Thiocyanate ligand substitution kinetics of the solar cell dye Z-907 by 3-methoxypropionitrile and 4-tert-butylpyridine at elevated temperatures

The dye-sensitized solar cell dye Z-907, [RuLL′(NCS)₂] may loose a thiocyanate ligand at elevated temperatures (80-100 °C) by ligand exchange with the solar cell additive 4-tert-butylpyridine (4-TBP) or the electrolyte solvent 3-methoxypropionitrile (3-MPN). The mechanism in homogeneous solution proceeds via three equilibrium reactions Eqs. (1)-(3) with the solvent complex [RuLL′(NCS)(3-MPN)] as an intermediate:[RuLL′(NCS)₂]+3-MPN=[RuLL′(NCS)(3-MPN)]⁺+NCS⁻ (1)[RuLL′(NCS)(3-MPN)]⁺+4-TBP=[RuLL′(NCS)(4-TBP)]⁺+3-MPN (2)[RuLL′(NCS)₂]+4-TBP=[RuLL′(NCS)(4-TBP)]⁺+NCS⁻ (3)A similar mechanism describes the heterogeneous substitution reactions of Z-907 attached to the surface of TiO₂ particles with 3-MPN and 4-TBP. All the six homogeneous and heterogeneous rate constants were obtained at 100 °C by monitoring the decay of Z-907 and product formation in test-tube experiments by HPLC coupled to UV/vis and electrospray mass spectrometry.A half-lifetime t_1/2=150 h was obtained for the Z-907 dye bound to TiO₂ nanocrystalline particles at 85 °C in the presence of 4-TBP and 3-MPN. Dye-sensitized solar cells (DSC) with Z-907 as a sensitizer and application of the so-called “non-robust” electrolytes containing 4-TBP and 3-MPN is therefore not expected to be able to pass a 1000 h thermal stress test at 85 °C. Addition of thiocyanate to the cell electrolyte may however, eliminate or reduce the problems caused by dye thiocyanate ligand substitution in DSC cells.     

The synthesis and characterization of carbon dots and their application in dye sensitized solar cell

Carbon dots (CDOTs) are increasingly becoming popular in the areas ranging from sensing and bioimaging to electronics. The interesting optical properties of CDOTs make it vital to explore its potential in the development of sustainable energy. In this work, one-step hydrothermally synthesized CDOTs were used as sensitizing agent in the fabrication of dye sensitized solar cell. The fabrication of the CDOT-based dye sensitized solar cell and its performance characteristics are explored in depth. The fabricated dye sensitized solar cell performance in terms of efficiency, voltage, and current was evaluated using a standard illumination of air-mass 1.5 global (AM 1.5 G) having an irradiance of 100 mW/cm [2]. The photon-to-current conversion efficiency (η) of only the carbon dot sensitized solar cell was 0.10% whereas the efficiency of the solar cell fabricated with a sensitizing dye made up of CDOT and N719 was 0.19%. As compared with the performance DSSCs fabricated with only 719 dye, it was observed that when CDOT was used in combination with N719 as sensitizing dye, the open circuit voltage increases yet the overall efficiency of the resulting solar cells decreases. It is clear from the result that CDOT could be used as a sensitizing dye in DSSCs. However, it is not very useful when used in combination with other sensitizing dyes due to energy transfer.     

Thermal properties of Li4/3Ti5/3O4/LiMn2O4 cell

The thermal properties of Li_4/3Ti_5/3O₄ and Li_1+xMn₂O₄ electrodes were investigated by isothermal micro-calorimetry (IMC). The 150-mAh g⁻¹ capacity of a Li/Li_4/3Ti_5/3O₄ half cell was obtained through the voltage plateau that occurs at 1.55 V during the phase transition from spinel to rock salt. Extra capacity below 1.0 V was attributed to the generation of a new phase. The small and constant entropy change of Li_4/3Ti_5/3O₄ during the spinel/rock-salt phase transition indicated its good thermal stability. Accelerated rate calorimetry confirmed that Li_4/3Ti_5/3O₄ has better thermal characteristics than graphite. The IMC results for a Li/Li_1+xMn₂O₄ half cell indicated less heat variation due to the suppression of the order/disorder change by lithium doping. The heat profiles of the Li_4/3Ti_5/3O₄/Li_1+xMn₂O₄ full cell indicated less heat generation compared with a mesocarbon-microbead graphite/Li_1+xMn₂O₄ cell.     

A model for the delamination kinetics of La0.8Sr0.2MnO3 oxygen electrodes of solid oxide electrolysis cells

A theoretical model is developed to simulate the delamination kinetics of La_0.8Sr_0.2MnO₃ (LSM) electrode from YSZ electrolyte in solid oxide electrolysis cells (SOECs). The delamination is caused by the total stress including the internal oxygen pressure in LSM near the electrode/electrolyte interface, and the tensile stress by the oxygen migration from the YSZ electrolyte to LSM lattice. Weibull theory is used to determine the survival probability of electrode/electrolyte interface under the total stress. The relaxation time corresponding to the time for oxygen diffusion from the interface to the microcracks in La_0.8Sr_0.2MnO₃ links the survival probability with polarization time, thus the survival interface area can be predicted with varying anodic polarization time. The model is validated with experimental data. The effects of applied anodic current and operating temperature are discussed. The present model provides a starting point to study more complex cases, such as composite oxygen electrodes.     

Silicon and solar-grade silicon production by solar dissociation of Si3N4

The temperature required for carbothermal reduction of silica—in the range 2100–2300 °C—is past the upper limit for combustion process heat. It is therefore an interesting candidate for solar–thermal processing. The production of solar-grade silicon from carbothermally produced silicon requires an energy-intensive long-duree high-temperature purification process. We propose here a two-step solar process for the production of silicon from silica: first, a carbothermal reduction in the presence of nitrogen to yield silicon nitride and second, the solar dissociation of the nitride to yield silicon. This last step could be combined with purification of the silicon if solar-grade silicon is the desired end-product. In this paper, we report on experimental results that indicate that silicon nitride can be dissociated to yield silicon with no detectable nitride content.     

Enhanced hydrogen sorption kinetics of Mg50Ni-LiBH4 composite by CeCl3 addition

Mg₅₀Ni-LiBH₄ and Mg₅₀Ni-LiBH₄-CeCl₃ composites have been prepared by short times of ball milling under argon atmosphere. Combination of HP-DSC and volumetric techniques show that Mg₅₀Ni-LiBH₄-CeCl₃ composite not only uptakes hydrogen faster than Mg₅₀Ni-LiBH₄, but also releases hydrogen at a lower temperature (225 °C). The presence of CeCl₃ has a catalytic role, but it does not modify the thermodynamic properties of the composite which corresponds to MgH₂. Experimental studies on the hydriding/dehydriding mechanisms demonstrate that LiBH₄ and Ni lead to the formation of MgNi₃B₂ in both composites. In addition, XRD/DSC analysis and thermodynamic calculations demonstrate that the addition of CeCl₃ accounts for the enhancement of the hydrogen absorption/desorption kinetics through the interaction with LiBH₄. The in situ formation and subsequent decomposition of Ce(BH₄)₃ provides a uniform distribution of nanosize CeB₄ compound, which plays an important role in improving the kinetic properties of MgH₂.     

Thermal, structural and crystallization kinetics of SiO2-BaO-ZnO-B2O3-Al2O3 glass samples as a sealant for SOFC

The present work describes the development of a glass-ceramic in SiO₂-BaO-ZnO-B₂O₃-Al₂O₃ system. The prepared glass samples were found to have good compatibility to act as a sealant in planar solid oxide fuel cell (SOFC) in terms of coefficient of thermal expansion (TEC) and glass transition temperature (T_g). The crystallization kinetics of present glass samples were investigated by various characterization techniques such as differential thermal analyzer (DTA), Dilatometery, X-Ray diffraction (XRD) and scanning electron microscopy (SEM). The crystallization behavior of the chosen glass samples was influenced by replacing B₂O₃ with Al₂O₃. With the addition of Al₂O₃ there is increase in glass transition temperature (T_g) and glass crystallization temperature (T_c). Also with the addition of Al₂O₃ crystallization phenomenon is hindered. XRD and SEM study was done at various temperatures for different time durations. The detail of the above discussed study is done in the present paper.     

Influence of oxygen and water related surface defects on the dye sensitized TiO2 solar cell

Oxygen- and water-related surface defects on porous TiO₂ (anatase) can be well controlled by the oxygen and water partial pressures and therefore such defects are of technological relevance for dye sensitized TiO₂ solar cells. We investigated the action of oxygen and water-related surface defects in situ by impedance spectroscopy, photoconductivity, photoluminescence, and optical transmission as well as by characterizing solar cells which were prepared under respective conditions. Oxygen loss from the TiO₂ surface leads to electrical doping by Ti³⁺/oxygen donor states. Such defects create recombination paths for injected electrons back into the electrolyte. Pre-treatment of porous TiO₂ by chemisorption of water increases the open circuit voltage of the solar cells without altering the short circuit current. Water-related surface defects decrease the saturation current of the diode, probably by raising the barrier height at the TiO₂/electrolyte interface.     

Thermal stability and moisture resistance of C/Al2O3/Al solar absorber surfaces

Mechanically manufactured C/Al₂O₃/Al solar absorber surfaces were exposed to thermal stability and moisture resistance tests following the IEA Solar Heating and Cooling Programme recommendations (draft ISO/DIS 12592). The main degradation mechanism is found to be hydration of aluminium oxide to pseudoboehmite and boehmite. We estimated the absorber service lifetime (with an optical performance more than 95% of its initial) based on two literature references, where time of wetness frequency distribution of a solar collector microclimate was measured. The estimated average service lifetime in normal use was 20 or 25 years, depending significantly on the time of wetness frequency distribution of the surface.     

Chemical storage of solar energy—kinetics of heterogeneous NH3 and H2SO4 reactions II. Process and reactor design

An important energy recovery step in the ammonium hydrogen sulfate (AHS) cycle is the recombination reaction producing NH₄HSO₄. It has been determined that the optimum way to accomplish this, and prevent side reactions, is by the heterogeneous gas-liquid reaction of H₂SO₄ and NH₃. A mathematical model is presented and applied to the two reaction zones and a method of numerical solution is discussed. Three horizontal pilot-scale configurations, 0.17 × 10⁶ to 4.2 × 10⁶ kJ/h energy release, are discussed and sizing is presented. The most important conclusion from the work is that the energy can be released most effectively by carrying out the reaction in a double pipe tubular reactor operating in the annular flow regime with both gas and liquid in turbulent flow.     

Improved CIGS thin-film solar cells by surface sulfurization using In2S3 and sulfur vapor

Surface sulfurization of Cu(In,Ga)Se₂ (CIGS) thin films was carried out using two alternative techniques that do not utilize toxic H₂S gas; a sequential evaporation of In₂S₃ after CIGS deposition and the annealing of CIGS thin films in sulfur vapor. A Cu(In,Ga) (S,Se)₂ thin layer was grown on the surface of the CIGS thin film after sulfurization using In₂S₃, whereas this layer was not observed for CIGS thin films after sulfurization using sulfur vapor, although a trace quantity of S was confirmed by AES analysis. In spite of the difference in the surface modification techniques, the cell performance and process yield of the ZnO:Al/CdS/CIGS/Mo/glass thin-film solar cells were remarkably improved by using both surface sulfurization techniques.     

Investigation of the damage as induced by 1.7 MeV protons in an amorphous/crystalline silicon heterojunction solar cell

Current–voltage under illumination and quantum yield characteristics of an amorphous silicon/crystalline silicon hetero solar cell have been measured before and after exposure to high-energy (1.7 MeV) protons. A comparison of the measured wavelength-dependent quantum yield with calculated values enabled to determine the effective electron diffusion length of the crystalline silicon, that dropped from a value of 434 μm before to a value of 4 μm after irradiation with 5×10¹² cm⁻² protons. Good agreement has been obtained between measured and simulated data using DIFFIN,¹ a finite-element simulation program for a-Si:H/c-Si heterojunction solar cells, enabling us to extract the depth profile of the recombination rate and the density of states distribution in the semiconductor layers before and after irradiation.     

Effects of chromium poisoning on the long-term oxygen exchange kinetics of the solid oxide fuel cell cathode materials La0.6Sr0.4CoO3 and Nd2NiO4

The influence of chromium poisoning on the long-term stability of the oxygen exchange kinetics of the promising IT-SOFC cathode materials La_0.6Sr_0.4CoO_3−δ (LSC) and Nd₂NiO_4+δ (NDN) is investigated in-situ by dc-conductivity relaxation experiments. The as-prepared LSC and NDN samples show high chemical oxygen surface exchange coefficients k_chem. After the deposition of a 10 nm thick Cr-layer onto the surface, k_chem of LSC decreases to 50% of the initial value. Additional chromium deposition of 20 nm on LSC leads to a further decrease of k_chem to 27% of the initial value. In contrast, the effect of a 10 nm thick Cr-layer on k_chem of NDN is negligible. Even with additional 20 nm of chromium and a total testing time of 1750 h, the nickelate retains a k_chem of 60% of the initial value. X-ray photoelectron spectroscopy (XPS) of the degraded. LSC shows a significantly altered surface cation composition with Sr-enrichment down to 30 nm depth while XPS analysis of the degraded NDN reveals a thin surface zone of approximately 30 nm containing nickel and chromium. In contrast to LSC, the changes in the surface composition of NDN due to Cr-poisoning ultimately had only a minor influence on the surface exchange properties.     

Burning velocities and kinetics of H2/NF3/N2, CH4/NF3/N2, and C3H8/NF3/N2 flames

The combustion characteristics and reaction mechanism of mixtures containing nitrogen trifluoride (NF₃) were investigated. Burning velocities for H₂/NF₃/N₂, CH₄/NF₃/N₂, and C₃H₈/NF₃/N₂ flames were determined for the first time at various equivalence ratios and N₂ mole fractions. The burning velocities of the latter two flames were similar and showed peaks at equivalence ratios of ∼1.0, while those of the H₂/NF₃/N₂ flames had the pronounced peak at low equivalence ratios where the formation of the wrinkled flames was observed. A detailed kinetic model was constructed to simulate the laminar burning velocities of H₂/NF₃/N₂ and CH₄/NF₃/N₂ flames. The model accurately reproduced the experimental results. Analyses of the reaction mechanism revealed the major reaction pathways that involve the decomposition of NF₃, the oxidation and chain-fluoridation of H₂ and CH₄, and the formation of N₂.     

Characterization of the PSG/Si interface of H3PO4 doping process for solar cells

The precipitation of P in the emitter region of H₃PO₄ spray doped silicon for solar cell applications has been investigated by electron microscopy, X-ray microanalysis and electrical measurements after annealing for two different times. P, Si and O concentration profiles show that the composition of the phosphorous silicate glass (PSG) is in agreement with a solid solution of P₂O₅ in SiO₂ and that P concentration is peaked at the PSG/Si interface. TEM observations have shown for the shorter annealing the formation of a 20 nm thick defect layer at the silicon surface; this layer evolves into a network of large rod-like monoclinic (or orthorhombic) SiP precipitates, which extend in depth up to about 100 nm for the longer treatment. The SiP crystal structure and the habit planes are the same as previously reported in literature. No deeper defect that could interact with the junction located at about 300 nm has been detected. Although the SiP precipitation takes place entirely at the Si surface, it is not significantly affected by the orientation of the crystals and by the texturing process. The amounts of both electrically active and inactive P obtained by the H₃PO₄ spray technique have been compared with the ones obtained by the conventional POCl₃ technique. The former process presents a larger amount of inactive dopant, a finding that is in keeping with the microstructural and microanalytical observations. Instead the amount of active P is similar in the two cases, a result attributed to the precipitation and clustering phenomena of the excess dopant.     

Optical characterization of In2S3 solar cell buffer layers grown by chemical bath and physical vapor deposition

In this paper, we study the optical properties of indium sulfide thin films to establish the best conditions to obtain a good solar cell buffer layer. The In₂S₃ buffer layers have been prepared by chemical bath deposition (CBD) and thermal evaporation (PVD). Optical behavior differences have been found between CBD and PVD In₂S₃ thin films that have been explained as due to structural, morphological and compositional differences observed in the films prepared by both methods. The resultant refractive index difference has to be attributed to the lower density of the CBD films, which can be related to the presence of oxygen. Its higher refractive index makes PVD film better suited to reduce overall reflectance in a typical CIGS solar cell.     

Chemical composition dependence of morphological and optical properties of Cu2ZnSnS4 thin films deposited by sol-gel sulfurization and Cu2ZnSnS4 thin film solar cell efficiency

The properties of Cu₂ZnSnS₄ (CZTS) thin films deposited by sol-gel sulfurization were investigated as a function of the chemical composition of the sol-gel solutions used. The chemical composition ratio Cu/(Zn+Sn) of the sol-gel solution was varied from 0.73 to 1.00, while the ratio Zn/Sn was kept constant at 1.15. CZTS films deposited using sol-gel solutions with Cu/(Zn+Sn)<0.80 exhibited large grains. In addition, the band gaps of these Cu-poor CZTS thin films were blue shifted. Solar cells with the structure Al/ZnO:Al/CdS/CZTS/Mo/soda lime glass were fabricated under non-vacuum conditions. The solar cell with the CZTS layer deposited using the sol-gel solution with Cu/(Zn+Sn)=0.80 exhibited the highest conversion efficiency of 2.03%.     

Design of novel efficient sensitizing dye for nanocrystalline solar cell; tripyridine-thiolato (4,,-tricarboxy-2,:,-terpyridine)ruthenium(II)

We have designed tripyridine-thiolato (4,4^′,4^″-tricarboxy-2,2^′:6^′,2^″-terpyridine)ruthenium(II) [complex 1], a novel efficient sensitizing dye for dye sensitized TiO₂ solar cells, based on the DFT MO calculations with PBE0 functional. Complex 1 is a modified BD (black dye: trithiocyanato (4,4^′,4^″-tricarboxy-2,2^′:6^′,2^″-terpyridine)ruthenium(II) complex) molecule where NCS ligands of BD are replaced by C₅H₄NS ligands. Molecular and electronic structures of complex 1 have been theoretically characterized. Complex 1 is expected to have the following two advantages over BD, in addition to the advantage of high electron transfer rate from the photoexcited dye to TiO₂ realized in BD: (1) higher electron transfer rate from redox systems to oxidized dyes; (2) higher absorption efficiency to solar spectrum. We propose complex 1 as a novel efficient sensitizing dye which provides the higher efficiency than does BD for dye sensitized solar cells.     

GC-MASS detection of methyl orange degradation intermediates by AgBr/g-C3N4: Experimental design,bandgap study,and characterization of the catalyst

As synthesized AgBr nanoparticles (NPs) and g-C₃N₄ nanosheets were synthesized and coupled to obtain the AgBr-g-C₃N₄ catalyst, It showed a boosted activity in the photodegradation of methyl orange (MO) in aqueous solution (1.6 and 1.3 times greater than just the AgBr and g-C₃N₄ NPs in the initial degradation experiments without any optimization, respectively). The composite was characterized by X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), cyclic voltammetry (CV), etc. The modified carbon paste electrode by the composite showed a significant increase in peak current, confirming a significant increase in charge transfer between the semiconductors of the coupled system. The bandgap energies of the samples were estimated by both DRS and CV methods. The composite with an AgBr:g-C₃N₄ mole ratio of 2:1 showed the best photocatalytic activity. The initial pH of the MO solution was changed from 6.5 to 5.5 during the photodegradation process. Experimental design by RSM was used for the study of the interaction effects between the influencing variables. The conditions of the optimized run were: pH: 3.5, Catalyst dosage: 0.9 g/L, Time: 83 min, C_MO: 3.2 ppm, while those of the central point were: pH: 6.1, Catalyst dosage: 0.99 g/L, Time: 82.50 min, C_MO: 2.9 ppm. Various degradation intermediates such as benzene, phenol, catechol, hydroquinone, aniline, dimethylamine, benzoquinone, p-amino phenol, ethendiol, ethylene glycol, oxalic acid, maleic acid, 1-propenoic acid, sulfate, etc. were detected by GC-Mass. Further attacking of hydroxyl and superoxide radicals can easily mineralize these intermediates to water, carbon dioxide, and other inorganic species.     

Electrophoretic deposition of (Mn,Co)3O4 spinel coating for solid oxide fuel cell interconnects

We discuss here our attempt to develop (Mn,Co)₃O₄ spinel coatings on the surface of Cr-containing steel through electrophoretic deposition (EPD) followed by reduced-atmosphere sintering for solid oxide fuel cell (SOFC) interconnect application. The effects of EPD voltages and sintering atmospheres on the microstructure, electrical conductivity and long-term stability of the coated interconnects are examined by means of scanning electron microscopy (SEM), energy dispersion spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), and four-probe resistance techniques. For the spinel coatings generated using smaller voltage than 400 V, the interconnect surfaces exhibit good packing behavior and high conductivity. The reduced atmosphere during sintering has a beneficial impact on the minimizing chromia subscale formation and thus reducing the area specific resistance (ASR) of the coated interconnects. Moreover, it is interesting to note that a more stable long-term performance is achieved for the spinel coating sintered in H₂/H₂O atmosphere with thin chromia sub-scale and no Cr penetration. Based on the current results, EPD followed by reduced-atmosphere sintering is a fast and economic way to deposit (Mn,Co)₃O₄ coating for SOFC interconnect applications.