Theoretical Framework and Guidelines for the Cyclic Voltammetry of Closed Bipolar Cells.

Closed bipolar cells (cBPCs) can offer valuable platforms for the development of electrochemical sensors. On the other hand, such systems are more intricate to model and interpret than conventional systems with a single polarizable interface, with the applied potential "splitting" into two polarized interfaces where two coupled charge transfers take place concomitantly. As a result, the voltammetry of cBPCs shows peculiarities that can be misleading if analyzed under the framework of classic electrochemical cells.

Voltammetric Kinetic Studies of Electrode Reactions: Guidelines for Detailed Understanding of Their Fundamentals.

Theoretical and practical foundations of basic electrochemical concepts of heterogeneous charge transfer reactions that underline electrochemical processes are presented for their detailed study by undergraduate and postgraduate students. Several simple methods for calculating key variables, such as the half-wave potential, limiting current, and those implied in the kinetics of the process, are explained, discussed, and put in practice through simulations making use of an Excel document. The current-potential response of electron transfer processes of any kinetics (i.

Investigating Comproportionation in Multielectron Transfers via UV-Visible Spectroelectrochemistry: The Electroreduction of Anthraquinone-2-sulfonate in Aqueous Media.

UV-vis spectroelectrochemistry is assessed as a tool for the diagnosis and quantitative investigation of the incidence of comproportionation in multielectron transfer processes. Thus, the sensitivity of the limiting current chronoabsorptometric signals related to the different redox states to the comproportionation kinetics is studied theoretically for different working modes (normal and parallel light beam arrangements) and mass transport regimes (from semi-infinite to thin layer diffusion). The theoretical results are applied to the spectroelectrochemical study of the two-electron reduction of the anthraquinone-2-sulfonate in alkaline aqueous solution, tuning the thermodynamic favorability of the comproportionation reaction through the electrolyte cation.

[Complication related factors in patients undergoing open simple prostatectomy due to Benign Prostate Hyperplasia in a Colombian hospital.].

Introduction: Open prostatectomy is an efficacious treatment for Benign Prostatic Hyperplasia (BPH), but its complication rates and risk factors for these might vary due to the characteristics of populations and health systems. OBJECTIVE: To determine the frequency of complications and the risk factors for these, in the first three months after open prostatectomy in a hospital in Medellín (Colombia). METHODS: This is a cohort study in which patients undergoing retropubic open prostatectomy were taken.

General Explicit Mathematical Solution for the Voltammetry of Nonunity Stoichiometry Electrode Reactions: Diagnosis Criteria in Cyclic Voltammetry.

Electrochemical reactions can effectively follow nonunity stoichiometries as can be found in the electrochemistry of halides, hydrogen, and metal complexes. The voltammetric response of these systems shows peculiar deviations with respect to the well-described features of the 1:1 stoichiometry. With the aim of specifying such differences, a rigorous and manageable analytical theory is deduced for the complete characterization of reversible electrode processes with complex stoichiometry in cyclic voltammetry (CV) at macroelectrodes.

Guidelines for the Voltammetric Study of Electrode Reactions with Coupled Chemical Kinetics at an Arbitrary Electrode Geometry.

A powerful, unified, and simplifying mathematical approach for the theoretical treatment of first-order chemical kinetics coupled to interfacial charge transfers at electrodes of arbitrary geometry and size, both uniformly accessible and nonuniformly accessible to the electroactive species, is presented. The general CEC mechanism at spherical and disc electrodes is considered to test the validity and benefits of such an approach, based on the application of the so-called kinetic steady state, that enables the reduction of the multivariable problem of kinetic-diffusive differential equations to a single variable problem of a diffusion-only differential equation. This is solved both analytically and numerically, showing how this approach leads to general, simple, and efficient solutions for the study of the influence of coupled chemical kinetics on the voltammetric response.

Quantitative Analysis of Cyclic Voltammetry of Redox Monolayers Adsorbed on Semiconductors: Isolating Electrode Kinetics, Lateral Interactions, and Diode Currents.

The design of devices whose functions span from sensing their environments to converting light into electricity or guiding chemical reactivity at surfaces often hinges around a correct and complete understanding of the factors at play when charges are transferred across an electrified solid-liquid interface. For semiconductor electrodes in particular, published values for charge-transfer kinetic constants are scattered. Furthermore, received wisdom suggests slower charge-transfer kinetics for semiconductors than for metal electrodes.

Double Transfer Voltammetry in Two-Polarizable Interface Systems: Effects of the Lipophilicity and Charge of the Target and Compensating Ions.

Analytical expressions are obtained for the study of the net current and individual fluxes across macro- and micro-liquid/liquid interfaces in series as those found in ion sensing with solvent polymeric membranes and in ion-transfer batteries. The mathematical solutions deduced are applicable to any voltammetric technique, independently of the lipophilicity and charge number of the target and compensating ions. When supporting electrolytes of semihydrophilic ions are employed, the so-called double transfer voltammograms have a tendency to merge into a single signal, which complicates notably the modeling and analysis of the electrochemical response.

Theoretical Treatment of Ion Transfers in Two Polarizable Interface Systems When the Analyte Has Access to Both Interfaces.

A new theory is presented to tackle the study of transfer processes of hydrophilic ions in two polarizable interface systems when the analyte is initially present in both aqueous phases. The treatment is applied to macrointerfaces (linear diffusion) and microholes (highly convergent diffusion), obtaining analytical equations for the current response in any voltammetric technique. The novel equations predict two signals in the current-potential curves that are symmetric when the compositions of the aqueous phases are identical while asymmetries appear otherwise.

Reproducible flaws unveil electrostatic aspects of semiconductor electrochemistry.

Predicting or manipulating charge-transfer at semiconductor interfaces, from molecular electronics to energy conversion, relies on knowledge generated from a kinetic analysis of the electrode process, as provided by cyclic voltammetry. Scientists and engineers encountering non-ideal shapes and positions in voltammograms are inclined to reject these as flaws. Here we show that non-idealities of redox probes confined at silicon electrodes, namely full width at half maximum <90.

Microelectrode voltammetry of multi-electron transfers complicated by coupled chemical equilibria: a general theory for the extended square scheme.

A very general and simple theoretical solution is presented for the current-potential-time response of reversible multi-electron transfer processes complicated by homogeneous chemical equilibria (the so-called extended square scheme). The expressions presented here are applicable regardless of the number of electrons transferred and coupled chemical processes, and they are particularized for a wide variety of microelectrode geometries. The voltammetric response of very different systems presenting multi-electron transfers is considered for the most widely-used techniques (namely, cyclic voltammetry, square wave voltammetry, differential pulse voltammetry and steady state voltammetry), studying the influence of the microelectrode geometry and the number and thermodynamics of the (electro)chemical steps.

Single Fusion Events at Polarized Liquid-Liquid Interfaces.

A new electrochemical framework for tracking individual soft particles in solution and monitoring their fusion with polarized liquid-liquid interfaces is reported. The physicochemical principle lies in the interfacial transfer of an ionic probe confined in the particles dispersed in solution and that is released upon their collision and fusion with the fluid interface. As a proof-of-concept, spike-like transients of a stochastic nature are reported in the current-time response of 1,2-dichloroethane(DCE)|water(W) submilli-interfaces after injection of DCE-in-W emulsions.

Voltammetry of the aqueous complexation-dissociation coupled to transfer (ACDT) mechanism with charged ligands.

The study of the so-called aqueous complexation-dissociation coupled to transfer (ACDT) mechanism is extended to systems where the ligand species is not neutral and so the charge of the two transferable ions is different (z1 ≠ z2). This has a profound effect on the voltammetric response of the system, which shows a complex behaviour depending on the chemical kinetics, the difference between the lipophilicity of the two ions and the applied potential. Such response is modelled making use of the diffusive-kinetic steady state (dkss) approach, obtaining analytical expressions for the current-potential-time curves in normal pulse, derivative and differential multipulse voltammetries.

Transfer of complexed and dissociated ionic species at soft interfaces: a voltammetric study of chemical kinetic and diffusional effects.

A new transfer mechanism is considered in which two different ionic species of the same charge can be transferred across a soft interface while they interconvert with each other in the original phase through a homogeneous chemical reaction: the aqueous complexation-dissociation coupled to transfer (ACDT) mechanism. This can correspond to a free ion in aqueous solution in the presence of a neutral ligand that complexes it leading to a species that can be more or less lipophilic than the free ion. As a result, the transfer to the organic phase can be facilitated or hindered by the aqueous-phase chemical reaction.

Recent Advances in Voltammetry.

Recent progress in the theory and practice of voltammetry is surveyed and evaluated. The transformation over the last decade of the level of modelling and simulation of experiments has realised major advances such that electrochemical techniques can be fully developed and applied to real chemical problems of distinct complexity. This review focuses on the topic areas of: multistep electrochemical processes, voltammetry in ionic liquids, the development and interpretation of theories of electron transfer (Butler-Volmer and Marcus-Hush), advances in voltammetric pulse techniques, stochastic random walk models of diffusion, the influence of migration under conditions of low support, voltammetry at rough and porous electrodes, and nanoparticle electrochemistry.

Application of voltammetric techniques at microelectrodes to the study of the chemical stability of highly reactive species.

The application of voltammetric techniques to the study of chemical speciation and stability is addressed both theoretically and experimentally in this work. In such systems, electrode reactions are coupled to homogeneous chemical equilibria (complexations, protonations, ion associations, ..

Strong negative nanocatalysis: oxygen reduction and hydrogen evolution at very small (2 nm) gold nanoparticles.

The electron transfer kinetics associated with both the reduction of oxygen and of protons to form hydrogen at gold nanoparticles are shown to display strong retardation when studied at citrate capped ultra small (2 nm) gold nanoparticles. Negative nanocatalysis in the hydrogen evolution reaction (HER) is reported for the first time.

Reversible surface two-electron transfer reactions in square wave voltcoulommetry: application to the study of the reduction of polyoxometalate [PMo12O40]3- immobilized at a boron doped diamond electrode.

Reversible surface two-electrons transfer reactions (stepwise processes) are analyzed using square wave voltcoulommetry (SWVC), which is a variety of square wave techniques based on the measurement of the transferred charge. Such reversible surface redox processes are exhibited by many two-redox center and multicenter biomolecules (proteins, enzymes, ..

Some insights into the facilitated ion transfer voltammetric responses at ITIES exhibiting interfacial and bulk membrane kinetic effects.

General analytical equations corresponding to the Facilitated Ion Transfer (FIT) at ITIES (Interface between Two Immiscible Electrolyte Solutions) are presented for the most frequent case in which the complexing agent is present only in the organic phase, and considering both the ion transfer and the chemical complexation kinetic effects. Under these conditions, the FIT process can be regarded as an EC mechanism. This study is of great interest to elucidate the origin of the kinetic effects which affect the electrochemical signal.

Kinetic effects of the complexation reaction in the facilitated ion transfer at liquid membrane systems of one and two polarized interfaces. Theoretical insights.

An in-depth study of the ion transfer facilitated by complexation in the organic phase (TOC mechanism) in liquid membrane systems of one and two polarized interfaces is carried out by taking into account the kinetic effects associated with the complexation reaction. Explicit analytical equations for the normal pulse voltammetric (I/E) and chronoamperometric (I/t) responses with an explicit dependence on the kinetic parameters of the chemical complexation are presented for both kinds of membrane system, which could be useful for modeling artificial and biological membranes. The equations are compared with those obtained by using the widely used approximation of total equilibrium conditions that leads to the transfer by interfacial complexation mechanism (TIC), which only depends on thermodynamic parameters.

Analytical theory of the catalytic mechanism in square wave voltammetry at disc electrodes.

A simple analytical expression is presented for the study of the first-order catalytic mechanism using Square Wave Voltammetry (SWV) at disc electrodes. These electrodes are extensively used in electrochemical studies but modelling the electrochemical response at this geometry is complex and usually requires the use of sophisticated numerical methods. By contrast, the analytical solution presented in this work is easy to compute and it is applicable to any size of the disc and for arbitrary kinetics of the catalytic reaction.

Catalytic mechanism in cyclic voltammetry at disc electrodes: an analytical solution.

The theory of cyclic voltammetry at disc electrodes and microelectrodes is developed for a system where the electroactive reactant is regenerated in solution using a catalyst. This catalytic process is of wide importance, not least in chemical sensing, and it can be characterized by the resulting peak current which is always larger than that of a simple electrochemical reaction; in contrast the reverse peak is always relatively diminished in size. From the theoretical point of view, the problem involves a complex physical situation with two-dimensional mass transport and non-uniform surface gradients.

Physical insights of salt transfer through solvent polymeric membranes by means of electrochemical methods.

A combined voltammetric study of the joint transfer of the two constituting ions of a water-soluble salt has been carried out using normal-pulse voltammetry, linear-sweep voltammetry and square-wave voltammetry in a system with two liquid-liquid polarized interfaces. As a result, we have explained the voltammetric features that allow us to distinguish this uptake from that corresponding to two equally charged ions, in spite of the appearance in both situations of two current peaks with the same sign in both square-wave and linear-sweep voltammograms, and we have found that linear-sweep voltammetry and square-wave voltammetry complement each other excellently.A theoretical comparison with a system of a single polarized interface has also been made, showing that these systems are much less appropriate for characterizing these salt-ion transfers.

Lability of metal complexes at spherical sensors. Dynamic voltammetric measurements.

The diffusive-kinetic steady-state (dkss) approximation is applied to the case of a metal ion reaching a transforming/consuming spherical surface (sensor) when the ion is involved in a complexation reaction in solution. Simple time-dependent expressions for the surface metal flux, the lability degree and the half-wave potential are presented, valid for any value of the ratio of concentrations at the surface and the sensor radius. The solution presented is compared with other theoretical approaches, such as the kinetic steady state (kss) and the total steady state (tss), pointing out that the easy dkss approach is much more accurate than the tss one to study the metal flux and the lability degree for any value of the radius, from ultramicro to planar sensors.