Modelling of electrochemical processes at microelectrodes

Abstract

In this work, the finite element modelling of 2D and 3D scanning electrochemical microsopy (SECM) systems is presented. The main focus has been on the influence of
tip geometry and the presence of defects on the limiting current of the SECM tip. The geometry of the electrode of particular interest is conical with conical insulation, as this is the shape of AFM-SECM probes fabricated by our coworkers. This thesis presents an extensive study of the electrochemical response of conical electrodes both in the bulk solution and close to a surface. Key equations were derived for conical electrodes and a thorough quantitative analysis of the influence of the tip geometry, be it the parameters describing it or the presence of defects, is reported. A novel equation was derived to calculate the current in the bulk at a conical electrode with conical insulation and an extensive study of possible defects was conducted to allow users to adjust the expression and obtain a more accurate estimation of the limiting current. The spatial resolution defined as the ability of an electroactive probe to detect a conducting region of a given
size- and the lateral resolution -the distance necessary to fully resolve a conducting region form an inert region- were both investigated for a range of geometries as well
as for a selection of defects. This enables us to draw conclusions on the ideal tip, and how sensitive it would be to features of the substrate. A set of equations was derived
to describe positive and negative feedback approach curves for cones, and steps were defined for users to determine the shape of the electrode from experimental approach
curves. Simulated curves are also provided to help with the extraction of kinetics at the substrate surface from the experimental approach curves. Finally, the influence of a ring disc tip geometry was evaluated by monitoring the collection efficiency as a function of tip-substrate distance for different disc-ring separations.

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Identifiers

ORCID for Guy Denuault: orcid.org/0000-0002-8630-9492

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