Low-temperature preparation and electrochemical capacitance of WC/carbon composites with high specific surface area

Abstract

WC/carbon composites (WCCs) with high specific surface area were synthesized by the direct carbonization of a mixture of hydroxylpropyl cellulose, polyvinyl alcohol, K 2WO 4 and K 2CO 3 at 900 °C in flowing N 2. The resultant material was characterized using X-ray diffraction, thermogravimetric analysis, nitrogen sorption and scanning electron microscopy. The electrode performance of this material for use as a capacitor was studied using cyclic voltammetry and galvanostatic charge–discharge measurements. The BET specific surface area of the WCCs varied from 300 to 1000 m 2/g depending on the amount of K 2CO 3 added during the preparation. Samples prepared with small amounts of K 2CO 3 contained a large amount of mesoporosity. Electrochemical characterization revealed that WC was slowly oxidized to tungsten oxy-hydroxides, and pseudocapacitance due to the redox reactions of tungsten oxy-hydroxides was superimposed on the double-layer capacitance of the carbon support. Consequently large specific capacitance was observed. Galvanostatic charge–discharge measurements of a WCC (ca. 5 wt% WC) resulted in total specific capacitances as high as 477 and 184 F/g at current densities of 20 and 1000 mA/g, respectively. The long-term cycle stability of WCC was also verified by a 5000 cycle charge–discharge test at 1 A/g.