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 (PMo12) and phosphotungstic acid (PW12)] 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-PMo12 and rGO-PW12 hybrid electrodes exhibited impressive electrochemical performances with specific capacitances of 299 (269 mF cm−2) and 370 F g−1 (369 mF cm−2) in 1 m H2SO4 as electrolyte at 5 mA cm−2. An asymmetric supercapacitor was then fabricated using rGO-PMo12 as the positive and rGO-PW12 as the negative electrode. This rGO-PMo12∥rGO-PW12 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 (1.3 mWh cm−3) at a power density of 658 W kg−1 (23 mW cm−3).