Curvature
Effects on the Interfacial Capacitance of
Carbon Nanotubes in an Ionic
Liquid
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Abstract
Carbon nanotube (CNT) electrodes
in supercapacitors have recently
demonstrated enhanced performance compared to conventional carbon-based
electrodes; however, the underlying relationships between electrode
curvature and capacitance remain unclear. Using computer simulations,
we evaluate the capacitive performance of metallic (6,6), (10,10),
and (16,16) CNTs in [BMIM][PF<sub>6</sub>] ionic liquid (IL), with
particular attention to the relative contributions of the electric
double layer (EDL) capacitance (<i>C</i><sub>D</sub>) at
the CNT/IL interface and the electrode quantum capacitance (<i>C</i><sub>Q</sub>). Our classical molecular dynamics simulations
reveal that <i>C</i><sub>D</sub> improves with increasing
electrode curvature, which we discuss in terms of how the curvature
affects both the electric field strength and EDL microstructure. In
addition, the <i>C</i><sub>Q</sub> of the CNTs is constant
near the Fermi level and increases with curvature, as also demonstrated
by density functional theory calculations. Our study shows that the
electrode curvature effect on the total interfacial capacitance can
be a strong function of applied voltage, which we attribute to the
shifting contributions of <i>C</i><sub>Q</sub> and <i>C</i><sub>D</sub>