A computational and experimental study of the cyclic voltammetry response of partially blocked electrodes, part III: interfacial liquid–liquid kinetics of aqueous vitamin B12s with random arrays of femtolitre microdroplets of dibromocyclohexane

The cyclic voltammetric response of electrochemically heterogeneous surfaces

“…In this paper, we build on our experience with partially blocked electrodes [1][2][3][4][5][6] to predict the cyclic voltammetric response of an electrode which is heterogeneous in its electrochemical behaviour with some spatial zones more active than others, resulting in an ''array of microelectrodes'' made of one material dispersed over a different electrode material. Thus, for a simple one electron redox couple the electrode kinetics will be described by two electron transfer rate constants, k 1 and k 2 and two transfer coefficients, a 1 and a 2 as shown in Fig.…”

Cyclic voltammetry at microdroplet modified electrodes. A comparison of the reaction of vicinal dibromides with vitamin B12s at the liquid/liquid interface with the corresponding homogeneous process: evidence for polar-solvent effects at the liquid/liquid interface

“…Thus, the overall reaction is electrocatalytic and in a cyclic voltammetry experiment, for example, an analysis of the increase in current compared to that of the inertly blocked equivalent partially blocked electrode (PBE) can lead to the deduction of kinetic parameters for the liquid/liquid reaction [5].…”

“…The mechanism for the coupled electrochemical reaction under investigation is assumed to proceed via one of two possible routes where the rate-determining step occurring at the liquid/liquid interface is either an S N 2-type nucleophilic attack of B 12s , generating a very short lived Co(III) organometallic intermediate, or an E2-type elimination [5,6]:…”

“…The two different rate-determining steps are kinetically indistinguishable [5,6], so the rate constants determined via our PBE approach will apply to both liquid/liquid reaction mechanisms. In a previous study of the liquid/liquid reaction of vitamin B 12s with a cyclic vicinal dibromide, trans-1,2-dibromohexane (t-DBCH), a similar mechanism was proposed and the bimolecular rate-determining step was found to be consistent with experimental results [5]. The partially blocked electrode is ideally suited to probe this reaction since the liquid/liquid boundary is immediately adjacent to the electrode surface, i.e.…”

“…Since then, the SECM/ITIES method has been applied to a wide range of systems and proceeding developments in the theoretical treatments have minimized the inaccuracies caused by initial approximations [10][11][12][13]. Our recent work on microdroplet PBEs has advanced to a stage where a quantitative study of liquid/liquid reaction kinetics is now possible [5,14,15]. This was demonstrated in a previous paper where cyclic voltammetry with a basal plane pyrolytic graphite electrode modified with microdroplets of pure and diluted trans-1,2-dibromocyclohexane (t-DBCH) was employed to determine the kinetic parameters of the liquid/liquid reaction between super-reduced vitamin B 12 , B 12s (aq), and the vicinal dibromide, t-DBCH(oil) [5].…”