Impedance Behavior of Electrochemical Supercapacitors and Porous Electrodes

3 Impedance Behavior of Electrochemical Supercapacitors and Porous Electrodes 

The history of the concept of the double layer at interfaces with liquid electrolyte solutions or ionic sohds, and at colloids, goes back to early work on colloids and electrode interfaces in the 19th century and through the 20th, but is beyond the scope of present article. However, general reference sources are Adam [1941], Adamson [1982], and Conway [1999]. 

The main factor of principal significance is that, per cm interfacial doublelayer capacitance values are very large in comparison with that of hardware capacitors of the same, 1 cm area where values are on the order of picofarads. Interfacial double-layer capacitance values are on the order of 20 jiFcm a figure that arises on account of the very small separation of charges across an electrode or colloid interface, on the order of 0.3 nm. 

for double-layers established at high specific-area materials, such as powdered or fibrous carbons, or metals, or their oxides, very high specific capacitance per gram can be attained. This is the principle that has underlain the development of electrochemical capacitors, now often referred to as supercapacitors (Conway [1999]) or ultracapacitors . 

Electrochemical capacitors are a relatively recent development in the technology of electric charge storage and delivery devices, though an early original patent 

---