Electric capacity of the compact layer

The interfacial electric double layer is represented by a combination of the improved jeUium model on the metal side and the hard sphere model of ions and dipoles on the aqueous solution side. Then, the electric capacity, Ch, of the compact layer is given by Eqn. 5-34  

Capacity Ch in Eqn. 5-34 may be conventionally divided into capacity Cm on the metal side and capacity Cs on the aqueous solution side as shown in Eqns. 5-35 and 5-36  

The third term of the right hand side of Eqn. 5-36 represents the inverse capacity of 1 /Cs,d4 due to the orientational polarization of adsorbed water molecules. Usually, Cm and Cs are of the same order of magnitude near the potential of zero charge. 

Molecular dynamics based on the jellium-sphere model has derived Eqn. 5-37 for the capacity of the compact layer formed near the potential of zero charge [Schmidder, 1993]  

As described in this section, the distance Xta, to the image plane increases with increasing electron density in the electrode metal. Correspondingly, as shown in Fig. 5-24, the capacity of fbo compact layer, Ch, of sp metal electrodes in aqueous solution increases with increasing electron density in the metal. It thus appears that the interfadal electric double layer is affected significantly by the nature (electron density) of the electrode metal. 

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