Impedance Insight in Catalytic Properties of Long-Lived Free-Radical Oxidizer Based on Silver(II)
Here we report electrochemical impedance studies of this interesting system . Typical impedance spectrum is shown in Fig. 1. For data analysis we developed analytical model for impedance of catalytic processes together with potential dependence of all impedance parameters derived for general case in rigorous treatment . The model is valid for various systems regardless the kinetics of the heterogeneous and homogeneous reactions and also for system with unequal diffusion coefficient. Resistance of the charge transfer was found to be potential independent at far anodic or far cathodic overpotentials for electrocatalytical oxidation and reduction, respectively. Resistance of the charge transfer in silver(I) oxidation is shown in Fig. 2 (top). The equivalent circuit for catalytic systems, in which the kinetics of the homogenous chemical step can be described by Gerisher element is shown in the inset to Fig. 1 (bottom). By fitting impedance spectra both the heterogeneous and the homogeneous rate constants for silver electrooxidation were obtained in various experimental conditions. We have found that the half-life of the free-radical oxidizer based on silver(II) is the largest in 100% sulfuric acid solutions (Fig.2 bottom) and it substantially decreases both for diluted sulfuric acid and as well as for oleums. The influence of water and SO3 on the silver(II) chemistry will be discussed.
Fig. 1. Impedance spectra of Ag(I) oxidation in 18 M (95%) H2SO4. Green continuous line (−) represent the fit result of experimental points (◆) by using equivalent circuit shown in the inset.
Fig. 2. (Top) Potential dependence of the charge transfer resistance for Ag(I) oxidation in 18 M(95%) H2SO4. (Bottom) Rate constant of homogenous chemical reaction in function of sulphuric acid concentration.
 P. Połczyński, R. Jurczakowski, W. Grochala, ChemComm, 2013, 49, 7480.
 P. Połczyński, R. Jurczakowski, W. Grochala, The Journal of Physical Chemistry C,2013, 117, 20689−20696.
 P. Połczyński, R. Jurczakowski, W. Grochala, manuscript in preparation.
 P. Połczyński, R. Jurczakowski, manuscript in preparation.