Two samples of commercial multi-walled carbon nanotubes (Sigma–Aldrich and Sun Nanotech) and a sample of carbon black (Vulcan XC-72R) were investigated in raw state and after the activation in nitric and sulfuric acid by ultrasound agitation. Atomic force microscopy revealed that activated Sigma–Aldrich nanotubes are straight with corrugated walls (bamboo-like structure), while Sun Nanotech nanotubes are tortuous with smooth walls. Fourier transform infrared spectroscopy showed that abundance of oxygen-containing functional groups was formed on both Sigma–Aldrich and Sun Nanotech carbon nanotubes, as well as on carbon black surfaces. Electrochemical properties were studied by cyclic voltammetry and electrochemical impedance spectroscopy. It was found that the electrochemically active surface area of all carbon samples is expanded, charge storage ability is enhanced and the electron-transfer kinetics, probed by Fe ( CN ) 6 3 - / Fe ( CN ) 6 4 - redox couple, is promoted upon activation. The characteristics of carbon nanotubes were superior to carbon black. Morphology of the carbon nanotubes was found to be important; nanotubes with corrugated walls showed faster electron-transfer and pseudocapacitive redox kinetics than nanotubes with smooth walls. This was explained by the higher proportion of edge and defect sites, which are known as more electrochemically active than the walls of uniform graphene structure.