Effects of CeO2 nanoparticles on electrochemical properties of carbon/CeO2 composites

Abstract

The electrochemical properties of carbon were improved when composited with CeO2 nanoparticles making this material a candidate for high performance energy storage devices. Carbon was obtained from coffee husks by calcining at a temperature of 600 °C for 1 h. Carbon/CeO2 composite mixtures were prepared with 0, 10, 20 and 30 wt% CeO2 nanoparticles referred to as carbon, carbon-10CeO2, carbon-20CeO2 and carbon-30CeO2, respectively. The structure, morphology and valence states of the carbon/CeO2 composites were characterized by X-ray diffraction (XRD), Raman spectroscopy (Raman), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Specific surface areas were measured using the Brunauer-Emmett-Teller method (BET) and the materials electrochemical properties were measured using a potentiostat/galvanostat cell system. The XRD and Raman results exhibited peaks corresponding to carbon and CeO2, confirming the formation of a composite. XPS measurements confirmed the presence of Ce4+ and Ce3+/oxygen vacancies in the CeO2 nanoparticles. The specific surface areas measured were 216, 317, 340 and 270 m2/g for carbon, carbon-10CeO2, carbon-20CeO2 and carbon-30CeO2, respectively. Both the discharge capacity and specific capacitance were optimal for electrodes made from the carbon-30CeO2 composite, being approximately 2 and 15 times better than that of carbon. These higher values are thought to be due to the contribution of the redox reaction Ce3+ ↔ Ce4+ within the CeO2 nanoparticles on the surface of the carbon.