Nitrogen-rich hollow carbon spheres decorated with FeCo/fluorine-rich carbon for high performance symmetric supercapacitors

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2018, Vol.6 (17), p.7522-7531
• Main Authors: Karuppannan, Mohanraju, Kim, Youngkwang, Sung, Yung-Eun, Kwon, Oh Joong
• Format: Article
• Language: English
• Subjects: Capacitance; Carbon; Chemical synthesis; Cobalt; Copolymerization; Dipole interactions; Electronegativity; Energy storage; Etching; Fluorine; Flux density; Iron; Maximum power density; Metals; Nitrogen; Polymerization; Shells; Silicon dioxide; Supercapacitors; X ray photoelectron spectroscopy
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c8ta00028j

A novel approach to fluorine-rich carbon (FC) shell formation on an electron-rich metal surface based on the electronegativity concept is reported. Basically, highly electronegative elements are strongly attracted by low electronegative/electron-rich elements through dipole interaction, which leads to the formation of fluorine-rich carbon shells on metals at various fluorine quantities. Herein, nitrogen-rich hollow carbon spheres decorated with fluorine-rich carbon shell covered metals (FC@M/NHCS, M = Fe, Co, and FeCo) were synthesized by co-polymerization on SiO 2 , adsorption of metal precursors, and etching of the SiO 2 , followed by sintering. The fluorine content, quantified by XPS and SEM-EDS studies, decreased according to FeCo > Fe > Co in FC@M/NHCS. HAADF-STEM elemental mapping studies clearly confirmed fluorine-rich carbon shell formation on the metal surface. The influence of fluorine content order in the as-synthesized materials was reflected in their capacitance performances. FC@FeCo/NHCS electrode depicted the maximum specific capacitance of 302.0 F g −1 at 0.2 A g −1 in 6 M KOH medium, delivering excellent stability with no losses over 5000 cycles at 5 A g −1 . The symmetric supercapacitor (SSC) devices operated at 1.5 V by delivering maximum device specific capacitance of 51.2 F g −1 at 0.2 A g −1 . It exhibited 81.3% of capacitance retention at 10 A g −1 with the FC@FeCo/NHCS. The maximum energy density of 15.3 W h kg −1 at 0.2 A g −1 and the maximum power density of 5100 W kg −1 at 10 A g −1 were delivered by the FC@FeCo/NHCS device. This study provides an ideal way for synthesizing fluorine-rich carbon materials for high energy storage/conversion applications. A novel investigation was performed on fluorine-rich carbon shell formation on metal (Fe/Co/FeCo) surfaces and their contribution to capacitance enhancement was evaluated.