The capacitive charge storage of carbon nanotube (CNT) based electrodes was investigated by acelectrogravimetrywhich couples fast quartz crystal microbalance (QCM) and electrochemical impedance spectroscopy(EIS). In contact with an aqueous NaCl electrolyte, evidence was found that there are two types of cations(Na+·H2O and H+) electroadsorbed with different kinetics for cathodic potentials and the Cl− ions for
anodic potentials together with free water molecules. The reconstruction of the total mass response from independent ac-electrogravimetry measurements agrees perfectly wellwith the global EQCMresponse. Our findingsreveal the unique sensitivity of the ac-electrogravimetry to provide a fair gravimetric and dynamic deconvolution of the global EQCM responses.