Nanocrystalline oxide supercapacitors

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 ∼130 F cm−3), at a voltage-sweeping rate of 50 mV s−1 in 1 M Na2SO4(aq) were demonstrated.