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C 2017, 3(3), 24; doi:10.3390/c3030024

Functionalized Graphene–Polyoxometalate Nanodots Assembly as “Organic–Inorganic” Hybrid Supercapacitors and Insights into Electrode/Electrolyte Interfacial Processes

1
Department of Physics and Astronomy, Western Kentucky University, 1906 College Heights Blvd, Bowling Green, KY 42101, USA
2
Department of Chemistry, Western Kentucky University, 1906 College Heights Blvd, Bowling Green, KY 42101, USA
3
Department of Electrical Engineering, Western Kentucky University, 1906 College Heights Blvd, Bowling Green, KY 42101, USA
*
Author to whom correspondence should be addressed.
Received: 2 July 2017 / Revised: 15 July 2017 / Accepted: 24 July 2017 / Published: 28 July 2017
(This article belongs to the Special Issue Carbon Hybrid Materials)
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Abstract

The stable high-performance electrochemical electrodes consisting of supercapacitive reduced graphene oxide (rGO) nanosheets decorated with pseudocapacitive polyoxometalates (phosphomolybdate acid-H3PMo12O40 (POM) and phosphotungstic acid-H3PW12O40 (POW)) nanodots/nanoclusters are hydrothermally synthesized. The interactions between rGO and POM (and POW) components create emergent “organic–inorganic” hybrids with desirable physicochemical properties (specific surface area, mechanical strength, diffusion, facile electron and ion transport) enabled by molecularly bridged (covalently and electrostatically) tailored interfaces for electrical energy storage. The synergistic hybridization between two electrochemical energy storage mechanisms, electrochemical double-layer from rGO and redox activity (faradaic) of nanoscale POM (and POW) nanodots, and the superior operating voltage due to high overpotential yielded converge yielding a significantly improved electrochemical performance. They include increase in specific capacitance from 70 F·g−1 for rGO to 350 F·g−1 for hybrid material with aqueous electrolyte (0.4 M sodium sulfate), higher current carrying capacity (>10 A·g−1) and excellent retention (94%) resulting higher specific energy and specific power density. We performed scanning electrochemical microscopy to gain insights into physicochemical processes and quantitatively determine associated parameters (diffusion coefficient (D) and heterogeneous electron transfer rate (kET)) at electrode/electrolyte interface besides mapping electrochemical (re)activity and electro-active site distribution. The experimental findings are attributed to: (1) mesoporous network and topologically multiplexed conductive pathways; (2) higher density of graphene edge plane sites; and (3) localized pockets of re-hybridized orbital engineered modulated band structure provided by polyoxometalates anchored chemically on functionalized graphene nanosheets, contribute toward higher interfacial charge transfer, rapid ion conduction, enhanced storage capacity and improved electroactivity. View Full-Text
Keywords: functionalized graphene hybrids; polyoxometalates; hydrothermal; pseudocapacitors; scanning electrochemical microscopy; modeling functionalized graphene hybrids; polyoxometalates; hydrothermal; pseudocapacitors; scanning electrochemical microscopy; modeling
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Gupta, S.; Aberg, B.; Carrizosa, S.B. Functionalized Graphene–Polyoxometalate Nanodots Assembly as “Organic–Inorganic” Hybrid Supercapacitors and Insights into Electrode/Electrolyte Interfacial Processes. C 2017, 3, 24.

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