Decrease In Capacitance Research Articles

Studies on corrosion inhibitory effect and adsorption behavior of waste materials on mild steel in acidic medium

ABSTRACTCorrosion inhibition behavior of orange peel waste extracts in 1 M hydrochloric acid medium on mild steel surface was studied using weight loss studies, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and surface phenomena using scanning electron microscopy (SEM) analysis. Better inhibition efficiency for orange extracts was achieved by weight loss measurements. The maximum inhibition efficiency of 99.19% was achieved for 0.25% of waste extract at room temperature. EIS analysis revealed that increase in concentration of orange peel extract (OPE) increases the charge transfer resistance with the continuous decrease in capacitance which confirms the development of dense protective layer on the metal surface at the electrolyte interface. Both the electrochemical investigation such as potentiodynamic polarization and impedance analysis confirmed the improved inhibitory efficiency of OPE by following Langmuir isotherm model. SEM analysis confirms that the corrosion inhibition of OPEs was proceeded by forming an organic protective layer over the mild steel surface by means of the adsorption process by physical contact. These results confirm that the ethanolic extract of orange waste can be used as a potential corrosion inhibitor in industrial applications.

Thermal, optical and gas sensing properties of ZnO films prepared by different techniques

Nowadays, for environmental protection, the use of portable gas sensor is essential to detect toxic gases. To control this problem of hazardous gases, metal oxide based sensors plays a vital role. In this recent study, Indium (2 at.wt.%) doped ZnO films has been prepared by sol gel spin coating and thermal evaporation techniques on glass substrates. To enhance the sensing properties, indium (In) was used as dopant and their annealing effect of temperature was observed. Thermal properties have shown the fruitful result that prepared films are useful for the fabrication of solar cell. Electrical properties revealed that capacitance and dielectric constant decreases with increase in frequency. X-ray Diffraction showed hexagonal wurtzite structure highly oriented along (1 0 1) plane. Field emission scanning electron microscope of these synthesis films prepared by different have shown the morphology as nanospheres having size of the order of 40–60 nm. 2.0 at.% of indium as modifier resulted in highest response and selectivity towards 5 ppm of NO2 gas at different operating temperature (50–200 °C). Highest sensitivity was obtained at operating temperature of 150 °C. Prepared films have quick response and recovery time in the range of 14–27 s and 67–63 s. The highest response and recovery time of gas sensor was explained by valence ion mechanism.

A Comparative Study of a Novel Technique for the Fabrication of Dye Sensitized Solar Cells Using NanoTiO2 and Different Dyes

Dye-sensitized solar cells (DSSCs) have gained widespread attention in recent years because of their low production cost, ease fabrication and tunable optical properties, such as colour and transparency. Now-a-days natural dye was used to sensitize the electrode and the counter electrode was prepared by the help of carbon black. In this study we report molecularly engineered different dyes (henna, pomegranate and beet root) and nanoTiO2 in the DSSCs, which features the prototypical structure of a donor–π-bridge–acceptor and maximizes electrolyte compatibility with improved light-harvesting properties. BulkTiO2 of sizes 150 micron were converted to nanoTiO2 particles having sizes less than 20 nm using planetary ball mill. Our design consists of a lattice of modulated-diameter nanoTiO2 particles and interstitial regions filled with electrolyte. This provides not only light trapping and absorption enhancement, but offers improved electrical transport through the nanoTiO2 particles. It is observed that when frequency increases both capacitance and resistance decreases. At certain point capacitance it maintains a steady state and resistance is nearly equal to zero. This is due to the internal resistance and the steady state capacitance of the cell. It conforms that the fabricated dye sensitized solar cell works like a conventional cell. It is found that henna and pomegranate dyes shows better energy conversion efficiency than beet root dye.

Corrosion Resistance Property of Mild Steel in Simulated Concrete Pore Solution Prepared in Well Water by Using an Aqueous Extract of Turmeric

Corrosion resistance property of mild steel immersed in simulated concrete pore solution (SCPS) prepared in well water has been evaluated by weight loss method, in the absence and presence of an aqueous extract of Turmeric (Curcuma longa L), The main constituent of the plant extract is curcumin It is observed that in the presence of an aqueous extract of turmeric corrosion inhibition efficiency increases. The mechanistic aspects of corrosion inhibition have been studied by weight loss method, polarisation study and AC impedance spectra. In the presence of the Turmeric extract, the inhibition efficiency increases, linear polarisation resistance value increases; corrosion current decreases; charge transfer resistance value increases and double layer capacitance decreases. Thus it is observed that in the presence of turmeric inhibitor the corrosion resistance of mild steel incorporated in concrete structure increases. Thus the corrosion resistance of mild steel incorporated in concrete structure can be improved by addition of an aqueous extract of turmeric.

Plasma modification of spoof plasmon propagation along metamaterial-air interfaces

We report on measurements of the shift in resonance frequency of “spoof” surface plasmon polariton propagation along a 2-D metamaterial slow-wave structure induced by a gaseous plasma near the metamaterial/air interface. A transmission line circuit model for the metamaterial structure interprets the introduction of a plasma as a decrease in unit cell capacitance, causing a shift in the plasmon dispersion to higher frequency. We show through simulations and experiments that the effects of this shift at the resonance frequency and attenuation below and above resonance depend on the plasma density. The shifts recorded experimentally are small owing to the low plasma densities generated near the structure, ∼1011 cm−3, but simulations show that a shift of ∼3% of the resonance frequency can be generated at plasma densities of ∼1012 cm−3.

Polypyrrole/titania-coated cotton fabrics for flexible supercapacitor electrodes

Flexible and wearable supercapacitors are mostly desired with the fast development of wearable electronics in recent years. Herein, polypyrrole (PPy)/titania (TiO2)-coated cotton fabrics as flexible supercapacitor electrodes were prepared using both the sol-gel approach and the in situ oxidative polymerization. The maximum electrical conductivity of the composite fabrics is 6.3 S cm−1, implying that these fabrics could be directly used as electrodes. The obtained quasi-rectangular shaped cyclic voltammetry (CV) curves indicate good capacitive behavior of the composite fabrics. The GCD results demonstrate that the fabric electrodes show a significantly improved specific capacitance of 733 F g−1 with a high energy density of 44.4 Wh kg−1 at a current density of 0.6 A cm-2 as compared with the value of 366 F g−1 without TiO2. Corresponding slow decrease in specific capacitance with the increased current density indicates superior rate capability. These excellent electrochemical properties of the PPy/TiO2-coated fabrics extend their potential applications in various self-powered wearable electronics.

Effect of Radiation on Reliability of Through-Silicon via for 3-D Packaging Systems

In this paper, radiation reliability of through-silicon via (TSV) was studied experimentally. Characterization of leakage current between adjacent TSVs and capacitance of an array of TSVs was used to evaluate the effects of radiation on reliability of TSVs. All samples were exposed to 60Co ${\gamma }$ radiation with a total radiation dose of 500 Gy. It was observed that leakage current increased and coupling capacitance decreased. The increase of leakage current was explained based on the percolation model for thin oxide layers. The decrease of capacitance was analyzed with the theory of coupling capacitance and equation of flat-band voltage and charge in the oxide layer. It is important and necessary to consider the effect of radiation on reliability of TSV for TSV-based applications under radiation conditions.

Online Parameter Identification for Supercapacitor State-of-Health Diagnosis for Vehicular Applications

In power electronic applications, aging of the electric double layer capacitors (EDLCs) is considered as a serious issue since it may lead to failure. Their degradation is usually evaluated by an increase of the internal resistance or a decrease of the equivalent capacitance. These aging indicators have a good correlation with the supercapacitor's state-of-health (SoH). Generally, SoH is measured by electrochemical impedance spectroscopy (EIS). However, this technique must be performed offline and requires interruption of the system's operation. In this paper, a sliding mode observer is designed to estimate online the EDLC's aging indicators. Unlike several online estimators, the supercapacitor's parameters are considered as a nonlinear random distribution with external noises which yields accurate estimation. In addition, the relationship between the capacitance and the bias voltage is considered to be nonlinear. Lyapunov stability analysis is also provided. The proposed approach is validated experimentally using a standardized dynamic current profile. Furthermore, comparison against EIS is carried out for different aging phases and under different environmental temperature conditions.

Multiferroicity around Verwey transition in Fe3O4 thin films

We report observation of finite remanent polarization (∼10-80 nC/cm2) and reasonably strong magnetoelectric coupling in thin film of Fe3O4 within a temperature range from ∼40 K to Verwey transition temperature TCO ∼120 K. Both the intrinsic capacitance and remanent ferroelectric polarization decrease by ∼20-60% under 0-50 kOe field within this temperature range. The measurements using conventional techniques do not yield convincing results as the ferroelectric polarization is small and loss is large. However, use of more sophisticated protocol - which eliminates the contribution from loss and nonhysteretic polarization effectively - provides reliable information about remanent polarization and its change under magnetic field around the Verwey transition.

The role of surface chemistry in the charge storage properties of graphene oxide

In the present study we have evaluated the contribution of particular oxygen functional groups in the charge storage properties of graphene oxide (GO). This was achieved by a gradual thermal reduction of GO in an inert atmosphere (up to 800 °C) and thorough examination of functional groups which remained after each de-functionalization step. After identification of functional groups, the character of additional cyclovoltammetric peak, less pronounced than the main redox quinone/hydroquinone pair, and overall charge storage properties of GO were discussed from the perspective of different thermal stability of its surface groups. The results indicated three-stage deoxidation process of GO, each comprising of specific surface chemistry, structural changes and electrochemical behavior. The low capacitance, ∼50 F g−1, at T ≤ 300 °C was attributed to the presence of epoxy and carboxyl groups. The highest capacitance (120–130 F g−1) was observed in the case of GO reduced at 400 and 500 °C, which we attributed to positive effects of phenol and carbonyl/quinone groups, while at high temperatures (T ≥ 600 °C, ∼30 F g−1) the extensive desorption of functional groups and structural changes were emphasized as the main reasons for additional decrease of capacitance. Our results highlight the cases where the duality of interpretation of surface functional groups is likely to happen and indicate that not all functional groups play a positive role in charge storage behavior of graphene oxide.

Fast in situ synthesis of CoFe layered double hydroxide onto multi-layer graphene for electrochemical capacitors

Homogeneous CoFe layered double hydroxide (LDH) was in situ synthesized onto the surfaces of multi-layer graphene (MLG) based on π-π interaction method just for 1-h reaction. The morphology, crystal structure, and electrochemical properties of the composite were systematically studied. The results showed that crystalline CoFe-LDH grown onto MLG was composed of two layers. The bottom layer was parallel to graphene sheet to increase the contact with graphene. The external layer was vertically assembled to allow the easy immersion of electrolyte into the pores between CoFe-LDH sheets. When being tested as electrochemical capacitor electrode, the composite could deliver a specific capacitance of 882.5 F g−1 at a current density of 1 A g−1. When prolonging the reaction time to 3 h, homogeneous CoFe oxide nanoparticles with a size of about 5 nm would be formed on the surface of CoFe-LDH. Its specific capacitance decreased to 462.5 F g−1 at 1 A g−1, but its cycle stability and rate capability were both improved. All CoFe-LDH sheets were transformed into CoFe oxide nanoparticles when the reaction time reaches 10 h, resulting in a further decrease of specific capacitance to 82.5 F g−1. Thus, to obtain a high electrochemical performance, the reaction time should be controlled because the phases and morphologies of the products are dependent on it.

Corrosion behaviour of laser-cleaned AA7024 aluminium alloy

Laser cleaning has been considered as a promising technique for the preparation of aluminium alloy surfaces prior to joining and welding and has been practically used in the automotive industry. The process is based on laser ablation to remove surface contaminations and aluminium oxides. However the change of surface chemistry and oxide status may affect corrosion behaviour of aluminium alloys. Until now, no work has been reported on the corrosion characteristics of laser cleaned metallic surfaces. In this study, we investigated the corrosion behaviour of laser-cleaned AA7024-T4 aluminium alloy using potentiodynamic polarisation, electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET). The results showed that the laser-cleaned surface exhibited higher corrosion resistance in 3.5 wt.% NaCl solution than as-received hot-rolled alloy, with significant increase in impedance and decrease in capacitance, while SVET revealed that the active anodic points appeared on the as-received surface were not presented on the laser-cleaned surfaces. Such corrosion behaviours were correlated to the change of surface oxide status measured by glow discharge optical emission spectrometry (GDOES) and X-ray photoelectron spectroscopy (XPS). It was suggested that the removal of the original less protective oxide layer consisting of MgO and MgAl2O4 on the as-received surfaces and the newly formed more protective oxide layer containing mainly Al2O3 and MgO by laser cleaning were responsible for the improvement of the corrosion performance.

Cholesterol depletion does not alter the capacitance or Ca handling of the surface or t-tubule membranes in mouse ventricular myocytes.

Cholesterol is a key component of the cell plasma membrane. It has been suggested that the t‐tubule membrane of cardiac ventricular myocytes is enriched in cholesterol and that this plays a role in determining t‐tubule structure and function. We have used methyl‐β‐cyclodextrin (Mβ CD) to deplete cholesterol in intact and detubulated mouse ventricular myocytes to investigate the contribution of cholesterol to t‐tubule structure, membrane capacitance, and the distribution of Ca flux pathways. Depletion of membrane cholesterol was confirmed using filipin; however, di‐8‐ANEPPS staining showed no differences in t‐tubule structure following Mβ CD treatment. Mβ CD treatment had no significant effect on the capacitance:volume relationship of intact myocytes or on the decrease in capacitance:volume caused by detubulation. Similarly, Ca influx and efflux were not altered by Mβ CD treatment and were reduced by a similar amount following detubulation in untreated and Mβ CD‐treated cells. These data show that cholesterol depletion has similar effects on the surface and t‐tubule membranes and suggest that cholesterol plays no acute role in determining t‐tubule structure and function.

Root and shoot extracts of Ajuga chamaecistus subsp. scoparia as natural inhibitors for 304 stainless steel corrosion in strong acidic medium

The inhibitive action of root and shoot extracts of Ajuga chamaecistus subsp. scoparia as a green inhibitors on corrosion of 304 stainless steel in the 6.0 M HCl solution was studied by the weight loss method, potentiodynamic polarization, electrochemical impedance spectroscopy, scanning electron microscopy, and atomic force microscopy. The results demonstrate that the extracts act as a show mixed-type inhibitor. The Nyquist plots display an increase of the charge transfer resistance with an increase of the inhibitor concentration and a decrease of the double layer capacitance. The effect of temperature and related activation parameters was deliberate. Adsorption of the extract followed the Langmuir isotherm model. The inhibition efficiencies found from electrochemical tests were in good agreement with those observed via the weight loss method. The inhibition efficiencies for root and shoot extracts are 99.4 and 99.6%, respectively.

Influence of nitrogen-doping in carbon on equivalent distributed resistance and capacitance – Implications to electrocatalysis of oxygen reduction reaction

Carbon-black is heat-treated with nitrogen-containing precursor (ammonia or melamine) to yield N-doped carbon. The nitrogen content in the sample depends on the type of the precursor and the heat-treatment temperature and it is estimated using CHN analysis. The electrochemical impedance spectroscopy (EIS) patterns of the samples recorded in argon-saturated 0.1M KOH show a high-frequency equivalent distributed resistance (EDR) and a low-frequency capacitive straight line, tilted slightly away from the y-axis. The EDR and the tilt of the capacitive straight line decrease with increase in nitrogen-content in the N-doped carbon samples. Further, EIS of oxygen reduction reaction (ORR) is recorded with carbon and N-doped carbon in oxygen-saturated 0.1M KOH. The EIS patterns of ORR suggest that the high-frequency EDR feature is not negligible, unlike that with carbon-supported and unsupported Pt catalysts in both acidic and alkaline media. Therefore, nitrogen content and EDR have important implications in deciding the electrocatalytic activity and the features of the EIS patterns of carbon-based metal-free catalysts. Because of the change in EDR and the capacitance with nitrogen-content, the EIS patterns of ORR with N-doped carbon are complex to analyze.

Cobalt Doping To Boost the Electrochemical Properties of Ni@Ni3 S2 Nanowire Films for High-Performance Supercapacitors.

Metal sulfides have aroused great interest for energy storage. However, their low specific capacities and inferior rate capabilities hinder their practical applications. In this work, a facile cobalt-doping process is used to boost the electrochemical performance of Ni@Ni3 S2 core-sheath nanowire film electrodes for high-performance electrochemical energy storage. Co ions are doped successfully and uniformly into Ni3 S2 nanosheets through a facile ion-exchange process. The electrochemical properties of film electrodes are improved greatly, and an ultrahigh volumetric capacity (increased from 105 to 730 C cm-3 at 0.25 A cm-3 ) and excellent rate capability are obtained after Co is doped into Ni@Ni3 S2 core-sheath nanowires. A hybrid asymmetric supercapacitor with Co-doped Ni@Ni3 S2 as the positive electrode and graphene-carbon nanotubes as the negative electrode is assembled and exhibits an ultrahigh volumetric capacitance of 142 F cm-3 (based on the total volume of both electrodes) at 0.5 A cm-3 and excellent cycling stability (only 3 % capacitance decrease after 5000 cycles). Moreover, the volumetric energy density can reach 44.5 mWh cm-3 , which is much larger than those of thin-film lithium batteries (1-10 mWh cm-3 ). These results may provide useful insights for the fabrication of high-performance film electrodes for energy-storage applications.

Network-Driven Activity and Neuronal Excitability in Hippocampus of Neonatal Rats with Prenatal Hyperhomocysteinemia

Maternal hyperhomocysteinemia (HHCy) correlated with a number of complications such as abruption placentae, preeclampsia syndrome, in utero fetal death and fetal neural tube defects, cognitive impairment, and neurodegeneration during postnatal development. In the present study, we investigated the effects of prenatal HHCy on electrophysiological features and spontaneous network activity of neurons in hippocampus of rats of the first postnatal week. The analysis of intrinsic electrophysiological properties of pyramidal neurons has shown the decrease of the membrane capacitance and the threshold of generation of action potentials in rats with prenatal HHCy without alteration of the input resistance and resting membrane potential. In trains of action potentials elicited with prolonged current injections, an increase of interspike intervals and a broadening of action potentials during repetitive firing were observed in control neurons. In the neurons of pups with prenatal HHCy, the changes in interspike intervals were not significant and the broadening of action potentials in train was less pronounced. Using extracellular field potential recordings from the hippocampal slices, we found that the network activity in hippocampal slices from rats with prenatal HHCy displayed several abnormalities including the increase in overall neuronal firing and reduction of frequency of giant depolarizing potentials in CA3 regions. We conclude that the increased neuronal excitability and impairment of network activity in hippocampus can underlie neurodevelopmental abnormalities and hyperexcitability in prenatal HHCy.

Scalable Synthesis of High-Tapped-Density N-doped Graphene by Polyethyleneimine-Mediated Thermal Treatment of Graphene Oxide and Its Application for Supercapacitors

Development of high-tapped-density graphene-based materials with satisfactory Brunauer–Emmett–Teller (BET) surface area can be beneficial to the optimization of the volumetric performance of supercapacitors for practical use. Herein, we report a simple and scalable route for the synthesis of high-tapped-density N-doped graphene (HNG). The success of this work relies on the use of polyethyleneimine (PEI) to react with graphene oxide under ambient conditions to realize fast cross-linking and thus rapid sedimentation, followed by thermal treatment of the precipitates. The resultant HNG exhibits a good balance between the tapped density and BET surface area, where the tapped density can be tuned in the range of 0.90–1.20gcm−3 and the BET surface area is maintained in the range of 457.0–119.6m2g−1. The interaction between PEI and graphene oxide successfully prevents restacking of the graphene layers during thermal treatment while allowing maximal volume shrinkage. When applied as an electrode material in supercapacitors, the HNG exhibits a volumetric capacitance up to 547.8Fcm−3 at a scan rate of 10mVs−1 and 317.3Fcm−3 at a current density 0.2Ag−1, and it shows no apparent decrease in the specific capacitance after 5000 cycles at 2Ag−1. The results demonstrate the feasibility of the new strategy for designing high-tapped-density graphene-based materials for supercapacitors.

Low-Temperature Performance of Symmetric MnOx-Carbon Nanofoam-Based Ecs with Mild-pH Aqueous Electrolytes

Electrochemical capacitors, ECs, should provide high performance over the broadest range of operating temperatures which is primarily determined by the properties of the electrolyte (freezing and boiling points, ionic conductivity and salt solubility as a function of temperature, flash point for flammable solvents). In the case of mild-pH aqueous electrolytes, where flammability is a non-issue, the sub-ambient temperature performance is the most critical factor. En route to demonstrating the performance of aqueous-electrolyte ECs at low temperature, we have characterized both the bulk thermal properties of single and multi-component electrolytes and their behavior when used in EC pouch cells. The ionic conductivities of bulk electrolytes with a fixed cation concentration of 5 M for single-component (e.g. Li2SO4, NaNO3) and multi-component electrolytes (e.g. Li2SO4 + NaNO3) ranged from 63 to 136 mS cm-1 at 20oC. The freezing points of these electrolytes were measured with differential scanning calorimetry. It was found that the anion dominates the freezing-point behavior, with sulfate-based electrolytes supporting freezing points down to –45oC and nitrate-based electrolytes down to –35oC. To assess the impact of temperature on performance as a function of electrolyte composition, we fabricated symmetric pouch cells comprising MnOx-carbon nanofoam electrodes and tested them over the temperature range of 25oC to –45oC in an environmental chamber. All ECs exhibited a gradual decrease in capacitance as the temperature decreased; however, upon re-warming to 25°C, the capacitance was recovered, indicating that freezing does not cause significant degradation to electrode or separator components. Aqueous electrolytes comprising mixtures of Li2SO4 and NaNO3 yielded the best combination of depressed freezing point and ionic conductivity among the compositions evaluated in EC pouch cells.

Adsorption and anticorrosion behavior of 1-((pyridin-2-ylamino)(pyridin-4-yl)methyl)pyrrolidine-2,5-dione on mild steel surface in hydrochloric acid solution

New Mannich base 1-((pyridin-2-ylamino)(pyridin-4-yl)methyl)pyrrolidine-2,5-dione (SAP) was synthesized, characterized, and investigated as a corrosion inhibitor on mild steel (MS) in 1.0 M HCl using weight loss, electrochemical experiments, and theoretical calculations. Impedance spectra validated the decrease in the double-layer capacitance (C dl) and increase in the charge-transfer resistance (R CT) of the corrosion process due to the addition of the inhibitor. Tafel polarization studies proved that the inhibitor has a mixed type inhibitive nature with predominant control of cathodic reaction. A maximum inhibition efficiency of 88.7% from weight loss measurements and above 94.5% from electrochemical analysis were observed in the presence of 200 ppm of SAP, and the adsorption of SAP on MS surface in 1.0 M HCl was found to follow Langmuir’s adsorption isotherm. The calculated values of thermodynamic parameters predict the adsorption of SAP molecules on the MS surface was physical adsorption. FTIR, SEM–EDX, and AFM were used to characterize the surface morphology of the mild steel samples in the presence and absence of inhibitor. Density functional theory based quantum chemical calculations also fortifies the experimental inferences revealing SAP as good inhibitor.