Mesoporous NiMoO4 microspheres decorated by Ag quantum dots as cathode material for asymmetric supercapacitors: Enhanced interfacial conductivity and capacitive storage

Nickel molybdate (NiMoO4) as a ternary metal oxide has great potential as advanced electrode material for energy storage. However, the practical application of NiMoO4 electrode is hindered by its poor electrical conductivity. In this work, the surface of mesoporous NiMoO4 microspheres is decorated with silver quantum dots (Ag QDs/NiMoO4) by means of dipping and drying. It is interesting to find that an ohmic contact interface (electron anti-barrier layer) generates between the Ag QDs and NiMoO4 microsphere. Benefitting from the high specific surface area, abundant surface active sites, enhanced interfacial conductivity and porous structure of the Ag QDs/NiMoO4 microspheres, the composite electrode presents high specific capacitance of 3342.7 F g(-1) at 1 mV s(-1) and 2074 F g(-1) at 1 A g(-1) (nearly twice the value of the pristine mesoporous NiMoO4 microsphere electrode), good rate capability and improved cycling stability. Furthermore, an asymmetric supercapacitor assembled with the Ag QDs/NiMoO4 microspheres as cathode, spore-derived activated carbon microspheres as anode and 3 M KOH as aqueous electrolyte, reveals a relatively high energy density (48.5 Wh kg(-1) at a power density of 212.5 kWh kg(-1)) and good cycling performance comparing with most of the reported NiMoO4-based asymmetric supercapacitors.