1. Lithographically Patterned Gold/Manganese Dioxide Core/Shell Nanowires for High Power Supercapacitors – Electrochemical and Raman Spectroscopic Characterization

MnO2 is the most investigated transition metal oxide electrode material for supercapaitor applications because of its intriguing features including natural abundance, low cost, and high theoretical specific capacitance (1370 F g−1). The theoretical specific capacitance has rarely been achieved in bulk MnO2 limited by the poor electrical conductivity and limited surface area. Hence there is a rapidly growing interest in developing nanosized MnO2 electrode materials to increase the surface area. In this project, a symmetrical MnO2 based hybrid capacitor consisting of interdigitated, horizontal nanowires is fabricated. The nanowires within the capacitor consists of a gold nanowire core encapsulated within a hemicylindrical shell of δ-phase MnO2. These Au@δ-MnO2 nanowires are patterned onto a planar glass surface using lithographically patterned nanowire electrodeposition (LPNE). A power density of 165 kW/kg and energy density of 24 Wh/kg were obtained for a typical nanowire array in which the MnO2 shell thickness was 68 ± 8 nm. Capacitors incorporating these ultralong nanowires lost ≈10% of their capacity rapidly, during the first 20 discharge cycles, and then retained 90% of their maximum capacity for the ensuing 6000 cycles. It has been demonstrated that ultralong Au@δ-MnO2 nanowires can simultaneously deliver high power and high capacity with acceptable cycle life.