ISSN:
1433-0768
Keywords:
Key words Sol-gel chemistry
;
Silica
;
Pore structure
;
Colloidal Prussian Blue
;
Cyanometallate redox sites
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract We describe a sol-gel approach by which iron hexacyanoferrate is immobilized in silica in a manner suited to investigation by electrochemistry in the absence of a contacting liquid phase. Such physicochemical parameters as concentration of redox sites (C o) and apparent (effective) diffusion coefficient (D app) are estimated by performing cyclic voltammetric and potential step experiments in two time regimes, which are characterized by linear and spherical diffusional patterns, respectively. Values of D app and C o thereby obtained are 2.0 × 10−6 cm2 s−1 and 1.4 × 10−2 mol dm−3. The D app value is larger than expected for a typical solid redox-conducting material. Analogous measurements done in iron(III) hexacyanoferrate(III) solutions of comparable concentrations, 1.0 × 10−2 and 5.0 × 10−3 mol dm−3, yield D app on the level of 5–6 × 10−6 cm2 s−1. Thus, the dynamics of charge propagation in this sol-gel material is almost as high as in the liquid phase. The residual water in the silica, along with the pore structure, are important to the overall mechanism of charge transport, which apparently is limited by physical diffusion rather than electron self-exchange. Under conditions of a solid state voltammetric experiment which utilizes an ultramicroelectrode, encapsulated iron hexacyanoferrate redox centers seem to be in the dispersed colloidal state rather than in a form of the rigid polymeric film.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s100080050195
