New Carbon Monoliths for Supercapacitor Electrodes. Looking at the Double Layer

Abstract

Carbon monoliths are prepared by combining two carbon phases. A major phase is activated anthracite, which provides microporosity and a large surface area. The other phase is a carbonized polymer that provides self-consistency and contributes to densifying the monolith. Different degrees of anthracite activation and different contents of the two phases are investigated. These all-carbon monoliths have surface areas up to 2600 m2 g−1, mechanical strengths up to 6 MPa, electrical conductivities up to 2–4 S cm−1, and densities between 0.4 and 0.7 g cm−3. In sulfuric acid electrolyte, gravimetric capacitances up to 307 F g−1 are achieved. The double-layer capacitances due to the hydronium and bisulfate ions are separately measured, the former being approximately 25% higher than the latter. The size of the two ions electro-adsorbed at the double layer is discussed. The pseudocapacitance associated with the hydronium ion is 10–25% of the total capacitance of this ion. All of the carbon monoliths show high capacitance retention with current density; the retention of the double-layer capacitance is similar for the two types of ions and higher than the retention of the pseudocapacitance associated with the hydronium ion.