The liquid-like layer between metal and frozen aqueous electrolytes: An electrochemical approach employing the quartz crystal microbalance

Abstract

The surface properties of any substance in the solid state differ from its bulk properties. This can give rise to the formation of a liquid-like layer (LLL) at the interface, at temperatures below the melting point. The phenomenon generated interest among both theoreticians and experimentalists for more than 150 years and was studied, employing different techniques. However, electrochemical techniques have not been implemented in studies of this phenomenon. We used, for the first time, the quartz crystal microbalance (QCM) to study the LLL at the ice/gold and the frozen electrolyte/gold interfaces. It was shown that the QCM in contact with ice or with frozen electrolyte at temperatures well below the melting point shows detectable resonance. The parameters of the resonance depend strongly on temperature, composition of the frozen phase, adsorption taking place at the gold surface (including gold surfaces modified by different thiol-derivates) and, in the case of electrolyte, on the potential applied across the interface. Corresponding theoretical models have been developed to understand the kind of information contained in the response of the QCM on the properties of the LLL. Independent data obtained with a device allowing direct optical measurement of the displacement show good agreement with the calculations of thickness of the LLL based on developed models.