Shaltiel Eloul

Advancing from Rules of Thumb: Quantifying the Effects of Small Density Changes in Mass Transport to Electrodes. Understanding Natural Convection

Understanding mass transport is prerequisite to all quantitative analysis of electrochemical experiments. While the contribution of diffusion is well understood, the influence of density gradient-driven natural convection on the mass transport in electrochemical systems is not. To date, it has been assumed to be relevant only for high concentrations of redox-active species and at long experimental time scales. If unjustified, this assumption risks misinterpretation of analytical data obtained from scanning electrochemical microscopy (SECM) and generator-collector experiments, as well as analytical sensors utilizing macroelectrodes/microelectrode arrays. It also affects the results expected from electrodeposition. On the basis of numerical simulation, herein it is demonstrated that even at less than 10 mM concentrations and short experimental times of tens of seconds, density gradient-driven natural convection significantly affects mass transport. This is evident from in-depth numerical simulation for the oxidation of hexacyanoferrate (II) at various electrode sizes and electrode orientations. In each case, the induced convection and its influence on the diffusion layer established near the electrode are illustrated by maps of the velocity fields and concentration distributions evolving with time. The effects of natural convection on mass transport and chronoamperometric currents are thus quantified and discussed for the different cases studied.

When does near-wall hindered diffusion influence mass transport towards targets?

The diffusion of a particle is slowed as it moves close to a surface. We identify the conditions under which this hindered diffusion is significant and show that is strongly dependant on the sizes of both the particle and the target. We focus particularly on the transport of nano-particles to a variety of targets including a planar surface, a sphere, a disc and a wire, and provide data which allows the frequency of impacts to be inferred for a variety of experimental conditions. Equations are given to estimate the particle fluxes and we explain literature observations reported on the detected frequency of impacts. Finally we observe a drastic effect on the calculation of the mean first passage time of a single particle impacting a sub-micron sized target, showing the importance of this effect in biological systems.

In Situ Detection of Particle Aggregation on Electrode Surfaces

Partially blocked electrodes (PBEs) are important; many applications use non-conductive nanoparticles (NPs) to introduce new electrode functionalities. As aggregation is a problem in NP immobilization, developing an in situ method to detect aggregation is vital to characterise such modified electrodes. We present chronoamperometry as a method for detection of NP surface aggregation and semi-quantitative sizing of the formed aggregates, based on the diffusion limited current measured at PBEs as compared with the values calculated numerically for different blocking feature sizes. In contrast to voltammetry, no approximations on electrode kinetics are needed, making chronoamperometry a more general and reliable method. Sizing is shown for two modification methods. Upon drop casting, significant aggregation is observed, while it is minimized in electrophoretic NP deposition. The aggregate sizes determined are in semi-quantitative agreement with ex situ microscopic analysis of the PBEs.

Thin film-modified electrodes: a model for the charge transfer resistance in electrochemical impedance spectroscopy

A simple but general model is derived for the charge transfer resistance for a solution phase redox couple reacting at an electrode modified with a thin film such as a self-assembled monolayer. The layer itself is non-electroactive but changes the impedance response by virtue of altering the solubilities and diffusion coefficients of the electroactive species within the layer as compared to bulk solution. Such effects can give the illusion of altered electron transfer characteristics.

Motion Tracking of a Fish as a Novel Way to Control Electronic Music Performance

ABSTRACT The authors have mapped the three-dimensional motion of a fish onto various electronic music performance gestures, including loops, melodies, arpeggio and DJ-like interventions. They combine an element of visualization, using an LED screen installed on the back of an aquarium, to create a link between the fish’s motion and the sonified music. This visual addition provides extra information about the fish’s role in the music, enabling the perception of versatile and developing auditory structures during the performance that extend beyond the sonification of the momentary motion of objects.