Mesoporous carbon spheres grafted with carbon nanofibers for high-rate electric double layer capacitors

Carbon nanofibers were grafted onto mesoporous carbon spheres to produce “sea urchin-like” mesoporous carbon with a nanofiber content of 25 wt.%. Because of its combined features of high electronic conductivity and efficient electrolyte transport, the sea urchin-like mesoporous carbon assembled in electric double layer capacitors shows outstanding high-rate performance with a voltammetric scan rate as high as 3000 mV s⁻¹. Ac impedance analysis shows that this method of carbon nanofiber grafting promotes electronic percolation and ionic transportation in the carbon electrode, reducing the capacitive relaxation time to less than one fourth of its original value. Electrochemical oxidation in sea urchin-like mesoporous carbon produces a capacitance increase of ca. 200% while retaining high electronic and ionic conductivities in the electrode.