The C U Curve of a Valve Metal Electrode

The total potential drop A ptot across an electrode is made up of four parts the potential drop at the metal/oxide interface, the potential drop in the oxide, the potential drop in the Helmholtz layer and the potential drop in the electrolyte (diffuse double layer)  

Hence a potential (bias) dependent capacitance Cscl can be defined with use of the simple capacitor equation Csd/A = ere0/dsci. (As the E field is completely shielded 

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