© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1316 wileyonlinelibrary.com www.MaterialsViews.com www.advenergymat.de FULL PAPER Dong Han Seo, Zhao Jun Han, Shailesh Kumar, and Kostya (Ken) Ostrikov* Structure-Controlled, Vertical Graphene-Based, Binder- Free Electrodes from Plasma-Reformed Butter Enhance Supercapacitor Performance D. H. Seo, Dr. Z. J. Han, Dr. S. Kumar, Prof. K. Ostrikov Plasma Nanoscience CSIRO Materials Science and Engineering P.O. Box 218, Lindfield, New South Wales 2070, Australia E-mail: kostya.ostrikov@csiro.au D. H. Seo, Prof. K. Ostrikov Plasma Nanoscience@Complex Systems School of Physics The University of Sydney New South Wales 2006, Australia DOI: 10.1002/aenm.201300431 1. Introduction Owing to continuous increase in the demand for energy stoarge, supercapcitors have attracted strong attention due to their distinct advantages such as high power density, long life- time, and fast charge and discharge capability. [1,2] Supercapac- itor is an ideal energy storage device to complement or replace batteries and fuel cells in various applications ranging from uninterruptible power supplies, pace- makers, consumer electronics, to hybrid electric vehicles and heavy load levelling. [3] However, for practical usages supercapaci- tors also need to satisfy a few important criteria, including high specific capaci- tance, stable charge and discharge prop- erty, large capacitance retention, as well as cost-efficient and environmentally-friendly fabrication. [4] These criteria to a large extent are determined by the structure, morphology, reactivity and binding of elec- trode materials in the fabrication process. Recently, vertical graphene nanosheets (VGNS) showed great promise as super- capacitor electrodes due to their excel- lent electrical conductivity, large surface area and in particular, an inherent three- dimensional (3D), open network structure with graphene flakes oriented perpen- dicularly to the electrode surface, in con- trast to the horizontal graphene. [5] Such structural and morphological advantages are expected to significantly enhance the capacitive mechanism of charge storage through increased ion diffusivity and ion accessibility. Indeed, previous studies have shown that VGNS-based electrodes had exceptionally high power density and stable performance that are desirable for applications such as miniaturized electronics and alternating current (ac) line filtering. [5–7] However, so far VGNS electrodes have not materialised their promises due to the low specific capacitance, which was only a few times larger than that of the commercial aluminum electrolytic capacitors of a similar size. [5] VGNS are commonly produced using hazardous, expen- sive purified hydrocarbon gases in a high-temperature environ- ment (700–1000 °C) with long fabrication time (20–45 min). It remains unclear on how to control the capacitance by adjusting the structural and morphological features of VGNS in these processes. Moreover, non-conductive polymeric binders are often needed to integrate VGNS and other nano-carbon struc- tures, [8] which inevitably results in increased electrical resist- ance and reduced power and energy densities. On the other hand, performance of carbon-based super- capacitor electrodes can be further improved by integrating metal oxide nanoparticles which store electrical charge through fast and highly reversible surface redox (Faradaic) reactions. [9] Vertical graphene nanosheets (VGNS) hold great promise for high-perfor- mance supercapacitors owing to their excellent electrical transport property, large surface area and in particular, an inherent three-dimensional, open network structure. However, it remains challenging to materialise the VGNS- based supercapacitors due to their poor specific capacitance, high tempera- ture processing, poor binding to electrode support materials, uncontrollable microstructure, and non-cost effective way of fabrication. Here we use a single-step, fast, scalable, and environmentally-benign plasma-enabled method to fabricate VGNS using cheap and spreadable natural fatty precursor butter, and demonstrate the controllability over the degree of graphitization and the density of VGNS edge planes. Our VGNS employed as binder-free supercapacitor electrodes exhibit high specific capacitance up to 230 F g -1 at a scan rate of 10 mV s -1 and >99% capacitance retention after 1,500 charge- discharge cycles at a high current density, when the optimum combination of graphitic structure and edge plane effects is utilised. The energy storage performance can be further enhanced by forming stable hybrid MnO 2 /VGNS nano-architectures which synergistically combine the advantages from both VGNS and MnO 2 . This deterministic and plasma-unique way of fabricating VGNS may open a new avenue for producing functional nanomaterials for advanced energy storage devices. Adv. Energy Mater. 2013, 3, 1316–1323