Christopher A. Paddon

Paired electrosynthesis: micro-flow cell processes with and without added electrolyte

Abstract The thin layer flow cell geometry with working and auxiliary electrodes directly facing each other, allows electrosynthetic processes to be conducted in flow-through mode. At sufficiently small cell height, the two diffusion layers of working and auxiliary electrode overlap or become ‘coupled’. As a result electro-generated acids or bases are instantaneously neutralised, products from anode and cathode can interact, and, more importantly, bulk electrolysis is possible without intentionally added electrolyte. In this preliminary report, the operation of a micro-flow cell with coupled diffusion layers is demonstrated for the one electron oxidation of ferrocene and for the two electron–two proton reduction of tetraethyl ethylenetetracarboxylate dissolved in ethanol. In proof-of-principle bulk electrolysis experiments without intentionally added electrolyte, high yields of the product, tetraethyl ethanetetracarboxylate are obtained at a nickel working electrode. It is demonstrated that a sufficient concentration of electrolyte for bulk electrolysis is generated locally and in situ between working and auxiliary electrode.

Hydrophobic silica sol–gel films for biphasic electrodes and porotrodes

Hydrophobic sol-gel films from methyltrimethoxysilane (MTMOS) are deposited onto glass and tin-doped indium oxide (ITO) coated glass substrates. Uniform and microporous films of ca. 200 nm thickness are obtained and investigated by scanning electron microscopy and by electrochemical techniques. From cyclic voltammograms for the oxidation of ferrocenedimethanol in aqueous 0.1 M KNO3 apparent diffusion coefficients and free volume data for processes within the film are derived and it is demonstrated that the film morphology can be controlled by the deposition timing. Two novel types of biphasic electrodes for observing liquid/liquid ion transfer reactions are introduced: (i) an ITO electrode coated with a hydrophobic sol-gel film and (ii) a hydrophobic sol-gel film on glass sputter-coated with 20 nm porous gold (porotrode). For the t-butylferrocene redox system deposited in the form of an organic liquid, very low and morphology dependent current responses are observed on modified ITO electrodes. However, the porotrode system allows biphasic electrode reactions to be driven with high efficiency and with no significant morphology effect of the hydrophobic sol-gel film. This type of nanofilm-modified electrode system will be of interest for biphasic sensor developments.

Cryovoltammetrically probing functional group reductive cleavage: alkyl–sulfur versus aryl–sulfur bond cleavage in an alkyl naphthyl thioether under single electron-transfer is temperature switchable

A series of single electron-transfer (SET) reactions on a naphthyl thioether have shown that the reductive cleavage mechanism changes at low temperatures and this selectivity is proved using an electrochemical analysis that mimics the SET reaction conditions.