Abstract:
Pyrrole undergoes oxidative polymerization from acetonitrile solution at a metallic anode to form a dark coloured skin that adheres firmly to the metal surface. This simple electropolymerization step, when applied to pyrrole monomers with covalently attached redox centres, offers a method for fixing these redox centres to an electrode. The very large range of modified electrodes prepared by this method is discussed here. A main aim of this area of research is the construction of electrodes on which a catalytic centre is present, and which can be activated by placing the electrode at the required redox potential. A number of important oxidation and reduction processes involve the transfer of atoms or groups of atoms and the making or breaking of bonds which involve a pair of electrons. These reactions do not occur readily at a normal electrode surface which promotes the transfer of single electrons only. Hence, there is a need to develop an electrode surface coating containing an electrocatalyst. If we consider an oxidation process, the catalyst is so designed that it reacts with the substrate and is itself reduced to an inactive form. This inactive form is in turn oxidized at the electrode surface by a sequence of single electron transfer steps. The advantage of such a system lies in constraining the catalyst to the electrode surface where it can be regenerated. The rate of the catalysed oxidation or reduction is limited by the diffusion of substrate to the coated electrode surface. Examples will be given where electrocatalytic processes have been achieved on a small scale.
