This paper studies the feasibility of performing Local Electrochemical Impedance Spectroscopy (LEIS) and Atomic Force Microscopy (AFM) within a single set-up, using a hybrid probe. The geometry of the set-up along with the extremely small size of the probe used is expected to result in distorted impedances and very low potentials, respectively. Numerical simulations using a multi-ion transport and reaction model (MITReM), show that the distortions can be mathematically corrected for and that our electronic equipment is capable of measuring the minute potentials.

Highlights•The results of measurements and simulations of oxygen reduction on Pt in NaCl solutions are presented.•For electrolytes films not changing in time, O2 reduction current obeys the Fick's law for thicknesses >50–75 μm.•The reasons of the deviation at lower thicknesses are: reduced oxygen uptake, ohmic drop and Cl− adsorption on Pt.•For evaporating electrolytes, besides the film thickness, reduced O2 solubility plays an important role.Measurements of oxygen reduction current are performed on a platinum electrode submerged under NaCl electrolyte films of different thickness. The chloride concentration is kept constant or increases due to evaporation. Measurements are supported by the numerical Multi-Ion Transport and Reaction Model (MITReM). In case of constant salt concentration, oxygen reduction current is proportional to the reciprocal of the electrolyte film thicknesses down to 50–75 μm; for lower thicknesses deviation from the Fick's law takes place. For evaporating films, oxygen current is the result of two counteracting phenomena: reducing film thickness and increasing salt concentration leading to decrease of oxygen solubility.

An elegant and accessible way to account for the local stirring created by the vibration of the SVET tip by adding a new diffusion–like term into the molar flux expression is proposed, in order to avoid solving the fluid flow. This term is maximal in the point of vibration and rapidly decreases with the distance. It is shown that the local mixing leads to a substantial increase of the migration current density in the vicinity of the probe with simultaneous decrease of the diffusion current contribution. This local mixing has no effect on the pH distribution, regardless the applied polarization, and increases under cathodic polarization the oxygen concentration only when the probe is close to the electrode surface which is confirmed by experimental observations. The proposed model is compared with the analytical current density distributions obtained from potential model and experimental data. All this indicates that local mixing might explain why the SVET technique, although based on the measurement of an ohmic current density, measures always the total current density.

Understanding the early stages of electrochemical nucleation and growth is the cornerstone for nanoscale electrodeposition. Although studied since decades, the process is not yet fully understood. In this paper, we introduce a new modelling approach to study the growth of a single hemispherical nucleus: Multi-Ion Transport and Reaction Model (MITReM). This approach takes into account the transport driven by diffusion and migration of all species in the electrolyte together with the electrochemical reactions at the electrode boundary. A Finite Element Method (FEM) is used to solve the balance equations for the concentration of all the active species and the electrolyte potential. In contrast to analytical models or discrete scale modelling techniques, the strength of this approach is that no assumptions on the diffusional or kinetic limitations have to be made. In addition, this novel platform allows to add further levels of complexity, such as multiple nuclei, adatom surface diffusion, aggregation, particle detachment, etc. The simulation results prove that, the initial growth stage of a 10 nm single hemispherical silver nucleus always starts under kinetic control, regardless of concentration and electrode potential. Later on, a transition from kinetic to diffusion control takes place. The time of transition depends on the imposed concentration and electrode potential. Moreover, the simulations clearly show that the growth rate is strongly affected by the imposed concentration and electrode potential, as it has been proven experimentally in countless occasions. Numerical simulation by MITReM proves to be of great interest to gain knowledge towards unravelling the early stages of electrochemical nucleation and growth processes.

Introduction of microcapillary techniques opened a new range of methods to study the behavior of microsystems. Although these measurements are widely employed and results obtained are generally recognized, certain aspects require careful consideration. We present the results of a parametric study performed by means of multi-ion modeling in order to clarify the influence of the microcapillary size and shape together with the permeability of the sealant for oxygen on the polarization curves obtained on metals with different corrosion activity. The obtained results show that when a corroding metal is (almost) non-active (e.g. aluminum), the oxygen limiting current increases with increase of the ratio between the radius of the capillary main part and the end radius γ = R/r but the corrosion potential remains the same. For more active metals and alloys (e.g. steel), a change of the aspect ratio γ leads not only to the proportional change of the limiting current, but also to a substantial shift of Ecorr. Analytical solutions derived for limiting current density in a microcapillary confirmed the simulated results. Permeability of the sealant for oxygen plays a significant role mostly for narrow capillaries with low ratio γ and more active metallic substrates. It is shown that the problem of comparison of polarization data obtained with capillaries of different size can be partially avoided by use of capillaries with the same aspect ratio γ but only if the quality of the sealant (low permeability for oxygen) is assured.

The ionic conductivity of doped ceria is strongly influenced by temperature, oxygen partial pressure, dopant concentration and microstructure of the material. While theory and experiments generally agree on the influence of the first two parameters, the other influences are still not fully understood. A reliable simulation model of the material’s electrical conductivity is thus necessary to interpret the existing measurements.Until now, prediction of the electrical conductivity of these materials relies mainly on analytical models. This approach yields useful insights but it also has drawbacks. We implement the partial differential equations that govern charge carrier transport and electrical potential in a finite element model. This numerical approach enables us to treat grains of arbitrarily small size and to predict electrical conductivities at any applied current density. The results predicted by our model are compared to the available measurements in literature.

Scanning electrochemical microscopy (SECM) with its high spatial resolution and chemical selectivity is a powerful technique for studying a wide range of corrosion processes. A common procedure to detect qualitatively a corrosion activity on a metal substrate consists of measuring the local oxygen concentration.The aim of this work is to clarify the local impact of the O2 measurement and the undesired effect on the corrosion process. By means of numerical simulation the variations of the anodic and cathodic currents on the aluminum substrate, as well as concentration profiles, are obtained. The multi-ion transport and reaction model (MITReM) is used considering the homogeneous reactions taking place in the solution, transport of species dominating the corrosion process and the electrochemical reactions. The model case study in this work is corrosion of pure aluminum in chloride solution. We concluded that amperometric O2 SECM measurements lead to a local increase of the solution pH and decrease of partial current densities for O2 reduction on the metal. This influence becomes significant when the distance to the substrate and when the size of the active surface is comparable with the size of the SECM probe.