Effects of pore diameters on the pseudocapacitive property of three-dimensionally ordered macroporous manganese oxide electrodes

MnO2 nanoparticles (NPs) with 1.8 +/- 0.2 nm in diameter were successfully produced using an ethylene glycol-assisted synthesis with successive hydrolysis and condensation reactions. The tiny NPs were used as precursors for producing three-dimensionally ordered macroporous (3DOM) electrodes using a colloidal crystal-templating method. The specific capacitances of 3DOM MnO2 electrodes depend on their pore diameters. The 3DOM electrode with about 200-nm pore diameter provides 3.0-, 2.0-, and1.3-fold higher specific capacitance than the dense film and the 3DOM electrodes with larger pores, 400 nm and 900 nm, respectively. The ultrahigh specific capacitance of the 200-nm 3DOM electrode is 765 F g(-1) measured in 0.5 M Na2SO4 at the scan rate of 2 mV s(-1). In addition, the capacity retention of the 200-nm 3DOM electrode is over 98% of the original capacitance after 2000 cycles while that of the dense film is only 78%. (C) 2011 Elsevier B.V. All rights reserved.