Two sets of SnO2-based supercapacitors (SCs) were synthesized and characterized. The first set, typical of double-layer(DL) capacitance, comprises Sb-doped SnO2 nanocrystallites synthesized by a sol-gel process. A surface-grafting technique was introduced to delay grain coarsening. giving rise to a maximum capacitance in 1 M KOH(aq) of 16 F g(-1) (or 64 F cm(-3)). The second set includes composite electrodes consisting of nanocrystalline SnO2 and RuO2 or Fe3O4 nanocrystallites, which are known to exhibit pseudocapacitance. Fe3O4-SnO2 composite electrodes exhibiting a capacitance of 33 F g(-1) (or similar to130 F cm(-3)) at a voltage-sweeping rate of 50 mV s(-1) in 1 M Na2SO4(aq) were demonstrated. (C) 2002 Elsevier Science B.V. All rights reserved.