At higher scanning rate, the one effect of internal resistanceif when changed the scan rate you will obtain different capacitance in calculation.

As the scan rate increases the diffusion of electrolyte ion into electrode internal structure and pore become difficult (diffusion limitation) and ineffective interaction between the electrolyte and electrode materials occurs therefore the specific capacitance is decrease.  

Generally when you increase the scan rate, you are increasing the electronic field within the cell setup, which will alter both faradaic and non-faradaic processes