A note on fast protonic solid state electrochromic device: NiOx/Ta2O5/WO3−x

In the present investigation, the electrochromic properties of a fast protonic solid state device: NiO_x/Ta₂O₅/WO_3−x prepared at room temperature (300 K) is reported. The non-stoichiometric tungsten oxide thin film is prepared by reactive DC magnetron sputtering technique on ITO coated glass; the oxides of tantalum (300 nm) and nickel (100 nm) are prepared by electron beam evaporation. This proton device has a coloration efficiency of 82.4 cm²/C and coloration and bleaching time of 6 and 5 s, respectively, and a transmittance variation of 60%. The work function of WO_3−x thin films by Kelvin probe in uncolored and colored states are 4.73 and 4.30 eV, respectively.     

Solid-state dye-sensitized photocell based on pentacene as a hole collector

A solid-state dye-sensitized photovoltaic cell consisting of vacuum deposited pentacene onto ruthenium dye-coated TiO₂ electrode doped with iodine was fabricated. Cell delivers a short-circuit current of 3.6 mA cm⁻² and an open-circuit voltage of 415 mV at 100 mW cm^–2 (1.5 air mass). The efficiency and the fill factors of the above cell are 0.8% and 0.5%, respectively. Studies of the photocurrent action spectra showed that the dye is mainly responsible for this photocurrent generation. Preliminary results under extended illumination suggested that “long term” stability of the cell is promising.     

Layered GdBa0.5Sr0.5Co2O5+δ as a cathode for intermediate-temperature solid oxide fuel cells

The layered GdBa_0.5Sr_0.5Co₂O_5+δ (GBSC) perovskite oxides are synthesized by Pechini method and investigated as a novel cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The single cell of NiO–SDC (Sm_0.2Ce_0.8O_1.9)/SDC (20 μm)/GBSC (10 μm) is operated from 550 to 700 °C fed with humidified H₂ as fuel and the static air as oxidant. An open circuit voltage of 0.8 V and a maximum power density of 725 mW cm⁻² are achieved at 700 °C. The interfacial polarization resistance is as low as 0.88, 0.29, 0.13 and 0.05 Ω cm² at 550, 600, 650 and 700 °C, respectively. The ratio of polarization resistance to total cell resistance decreases with the increase in the operating temperature, from 60% at 550 °C to 21% at 700 °C, respectively. The experimental results indicate that GBSC is a promising cathode material for IT-SOFCs.     

Photon-assisted synthesis of ultra-thin yttria-doped zirconia membranes: Structure, variable temperature conductivity and micro-fuel cell devices

We report on the synthesis and functional properties of nanoscale (50 nm) dense Y-doped zirconia (YDZ) electrolyte thin films by photon-assisted oxidation of Zr–Y precursor alloy thin films. Crystalline zirconia films with grain size of 5 nm were successfully grown at room temperature by oxidation under ultra-violet (UV) photon irradiation. Microstructure of the films was characterized by transmission electron microscopy. The electrochemical conductivity of UV grown YDZ electrolytes was investigated over a broad range of temperatures using Pt electrodes as a function of yttria doping concentration. The slightly lower electrical conductivity in UV grown films at intermediate temperature range (400–550 °C) is consistent with previous reports on oxygen defect annihilation under photo-excitation. Micro-fuel cells utilizing such ultra-thin YDZ membranes yielded 12 mW cm⁻² power density at 550 °C. The results are of potential relevance in advancing low temperature ultra-thin oxide membrane synthesis for energy applications.     

Miniaturization limits for single-chamber micro-solid oxide fuel cells with coplanar electrodes

Single-chamber solid oxide fuel cells with coplanar microelectrodes were operated in methane–air mixtures (R_mix = 2) at 700 °C. The performance of cells with one pair of NiO–YSZ (yttria stabilized zirconia) anode and (La_0.8Sr_0.2)_0.98MnO₃–YSZ cathode, arranged parallel on a YSZ electrolyte substrate, was found to be significantly dependent on the electrode width. For an interelectrode gap of 250 μm, cells with average electrode widths exceeding 850 μm could establish a stable open circuit voltage (OCV) of 0.8 V, while those with widths less than 550 μm could not establish any OCV. In the intermediate range, the cells exhibited significant fluctuations in voltage and power under our testing conditions. This behavior suggests that a lower limit to electrode dimensions exists for cells with single electrode pairs, below which neither a stable difference in oxygen partial pressure, nor an OCV, can be established. Conversely, increasing the electrode width imposes a penalty in the form of an increase in the cell resistance. However, both size limits can be circumvented by employing multiple pairs of microscale electrodes in an interdigitated configuration.     

Electrical and optical properties of highly conducting CdO:F thin film deposited by sol–gel dip coating technique

Highly conducting fluorine-doped cadmium oxide (CdO:F) thin films were deposited by sol–gel dip coating technique on glass and Si substrates. F concentration in the films was varied from 2.0% to 13.8% as determined from energy dispersive X-ray analysis. X-ray diffraction pattern showed that the films were polycrystalline in nature. The optimum F concentration for obtaining maximum conductivity was found to be 9.7%. The corresponding electrical conductivity was found to be 1.088×10⁴ S/cm and mobility 60.41 V/cm². Analysis of UV-VIS-NIR spectrum of the film with F concentration 9.7% showed a direct band gap energy of 2.3 eV.     

Highly conducting transparent nanocrystalline Cd1−xSnxS thin film synthesized by RF magnetron sputtering and studies on its optical, electrical and field emission properties

Transparent conducting Cd_1−xSn_xS thin films have been synthesized by radio frequency magnetron sputtering technique on glass and Si substrates for various tin concentrations in the films. X-ray diffraction studies showed broadening of peaks due to smaller crystal size of the Cd_1−xSn_xS films, and SEM micrographs showed fine particles with average size of 100 nm. Sn concentration in the films was varied from 0% to 12.6% as determined from energy-dispersive X-ray analysis. The room-temperature electrical conductivity was found to vary from 8.086 to 939.7 S cm⁻¹ and corresponding activation energy varied from 0.226 to 0.076 eV. The optimum Sn concentration for obtaining maximum conductivity was found to be 9.3%. The corresponding electrical conductivity was found to be 939.7 S cm⁻¹, and the mobility 49.7 cm² V⁻¹ s⁻¹. Hall measurement showed very high carrier concentrations in the films lying in the range of 8.0218×10¹⁸–1.7225×10²⁰ cm⁻³. The conducting Cd_1−xSn_xS thin films also showed good field emission properties with a turn on field 4.74–7.86 V μm⁻¹ with variation of electrode distance 60–100 μm. UV–Vis–NIR spectrophotometric studies of the films showed not needed the optical band gap energy increased from 2.62 to 2.80 eV with increase of Sn concentration in the range 0–12.6%. The optical band gap was Burstein–Moss shifted, and the corresponding carrier concentration obtained from the shift also well matched with that obtained from Hall measurement.     

Structural, electrical and photovoltaic characterization of Si nanocrystals embedded SiC matrix and Si nanocrystals/c-Si heterojunction devices

Thin films of Si nanocrystals (Si NCs) embedded in a silicon carbide (SiC) matrix (Si-NC:SiC) were prepared by alternating deposition of Si-rich silicon carbide (Si_1−xC_x) and near-stoichiometric SiC mutilayers (Si_1−xC_x/SiC) using magnetron cosputtering followed by a post-deposition anneal. Transmission electron microscopy and Raman spectroscopy revealed that the Si NCs were clearly established, with sizes in the range of 3–5 nm. Optical studies showed an increase in the optical band gap after annealing from 1.4 eV (as-deposited) to 2.0 eV (annealed at 1100 °C). P-type Si-NC:SiC/n-type crystalline silicon (c-Si) heterojunction (HJ) devices were fabricated and their electrical and photovoltaic properties were characterized. The diode showed a good rectification ratio of 1.0×10⁴ at the bias voltage of ±1.0 V at 298 K. The diode ideality factor and junction built-in potential deduced from current–voltage and capacitance–voltage plots are 1.24 and 0.72 V, respectively. Illuminated I–V properties showed that the 1-sun open-circuit voltage, short-circuit current density and fill factor of a typical HJ solar cell were 463 mV, 19 mA/cm² and 53%, respectively. The external quantum efficiency and internal quantum efficiency showed a higher blue response than that of a conventional c-Si homojunction solar cell. Factors limiting the cell's performance are discussed.     

Dye-sensitized titania aerogels as photovoltaic electrodes for electrochemical solar cells

We describe the fabrication and performance of dye-sensitized photoanodes derived from TiO₂ aerogel. Nanocrystalline titania aerogel is a bicontinuous, nanostructured pore–solid architecture featuring specific surface areas of 85–150 m²/g and a continuous mesoporous network, allowing chemisorption of high concentrations of sensitizing dye and rapid mass-transport of electron-transfer mediators. Considerable design and processing flexibility arises with aerogels because the continuous pore–solid networks are fixed by the supercritical drying process, allowing the creation of multifunctional, nanostructured films of single or multiple layers. Titania aerogels can be processed as powders and deposited as nearly opaque films from 2 μm to >35-μm thick while retaining their bicontinuous nanoscale networks. Two-layer, 30-μm-thick TiO₂ aerogel films yield incident photon-to-electron conversion efficiency (IPCE) values of 85% in the 500–600 nm range and 52% at 700 nm with N719 as a sensitizing dye and after correcting for transmittance of the 3.2-mm-thick FTO-coated glass substrates at these wavelengths.     

Ruthenium oxide films for selective coatings

Although commercial selective surfaces are already available, investigation on different deposition methods and materials still goes on at many laboratories. In this work, ruthenium oxide films upon metallic substrates are assessed for this usage. Deposition of the films was made at room temperature by either spraying or dipping method in a ruthenium chloride alcoholic solution. After deposited on titanium substrates, the films were heat-treated at temperatures between 450 and 500 °C. When deposited on no-polished substrates, such films not only exhibit a high solar absorptance (α0.98), but also a high infrared emittance (ε0.8), which yield a low selectivity (S=α/ε=1.2). By deposition of similar films on polished substrates, absorptance decreases (α0.74), but emittance significantly decreases as well (ε0.12), resulting in a net selectivity increase (S6). On the other hand, evaporating a thin (20 nm) gold film upon the surface of a coating on a no-polished substrate also improves noticeably its emittance value (ε0.16) and a lower decrease in absorptance is achieved (α0.91), resulting in a selectivity increase (S5.7). These preliminary promising results indicate the high potential for using these films as solar selective coatings, but in order to optimize such selectivity values, further work to establish a close control on the deposition parameters and the substrate roughness value, should be done.     

Structure, morphology and electrochemical behaviour of manganese oxides prepared by controlled decomposition of permanganate

Hydrothermal decomposition of permanganate, conducted in a range of pH-controlled solutions (from strongly acidic to strongly basic), is used to prepare manganese dioxides that are well-suited for use as supercapacitor electrode materials. While permanganate is thermodynamically unstable, the kinetics of its decomposition in an aqueous environment are very slow, until the temperature is raised to 200 °C. Although the resultant materials are relatively crystalline and have low total pore volume, their prominent meso-porosity leads to good electrochemical performance. Best behaviour is obtained for material from permanganate decomposition in 0.01 M H₂SO₄ solution, for which composite electrodes (150 μm thick) yield 150 F g⁻¹ at 5 mV s⁻¹ in a 9 M KOH electrolyte.     

Energy analysis of silicon solar cell modules based on an optical model for arbitrary layers

An optical model for arbitrary layers is developed and a one-dimensional steady-state thermal model is applied to analyze the energy balance of silicon solar cell modules. Experimental measurements show that simulations are in good agreement, with a maximum relative error of 8.43%. The wind speed v_wind, ambient temperature T_amb and irradiance G are three main factors influencing the temperature of a photovoltaic panel. Over the course of a day the electrical output is reduced by the module temperature to only 32.5% of the rated value. Optical studies reveal that before 8:00 hours and after 16:00 hours, significant incident energy is lost by reflection because of the large angle of incidence θ_in, while at other times of day optical losses are nearly the same due to only small changes of transmission for θ_in < 45°. In addition, some optical losses result from the mismatched refractive indexes of encapsulating materials, especially at the ethylene-vinyl-acetate (EVA)/anti-reflection coating (ARC) and the ARC/Si interfaces. The uses of SiO₂ and TiO₂ as ARC materials for un-encapsulated and encapsulated Si solar cells are investigated by simulation. Comparing the results indicates that TiO₂ as ARC reduces the reflective optical loss within λ = 0.4–1.1 μm after encapsulation, while SiO₂ as ARC increases the loss by 5%. Energy allotment analysis shows that from 9:00 to 15:00, the reflective and transmissive optical losses are relatively steady at 26% and 13% of the incident energy, while the convective and radiative heat losses account for a further 30% and 24%, respectively. Thus, only 7% of incident energy is converted to electrical power.     

Thermoeconomic analysis of a novel zero-CO2-emission high-efficiency power cycle using LNG coldness

This paper presents a thermoeconomic analysis aimed at the optimization of a novel zero-CO₂ and other emissions and high-efficiency power and refrigeration cogeneration system, COOLCEP-S (Patent pending), which uses the liquefied natural gas (LNG) coldness during its revaporization. It was predicted that at the turbine inlet temperature (TIT) of 900 °C, the energy efficiency of the COOLCEP-S system reaches 59%. The thermoeconomic analysis determines the specific cost, the cost of electricity, the system payback period and the total net revenue. The optimization started by performing a thermodynamic sensitivity analysis, which has shown that for a fixed TIT and pressure ratio, the pinch point temperature difference in the recuperator, ΔT_p1, and that in the condenser, ΔT_p2 are the most significant unconstrained variables to have a significant effect on the thermal performance of novel cycle. The payback period of this novel cycle (with fixed net power output of 20 MW and plant life of 40 years) was 5.9 years at most, and would be reduced to 3.1 years at most when there is a market for the refrigeration byproduct. The capital investment cost of the economically optimized plant is estimated to be about 1000 $/kWe, and the cost of electricity is estimated to be 0.34–0.37 CNY/kWh (0.04 $/kWh). These values are much lower than those of conventional coal power plants being installed at this time in China, which, in contrast to COOLCEP-S, do produce CO₂ emissions at that.     

Superprotonic KH(PO3H)–SiO2 composite electrolyte for intermediate temperature fuel cells

Novel thin film composite electrolyte membranes, prepared by dispersion of nano-sized SiO₂ particles in the solid acid compound KH(PO₃H), can be operated under both oxidizing and reducing conditions. Long-term stable proton conductivity is observed at 140 °C, i.e., slightly above the superprotonic phase transition temperature of KH(PO₃H), under conditions of relatively low humidification (pH₂O ≈ 0.02 atm).     

Microcrystallisation in Si:H: the effect of gas pressure in Ar-diluted SiH4 plasma

Using noble gas argon as a diluent of SiH₄ in RF glow discharge, undoped μc-Si:H thin films have been developed at a low power density of 30 mW/cm². It has been found that the gas pressure is a critical factor for the growth of μc-Si:H films. Undoped μc-Si:H films having σ_D10⁻⁶ S/cm and ΔE<0.57 eV have been obtained at and above a critical pressure of 0.8 Torr. When the RF power density is increased to 90 mW/cm², a more crystalline as well as highly conducting (σ_D10⁻⁴ S/cm) μc-Si:H film has been achieved at a deposition rate of 30 Å/min, which is much higher than that attained from H₂-diluted SiH₄ plasma, by conventional approach. The crystallinity of the films has been identified by the sharp Raman peak at 520 cm⁻¹ and a large number of micrograins in the TEM micrographs. The metastable state of Ar, denoted as Ar^*, plays the crucial role in inducing microcrystallisation by transferring its de-excitation energy at the surface of the growing film. A mechanism has been proposed to explain the dependence of the formation of μc-Si:H film on the working gas pressure in the plasma.     

Magnesium ion-conducting gel polymer electrolytes dispersed with nanosized magnesium oxide

Experimental investigations are performed on novel magnesium ion-conducting gel polymer electrolyte nanocomposites based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), dispersed with nanosized magnesium oxide (MgO) particles. The nanocomposite materials are in the form of free-standing films. Various physical and electrochemical analyses demonstrate promising characteristics of these films, suitable as electrolytes in rechargeable magnesium batteries. The optimized material with 3 wt.% MgO offers a maximum electrical conductivity of 8 × 10⁻³ S cm⁻¹ at room temperature (25 °C) with good thermal and electrochemical stabilities. The ion/filler–polymer interactions and possible conformational changes in host polymer PVdF-HFP due to the liquid electrolyte entrapment and dispersion of nanosized MgO are examined by Fourier transform infrared (FTIR), X-ray diffraction (XRD) and scanning electron microscopic (SEM) methods. The Mg²⁺ ion conduction in the gel film is confirmed from the cyclic voltammetry, impedance spectroscopy and transport number measurements. The Mg²⁺ ion transport number (t₊) is enhanced substantially and found to have a maximum of 0.44 for the addition of 10 wt.% MgO nanoparticles. The enhancement in t₊ is explained on the basis of the formation of space-charge regions due to the presence of MgO:Mg²⁺-like species, that supports Mg²⁺ ion motion.     

Synthesis and assessment of La0.8Sr0.2ScyMn1−yO3−δ as cathodes for solid-oxide fuel cells on scandium-stabilized zirconia electrolyte

Perovskite-type La_0.8Sr_0.2Sc_yMn_1−yO_3−δ oxides (LSSMy, y = 0.0–0.2) were synthesized and investigated as cathodes for solid-oxide fuel cells (SOFCs) containing a stabilized zirconia electrolyte. The introduction of Sc³⁺ into the B-site of La_0.8Sr_0.2MnO_3−δ (LSM) led to a decrease in the oxides’ thermal expansion coefficients and electrical conductivities. Among the various LSSMy oxides tested, LSSM0.05 possessed the smallest area-specific cathodic polarization resistance, as a result of the suppressive effect of Sc³⁺ on surface SrO segregation and the optimization of the concentration of surface oxygen vacancies. At 850 °C, it was only 0.094 Ω cm² after a current passage of 400 mA cm⁻² for 30 min, significantly lower than that of LSM (0.25 Ω cm²). An anode-supported cell with a LSSM0.05 cathode demonstrated a peak power density of 1300 mW cm⁻² at 850 °C. The corresponding value for the cell with LSM cathode was 450 mW cm⁻² under the same conditions. The LSSM0.05 oxide may potentially be a good cathode material for IT-SOFCs containing doped zirconia electrolytes.     

X-ray scattering measurements on nanosized TiO2 micelles

Titanium dioxide, micelles on glass substrate were generated in situ in a water-in-oil (w/o) microemulsion composed of water, dioctyl sulfosuccinate sodium salt (AOT), and cyclohexane, by controlled hydrolysis of TiCl₄. The average grain size R, obtained by grazing-incidence small-angle X-ray scattering (GISAXS), was 6.3±0.8 nm. “Corrected specific surface” of TiO₂ micelles was determined as 5.0×10⁵ cm⁻¹. The average grain size R of 5.0±1.3 nm obtained by grazing-incidence wide-angle X-ray scattering (GIWAXS) agrees with GISAXS value. GIWAXS can detect smaller amounts of additional phases or impurities than classical X-ray diffraction equipment.     

Influence of the preparation conditions of TiO2 electrodes on the performance of solid-state dye-sensitized solar cells with CuI as a hole collector

Solid-state dye-sensitized solar cells (DSSCs) were fabricated in which the thin p-CuI film acts as a hole collector. Influences of the different preparation methods, composition, aging time of the TiO₂ pastes and sensitizing time on the performance of the cells were investigated. Different preparation routes for the TiO₂ paste do not obviously affect the performance of the cells. The volume of water, acetic acid and 2-propanol contained in the TiO₂ pastes and the amount of the TiO₂ powder were determined. The efficiency of the cells remains nearly stable when the aging period of the TiO₂ pastes is within one week. The favorable dying time is above 2 h. The cells having a favorable performance deliver a mean short-circuit photocurrent of 10.8 mA cm⁻² and mean open-circuit voltage of 0.61 V at 100 mW cm⁻² (1.5 AM). The mean fill factor and the mean efficiency of these cells are 0.55% and 3.7%, respectively. The short-circuit photocurrent rapidly decays after 3 h, and at the same time, the open-circuit voltage slowly decreases when the time increases, and then remains nearly stable after 24 h.     

Purification and characterization of [Fe]-hydrogenase from high yielding hydrogen-producing strain, Enterobacter cloacae IIT-BT08 (MTCC 5373)

Fe-hydrogenase from Enterobacter cloacae IIT-BT08 was purified 1284 fold with specific activity of 335 μmol H₂/min/mg protein for hydrogen evolution using reduced methyl viologen as an electron-donor at 25 °C. The molecular weight of the monomeric enzyme was determined to be 51 kDa by MALDI-ToF mass spectrometry. The PI of the enzyme was 5.6 displaying its acidic nature. The optimal temperature and pH for hydrogen evolution was 37 °C and 7–7.2 respectively. The affinity constant, K_m for reduced methyl viologen was 0.57 ± 0.03 mM and that of reduced ferredoxin was 0.72 ± 0.04 μM. The enzyme contained 11.47 gm-atom Fe/mol of Fe-hydrogenase. Electron paramagnetic resonance analysis ascertained the existence of iron molecules as [4Fe–4S] clusters. The internal amino acid sequences of trypsin digested peptides of hydrogenase as determined by ESI MS/MS Q-ToF showed 80-87% identities with the respective sequences of Clostridium sp. and Trichomonas sp. hydrogenase.