Electrochemistry in confined microsystems: Part 1. CV-SECM of reversible system at a confined disk ultramicroelectrode

This work is the first part of a series of papers concerning the study of electrochemical method in case of ultramicroelectrode (UME) confinement in integrated chemical microsystems. This paper is devoted to the discussion of numerical simulation obtained in the case of a transient electrochemical method – i.e. cyclic voltammetry (CV) – applied to a finite disk ultramicroelectrode confined in front of an insulating surface. This configuration corresponds to scanning electrochemical microscopy (SECM) in negative feedback configuration. We describe a new electrochemical method, with acronym CV-SECM, based on the coupling of cyclic voltammetry with scanning electrochemical microscopy. The main advantage of this method is the obtention of a time resolved measurement simultaneously with a high local resolution. The results of the simulation show that adjusting the scan speed of the potential sweep allows the exploration of a controlled range of distance between the UME and the insulating surface. The reverse peak current obtained in cyclic voltammetry exhibits unexpected variations with the approach distance of the UME: (i) a regime of depletion of the electroactive reactant during the forward scan at short distance, associated to a decrease of the peak current and (ii) a regime of accumulation of the electroactive product at larger distance, associated to an increase of the reverse peak current identified in comparison with the free diffusion regime.