Papers by Keyword: Electrochemical Impedance Spectroscopy

Abstract: Electrochemical analysis of corrosion in molten nitrate salt of stainless steel grade SS 430, SS 2205, SS 2507 and SS 304 is directly performed to evaluate corrosion resistance. Stainless steels are exposed to molten nitrate salt at 600 °C for two hours. This is done in a furnace equipped with a working electrode terminal, reference and counter electrodes. According to this, electrochemical impedance spectroscopy and potentiodynamic polarization techniques are applied in situ to measure corrosion rates and corrosion resistance. Microstructures of stainless steel reveal the ferrite phase for SS 430, the austenite phase for SS 304 and the duplex phase for SS 2205 and SS 2507. In this study, the existence of an austenite phase promotes corrosion resistance in molten nitrate salt.

Abstract: Battery-supercapacitor hybrids (BSHs) are promising energy storage devices that exhibit large energy density, high power density. In this research, BSH devices based on Li₄Ti₅O₁₂ and Ti₃C₂ electrodes are fabricated. Through cyclic voltammetry, it is discovered that the kinetics of charging/discharging are diffusion-controlled. 3D Bode plots and Nyquist Plots indicate that bounded diffusion might occur. Regarding the performance, the 70 wt.% Li₄Ti₅O₁₂-Ti₃C₂ BSH shows the most balanced specific energy (9.9 mW∙h/kg) and specific power (3.0 W/kg) at 100 mV/s. The largest specific capacitance of the 70 wt.% Li₄Ti₅O₁₂-Ti₃C₂ BSH is 81.6 F/kg at 5 mV/s.

Abstract: Tissue engineering has focused on the development of biomaterials, modulating the morphological and electrochemical characteristics based on their final application. In this setting, the purpose of the present study was to determine the physicochemical response of electrospun membranes of silk fibroin extracted from sericulture wastes and their functionalization with choline based bio-ionic liquids. A comparative study of their response was carried out with membranes obtained from the same protein but functionalized with gold nanoparticles. The biomaterials developed were characterized by UV-Visible spectrophotometry, FTIR spectroscopy, electron microscopy (SEM and FESEM), dynamic light scattering (DLS), and Linear sweep voltammetry. The results obtained showed a fibrillar morphology and the conduction of electrical stimuli by the membranes functionalized with the gold nanoparticles or the bio-ionic liquids, where for the latter the response is modulated by the concentration used in the development of the biocomposite.

Abstract: Prices of lithium raw materials keep on increasing exponentially due to their heavy consumption for lithium batteries used in portable electronic devices as well as automobiles. Also, the global lithium deposits are very limited. Hence, sodium-ion batteries (SIBs) have been heavily investigated as cheaper alternatives to expensive lithium-ion batteries, mainly due to the abundance of sodium raw materials. However, one of the major bottlenecks faced by the material research community to commercialize SIBs is the poor ionic conductivity of sodium-ion conducting electrolytes at ambient temperature, especially in the solid-state. Very recently, quasi-solid state polymer electrolytes (QSSPEs) have been proposed to overcome this challenge. In this work, a set of QSSPEs have been synthesized by using poly (vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) host polymer and NaBF₄ ionic salt dissolved in EC/PC plasticizer/solvent mixture. The highest conducting composition; 6 PVdF-HFP: 14 NaBF₄: 40 EC: 40 PC (wt.%); showed an ambient temperature ionic conductivity of 4.1x10^-3 S cm^-1. The activation energy is almost same for all the sample compositions studied in this work suggesting that the activation process is mainly controlled by EC/PC. DC polarization test on highest conducting electrolyte composition with a configuration of SS/QSSPE/SS revealed that the electrolyte is predominantly ionic conductor with negligible electronic conductivity; a much desired property for a good electrolyte. Linear sweep voltammetric studies confirmed that the electrochemical stability window of the highest conducting electrolyte is about 3.6 V. This highest conducting electrolyte composition is found to be highly suitable for practical applications in sodium batteries.

Abstract: Research and development works in the field of multi-valent metal-ion batteries are intensified these days because of the abundance of multi-valent elements such as magnesium, aluminum, calcium and so on in the Earth’s crust. Magnesium-ion batteries are particularly important, because they have high theoretical volumetric capacity (3832 mAh cm^-3) compared to that of well-known lithium-ion batteries (2062 mAh cm^-3). However, there are potential challenges, typically, designing suitable electrolytes with sufficient ambient temperature ionic conductivities is a major challenge. In this work, a set of gel-polymer electrolytes based on poly (ethylene oxide) (PEO) host polymer and magnesium acetate (Mg(CH₃COO)₂) ionic salt have been synthesized and characterized by electrochemical impedance spectroscopy (EIS), DC polarization and linear sweep voltammetry (LSV) techniques. Among the compositions studied in this work, the optimized PEO-Mg(CH₃COO)₂-EC-PC electrolyte (6:14:40:40 wt.%) showed an ambient temperature ionic conductivity of 6.1x10^-5 S cm^-1. Ionic conductivity vs inverse temperature showed Arrhenius behavior with almost same activation energies (0.15 - 0.18 eV) for all the compositions. DC polarization studies performed with stainless steel blocking electrodes under an externally applied voltage of 1V showed that the highest conducting composition is dominantly an ionic conductor with an ionic transference number of 0.99. The electronic contribution to conductivity was found to be almost negligible, which is desirable to avoid short circuits within the cell. The LSV test on highest conducting composition revealed that the electrochemical stability window of these electrolytes is about 2.2 volts.

Abstract: This study employed the template-free chemical oxidative polymerisation method to synthesise polyaniline (PANI) and polyaniline/tin-doped titania (PANI/Sn-doped TiO₂) nanocomposite as corrosion inhibitors. FTIR and XRD were employed to characterise the chemical composition of the prepared samples. TEM and FESEM microscopy validated the presence of the PANI and that the Sn-doped TiO₂ nanoparticle were successfully incorporated into PANI to form the nanocomposite. The synthesised materials were mixed in the polyvinyl butyral (PVB) binder, coated onto mild steel substrates, and exposed to 3.5 wt.% NaCl solution for 30 days. Altogether, three coating systems were tested, i.e., pure PVB, PVB + PANI, and PVB + PANI/Sn-doped TiO_2. The corrosion parameters were measured via EIS and Tafel polarisation techniques. Overall, the PANI/Sn-doped TiO₂ nanocomposite as a corrosion inhibitor effectively inhibited the corrosion of the mild steel, and its corrosion rate was 3.484 x 10^-7 mm/year.

Abstract: Presented paper studies corrosion kinetics of zinc dust in cement paste using acoustic emission and impedance spectroscopy (measurement of electric resistance of compact samples) method. The focus is on determination of hydrogen evolution period and its effect on porous structure of cement paste. Results more or less confirm results of other authors that the corrosion products of zinc are unable to efficiently fill the pores forming due to hydrogen. Time period of hydrogen evolution - cathodic corrosion reaction of zinc in alkaline environment of cement paste can be up to several days long. Keywords: hot-dip galvanized reinforcement, corrosion of zinc dust, acoustic emission method, hydrogen evolution, porosity of cement paste, electrochemical impedance spectroscopy

Abstract: Illegal disposal and recirculation of expired drugs is a global menace which can be solved by their re-utilization as corrosion inhibitors. Thus, helping to combat the current widespread corrosion-induced wastage of expensive mild steel infrastructure. The experimental investigation evaluated the capability and effectiveness of an expired drug (piroxicam) for inhibiting mild steel corrosion in blank 0.5M HCl and acidic environments containing 2 to 8 g/L of the expired drug. Spectrometry, weight loss analysis, atomic absorption spectroscopy, microscopy, polarisation and electrochemical impedance study (EIS) were employed. Analyses revealed drastic inhibition of corrosion in mild steel by expired piroxicam drug in the acid. Corrosion currents ( ) obtained at all concentrations of the expired drug were reduced in comparison to that of the uninhibited environment. The solution resistance recorded was not significantly altered; charge transfer resistances were increased while the capacitance of the electrochemical double layers (Double layer capacitance) as well as the concentration of dissolved iron (Feⁿ⁺) ions in the environment, were all reduced with increasing concentration of the expired drug. Although moderate amounts of the expired drug delivered appreciable levels of corrosion inhibition when dissolved directly into the corrosive environment and without any pre-treatment, increased concentration of expired drug resulted in increased corrosion inhibition efficiency. The highest corrosion inhibition efficiency obtained was 97.6% and was from the acidic environment that contained 8 g/L of expired piroxicam drug. The expired piroxicam drug inhibited corrosion of mild steel in 0.5M HCl acid via spontaneous physical adsorption (physisorption) process(s), obeying Langmuir’s adsorption isotherm.

Abstract: Microelectrode arrays (MEAs) are gaining interest in electroanalysis owing to its distinctive voltammetry properties compared to its macro counterparts. Among the MEAs widely fabricated and studied are microdisc array and microband array. We report here the microfabrication of 10 μm microband array (number of band in an array, N=17) and its application in labelless impedimetric sensing of T-2/HT-2 toxin. The microband array has recess depth (i.e. Si₃N₄ passivation thickness) of 200 nm. Upon fabrication, the device was first characterized via visual inspection and electrochemical analysis. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) studies were performed in 1 mM ferrocenecarboxylic acid (FCA) in 0.01 M PBS, pH 7.4. At scan rate of 100 mv s^-1, cyclic voltammogram for the microband array exhibited a slight peak-shaped CV; and was found to be scan-rate dependent. Experimental limiting current of the microband array (529±7 nA) was slightly lower compared to the calculated theoretical current (632 nA) indicating mixed diffusion profile of the microband array. The device was then employed in immunosensor construction for T-2/HT-2 toxins detection. T-2 mycotoxin and its metabolite (HT-2), are target of concern in the biosensing application due to its lethal toxicity and prominent presence in EU grains industry. Surface functionalization for anti-T-2 monoclonal antibody (mAb) immobilization was first achieved via surface hydroxylation with plasma cleaning and piranha solution treatment, followed by (3-Aminopropyl) triethoxysilane (APTES) silanization and 15 minutes pre-incubation with various concentrations of anti-T-2 toxin mAb in EDC/NHS mixture. The optimal concentrations for anti-T-2 toxin mAb immobilization on the microband array surface was determined at 0.75 mg mL^-1. Based on the calibration curve developed in buffer solution system, the functionalized microband array was proven sensitive as it was able to detect T-2/HT-2 toxin at low dynamic working range (0-25 ppb) and limit of quantitation (LOQ) achieved at 4.89 ppb.

Abstract: Global lithium deposits have been consumed a lot because of the heavy usage of lithium-ion batteries (LIBs) in almost all portable electronic devices and in automobiles. Due to the very limited global lithium resources, the so-called ‘batteries beyond lithium-ion’ such as sodium-ion batteries (SIBs) are becoming popular, particularly in the R&D level. One of the common problems in the commercial level production of SIBs is the synthesis of suitable electrolytes with sufficient ambient temperature ionic conductivities. In this work, a set of novel gel-polymer electrolytes (GPEs) based on poly (methyl methacrylate) (PMMA) host polymer have been synthesized and characterized by electrochemical impedance spectroscopic (EIS), DC polarization and cyclic voltammetric (CV) techniques. The optimized PMMA-NaClO₄-EC-DMC GPE composition (10:14:38:38 wt.%) showed an ambient temperature ionic conductivity of 8.4 mS cm^-1. Ionic conductivity vs inverse temperature showed Arrhenius behavior with almost same activation energies of 0.16 eV for all the compositions studied. DC polarization test on SS/GPE/SS configuration showed that the best conducting composition is dominantly an ionic conductor (t_ion ~ 0.998) with negligible electronic conductivity, which is highly desirable to avoid short circuits within the cell. The CV test on best conducting composition revealed that the electrochemical stability window (ESW) of these GPEs is about 4 volts (- 2 to + 2 volts). This optimized composition with highest ambient temperature ionic conductivity and negligible electronic conductivity seems to be a promising candidate for practical applications in sodium-ion secondary batteries.