Electrochemical reactions at very small electrodes

Abstract

To measure fast electrode processes, high rates of mass transfer of the electroactive species to the electrode surface are essential. This has been achieved in the present study by forming very small electrodes of radius <5am (appropriately termed microelectrodes); it is shown that mass transfer to these electrodes is enhanced above the rate to a planar electrode of equivalent area by virtue of an additional steady state flux term inversely proportional to the electrode radius,so that under conditions of very slow linear potential sweep, i.e. pseudo steady state, the rate of mass transfer is determined by the steady state term alone. In the first part of this work, electrodes prepared from lead, tungsten and platinum, all sealed into glass, have been used to measure the rate of the heterogeneous electron transfer reactions of a number of aromatic, nitroaromatic and nitroaliphatic compounds in Dimethylformamide. Both slow linear potential sweep and fast linear potential sweep analyses were performed; the latter with the development of convolution potentialsweep voltammetry methods applicable to very small electrodes. It is shown that for the reduction of tert - nitirobutane this technique can be applied over a wide potential range giving results in close agreement with those obtained by other workers using alternative non steady state methods. Deviation from Butler -Volmer behaviour was observed for this reaction and interpreted in terms of the Marcus theory. For faster electron transfer reactions, however, electrode dimensions available at the time were found to be too large to allow measurement of the electron transfer rates due to partial mass transfer control of the electrode reaction, even under fast linear potentialsweep conditions. In the second part of this work, the rates of homogeneous chemical reactions preceding the electron transfer step were studied. The rate of dissociation of acetic acid in sodium acetate solutions was investigated using platinum microelectrodes under conditions of slow linear potential sweep and found to be in reasonable agreement with values obtained by other workers, indicating that enhanced rates of mass transfer at microelectrodes may be employed to measure the rates of both homogeneous and heterogeneous electrode reactions under pseudo steady state conditions.

More information

Identifiers

Catalogue record

Export record

ASCII CitationAtomBibTeXData Cite XMLDublin CoreDublin CoreEP3 XMLEndNoteHTML CitationHTML CitationHTML ListJSONMETSMODSMPEG-21 DIDLOpenURL ContextObjectOpenURL ContextObject in SpanRDF+N-TriplesRDF+N3RDF+XMLRIOXX2 XMLReferReference ManagerSimple Metadata