Abstract
Herein, we report a simple hydrothermal method to synthesize CeO2/Ce2O3 quantum dots anchored on reduced graphene oxide (RGO) sheets of different weight fractions for application as supercapacitor electrode. Of all the tested samples, the one containing 7 wt% RGO (CRGO3) as measured by thermogravimetry, exhibited the highest specific capacitance of 1027 F/g at 1 A/g along with good cycling stability. At current density of 4 A/g, the CRGO3 sample showed charge retention of 79% after 5000 cycles, whereas at 20 A/g, it showed 85% charge retention after 3000 cycles. The values obtained for CRGO3 electrode are better than all previous ceria and RGO based electrode suggesting its potential use in supercapacitor. High resolution transmission electron microscopy (HRTEM) revealed well crystalline CeO2 nanoparticles (similar to 5 nm) uniformly distributed on the RGO sheets as well as few lattice planes indicative of presence of some Ce2O3 mixed with CeO2. X-ray photoelectron spectroscopy (XPS) revealed presence of a mixed oxides containing mostly CeO2 with some Ce2O3 phase on the surface. The enhanced performance of the CRGO3 electrode was attributed to the optimized weight fraction and large surface area of electrically conducting RGO combined with enhanced electrocatalytic activity of CeO2/Ce2O3 mixed oxides.