Asymmetric Supercapacitors Based on Reduced Graphene Oxide with Different Polyoxometalates as Positive and Negative Electrodes.

Nanofabrication using a "bottom-up" approach of hybrid electrode materials into a well-defined architecture is essential for next-generation miniaturized energy storage devices. This paper describes the design and fabrication of reduced graphene oxide (rGO)/polyoxometalate (POM)-based hybrid electrode materials and their successful exploitation for asymmetric supercapacitors. First, redox active nanoclusters of POMs [phosphomolybdic acid (PMo ) and phosphotungstic acid (PW )] were uniformly decorated on the surface of rGO nanosheets to take full advantage of both charge-storing mechanisms (faradaic from POMs and electric double layer from rGO). The as-synthesized rGO-PMo and rGO-PW hybrid electrodes exhibited impressive electrochemical performances with specific capacitances of 299 (269 mF cm ) and 370 F g (369 mF cm ) in 1 m H SO as electrolyte at 5 mA cm . An asymmetric supercapacitor was then fabricated using rGO-PMo as the positive and rGO-PW as the negative electrode. This rGO-PMo ∥rGO-PW asymmetric cell could be successfully cycled in a wide voltage window up to 1.6 V and hence exhibited an excellent energy density of 39 Wh kg (1.3 mWh cm ) at a power density of 658 W kg (23 mW cm ).