Functional Group-Dependent Supercapacitive and Aging Properties of Activated Carbon Electrodes in Organic Electrolyte

• Published in: ACS sustainable chemistry & engineering Vol. 6; no. 1; pp. 1208 - 1214
• Main Authors: Yang, Cheng-Hsien, Nguyen, Quoc Dat, Chen, Ting-Hao, Helal, Ahmed S, Li, Ju, Chang, Jeng-Kuei
• Format: Journal Article
• Language: English
• Published: American Chemical Society 02.01.2018
• Subjects: activated carbon; capacitance; carbon electrodes; dielectric spectroscopy; durability; electrolytes; heat treatment; phenol; propylene; scanning electron microscopy; surface area; temperature; tetraethylammonium compounds; Supercapacitors; Aging; Leakage current; Gas evolution; Activated carbon; Functional groups
• ISSN: 2168-0485; 2168-0485
• DOI: 10.1021/acssuschemeng.7b03492

The concentrations of surface functional groups on activated carbon (AC) are manipulated via heat treatment at various temperatures. The carboxyl (O–C = O) population clearly decreases at 600 °C, whereas the lactone (RO–C = O) and phenol (C–OH) populations decrease if the temperature exceeds 750 °C. Their effects on electrode capacitance, leakage current, and gas evolution are systematically investigated in 1 M tetraethylammonium tetrafluoroborate/propylene carbonate electrolyte. The assembled symmetric supercapacitors are also subjected to an aging test, where the cells are held at 2.5 V and 70 °C. The decreased functional group populations significantly reduce gassing and improve the cell durability; the mechanisms are explored using electrochemical impedance spectroscopy and post-mortem SEM. Nevertheless, the AC surface area drops dramatically at 850 °C, resulting in a considerable reduction in capacitance. A rational control of heat-treatment temperature is critical for obtaining AC with balanced supercapacitor performance.