Oxide stern capacitance

Co/pH and V o/pH results are sensitive to different aspects of the surface chemistry of oxides. Surface charge data allow the determination of the parameters which describe counterion complexation. Surface potential data allow the determination of the ratio /3 —< slaDL- Given assumptions about the magnitude of the site density Ns and the Stern capacitance C t, this quantity can be combined with the pHp2C to yield values of Ka and Ka2. Surface charge/pH data contain direct information about the counterion adsorption capacitances in their slope. To find the equilibrium constants for adsorption, a plot such as those in Figures 7 and 8 can be used, provided that Ka and Kai are independently known from V o/pH curves. 

Equation 3.74 is a parameterization of ctm =/ (cp ) based on the Stern-Grahame double layer model. This relation requires as input the potential of zero charge and the Helmholtz capacitance. As mentioned, finding =f(

various surface and bulk oxide species, occurring simultaneously with double layer charging. 

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