engleski

Application of the Surface Potential Data to Elucidate Interfacial Equilibrium

Surface potential (Ψ0) is essential physical quantity which influences the equilibrium of surface reactions at solid/electrolyte aqueous solution interface [1]. Several years ago the new method for direct measurement of surface potential, by means of Single Crystal Electrode, was introduced [2]. The value of surface potential depends on three terms: the activities of potential determining ions in bulk of the solution (i.e. pH for metal oxides ; pAg for silver halides) ; the location of the electroneutrality point ; and, what is most important for studying surface reactions, surface potential depends on the ratio of surface concentrations of positive and negative surface groups. Neglecting this third factor leads to conclusion that surface potential is a Nernstian potential i.e. for metal oxides the slope of the function Ψ0(pH) would be –RTln10/F. This hypothesis was tested by direct measurements of surface potential by examining the influence of electrolyte concentration. The measurements showed that surface potential could be linear function of lg a(pdi) with slope lower than Nernstian [3], or non-linear function with shape depending on the ratio of surface equilibrium constants [4]. By knowing the value of surface potential, extensive interpretation of state and reactions at the solid/aqueous electrolyte solution interfaces, is enabled. By means of Single Crystal Electrode the surface potential of different surface planes was measured, and from these results the reactivity of different surface coordination was analyzed [5]. The kinetics of surface reactions was studied from hysteresis of surface potential data in course of the acid-base titrations [6]. Moreover, from the hysteresis of Ψ0(pH) function the method for the point of zero potential determination was proposed [7]. The point of zero potential could also be evaluated from the nonlinear symmetric Ψ0(pH) function [4]. The transformation of 001 hematite surface was studied. The influence of binding and adsorption of ions from the solution on the surface potential was also investigated, leading to the information of the nature of formed interfacial complexes [8].

surface potential ; single crystal electrode ; metal oxide ; electrical interfactial layer ; surface complexation

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