Direct contact thermal energy storage system using Na2CO3·10H2O solution

The volumetric coefficient of heat transfer and the energy storage capacity in a direct contact thermal energy storage system using Na₂CO₃·10H₂O solution as thermal energy storage medium have been investigated. Hot kerosene was used as a heat transfer fluid. The experiments were carried out by bubbling hot kerosene from the bottom of a column containing Na₂CO₃·10H₂O solution. The column used in this experiment was made from glass of 3 mm in thickness with the inside diameter of 7 cm and 100 cm in height. The effects of kerosene flow rate and kerosene bubble diameter to the volumetric coefficient of heat transfer and the storing rate of energy have been studied. The volumetric coefficient of heat transfer was strongly affected by the flow rate of the kerosene. The effect of the kerosene flow rate on the storing rate of energy was relatively high, while the effect of the bubble diameter was small.     

Multi-electron storage of photoenergy using Cu2O–TiO2 thin film photocatalyst

UV–vis irradiation of thin films of TiO₂ (ITO/TiO₂) and Cu₂O/TiO₂ (ITO/Cu₂O/TiO₂) coated on conducting glasses generate H₂ from H₂O and once the illumination is ceased, the H₂ production was still noticeable under dark for ITO/Cu₂O/TiO₂ at a lesser production rate for up to 2 h. No such dark reactions were observed for ITO/TiO₂ or TiO₂-coated copper metal foil (Cu/TiO₂). It was noticed that the irradiation of ITO/Cu₂O/TiO₂ leads to formation of trapped electrons and this stored energy leads to generate H₂ from H₂O in the dark.     

Tri-layer antireflection coatings (SiO2/SiO2–TiO2/TiO2) for silicon solar cells using a sol–gel technique

Antireflection coatings (ARCs) have become one of the key issues for mass production of Si solar cells. They are generally performed by vacuum processes such as thermal evaporation, reactive sputtering, and plasma-enhanced chemical vapor deposition. In this work, a sol–gel method has been demonstrated to prepare the ARCs for the non-textured monocrystalline Si solar cells. The spin-coated TiO₂ single-layer, SiO₂/TiO₂ double-layer and SiO₂/SiO₂–TiO₂/TiO₂ triple-layer ARCs were deposited on the Si solar cells and they showed good uniformity in thickness. The measured average optical reflectance (400–1000 nm) was about 9.3, 6.2 and 3.2% for the single-layer, double-layer and triple-layer ARCs, respectively. Good correlation between theoretical and experimental data was obtained. Under a triple-layer ARC condition, a 39% improvement in the efficiency of the monocrystalline Si solar cell was achieved. These indicate that the sol–gel ARC process has high potential for low-cost solar cell fabrication.     

Basic molten salt process—A new route for synthesis of nanocrystalline Li4Ti5O12-TiO2 anode material for Li-ion batteries using eutectic mixture of LiNO3-LiOH-Li2O2

A nanocrystalline Li₄Ti₅O₁₂-TiO₂ duplex phase has been synthesized by a simple basic molten salt process (BMSP) using an eutectic mixture of LiNO₃-LiOH-Li₂O₂ at 400-500 °C. The microstructure and morphology of the Li₄Ti₅O₁₂-TiO₂ product are characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The sample prepared by heat-treating at 300 °C for 3 h (S-1) reveals dense agglomerates of ultra-fine nanocrystalline Li₄Ti₅O₁₂; with heat treatment at 400 °C for 3 h (S-2), there is a duplex crystallite size (fine < 10 nm, and coarse > 20 nm) of Li₄Ti₅O₁₂-TiO₂; at 500 °C for 3 h (S-3), a much coarser and less-dense distribution of lithium titanate (crystallite size ∼15-30 nm) is observed. According to the results of electrochemical testing, the S-2 sample shows initial discharge capacities of 193 mAh g⁻¹ at 0.2 C, 168 mAh g⁻¹ at 0.5 C, 146 mAh g⁻¹ at 1 C, 135 mAh g⁻¹ at 2 C, and 117 mAh g⁻¹ at 5 C. After 100 cycles, the discharge capacity is 138 mAh g⁻¹ at 1 C with a capacity retention of 95%. The S-2 sample yields the best electrochemical performance in terms of charge-discharge capacity and rate capability compared with other samples. Its superior electrochemical performance can be mainly attributed to the duplex crystallite structure, composed of fine (<10 nm) and coarse (>20) nm nanoparticles, where lithium ions can be stored within the grain boundary interfaces between the spinel Li₄Ti₅O₁₂ and the anatase TiO₂.     

Sm0.5Sr0.5CoO3 + Sm0.2Ce0.8O1.9 composite cathode for cermet supported thin Sm0.2Ce0.8O1.9 electrolyte SOFC operating below 600 °C

The cathode is a key component in low temperature solid oxide fuel cells. In this study, composite cathode, 75 wt.% Sm_0.5Sr_0.5CoO₃ (SSC) + 25 wt.% Sm_0.2Ce_0.8O_1.9 (SDC), was applied on the cermet supported thin SDC electrolyte cell which was fabricated by tape casting, screen-printing, and co-firing. Single cells with the composite cathodes sintered at different temperatures were tested from 400 to 650 °C. The best cell performance, 0.75 W cm⁻² peak power operating at 600 °C, was obtained from the 1050 °C sintered cathode. The measured thin SDC electrolyte resistance R_s was 0.128 Ω cm² and total electrode polarization R_p(a + c) was only 0.102 Ω cm² at 600 °C.     

Effect of hydrogen on H2/CH4 flame structure of MILD combustion using the LES method

Large eddy simulation (LES) method is employed to investigate the effect of the hydrogen content of fuel on the H₂/CH₄ flame structure under the moderate or intense low-oxygen dilution (MILD) condition. The turbulence–chemistry interaction of the numerically unresolved scales is modelled using the PaSR method, where the full mechanism of GRI-2.11 represents the chemical reactions. The influence of hydrogen concentration on the flame structure is studied using the profiles of temperature, CH₂O and OH mass fractions and the diffusion profiles of un-burnt fuel through the flame front. Furthermore, more details are investigated by contours of OH, HCO and CH₂O radicals in an area near the nozzle exit zone. Results show that increasing the hydrogen content of fuel reinforces the MILD combustion zone and increases the peak value of the flame temperature and OH mass fraction. This increment also increases the flame thickness and reduces the OH oscillations and diffusion of the un-burnt fuel through the flame front.     

Ba0.5Sr0.5Co0.8Fe0.2O3 − δ + LaCoO3 composite cathode for Sm0.2Ce0.8O1.9-electrolyte based intermediate-temperature solid-oxide fuel cells

A novel Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ + LaCoO₃ (BSCF + LC) composite oxide was investigated for the potential application as a cathode for intermediate-temperature solid-oxide fuel cells based on a Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte. The LC oxide was added to BSCF cathode in order to improve its electrical conductivity. X-ray diffraction examination demonstrated that the solid-state reaction between LC and BSCF phases occurred at temperatures above 950 °C and formed the final product with the composition: La_0.316Ba_0.342Sr_0.342Co_0.863Fe_0.137O_3 − δ at 1100 °C. The inter-diffusion between BSCF and LC was identified by the environmental scanning electron microscopy and energy dispersive X-ray examination. The electrical conductivity of the BSCF + LC composite oxide increased with increasing calcination temperature, and reached a maximum value of ∼300 S cm⁻¹ at a calcination temperature of 1050 °C, while the electrical conductivity of the pure BSCF was only ∼40 S cm⁻¹. The improved conductivity resulted in attractive cathode performance. An area-specific resistance as low as 0.21 Ω cm² was achieved at 600 °C for the BSCF (70 vol.%) + LC (30 vol.%) composite cathode calcined at 950 °C for 5 h. Peak power densities as high as ∼700 mW cm⁻² at 650 °C and ∼525 mW cm⁻² at 600 °C were reached for the thin-film fuel cells with the optimized cathode composition and calcination temperatures.     

Stable, easily sintered BaCe0.5Zr0.3Y0.16Zn0.04O3−δ electrolyte-based protonic ceramic membrane fuel cells with Ba0.5Sr0.5Zn0.2Fe0.8O3−δ perovskite cathode

A stable, easily sintered perovskite oxide BaCe_0.5Zr_0.3Y_0.16Zn_0.04O_3−δ (BCZYZn) as an electrolyte for protonic ceramic membrane fuel cells (PCMFCs) with Ba_0.5Sr_0.5Zn_0.2Fe_0.8O_3−δ (BSZF) perovskite cathode was investigated. The BCZYZn perovskite electrolyte synthesized by a modified Pechini method exhibited higher sinterability and reached 97.4% relative density at 1200 °C for 5 h in air, which is about 200 °C lower than that without Zn dopant. By fabricating thin membrane BCZYZn electrolyte (about 30 μm in thickness) on NiO–BCZYZn anode support, PCMFCs were assembled and tested by selecting stable BSZF perovskite cathode. An open-circuit potential of 1.00 V, a maximum power density of 236 mW cm⁻², and a low polarization resistance of the electrodes of 0.17 Ω cm² were achieved at 700 °C. This investigation indicated that proton conducting electrolyte BCZYZn with BSZF perovskite cathode is a promising material system for the next generation solid oxide fuel cells.     

Development of electrolyte-supported intermediate-temperature single-chamber solid oxide fuel cells using Ln0.7Sr0.3Fe0.8Co0.2O3−δ (Ln = Pr, La, Gd) cathodes

Iron-cobalt-based perovskite oxides with general formula Ln_0.7Sr_0.3Fe_0.8Co_0.2O_3−δ (where Ln = La, Pr and Gd) have been investigated for their application as intermediate-temperature cathodes in solid oxide fuel cells (SOFCs). Powdered samples of these materials were synthesized by a novel gel combustion process and then characterized by X-ray powder diffraction (XPD) and scanning electron microscopy (SEM). XPD patterns were satisfactorily indexed with an orthorhombic GdFeO₃-type structure and, for all samples, a mean particle size of less than 1 μm was estimated from the SEM data. Experimental single-chamber SOFCs using with these materials as cathodes and NiO-SDC (samaria-doped ceria) and SDC as anode and electrolyte, respectively, were evaluated at 600 °C in a methane/oxygen mixtures. Peak power densities of 65.4, 48.7 and 46.2 mW cm⁻² were obtained for Ag|Ln_0.7Sr_0.3Fe_0.8Co_0.2O_3−δ|SDC|NiO-SDC|Pt cells with Ln = Pr, La and Gd, respectively. The relatively high power density obtained for the Pr compound shows that it could be an interesting material for cathode of single-chamber SOFCs.     

Photocatalytic degradation of organophosphorus pesticides using floating photocatalyst TiO2 · SiO2/beads by sunlight

In this paper, the floating TiO₂ · SiO₂ photocatalyst beads are prepared by the dip-coating method, which use hollow glass microbeads as the carrier and titanium tetraisopropoxide [Ti(iso-OC₃H₇)₄] and ethyl silicate as the raw materials. The feasibility of photocatalytic degradation of organophosphorus pesticides using TiO₂ · SiO₂ beads as a floating photocatalyst by sunlight is studied. The results show that the best heat treatment condition for TiO₂ · SiO₂ beads is at 650 °C for 5 h. Apart from heat treatment temperature and time, the amount of SiO₂ also influences the photocatalytic activity of TiO₂ · SiO₂ beads. The optimum amount of SiO₂ is 0.20 (molecular fraction). 0.65 × 10⁻⁴ mol/dm³ of four organophosphorus pesticides of three structures can be completely photocatalytically degraded into after 420 min illumination by sunlight. The effects of parameters such as the amount of TiO₂ · SiO₂ beads, initial pH and metal ions on the photocatalytic degradation of the organophosphorus pesticides are also studied. The possible mechanisms of photocatalytic degradation of phosphate ester pesticides are proposed. After 120 h illumination by sunlight, there is no significant loss of the photocatalytic activity of TiO₂ · SiO₂ beads.     

Heat-transfer characteristics of a latent heat storage system using MgCl2 · 6H2O

Heat-transfer characteristics have been determined for the circular finned and unfinned-tube units during the freezing of magnesium chloride hexahydrate (MgCl₂ · 6H₂O) used as a phase-change material (PCM) with a melting temperature of 116.7 °C. The effects on the heat-transfer characteristics have been determined of the inlet temperature and the flow rate of air used as the heat-transfer fluid (HTF). With the unfinned-tube unit, the heat-transfer coefficients obtained between the PCM and the tube are larger than the calculated values based on the theory of steady-state heat conduction due to the dendritical crystal growth of PCM. The ratio of the heat-transfer coefficient of the finned-to the unfinned-tube systems is about 3.5 within the finned section and decreases gradually far from the finned section with an increase in crystal volume. The total amounts of heat recovered have been correlated in terms of the Fourier, Stefan, and Reynolds numbers to provide basic design data for circular finned- and unfinned-tube heat-storage units.     

Hydrogen purification for fuel cell using CuO/CeO2-Al2O3 catalyst

CuO/CeO₂, CuO/Al₂O₃ and CuO/CeO₂-Al₂O₃ catalysts, with CuO loading varying from 1 to 5 wt.%, were prepared by the citrate method and applied to the preferential oxidation of carbon monoxide in a reaction medium containing large amounts of hydrogen (PROX-CO). The compounds were characterized ex situ by X-ray diffraction, specific surface area measurements, temperature-programmed reduction and temperature-programmed reduction of oxidized surfaces; XANES-PROX in situ experiments were also carried out to study the copper oxidation state under PROX-CO conditions. These analyses showed that in the reaction medium the Cu⁰ is present as dispersed particles. On the ceria, these metallic particles are smaller and more finely dispersed, resulting in a stronger metal-support interaction than in CuO/Al₂O₃ or CuO/CeO₂-Al₂O₃ catalysts, providing higher PROX-CO activity and better selectivity in the conversion of CO to CO₂ despite the greater BET area presented by samples supported on alumina. It is also shown that the lower CuO content, the higher metal dispersion and consequently the catalytic activity. The redox properties of the ceria support also contributed to catalytic performance.     

Efficient H2 production by water-splitting using indium–tin-oxide/V-doped TiO2 multilayer thin film photocatalyst

In order to sensitize TiO₂ in visible light and to reduce photo-induced charge recombination, the multilayer films of Indium-Tin Oxide (ITO)/V-doped TiO₂ were synthesized by radio-frequency magnetron sputtering. V-doped TiO₂ thin films showed red shift in TiO₂ absorption edge with increasing dopant concentration and, most importantly, the dopant energy levels are formed in the TiO₂ band gap due to V⁵⁺/V⁴⁺ ions as confirmed by UV-Visible and XPS spectra. Multilayer films with different numbers of ITO/V-doped TiO₂ (6 at.%) bilayers (namely, 2-, 3-, 4-, 5-, 6- and 7-bilayers) were deposited, in order to reduce the charge recombination rate, by keeping the total thickness of TiO₂ constant in each multilayer film. In multilayer films, when exposed to visible light the photocurrent increases as function of the number of bilayers by reaching the maximum with 6-bilayers of ITO/V-doped TiO₂. The measured enhanced photocurrent is attributed to: 1) ability of V-doped TiO₂ to absorb visible light, 2) number of space-charge layers in form of ITO/TiO₂ interfaces in multilayer films, and 3) generation of photoelectrons just in/or near to the space-charge layer by decreasing the V-doped TiO₂ layer thickness. The reduced charge recombination rate in multilayer films was also confirmed by the photocurrent kinetic curves. The superior photocatalytic efficiency of the 6-bilayers film is also reflected in hydrogen production rate through water-splitting: we obtained indeed 31.2 μmol/h of H₂ production rate.     

Solution combustion synthesis of Ce0.6Mn0.3Fe0.1O2 for anode of SOFC using LaGaO3-based oxide electrolyte

This paper describes the potential of solution combustion synthesis (SCS) method for preparing Ce_0.6Mn_0.3Fe_0.1O₂ (CMF) as the anode material for solid oxide fuel cells (SOFC). The stability, crystallinity, morphology, and surface area of the products were depended on the fuel ratio used in SCS as investigated by TGA, XRD, SEM, and BET, which correspondingly influenced their electrochemical properties. The SCS-derived products were directly used for preparing anodes by sintering the screen-printed powders on the electrolyte membrane, and were evaluated from power generation performance, which were compared with the conventional solid-state-reaction (SSR) sample. Significantly, under configuration of the cell of CMF/La_0.8Sr_0.2Ga_0.8Mg_0.15Co_0.05O₃/Sm_0.5Sr_0.5CoO₃ using humidified hydrogen gas as a fuel and O₂ as an oxidizing agent, the maximum power densities obtained were 1.23 W/cm² at 1000 °C for the SCS product (CMF1) obtained at ? = 0.5. This value was higher than 1.09 W/cm² for the SSR-derived sample under the same evaluation conditions. The results appealed benefits of SCS method for preparing CMF as the anode material with high power generation performance for SOFC, due to its large surface area and nanosized grains, in which fuel ratio was a key parameter for its synthesis.     

Determination of the dissociation constant of molten Li2CO3/Na2CO3/K2CO3 using a stabilized zirconia oxide-ion indicator

An Li₂CO₃/Na₂CO₃/K₂CO₃ eutectic melt has been selected as an example of a molten-carbonate system and the suitability of a stabilized zirconia—air electrode as an oxide-ion concentration indicator for this melt has been confirmed.With this indicator, the dissociation constant of the reaction CO₃^2? (?) = CO₂(g) + O^2? (?) in this melt has been determined to be K_d = P_CO2 [O^2?] = 4.03 × 10^?3 Pa at 873 KReproducible measurements were obtained throughout the experiment and this method might find further application in the study of reactions related to the oxide ion in carbonate melts.     

Optical filters from SiO2 and TiO2 multi-layers using sol–gel spin coating method

Sol–gel spin coating process is used to produce optical filters from SiO₂ and TiO₂ multi-layers. By coating the films symmetrically on both sides of the glass substrates, we designed two types of three-layer anti-reflective (AR) filters for the near–infrared region, and a nine-layer reflective filter for the near–UV region. We develop a simple theoretical model for these filters, which incorporates sol–gel film densification during the coating process, and fit it to the experimental data to extract properties of the individual layers in the coatings.     

High-rate performance of all-solid-state lithium secondary batteries using Li4Ti5O12 electrode

The all-solid-state Li–In/Li₄Ti₅O₁₂ cell using the 80Li₂S·20P₂S₅ (mol%) solid electrolyte was assembled to investigate rate performances. It was difficult to obtain the stable performance at the charge current density of 3.8 mA cm⁻² in the all-solid-state cell. In order to improve the rate performance, the pulverized Li₄Ti₅O₁₂ particles were applied to the all-solid-state cell, which retained the reversible capacity of about 90 mAh g⁻¹ at 3.8 mA cm⁻². The 70Li₂S·27P₂S₅·3P₂O₅ glass–ceramic, which exhibits the higher lithium ion conductivity than the 80Li₂S·20P₂S₅ solid electrolyte, was also used. The Li–In/70Li₂S·27P₂S₅·3P₂O₅ glass–ceramic/pulverized Li₄Ti₅O₁₂ cell was charged at a current density higher than 3.8 mA cm⁻² and showed the reversible capacity of about 30 mAh g⁻¹ even at 10 mA cm⁻² at room temperature.     

Characterization of interphases appearing on LiNi0.5Mn0.5O2 using Li MAS NMR

⁷Li MAS NMR, usually a bulk characterization technique, is used here to analyze the positive electrode/electrolyte interphase. The sharpening of the NMR spectra line shape as the amount of surface species increases shows that the observed signal is clearly the sum of signals due to the distribution of lithium ions in the interphase in terms of distance from the bulk of electrode active material. This technique is then used to compare characteristics of the interphase coming from the contact with LiPF₆-based electrolyte in the case of storage or electrochemical cycling. A clear influence of the change of potential on the interphase configuration and in particular on its intimacy with the bulk of active material is deduced from the change in NMR spectra lineshape. This information is hardly obtained by other characterization technique, making NMR a powerful tool for the study of interphases and passivation layers in lithium batteries materials.     

Anodic behavior of 8Y2O3-ZrO2/NiO cermet using an anode-supported electrode

8Y₂O₃-ZrO₂ (8YSZ)/NiO cermet anode-supported symmetric cell is introduced and fabricated using a tape casting process to analyze the anodic behavior of an anode-supported cell. An anode-supported symmetric cell helps us understand the complex anode structure of cermets. The anodic behavior of 8YSZ/NiO is compared to a MIEC electrode of Sm_0.2Ce_0.8O_1.9 (SDC)/NiO. The anodic behavior of a 8YSZ/NiO cermet electrode is investigated and discussed with respect to the hydrogen partial pressure (p(H₂)), water partial pressure (p(H₂O)), area specific resistance (ASR), activation energy (E_a), thermal cycle, and redox process. Based on these studies, an empirical reaction model of 8YSZ/NiO is established, and the related reaction processes are discussed. On impedance spectra diagram, high and medium frequency arcs are associated with the charge transfer process and the H₂O formation reaction, while the low frequency arc corresponds to the dissociative adsorption and the surface diffusion/gas phase diffusion process. Changes in microstructure by redox and thermal cycling have a significant effect on the electrochemical properties and structural stability of a thick anode-supported cermet structure.     

Fabrication of all-solid-state rechargeable lithium-ion battery using mille-feuille structure of Li0.35La0.55TiO3

A mille-feuille structure, which comprises both sides of dense layer are sandwiched by porous layers, is one of the promising structures for 3-dimensional (3D) all-solid-state battery. The porous layers should have 3-dimensionally ordered macroporous structure to obtain large contact area between electrolyte and electrode. Li_0.35La_0.55TiO₃ (LLT) solid electrolyte with the mille-feuille structure was fabricated by the suspension filtration method. The dense layer was sintered well, no grain boundary was observed. The porous layers contacted well with dense layer. Thicknesses of dense and porous layers were 30 and 26 μm, respectively. To check compatibility of the mille-feuille LLT with all-solid-state Li ion battery, chronopotentiometry of symmetric cell with LiMn₂O₄/mille-feuille LLT/LiMn₂O₄ configuration was measured. Charge and discharge currents were clearly observed, indicating that the cell was successfully operated.