3 years ago

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

Asymmetric Supercapacitors Based on Reduced Graphene Oxide with Different Polyoxometalates as Positive and Negative Electrodes
Ajayan Vinu, Nilesh R. Chodankar, Deepak P. Dubal, Do-Heyoung Kim, Pedro Gomez-Romero
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). Twins, but not twins: Polyoxometalates (POMs) can exhibit high energy density for supercapacitors (SCs) due to rapid and reversible multielectron redox reactions. On the other hand, the energy storing capacity can be also increased by extending the operating voltage boundary of the device by creating an asymmetric SC. Both of these strategies are combined herein: reduced graphene oxide (rGO) is combined with either PMo12 to be used as positive electrode or with PW12, which is used as negative electrode.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/cssc.201700792

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