A facile method for high yield synthesis of carbon nano onions for designing binder-free flexible supercapacitor

Abstract

Carbon nano onion (CNO) is a promising material for diverse application areas such as energy devices, catalysis, lubrication, biology and gas storage, etc. However, its implementation is fraught with the production of high-quality powders in bulk quantity. Herein, we report a facile scalable and one-step “wick-and-oil” flame synthesis of pure and water dispersible CNO nanopowder. Other forms of carbon did not contaminate the as-prepared CNO; hence, a post processing purification procedure was not necessary. Brunauer Emmett Teller (BET) specific surface area of as-prepared CNO was 218 m2/g, which is higher as compared to other reported flame synthesis methods. Locally available daily used cotton wipe has been used for fabrication of such an ideal electrode by “dipping and drying” process providing outstanding strechability and mechanical flexibility with strong adhesion between CNOs and porous wipe. The specific capacitance 102.16 F/g, energy density 14.18 Wh/kg and power density 2448 W/kg at 20 mV/s scan rate are the highest values that ever recorded and reported so far in symmetrical two electrode cell configuration with 1M Na2SO4 electrolyte; indicating a very good synthesis conditions employed with optimum pore size in agreement with electrolyte ion size. This free standing CNOs electrode also showed an excellent cyclic performance and stability retaining 95% original capacity after 5000 charge –discharge cycles. Simple preparation of high-purity CNOs and excellent electrochemical behavior of functionalized CNOs make them a promising electrode material for supercapacitor applications. Furthermore, this unique method not only affords binder free - freestanding electrode, but also provide a general way of fabricating such multifunctional promising CNOs based nanocomposites for their potential device applications in flexible solar cells and lithium ion batteries.