 mg L−1 for Zn, while no significant concentrations were found during Cd analyses. The honey samples were also analysed by Hg-coated glassy carbon electrode and graphite furnace atomic absorption spectrometry (GF AAS) through non-parametric ANOVA and no evidence of significant differences among the results was observed within a 95% confidence interval.

Charge Transfer in Nanocrystalline Semiconductor Electrodes

Nanocrystalline electrodes in liquid junction devices possess a number of unique properties arising from their convoluted structure and the dimensions of their building units. The light-induced charge separation and transport in photoelectrochemical systems using nanocrystalline/nanoporous semiconductor electrodes is discussed here in connection with the basic principles of the (Schottky) barrier theory. Recent models for charge transfer kinetics in normal and unipolar (dye-sensitized) cells are reviewed, and novel concepts and materials are considered.

Monodisperse and Inorganically Capped Sn and Sn/SnO2 Nanocrystals for High-Performance Li-Ion Battery Anodes

We report a facile synthesis of highly monodisperse colloidal Sn and Sn/SnO2 nanocrystals with mean sizes tunable over the range 9-23 nm and size distributions below 10%. For testing the utility of Sn/SnO2 nanocrystals as an active anode material in Li-ion batteries, a simple ligand-exchange procedure using inorganic capping ligands was applied to facilitate electronic connectivity within the components of the nanocrystalline electrode. Electrochemical measurements demonstrated that 10 nm Sn/SnO2 nanocrystals enable high Li insertion/removal cycling stability, in striking contrast to commercial 100-150 nm powders of Sn and SnO2. In particular, reversible Li-storage capacities above 700 mA h g(-1) were obtained after 100 cycles of deep charging (0.005-2 V) at a relatively high current of 1000 mA h g(-1).

The impact of enzyme orientation and electrode topology on the catalytic activity of adsorbed redox enzymes

It is well established that the structural details of electrodes and their interaction with adsorbed enzyme influences the interfacial electron transfer rate. However, for nanostructured electrodes, it is likely that the structure also impacts on substrate flux near the adsorbed enzymes and thus catalytic activity. Furthermore, for enzymes converting macro-molecular substrates it is possible that the enzyme orientation determines the nature of interactions between the adsorbed enzyme and substrate and therefore catalytic rates. In essence the electrode may impede substrate access to the active site of the enzyme. We have tested these possibilities through studies of the catalytic performance of two enzymes adsorbed on topologically distinct electrode materials. Escherichia coli NrfA, a nitrite reductase, was adsorbed on mesoporous, nanocrystalline SnO2 electrodes. CymA from Shewanella oneidensis MR-1 reduces menaquinone-7 within 200nm sized liposomes and this reaction was studied with the enzyme adsorbed on SAM modified ultra-flat gold electrodes.

An integrated passive impedance-loaded SAW sensor

An integrated passive impedance-loaded SAW H2S sensor working at room temperature has been presented in this paper. The sensor consists of a SAW transponder with delay line structure and a resistive H2S sensor as an impedance-loaded sensor. The SAW delay line was fabricated on a 128° LiNbO3 substrate and its center frequency is 233MHz. The resistive sensor composed of the nano-crystalline SnO2 film and aluminum electrodes was also fabricated on the same substrate. The gas sensing properties of the resistive H2S sensor have been tested separately. In order to maximize the sensitivity of the whole sensor, the resistance of the impedance-loaded sensor was adjusted to match the output impedance of the SAW interdigital transducer (IDT) by changing the resistivity of the Sb-doped SnO2 nano-crystalline films and optimizing the electrode structure. The variation in the return loss magnitude was increased to 2.51dB. Finally, the impedance-loaded SAW sensor was configured and measured wirelessly for various H2S concentrations at room temperature. The measurement results show that the proposed H2S sensor not only has good repeatability and high sensitivity but also is capable of passive wireless detection at room temperature.

Electrochemically active nanocomposites of Li4Ti5O12 2D nanosheets and SnO2 0D nanocrystals with improved electrode performance

Electrochemically active nanocomposites consisting of Li4Ti5O12 2D nanosheets and SnO2 0D nanocrystals are synthesized by the crystal growth of tin dioxide on the surface of 2D nanostructured lithium titanate. According to powder X-ray diffraction and electron microscopic analyses, the rutile-structured SnO2 nanocrystals are stabilized on the surface of spinel-structured Li4Ti5O12 2D nanosheets. The homogeneous hybridization of tin dioxide with lithium titanate is confirmed by elemental mapping analysis. Ti K-edge X-ray absorption near-edge structure and Sn 3d X-ray photoelectron spectroscopy indicate the stabilization of tetravalent titanium ions in the spinel lattice of Li4Ti5O12 and the formation of SnO2 phase with tetravalent Sn oxidation state. The electrochemical measurements clearly demonstrate the promising functionality of the present nanocomposites as anode for lithium secondary batteries. The Li4Ti5O12–SnO2 nanocomposites show larger discharge capacity and better cyclability than do the uncomposited Li4Ti5O12 and SnO2 phases, indicating the synergistic effect of nanocomposite formation on the electrode performance of Li4Ti5O12 and SnO2. The present experimental findings underscore the validity of 2D nanostructured lithium titanate as a useful platform for the stabilization of nanocrystalline electrode materials and also for the improvement of their functionality.

Co-Sedimentation of TiO<SUB>2</SUB> Nanoparticles and Polymer Beads to Fabricate Macroporous TiO<SUB>2</SUB> Photoelectrodes

Dye-sensitized solar cells based on highly porous nanocrystalline TiO2 films have drawn considerable attention due to their high conversion efficiency and low production cost. TiO2 nanocrystalline electrodes have been investigated extensively as a key material. In this study, we discuss dye-sensitized solar cells based on macroporous TiO2 films using a highly-dispersed aqueous solution of TiO2 nanoparticles and polymeric particles. After drying this solution on the conducting glass substrate, the sacrificial polymer particles were removed selectively by thermal sintering at high temperatures over 400 degrees C or chemical treatment at the low temperature of 150 degrees C. This method provides the flexible control of TiO2 fractions or pore size or fabrication temperature. Also highly-dispersed TiO2 particles with a high crystallinity would provide a promising solution on low-temperature process for flexible DSSCs.

Efficiency enhancement in dye sensitized solar cells through co-sensitization of TiO2 nanocrystalline electrodes

We have demonstrated that co-sensitization of TiO2 electrode with an inexpensive rhodamine 19 perchlorate laser dye along with N3 dye not only enhances the incident-photon-to-current conversion efficiency but also reduces dark current. Consequently, the devices yield an average power efficiency of 4.7% as against 2.3% and 0.6% obtained for N3 and rhodamine 19 perchlorate dye based devices, respectively. The improvement in efficiency is attributed to the enhanced dye absorption on TiO2 electrode as well as reduced dye aggregation that resulted from the usage of two dyes on different anchoring sites of single TiO2 electrode.

Nano-TiO<sub>2</sub> for Dye-Sensitized Solar Cells

Photovoltaics are amongst the most popular renewable energy sources and low-cost solar cell technologies are making progress to the market. Research on dye-sensitized solar cells (DSSCs) usually based on nanocrystalline TiO2 has been extensively pursued, and the number of papers and patents published in this area has grown exponentially over the last ten years. Research efforts have largely focused on the optimization of the dye, but recently the TiO2 nanocrystalline electrode itself has attracted more attention. It has been shown that particle size and shape, crystallinity, surface morphology and chemistry of the TiO2 material are key parameters to be controlled for optimized performance of the solar cell. This article will review the most recent research activities on nanostructured TiO2 for improvement of the DSSC performance.

Nano-TiO2 for Solar Cells and Photocatalytic Water Splitting: Scientific and Technological Challenges for Commercialization

Nanosized titanium dioxide (nano-TiO2) particles are used in diverse products and devices, including photocatalytic water splitting and solar cells whose successful commercialization is still facing scientific and technologi- cal challenges. Particularly, dye-sensitized solar cells (DSSCs) have recently attracted a lot of attention. The number of papers and patents published in this area has grown exponentially over the last ten years. However, at the present, commercial devices are of small sizes and produced in limited quantities, thus addressing niche markets. Research efforts have largely focused on the optimization of the dye, but the TiO2 nanocrystalline electrode itself also needs to be optimized. It has been shown that particle size and shape, crystallinity, surface morphology and chemistry of the TiO2 material are key parameters to be controlled for enhanced performance of the cell. This article gives an overview of the state-of-the-art on nano-TiO2 for applications in photocatalytic water splitting and, more specifically, in DSSCs. After a brief analysis of the commercial perspectives of DSSCs and of the remaining challenges for their successful commercialization, our approach to the control of the nano-TiO2 surface chemistry for improvement of the DSSC performance is briefly introduced.

10% Efficiency Dye-sensitized Solar Cells Using P25 TiO2 Nanocrystalline Electrode Prepared by a Bead-milling Method

Abstract Dispersions of TiO2 nanoparticles were prepared from titania powder (P25, Degussa) using a bead-mill method. The dispersion was controlled by the mixing time and was observed using dynamic laser-light scattering. TiO2 screen-printing pastes were prepared from the TiO2 dispersions for application as photoelectrodes in dye-sensitized solar cells (DSSCs). The coated nanocrystalline TiO2 electrodes were evaluated using X-ray diffraction (XRD) and a haze meter. The shape and crystallinity of the TiO2 nanoparticles were not changed, but the transparency was improved by the bead-milling process. However, aluminum contamination on the TiO2 surface was found to increase with bead-milling time. A TiO2 paste prepared from an optimized dispersion was used to fabricate a DSSC with 10% photoenergy-conversion efficiency.

Dye-sensitized solar cell based on optically transparent TiO 2 nanocrystalline electrode prepared by atomized spray pyrolysis technique

Preparation of crack-free thin films of interconnected and non-agglomerated TiO 2 nanoparticles on electronically conducting fluorine doped tin oxide surfaces is instrumental in designing and developing transparent dye-sensitized solar cells (DSCs). A novel technique called “Atomized Spray Pyrolysis” (ASP) has been designed and developed to achieve such perfectly transparent thin films. Optical transmittance of TiO 2 films produced on FTO surface by this ASP method has been compared with those obtained by doctor-blading and by hand spray methods and found that the atomized spray pyrolysis technique give films with high transparency. Dye adsorption per gram of TiO 2 is 2.16 times higher in the sample produced by the ASP method when compared to the film produced by the hand spray method and is 1.60 times higher than that produced by the doctor-blading method using a commercially available TiO 2 nanocrystalline paste. SEM studies show the presence of interconnected discrete particles in the film produced by the ASP method. The fill factor (ff) remains almost constant for the cells with thickness from 6 μm to 13 μm but the highest photovoltage and photocurrent were found in ∼10 μm film based DSC which gave 8.2% conversion efficiency at AM 1.5 irradiation for cells of 0.25 cm 2 active area.

Current Trends in Materials for Dye Sensitized Solar Cells

Here, we intend to review those patents related with the technology of dye sensitized solar cells. In particular we discuss patents and papers that enable metal oxide layer to be more controllable and feasible for applications, and new and innovative dyes, sensitizers and electrolytes with promising features. Finally various methods were reviewed for fabricating semiconductor layers and complete DSSC devices focusing on the mass production of photovoltaic cells.

Enhanced electrochemical characteristics of as-spun nanocrystalline and amorphous Mg 2Ni-type alloy electrodes

The nanocrystalline and amorphous Mg 2Ni-type electrode alloys with nominal compositions of Mg 2Ni 1− x Mn x ( x = 0, 0.1, 0.2, 0.3, 0.4) are synthesized by melt-spinning technique. The spun alloy ribbons with a continuous length, a thickness of about 30 μm and a width of about 25 mm are obtained. The structures of the as-spun alloy ribbons are characterized by XRD, SEM and TEM. The electrochemical characteristics as well as the electrochemical impedance spectrums (EIS) of the as-spun alloy electrodes are measured. The hydrogen diffusion coefficients ( D) in the alloys were obtained by virtue of potential-step method. The results show that the as-spun ( x = 0) alloy holds a typical nanocrystalline structure, whereas the as-spun ( x = 0.4) alloy displays a nanocrystalline and amorphous structure, confirming that the substitution of Mn for Ni evidently intensifies the glass forming ability of the Mg 2Ni-type alloy. The substitution of Mn for Ni significantly improves the electrochemical hydrogen storage performances of the alloys, involving the discharge capacity and the electrochemical cycle stability. Furthermore, the high rate discharge ability (HRD), the electrochemical impedance spectrum (EIS) and the potential-step measurements all indicate that the electrochemical kinetics of the alloy electrodes first increases then decreases with rising the amount of Mn substitution.

Femtosecond Diffuse Reflectance Transient Absorption for Dye-Sensitized Solar Cells under Operational Conditions: Effect of Electrolyte on Electron Injection

By applying diffuse reflectance transient absorption spectroscopy to dye-sensitized solar cells under operational conditions, we were able to directly correlate interfacial electron injection kinetics from a Ru complex sensitizer to a TiO(2) nanocrystalline electrode with the incident photon to current efficiency values. It was revealed that ionic liquid electrolytes reduced the initial electron injection efficiency by suppression of the approximately 100 ps process.

Two-Dimensional Graphene Bridges Enhanced Photoinduced Charge Transport in Dye-Sensitized Solar Cells

As a novel two-dimensional (2D) material, graphene shows great benefits in electric and material science. Compared to 1D nanomaterials, it may show more excellent properties. Here, we introduced graphene as 2D bridges into the nanocrystalline electrodes of dye-sensitized solar cells, which brought a faster electron transport and a lower recombination, together with a higher light scattering. On the basis of these advantages, the short-circuit current density was increased by 45% without sacrificing the open-circuit voltage, and the total conversion efficiency was 6.97%, which was increased by 39%, comparing with the nanocrystalline titanium dioxide photoanode, and it was also much better than the 1D nanomaterial composite electrode.

TiO 2- and ZnO-based solar cells using a chlorophyll a derivative sensitizer for light-harvesting and energy conversion

TiO 2- and ZnO-based solar cells sensitized by a chlorophyll a derivative (methyl trans-3 2-carboxy-pyropheophorbide a) were fabricated and compared. The TiO 2-based solar cell produces higher values for the short-circuit photocurrent ( J sc), open-circuit photovoltage ( V oc), and energy-to-electricity conversion efficiency ( η) than the ZnO-based solar cell. The observed ATR-FTIR data on the dye-sensitized semiconductor electrodes and the spectra estimated from the density functional theory (DFT) suggest that the dye sensitizer is bound to TiO 2 with both the bidentate chelating and monodentate modes but is bound to ZnO with the monodentate mode exclusively. The frontier orbitals of the dye molecule bound to semiconductors suggest that the HOMO-2 and LUMO + 2 orbitals of the dye sensitizer do not participate in electron transfer processes for the dye–ZnO system, resulting in a lower J sc value and a relatively narrow response for the incident photon-to-current conversion efficiency in the solar cell. Transition component analysis based upon the time-dependent DFT results explains well the experimental UV–vis spectra and difference in the η values between the dye-sensitized solar cells based upon TiO 2 and ZnO nanocrystalline electrode materials.