Carbon nano-onions (NCNOs), concentrically multilayered
fullerenes,
are among the least studied carbon allotropes. NCNOs have high surface
area, high mesoporosity, facile electrical conductivity, and electrochemical
stability. NCNOs are chemically oxidized (ONCNOs) to introduce hydrophilic
functional groups, improving their wettability for use in supercapacitor
electrodes. RuO2·xH2O/ONCNOs
composites are prepared by chemical precipitation of RuO2 on ONCNOs, optimized for homogeneous distribution and maximum utilization
of the metal oxide nanoparticles. The materials are characterized
by high-resolution transmission electron microscopy, N2 absorption–desorption isotherm, and thermogravimetric analysis.
Electrochemical performance of the electrodes is studied by cyclic
voltammetry, galvanostatic charge–discharge, and electrochemical
impedance measurements in 1.0 M H2SO4. While
ONCNOs have specific capacitance of 45 F·g–1, a composite with 67.5 wt.% RuO2 has specific capacitance
of 334 F·g–1 at a potential sweep rate of 20
mV·s–1 with high power (242.8 kW·kg–1) and high energy density (11.6 Wh·kg–1). Both the ONCNO and the composites show excellent capacitance behaviors
even at very high potential scan rates (>8 V·s–1). Simple preparation of high-purity NCNOs and excellent electrochemical
behavior of functionalized NCNOs make them a promising electrode material
in supercapacitor applications.
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