The main subject of this paper is to examine and to evaluate the capacitive behaviour of activated carbon electrodes electrochemically decorated by quinone-type functional groups. For this purpose, different electrolytes, i.e. hydroquinone, catechol and resorcinol at the concentration of 0.38 mol L-1, dissolved in 1 mol L-1 H2SO4, 1 mol L-1 Li2SO4 and 6 mol L-1 KOH were used. These electrolytes could generate electroactive groups (able to undergo reversible redox reactions) on the surface of electrode material. Apart from typical adsorption of the mentioned dihydroxybenzenes, so called grafting could occur and might cause generation of quinone|hydroquinone functionals on carbon surface. As an effect of functional reversible redox reaction, additional capacitance value, called pseudocapacitance, could be achieved. Hence, besides typical charge originating from charging/discharging of the electrical double layer on the electrode/electrolyte interface, additional capacitance comes also from faradaic reactions. Activated carbons are the most promising electrode materials for this purpose; apart from great physicochemical properties, they are characterized by well-developed specific surface area over 2000 m2 g-1 which results in high capacitance values.

In the manuscript the influence of the hydroxyl group location as well as electrolyte solution pH on the electrochemical performance of the electrode is discussed.