SCHEDULED MAINTENANCE
Green synthesis of vertical graphene nanosheets and their application in high-performance supercapacitors
Abstract
Vertical standing graphene sheets are highly desirable in energy storage applications because without π–π stacking their surface can be fully utilized. In this work, vertical graphene nanosheets (VGS) are successfully synthesized on nickel foam via a simple plasma enhanced chemical vapor deposition (PECVD) technique. Instead of hazardous and costly hydrocarbon gases, we adopt a green approach by using a low-cost, non-toxic, sustainable and environmentally-friendly natural organic material, M. alternifolia essential oil (containing a hydrocarbon monomer), as the precursor. The 4 minute deposition duration results in multilayered horizontal graphene (h-GS) with sparsely distributed vertical graphene while 16 minute deposition leads to fully covered vertical graphene nanosheets (f-VGS). To demonstrate their application as a conductive and high-surface-area substrate in energy storage, MnO2 thin films are hydrothermal grown to form MnO2@f-VGS core–shell structure and MnO2@h-GS. The core@shell electrode of MnO2@f-VGS demonstrates a significantly higher specific capacitance of 203 F g−1 at a current density of 10 A g−1 compared to that of 82 F g−1 at 10 A g−1 shown by MnO2@h-GS. Moreover, the assembled full supercapacitors containing MnO2@f-VGS‖active carbon as electrodes can deliver a reasonably high specific capacitance of 250 F g−1 at 2 A g−1. Such f-VGS may have application also in battery and fuel cell electrodes.
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