The Advantages of Using an Electrochemical Quartz Nanobalance to Study the Electrochemical Conversions of Solid Microparticles

The investigation of particles and droplets immobilized on electrode surface has become an interesting and important field of electrochemistry.1–38 It has proven useful in solving both fundamental and applied issues, e.g. determination of thermodynamic data of solid compounds, elucidation of solid-to-solid electrochemical reactions accompanied by phase transitions, qualitative and quantitative determination of the composition of different solid materials including alloys, mixtures of inorganic compounds (such as minerals, archaeological ceramic glazes), organic and organometallic compounds, or gaining a deeper understanding of insertion reactions.1–4 The method of voltammetry of immobilized microparticles1–4 in combination with electrochemical nanogravimetry by using quartz crystal nanobalance (EQCN) – also called microbalance, and abbreviated as EQCM – is especially useful for the characterization of microcrystals attached to an electrode surface.1–4,17,29,31–38 Although the cyclic voltammetry supplies information regarding the redox reactions occurring in these systems, the elucidation of the voltammograms is a very difficult, often impossible task without additional data concerning the sorption/desorption of ionic species and neutral molecules as well as dissolution and deposition processes. A unique opportunity is the investigation of the solid-solid phase transition. In order to demonstrate the importance of the application of this combined technique, the results obtained for phenazine,33 tetracyanoquinodimethane,37 -RuCl3 and carbazole31 microcrystals will be presented. Usually the ‘stabilized responses’ are studied, however, in many cases the parent microcrystals undergo irreversible transformations during the first reduction-oxidation cycle. Therefore, it is also important to investigate this ‘break-in’ process which differs from that characteristic of conducting polymer films where usually only morphological changes occur. In this paper, the first-cycle or break-in phenomenon is emphasized.