Carbon electrodes with high pseudocapacitance for supercapacitors

Electrochemical properties of electrodes on the basis of CH900-20 activated carbon (AC) cloth were studied in concentrated H ₂SO ₄ solutions in a wide range of potentials from -0.8 to +1 V RHE. Cyclic voltammetric curves measured in two ranges of potentials were analyzed: in the reversibility range (from 0.1 to 0.9 V) and in the deep cathodic charging range (from -0.8 to 1 V). Electric double layer (EDL) charging occurs in the reversibility range, while faradaic processes of hydrogen chemisorption and its intercalation into carbon take place in the range of negative potentials (<-0.1 V). The intercalation process is controlled by slow solid-phase hydrogen diffusion. For the first time, the maximum value of specific discharge capacity of 1560 C/g was obtained, which is much higher than the values known from the literature for carbon electrodes. On the basis of this value and Faraday's law, it was assumed that the compound of C ₆H is formed in the limiting case of AC deep cathodic charging. The specific charge value grows at an increase in the concentration of H ₂SO ₄. The mechanism of double intercalation of sulfuric acid and hydrogen into the AC is suggested. The data obtained are used to develop a mathematical charging-discharge model for an AC electrode taking into account the EDL charging, chemisorption, and hydrogen intercalation.