Cyclic Staircase Voltammetry Research Articles

Studies of oxygen reduction in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide by microdisk voltammetry

The electrochemical behavior of oxygen reduction in the room temperature ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide (BMPTFSI) was examined using staircase cyclic voltammetry on a 50μm diameter platinum microdisk electrode. The diffusion coefficients for oxygen and superoxide, and the heterogeneous rate constants were obtained with a fit to experimental voltammograms. A modified transport equation in 1D spherical symmetry and Tsallis’ q-exponential function were utilized in the fit procedure, and its applicability was compared to 2D simulations made with Comsol Multiphysics. In addition, the formal standard potential of oxygen reduction was referenced to the cobaltocene/cobaltocenium (Co(cp)2+/0) redox couple. It was found that oxygen reacts with homogeneously with Co(cp)2+, making the quantitative determination of oxygen reaction kinetics rather difficult. Also, small amounts of water in the liquid cause complex reaction mechanisms. Finally, proton reduction was also measured, and its formal potential resides at ca. 1.45V vs. Co(cp)2+/0 reference, which more than 1V positive to those of water or oxygen reduction.

Theory for Anomalous Response in Cyclic Staircase Voltammetry: Electrode Roughness and Unequal Diffusivities

We develop a theory for cyclic staircase voltammetry (CSCV) of a reversible charge transfer process with unequal diffusivities on a randomly rough electrode. The roughness power spectrum based approach is developed and detailed analysis is performed for a finite fractal model. An elegant expression for the statistically averaged CSCV current is obtained in terms of single potential step current at a rough electrode. The extent of anomalous response due to finite fractal roughness is determined by scan rate. The characteristic peak current and peak to peak separation in CV are dependent on finite fractal features, namely, fractal dimension (DH), topothesy length (lτ), and finest length scale of fractality (l). Peak to peak separation is reduced while peak current is enhanced with increase in DH and lτ and decrease in l. The roughness induced anomalous regime often introduces errors in estimating diffusion coefficient from classical Randles–Secvik equation. Our theory suggests that this error can be reduce...

An electrochemical and spectroscopic study of Nd(III) and Pr(III) coordination in the 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid containing chloride ion.

The coordination and accessible oxidation states of Nd and Pr were investigated in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BuMePyroTf2N) by using electronic absorption spectroscopy, cyclic staircase voltammetry, and controlled potential coulometry. These experiments were carried out in the neat ionic liquid (IL) and in the IL containing free Cl(-) from the dissolution of BuMePyroCl. The electrolytic dissolution of Ln = Nd and Pr metal in this IL produces only the respective Ln(3+) ions. These trivalent species can be reduced to Ln(2+), but the resulting divalent species exhibit only transient stability, undergoing rapid disproportionation to Ln(3+) and Ln(0). The intensity of the hypersensitive (4)G5/2 ← (4)I9/2 electronic transition for Nd(3+) dissolved in the IL was substantially larger than it was in noncoordinating solvents such as aqueous HClO4, indicating moderate interactions between Nd(3+) and Tf2N(-) ions, probably resulting in anionic species such as [Nd(Tf2N)x]((x-3)-). The addition of Cl(-) to [Ln(Tf2N)x]((x-3)-) solutions results in the precipitation of LnCl3(s) (s = solid). The LnCl3(s) redissolves to give the octahedral complex [LnCl6](3-) as the Cl(-) concentration is raised further. In the IL containing excess chloride, the (3)P0 ← (3)H4 transition for [PrCl6](3-) exhibits ligand-mediated pseudohypersensitive behavior.

Staircase and pulse potential electrochemical techniques for the facile and rapid synthesis of Pt and PtAg materials

Electrochemical synthesis is an attractive option for the synthesis of materials because electrocrystallization is faster (microseconds), easier (fewer variables influence structure) and more cost-effective (only requiring an ion source and electrolyte) than traditional chemical methods. Pt and PtAg materials were synthesised using electrochemical techniques, including staircase cyclic voltammetry (CV). Differential pulse amperometry (DPA), square wave voltammetry (SWV) and second harmonic AC voltammetry (2nd H AC V) were employed as pulse potential techniques. Characterisation was conducted using X-ray diffraction, field emission scanning electron microscopy, X-ray fluorescence, cyclic voltammetry in acidic and basic media and by assessing the behaviour of the synthesised materials in oxygen reduction reaction (ORR). For the cyclic voltammetry and DPA techniques, a decrease in the interfacial electrode/solution concentration resulted in the formation of semi-spherical nanoparticles with dendritic nanosheet growth. Semi-spherical Pt nanoparticles with small crystal sizes were obtained using SWV and 2nd H AC V due to the enhancement of the Pt seed growth by the low-time pulse potential period. Silver incorporation allowed the formation of well-defined cubic-shaped and flower-like PtAg nanoparticles without the need for surfactants and/or reductants. Silver acted both as a silver ion source and an additive, due to its passivation of the particle surfaces.

Electrochemical behavior of PbO2 nanowires array anodes in a zinc electrowinning solution

Free-standing PbO2 nanowires were prepared by an electrodeposition process onto the titanium foil. The morphology of nanowires was investigated by SEM analyses. The contact angle of the nanowires was compared with that of planar film, which indicated higher hydrophilicity and surface energy of nanowires. Cyclic voltammetric and real-time Fourier transform electrochemical impedance spectroscopy (FTEIS) experiments were employed to study the anodic reaction on the surface. The cyclic voltammetric data showed the overpotential of nanowire array electrode decreased by more than 100mV compared to that of the planar film electrode at an anodic current density of 400A/m2. A large body of impedance data acquired from the two electrodes as a function of scanned potential by running combined staircase cyclic voltammetry and FTEIS experiments led to systematic comparative analysis on the electrode/electrolyte interface. The changes in solution resistances, film resistances and capacitances, double layer capacitances, and polarization resistances observed during oxygen evolution process were compared and explained by corresponding electrochemical reactions. The nanowires of PbO2 showed a large active surface area led to higher capacitance than that of the planar electrode.

Chemometrics assisted resolving of net faradaic current contribution from total current in potential step and staircase cyclic voltammetry

Total current in the electroanalytical data is assumed to be consisting of three main constituents: faradaic current, step charging current and induced charging current. Both charging currents can cause an interfering effect on precise determination of faradaic currents, and hence insert direct effects on sensitivity and detection limit of the electroanalytical techniques. Despite the widespread techniques introduced until now, the extraction of the net faradaic current from total current still remains a challenge. In this work, by using multivariate curve resolution-alternating least square (MCR-ALS) as a powerful curve resolution-based chemometrics method, a straightforward method has been introduced for resolving faradaic current from the two types of charging currents (step charging current and induced charging current) in single potential step and staircase cyclic voltammetric methods. By simultaneous analyses of the current data matrices for different electrochemical systems, the three sources of current were successfully identified and their contributions in the total signal were easily calculated. Also, in this manner, the cell time constant can be obtained easily. Contrary to the previously reported methods, the present method does not need any pre-determined mathematical method; particularly there is no need to know the cell time constant.

Electrodeposition of aluminum–hafnium alloy from the Lewis acidic aluminum chloride-1-ethyl-3-methylimidazolium chloride molten salt

The electrochemistry of Hf(IV) and the electrodeposition of Al–Hf alloys were examined in the Lewis acidic 66.7–33.3 mol% aluminum chloride-1-ethyl-3-methylimidazolium chloride molten salt containing HfCl4. When cyclic staircase voltammetry was carried out at a platinum disk electrode in this melt, the deposition and stripping waves for Al shifted to negative and positive potentials, respectively, suggesting that aluminum stripping is more difficult due to the formation of Al–Hf alloys. Al–Hf alloy electrodeposits containing ~13 at.% Hf were obtained on Cu rotating wire and cylinder electrodes. The Hf content in the Al–Hf alloy deposits depended on the HfCl4 concentration in the melt, the electrodeposition temperature, and the applied current density. The deposits were composed of dense crystals and were completely chloride-free. The chloride-induced pitting corrosion potential of the resulting Al–Hf alloys was approximately +0.30 V against pure aluminum when the Hf content was above 10 at.%.

Electrochemical and Spectroscopic Study of Ce(III) Coordination in the 1-Butyl-3-methylpyrrolidinium Bis(trifluoromethylsulfonyl)imide Ionic Liquid Containing Chloride Ion

Cyclic staircase voltammetry, controlled potential coulometry, and electronic absorption spectroscopy were used to probe the coordination and accessible oxidation states of Ce(3+) dissolved in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BuMePyroTf(2)N) before and after the addition of chloride ion as BuMePyroCl. Controlled potential coulometry indicated that the oxidation of Ce metal in this ionic liquid produces only Ce(3+). Spectroscopic examination of the resulting solutions indicated that Ce(3+) was weakly solvated by Tf(2)N(-) ions as [Ce(Tf(2)N)(x)]((x-3)-), x ≥ 3. This species can be reduced at negative potentials, probably to a related Ce(2+) species, but the latter is unstable and quickly disproportionates to Ce(3+) and Ce(0); the latter appears to react with the ionic liquid. The addition of Cl(-) to solutions of [Ce(Tf(2)N)(x)]((x-3)-) causes the precipitation of CeCl(3)(s), providing a convenient route to the nondestructive recovery of Ce(3+) from the ionic liquid. However, as the Cl(-) concentration is further increased, the CeCl(3)(s) redissolves as the octahedral complex, [CeCl(6)](3-), and the voltammetric and spectroscopic signature for [Ce(Tf(2)N)(x)]((x-3)-) disappears. Absorption spectroscopy indicated that the bulk controlled potential oxidation of solutions containing [CeCl(6)](3-) produces [CeCl(6)](2-). Although stable on the time scale of voltammetry, this species slowly reacts with the ionic liquid and is converted back to [CeCl(6)](3-).

Electrochemical study of copper chloride complexes in the RTIL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide

The electrochemistry of copper(I) and copper(II) chloride complexes in the RTIL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, BMPTf2N, has been studied with constant current electrolysis and cyclic staircase voltammetry at temperatures between 21.0 and 96.0°C and in different concentrations of chloride. The chloride concentration was controlled by addition of 1-butyl-1-methylpyrrolidinium chloride, BMPCl. An important finding is the evidence of a three-coordinated complex, Cu(I)Cl32− which has not been found in organic chloroaluminates without a significant increase in temperature. Two Cu(I) species were found at molar ratios of [Cl−]/[Cu]<4. The kinetic parameters for the quasi-reversible Cu(I)–Cu(II) electron transfer were obtained with non-linear fitting. Successful fits required that the charge transfer coefficients for the reduction of Cu(II) (α) and oxidation of Cu(I) (β) did not sum up to unity, i.e. α+β≠1. This result was interpreted using Tsallis non-extensive thermostatistics.

Fourier transform electrochemical impedance spectroscopic studies on anodic reaction of lead

Lead oxidation and subsequent oxygen evolution have been studied in a zinc electrowinning solution employing cyclic voltammetric and real-time Fourier transform electrochemical impedance spectroscopy (FTEIS) experiments. A large body of impedance data obtained as a function of scanned potential by running combined staircase cyclic voltammetry and FTEIS experiments led to systematic analysis on the electrode/electrolyte interface. The changes in solution resistances, film resistances as well as film capacitances, double layer capacitances, polarization resistances, and Warburg admittances observed during lead oxidation satisfactorily explain corresponding electrochemical reactions. Various electrode reaction kinetic parameters for oxidation of lead and oxygen evolution were obtained from the impedance data. The reaction mechanism is discussed based on the impedance data.

Analytical Solutions for the Study of Multielectron Transfer Processes by Staircase, Cyclic, and Differential Voltammetries at Disc Microelectrodes

Key processes in (bio)electrochemistry involve multiple electron transfers. The study of the stability of the different oxidation states and the interaction between redox centers is fundamental to understand these processes. In this paper, simple analytical equations are presented for multielectron transfer processes in cyclic voltammetry (CV) and staircase cyclic voltammetry (SCV) at disc electrodes of any size. This provides a simple simulation method for the electrochemical response without demanding computing. The use of CV and SCV, and the corresponding differential techniques, for the characterization of these redox systems is analyzed. Procedures and criteria are given for transient and stationary conditions. The theoretical results are applied to the experimental study of the reduction of anthraquinone-2-sulfonate in water on gold macro- and microdisc electrodes.

Zinc Oxidation in Dilute Alkaline Solutions Studied by Real-Time Electrochemical Impedance Spectroscopy

Electrochemical oxidation of zinc has been studied in dilute alkaline solutions, 0.010 and 0.10 M KOH, employing cyclic voltammetric and real-time Fourier transform electrochemical impedance spectroscopy (FTEIS) experiments. Thermodynamic analysis of cyclic voltammetric data indicates that Zn(OH)42– is produced as a major product in both 0.10 and 0.010 M KOH although ZnO/Zn(OH)2 may also be produced as a minor product in 0.010 M. A large body of impedance data was obtained as a function of swept potential by running combined staircase cyclic voltammetry and FTEIS (SCV-FTEIS) experiments at every 10 mV and 200 ms interval, which allowed a systematic and complete analysis to be made on the interface. Analysis of the extensive impedance data demonstrates that electron transfer takes place across the thin oxide/hydroxide film, whose electrical state undergoes drastic changes at the potential where charge transfer occurs. The capacitance of the film covering the surface was shown to undergo a large change during the charge transfer indicating that the electrode/electrolyte interface is strongly electrified during the charge transfer across it. Various electrode reaction kinetic parameters for oxidation of zinc are also reported by treating the impedance data and the reaction mechanism is discussed based on the data.

Theoretical aspects of several successive two-step redox mechanisms in protein-film cyclic staircase voltammetry

Protein-film voltammetry (PFV) is a versatile tool designed to provide insight into the enzymes physiological functions by studying the redox properties of various oxido-reductases with suitable voltammetric technique. The determination of the thermodynamic and kinetic parameters relevant to protein's physiological properties is achieved via methodologies established from theoretical considerations of various mechanisms in PFV. So far, the majority of the mathematical models in PFV have been developed for redox proteins undergoing a single-step electron transfer reactions. However, there are many oxido-reductases containing quinone moieties or polyvalent ions of transition metals like Mo, Mn, W, Fe or Co as redox centers, whose redox chemistry can be described only via mathematical models considering successive two-step electron transformation. In this work we consider theoretically the protein-film redox mechanisms of the EE (Electrochemical–Electrochemical), ECE (Electrochemical–Chemical–Electrochemical), and EECat (Electrochemical–Electrochemical–Catalytic) systems under conditions of cyclic staircase voltammetry. We also propose methodologies to determine the kinetics of electron transfer steps by all considered mechanisms. The experimentalists working with PFV can get large benefits from the simulated voltammograms given in this work.

Staircase Voltammetry Application to Electrocatalytic Gas Sensor

Principle of operation of electrocatalytic gas sensors is based on the excitation of a sensor with a periodic potential signal, while current response is recorded. Usually such sensors employ cyclic voltammetry, where linearly changing voltage excitation of symmetrical triangular shape, typically in range of ±5 V, is used. In this work we present results of electrocatalytic sensors employing staircase cyclic voltammetry technique. Presented results concern sensors based on Nasicon with platinum electrodes. It is demonstrated that such sensor can be used for measuring NO2 concentration in mixtures with synthetic air.

Voltammetry of Electrochemically Reversible Systems at Electrodes of Any Geometry: A General, Explicit Analytical Characterization

A general, explicit analytical solution for volta-mmetry using any multipotential waveform for an electrochemically reversible system at an electrode of any geometry is derived. This expression has special physical relevance in the case of electrodes and microelectrodes which possess nonuniform current densities such as disks and bands, where analytical descriptions of voltammetry are confined to predictions of limiting currents. We have applied our analytical expressions to normal pulse voltammetry, staircase cyclic voltammetry, and cyclic voltammetry for disks, spheres, bands, and cylinders. The results have been validated against those obtained by using numerical simulation with the agreement found to be excellent.

Fourier transform electrochemical impedance spectroscopic studies on platinum electrodes in an acidic medium

The platinum electrode/electrolyte interface has been characterized in 0.50 M H 2SO 4 by staircase cyclic voltammetry–Fourier transform electrochemical impedance spectroscopy combined experiments in a wide potential range. From analysis of a large body of data, we propose a single equivalent circuit for the description of the interface, which accommodates impedance responses from capacitance dispersions, hydrogen underpotential deposition (H-UPD), and Faradaic reactions in 0.50 M H 2SO 4 within the potential range of 0.05–1.5 V. Analysis of the impedance data revealed that the equivalent circuits reported in the literature in specific potential regions represent specific forms of the circuit proposed here. The capacitance dispersions are rather small in H-UPD and oxide-covered capacitive regions due to large double-layer capacitances in relation to pseudo-capacitances. Electrochemical oxidation of platinum and its oxide reduction are shown to proceed via two step one-electron-transfer reactions and their respective kinetic parameters are reported.

Study of the Electrocatalytic Reaction of Hydrogen Peroxide Mediated by Azobenzene Monolayer with Several Multipotential Pulse Techniques

The comparison between the response corresponding to a simple charge transfer taking place at an electroactive monolayer with that of an electrocatalytic process at a modified electrode are presented by using the multipulse potential techniques cyclic staircase voltammetry (CSCV) and cyclic square wave voltammetry (CSWV). General analytical and explicit equations for the IE responses have been tested by means of the study of the reduction of azobenzene monolayer at mercury electrode. The value of the chemical rate constant ( k c ' = 40 M  1 s  1 ) has been easily obtained from the cathodic plateau of the CSCV curves and from the best fitting between theoretical and experimental CSWV curves.

Real-Time Staircase Cyclic Voltammetry Fourier Transform Electrochemical Impedance Spectroscopic Studies on Underpotential Deposition of Lead on Gold

We report results of detailed studies on the underpotential deposition of lead (Pb UPD) and effects of specifically adsorbed halide anions on the UPD reaction at polycrystalline gold electrodes employing real-time staircase cyclic voltammetry Fourier transform electrochemical impedance spectroscopy (SCV-FTEIS). Potential shifts observed during the Pb UPD in the presence of halide ions are partially attributed to the chemical interaction of halide ions with Pb2+ as well as the physical obstruction by the preadsorbed halide ions. More importantly, the presorbed halides, on the top of which Pb2+ ions are adsorbed, form a pseudocapacitor on the gold surface, and its electrical discharge leads to the Pb UPD. Real-time SCV-FTEIS measurements in a chloride solution without Pb2+ reveal that the voltammetric currents arise from charging both the double-layer and pseudocapacitors formed due to the presorption of halide ions at the surface, indicating that the capacitors formed upon adsorption of halide ions on the ...

Coupling of Cyclic Voltammetry and Electrochemical Impedance Spectroscopy for Probing the Thermodynamics of Facilitated Ion Transfer Reactions Exhibiting Chemical Kinetic Hindrances

Mathematical models under conditions of cyclic staircase voltammetry and electrochemical impedance spectroscopy (EIS), which consider the kinetic effects due to the complexation reaction by the facilitated transfer of metal ions at polarized interfaces, are presented. Criteria for qualitative recognition of these kinetic effects from the features of simulated cyclic voltammograms are given. In case of the existence of these effects, only the EIS can bring access to the thermodynamics and kinetics of the complexation chemical reaction. Analytical equations for estimating the thermodynamic parameters by such systems under EIS conditions are evaluated. The theoretical results are compared with the experimental results of the facilitated Cu 2+ transfer at the polarized water-1,2-dichlorethane interface, assisted by two phenanthroline-containing macrocycles. In the experimental case where kinetic effects due to the complexation step exist, we show how elegantly EIS can be used as a tool for estimation of the complexation constant of Cu 2+ and 5-oxo-2,8-dithia [9],(2,9)-1,10-phenanthrolinophane (PhenOS2).

Electrochemical study and electrodeposition of manganese in the hydrophobic butylmethylpyrrolidinium bis((trifluoromethyl)sulfonyl)imide room-temperature ionic liquid

The electrochemistry of manganese was investigated at solid disk electrodes in the hydrophobic room-temperature ionic liquid butylmethylpyrrolidinium bis((trifluoromethyl)sulfonyl)imide (BuMePy-TFSI) by using staircase cyclic voltammetry and chronoamperometry. The Mn(II) species was introduced into the ionic liquid by anodic dissolution of the metallic manganese electrode. The reduction of Mn(II) ions at tungsten and platinum electrodes accompanies with nucleation mechanism and the coupled oxidation wave encounters kinetic hindrance that results in incomplete reoxidation of Mn electrodeposits. The density and absolute viscosity of BuMePy-TFSI were measured over a temperature range from 301.0 to 348.0 K. A polynomial equation describing the temperature dependence of the density is presented. The viscosity exhibits the Arrhenius temperature dependence and the relevant equation is provided. The manganese coatings were prepared by electrodeposition at several substrates. The surface morphology and X-ray diffraction patterns of these deposits were studied by scanning electron microscopy and powder X-ray diffraction spectroscopy, respectively. The as-electrodeposited manganese coatings were amorphous; however, α-phase manganese was observed after the deposits were annealed under 723 K for 1 day.