For devices using PC, most electric charge is transported to the bulk or surface adjacent to the solid electrode surfaces [87]. Thus, the interactions between the electrolyte and the solid material involve a Faradaic reaction to reflect the mechanism of charge transfer, which depends on voltage. Therefore, PC is voltage dependent. In the development of ultra-capacitors using PC, three types of electrochemical processes are commonly involved: surface adsorption of electrolyte ions, redox reactions involving electrolyte ions, and doping/de-doping of CP materials in the electrode. The first two processes rely mainly on surface mechanisms, so the specific area of the electrode materials greatly affects the performance. The last process, using CP materials in the electrode, relies on a bulk process, so the surface area does not much affect the capacitance. In all cases, the electrode materials must exhibit maximum electronic conductivity for the distribution and collection of the electric current.