Tetramethylammonium based lead free perovskite active layer for solar cell application

Here we report the synthesis of a novel lead free organic-inorganic halide perovskite layer, tetramethylammonium tin tri-iodide (TMASnI₃), by simple and cost-effective chemical synthesis technique. The microstructural and optical studies confirm the formation of hexagonal perovskite structure with optical band gap ∼2.44 eV. A solar cell structure is fabricated by depositing the perovskite layer on zinc oxide thin film to demonstrate stable photovoltaic response under solar spectrum, where a thin layer of graphene oxide flakes on top of the perovskite layer acts as the charge transport layer. The open-circuit voltage (V_oc) and short circuit current density (J_sc) for this cell as extracted from the current-voltage measurement under one sun illumination of AM1.5 solar radiation are 0.60 V and 8.65 mA/cm², respectively. Without using any conventional hole transport layer, the power conversion efficiency (η) has been obtained as 1.92% which indicates the suitability of this perovskite material as an active layer for perovskite solar cell.     

DIRECT ELECTROCHEMICAL POWER GENERATION FROM CARBON IN FUEL CELLS WITH MOLTEN HYDROXIDE ELECTROLYTE

Historically, despite its compelling cost and performance advantages, the use of a molten metal hydroxide electrolyte has been ignored by direct carbon fuel cell (DCFC) researchers, primarily due to the potential for formation of carbonate salt in the cell. This article describes the electrochemistry of a patented medium-temperature DCFC based on a molten hydroxide electrolyte, which overcomes the historical carbonate formation.

An important technique discovered for significantly reducing carbonate formation in the DCFC is to ensure a high water content of the electrolyte. To date, four successive generations of DCFC prototypes have been built and tested to demonstrate the technology – all using graphite rods as their fuel source. These cells all used a simple design in which the cell containers served as the air cathodes and successfully demonstrated the ability to deliver more than 40 A with the current density exceeding 250 mA/cm². Conversion efficiency greater than 60% was achieved.     

Electrochemical impedance spectra of solid-oxide fuel cells and polymer membrane fuel cells

Electrochemical impedance spectroscopy (EIS) is a very useful method for the characterization of fuel cells. The anode and cathode transfer functions have been determined independently without a reference electrode using symmetric gas supply of hydrogen or oxygen on both electrodes of the fuel cell at open circuit potential (OCP). EIS are given for both polymer electrolyte fuel cells (PEFC) and solid oxide fuel cells (SOFC) at current densities up to 0.76 A cm⁻² (PEFC) and 0.22 A cm⁻² (SOFC). With increasing current density the PEFC-impedance decreases significantly in the low frequency range reaching a minimum at 0.4 A cm⁻². At even higher current densities an increasing contribution of water diffusion is observed: the cell impedance increases again. From EIS of SOFC a finite diffusion behavior is observed even at OCP, depending on water partial pressure of the anodic gas supply. This additional element reflects the influence of water partial pressure on the cell potential. The simulation of the measured EIS with an equivalent circuit enables the calculation of the individual voltage losses in the fuel cell.     

Surface modification of non‐woven poly (ethylene terephthalate) fibrous scaffold for improving cell attachment in animal cell culture

BACKGROUND: The development of carriers with biocompatible surfaces are required to meet the needs in animal cell culture. In this work, poly (ethylene terephthalate) (PET) fibrous scaffold surfaces were chemically modified to introduce diethylaminoethyl (DEAE) groups. A packed‐bed bioreactor with DEAE‐conjugated PET fibrous scaffolds was investigated for continuous production of HBsAg by r‐CHO cells. RESULTS: The changes of surface properties were characterized by surface hydrophilicity, Attenuated total reflectance (ATR) analysis, element measurement, and scanning electron microscopy. The results showed that this treatment could improve surface hydrophilicity and roughness. Using an r‐CHO cell line as model cells, the feasibility of the DEAE‐conjugated PET fibrous scaffold in animal cell culture was evaluated by means of cell attachment efficiency measurement, MTT (3‐(4,5)‐dimethylthiathiazo(‐z‐yl)‐3,5‐di‐phenytetrazoliumromide) assay, and scanning electron microscopy observation. Enhancement of cell attachment and proliferation was exhibited in the cell culture on DEAE‐conjugated PET fibrous scaffolds. r‐CHO cells were cultured for continuous HBsAg production in a packed‐bed bioreactor with DEAE‐conjugated PET fibrous scaffolds. A cell density of 1.2 × 10⁷ cells mL^?1 working volume, cell viability of 92.8% and maximum HBsAg concentration of 3.1 mg L^?1 were achieved. CONCLUSION: The packed‐bed bioreactor system with DEAE‐conjugated PET fibrous scaffolds has the potential for industrial animal cell culture application. Copyright © 2008 Society of Chemical Industry     

H2/Cl2 fuel cell for co-generation of electricity and HCl

A H₂/Cl₂ fuel cell system with an aqueous electrolyte and gas diffusion electrodes has been investigated and the effects of electrolyte concentration and temperature on the open circuit voltage (OCV) and cell performance have been evaluated. Furthermore, the kinetics and long-term stability of Pt as electrocatalyst have been studied under various conditions. In addition, the long-term stability of Rh electrocatalyst has been evaluated. The OCV obtained showed that the Cl₂ reduction is more reversible than O₂ reduction. The ohmic drop was determining the cell performance at high current densities. An output power of about 0.5 W cm^–2 was achieved with this system.     

High Flux Layer by Layer Polyelectrolyte FO Membrane: Toward Enhanced Performance for Osmotic Microbial Fuel Cell

Combination of microbial fuel cell (MFC) and forward osmosis (FO) is called an osmotic microbial fuel cell (OMFC). Because of the high cost of FO membranes, for the first time laboratory made FO membrane has been used in OMFC. This study investigates the performance of FO membrane in OMFC treating glucose as substrate and 2M NaCl as draw solution. The FO membrane was able to achieve 18.43 lm^?2 h^?1 (LMH) and for fouled FO membrane it was 15.26 lm^?2 h^?1. The OMFC constantly produced bioelectricity and achieved maximum current density 139.52 A/m³ and power density 27.38 W/m³. The energy production of OMFC was 0.438 kWh/m³.     

Performance degradation study of a direct methanol fuel cell by electrochemical impedance spectroscopy

A stability test of a direct methanol fuel cell (DMFC) was carried out by keeping at a constant current density of 150 mA cm⁻² for 435 h. After the stability test, maximum power density decreased from 68 mW cm⁻² of the fresh membrane-electrode-assembly (MEA) to 34 mW cm⁻² (50%). Quantitative analysis on the performance decay was carried out by electrochemical impedance spectroscopy (EIS). EIS measurement of the anode electrode showed that the increase in the anode reaction resistance was 0.003 Ω cm². From the EIS measurement results of the single cell, it was found that the increase in the total reaction resistance and IR resistance were 0.02 and 0.05 Ω cm², respectively. Summarizing the EIS measurement results, contribution of each component on the performance degradation was determined as follows: IR resistance (71%) > cathode reaction resistance (24%) > anode reaction resistance (5%). Transmission electron microscopy (TEM) results showed that the average particle size of the Pt catalysts increased by 30% after the stability test, while that of the PtRu catalysts increased by 10%.     

Development and operation of a 150 W air-feed direct methanol fuel cell stack

A five-cell 150 W air-feed direct methanol fuel cell (DMFC) stack was demonstrated. The DMFC cells employed Nafion 117^® as a solid polymer electrolyte membrane and high surface area carbon supported Pt-Ru and Pt catalysts for methanol electrooxidation and oxygen reduction, respectively. Stainless steel-based stack housing and bipolar plates were utilized. Electrodes with a 225 cm² geometrical area were manufactured by a doctor-blade technique. An average power density of about 140 mW cm^–2 was obtained at 110 °C in the presence of 1 M methanol and 3 atm air feed. A small area graphite single cell (5 cm²) based on the same membrane electrode assembly (MEA) gave a power density of 180 mW cm^–2 under similar operating conditions. This difference is ascribed to the larger internal resistance of the stack and to non-homogeneous reactant distribution. A small loss of performance was observed at high current densities after one month of discontinuous stack operation.     

Electrowinning of copper in two- and three-compartment reactive electrodialysis cells

Two- and three-compartment copper electrowinning (EW) cells based on reactive electrodialysis (RED) have been studied. The catholyte was cupric sulphate and the anolyte was ferrous sulphate, both dissolved in sulphuric acid. Copper mesh cathodes and graphite bar anodes have been used. The effects of cell current density, temperature, electrolyte recirculation flowrate and nitrogen sparging flowrate on cell performance (cathodic current efficiency, cell voltage and specific energy consumption (SEC)) have been determined. The cell voltage increased with cell current and it decreased with temperature and nitrogen sparging flowrate. The effect of nitrogen sparging flowrate on the cell voltage is stronger than the effect of electrolyte recirculation flowrate, whereas its enhancing effect on mass transfer is stronger than its deleterious effect on electrolyte conductivity. The SEC ranged from 0.94 to 1.39 kW h/kg at cell current densities between 200 and 600 A/m². These values are considerably better than those for conventional copper EW (about 2 kW h/kg at 350 A/m²). The morphology of the electrodeposits has been observed and a comparison between a three-compartment cell and a previously studied squirrel-cage cell (both based on RED) has been drawn.     

Performance of a pressurized electrochemical ozone generator

The performance of a novel electrolytic ozone generator using a solid polymer electrolyte and a PbO₂ anode is described. The operating parameters studied were: current density, water flow, temperature and pressure. Optimum current yields in the order of 20% are reached with a 30 cm² cell at a current of 40 A, a temperature of 30°C and a volume feed rate of water >301 h^–1. The system pressure does not influence the current efficiency or the cell voltage. The specific power consumption of a state-of-the-art cell is in the order of 65 W h g^–1. The technique has been applied commercially in the field of disinfection of purified water for more than 3 years.     

Polystyrene Foam with High Cell Density and Small Cell Size by Compression‐Injection Molding and Core Back Foaming Technique: Evolution of Cells in Cavity

Many efforts have been made to obtain uniform cell structures from foam injection molding techniques. However, cell nucleation mechanism and complex dynamics during the cell formation have rarely been well understood. Here, high‐pressure foam injection molding (HPFIM) is achieved by combining the injection–compression molding with core back foaming (ICMCBF) technique. The influences of compression pressure and time on the cell structure of polystyrene foam during the foaming process are studied. Compared with low pressure for conventional foam injection molding, high compression pressure (200 bar) and fast pressure drop rate of ICMCBF endow the foam with the highest cell density (1.59 × 10⁷ cells cm^?3), and the smallest cell size (15 µm). The tensile strength and impact strength are enhanced by about 60% (from 22.3 to 35.6 MPa) and 80% (from 3.6 to 6.8 MPa), respectively. This study gives a critical understanding of the cell nucleation and growth mechanism of the foam injection molding and supplies a new strategy for the fabrication of foam with uniform cell structure.     

Continuous microbial fuel cell using a photoautotrophic cathode and a fermentative anode

A complete microbial fuel cell (MFC) operating under continuous flow conditions and using Chlorella vulgaris at the cathode and Saccharomyces cerevisiae at the anode was investigated for the production of electricity. The MFC was loaded with different resistances to characterise its power capabilities and voltage dynamics. A cell recycle system was also introduced to the cathode to observe the effect of microalgae cell density on steady‐state power production and dynamic voltage profiles. At the maximum microalgae cell density of 2140 mg/L, a maximum power level of 0.6 mW/m² of electrode surface area was achieved. The voltage difference between the cathode and anode decreased as the resistance decreased within the closed circuit, with a maximum open circuit voltage (infinite resistance) of 220 mV. The highest current flow of 1.0 mA/m² of electrode surface area was achieved at an applied resistance of 250 Ω.     

A new method for the measurement of the diffusivity of carbon in alpha-iron using an electrochemical cell

A new method has been employed to measure the diffusivity of carbon in alpha iron. The method involves the measurement of ionic current of a carbon concentration cell which employs an iron cylinder as the anode. The design of the cell is such that when a constant external potential is applied, the ionic current is determined by the concentration polarization of carbon in the two electrodes. From the values of ionic current, the diffusivity of carbon (D _c) is calculated by the application of Fick's law. The results in the temperature range 854–975 K have been fitted by regression analysis to obtain the expression:D _c = 2.448 × 10^–5 exp(–102900.7/RT) withD _c in m² s^–1 andR in JK^–1 mol^–1. The results agree well with data in the literature.     

Determination of diffusion coefficient of oxygen into polymers by using electron spin resonance spectroscopy. I. Poly(methyl methacrylate)

A simple technique has been proposed for the measurement of the diffusion coefficient of oxygen into polymeric spheres. The technique is based on the scavenging of radicals produced by high energy radiation by oxygen. The diffusion coefficient of oxygen determined for poly(methyl methacrylate) has shown an inverse dependency on the dose received. Diffusion coefficient determined for low doses (D = 3.4 × 10^?8 cm²/s) as well as that determined after extrapolation to zero dose (D₀ = 3.7 × 10^?8 cm²/s) are in excellent agreement with the values reported in the literature.     

Electrochemical oxidation of boron containing compounds on titanium carbide and its implications to direct fuel cells

Electrochemical oxidation of sodium borohydride (NaBH₄) and ammonia borane (NH₃BH₃) (AB) have been studied on titanium carbide electrode. The oxidation is followed by using cyclic voltammetry, chronoamperometry and polarization measurements. A fuel cell with TiC as anode and 40 wt% Pt/C as cathode is constructed and the polarization behaviour is studied with NaBH₄ as anodic fuel and hydrogen peroxide as catholyte. A maximum power density of 65 mW cm⁻² at a load current density of 83 mA cm⁻² is obtained at 343 K in the case of borhydride-based fuel cell and a value of 85 mW cm⁻² at 105 mA cm⁻² is obtained in the case of AB-based fuel cell at 353 K.     

A Modified Hull Cell and its Application to the Electrodeposition of Zinc

An analytical electrochemical cell based on the Hull cell is described. The cell was tailored specifically for the analysis of electrowinning or electroplating. Current density distributions were generated by asymmetric insertion of an insulating baffle between parallel electrodes. The position and length of the baffle were easily altered, giving 12 possible distributions for a single total current. The cathode consisted of 10 electrically isolated 1cm², aluminium segments. By logging the potential drop across 1 resistors in each of the 10 isolated parallel branches, quantitative determination of current densities across the cathode was made possible. The small segments facilitated microscopic analysis of deposit morphologies. A technique for the determination of current efficiencies on each segment is described and demonstrated. The technique obviates the necessity to determine deposited masses directly. Development of the technique for industrial application is detailed. The system is demonstrated by evaluating known effects of variables in zinc electrowinning. The variables examined were temperature, deposition time, acid concentration and antimony contamination.     

An empirical equation for polymer electrolyte fuel cell (PEFC) behaviour

A simple analytical expression to determine cell potential (E) against current density (i) behaviour in polymer electrolyte fuel cells (PEFCs) was derived. The equation describes experimental data over the whole range of current density taking into account possible mass transport limitations. The empirical equation was used to fit experimental data obtained in a 50 cm² single cell in H₂/air operation using electrodes with low Pt loading (0.1 mg cm^-). A good agreement between theoretical and experimental data was found.     

Annealing-temperature-modulated optical,electrical properties,and leakage current transport mechanism of sol–gel-processed high-k HfAlOx gate dielectrics

Deposition of HfAlO_x gate dielectric films on n-type Si and quartz substrates by sol-gel technique has been performed and the optical, electrical characteristics of the as-deposited HfAlO_x thin films as a function of annealing temperature have been investigated. The optical properties of HfAlO_x thin films related to annealing temperature are investigated by ultraviolet-visible spectroscopy (UV–vis) and spectroscopy ellipsometry (SE). By measurement of UV–vis, average transmission of all the HfAlO_x samples are about 85% owing to their uniform composition. And the increase in band gap has been observed with the increase of annealing temperature. Moreover, the increase of refractive index (n) and density with the increase of annealing temperature are obtained by SE measurements. Additionally, the electrical properties based on Al/Si/HfAlO_x/Al capacitor are analyzed by means of the high frequency capacitance-voltage (C-V) and the leakage current density-voltage (J-V) characteristics. Results have shown that 400 °C-annealed sample demonstrates good electrical performance, including larger dielectric constant of 12.93 and lower leakage current density of 3.75×10⁻⁷ A/cm² at the gate voltage of 1 V. Additionally, the leakage current conduction mechanisms as functions of annealing temperatures are also discussed systematically.     

Electrodeposited vertically aligned ZnO nanorods thin films on steel substrate for CdS quantum dots sensitized solar cell

In the present study, we report the optimization of various deposition parameters viz. bath temperature, deposition time and current density to deposit densely packed and vertically aligned ZnO nanorod thin films on cost effective substrate, i.e. steel, by electrodeposition technique. The obtained vertically aligned ZnO nanorod thin films are sensitized by CdS quantum dots (QDs) and utilized for photoelectrochemical (PEC) cell application. Effect of redox electrolyte on the PEC cell properties of CdS QDs sensitized ZnO nanorod thin films is investigated using two different electrolytes viz. polysulfide and ferro(i)cyanide.¹ CdS QDs, of around 10 nm in diameter, are synthesized by chemical bath deposition (CBD) method. The deposited ZnO nanorods having diameter in the range 100–120 nm showed hydrophobic nature, which changed to hydrophilic after CdS QDs sensitization. The maximum short circuit current density (J_sc) and open circuit voltage (V_oc) are observed for ferro(i)cyanide electrolyte and are found to be 680 μA cm⁻² and 520 mV, respectively, under 10 mW cm⁻² of illumination. However, better photoelectrode stability is observed for polysulfide electrolyte.     

Recovery and concentration by electrodialysis of tartaric acid from fruit juice industries waste waters

Electrodialysis (ED) has been used as a membrane technique to concentrate tartaric acid from ion exchange regeneration waters obtained in grape juice treatment. The initial ion tartrate concentration in these streams varies between 1 and 10 kg m⁻³ and can be concentrated more than 60% (53·2 kg m⁻³ after 13300 s). Permeate flux of other common ionic components has been shown. Optimum intensities and current efficiency have been calculated with synthetic solutions. A mathematical approach has been used to predict final tartaric acid concentration and electro-osmotic effects. ©1997 SCI