Electrochemical Capacitors Fabricated with Tin Oxide/Graphene Oxide Nanocomposites

We report the high specific capacitance, superior rate capability, and excellent cyclic stability of reduced graphene oxide (rGO) nanosheets decorated with SnO2 nanocrystals as electrode materials for electrochemical capacitors (ECs). A pulse microwave-assisted deposition method is adopted to grow SnO2 crystals, which are homogeneously inserted into the rGO sheets, forming SnO2/rGO composites. The specific capacitance of the ECs fabricated with the SnO2/rGO composites can reach 348 F g(-1) at a current density of 50 mA g(-1), showing an increase of up to 98% in comparison with that of a fresh rGO electrode. This enhanced capacitance can be attributed to the fact that the SnO2 crystals not only serve as spacers to create more active sites on the rGO surface but also maximize the fraction of hydrophilic surface, which is more accessible for the formation of the electric double layer. The maximal energy density of the SnO2/rGO electrode is maintained at 32.2 Wh kg(-1) with a power density of 1000 W kg(-1), according to the analysis of the Ragone plot. Impedance spectroscopy incorporated with an equivalent circuit reveals that the decoration of SnO2 crystals allows the decrease in the equivalent series resistance, which originated from the creation of a three-dimensional architecture for charge transfer and good electrical connection to the flexible substrate. Accordingly, the graphene-based composites by intercalating SnO2 nanocrystals into rGO sheets have proven to be promising electrode materials for EC applications.