Current-step Method Research Articles

Experimental Investigation of Heat Dissipation of Lithium–Ion Cells and Its Correlation with Internal Resistance

Power loss is a limiting factor for batteries and individual cells. The resulting heat generation due to the power loss leads to reduced battery performance and, thus, lower efficiency. These losses are largely due to the internal resistance of the cells. Therefore, it is important to accurately determine the value of the internal resistance of lithium–ion cells. From the literature, it was found that there are three widely used internal resistance-measurement methods (current step method, direct-energy-loss method, and calorimeter measurement), with negligible research on their comparison demonstrating the most efficient method. Henceforth, to find the most optimal method, this research adopts all three methods on a variety of cell chemistries, including Lithium-ion Manganese Oxide (LMO), Lithium Iron Phosphate (LFP), Nickel Manganese Cobalt (NMC), and Lithium Titanium-Oxide (LTO) for different c-rates (1 C, 2 C, and 3 C), with a wide temperature range (from 0 °C to 40 °C).

Evaluation of Crevice Corrosion Propagation by Continuous Current Step Method for Various Stainless Steels in Artificial Seawater

Evaluation of Crevice Corrosion Propagation by Continuous Current Step Method for Various Stainless Steels in Artificial Seawater

Comparison of Several Methods for Determining the Internal Resistance of Lithium Ion Cells

The internal resistance is the key parameter for determining power, energy efficiency and lost heat of a lithium ion cell. Precise knowledge of this value is vital for designing battery systems for automotive applications. Internal resistance of a cell was determined by current step methods, AC (alternating current) methods, electrochemical impedance spectroscopy and thermal loss methods. The outcomes of these measurements have been compared with each other. If charge or discharge of the cell is limited, current step methods provide the same results as energy loss methods.

Bond strength degradation of corrosive reinforced lightweight concrete

The influence of reinforced bar corrosion on the bond degradation in lightweight concrete was studied. Accelerated constant current corrosion tests were performed on lightweight reinforced concrete samples, and the influential factors, such as protective layer thickness, reinforced bar diameter and corrosive level were investigated. The constant current step method was used to measure the electric resistance of the concrete protective cover, which was used to characterize the corrosion level of the rebar. Experimental results indicated that the corrosive resistance increased with increasing the cover dimension and decreasing the reinforced bar diameter, and the rate of decrease in the specimen impedance after cracking depended on the cover dimension. A new medium was offered for the further research on the performance degradation of corrosion lightweight concrete.

Diffusion layer approximation under transient conditions

First, a theoretical expression of diffusion layer thickness is derived for simple (one-step) electrochemical reactions with reversible electron-transfer processes investigated by LSV under semi-infinite linear diffusion conditions in the electrolytic solution. The above expression is compared to previous results in electrochemical literature. In particular, it is shown that Padé-approximants used in previous works fail to predict the potential dependence of diffusion layer thickness over the whole potential domain. More generally, the change of diffusion layer thickness with respect to time is derived in this article in terms of reaction rate and mass-transport conditions, irrespective of the interfacial reaction mechanism and the electron-transfer kinetics. The formulation applies to one-dimensional diffusion processes eventually coupled with homogeneous chemical reactions, using electrochemical techniques such as potential and current step methods, linear sweep voltammetry (LSV), etc. Finally, experimental investigation of Fe III/Fe II redox couple by LSV is presented as an illustration of the theoretical derivation in this work.

Nucleation and growth of tin on low carbon steel

The nucleation and growth of tin from stannous sulfate and sulfuric acid with an organic additive of gelatin was studied on low carbon steel. Investigations were conducted by linear sweep voltammetry and current step methods. The agitation effect on the morphology of tin deposits was also studied. From the results, a mechanism of tin deposition on a steel substrate is suggested. Initially, 3D tin crystallites are formed preferentially on step edges, and this is followed by fast covering of neighboring sites with much smaller and densely packed crystallites of about 150–180 nm in size. Without gelatin, the coverage was poor and tri-modal structures were dominating. It is discovered that the synergy between hydrogen co-evolution and gelatin contributes to fast and complete coverage of the steel substrate and the bi-modal grain size distribution is observed. The diffusion coefficient of tin ion was determined according to the Sand equation.

Nucleation and growth of copper on glassy carbon and steel

The nucleation and growth of copper from sulphate solution have been studied on two substrates, glassy carbon and stainless steel. Investigations were performed by linear sweep voltammetry, potential and current step methods. The results suggest that a copper coating is formed on glassy carbon by three-dimensional nucleation and growth of the crystallites up to coalescence. On steel, after the formation of crystallites by the same mechanism as above, a second step was observed. The oxide layer, which was on the parts of the substrate not covered by the first crystallites, was reduced, allowing copper to deposit on the renewed surface by a non-nucleated process. This may explain the rapid covering of steel, as compared with the slow covering of glassy carbon, and the different morphology of the deposits obtained on the two substrates.

Participation of dinuclear metal complexes in charge transfer at electrodes: The Cu(II)/Cu(Hg) electrode reaction in acetate solutions

The electrode reaction Cu(II)/Cu(Hg) in complex acetate (Ac −) solutions has been studied at the equilibrium electrode potential by a cyclic current-step method. The data refer to an ionic strength of 1 M with sodium perchlorate as the supporting electrolyte and to a temperature of 25°C. Double-layer data were obtained from electrocapillary measurements. The kinetics indicates that the electron transfer Cu(II)/Cu(I) via the amalgam, which is the slowest step in the overall charge transfer, is substantially accelerated at increasing ligand concentrations within the range covered ([Ac −] ⩽ 20 mM). The results obtained show that Cu 2+, CuAc +, CuAc 2 and Cu 2Ac 3 + take part as oxidants. For ligand numbers n & > 0.2, CuAc + and Cu 2Ac 3 + are predominant. The rate enhancement can primarily be explained by the formation of an electron-mediating carboxylate bridge between Cu(II) and the amalgam. Both Cu 2Ac 3 + and the corresponding reductant, the mixed-valence complex Cu IICu IAc 3, can form such bridges, which probably is the cause of the very strong electrocatalysis displayed by these dinuclear complexes.

Electrochemical investigations of electronically conductive polymers: Part VI. Mechanism of the redox reactions for the electronically conductive form of polypyrrol

A small amplitude current-step method has been developed to study redox reactions of polypyrrole at high doping levels (equilibrium potentials between 0.1 and 0.6 V vs. SCE). The polymer is an electronic conductor in this potential window. It has been proven rigorously that both the oxidation and reduction processes of polypyrrole films are purely capacitive in this potential region. The effect of external electrolyte concentration on the film resistance and capacitance was studied. The results suggest that the film ionic conductivity is determined by the concentration of excess free electrolyte inside the film. Charge balancing anions do not contribute to the ionic conductivity. It was also found that the morphology of polypyrrole films is uniform throughout the film thickness. Finally, we present here a simple heuristic model for redox reactions of conductive polymers.

In situ measurements of conductivity and active surface area of porous electrodes by the current step method—II. Experiments

The electrical conductivity of a laboratory lead dioxide electrode immersed in a solution of H 2SO 4 was measured by the four-point dc method using a current step. Analysis of the potential drop as function of the time yielded information about conductivity of the solid phase, double layer capacity related to the internal active surface area, and transport hindrance in the pores. The conductivity decreases by less than an order of magnitude during discharge, hence it does not seem to be the limiting factor of the discharge capacity.

In situ measurement of conductivity and active surface area of porous electrodes by the current step method—I. Theory

If the electrical conductivity of a plate-shaped porous electrode immersed in an electrolyte is measured by the four-point d.c. method using a current step, the potential drop, Δφ 1, is a function of the time, t. The course of this function can be derived theoretically by solving two simultaneous partial differential equations describing the potential distribution in both the solid and liquid phases. It is shown that the Δφ 1 − t dependence permits not only to determine the conductivity of the electrode but also to estimate its true surface area and the conductivity of the pore electrolyte.

Kinetics of Hg(II)/Hg electrode reaction in DMSO solutions of chloride ions

The electrode reaction Hg(II)/Hg in complex chloride solutions with dimethyl sulfoxide as solvent has been investigated at the equilibrium potential by the faradaic impedance method and a cyclic current-step method. The ionic strength was 1 M with ammonium perchlorate as supporting electrolyte, and the temperature was 25°C. Double-layer data have been determined by electrocapillary measurements. From the results of the kinetic measurements at ligand numbers ≤1.1 or ≥2.3 it is concluded that the overall charge transfer proceeds step-wise. The solvated Hg2+ and Hg22+ as well as the complexes HgClj2−j and the dinuclear Hg2Cl3+ contribute to the exchange current density. The rate constant of the step HgClj2−j/ Hg(I) is found to increase with the number of Cl− coordinated. This increase can be correlated to a decrease in solvation and a lengthening of the Hg−Cl distance. For 1.1 << 2.3, impedance measurements indicate a rate-controlling adsorption step. It is suggested that the uncharged HgCl2 then forms an adsorbed network on the mercury surface.

Kinetics of the Hg(II)/Hg electrode reaction in DMSO solutions of chloride ions

The electrode reaction Hg(II)/Hg in complex chloride solutions with dimethyl sulfoxide as solvent has been investigated at the equilibrium potential by the faradaic impedance method and a cyclic current-step method. The ionic strength was 1 M with ammonium perchlorate as supporting electrolyte, and the temperature was 25°C. Double-layer data have been determined by electrocapillary measurements. From the results of the kinetic measurements at ligand numbers ≤1.1 or ≥2.3 it is concluded that the overall charge transfer proceeds step-wise. The solvated Hg 2+ and Hg 2 2+ as well as the complexes HgCl j 2− j and the dinuclear Hg 2Cl 3+ contribute to the exchange current density. The rate constant of the step HgCl j 2− j / Hg(I) is found to increase with the number of Cl − coordinated. This increase can be correlated to a decrease in solvation and a lengthening of the Hg−Cl distance. For 1.1 << 2.3, impedance measurements indicate a rate-controlling adsorption step. It is suggested that the uncharged HgCl 2 then forms an adsorbed network on the mercury surface.

Kinetics and mechanism of the Cu(I)/Cu(Hg) electrode reactions in DMSO solutions of halide ions

The electrode reaction Cu(I)/Cu(Hg) in complex chloride, bromide and iodide solutions with DMSO as solvent has been studied at the equilibrium potential by the faradiac impedance method and a cyclic current-step method. The kinetic data refer to the ionic strength 1 M with ammonium perchlorate as supporting electrolyte and to the temperature 25°C. Double-layer data have been obtained from electrocapillary measurements. From the results for the chloride system at [Cl − ]>15 m M it is concluded that the charge transfer is catalysed by ligand bridging at the amalgam and the following parallel reactions predominate: Cl ads − -Cu + +e − (am)Cl ads − +Cu(am) Cl ads − -Cu 2 Cl j 2−j +e − (am)Cl ads − +Cu(am)+CuCl j 1−j At lower [Cl − ] and in the whole ligand concentration range available in the bromide and iodide systems the impedance measurements indicate a rate-controlling adsorption step. It is suggested that uncharged complex CuL (L − =halide ion) then forms an adsorbed two-dimensional network on the amalgam surface.

Kinetics and mechanism of the Cu(I)/Cu(Hg) electrode reactions in DMSO solutions of halide ions

The electrode reaction Cu(I)/Cu(Hg) in complex chloride, bromide and iodide solutions with DMSO as solvent has been studied at the equilibrium potential by the faradiac impedance method and a cyclic current-step method. The kinetic data refer to the ionic strength 1 M with ammonium perchlorate as supporting electrolyte and to the temperature 25°C. Double-layer data have been obtained from electrocapillary measurements. From the results for the chloride system at [Cl −]>15 m M it is concluded that the charge transfer is catalysed by ligand bridging at the amalgam and the following parallel reactions predominate: Cl ads −-Cu ++e −(am)Cl ads −+Cu(am) Cl ads −-Cu 2Cl j 2−j+e −(am)Cl ads −+Cu(am)+CuCl j 1−j At lower [Cl −] and in the whole ligand concentration range available in the bromide and iodide systems the impedance measurements indicate a rate-controlling adsorption step. It is suggested that uncharged complex CuL (L −=halide ion) then forms an adsorbed two-dimensional network on the amalgam surface.

Kinetics and mechanism of corrosion of zinc in sodium hydroxide solutions by steady-state and transient methods

The kinetics and mechanism of corrosion of zinc in 1–10 M NaOH solutions are presented with the help of steady-state and transient measurements. Both current step and potential step methods were used for the transient measurements. The individual electrode reactions giving rise to the observed corrosion were studied in detail for transfer coefficients, reaction orders with respect to OH−, Na+, Zn(OH)42− ions, and the rate-determining steps identified. Using this information, equations relating icorr and Ecorr to solution parameters were derived and compared with the experimental dependence. The rate-determining step for the anodic reaction obtained from transient measurements differs from that obtained from the steady-state measurements.

Kinetics and mechanism of corrosion of zinc in sodium hydroxide solutions by steady-state and transient methods

The kinetics and mechanism of corrosion of zinc in 1–10 M NaOH solutions are presented with the help of steady-state and transient measurements. Both current step and potential step methods were used for the transient measurements. The individual electrode reactions giving rise to the observed corrosion were studied in detail for transfer coefficients, reaction orders with respect to OH −, Na +, Zn(OH) 4 2− ions, and the rate-determining steps identified. Using this information, equations relating i corr and E corr to solution parameters were derived and compared with the experimental dependence. The rate-determining step for the anodic reaction obtained from transient measurements differs from that obtained from the steady-state measurements.

Kinetics of the Cd(II)/Cd(Hg) electrode reactions in DMSO solutions of halide ions

The electrode reaction Cd(II)/Cd(Hg) in complex chloride, bromide and iodide solutions with dimethyl sulfoxide as solvent has been studied by a cyclic current-step method. The ionic strength was 1 M with ammonium perchlorate as supporting electrolyte. The φ 2-potential of the double-layer has been determined by electrocapillary measurements. The results indicate that the overall charge transfer proceeds step-wise and is accompanied by a fast disproportionation of the intermediate Cd(I). In the chloride system it is not possible to detect that the complexes formed take part in the electrode reaction, while in the bromide and iodide systems Cd 2+ as well as the complexes CdX + and CdX 2 contribute to the exchange current density. It is suggested that the rate constant of the step CdX j 2− j /Cd(I) depends on the possibility of ligand bridging at the amalgam by X − and on the total enthalpy change at the formation of CdX j 2− j from the solvated Cd 2+.

ChemInform Abstract: ELECTRODE REACTION OF SILVER ON A SILVER BROMIDE CRYSTAL

AbstractDie Elektrodenreaktionen von Ag auf einem AgBr‐Einkristall werden unter Anwendung einer Stromsprung methode mit kleinem Elektrizitätsdurchgang ( l0 um C) beobachtet.

Electrode reaction of silver on a silver bromide crystal

The electrode reactions of silver on a silver bromide single crystal were observed employing a current step method with a small amount of electricity passed. Special attention was paid to the preparation of the electrode contact. From the overvoltage change, the kinetic parameters, i O, Fv and a O were obtained in the temperature range 300–400°C. It is concluded that the reactions proceed with two steps, the one is a formation of interfacial silver ions, through a charge transfer process and the other the incorporation of the formed ion into the electrolyte crystal, which is a specific character for the solid electrolyte system. In this system, the iterfacial silver ion seems to be incorporated through a vacant site of lattice with an accompanying surface diffusion.