Characterization of Sol-Gel Derived Composite Silica Carbon Electrodes
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GENIA GUN, MICHAEL TSIONSKY AND OVADIA LEV Division of Environmental Science, Fredy and Nadin Herrmann School of Applied Sciences, The Hebrew University, Jerusalem, 91904, Israel
ABSTRACT Sol-gel derived composite silica-carbon electrodes exhibit favorable electrochemical characteristics. The electrodes benefit from the conductivity and electrochemical advantages of the carbon powder, from the favorable properties of the ceramic network and from the versatility of the sol-gel process. Hydrophobic composite electrodes reject water, only their outermost surface is wetted and they exhibit good signal to background currents. A comparison of several types of carbon powders reveals that higher carbon loading and larger surface area electrodes can be attained by incorporation of dense graphite powder. When high surface area, small size carbon-black powder is used, a homogeneous distribution of microelectrodes, separated by insulating modified silica is formed. This ensemble of microelectrodes increases the sensitivity of the CCEs by more than two orders of magnitude as compared to glassy carbon electrode and graphite CCEs.
INTRODUCTION Recently, we have demonstrated that composite Ceramic Carbon Electrodes (CCEs) made of organically modified silica and carbon filler are highly versatile electrochemical tools'. When hydrophilic glass forming monomers such as tetraalkoxisilanes or cyanoalkyltrimethoxysilane are used, water penetrates through the porous network of the composite. These conditions yield large surface area electrodes suitable for heavy duty applications such as electrocatalyses and reference electrodes. When hydrophobic ceramic forming compounds, such as alkyltrialkoxesilane or phenyltrialkoxysilane are used, water is rejected by the hydrophobic modifier as well as by the graphite surface leaving only the outermost surface wetted. These conditions are most favorable for electrosensing, since the signal contribution of diffusing species is increased relative to double layer capacitive current and the Faradaic contribution of surface and adsorbed species. CCEs benefit from the versatility of the sol-gel process, the electrodes can be molded in virtually any desirable configuration including thin coatings on insulating or conductive substrates, and in the forms of sheets, rods and even microelectrodes. The CCEs can be bulk modified by covalent bonding, sol-gel doping or impregnation, and mechanical polishing reveals a fresh renewed surface area 1,2 This publication examines the effect of the type of carbon powder on the physical and electrochemical properties of indicator CCEs. High purity, large size (200 mesh) graphite powder and two types of carbon black powders were examined. Acetylene black and Ketjenblack EC-600JD were selected as representatives of medium and high surface area carbon black powders. The physical characteristics of the three types of carbon powders are tabulated in Table I.
1011 Mat. Res. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society
Errata TABLE I Physical Properties of Ca
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