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

Abstract

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 m 2 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.