Study of fractal electrode designs for buckypaper-based micro-supercapacitors

Abstract

This work reports the fractal designs of planar interdigital electrodes for buckypaper-based micro-supercapacitors (MSC) and studies their influences on MSC performance for different fractal levels. The fractal designs used in this study were derived from the H-tree structure. The electrodes were realized using a standard lithography process followed by the vacuum-filtration technique. The geometrical complexity of MSC electrodes increases with the level of the fractal structures and possibly results in higher electrical capacitance. The areal capacitance as measured by cyclic voltammetry indicates that the device with the fractal design of Level 3 gives the greatest areal capacitance (18.82 mF/cm2). The measured galvanostatic charge/discharge curves reveal that as the level of the MSC fractal electrode increases the measured areal capacitance increases as well. With a measured current density of 1 mA/cm2, the areal capacitance of the Level-3 fractal-electrode MSC design (17.25 mF/cm2) is 33% greater than that of the standard interdigital-electrode design. A Ragone plot shows that the power density as well as the energy density of MSCs increases with the level of fractal design. Electrochemical impedance spectroscopy measurements are also reported. These measured results confirm that the fractal designs of interdigital electrodes improve the energy-storage performance of MSCs.