Characterisation of biphasic electrodes based on the liquid N,N-didodecyl-N′N′-diethylphenylenediamine redox system immobilised on porous hydrophobic silicates and immersed in aqueous media

Biphasic electrodes based on the water-insoluble redox liquid N,N-didodecyl-N′,N′-diethylphenylene-diamine (DDPD) neat and dissolved in di-(2-ethyl-hexyl)phosphate (HDOP) deposited onto silicate matrices were prepared and studied in aqueous electrolyte media. As electrode substrates (i) bare gold, (ii) a gold surface covered with a hydrophobic silicate film, and (iii) a hydrophobic silicate carbon composite were employed. Both hydrophobic silicate based materials act as a host for the organic redox liquid and modify the electrochemical response in characteristic manner. The electrooxidation of DDPD occurs at the organic phase|aqueous phase|electrode triple phase boundary and is accompanied by the transfer of the anion from the water into the organic phase. In the presence of an organic acid, HDOP, the oxidation process is accompanied by the expulsion of protons instead. This electrochemically driven proton exchange process results in a shift of redox potentials, which can be described by Nernst-type dependence with a slope strongly dependent on the electrode/host material and the deposition method. The formation of an DDPD–HDOP acid–base complex within microdroplets deposited on gold surfaces is confirmed by IR reflectance spectra.