A method for cleaning carbon black before using it as material for supercapacitor electrode. The method consisting on washing the carbon material with an acid choosen in the group consisting on hydrochloric acid, nitric acid, citric acid, formic acid, acetic acid and oxalic acid. A supercapacitor includes an electrode comprising activated carbon and carbon black particles containing less than or equal to about 100 ppm of calcium. A method includes treating base carbon black particles to form treated carbon black particles containing less than or equal to about 100 ppm of calcium; and using the treated carbon black particles to form an electrode of a supercapacitor. Carbon black particles having a Brunauer, Emmett and Teller (BET) surface area ranging from 650 m 2 /g to 2,050 m 2 /g, and comprising less than or equal to about 100 ppm of calcium.