Supercapacitor
Since capacitors' energy content increases with the square of the voltage, researchers were looking for a way to increase the electrolyte's breakdown voltage. In 1994 using the anode of a 200V high voltage tantalum electrolytic capacitor, David A. Evans developed an "Electrolytic-Hybrid Electrochemical Capacitor". These capacitors combine features of electrolytic and electrochemical capacitors. They combine the high dielectric strength of an anode from an electrolytic capacitor with the high capacitance of a pseudocapacitive metal oxide (ruthenium (IV) oxide) cathode from an electrochemical capacitor, yielding a hybrid electrochemical capacitor. Evans' capacitors, coined Capattery, had an energy content about a factor of 5 higher than a comparable tantalum electrolytic capacitor of the same size. Their high costs limited them to specific military applications.
Experiments and Observations on Electricity
Franklin's first experiments explained in this first set of letters to Collinson that the Leyden jar, a type of capacitor, had equal and opposite charges on the inner and outer conductors. This was shown in illustrations in his book. The significant Franklin theory introduced to Collinson in a letter dated April 29, 1747, was the concept of the "dissectible condenser." Today we call this distribution of charges in a device, a capacitor. He observed that a charge was built up on both sides between a piece of nonconducting material. In the case of the Leyden jar this was glass (nonconducting matter) and on each side of it was a metal material (conducting matter). These opposite metal layers had the exact opposite electric charges (positive and negative). He observed that when the wire on the inside of the jar was "electrised" positively by a certain amount, that the outer conductor simultaneously became "electrised" negatively in the same proportion.