The presence of some chemical functionality containing heteroatoms, such as oxygen or nitrogen, gives carbon materials acid/base character and thus enhances the capacitance
by the same pseudocapacitive effect. These electrochemically active centers contribute to the overall capacitance, with pseudocapacitance that generally originates from the faradaic interactions between the ions of electrolytes and the carbon electrode surface. The oxygen surface groups, formed in most of the activated carbons, have an acidic character, thus introducing electron-acceptor properties into the carbon surface. On
the other hand, nitrogen functionalities have generally basic characters, inducing electron-donor properties.The origin of pseudocapacitance in nitrogen-enriched carbons is however yet to be clarified in detail.