A porous ITO nanoparticles modified electrode for the redox liquid immobilization

Tin-doped indium oxide (ITO) nanoparticles (ca. 20 nm in diameter) were deposited onto electrode surfaces employing a simple immersion, withdrawal and solvent evaporation method. The resulting ITO films are irregularly packed and highly porous and they promote electron transport. When water insoluble redox liquids are immobilized within the porous film efficient electrochemical reactions occur at the solid-liquid and at liquid-liquid interfaces. Scanning electron microscopy reveals a macroscopically uniform surface of the deposit. The thickness of the film estimated by atomic force microscopy is proportional to the number of deposited layers with a thickness increase per single immersion and withdrawal step equal to approximately 60 nm. However, the films are deposited non-uniformly and the thickness only provides an average parameter. The results of voltammetric experiments performed in aqueous electrolyte solution indicate good adhesion and wetting of the deposit. The surface electroactivity towards the electrooxidation of ferrocenedimethanol provides highly reversible responses without any blocking effects. The ITO nanoparticle modified electrode surface was impregnated with nanomole amounts of a hydrophobic redox liquid, tert-butylferrocene, and then immersed in the aqueous electrolyte solutions. ne value of the voltammetric peak current and the efficiency of the multi-phase electrode process improved proportional to the number of immersion and withdrawal steps from ITO nanoparticles suspension. This improvement is also observed after further electrode modification with a hydrophobic thin film via sol-gel processing of methyltrimethoxysilane. In this case the porous film at the electrode surface can be surface modified to provide affinity to certain liquids or analytes.