Electrochemical noise of a hydrogen-air polymer electrolyte fuel cell operating at different loads

The electrochemical noise of a polymer membrane hydrogen-air fuel cell operating at different load currents was measured in serial experiments. Spectral power densities of the noise are shown to be divided into three regions. At frequencies greater than 3–10 Hz, the spectrum dependence has a constant slope of ??2 in the bilogarithmic coordinates. At frequencies 0.3–5 Hz, there is a horizontal plateau in which length is determined by the value of a load. At frequencies less than 0.3 Hz, the dependence of spectral power density has a slope of ??2. Medium-frequency plateau and high-frequency slope of spectral power densities of the noise were approximated by model RC circuits. The values of Faradic resistance and double-layer capacitance connected in parallel were obtained from the electrochemical impedance data. At load voltages higher 0.5 V, the height of the plateau was shown to be proportional to the 2.68 power of the load current value.     

Low-frequency noise in analytical soil measurements

Fourier analysis of the real-time quality-control charts for colorimetric, photometric, and pH soil measurements shows 1/f ⁿ (n=1±0.05) noise intensity dependence on frequency, in correspondence to the earlier test for atomic absorption measurements. In addition, the prevailing character of the sample preparation in the general noise frequency dependence is clearly demonstrated. Some important analytical problems are addressed where knowledge of the specific character of the time variation in the analytical data sets is essential.     

Densitometric high-performance thin-layer chromatography methods for the quantification of oleuropein in Olea europaea leaves and pharmaceutical preparation utilizing normal- and reversed-phase silica gel plates

Two validated, simple and precise densitometric high-performance thin-layer chromatography (HPTLC) quantification methods were proposed for both qualitative and quantitative estimation of oleuropein in Olea europaea leaves and a pharmaceutical product utilizing normal-phase and reversed-phase silica gel TLC plates. In method I, 10 × 20 cm glass plates coated with 0.2 mm thin layers of normal-phase silica gel 60 containing F₂₅₄ (E-Merck, Germany) and a mixture of ethyl acetate‒methanol‒water (8:1:0.5, V/V) were used as the stationary and the mobile phase, respectively. Method II utilized 10 × 20 cm glass-backed plates supporting 0.2 mm layers of RP-18 silica gel 60 containing F₂₅₄ (E-Merck, Germany) as the stationary phase and green solvents mixture composed of ethanol‒water (5.5:4.5, V/V) as the mobile phase. The two methods resulted in sharp, symmetrical, well-resolved peaks at R_F values of 0.47 ± 0.02 and 0.78 ± 0.03 with linearity ranges 200‒1400 ng/spot (r² = 0.9994) and 200‒1400 ng/spot (r² = 0.9996) for method I and method II, respectively. Spots corresponding to oleuropein were scanned at 200 nm. The two methods complied with the ICH guidelines for validation. Due to simplicity, low cost and short analysis time, the methods can be good alternatives for the quality control of different products containing olive leaves extract or pure oleuropein.

     

Carrier-mediated hollow fiber liquid-phase microextraction for preconcentration followed by spectrophotometric determination of amoxicillin

Preconcentration followed by ultraviolet spectrophotometric determination of amoxicillin (Amox) in pharmaceuticals and water samples by using a three-phase hollow fiber microextraction technique based on carrier-mediated transport has been presented. Amox was extracted from an aqueous solution (source phase) at pH 9.0 into 1-octanol containing 5% (w/v) Aliquat-336 impregnated in the pores of a hollow fiber. It was then back-extracted into NaCl solution (pH = 4.0) which was already positioned as the receiving phase inside the lumen of the hollow fiber. The extraction took place due to the concentration gradient of the counterion between the source and the receiving phases. Under the optimized conditions, an enrichment factor of 240 and a limit of detection of 0.2 μmol L⁻¹ were obtained. The calibration curve was linear (R² = 0.9967) in the concentration range of 0.5–10.0 µmol L⁻¹ Amox. The interday relative standard deviation (n = 9) and the intraday relative standard deviation (n = 3) for 1.0 × 10⁻⁶ mol L⁻¹ Amox solution were 7.3 and 6.4%, respectively.

     

dc Proton conductivity at low‐frequency in Nafion conductivity spectrum probed by time‐resolved SAXS measurements and impedance spectroscopy

The electric transport properties of Nafion membranes are investigated by impedance spectroscopy (IS) and correlated with small angle X‐ray scattering (SAXS). Detailed IS measurements in a wide range of temperature and frequencies (f) allowed separating contributions from different charge carriers in Nafion. At controlled relative humidity and temperature, Nafion IS spectrum exhibits at T > 160 °C two distinct frequency‐independent conductivities occurring at high f ～ 10⁶ Hz and low f < 10^?2 Hz. Such IS measurements were combined with time‐dependent SAXS measurements under applied dc electric potential, which provided compelling evidence that the low‐f dc conductivity is related to the motion of protons via ion‐hopping in hydrated Nafion membranes. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 822–828     

The signal/noise of an HMBC spectrum can depend dramatically upon the choice of acquisition and processing parameters

The effect of various acquisition and processing parameters on the sensitivity of HMBC spectra for typical organic molecules has been systematically investigated. For molecules in the 200–600 molecular weight range, an acquisition time of 0.2 to 0.4 s, a recycle time of no more than 1.0 s, optimization for ⁿJ_CH = 8 Hz and 512 time increments (with two‐ to fourfold linear prediction) are recommended. Some form of sine bell weighting along f₂ and either Gaussian or sine bell weighting along f₁ is suggested. The use of a 0.1‐s acquisition time and/or Gaussian or exponential weighting along f₂ can result in dramatic sensitivity loss, particularly for correlation peaks involving protons with complex splitting patterns, and should be avoided. Copyright © 2009 John Wiley & Sons, Ltd.     

Koo–Kleinstreuer–Li correlation for simulation of nanofluid natural convection in hollow cavity in existence of magnetic field

The lattice Boltzmann method is used to study natural convection of a CuO/water nanofluid in a hollow cavity. The hollow walls are fixed at a uniform temperature, and the effect of an applied magnetic field is examined. The Koo–Kleinstreuer–Li model, which accounts for nanoparticle’s Brownian motion, is used to gain the nanofluid effective thermal conductivity and nanofluid viscosity. The mechanisms how the inclination angle of magnetic field, Hartmann number, Rayleigh number, hollow width and nanoparticle volume fraction affect the streamlines, isotherms and rate of heat transfer are also studied. The results show that the average Nusselt number is increased by incrementing the nanoparticle volume fraction, Ra, magnetic field inclination angle and hollow width, but decreased by the Ha. For L = 0.4, the value of Ra where the dominant mechanism of heat transfer is changed from conduction to convection is larger than 10⁵. But for L = 0.48 or 0.56, the turning point of the dominant heat transfer mechanism is at Ra < 10⁵. Besides, at L = 0.4 or 0.48, the average Nusselt numbers in hot walls are higher than those in cold wall, but the opposite trend is found at L = 0.56.

     

Sorption/desorption study of strontium on Ain Oussera soils around the Es-Salam reactor facility

Four types of undisturbed soils around the Es-Salam reactor (Algeria) were used to evaluate the sorption behavior of strontium. The batch study was carried out under different experimental conditions. The kinetics were well fited by pseudosecond order model. Soils’s activation energies were 12.37, 14.76, 15.5 and 16.17 kJ mol⁻¹, corresponding to ion-exchange-type sorption. Sorption was exothermic (ΔH° < 0), spontaneous (ΔG° < 0) and favorable at low temperature. Competing cations, particularly Ca²⁺ reduce the Sr adsorption. Desorption reaction showed a higher value of Sr in the easily extractible phase indicating a relative availability of the element.

     

Sub‐millisecond response phase modulator using a low crossover frequency dual‐frequency liquid crystal

A high birefringence (Δn = 0.292 at λ = 633 nm, 25°C) and low crossover frequency (<1 kHz at T = 25°C) dual‐frequency liquid crystal (DFLC) mixture was developed. The high birefringence enabled us to use a thin liquid crystal cell, which is helpful for fast response time and low operating voltage. The initially low crossover frequency allowed us to operate the DFLC device at an elevated temperature, which significantly lowers the viscosity while keeping the crossover frequency in an acceptable range (<10 kHz). We demonstrated a 2π phase shifter at λ = 633 nm using such a DFLC and obtained a sub‐millisecond response time at T～45°C. This type of DFLC mixture together with elevated temperature operation opens a new way for achieving fast response time.     

Ionic conductivity and interfacial stability of Li6PS5Cl–Li6.5La3Zr1.5Ta0.5O12 composite electrolyte

Solid electrolytes which possess excellent lithium-ion conductivity and chemical compatibility with electrode materials are necessary for the commercialization of all-solid-state lithium batteries. However, a single solid electrolyte meeting above requirements is difficult. Consequently, the composite electrolytes have attracted more attention. In this paper, Li₆PS₅Cl–xLi_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZTO) (x = 0, 2.5 wt%, 5 wt%, 10 wt%) composite electrolytes are prepared by a simple planetary grinding process. It has been found that adding an appropriate amount of LLZTO can increase the lithium-ion conductivity. At 30 °C, the lithium-ion conductivity increases from 2.6 × 10⁻⁴ S/cm (Li₆PS₅Cl) to 5.4 × 10⁻⁴ S/cm (Li₆PS₅Cl-5 wt% LLZTO). Besides, the addition of LLZTO to the Li₆PS₅Cl can influence the growth rate of the SEI. It has been shown that the SEI growth rate obeys a parabolic rate law, and the growth rates of Li₆PS₅Cl, Li₆PS₅Cl-2.5 wt% LLZTO, Li₆PS₅Cl-5 wt% LLZTO, and Li₆PS₅Cl-10 wt% LLZTO are 8.62, 3.53, 3.33, and 3.38 Ω/h^1/2 at 60 °C, respectively. In lithium plating and stripping experiment, the voltage of symmetrical Li/Li₆PS₅Cl/Li cell suddenly drops to 0 V after cycling 39 h at 0.103 mA/cm² (0.097 mAh/cm²). On the contrary, the Li/Li₆PS₅Cl–xLLZTO (x = 2.5 wt%, 5 wt%, 10 wt%)/Li symmetrical cell exhibits a stable voltage profile over 100 h at the same test conditions. The corresponding interfacial impedance of Li/Li₆PS₅Cl–xLLZTO (x = 2.5 wt%, 5 wt%, 10 wt%) remains stable after 10, 30, and 50 charge/discharge cycles.

     

Assessment of 1/f noise associated with nanopores fabricated through chemically tuned controlled dielectric breakdown

Recently, we developed a fabrication method—chemically-tuned controlled dielectric breakdown (CT-CDB)—that produces nanopores (through thin silicon nitride membranes) surpassing legacy drawbacks associated with solid-state nanopores (SSNs). However, the noise characteristics of CT-CDB nanopores are largely unexplored. In this work, we investigated the 1/f noise of CT-CDB nanopores of varying solution pH, electrolyte type, electrolyte concentration, applied voltage, and pore diameter. Our findings indicate that the bulk Hooge parameter (α_b) is about an order of magnitude greater than SSNs fabricated by transmission electron microscopy (TEM) while the surface Hooge parameter (α_s) is ∼3 order magnitude greater. Theα_s of CT-CDB nanopores was ∼5 orders of magnitude greater than theirα_b, which suggests that the surface contribution plays a dominant role in 1/f noise. Experiments with DNA exhibited increasing capture rates with pH up to pH ∼8 followed by a drop at pH ∼9 perhaps due to the onset of electroosmotic force acting against the electrophoretic force. The1/f noise was also measured for several electrolytes and LiCl was found to outperform NaCl, KCl, RbCl, and CsCl. The 1/f noise was found to increase with the increasing electrolyte concentration and pore diameter. Taken together, the findings of this work suggest the pH approximate 7–8 range to be optimal for DNA sensing with CT-CDB nanopores.     

The role of phosphate released from Na–Al–P glass under repository conditions in speciation and transport of americium

The uptake of natural radioactivity by pasture-grass collected from seven different grasslands of Digor was calculated. The activities of ²²⁶Ra, ²³²Th and ⁴⁰K in pasture-grass were in the range of 21.8 ± 6.3–49.6 ± 13.4, 51.9 ± 13.2–127.7 ± 23.8 and 309.5 ± 33.5–807.3 ± 64.4 Bq kg⁻¹, respectively. The soil to pasture-grass transfer factors were evaluated and determined to be in the range from 0.26 ± 0.13 to 0.69 ± 0.34, 0.64 ± 0.27 to 1.99 ± 0.40 and 0.64 ± 0.014 to 1.40 ± 0.032 for ²²⁶Ra, ²³²Th and ⁴⁰K, respectively. The distribution of ²²⁶Ra and ²³²Th in different parts of pasture-grass indicated a decreasing tendency in order of root > stem > leaf. ⁴⁰K mainly accumulated in stem of pasture-grass and is followed by declining trend stem > leaf > root.

     

Rubber elasticity in the range of small uniaxial tensions and compressions. Results for poly(dimethylsiloxane)

Results of uniaxial tension and compression experiments are reported on crosslinked polydimethylsiloxane (PDMS) networks in the unswollen state over the range 0.5 < α^?1 < 1.2 where α is the extension ratio. Curves representing the reduced force [f] = f(V⁰/V)^1/3(α – α^?2)^?1 plotted against α^?1 can be approximated by straight lines for 0.5 < α^?1 < 0.9, in agreement with the phenomenological Mooney equation. As α^?1 approaches 1, however, they tend to level off and continue into the α^?1 > 1 region with decreasing slope. These results are in agreement with the predictions of recent elasticity theories that incorporate the effect of junction-chain entanglements in the elastic free energy.     

Ethylene Epoxidation over Alumina-Supported Silver Catalysts in Low-Temperature AC Corona Discharge

In this paper, the epoxidation of ethylene over different catalysts—namely Ag/(low-surface-area, LSA)α-Al₂O₃, Ag/(high-surface-area, HSA)γ-Al₂O₃, and Au–Ag/(HSA)γ-Al₂O₃—in a low-temperature corona discharge system was investigated. In a comparison among the studied catalysts, the Ag/(LSA)α-Al₂O₃ catalyst was found to offer the highest selectivity for ethylene oxide, as well as the lowest selectivity for carbon dioxide and carbon monoxide. The selectivity for ethylene oxide increased with increasing applied voltage, while the selectivity for ethylene oxide remained unchanged when the frequency was varied in the range of 300–500 Hz. Nevertheless, the selectivity for ethylene oxide decreased with increasing frequency beyond 500 Hz. The optimum Ag loading on (LSA)α-Al₂O₃ was found to be 12.5 wt.%, at which a maximum ethylene oxide selectivity of 12.9% was obtained at the optimum applied voltage and input frequency of 15 kV and 500 Hz, respectively. Under these optimum conditions, the power consumption was found to be 12.6 × 10^?16 W s/molecule of ethylene oxide produced. In addition, a low oxygen-to-ethylene molar ratio and a low feed flow rate were also experimentally found to be beneficial for the ethylene epoxidation.     

Demonstration of an optical biosensor for the detection of faecal indicator bacteria in freshwater and coastal bathing areas

ColiSense, an early warning system developed for Escherichia coli detection, is assessed using environmental samples. The system relies on the detection of β-glucuronidase (GUS), a biomarker enzyme for E. coli. In contrast with other rapid GUS-based methods, ColiSense is the only method that uses 6-chloro-4-methyl-umbelliferyl-β-d-glucuronide (6-CMUG) as a fluorogenic substrate. The system measures a direct kinetic response of extracted GUS, and the detection was carried out in the absence of particles or bacteria. It is necessary to evaluate the system with environmental samples to establish the relationship between faecal indicator bacteria E. coli and the response measured by the ColiSense. This paper presents the results of tests carried out with the ColiSense system for 2 trials, one conducted with freshwater samples collected from rivers in the Dublin area and a second conducted with seawater samples from coastal areas collected over the bathing season. A positive linear correlation was found between E. coli (MPN 100 mL⁻¹) and ColiSense response (R² = 0.85, N = 125, p < 0.01) for the seawater sample. A ColiSense response threshold was identified as 0–1.8 pmol min⁻¹ 100 mL⁻¹, equivalent to 0–500 E. coli 100 mL⁻¹. Using this threshold, 96.8% of the samples were correctly classified as being above or below 500 E. coli 100 mL⁻¹ by the ColiSense system. Results presented demonstrate that the ColiSense system can be used as an early warning tool with potential for active management of bathing areas by providing results in 75 min from sample collection.

     

Computerized measurement of viscoelastic properties of macromolecular solutions: Frequency dependence over and extended range of solvent viscosity

The modified Birnboim transducer and a computerized data acquisition and processing system (DAPS) for the measurement of viscoelastic properties of macromolecular solutions are described. The apparatus has a continuous frequency range from 0.01 to ca. 700 Hz and a viscosity range from 2 to ca. 30,000 poise (sample volume 1 to 1.5 cm²). Sample temperature is controlled to within 0.002°C from ?30°C to +80°C. Working displacements are 10² to 10⁴ Å. The DAPS is designed for precise determinations of the magnitudes and relative phasing of two sinusoidally time-varying electrical signals (0.02%, 0.02°, respectively, for signals > 2 V peak) from 10^?2 to 10⁵ Hz. Cross-correlation techniques are used for noise rejection. For frequencies below 30 Hz values of the storage (G') and loss (G″) components of the complex shear modulus (G^*) of 1 dyne/cm² are determined to within 10% and 4%, respectively, for liquids of moderately low viscosity. Proportionately higher measurement accuracies for typical values of G' and G″ and the wide frequency and viscosity ranges permit extrapolation to infinite dilution and studies of limited molecular flexibility for many polymer—solvent systems.     

A new method for electrocrystallization of AgTCNQF4 and Ag2TCNQF4 (TCNQF4 = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) in acetonitrile

Semiconducting AgTCNQF₄ (TCNQF₄ = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) has been electrocrystallized from an acetonitrile (0.1 M Bu₄NPF₆) solution containing TCNQF₄ and Ag(MeCN) ⁺₄ . Reduction of TCNQF₄ to the TCNQF ¹⁻₄ anion, followed by reaction with Ag(MeCN) ⁺₄ forms crystalline AgTCNQF₄ on the electrode surface. Electrochemical synthesis is simplified by the reduction of TCNQF₄ prior to Ag(MeCN) ⁺₄ compared with the analogous reaction of the parent TCNQ to form AgTCNQ, where these two processes are coincident. Cyclic voltammetry and surface plasmon resonance studies reveal that the electrocrystallization process is slow on the voltammetric time scale (scan rate = 20 mV s⁻¹) for AgTCNQF₄, as it requires its solubility product to be exceeded. The solubility of AgTCNQF₄ is higher in the presence of 0.1 M Bu₄NPF₆ supporting electrolyte than in pure solvent. Cyclic voltammetry illustrates a dependence of the reduction peak potential of Ag(MeCN) ⁺₄ to metallic Ag on the electrode material with the ease of reduction following the order Au < Pt < GC < ITO. Ultraviolet-visible, Fourier transform infrared, and Raman spectra confirmed the formation of reduced TCNQF ¹⁻₄ and optical microscopy showed needle-shaped morphology for the electrocrystallized AgTCNQF₄. AgTCNQF₄ also can be formed by solid–solid transformation at a TCNQF₄-modified electrode in contact with aqueous media containing Ag⁺ ions. Chemically and electrochemically synthesized AgTCNQF₄ are spectroscopically identical. Electrocrystallization of Ag₂TCNQF₄ was also investigated; however, this was found to be thermodynamically unstable and readily decomposed to form AgTCNQF₄ and metallic Ag, as does chemically synthesized Ag₂TCNQF₄.

     

The electrochemical behaviour of butyltrimethylammonium bis(trifluoromethylsulfonyl)imide at negatively polarised aluminium electrode studied by in situ soft X-ray photoelectron spectroscopy,electrochemical impedance spectroscopy and cyclic voltammetry techniques

The in situ X-ray photoelectron spectroscopy data indicate that butyltrimethylammonium bis(trifluoromethylsulfonyl)imide (N4111(TFSI)) adsorbs strongly within the potential range −3.25 V < E < −2.25 V and specifically at E < −3.25 V (vs. Ag-QRE) at the Al electrode. Strong adsorption of the intermediates of N4111(TFSI) electrochemical decomposition was observed in electrochemical impedance spectroscopy and cyclic voltammetry measurements. At E < −4.25 V (vs. Ag-QRE), very intensive electrochemical reduction of N4111(TFSI) took place at the Al electrode giving gaseous products. In the potential range from − 2.25 to 0.00 V (vs. Ag-QRE), non-specific adsorption of N4111(TFSI) exists et al. surface.

     

Electrochemical behaviour and determination of rimsulfuron herbicide by square wave voltammetry

The voltammeric behaviour of rimsulfuron herbicide has been studied by square wave stripping voltammetry on static hanging mercury drop electrode. It exhibited a well-defined peak within the pH range of 1.0–6.0, having a maximum peak response at ?600 mV (vs.Ag/AgCl) at pH 3.0. The factors such as accumulation potential (E_acc), accumulation time (t_acc), frequency (f), pulse amplitude (ΔE) and step potential (ΔE_s) have been optimised. The calibration plot was a straight line in the range of 4.4–134.4 μg L^?1 with a detection limit of 1.3 μg L^?1. The validity of the method was assessed from the recoveries of spiked lake water, tomato juice and agrochemical formulation of Doncep^®. The results of the experiments conducted for five recoveries were 48.8 ± 1.7 and 49.7 ± 1.0 μg L^?1, which are very close to the rimsulfuron spiked to lake water and tomato juice (50 μg L^?1), with a relative error of –2.4% and ?0.6%, respectively. The electrode reaction mechanism was also postulated.     

Qualitative and quantitative analysis of arctiin and arctigenin in Arctium tomentosum Mill. by high-performance thin-layer chromatography

A sensitive, reliable and rapid high-performance thin-layer chromatography (HPTLC) method for the determination of arctiin and arctigenin in Arctium tomentosum Mill. was established. A. tomentosum Mill. extract was used for chromatographic analysis. The ratio of chloroform and methanol was 48:5 as mobile phase. Temperature is 20–23 °C and humidity is less than 30%. The scanning wavelength is 280 nm. The results showed that arctiin had a good linear relationship in the range of 0.5315–5.8465 μg, r = 0.9982; arctigenin had a good linear relationship in the range of 0.5654–6.2194 μg, r = 0.9951. Precision analysis showed that the RSD < 3.0%. The stability study showed that the sample was stable within 24 h at room temperature, RSD < 2.0%. The average recoveries were 103.07 ± 1.57% and 98.55 ± 2.71%, respectively. The antioxidant activity of Arctium tomentosum Mill. was also identified. The results showed that the antioxidant component identified by thin-layer chromatography–1, 1-diphenyl-2-trinitrophenylhydrazine (TLC-DPPH) was arctigenin not arctiin. The proposed HPTLC is a simple and accurate method for the qualitative and quantitative analysis of arctiin and arctigenin in Arctium tomentosum Mill. from different areas.