A new form of nanofibre web electrode has been fabricated for a supercapacitor using electrospun polybenzimidazol (PBI)-based activated carbon nanofibres. A PBI solution in dimethyl acetamide (DMAc) is electrospun to a fibre web that consists of 250 nm ultra-fine fibres. The web is successfully activated by steam of 30 vol.% and the specific surface area of the activated web is in the range of 500-1220 m(2) g(-1). The electrochemical properties of electrodes and the capacitive behaviour of the resulting capacitors are systematically studied using cyclic voltammetry, ac impedance and constant-current discharge tests. The specific capacitance ranges from 35 to 202 F g(-1), depending on the activation temperature. The nanofibre web activated at 800 degrees C exhibits the largest specific surface area and results in the highest capacitance. The capacitance of the electrical double-layer capacitor is strongly dependent on the specific surface area, pore volume, and resistivity of the samples. (c) 2004 Elsevier B.V. All rights reserved.