Electrochimica Acta 48 (2003) 4149–4155 Solid electrolyte based on silicate matrix functionalised with tetraalkylammonium group solvated by organic solvent M. Opallo a,∗,1 , J. Niedziolka a , M. Saczek-Maj a , G. Shul a , E. Utzig a , J. Mrowiec-Bialon b , J. Stygar c , W. Wieczorek c a Institute of Physical Chemistry, Polish Academy of Sciences, ul. Kasprzaka 44/52, 01-224 Warszawa, Poland b Institute of Chemical Engineering, Polish Academy of Sciences, ul. Baltycka 5, 44-100 Gliwice, Poland c Faculty of Chemistry, Warsaw University of Technology, ul. Noakowskiego 3, 00-664 Warszawa, Poland Received 8 May 2003; received in revised form 14 July 2003; accepted 18 July 2003 Abstract Solid electrolyte composed of hybrid organic–inorganic silicate matrix functionalised with tetraalkylammonium group, solvated by viscous organic polar solvent (propylene carbonate (PC) or sulpholane (TMS)), was prepared by the sol–gel method under controlled drying condi- tions. Tetramethoxysilane (TMOS), N-trimethoxysilylpropyl-N,N,N-tributylammonium chloride (TMOSPTBACl) and organic solvent were principal sol components. Gel formed within 2 h and 2 days depending on substrate ratio and the solvent additive. The obtained material was transparent and it loosed about 15% of its mass during first 30 days of ageing. It was characterised by thermogravimetry (TGA), differential scanning calorimetry (DSC), NMR, FT-IR spectroscopy, small angle X-ray scattering (SAXS), and impedance spectroscopy. The transport of redox active molecules was studied by electrochemical methods. The porosity of samples dried in supercritical CO 2 was also estimated. The shape of TGA and DSC curve appeared to be similar to that of pure solvent. The IR spectra indicated the silicate network formation with some silanol groups left. The NMR spectrum of the solution used to wash crushed sample indicated that all organic substrate is embedded in silicate matrix. The magnitude of electrical conductivity was close to 10 -4 to 10 -5 S cm -1 , i.e. least more than one order of magnitude larger than that of TMOS based silicate matrix modified with a pure solvent. This conductivity is high enough for electrochemical experiments. Both conductivity and diffusion coefficient of redox probe-ferrocene (Fc) depended on time elapsed after gelation. Their most substantial decrease was observed during first 10 days after gelation and it correlated with mass loss. © 2003 Elsevier Ltd. All rights reserved. Keywords: Sol–gel; Solid electrolyte; Organically modified silicate; Conductivity; Redox reaction 1. Introduction Inorganic materials obtained under mild reaction con- ditions, e.g. by the sol–gel method [1] are considered to be versatile matrices for preparation of solid electrolytes. Among them, silicates seem to be especially attractive, because of several advantages over organic polymers as: physical rigidity, chemical inertness (except high pH con- ditions) and negligible swelling [2,3]. They become good ionic conductors after impregnation with salt solution in organic polar solvent [4–15] or in water [16–19]. In such a case one can obtain macroscopically solid electrolyte with ∗ Corresponding author. Tel.: +48-22-632-3221x3375; fax: +48-22-631-1619. E-mail address: mopallo@ichf.edu.pl (M. Opallo). 1 ISE member. some properties of liquid electrolyte preserved. These ma- terials are attractive from a practical point of view because of the use organic electrolytes in batteries, electrochemi- cal sensors, electrochromic and electrochemiluminescent devices. The use of organic solvent for impregnation is much better form the point of view of its durability and electrode|electrolyte interface stability, because of small shrinkage of material during gelation and ageing. The use of tetraalkylammonium cations is desirable in devices, where strong ion pairing of alkali metal substrates with the product of electrode reaction should be avoided. This is important in electrochemical gas (O 2 , CO 2 ) sensors [20] or electrochemiluminescent systems involving organic donors [21] with salt solution in organic solvent. There are two strategies of silicate matrix modification by salt solution. It can be added either directly to the sol before sol–gel transition occurs [5,9–19] or it can be 0013-4686/$ – see front matter © 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0013-4686(03)00583-8