Silver Nanoparticle-Induced Growth of Nanowire-Covered Porous MnO2 Spheres with Superior Supercapacitance

We report a facile, low-cost, ultrasound-assisted synthesis of nanowire-covered porous MnO 2 spheres with superior supercapacitance at high charging rates with long-term durability. The use of catalytic silver nanoparticles is crucial to the growth mechanism in the initial stage, and the resulting silver oxides later grow the nanowires in such a way that they always terminate the wires, thus automatically covering the structures and increasing conductivity. The optimal Ag 2 O–MnO 2 structures have a specific capacitance of 536.4 F/g at 5 mV/s. At a high scan rate of 100 mV/s, only 200 F/g remain for the reported carbon nanotube/MnO 2 material with an excellent capacitance at low scan rate (1230 F/g, 1 mV/s), while the Ag 2 O–MnO 2 reported here still has 417.2 F/g. The material reaches a stable region of 91.3% capacitance retention over 10000 charge/discharge cycles at 5 A/g.