Due to their high versatility, high electrical conductivity and low cost, activated carbons are excellent electrode materials for supercapacitors. However, for high energy applications, their capacitance is too low, very often due to poor wettability by the electrolyte. Surface modification by chemical grafting of electrografting has been proposed to enhance wettability and capacitance of carbons through pseudo capacitance effects [1]. Recently, electrografting of carbons by use of diazonium salts has been described to modify the surface by different functional groups [1,2]. This reaction leads to the loss of dinitrogen with the formation of an aryl radical or cation which is grafted on the material surface. By this way, amino, carboxyl or alcohol groups can be electrografted to carbon surface under oxidative conditions [1]. Electrografting of phenol precursors has been also proposed on the surface of glassy carbon, activated carbon and carbon nanotubes [3,4]. During anodic oxidation in protic medium, radical cations appear after hydroxyl and carboxyl groups are detached from the carbon surface [1,5]. On the other hand, oxidation of hydroquinone leads to radical anions [6] which react with the radical cations to form a chemical bond.
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