Synthesis of carbon nano-onion and nickel hydroxide/oxide composites as supercapacitor electrodes

Abstract

“Small” carbon nano-onions (CNOs) are spherical, ca. 5 nm in diameter, concentric shells of graphitic carbon that can be also described as multi-shelled fullerenes. Given the easy functionalization and high thermal stability of the CNOs produced from nanodiamond, they are the most obvious choice for studying the potential applications of these multi-shelled fullerenes in electrochemical supercapacitors (ES). Since limited accessibility of the carbon surface to electrolyte penetration is observed for carbon nano-onions, performance enhancement was accomplished by modifying the CNO surfaces with pseudocapacitive redox materials: Ni(OH)₂ and NiO. These composites were characterized by TEM, SEM, XRD, TGA-DTG-DTA and Raman spectroscopy. The electrochemical properties of these composites were also investigated. Compared with pristine CNOs (30.6 F g⁻¹ at 5 mV s⁻¹), modified CNOs (1225.2 F g⁻¹ for CNOs/Ni(OH)₂ and 290.6 F g⁻¹ for CNOs/NiO, both at 5 mV s⁻¹) show improved electrochemical performance, promising for the development of supercapacitors.