Quinone/hydroquinone redox couple as a source of enormous capacitance of activated carbon electrodes
- PDF / 1,661,306 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 87 Downloads / 223 Views
Quinone/hydroquinone redox couple as a source of enormous capacitance of activated carbon electrodes Krzysztof Fic, Mikolaj Meller, Grzegorz Lota and Elzbieta Frackowiak Poznan University of Technology, Institute of Chemistry and Technical Electrochemistry, Piotrowo 3, 60965 Poznan, Poland ABSTRACT 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. INTRODUCTION Electrochemical capacitors, known also as pseudocapacitors or electrochemical double layer capacitors (EDLC), are very interesting devices for energy storage. Process of energy storage is based on charging and discharging of electrical double-layer (EDL) on the electrode/electrolyte interface, therefore, it has strictly electrostatic character. For this reason, electrochemical double layer capacitors are able to be charged and discharged even in a few seconds. This characterization of electrical double layer causes that the most promising electrode materials for this purpose are carbon materials with well-developed specific surface area (even higher than 2000 m2 g-1). Generally, one can assume that the higher specific surface area of the electrode material, the higher capacitance value of the electrode. Obviously, the pore size and their distribution in the material play very important role in charge accumulation [1]. Higher capacitance values of electrochemical capacitors can be provided by using pseudocapacitive materials, such as MnO2, InO2, SnO2, Fe3O4, V2O5 or RuO2. This additional capacitance originates from faradaic reactions. Hydrated form of ruthenium dioxide is characterised by higher conductivity than commonly known manganese dioxide. Unfortunately, one of the biggest problem which eliminates
Data Loading...
