Partial Oxidation to Extend the Lifetime of Nanoporous Carbon in an Ultracapacitor with Li2SO4 Electrolyte

Abstract

A TiC-derived carbon (CDC) and its partially oxidized derivative (ox-red-CDC), oxidized by a modified Hummers method, were studied as promising electrode materials for electrochemical energy storage. To evaluate the electrochemical properties of the carbon materials, cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy measurements were performed in 1 M Li2SO4 using 2- and 3-electrode cells. A partially oxidized surface was shown to improve the capacitance and electrochemical stability of a nanoporous CDC at positive potential values. The respective anodic capacitance of 80 F cm-3 reveals a 15% improvement over the non-oxidized CDC. At negative potential values, the capacitance of two carbon materials is almost equal, 97 vs. 93 F cm-3, for the non-oxidized and partially oxidized CDC materials, respectively. An asymmetric 2-electrode ultracapacitor containing ox-red-CDC as the anode and pristine CDC as the cathode demonstrated an excellent cycle life. The temporary repolarization of the 2-electrode cell after thousands of charge-discharge cycles increased the capacitance and improved the cycling characteristics, likely due to regeneration and cleaning of the electrode surface.