MnO2/Poly(3,4-ethylenedioxythiophene) coaxial nanowires by one-step coelectrodeposition for electrochemical energy storage

We introduce a simple one-step method to synthesize MnO2/poly(3,4-ethylenedioxythiophene) (PEDOT) coaxial nanowires by coelectrodeposition in a porous alumina template. Constant potential (typically 0.75 V vs Ag/AgCl) is applied on the bottom electrodes in the pores of the alumina template in aqueous solution containing manganese acetate (10 mM) and EDOT monomers (80 mM). We can easily control the structures of coaxial nanowires such as PEDOT shell thickness and nanowire length by varying the applied potential. Electrochemical properties of the coaxial nanowires were investigated for an electrochemical supercapacitor. Coaxial nanowires not only exhibit high specific capacitance values but also maintain them well at high current density. The well-maintained specific capacitance is mainly due to short paths of ion diffusion in the nanowires. Therefore, even at high current density (high power demand), the nanowire materials can be fully utilized. The porous nature of the PEDOT shell allows such fast ion diffusion into the core MnO2 of the coaxial nanowires. In addition, the highly electrical conductive PEDOT shell facilitates electron transport to the core MnO2, which has low conductivity that can limit its charge/discharge rate. As a consequence, the coaxial nanowires preserved 85% of their specific capacitance (from 210 to 185 F/g) as the current density increases from 5 to 25 mA/cm(2).