The role of the electrical double layer and ion pairing on the electrochemical oxidation of hexachloroiridate(III) at Pt electrodes of nanometer dimensions.

摘要: The steady-state voltammetric oxidation of hexachloroiridate(III), IrCl6(3-) (1-5 mM), in the presence and absence an excess supporting electrolyte was investigated at disk- hemispherical-shaped Pt electrodes with radii ranging from 48 nm to 12.5 microm. Thermodynamic, kinetic, transport parameters that define shape magnitude wave exhibit a complex dependence on whether is present solution. First, half-wave potential, E1/2, for shifts more positive potentials electrolyte, consequence relative difference strength ion pairing IrCl6(2-) by cation. E1/2 increases order no < n-tetrabutylammonium Na+ approximately K+ Ca2+, but independent anion (Cl-, NO3-, PF6-). Second, heterogeneous electron-transfer rate constant electrolyte. Third, mass limited currents deviate significantly predicted values based Nernst-Planck equation, only when electrode radius smaller than ca. 1 latter two effects (Frumkin dynamic diffuse layer effects) result interfacial electrical fields and, thus, rates migration, concentration. We also demonstrate theoretical response or reduction highly charged redox species (e.g., IrCl6(3-)) essentially This finding can greatly simplify analysis using voltammetry low ionic solutions.