Cottrellian Behavior Research Articles

Ambient-temperature aqueous electrochemical route for direct Re-functionalization of spent LFP cathodes of lithium-ion batteries

Relithiation is a critical step in the direct recycling process, which is the most promising method for spent LiFeIIPO4 (LFP) batteries recycling. It involves the reduction of FeIIIPO4 (FP) in a Li-ion-rich environment and is generally performed by high-temperature sintering or hydrothermal methods. This study proposes an ambient temperature electrochemical relithiation method in an aqueous solution. It follows a preliminary delithiation step described in our previous publications. The results confirmed that FP can be efficiently relithiated in either Li2SO4 or LiHCO3 electrolyte. The reaction follows mostly a Cottrellian behavior, determined from potentiostatic experiments, indicating that diffusion in solution is a critical mechanism. Application of this electrochemical relithiation process to FP originating from spent LFP resulted in a 96 % relithiation yield at a current efficiency of 91 %. The overall recycling process successfully re-functionalized deeply damaged spent LFP by recovering up to 99 % of the LFP's original discharge capacity, achieving up to 153 mAh g−1 at C/12. Meanwhile, the initial discharge capacity of the re-functionalized LFP at 1C attained 119 mAh g−1, which interestingly increased upon cycling, reaching 131 mAh g−1 after 225 cycles. This increase could be associated with electrochemical activation promoted by cycling-induced LFP crystal annealing and/or by electrochemical milling.

The Effect of Naphthalene‐Based Additives on the Kinetics of Tin Electrodeposition on Boron‐Doped Diamond Electrodes

AbstractThe effect of naphthalene‐based additives: naphthalene (NPT), naphthalenesulfonate (NPTS) and hydroxynaphthalenesulfonate (HNPTS) on the kinetics of tin electrodeposition on a boron‐doped diamond (BDD) electrode has been studied by means of chronoamperometry and scanning electron microscopy (SEM). Potentiostatic current transients in the absence and the presence of naphthalene‐based additives are analyzed by using the Scharifker‐Hills model. A strong decrease of the kinetics of tin nucleation on BDD was observed in the presence of naphthalene‐based additives, NPT showing the smallest effect and HNPTS showing the largest effect. From the long‐term Cottrell behavior of the transients, similar values of tin(II) diffusion coefficients were obtained for all additives, suggesting that there is no complexation of Sn(II) by the additives and that the charge‐transfer kinetics itself is not substantially influenced by the presence of the additives. In the absence of additives, tin deposition on BDD displays a progressive nucleation and growth mechanism at the least negative potentials, switching to instantaneous nucleation and growth at more negative potential. In the presence of NPTS and HNPTS, progressive nucleation and growth transients are observed. The growth mode results are confirmed by the tin features observed in the scanning electron micrographs. In conclusion, NPT, NPTS and HNPTS mainly decrease the rate of the nucleation of tin deposition, most likely by blocking or reducing access to active nucleation sites. In comparison, ethoxylated α‐napthalenesulfonic acid (ENSA, a commonly used additive in the tin plating industry) inhibits tin deposition process on BDD even more strongly. These observations show a striking similarity to our previous study of tin deposition on gold electrodes.

Determination of transport parameters in [EMIm]Cl–based Ionic Liquids – Diffusion and electrical conductivity

The density, electrical conductivity and diffusion coefficients of anions and cations in the ionic liquid AlCl3/1-ethyl-3-methylimidazolium chloride, [EMIm]Cl, were determined to study physical correlations of these important parameters. The density was measured for different molar ratios of AlCl3:[EMIm]Cl from 0.5:1 to 2.0:1 at ambient temperature. The diffusion coefficient of the electrochemically active heptachloroaluminate complex, Al2Cl7−, was measured for a molar ratio of 2:1 in the range of 25°C to 100°C. The corresponding current density and potential transients were discussed regarding the decomposition of the [EMIm]+ cation and deviation from the theoretical Cottrell behavior. The electrical conductivity was measured for molar ratios of 1.5:1 and 2:1 in the range of 25°C to 100°C. Both the diffusion coefficient and electrical conductivity can be described well by an Arrhenius law. The diffusion coefficients of AlCl4−, Al2Cl7− and [EMIm]+ were estimated from the Nernst–Einstein and Stokes–Einstein relation. The results indicate a strong impact of ion pairing in these electrolytes.

A Study of the Electro-Catalytic Oxidation of Methanol on a Ni-Functionalized Graphene Oxide/p-Type Conductive Polymer Modified Graphite Electrode: Experimental and Theoretical Approach

The preparation of Ni-functionalized graphene oxide/poly orthoaminophenol composites (Ni–FGO–POAP) is presented and the composites were used as graphite electrode modifier for methanol electrooxidation in NaOH. Nickel was accumulated by complex formation between Ni(II), in solution and amines sites in the polymer backbone to obtain Ni–FGO–POAP/G electrode. The electrochemical performance of Ni–FGO–POAP composite electrodes was investigated by common electrochemical techniques. The peak on the potentiodynamic curve for Ni–FGO–POAP electrode in alkaline solutions of methanol is observed which is ascribed to the methanol oxidation in alkaline medium. Under the CA regimes the reaction followed a Cottrellian behavior. The results obtained are discussed from the point of view of employment of the Ni–FGO–POAP composites for the catalytic electrodes of fuel cells. In addition, the atoms-in-molecule (AIM) theory is used to study atomic-scale charge/energy transfer in grapheme-like molecular system.

Effect of Copper Alloying on Electro-Catalytic Activity of Nickel for Ethanol Oxidation in Alkaline Media.

In this research, the electro-catalytic activity of nickel-copper (Ni-Cu) alloy towards oxidation of ethanol and its possible redox process were investigated in alkaline solution. For this purpose, cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy techniques were employed. According to the cyclic voltammetry studies, Ni- Cu alloy compared to pure nickel can demonstrate a significantly higher response for ethanol oxidation. So, the enhancement of the anodic peak current corresponding to the oxidation of nickel hydroxide was accompanied with attenuated cathodic current in the presence of ethanol. The anodic peak currents have a linearly dependence on the square root of scan rate which is the characteristic of diffusion-controlled processes. Based on the chronoamperometry measurements, the reaction exhibited a Cottrellian behavior and the diffusion coefficient of ethanol was found to be 1.26 - 10-5 cm2 s-1. The impedance spectroscopy declared electro-catalytic behavior of Ni-Cu electrode for oxidation of ethanol and showed that the charge transfer resistance decreases by increasing the ethanol concentration.

Electrocatalytic oxidation of methanol on NiZnsalenA modified glassy carbon electrode

Nickel and zinc salen complexes were simultaneously encapsulated in the supercages of the mesoporous zeolite A by using the flexible ligand method. This heterogeneous catalyst NiZnsalenA was characterized by X-ray diffraction, infrared spectroscopy, diffuse reflectance UV-vis spectroscopy, elemental analysis, and N2 adsorption/desorption experiments. The techniques of cyclic voltammetry (CV) and chronoamperometry (CA) were employed to investigate the electrochemical behavior and electrocatalytic activity toward the oxidation of methanol on NiZnsalenA glassy carbon electrode (GCE) in 0.1-M NaOH solution. The CV results presented a pair of redox peaks associated with the Ni2+(salen)(OH)2/Ni3+(salen)O(OH) redox couple. NiZnsalenA also showed the superior electrocatalytic activity to the oxidation of methanol than pure Ni-modified electrode, mainly due to a synergetic effect in NiZnsalenA. This synergetic effect may originate from the interaction of Ni(salen) and Zn(salen) and/or the formation of dinuclear salen complexes via the lattice oxygen of the zeolitic host. The effects of the scan rate, methanol concentration, and OH− concentration on methanol oxidation are investigated, and a possible mechanism is proposed that the oxidation of methanol is done by reaction with Ni3+(salen)O(OH) and also direct electrooxidation reaction. The kinetic parameters such as the electron transfer coefficient α and the rate constant k s of the electrode reaction were estimated to be 0.39 and 1.59 s−1, respectively. In both the CA and CC studies, the process of methanol oxidation followed a Cottrellian behavior, and the diffusion coefficients D CA and D CC of methanol represented the similar tendency, where an initial sharp drop was terminated to a very slow change as the concentration of methanol was approaching 0.7 M. The catalytic rate constant k cat increased rapidly until the concentration of methanol was increased above 0.7 M, and then the values of k cat remained almost constant.

Methanol electrooxidation on glassy carbon electrode modified with bimetallic Ni(II)Co(II)salen complexes encapsulated in mesoporous zeolite A

Nickel and cobalt salen complexes were simultaneously encapsulated in mesoporous zeolite A by flexible ligand method. The prepared catalyst NiCosalenA was investigated for its electrochemical behavior and electrocatalytic activity towards the oxidation of methanol on glassy carbon electrode in 0.1M NaOH solution. Upon encapsulation in zeolite A, the NiCosalen complex exhibits the typical cyclic voltammetric response, which can be anticipated for the Ni2+Co2+(Salen)(OH)2/Ni3+Co3+(Salen)O(OH) redox couple. It also showed much higher electrocatalytic activity towards the oxidation of methanol than pure NisalenA, due to a synergetic effect that may originate from the interaction of Ni(salen) and Co(salen) and/or the formation of dinuclear salen complexes in adjacent or appropriate sites in a nano-cage through the lattice oxygen of the zeolitic host. The mechanism of electrocatalytic oxidation of methanol on NiCosalenA modified electrode was proposed to be EC process. In both the chronoamperometric and chronocoulometric studies, the reaction of methanol electrooxidation followed a Cottrellian behavior and similar diffusion coefficients (D) of methanol were found to be 3.82×10−7cm2s−1 and 3.91×10−7cm2s−1, respectively. The catalytic rate constant (kcat) was also calculated to be 5.52×105cm3mol−1s−1 in the range of 0.005–2.0M of methanol.

Effective performances of chronoamperometry on the passivation process of n-InP in acidic liquid ammonia (-55 °C)

Chronoamperometry has proven to be a useful in-situ technique to investigate on the anodic passivation mechanism on n-InP semiconductors in acidic liquid ammonia. From our preliminary work, we assumed that the phosphazene film results from parallel electrochemical reactions: InP dissolution and ammonia oxidation. The main question posed here was based on the involvement of bromide (Br−) from the conductive salt (NH4Br) in the anodic process. From chronoamperometry, the decrease in the current deviated from Cottrell behavior. No variation of the anodic charge and no shift of the anodic peak potential was found by using various ammonium halogenides (I-, Br-, Cl−). Contrary to ammoniacate solvent, the reduction of Br2 was never observed. These results suggested that the oxidation of Br− into Br2 apparently could not occur during the anodic process. Thanks to chronoamperometry, the passivation rate constant was determined for the first time on InP in liquid ammonia. This constant (–k≈ 10−2 s−1) was roughly similar to that described in the literature on Pt in aqueous alkaline solution during ammonia oxidation. As for on Pt, the deactivation of the surface could be interpreted as a partial electrochemical oxidation of ammonia on n-InP.

Electrocatalytic Oxidation of Paracetamol on Ni and NiCu Alloy Modified Glassy Carbon Electrode

AbstractIn this study we investigated the electrocatalytic oxidation of anti‐inflammatory drug (paracetamol) on Nickel and Nickel–copper alloy modified glassy carbon electrodes (GC/Ni and GC/NiCu) in alkaline solution. These electrodes prepared by galvanostatic method and different electrochemical techniques such as cyclic voltammetry and chronoamperometry were used to track the oxidation process and its kinetics. From Voltammetric studies we concluded that in the presence of drugs the anodic peak current of low valences Nickel species increased, followed by a decrease in the corresponding cathodic current peak. This indicates that drugs were oxidized on the redox mediator which was immobilized on the electrode surface via an electrocatalytic mechanism. Using Laviron's equation, the values of α and ks for the immobilized redox species were determined. The anodic peak currents show linear dependency with the square root of scan rate. This behavior is the characteristic of a diffusion controlled process. Under the CA regime the reaction followed a Cottrellian behavior and the diffusion coefficient of paracetamol was found in agreement with the values obtained from CV measurements.

A Kinetic Investigation of Ethanol Oxidation on a Nickel Oxyhydroxide Electrode

ABSTRACT: Nickel modified NiOOH electrodes were used for the electrocatalytic oxidation of ethanol in alka-line solutions where the methods of cyclic voltammetry (CV) and chronoamperometry (CA) wereemployed. In CV studies, in the presence of ethanol, an increase in the current for the oxidationof nickel hydroxide is followed by a decrease in the corresponding cathodic current. This suggeststhat the oxidation of ethanol is being catalysed through mediated electron transfer across the nickelhydroxide layer comprising of nickel ions of various valence states. Under the CA regime thereaction followed a Cottrellian behavior and the diffusion coefficient of ethanol was found to be1 × 10 7 cm 2 s −1 . Keywords: Ethanol, Electrocatalytic, Nickel, Modified electrode Received March 18, 2012 : Accepted March 28, 2012 1. Introduction In the past decades, the direct methanol fuel cell(DMFC) has drawn attention for its simple construc-tion with reduced dimensions and high-energy effi-ciency. Progress has been made in this field.

Kinetic studies of glucose electrocatalytic oxidation on GC/Ni electrode

AbstractNickel‐modified glassy carbon electrode (GC/Ni) prepared by galvanostatic deposition was used for the electrocatalytic oxidation of glucose in alkaline solutions where different electrochemical methods were employed. In cyclic voltammetry studies, in the presence of glucose an increase in the peak current of the oxidation of nickel hydroxide is followed by a decrease in the corresponding cathodic current. This suggests that the oxidation of glucose is being catalyzed through mediated electron transfer across the nickel hydroxide layer comprising nickel ions of various valence states. Under the chronoamperometric regime, the reaction followed a Cottrellian behavior and the diffusion coefficient of glucose was found to be 8 × 10−6 cm2 s−1. A mechanism based on the electrochemical generation of Ni3+‐active sites and their subsequent consumptions by glucose has been discussed, and kinetic parameters have been derived. The heterogeneous rate constants for the oxidation of glucose at the surface of modified electrodes were determined by rotating disk electrode using the Koutecky–Levich plots, which are in agreement with the data obtained by chronoamperometry. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 712–721, 2012

Kinetics of electrochemical insertion of lithium ion into LiFePO 4 from aqueous 2 M Li 2SO 4 solution studied by potentiostatic intermittent titration technique

Potentiostatic intermittent titration technique (PITT) has been used to study the lithium ion insertion into LiFePO 4 from aqueous 2 M Li 2SO 4 electrolyte along with cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques. The current–time response to an applied potential step has been discussed for lithium insertion into LiFePO 4 from aqueous electrolyte and it is compared with that obtained with an organic electrolyte. The PITT technique is very useful in describing the whole intercalation mechanism. The effects of ohmic potential drops and charge-transfer resistances have been taken into account while predicting the current transients obtained with aqueous electrolyte and non-aqueous electrolyte. The deviation of current transients from ideal Cottrell behavior has been discussed in aqueous electrolyte and it is compared with that in presence of non-aqueous electrolyte. The characteristic diffusion time constant ( t o) in 2 M Li 2SO 4 is found to be 4.71 s and that in non-aqueous LiAsF 6/EC–DMC electrolyte is 248 s. The chemical diffusion coefficient ( D), an important kinetic parameter, calculated from PITT during intercalation process is found to be varying between 10 −12 and 10 −14 cm 2 s −1 in aqueous electrolyte and between 10 −13 and 10 −15 cm 2 s −1 in non-aqueous electrolyte.

Theory of Generalized Cottrellian Current at Rough Electrode with Solution Resistance Effects

A theory for effect of uncompensated solution resistance on Nernstian (reversible) charge transfer at an arbitrary rough electrode is developed. The significant deviation from the Cottrellian behavior is explained, as arising from the resistivity of the solution and geometric irregularity of the interface. Results are obtained for various electrode roughness models, viz., (i) deterministic surface profile, (ii) roughness as random surface profile with known statistical properties, and (iii) random functions with limited self-affine fractal properties. Expressions for concentration, current density, and total current transients have a systematic operator structure in Fourier transformed (deterministic) surface profile function. For a randomly rough electrode, the statistically averaged response is obtained by ensemble averaging over all possible surface configurations. An elegant mathematical formula between the average electrochemical current transient and surface structure factor of roughness is obtained. Realistic fractal roughness is characterized as self-affine scaling property over limited length scales. Limiting behavior in short time, is attributed to resistive effects of the electrolyte, roughness factor and surface curvatures. In the intermediate time, the anomalous power law behavior is attributed to the diffusion length weighted spatial frequency features of roughness. Our results help with the quantitative understanding of generalized Cottrellian response of moderately supported electrolytic solution at rough electrode/electrolyte interface.

Electrochemical Oxidation of Saccharose on Copper (Hydr)oxide-Modified Electrode in Alkaline Media

A stable copper (hydr)oxide-modified electrode was prepared in 0.5 mol/L NaOH solution by cyclic voltammetry in the range of −250 to 1000 mV. It can be used for electrochemical studies in the range of −250 to 1 000 mV without interfering peaks because there is no oxidation of copper. During an anodic potential sweep, the electro-oxidation of saccharose on Cu occurred by the formation of Cu III and this reaction also occurred in the early stages of the reversed cycle until it is stopped by the negative potentials. A mechanism based on the electro-chemical generation of Cu III active sites and their subsequent consumption by saccharose was proposed, and the rate law and kinetic parameters were obtained. The charge transfer resistance from theoretical and impedance studies was used to verify the mechanism. Under chronoamperometry regimes, the reaction followed Cottrellian behavior. The transfer of up to 21 electrons was observed in further investigations of the electro-oxidation of saccharose on a (hydr)oxide Cu rotating disk electrode. The electrochemical oxidation of saccharose on a copper (hydr)oxide-modified electrode by the electrochemical generation of Cu III active sites and their consumption by saccharose is discussed.

Electrooxidation of methanol on NiMn alloy modified graphite electrode

Nickel and nickel–manganese alloy modified graphite electrodes (G/Ni and G/NiMn) prepared by galvanostatic deposition were examined for their redox process and electrocatalytic activities towards the oxidation of methanol in alkaline solutions. The methods of cyclic voltammetery (CV), chronoamperometry (CA) and impedance spectroscopy (EIS) were employed. In CV studies, in the presence of methanol NiMn alloy modified electrode shows a significantly higher response for methanol oxidation. The peak current of the oxidation of nickel hydroxide increase is followed by a decrease in the corresponding cathodic current in presence of methanol. The anodic peak currents show linear dependency upon the square root of scan rate. This behavior is the characteristic of a diffusion controlled process. Under the CA regime the reaction followed a Cottrellian behavior and the diffusion coefficient of methanol was found to be 4 × 10 −6 cm 2 s −1. A mechanism based on the electro-chemical generation of Ni 3+ active sites and their subsequent consumptions by methanol have been discussed and the corresponding rate law under the control of charge transfer has been developed and kinetic parameters have been derived. The charge transfer resistance accessible both theoretically and through the EIS have been used as criteria for derivation of the rate constant.

Cobalt hydroxide nanoparticles modified glassy carbon electrode as a biosensor for electrooxidation and determination of some amino acids

The electrochemical behavior of some amino acids was investigated on cobalt hydroxide nanoparticles modified glassy carbon (CHM–GC) electrode in alkaline solution. The process of oxidation and its kinetics were established by using cyclic voltammetry, chronoamperometry techniques, and steady-state polarization measurements. The results revealed that cobalt hydroxide promotes the rate of oxidation by increasing the peak current, so these bimolecular reactions are oxidized at lower potentials. Cyclic voltammograms and chronoamperometry indicate a catalytic EC′ mechanism to be operative with electrogeneration of Co(IV) as the electrochemical process. Also, the process is diffusion controlled and the current–time responses follow Cottrellian behavior. This result was confirmed by steady-state measurements. The rate constants of the catalytic oxidation of amino acids and the electron transfer coefficients are reported.

Determination of Kinetic and Diffusional Parameters for Sodium Borohydride Oxidation on Gold Electrodes

Direct borohydride fuel cells are among the latest fuel cell types under considerable research and development. There is a clear need for further elucidation of the borohydride electrochemical oxidation. From this perspective, potential step experiments were carried out with a Au disk electrode in alkaline sodium borohydride solutions of varying concentrations and temperatures. Analysis of the current transients for the full time scale enabled the delimitation of the domains where diffusion, electron transfer, and mixed control prevail. Chronoamperometric measurements in the diffusion-controlled region led to current responses exhibiting Cottrellian behavior, from which accurate diffusion coefficients, , were estimated. Arrhenius plots of allowed determination of the diffusion activation energies and maximum diffusion coefficients. Chronocoulometric measurements generated Anson plots from which the kinetic rate constants and charge transfer activation energies were calculated. Analysis of the current densities in conditions of infinite mass transfer led to Tafel plots from which exchange current densities, transfer coefficients, standard rate constants, and standard activation energies for charge transfer were determined. Purely charge-transfer regimes were not recognized in the studied system under the imposed potentials.

Cyclic voltammetry at shallow recessed microdisc electrode: Theoretical and experimental study

This study focuses on the cyclic voltammetry behavior at shallow recessed microdisc electrode, particularly on the transition from cottrellian behavior to steady state behavior. Diffusion to the inlaid and recessed microdisc electrode is simulated. From the shape of the CVs, for a given radius and potential scan rate, the transition time from planar diffusion to hemispherical diffusion presents a minimum as the recess increases. Theoretical prediction was confirmed by fitting the simulated CVs with experimental results. Dimensionless transition scan rate has been defined and determined by simulation for inlaid and recessed microdisc electrodes.

Electro-oxidation of ascorbic acid catalyzed on cobalt hydroxide-modified glassy carbon electrode

The electrochemical behavior of ascorbic acid on a cobalt hydroxide modified glassy carbon (CHM-GC) electrode in alkaline solution was investigated. The process of the involved oxidation and its kinetics were established using the cyclic voltammetry, chronoamperometry techniques, as well as by steady state polarization measurements. The results revealed that cobalt hydroxide promotes the rate of oxidation by increasing the peak current; hence ascorbic acid is oxidized at lower potentials, which is thermodynamically more favorable. The cyclic voltammograms and chronoamperometry indicate a catalytic EC mechanism is operative with the electrogeneration of Co(IV) as the electrochemical process. Also, the process is diffusion-controlled and the current- time responses follow Cottrellian behavior. This result was confirmed by steady state measurements. The rate constants of the catalytic oxidation of ascorbic acid and the electron-transfer coefficient are reported.

Electrocatalytic oxidation of glucose on Ni and NiCu alloy modified glassy carbon electrode

Nickel and nickel–copper alloy modified glassy carbon electrodes (GC/Ni and GC/NiCu) prepared by galvanostatic deposition were examined for their redox processes and electro-catalytic activities towards the oxidation of glucose in alkaline solutions. The methods of cyclic voltammetry (CV) and chronoamperometry (CA) were employed. The cyclic voltammogram of NiCu alloy demonstrates the formation of β/β crystallographic forms of the nickel oxyhydroxide under prolonged repetitive potential cycling in alkaline solution. It is also observed that the overpotential for O2 evolution increases for NiCu alloy modified electrode. In CV studies, NiCu alloy modified electrode yields significantly higher activity for glucose oxidation compared to Ni. The oxidation of glucose was concluded to be catalyzed through mediated electron transfer across the nickel hydroxide layer comprising of nickel ions of various valence states. The anodic peak currents show linear dependency with the square root of scan rate. This behavior is the characteristic of a diffusion-controlled process. Under the CA regime, the reaction followed a Cottrellian behavior, and the diffusion coefficient of glucose was found to be 1 × 10−5 cm2 s−1, in agreement with diffusion coefficient obtained in CV studies.