The Quartz Crystal Microbalance In Electrochemistry

Abstract

Abstract The electrochemical quartz crystal microbalance (EQCM) has found wide acceptance as an analytical tool. Nanogram mass changes that occur on the surface of a quartz crystal can be correlated with the amount of charge passed during an electrochemical process. This technique has been widely reviewed. That a mass change can be determined from the resonant frequency change of a quartz crystal has been extensively used in vapor deposition techniques for many years. However, the use of the quartz crystal microbalance (QCM) in contact with a liquid during electrochemical studies is more recent. Initial investigations were applied to the underpotential deposition of metals. The EQCM has since been applied to a wide variety of electroactive materials. Examples include conducting polymers, conducting polymer bilayers, redox polymers, charge‐transfer salts, hydrogen uptake by a metal, electrochromic behavior of metal oxide electrodes, polymerization of disulfides, self‐assembled ferrocene‐based monolayers, Prussian blue and nickel ferricyanide. The fact that the mass change of any electroactive material during any electrochemical change can be evaluated with the EQCM has led to its widespread application. The ability to simultaneously determine the mass and the charge passed during an electrochemical process in an electroactive material is critical for characterization in many instances. For example, the polymerization mechanism of an electrochemically synthesized material can be studied as well as quantifying the amount of ion and/or solvent transport during oxidation/reduction. In addition, recent applications of the QCM include simultaneous QCM and ellipsometry, investigating solvent dynamics in polymer films and determining contact angles and surface tensions. This article provides a general overview of the EQCM technique and provides details about particular interpretative precautions. The QCM has also been called a thickness‐shear‐mode (TSM) oscillator. Related techniques involve the surface‐acoustic wave and flexural‐plate wave devices.