Effects of Surface Oxygenic Functional Groups on the Electrochemical Properties of Supercapacitor

The surface oxygenic functional groups are significant to the capacity and cycle stability of supercapacitor. Coconut shell-based activated carbon (CS) with high surface oxygen content was used as starting material and reduced by hydrogen. The measurement results of microstructure showed that the specific surface area and total pore volume increased a little. While the surface oxygen content decreased greatly according to the results of X-ray photoelectron spectroscopy (XPS). Electrochemical behaviors of the electrode built with CS and hydrogen reduced CS (HCS) were investigated in two kinds of electrolytes, 6 mol L⁻¹ KOH and 1 mol L⁻¹ Et⁴NBF₄/PC, respectively. The results showed that the surface oxygen groups have little influence to the electrochemical properties of supercapacitor in KOH electrolyte. As for supercapacitor in Et₄NBF₄/PC, HCS presents higher specific capacitance, higher energy density, better capacity retention and lower leakage current than those of original CS. This indicates that the surface oxygenic functional groups have reaction and impediment to the organic electrolyte. The study not only provides a simple and effective method for large-scale and safe application of supercapacitors using organic electrolyte, but also offers a better understanding of the action of surface functional groups on the electrochemical performances of porous carbon materials.