Ferrites including MFe2O4 where M = Mn, Fe, Co, or Ni have been synthesized by solution methods and tested for their capacitive behaviors in aqueous NaCl solution. MnFe2O4 has been found to exhibit unusually large capacitances, while the other ferrites do not. The results indicate unique pseudocapacitive property associated with the Mn+2 ions at the tetrahedral sites in the spinel structure. The pseudocapacitance was observed only for crystalline, rather than amorphous, MnFe2O4 phase, which has exhibited specific capacitances of > 100 F/g and high-power delivering capabilities of > 10 kW/ kg. (c) 2005 The Electrochemical Society.