| Abstract
| - The diffusional mobilities of potassium ferricyanide (Fe(CN)63-) and ferrocene methanol (FcCH2OH)encapsulated within silica monoliths have been investigated using cyclic voltammetry and chronoamperometry at an ultramicroelectrode. In this work, a 13-μm-radius Pt microdisk working electrode and a silverchloride coated silver wire (r = 0.5 mm) reference electrode were inserted into doped silica sols preparedby the sol−gel process. The resultant gels were aged and slowly dried under a relative humidity atmosphereof 60−70% to minimize gel cracking. Fast-scan voltammetry (up to 100 V/s) confirmed that the gel−electrode interface remained intact throughout the duration of the drying period (typically 20−50 days).During this time frame, an ca. 30% loss in mass and ca. 50% reduction in volume of the gels were observed.The diffusion coefficients of gel-encapsulated Fe(CN)63- and FcCH2OH were measured without priorknowledge of dopant concentration via normalization of the chronoamperometric response with the steady-state limiting current obtained from a 2 mV/s potential sweep. For gel-encapsulated FcCH2OH, the diffusioncoefficient dropped from ca. 4 × 10-6 cm2/s to less than 0.6 × 10-6 cm2/s as the gel dried, whereas forgel-encapsulated Fe(CN)63-, a near constant value of 2 × 10-6 cm2/s was obtained. These results suggestthat transport in these solids is influenced by both gel structure and by the nature of the entrappedreagent.
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