High-performance activated carbons for electrochemical double layer capacitors: Effects of morphology and porous structures

In this work, we prepare a series of activated carbons (ACs) from xylose with different combinations of hydrothermal synthesis (HTS) and chemical activation with KOH. The prepared ACs exhibit a variety of morphologies and porous structures, which depend on the conditions used in the hydrothermal synthesis and the chemical activation. The largest surface area (S_BET) of the prepared ACs, which is calculated by the Brunauere Emmette Teller (BET) method, is ~3500 m²/g, and the largest volume fraction of mesopores of the prepared ACs is 60%. The correlations between the specific electrochemical properties of the ACs and the structures of the ACs (ie, porous structures and morphologies) are discussed. Spherical ACs exhibit superior rate performance with low impedance. The ACs with three-dimensional interconnected network of large surface area and porosity possess high specific capacitance. The largest specific capacitance reaches 340 F/g at a current density of 0.5 A/g and 220 F/g at a current density of 50 A/g, which are superior or comparable to those of similar systems. The long-term capacitance retention is ~86.8% after 10 000 cycles at a current density of 50 A/g. The energy density reaches 48 Wh/kg at a power density of 13.6 kW/kg.