A Porous ITO Nanoparticles Modified Electrode for the Redox Liquid Immobilization

Abstract

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, tertbutylferrocene, and then immersed in the aqueous electrolyte solutions. The 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.

Spectroelectrochemical Investigation of TPPMn(III/II)‐Driven Liquid | Liquid | Electrode Triple Phase Boundary Anion Transfer into 4‐(3‐Phenylpropyl)‐Pyridine: ClO4−, CO3H−, Cl−, and F−

“…A transparent electrode based on ITO is employed. A thin film of ITO nanoparticles applied to the surface allows PPP microdroplet deposits to be distributed evenly with an extended triple phase boundary reaction zone [5]. Figure 5 shows typical cyclic voltammetry data for a deposit of 18 mM TPPMn(III) (ca.…”

“…A reasonably uniform particulate coating is clearly visible. This coating is approximately 80 nm thick for a two-step coating [5] and optically opaque. However, coloured oil deposits on this substrate give well-defined UVvis absorbance spectral data (vide infra).…”

“…8 mm wide and 40 mm long stripes) in an ethanol/water solution and then heating in air for one hour at 500 8C), then heating for two hours in a vacuum furnace (500 8C), and dipping into ITO nanoparticle dispersed in methanol (commercial ITO nanoparticle solution, diameter ca. 20 nm, dispersion in water, Nanophase Technologies Corp. USA, was evaporated close to dryness and then re-dispersed in methanol [5]). After removal from the solution and drying, the dip and dry step was repeated to the desired thickness.…”

“…Porous metal surfaces [15] as well as porous carbon surfaces [16] have been suggested. The application of tin-doped indium oxide (ITO) nanoparticles has been proposed [5] for the formation of thin mesoporous films with both conductivity and optical transparency. Here, this type of transparent mesoporous ITO film electrode is revisited and employed for in situ spectroelectrochemical measurements.…”

“…Spectroelectrochemical methods are similarly powerful in solution processes and in processes involving immobilised redox species at transparent electrodes (e.g. proteins in mesoporous ITO [4]) and is employed here for the case of redox driven anion transfer from the aqueous phase into an organic oil phase at a mesoporous tin-doped indium oxide (ITO) electrode impregnated with organic oil phase [5].…”