Electrode responsiveness and electrochemical capacitance behavior of nanodiamond-derived carbon nano-onions (N-CNOs) were studied. N-CNOs were prepared by thermal annealing of nanodiamond powders. A thin film of N-CNOs was mounted on glassy carbon (GC) current collector and showed an excellent electrochemical behavior with rectangular voltammetric curves as well as great scan rate dependence of capacitance. The capacitance showed negligible drops over a wide range of scan rates (50 mV/s - 5 V/s) in both KCl and H2SO4. This excellent capacitive behavior was attributed to good electrical conductivity and mesoporous nature of N-CNOs. In order to further enhance capacitance, electrochemical oxidation of N-CNOs was carried out by iterating anodic cycling in acidic electrolytes. The capacitance enhancement of oxidized N-CNOs was probed by cyclic voltammetry as well as galvanostatic charging-discharging measurement. This study demonstrates that electrochemical oxidation can be an effective method to improve capacitance and energy density of carbon nanomaterials while maintaining a good scan rate performance. (C) 2014 Elsevier Ltd. All rights reserved.