IISER team makes supercapacitors of graphene to replace car batteries, page-2

High-Level Supercapacitive Performance of Chemically Reduced Graphene Oxide

mce-anchorPlawan Kumar Jha
,
mce-anchorSantosh Kumar Singh
,
mce-anchorVikash Kumar
,
mce-anchorShammi Rana
,
mce-anchorSreekumar Kurungot
,
mce-anchorNirmalya Ballav^4,mce-anchorCorrespondence information about the author Nirmalya BallavEmail the author Nirmalya Ballav
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DOI: http://dx.doi.org/10.1016/j.chempr.2017.08.011





Highlights

• •Reduction of graphene oxide by a non-conventional and recyclable reducing agent
• •Slow reduction kinetics lead to optimally healed reduced graphene oxide
• •Higher specific capacitance values than with conventional reducing agents
• •Organic electrolyte boosts energy and power density of supercapacitors

The Bigger Picture

Electrode materials of commercial supercapacitors are mostly made of activated carbons, offering insufficient capacitance at high cost. Graphene-based materials with characteristic electrical double-layer capacitance (EDLC) are emerging as smart alternatives. Hybrids of EDLC and pseudocapacitance are being explored for boosting the overall performance. However, the cycling stability of such hybrid supercapacitors is often far below 100,000 cycles. Here, we report an unconventional approach to producing reduced graphene oxide (rGO), which can be readily used as an active material for the fabrication of supercapacitor electrodes. The reducing agent can be easily recycled for subsequent feeds of graphene oxide (GO) reduction. The impressive performance of our as-synthesized rGO in all-solid-state-supercapacitor applications holds promise for translation to the industrial level. The potential window was also increased up to 2.5 V with the use of organic electrolyte.
Summary

Reduction of graphene oxide (GO) is an important process because it holds promise for the production of reduced graphene oxide (rGO) with physicochemical properties similar to those of pristine graphene. In conventional chemical reduction, strong reducing agents, such as sodium borohydride and hydrazine, cannot be recycled. Also, fast reaction kinetics bring an imbalance in the desirable properties of rGO. Here, we present one-pot chemical reduction of GO in aqueous medium by an unconventional mild reducing agent (FeCl₂/HCl) where rGO is isolated as the precipitate and the reducing agent is recycled upon simple treatment of the filtrate with HCl. The fabricated all-solid-state supercapacitors of as-synthesized rGO exhibited significantly higher specific capacitance than those obtained with rGO derived from conventional reducing agents. The cycling stability of the all-solid-state supercapacitor (>80% retention of capacitance beyond 100,000 continued cycles) and its flexibility (>500 bending cycles) were remarkable. Use of commercially available organic electrolyte further boosted the supercapacitor performance.

http://www.cell.com/chem/fulltext/S2451-9294(17)30358-3


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