High supercapacitive stability of spray pyrolyzed ZnO-added manganese oxide coatings

Zinc oxide (ZnO) has recently been reported to exhibit electrochemical supercapacitive properties. We demonstrate, for the first time, a nanocrystalline (<10 nm) composite powder electrochemical supercapacitor in which ZnO-added manganese oxide is used as the active electrode material. The ZnO-added (≤10 at%) manganese oxide powders were prepared from their acetate-based salts by spray pyrolysis (SP) at 500 °C and subsequently coated onto graphite substrates by electrophoretic deposition (EPD) to produce supercapacitor electrodes. XRD data and TEM observation identified the ZnO-added manganese oxide as tetragonal Mn3O4 phase with a nanocrystalline structure. ZnO may dissolve in manganese oxide and inhibit the grain growth of the manganese oxide. Cyclic voltammetry showed that the specific capacitance (SC) of the manganese oxide coating in 1 M Na2SO4 electrolyte increased from 196 F/g to 230 F/g at 25 mV/s for 5 at% ZnO-added manganese oxide. After activation, the cycling efficiency of the composite electrode exhibited a high value of >90% for up to 1200 cycles for all the compositions.