Despite the strong development of polymer modified electrodes since 1976 there is still a need for new modification methods. The deposition of redox liquid droplets on the electrode surface is one of the recent examples [1]. Recently, we have reported immobilisation of redox liquid in carbon ceramic composite electrode [2]. Here, the silicate thin film modified electrode with redox liquid will be presented.
The gold electrode modified with thin hydrophobic silicate film and impregnated with redox liquid - t-butyloferrocene (t-BuFc) has been prepared and studied. Two types of electrode: disc and wire were used. The film was prepared from sol based on methyltrimethoxysilane. The disc electrode was modified by evaporation of the sol drop. The wire was covered by dip coating and after drying silicate layer was removed from the tip. These electrodes and bare gold electrodes were modified with t-BuFc by immersion (wire) in pure redox liquid or deposition of droplet of redox liquid diluted in hexane (disc). Their electrochemical properties were investigated by cyclic voltammetry and chronoamperometry in aqueous nitrate solution. The slow scan peak shaped voltammogram due to the redox process of t-BuFc was obtained. The decrease of the current magnitude during the subsequent scans is observed and this effect is smaller for silicate modified electrodes than for the bare ones.
It has been concluded that the electrode process occurs at the three phase junction formed by gold and liquid organic|aqueous interface supported by hydrophobic silicate. The current decrease is probably caused by the expulsion of t-BuFc⁺ to the aqueous phase [3]. Thin film of hydrophobic silicate acts as the reservoir for the liquid redox probe and it decreases the rate of the above mentioned process.

References
1. F. Marken et al., J. Electroanal. Chem. 437 (1997) 209.
2. M. Opallo, M. Saczek-Maj, Chem. Commun. (2002) 448.
3. R. G. Compton et al., J. Electroanal. Chem. 533 (2002) 71.

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