AC Impedance Spectroscopy Studies Research Articles

Experimental Studies on the Effect of Expired Amiodarone Drug (EAD) as a Corrosion Inhibitor on Mild Steel in 1 M HCl.

In the present investigation, the corrosion tendency of mild steel under acidic pH was studied by employing unused expired amiodarone (EAD) drug as a potential corrosion inhibitor by adopting the weight loss measurement method. The corrosion inhibition efficiency (IE) of the formed protective film (EAD) on the steel surface was analyzed using potentiodynamic polarization and AC-impedance spectroscopy studies. The surface morphology of the mild steel before and after corrosion (in 1.0 M HCl) was analyzed via scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDAX), atomic force microscopy (AFM), and thermodynamic studies. The weight loss measurement under different concentrations of EAD indicated that an excellent inhibition was displayed at a concentration of 0.001 M, and the IE was found to depend on both the concentration and molecular structure of EAD. A potentiodynamic polarization study revealed that EAD predominantly acted as a cathode inhibitor, and electrochemical impedance spectroscopy (EIS) confirmed the adsorption of EAD on the surface of mild steel, which obeyed Temkin's adsorption isotherm model. The calculated thermodynamic parameters revealed that adsorption was spontaneous and exothermic.

1D aligned, n–p and n–n type ZnO heterojunction nanofibers for NO2 sensors: exploration of conduction mechanism using in situ impedance spectroscopy

1D aligned n–p type ZnO/Bi2O3 and n–n type ZnO/In2O3 heterojunction nanofibers have been developed via coaxial electrospinning approach and its complex sensing mechanisms have been deduced using in situ AC impedance spectroscopic studies.

Reduction of copper corrosion in 5 M HCl solution by expired nontoxic Ofloxacin drug

Several corrosion inhibitors have been used in industry to eliminate the corrosive influence of harsh hydrochloric acid solutions on the mechanical behavior of copper structures. Recently, expired drug products as corrosion inhibitor have been developed to replace the organic compounds (synthesized) which are expensive and toxic molecules. In this work, the expired nontoxic Ofloxacin drug is used to study the its effectiveness as a corrosion inhibitor for copper metal in 5 M HCl solution with the aid of weight loss, potentiodynamic polarization, AC impedance spectroscopy and scanning electron microscopy (SEM) studies. The weight loss results demonstrated that, 4 mg/L of expired Ofloxacin drug was the optimum concentration for inhibition of copper corrosion in acidic system. Tafel plot results revealed the mixed corrosion inhibition property of expired Ofloxacin drug. AC impedance spectroscopy and scanning electron microscope (SEM) results well supported the weight loss and potentiodynamic polarization results.

Na/Li substitution effect on the structural, electrical and magnetic properties of LiCr(MoO4)2 and β─Li0.87Na0.13Cr(MoO4)2

The novel bi-molybdate β─Li0.87Na0.13Cr(MoO4)2 was prepared by solid state reaction route. Single crystal X-ray diffraction experiment revealed that the compound crystallizes in the triclinic system, in P −1 space group with a = 6.715 (2), b = 7.160 (3), c = 7.237 (1) Å, α = 91.16° (3), β = 110.59° (2), γ = 105.54° (3). Its crystal structure is isotypic to LiCr(MoO4)2 which has interesting magnetic and electrochemical properties [1–3]. Bond valence sum (BVS) and charge distribution (CHARDI) validation tools supported the structural model.The electrical properties were systematically studied by impedance spectroscopy. The ionic conductivity measurements are performed on pellets of 82% and 87% relative density for LiCr(MoO4)2 and β─Li0.87Na0.13Cr(MoO4)2 respectively. AC impedance spectroscopy studies show that the highest overall conductivity is σ326°C = 7.86 × 10−7 S cm−1Probable diffusion pathways of Li+ ions in the both structures were simulated using the bond valence sum BVS maps method. This analysis shows that the ionic transport in these materials is essentially due to simple hopping of Li+ ions parallel to (101) plane.For β─Li0.87Na0.13Cr(MoO4)2 compound, the in-situ High Temperature X-Ray Diffraction (HTXRD), in the temperature range from 25 to 650 °C, were also performed and Unit-cell thermal expansion has been discussed.The magnetic study show that these compounds present an antiferromagnetic order below the temperatures TN = 16 and 30 K for LiCr(MoO4)2 and β─Li0.87Na0.13Cr(MoO4)2 respectively.

Investigations of lithium ion conducting polymer blend electrolytes using biodegradable cornstarch and PVP

Solid polymer electrolytes used in energy storage devices based on Cornstarch and Poly (vinyl Pyrrolidone) blend incorporated with lithium acetate was prepared using the solution casting method. XRD results confirmed that the amorphous nature of the as-prepared polymer electrolyte was increased by addition of salt. 80 wt % Cornstarch/20 wt % PVP/60 wt % lithium acetate added polymer blend system attains better amorphous nature than others. At ambient temperature, 60 wt % of lithium acetate added system has better bulk conductivity of 3.52 × 10−5Scm−1 over the frequency range of 42 Hz to 1 MHz using AC impedance spectroscopy studies. The dielectric analysis is confirmed that the higher conducting sample was having high dielectric constant and low relaxation time for enhancing ions dynamic behaviour. The conduction mechanism of the higher conducting polymer electrolyte is explained by small polaron hopping and overlapping large polaron tunnelling conduction mechanism. From the argand plot, it is confirmed that higher conducting sample has low relaxation time.

Ac conductivity and impedance spectroscopy study and dielectric response of MgPc/GaAs organic heterojunction for solar energy application

The study concerns the C/ω-V performances and examination of dielectric response of MgPc/GaAs organic heterojunction (OHJ) structure of solar energy applications. Throughout this work, many characterizations have been achieved and various parameters have been extracted. C/ω-V and G/ω-V plots are subject to give much knowledge about the mechanism and behavior inside the OHJ. It is revealed that capacitance of OHJ increases with voltage defining deep depletion (dd), depletion (dep) and accumulation (ac) regions. Besides, Ac conductivity at room temperature increases with frequency in particular within the forward biasing voltage, reaching a high point of 28 × 10−7 S/cm at 5 V. Real and imaginary terms of complex dielectric constant or well known by permittivity, ε versus lnω are studied inside the 1.5V–2.5 V range. The real and imaginary parts of the impedance are found to be frequency dependence within the 1.5 V and 2.5 V bias range. Ac current conductivity σAc against frequency (lnω) of MgPc/GaAs OHJ inside 1.5V–2.5 V bias voltage range is well detailled; the average of conductivity about 8 × 10−7 S/cm is then recorded. The impedance spectroscopy study is evidenced by the complex impedance M where real and imaginary part are M′ and M’’. Profile of M′ and M″ as function of voltage exhibits peaks for 3 kHz–300kHz frequency range. It is indicated that M″ and M’ are roughly comprised between 0.08 and 1.12 and 0 and 2 respectively. Conduction mechanism is then determined by lnσ-lnω plots. The Cole-Cole diagram displays different curves of impedance as distinct semicircle for measured frequencies.

Development of novel Nd2WO6/ZnO incorporated on GO nanocomposite for the photocatalytic degradation of organic pollutants and biological studies

In this work, the Nd2WO6/ZnO–GO (NWZG) nanocomposite were prepared by simple hydrothermal route. The crystalline structure, morphology and elemental composition of the as prepared NWZG nanocomposite were characterized by numerous spectroscopic techniques. For the first time, Nd2WO6/ZnO–GO was utilized as a photocatalyst for the degradation of ciprofloxacin (CIP) antibiotic drug and methylene blue (MB) dye solution under UV light irradiation. Interestingly, NWZG nanocomposite exhibited enhanced photocatalytic performance could degrade above 96% and 98% of CIP and MB solution, respectively. The radical trapping experiment results revealed that the O 2 radicals are the major active species. Furthermore, NWZG nanocomposite demonstrated extraordinary chemical stability and reusability even after five repeated cycles. Besides, NWZG nanocomposite portrayed significant antibacterial properties against both Gram-positive (Bacillus cereus) and Gram-negative (Escherichia coli) bacterial strains. Moreover, AC impedance spectroscopy studies showed that NWZG nanocomposite have the superior electrical conductivity and dielectric behaviour when compared to pristine one.

Studies on ionic liquid incorporated polymer blend electrolytes for energy storage applications

Solid polymer blend electrolytes (SPBEs) were prepared using poly(ethylene oxide) (PEO), poly(vinylidene fluoride-hexafluoro propylene) (P(VdF-HFP)) as polymer hosts, zinc triflate (ZnTr) as an electrolyte, and 1-butyl-3-methylimidazolium hexafluorophosphate (1B3MIHFP) as an ionic liquid (IL) via a conventional solvent casting technique. Various techniques like AC impedance spectroscopy, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and thermogravimetric/differential thermal analysis (TG/DTA) respectively were carried out for the prepared samples. From AC impedance spectroscopic studies, maximum ionic conductivity of 95.72 × 10−4 S cm−1 was observed for the system with 20 wt% of 1B3MIHFP at room temperature. Further, the temperature-dependent ionic conductivity study seems to obey Arrhenius behavior. Complexation and increase in degree of amorphicity for IL incorporated system was confirmed through XRD analysis. Ionic transference number was calculated by Wagner’s polarization technique, and it was found to be 0.991 for the sample which possessed maximum ionic conductivity. This value suggested that the charge transport in the polymer blend electrolyte matrix is mainly due to the Zn2+ ions. The dielectric properties of the SBPEs were also studied using the complex dielectric permittivity spectra, complex electric modulus spectra, and loss tangent analysis. Significant morphological changes were observed from SEM micrographs. From the TG-DTA analysis, thermal stability of the sample was found to be 245 °C.

Preparation, structure, electrical properties and diffusional sodium pathways in the new Na5.2Cu1.9Al(AsO4)4

The novel arsenate Na5.2Cu1.9Al(AsO4)4 was synthesized using solid-state reaction route. Single crystal X-ray diffraction experiment revealed that the title compound crystallizes in a triclinic space group P-1 with a = 5.111(3) Å; b = 7.577(2) Å; c = 9.332(4) Å, α = 88.73(3)°, β = 75.74(5)°, γ = 89.56(4)° and Z = 2. The structural model was supported by bond valence sum (BVS) and charge distribution (CHARDI) validation tools. The crystal structure is based on an open 3D framework made up of CuO4 square planar units, MO5 square-based pyramids and AsO4 tetrahedra sharing corners. The framework tunnels in [100] direction accommodate the Na ions. AC impedance spectroscopy studies show that the conductivity is 1.49 × 10−5 S cm−1 at 575 °C and the activation energy is 1.14 eV. In addition, probable diffusion pathways of Na ions in the structure were simulated using the bond valence sum (BVS) maps method.

The synergistic catalyst-carbonates effect on the direct bituminous coal fuel cell performance

The current work explores the feasibility to improve the performance of a Direct Carbon Fuel Cell (DCFC): CO2 + bituminous coal|Co-CeO2/YSZ/Ag|Air by infusing a gasification catalyst (Co/CeO2) and/or Li-K carbonates mixture into the carbon fuel. The different fuel feedstock mixtures were characterized by various methods, involving chemical composition and proximate analysis, particle size distribution (PSD), X-ray diffraction (XRD), N2 adsorption-desorption (BET method), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM), to gain insight into the effect of catalyst and/or carbonates addition to fuel mixture physicochemical characteristics. An increase of the power output up to ca. 20 and 80% is achieved for carbon/catalyst and carbon/catalyst/carbonates mixtures, respectively, in comparison to bare carbon at 700 °C, demonstrating the pronounced effect of catalyst as well as its potential synergy with carbonates. It was also shown that the achieved maximum power density is directly associated with the CO formation rate, implying the importance of in situ formed CO on the electrochemical performance. The obtained findings are further discussed based also on the corresponding AC impedance spectroscopy studies, which revealed the beneficial effect of fuel feedstock additives (catalyst and/or carbonates) on ohmic and electrode polarization resistances. The present results clearly revealed the feasibility to improve the DCFC performance by concurrently infusing a gasification catalyst and carbonates mixture into fuel feedstock.

Structural and Electrochemical Characterization of Thin Film Li2MoO3 Electrodes

Li2MoO3 is a promising structural stabilizing unit for use in composite layered-layered cathodes for Li-ion batteries. To enable the rational design of such cathodes, studies on fundamental phenomena related to the active material structure and electrode/electrolyte interface are needed. The present work details the fabrication and characterization of thin film Li2MoO3 cathodes and shows that their electrochemical performance greatly depends on the nature of the cathode/electrolyte interface. The Li2MoO3 thin films exhibit poor cyclability in a liquid carbonate electrolyte (e.g., initial capacity of 166 mAh/g with 40% capacity fade over 20 cycles) whereas all-solid-state Li2MoO3/Lipon/Li batteries show negligible fade during cycling. A suite of characterization methods including Raman spectroscopy and X-ray photoelectron spectroscopy are used to study the evolution of the cathode structure and cathode electrolyte interphase (CEI) layer during charge/discharge cycling. Li transport rates are another important factor which affect cathode performance. AC impedance spectroscopy studies reveal that the Li diffusion coefficient (DLi) in Li2MoO3 decreases from 4.36 × 10−11 cm2/s in the fully discharged state to 4.51 × 10−13 cm2/s when charged to 3.6 V vs. Li/Li+. Overall, the results presented herein provide insight on the fundamental phenomena which govern Li2MoO3 cathode performance.

Expired Fluoxymesterone Drug as Sustainable Corrosion Inhibitor for Mild Steel (MS) in 3 M HCL Solution: Experimental Investigations towards Mitigation of Metal Dissolution

The current research presents corrosion inhibition activity of expired Fluoxymesterone drug on the mild steel (MS) in the 3 M HCl solution. The atomic absorption spectroscopy, Tafel polarization and AC impedance spectroscopy studies have been done to verify the corrosion protection efficiency. The surface studies were carried out by scanning electron microscopy (SEM) technique. Atomic absorption spectroscopy results show that, the amount of iron content is low in the presence of corrosion inhibitor when compared with bare system. Tafel plots clearly hint the mixed corrosion inhibition property (inhibition of both anodic and cathodic corrosion process) of expired Fluoxymesterone drug over the MS surface in the acidic environment. From the AC impedance spectroscopy technique, it is observed that, the charge transfer resistance values enhances with a rise in the concentration of the corrosion inhibitor. Surface studies by SEM also support the atomic absorption spectroscopy, potentiodynamic polarization (Tafel plot) and AC impedance spectroscopy results.

Preparation and electrical conductivity of potassium phosphate glasses containing Al2O3

The effect of Al2O3 content on electrical conductivity and glass stability against crystallization in the system KH2PO4–Al2O3–P2O5 was investigated using Raman, IR, and impedance spectroscopies.DSC observations were carried out on glasses from a series of KH2PO4/(1−x) P2O5/x Al2O3, with x=0, 0.5, 0.1, 0.2 and 0.3mol, to determine the relative glass stability. The DSC observations indicate that from x=0.1 the glasses become more stable. For this composition (x=0.1) the conductivity, which was obtained by AC-impedance spectroscopic studies, was 7.0×10−6S·cm−1 at room temperature.Spectroscopic investigations reveal the depolymerization of the phosphate glass network by systematic conversion of Q2 structural units into Q1 and finally into Q0 structural units. Even though Q2 to Q1 conversion is taking place due to breaking of P-O-P linkages, formation of P-O-Al linkages provide cross linking between short P-structural units, which make the glass network more rigid.

Mixed Ionic–Electronic Conduction in Binary Polymer Nanoparticle Assemblies

AbstractPolymer‐based mixed ionic–electronic conductors (MIECs) are desired for both bulk and interfacial materials in next‐generation energy storage and electronic devices. Polymer‐based MIECs contain two principal components, one for electronic conduction and the other for ionic conduction. The central problem is the lack of a general approach to control the molecular packing and morphology of the constituent components that will afford the ability to easily tune transport properties. This study demonstrates the efficacy of a modular method based on polymer nanoparticle self‐assembly to achieve MIECs with tunable conductivity. This work uses poly(3‐hexylthiophene) nanoparticles as the electronic conductor and lithium ion‐doped poly(vinylpyridine) nanoparticles as the ionic conductors. AC impedance spectroscopic studies show that nanoparticle–nanoparticle interfaces in unary assemblies do not impede ion transport in the solid state. AC impedance spectroscopy and DC steady‐state conductivity measurements show that binary nanoparticle assemblies exhibit concurrent ionic and electronic conduction. The power‐law scaling percolation of both the ionic and electronic transport displays nonuniversal values of transport critical exponent, revealing different transport mechanisms. The simplicity of fabrication combined with the versatility in obtainable transport properties illustrates the power of using nanoparticle assemblies as a means to realize MIEC polymer mesoscale morphologies.

INFLUENCE OF COFFEE ON THE CORROSION RESISTANCE OF ORTHODONTIC WIRES IN ARTIFICIAL SALIVA

Corrosion resistance of Ni-Ti, Thermoactive alloy, and SS 316 L alloy in artificial saliva (AS) in the absence and presence of coffee has been evaluated by electrochemical studies such as polarization study and AC impedance spectroscopy. The polarization and AC impedance spectroscopy studies lead to the conclusion that corrosion resistance of the alloys decreases in the following order: SS 316 L alloy > Thermoactive alloy> Ni-Ti alloy. In all the three cases, the corrosion resistance of the wires increases in the presence of coffee. Among the three orthodontic wires, SS316L alloy is the best candidate.

AC impedance spectroscopy and conductivity studies of Dy doped Bi4V2O11 ceramics

The ac impedance and conductivity properties of Dy doped Bi4V2 − xDyxO11 (x = 0.05, 0.10, 0.15 and 0.20) ceramics prepared by solid-state reaction technique, in a wide frequency range at different temperatures have been studied. All the samples exhibited β-type phase orthorhombic structure at room temperature. The Nyquist plot confirmed the presence of both grain and grain boundary effects for all Dy doped samples. Double relaxation behavior was also observed. The grain and grain boundary resistance decreases with rise in temperature for all the concentration and exhibits a typical negative temperature co-efficient of resistance (NTCR) behavior. An analysis of the electric modulus suggests the possible hopping mechanism for electrical transport processes of all the materials. The ac conductivity spectrum obeys Jonscher’s universal power law. DC conductivity of the materials were also studied and values of the activation energy found to be 0.40, 0.49, 0.73 and 0.78 eV for the compositions x = 0.05, 0.10, 0.15 and 0.20, respectively, at different temperatures (150–375 °C).

Compact layer influence on hysteresis effect in organic–inorganic hybrid perovskite solar cells

Organic–inorganic hybrid perovskite solar cells have attracted great attention due to their high power conversion efficiency and low cost. However, an anomalous hysteresis effect exists in the perovskite solar cells, especially with TiO2 as the n-type electron extraction layer. In this communication, we prepare two kinds of TiO2 compact layers using Atomic Layer Deposition (ALD) and Spin-Coating (SC) methods and compare their influences on the hysteresis effect. By efficiency comparison and AC impedance spectroscopy study, we find that the thickness and morphology of compact layer have a significant influence on the hysteresis effect. Compared to the SC approach, the ALD prepared compact layer is ultra-thin with uniform morphology and shows small interfacial capacitance and large recombination resistance, meaning reduced interfacial charge accumulation and accelerated electron transport, which would relieve the hysteresis effect.

Biocidal Behaviour of (Dodecyltrimethylammonium Bromide) on Carbon Steel in Well Water

The inhibition of corrosion of carbon steel in well water using diethylenetriamine penta (methylene phosphonic acid) (DETPMP), Zinc ions and dodecyltrimethylammonium bromide (DTAB) was investigated using weight-loss measurement, electrochemical polarization and impedance methods. Inhibition efficiency of above ternary inhibitor reaches maximum values at 93 %. The biocidal efficiency of DTAB was studied which reaches maximum of 88 % at 125 ppm DETPMP, 10 ppm Zn2+ and 150 ppm DTAB. The shape of DC polarization profile revealed the new ternary system which acts as anodic type inhibitor. AC impedance spectroscopic studies indicated the formation of a protective film onto the metal surface in the presence of inhibitors. Analyses of the protective film using scanning electron microscope, energy dispersive X-ray analysis, atomic force microscopy and Fourier transfer infrared spectroscopy have revealed that the film consists of Zn(OH)2, oxides and hydroxides of iron and the inhibitor molecules in the form of a complex.

Electro-Catalytic and Fuel Cell Studies in an Internal Reforming Iso-Octane Fed SOFC Using Cu/CeO2 Composites As Anodic Electrodes

The worldwide demand for energy is continuously growing and is expected to be met largely by fossil fuels. However, several aspects related to i) the depletion of fossil fuels, ii) the environmental and public health concerns arise from the associated emissions, and iii) the lower energy conversion efficiency in conventional power plants, render the development of alternative, energy-efficient technologies increasingly demanding. Fuel cells have emerged as a promising energy conversion technology, able to satisfy the needs of high efficiency and low environmental footprint [1]. Although H2 can be considered as the ideal fuel cell feedstock, several barriers dealing with its limited availability in nature as a free substance, the absence of relevant infrastructure and the associated difficulties with its storage and distribution prevent the development and commercialization of H2-fed fuel cells [2]. Commercial-grade liquid hydrocarbons, such as gasoline, comprise the most proper feedstock for on-board reformation into hydrogen, due to their well-established infrastructure for storage and transportation. SOFCs due to their high operating temperature, can be potentially operated directly (internal reforming) on conventional hydrocarbons fuels [2]. However, the development of high efficiency electro-catalysts, with adequate activity, electron conductivity and carbon tolerance should be developed. Ni-based anode materials are usually employed in SOFC applications, since they exhibit adequate catalytic activity toward reforming reactions and thermal stability [3]. However, Ni-based anodes are prone to carbon poisoning when directly exposed to hydrocarbon fuels [3]. Recently, the substitution of Ni cermets by Cu-based catalysts in direct hydrocarbons fuel cells has been proposed, owing to their electrochemical activity and resistance to carbon [2]. It has been demonstrated that the employment of Cu-CeO2/YSZ composites as anode materials results in a stable power generation in direct hydrocarbons fuel cells [2]. In the present communication, iso-octane, a common surrogate for gasoline, is employed as a fuel in a Cu-CeO2/YSZ/Pt type SOFC reactor, at atmospheric pressure. The effect of cell temperature, reactants’ partial pressure and imposed overpotentials on products’ distribution and overall catalytic and electro-catalytic activity was examined. Furthermore the as prepared cell was electrochemically characterized employing typical fuel cell measurements and AC impedance spectroscopy studies. Iso-octane was efficiently reformed by H2O to syngas over Cu/CeO2 electrodes. In all cases examined, no carbon was detected, which was attributed to the favoured gasification of carbonaceous deposits by H2O. Cu-CeO2 exhibited high catalytic activity toward the electro-oxidation of all combustible species that are present at the anode. Under “fuel cell” mode of operation, the achieved power densities were substantially increased with increase in temperature and Pi-C8H18/PH2O feed ratios (Fig. 1). AC impedance spectra showed contributions both from charge and mass transfer processes depicted at high and low frequencies, respectively. Increase in temperature reduced both the Area Specific Resistance (Eact= 1.15 eV) and interfacial resistance, with the latter being attributed to charge transfer processes (Eact= 1.59 eV) and diffusion limitations (Eact= 1.07 eV). The effect of H2O and i-C8H18 concentrations was more intense in the case of the resistance associated to mass transfer limitations, while both the ASR and the resistance attributed to the charge transfer processes at electrode and electrode/electrolyte interface were almost independent of reactants feed concentration.

Electro-Catalytic and Fuel Cell Studies in an Internal Reforming Iso-Octane Fed SOFC Using Cu/CeO2 Composites As Anodic Electrodes

The internal reforming of iso-octane is examined in a solid oxide fuel cell of the type Cu-CeO2/YSZ/Pt. The results show that i-C8H18 is efficiently reformed by H2O to syngas over Cu/CeO2 composites, free of carbon deposits. Apart from iso-octane reforming, the products distribution at open circuit conditions is also influenced by the associated i-C8H18 thermal cracking and catalytic decomposition reactions as well as by the reverse water gas shift and methanation reactions. At closed circuit operation, the prevailing reactions are related to the electro-oxidation of H2 and CO and the co-electrolysis of H2O and CO2, at anodic and cathodic polarization conditions, respectively. AC impedance spectroscopy studies revealed that the cell and electrode resistances are substantially decreased with increasing temperature leading consequently to higher maximum power densities (12.6 mW/cm2, 850oC). The diffusion of charged and/or neutral species at the electrode surface is possibly the rate limiting step during fuel cell operation.