Electrochemical Impedance Spectroscopy Experiments Research Articles

Investigation of the Electrochemical Kinetics of Aluminum Deposition from Ionic Liquids

Aluminum is one of the first metals that has been successfully deposited from ionic liquids (ILs) and has been in the focus of intense research. However, the electrochemical kinetics of the aluminum deposition from ILs is still not fully understood.This paper will discuss recent results from the authors’ lab on the electrochemical kinetics of the deposition of aluminium from 1-ethyl-3-methyl-imidazolium based ILs. Overpotential measurements and electrochemical impedance spectroscopy (EIS) experiments were employed to extract kinetic data from potential-time transients (see Fig. 1). The transients were interpreted in terms of different contributions to the total overpotential. This includes a detailed discussion of the Ohmic drop, charge transfer, concentration and nucleation overpotential. The charge transfer mechanism of aluminum was investigated in terms of the anodic and cathodic rate-determining step (RDS) and oxidation and reduction mechanisms are suggested. Density Functional Theory (DFT) calculations were performed to evaluate if the suggested mechanism is thermodynamically reasonable.Fig. 1 Potential-time transient for a constant-current step (j = 1.25 mA cm-2) at an aluminum electrode in [EMIm]Al2Cl7 at 300 K. The inset shows the first 500 ms of the potential-time transient. Figure 1

P-doped WO<sub>3</sub> semiconductor with enhanced conduction band on highly efficient photoelectrocatalytic reduction of CO<sub>2</sub>

Global warming is considered a serious climate problem caused by excessive emissions of carbon dioxide. Studies on catalytic conversion of CO2 are significant in terms of reducing CO2 concentration in the atmosphere, thus remain popular in the field. The photoelectrocatalytic (PEC) reduction of CO2 is an environment-friendly and efficient method to convert excessive CO2 into chemicals. With such conversion, the greenhouse effect can be alleviated through the storage and transformation of solar energy into chemical energy. WO3 is an n-type semiconductor with wide band gap and low conduction band position. Therefore, the use of WO3 is rare for photocatalytic water splitting and CO2 reduction. Although some techniques are used to improve the ability of WO3 in photocatalytic water splitting, the light quantum efficiency (AQE) is still less than TiO2. In current study, a facile method is explored to enhance the conduction band position of semiconductors, thereby improving the photoelectrocatalytic reduction of CO2. To the best of our knowledge, this is the first paper includes novel P-doped WO3 catalysts being designed, prepared, and used in the reduction of CO2 to carbon-based chemicals in water. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), and electron paramagnetic resonance (EPR) experiments were applied to confirm the formation of new catalysts. The photoelectric properties of new catalysts were characterized by UV-vis, linear sweep voltammetry (LSV), Mott-Schottky, and electrochemical impedance spectroscopy (EIS) experiments. We have developed a new type of hybrid semiconductor (P-doped WO3 vertical bar) as catalytic materials by introducing the vaporized phosphide (NaH2PO2) onto the surface of WO3 substrate under the flow of argon gas in a tube furnace. The PEC cell of P-doped WO3 vertical bar SCE vertical bar BiVO4 was equipped with a trielectrode system and powered by a chemical workstation, in which, p-doped WO3 vertical bar was used as photocathodes in photoelectrocatalytic reduction of CO2. The PEC cell was fulfilled with an electrolyte containing 1 mmol/L photosensitizer Eosin Y and 0.1 mol/L KHCO3, and bubbled with pure CO2 in 30 min to saturation, the experiment of CO2 reduction in water was carried out with a proper voltage under irradiation of simulated sun light (300W Xe lamp) to generate methanol, ethanol, acetone, etc. Our results indicates that the conduction band position of p-doped WO3 increases from -0.13 to -0.54 V along with the increase of P-doped quantity, augmenting its ability to reduce CO2. It can be seen that p-doped WO3 with oxygen vacancies has higher activity than pure WO3, in which, the highest activity is the catalyst 15-P, approaching to 0.4% AQE equal to natural plant, yielding methanol in a rate of 20.8 mu mol/(L h cm(2)) and acidic acid at a rate of 4.7 mu mol/(L h cm(2)). The influence of oxygen vacancies on the reaction is positive and verified by the quenching experiments of H2O2. The more oxidation time, the less oxygen vacancies. The EPR signal of 15-P catalyst treated by 2 h oxidation was reduced to 10%. The catalytic activity of CO2 reduction was decreased to 50%. In summary, we designed and prepared a new type of p-doped WO3 hybrid semiconductor material as efficient catalysts for photoelectrocatalytic reduction of CO2, resulting carbon-based chemicals. P-doped WO3 improves the conduction band position of the semiconductors, increases oxygen vacancies and defect sites. Therfore, the activity and efficiency of catalytic reduction of CO2 can be improved. The low voltage is favoured to ethanol production, and high voltage is favoured to acid production. The experimental results have guiding significance for the development of new hybrid semiconductor materials and their photoelectrocatalytic reduction of CO2.

Fabrication of graphene-coated poly(glycidyl methacrylate) microspheres by electrostatic interaction and their application in epoxy anticorrosion coatings

The uneven dispersion of graphene in the resin matrix hinders its application in anticorrosion coatings. This study reports a new method where graphene oxide (GO) is coated on the surface of the poly(glycidyl methacrylate) (PGMA) microspheres to promote the dispersion of GO in epoxy resin (EP) to improve the anticorrosion performance of EP. GO-coated PGMA microspheres (PGMA@GO) were successfully fabricated by electrostatic interaction, which was confirmed by Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and zeta potential analysis. The scanning electron microscopy results showed that the PGMA microspheres were uniformly coated with GO, when the weight ratio of PGMA@GO was 1:2 (PGMA: GO). Electrochemical impedance spectroscopy and salt immersion experiments were performed to evaluate the corrosion resistance of the EP composite coatings. Comparing with pure EP and GO/EP coatings, the mechanical properties and anticorrosion properties of coatings were improved after adding PGMA@GO. When the addition amount of PGMA@GO (of 50 g EP) was 1.0 wt% and about 0.67 wt% GO was only needed, the PGMA@GO/EP composite coating possessed a high impedance of 5.68 × 108 Ω cm2 and a low breakpoint frequency of 0.39 Hz for 21-day immersion in 3.5 wt% NaCl solution. The anticorrosion mechanism of PGMA@GO/EP composite coating was also discussed.

Direct Solid Oxide Electrolysis of Carbon Dioxide: Analysis of Performance and Processes

Chemical industries rely heavily on fossil resources for the production of carbon-based chemicals. A possible transformation towards sustainability is the usage of carbon dioxide as a source of carbon. Carbon dioxide is activated for follow-up reactions by its conversion to carbon monoxide. This can be accomplished by electrochemical reduction in solid oxide cells. In this work, we investigate the process performance of the direct high-temperature CO2 electrolysis by current-voltage characteristics (iV) and Electrochemical Impedance Spectroscopy (EIS) experiments. Variations of the operation parameters temperature, load, fuel utilization, feed gas ratio and flow rate show the versatility of the procedure with maintaining high current densities of 0.75 up to 1.5 A·cm−2, therefore resulting in high conversion rates. The potential of the high-temperature carbon dioxide electrolysis as a suitable enabler for the activation of CO2 as a chemical feedstock is therefore appointed and shown.

Insight into the anti-corrosion mechanism of 2-aminobenzenethiol as the inhibitor for copper in acid environment

2-Aminobenzenethiol (ABT) was first reported as a corrosion inhibitor for copper in sulfuric acid environment. The biggest bright spot in this work is the discovery that ABT as a corrosion inhibitor can show high-quality anti-corrosion feature at low concentrations (0.01 M–0.5 M). The polarization curve experiment data shows that the corrosion inhibition efficiency of ABT for Cu in 0.5 mol/L sulfuric acid environment is obviously more than 90%, and the corrosion inhibition efficiency is proportional to ABT concentration. Electrochemical impedance spectroscopy (EIS) experiment shows that the polarization resistance (Rp) in the blank solution is 0.38 kΩ cm2, and the Rp increased to 21.18 kΩ cm2 after adding 0.5 M ABT, and the corrosion inhibition efficiency is as high as 98.2%. The surface morphology test results show that the copper surface after adding ABT is significantly smoother than the copper surface in the blank solution. The X-ray photoelectron spectroscopy (XPS) experimental results show that the sulfur and nitrogen atoms in ABT can form coordination bonds with copper atoms, resulting in chemisorption. In addition, the adsorption isotherm model shows that the adsorption of ABT on the copper surface conforms to the Langmuir isotherm model. Quantum chemical (QC) calculations and molecular dynamics (MD) simulations have shown that ABT can show decent anti-corrosion feature.

A 2D tungsten disulphide/diamond nanoparticles hybrid for an electrochemical sensor development towards the simultaneous determination of sunset yellow and quinoline yellow

We present the development of an electrochemical sensor towards the simultaneous analysis of a mixture of food additives: sunset yellow (SY) and quinoline yellow (QY) dyes. The sensor is based on the synergetic effect observed between diamond nanoparticles (DNPs) and WS2 nanosheets obtained by liquid exfoliation. The prepared TMDs were characterized using Raman spectroscopy, X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM). The AFM characterization showed isolated WS2 flakes with different lateral dimensions scattered over the flat background. The combination of WS2 and DNPs allows resolution of the oxidation signals of the analytes, which overlap working with the bare glassy carbon (GC) electrode. The best electroanalytical response was obtained with a sensor containing both nanomaterials deposited employing the drop-casting method in a sequential manner, a first layer of WS2 and a second layer of DNPs (GC/WS2/DNPs). Electrochemical impedance spectroscopy experiments showed that for the GC/WS2/DNPs system the charge transfer is clearly improved. Under optimized differential pulse voltammetry conditions, the GC/WS2/DNPs sensor allows the determination of SY at +100 mV and QY at +850 mV with detection limits of 0.086 and 3.4 μM respectively, with relative errors ≤ 8.40 % and a relative standard deviation ≤ 12.6 %. The proposed methodology was applied to the determination of SY and QY in commercial throat lozenge samples with very good recoveries on average: 93 %, for QY and 106 % for SY.

Designing and construction of carboxyl functionalised MWCNTs/Co-MOFs-based electrochemical sensor for the sensitive detection of nitrite

ABSTRACT A simple and sensitive electrochemical sensor based on metal-organic framework carboxyl functionalised MWCNTs/Co-MOFs have been successfully fabricated towards nitrite detection. Electrochemical techniques such as cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) experiments were conducted on carboxyl functionalised MWCNTs/Co-MOFs electrochemical sensor to decipher the electrochemical sensing performance. Several important electrochemical sensor parameters have been evaluated for nitrite oxidation, such as pH, deposition potential and preconcentration time. The observed results showed that the proposed electrochemical sensor provide a wide linear working range i.e. 80–1160 µM with a detection limit (3σ) of 18.8 µM and sensitivity of 0.01 µA µm−1 cm−2. Furthermore, the proposed sensor also applied to determine the nitrite level in beverage and water samples with satisfactory recoveries.

Concentration effect on properties of Pt-NiOx nanocompounds converted from mixed chloroplatinic acid and nickel acetate precursor films using an atmospheric-pressure plasma jet

A direct current-pulse nitrogen atmospheric-pressure plasma jet (APPJ) is used to convert Pt-NiOx nanocompounds from liquid precursor films consisting of a mixture of chloroplatinic acid and nickel acetate. The Pt-NiOx nanoparticles are well-distributed on the fluorine-doped tin oxide (FTO) glass substrates. X-ray photoelectron spectroscopy results indicate that the reaction product mainly contains metallic Pt and oxidized Ni. Electrochemical impedance spectroscopy and Tafel experiments reveal an improvement in electrochemical catalytic effects. The APPJ-processed Pt-NiOx nanocompounds on FTO glass substrates are used as the counter electrodes (CEs) of dye-sensitized solar cells (DSSCs). J − V curves indicate that DSSCs with 5-s APPJ-processed Pt-NiOx CEs showed significantly improved performance. The sample properties become stable after ∼45 s of APPJ calcination. Precursor solutions with three different mole ratios of chloroplatinic acid and nickel acetate are investigated. With the addition of an adequate amount of oxidized nickel, the transfer charge current density and electrochemical catalytic effects are enhanced.

Hydrostatic pressure effect on double layer capacity of iron

The effect of deep sea hydrostatic pressure on double layer capacity still remains unknown. In this study, a novel method to characterize the double layer capacity was put forward. Combining with the potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) experiments under different hydrostatic pressures, it was found that pressure increased the capacity both in diffuse layer and Stern layer, which induced the increase of the current density of both oxidation and reduction reaction near the equilibrium potential.

In-situ electrochemical study of zirconium alloy in high temperature hydrogenated Water conditions

The electrochemical characteristics of a Zr-Nb-Sn zirconium alloy have been investigated at 360 ℃ in simulated primary water condition of pressurized water reactor with two different dissolved hydrogen contents. In-situ electrochemical impedance spectroscopy experiment was performed for 100 d, and the thickness and resistivity of the zirconium oxide films were measured as function of time. The results show that there is a difference in oxide resistivity as function of dissolved hydrogen content in the environment. The resistivity of the oxide film on Zr-Nb-Sn alloy is lower at higher dissolved hydrogen condition, resulting in a higher corrosion rate at that condition.

Effect of AuM (M: Ag, Pt & Pd) bimetallic nanoparticles on the sorbitol electro-oxidation in alkaline medium

In this work, the effect of the second metal of AuM (M: Ag, Pd & Pt) materials on the sorbitol electro-oxidation reaction (SOR) in alkaline medium was evaluated. For this purpose, AuM nanoparticles were synthesized following the Brust’s method. The obtained nanoparticles presented similar average particle size (~7 nm), while the gold content ranged between 53 and 77 atomic %, the Vulcan carbon support loading was found to be close to 80 ± 5 wt%. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical analyses confirmed the formation of the bimetallic catalysts and revealed close electronic interactions between the noble metals. Cyclic voltammograms performed using 0.1 M sorbitol in 0.3 M KOH indicated that AuPt/C displayed the lowest onset potential (−0.36 V vs. NHE), which is 120 mV lower to that determined for Au/C as the reference material. Furthermore, AuPd/C catalyst presented the highest current density (43.65 [mA mgAuPd−1] at a fixed potential of 0.14 V vs. NHE). Further experiments varying the sorbitol and KOH concentrations, the scan rate and the operating temperature were performed as well as electrochemical impedance spectroscopy (EIS) experiments. These results shown that the SOR followed the typical trend for the electro-oxidation of polyol fuels (such as glycerol), where Pt promotes lower onset potentials, but the adsorption of intermediates limits the maximum current density in comparison with Pd-based catalysts. As summary, this study found that AuPd and Pd-containing materials could be excellent candidates for sorbitol oxidation in alkaline medium.

The impact of Ni on the corrosion behavior and microstructure of weld metal fabricated from E8018-G electrodes

Due to the importance of the weld metal corrosion, this study aims at the effect of using Ni in weld metals on their corrosion parameters and microstructures. In this regard, the effect of negligible amounts of Ni up to 8.0 wt.% is examined on weld metals made of weld electrodes of the E8018-G type in conditions equal to industrial standards. The corrosion parameters of the weld metals are evaluated through potentiodynamic polarization and electrochemical impedance spectroscopy experiments in a corrosive solution of 3.5% NaCl. The morphology of the weld metals is examined using field emission scanning electron microscopy and optical microscopy. Through evaluating the morphology, corrosion current density (Jcorr), corrosion rate (CR), and polarization resistance (RP) of the weld metals containing different amounts of Ni, it is indicated that Ni plays an important role in creating anti-corrosion properties. The microstructure studies indicate that a weld metal containing 2.91 wt.% Ni is homogeneous, and its major phase is acicular ferrite (AF). The results also show that an optimal amount of 2.91 wt.% Ni in a weld metal provides the highest corrosion resistance in a corrosive solution.

Incorporating Diamondoids as Electrolyte Additive in the Sodium Metal Anode to Mitigate Dendrite Growth.

Owing to the high abundance and gravimetric capacity (1165.78 mAh g−1) of pure sodium, it is considered as a promising candidate for the anode of next‐generation batteries. However, one major challenge needs to be solved before commercializing the sodium metal anode: The growth of dendrites during metal plating. One possibility to address this challenge is to use additives in the electrolyte to form a protective solid electrolyte interphase on the anode surface. In this work, we introduce a diamondoid‐based additive, which is incorporated into the anode to target this problem. Combining operando and ex situ experiments (electrochemical impedance spectroscopy, optical characterization, and cycling experiments), we show that molecular diamondoids are incorporated into the anode during cycling and successfully mitigate the growth of dendrites. Furthermore, we demonstrate the positive effect of the additive on the operation of sodium‐oxygen batteries by means of increased energy density.

Optimization of platinum precursor concentration for new, fast and simple fabrication method of counter electrode for DSSC application

The new, fast, and simple preparation method of counter electrodes for dye-sensitized solar cells has been presented and the optimization of the Pt precursor solution concentration has been described. The counter electrodes prepared with the use of the Pt precursor solutions in six different concentrations have been applied for the solar cells assembly and the parameters of the devices have been well characterized with photocurrent-photovoltage measurements and electrochemical impedance spectroscopy experiments. 90 mM has been found as an optimal concentration of Pt precursor solution.

Selective sensing of dopamine by sodium cholate tailored polypyrrole-silver nanocomposite

Conducting polymer-noble metal nanocomposites have attracted considerable interest as electrochemical sensors because they provide better sensing responses to different analytes. We report the synthesis of rod like polypyrrole (PPY)-Ag nanocomposite using sodium cholate as soft-template for sensing nanomolar concentration of dopamine (DA). The nanocomposites were characterized by employing FT-IR, XRD, scanning and transmission electron microscopic analysis. Electrochemical impedance spectroscopy and cyclic voltammetry experiments were performed for electrochemical characterization of the PPY-Ag nanocomposite deposited on glassy carbon electrode (GCE). Electrochemical detection of DA using this nanocomposite deposited on GCE was done following linear sweep voltammetry. The PPY-Ag nanocomposite deposited electrode showed improved sensitivity value of 8.22 mAμM−1 for DA and a detection limit of 0.00005 μM. Biocompatibility assay of the developed PPY-Ag nanocomposites have exhibited less toxicity to mouse fibroblast cell even in comparison to that of PPY without silver. Antimicrobial property of the PPY-Ag nanocomposites towards E.coli and S. Aureus have also been observed.

Analysis of Electrochemical Impedance Spectra Using Phase Angle Symmetry Across Log Frequency

A new method for analysis of the impedance behavior of electrochemical impedance circuits (or, in general, the Transfer Function for input-output systems) has been developed which utilizes the symmetry of the phase angle response and its derivative with the Log of the frequency to determine the value of the equivalent circuit elements. In addition, because of this symmetry, the lower frequency half of the impedance response over Log frequency can be calculated based only on information from the upper-half frequency response. The underlying analytical basis for the symmetry of the phase angle and the methods for applying this analysis are presented. Analysis of simple R-C circuits, Randle circuits and Constant Phase Element (CPE)-Randles are presented to derive the symmetric functions for these commonly used circuits. Experimental Electrochemical Impedance Spectroscopy (EIS) data focused on CoCrMo alloy performance in physiologically representative solutions were collected, analyzed using the described method and compared to standard non-linear least squares fitting. Excellent correlation between the analytical equations and experimental data was obtained. A substantial advantage of this approach is that it only requires knowledge of the high frequency-based response to predict the behavior in the low frequency range. Thus, determining the low frequency behavior requires capturing the high frequency impedance in a few seconds rather than in what had, until now, required up to many hours of experimental effort to obtain. Although the mathematical approach presented here is focused on corrosion parameters, it is applicable to other Transfer Function analyses that include dielectric constants, complex modulus and others.

High performance flexible supercapacitors including redox active molybdate incorporated Poly(vinylphosphonic acid) hydrogels

Novel gel polymer electrolyte (hydrogel) was prepared by incorporation of poly (vinylphosphonic acid) (PVPA) as a host matrix and redox active ammonium molybdate, Mo. Supercapacitors including active carbon electrodes were fabricated using hydrogels, PVPA/MoX where X represents the percent fraction of Mo in PVPA. All the electrolytes were in gel form and show excellent bending and stretching properties in a device. The electrochemical performance of the devices was investigated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) experiments. Surprisingly, the specific capacitance (Cs) of the device increased to 1276 F g−1 which is at least 50 times enhancement by introducing Mo as mediator compared to the PVPA based system. The supercapacitor with PVPA/Mo10 has the highest energy density of 180.2 Wh kg−1 at a power density of 500 W kg−1. The device with the same hydrogel structure exhibited higher performance after 2300 charge-discharge cycles and the maintained 85% of its initial capacitance performance. A supercapacitor was fabricated using PVPA/Mo10 and tested under bent and twisted conditions confirming remarkable capacitance retention.

Influence of Ce(IV) ions amount on the electrochemical behavior of hybrid films in 0.1 mol L-1 NaCl solution

In this work, the influence of ceric ions (Ce(SO4)2) addition to the hydrolysis solution on the corrosion protection afforded by organic-inorganic hybrid coating obtained from tetraethoxysilane (TEOS) and 3-methacryloxy-propyl-trimethoxysilane (MPTS) to a carbon steel substrate in 0.1 mol L-1 NaCl solution was studied. Open circuit potential (EOC) and electrochemical impedance spectroscopy (EIS) experiments were carried out and showed that the protection afforded by the organic-inorganic hybrid coating was extremely dependent on the Ce4+ ions amount. These results were in close agreement with optical microscopy observation of the degrading surfaces, both procedures showing that more protective coating was produced when 500 ppm of Ce4+ ions were added to the organic-inorganic hybrid solution. The chemical state of the organic-inorganic hybrid coating investigated by X-ray photoelectron spectroscopy (XPS) indicated that the addition of Ce4+ ions enhances the polycondensation degree of the organic-inorganic hybrid coating leading to a denser siloxane (Si-O-Si) network. A strategy using laser-induced breakdown spectroscopy (LIBS) and UV-Vis spectrometry was set up in order to verify, respectively, the presence of Ce ions within the coating structure and its oxidation state. LIBS results confirmed the incorporation of Ce ions in the coating, which, according to UV-Vis measurements, are mainly in the (IV)-oxidation state.

Identifiability and Parameter Estimation of the Single Particle Lithium-Ion Battery Model

This paper investigates the identifiability and estimation of the parameters of the single particle model (SPM) for lithium-ion battery simulation. Identifiability is addressed both in principle and in practice. The approach begins by grouping parameters and partially non-dimensionalising the SPM to determine the maximum expected degrees of freedom in the problem. We discover that, excluding open circuit voltage, there are only six independent parameters. We then examine the structural identifiability by considering whether the transfer function of the linearised SPM is unique. It is found that the model is unique provided that the electrode open circuit voltage functions have a known non-zero gradient, the parameters are ordered, and the electrode kinetics are lumped into a single charge transfer resistance parameter. We then demonstrate the practical estimation of model parameters from measured frequency-domain experimental electrochemical impedance spectroscopy (EIS) data, and show additionally that the parametrised model provides good predictive capabilities in the time domain, exhibiting a maximum voltage error of 20 mV between model and experiment over a 10 minute dynamic discharge.

Facile fabrication of BTA@ZnO microcapsules and their corrosion protective application in waterborne polyacrylate coatings

This work presents a simple and facile one-step encapsulation method to fabricate benzotriazole@zinc oxide (BTA@ZnO) microcapsules. The morphology, size and chemical composition of as-prepared microcapsules were characterized by electron microscopy, Fourier-transform infrared spectroscopy and X-ray diffraction. Meanwhile, the encapsulation and releasing behaviour of BTA in BTA@ZnO microcapsules were investigated. Results showed that BTA had higher encapsulation efficiency and could be slowly released over a time period of 56 h. In addition, the electrochemical impedance spectroscopy and water uptake experiments demonstrated improved performance in corrosion and water resistance of waterborne polyacrylate coating through introducing BTA@ZnO microcapsules.