Most people think of batteries when they consider energy storage, but capacitors are an alternative in some use cases. Capacitors are used in almost all electronic devices, often to supply temporary power when batteries are being changed to prevent loss of information. In addition to everyday devices, they are also used in more obscure technologies, including certain types of weapons.
Unlike batteries, capacitors use static electricity to store energy. In their simplest form, they contain two conducting metallic plates with an insulating material (dielectric) placed in between. A typical capacitor charges instantly but usually cannot hold a great deal of charge.
Supercapacitors can at least partly overcome this shortcoming. They differ from the typical capacitor in that their "plates" provide significantly larger surface area and are much closer together. The surface area is increased by coating the metal plates with a porous substance. Instead of having a dielectric material between them, the plates of a supercapacitor are soaked in an electrolyte and separated by an extremely thin insulator.
Carbon supercapacitors offer high electrical power, low weight, and fast charge-discharge cycles. But it's difficult to get carbon to provide a high enough surface area to bring the energy density up to where it could compete directly with batteries.
Though some carbon materials have been made to exhibit a high supercapacitance in theory, they are not able to translate those gains into real-world applications. For example, graphene supercapacitors exhibit a theoretical capacitance of 550 F/g but only reach 300 F/g when used in real-life applications.
Recently, scientists have focused on altering the surface of carbon-based supercapacitors to increase their potential to store charge. In this case, the supercapacitor system under investigation is composed of carbon plates that contain nano-sized pores (mesoporous carbon) with a polymer insulator. They have altered the surface of the mesoporous carbon plates by the addition of nitrogen. Doping in nitrogen has allowed for reactions between the nitrogen and carbon. These "redox" reactions result in the movement of electrons from one species to another.
In this study, the scientists demonstrated the ability to produce an electrochemically active substance from layered carbon (similar to graphene) by nitrogen doping.
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