Microphase voltammetry of diluted and undiluted redox liquids deposited on sol-gel ceramic carbon electrodes

Ceramic carbon electrodes (CCEs) modified with microphases of diluted and undiluted redox liquids were prepared and studied. The electrodes consisting of graphite powder, homogeneously dispersed in a hydrophobic silica matrix, were prepared by reaction of a methyltrimethoxysilane-based sol and graphite powder following a sol-gel methodology. The electrode surface was modified with different amounts of redox liquids (pure t-butylferrocene, solutions of t-butylferrocene in 2-nitrophenyloctylether, and N,N,N',N'-tetraoctyl-1,4-phenylenediamine) using hexane solutions and a solvent evaporation approach. For comparison, a glassy carbon electrode modified analogously with t-butylferrocene was also prepared and studied. The electrochemical behaviour of the electrodes was examined by cyclic voltammetry in aqueous salt solutions. The electrodes exhibited anticipated electroactivity connected with the presence of redox liquids. The shape of voltammograms and the degree of conversion were very different for processes on CCEs compared to those observed on glassy carbon. Presumably due to the promotion of formation of microphases, the magnitude of the current responses obtained with CCEs modified with t-butylferrocene is substantially larger than that obtained with GC electrodes modified with the same amount of redox liquid. In contrast to CCEs modified with diluted and undiluted t-butylferrocene where after 5-10 scans stable voltammetric curves were obtained, glassy carbon failed to give stable cyclic voltammograms. The results can be explained by the extent of triple interface formation in the CCE silicate network. Due to the electrode microstructure, the voltammetric response of CCEs modified with microphases of N,N,N',N'-tetraoctyl-1,4-phenylenediamine shows similar enhancement effects. (C) 2004 Elsevier Ltd. All rights reserved