Applications for CO₂‐Activated Carbon Monoliths: II. EDLC Electrodes

Abstract

The use of high-density carbon monoliths (CM) for preparing supercapacitor electrodes is analyzed. The starting CMs, produced by ATMI Co, were treated as follows: (1) under a N 2 flow at 1073 K to modify the carbon surface chemistry and (2) activated with CO 2 at the same temperature, using different activation times, to increase their porosity. Electrochemical measurements were performed on disks of 1-2 mm thickness which are suitable for direct use in practical devices. Two-and three-electrode cells were used with 2 M H 2 SO 4 solution as electrolyte. The contents of surface oxygen groups were measured by temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). The porosity of the starting monolith is increased by physical activation with CO 2 , the BET surface area increasing from 957 to 1684 m 2 /g. Upon heat treatments, both, the high density (1.2 g/cm 3 ), as well as the high amount of surface oxygen groups (2411 lmol CO/g) of the starting monolith are reduced; however, the densities of the treated monoliths remain higher than values reported for other porous carbon monoliths. The performance of the CMs as supercapacitor electrodes show as follows: (1) high specific and exceptionally high volumetric capacitances (up to 292 F/g and 342 F/cm 3 , respectively) due to their appropriate structure, porosity, and density, (2) a long and stable cyclability, (3) a decrease of power density with disk thickness, and (4) a decrease of pseudocapacitance with activation time.

Supercapacitors: Electrical Characteristics, Modeling, Applications, and Future Trends

“…Other authors [78] propose the use of salt, so that the electrode material crystallizes around the salt ions, which are then removed using water. Surface areas as high as 1400-2100 m 2 cm −3 have been recently reported for different electrode materials and manufacturing processes [79]- [81]. Moreover, significant research efforts are devoted to achieving electrodes for organic and ionic liquid electrolytes with higher surface areas.…”

Impact of CO2 activation on the structure, composition, and performance of Sb/C nanohybrid lithium/sodium-ion battery anodes

“…42,43 Due to the reaction between carbon and carbon dioxide at high temperatures (as shown by eqn (1)), CO 2 activation can not only reduce the carbon content of the Sb/C composite but also create more porous structures within the carbon matrix. [42][43][44][45][46]…”