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

• Ag quantum dots are assembled on the surface of mesoporous NiMoO 4 microspheres. • Ohmic contact interface boosts the conductivity of the composite material. • Synergistic effects dramatically enhance the specific capacitance of the electrode. • The asymmetric supercapacitor shows high energy density and cycling stability. Nickel molybdate (NiMoO 4) as a ternary metal oxide has great potential as advanced electrode material for energy storage. However, the practical application of NiMoO 4 electrode is hindered by its poor electrical conductivity. In this work, the surface of mesoporous NiMoO 4 microspheres is decorated with silver quantum dots (Ag QDs/NiMoO 4) 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 NiMoO 4 microsphere. Benefitting from the high specific surface area, abundant surface active sites, enhanced interfacial conductivity and porous structure of the Ag QDs/NiMoO 4 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 NiMoO 4 microsphere electrode), good rate capability and improved cycling stability. Furthermore, an asymmetric supercapacitor assembled with the Ag QDs/NiMoO 4 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 NiMoO 4 -based asymmetric supercapacitors. [ABSTRACT FROM AUTHOR]