Asymmetric capacitors composed of carbon electrodes with different pore size distributions (PSD) were constructed in order to study the fundamental relationship between the PSD of positive and negative carbon electrodes and the performance of electric double layer capacitors. The performance of asymmetric capacitors in a non-aqueous electrolyte solution (TEMA-BF4/PC) was found to be governed by the PSD of the carbon used in the negative electrode. Capacitance depends on the BET surface area of the negative electrode and the rate performance depends on its mesoporous surface area. These results were explained by the fact that it is more difficult to adsorb large solvated cations (TEMA(+)) in micropores (less than 2 nm wide) than in mesopores (2-50 nm wide), and that this is more difficult with a higher rate of charge-discharge. (C) 2007 Elsevier Ltd. All rights reserved.