The Electrochemical Quartz Crystal Microbalance

Abstract

Abstract This chapter reviews the development and use of the electrochemical quartz crystal microbalance (EQCM) as an in situ probe of interfacial processes involving the formation, properties, and redox switching of multilayer films. For films that are sufficiently rigid and/or thin (termed acoustically thin ), the EQCM functions as a quantitative gravimetric probe of surface population changes. This well‐established methodology is now being used to explore both thermodynamic and kinetic aspects of film compositional changes, for example, in response to electrochemical stimuli. Correlation of mobile species (ion and solvent) population changes—within the effectively static film matrix—with electrochemical control and response functions (potential, current, and charge) now provides mechanistic information. Combination with other in situ (e.g. optical or spectroscopic) techniques is a developing area and can facilitate separation of individual ion and solvent transfers. For films that are softer and/or thicker (termed acoustically thick ), the acoustic wave is attenuated during passage across the film, which in turn undergoes acoustic deformation. The EQCM now responds primarily to film viscoelastic properties, that is, film (rather than mobile species) dynamics. This is a developing area, but it is now possible to extract film shear modulus components (storage and loss moduli); these are found to respond significantly to the film redox state (controlled via potential or charge), temperature, timescale (frequency), and environment (both solvent and electrolyte ions). These effects are reviewed with selected examples from a diverse range of materials, encompassing metals, metal oxides, semiconductors, metal coordination complexes, and redox, conducting, and insulating polymers.