Nanocrystalline manganese oxides for electrochemical capacitors with neutral electrolytes

With an objective to develop inexpensive electrode materials for electrochemical redox capacitors, nanocrystalline manganese oxides have been synthesized by reducing aqueous KMnO4 solution with various reducing agents such as potassium borohydride, sodium dithionite, sodium hypophosphite, and hydrochloric acid under various controlled pH conditions. The products have been characterized by X-ray diffraction, thermogravimetric analysis, surface area measurements, and cyclic voltametry in various neutral electrolytes such as aqueous NaCl, KCl, LiCl, and Na2SO4. Optimized samples exhibit specific capacitance values of around 250 F/g in the range of 0-1 V vs. SCE with excellent cyclability in 2 M NaCl electrolyte. (C) 2002 The Electrochemical Society.