MnO₂/Poly(3,4-ethylenedioxythiophene) Coaxial Nanowires by One-Step Coelectrodeposition for Electrochemical Energy Storage

Abstract

One-dimensional (1D) nanostructured materials have been intensively investigated as building components in electrochemical energy storage 1 and solar energy conversion 2 devices because they provide short diffusion path lengths to ions and excitons, leading to high charge/discharge rates 1 and high solar energy conversion efficiency. 2 More recently, coaxial nanowires have attracted greater attention in this field due to their added synergic properties (e.g., high conductivity) 3a or functionalities (e.g., core/shell p-n junction) 3b,c arising from the combination of different materials. 3 Various materials such as semiconductor/semiconductor, metal/ metal oxide, and metal oxide/metal oxide, have been employed as core/shell in coaxial nanowires. 3 However, there have been few studies on the coaxial nanowires with transition metal oxide and conductive polymer, although both of them are important electroactive materials used in electrochemical energy storage. 4 The combination of these two materials at 1D nanostructures may exhibit excellent electrical, electrochemical, and mechanical properties for electrochemical energy storage. To date, only a few reports have been published on the synthesis of metal oxide/ conductive polymer with core/shell structures. 5 In all of these reports, a stepwise synthetic approach was adopted: metal oxide nanoparticles, 5a nanostrands, 5b or nanotubes 5c were first synthesized and subsequently coated chemically by conductive polymers as shells.In this paper, we introduce a simple one-step method to synthesize MnO 2 /poly(3,4-ethylenedioxythiophene) (PEDOT) coaxial nanowires by coelectrodeposition in a porous alumina template. 6 MnO 2 is one of the most popular electrochemical energy storage materials because of its high energy density, low cost, environmental friendliness, and natural abundance, 7 but it has poor conductivity. 4c PEDOT has merits of excellent conductivity, high stability, and mechanical flexibility, 8 but it provides low electrochemical energy density. Electrodeposition is used here because it is a simple yet versatile method in controlling structures and their composition by tuning applied potentials and electrolyte ingredients. 9 In this report, MnO 2 /PEDOT coaxial nanowires are found to be promising electrochemical energy storage materials. The core MnO 2 provides high energy storage capacity, while the highly conductive, porous, and flexible PEDOT shell facilitates the electron transport and ion diffusion into the core MnO 2 and protects it from structurally significant collapsing and breaking. These combined properties enable the coaxial nanowires to have very high specific capacitances at high current densities.Scheme 1 illustrates the growth of MnO 2 /PEDOT coaxial nanowires. Under a constant potential (typically 0.75 V vs Ag/ AgCl), Mn 2+ (10 mM manganese acetate) is converted to its higher oxidization state, which can readily undergo hydrolysis to yield MnO 2 . 7 Simultaneously, EDOT monomer (80 mM) is electropolymerized into PEDOT in the pores of t...

Highly conductive poly(3,4-ethylenedioxypyrrole) and poly(3,4-ethylenedioxythiophene) enwrapped Sb2S3nanorods for flexible supercapacitors

“…12 In yet another study, a specific capacitance of 210 F g À1 was achieved for coaxial MnO 2 -PEDOT nanowires. 13 Our values are comparable to literature values for conducting polymer nanostructured electrodes. The rate capability of the neat polymer and composite based cells was determined by recording the charge-discharge curves at different current densities of 0.2, 0.4, 0.6 and 1 A g À1 ( Fig.…”

Graphene/polymer composites for energy applications

“…In comparison, the distance of two oxygen atoms in the six-atom ring of PEDOT is around 2.94 Å, equal to the distance between two manganese atoms in the (001) face of MnO 6 octahedra in LMO. 127,128 Furthermore, the affinity of manganese atoms for oxygen atoms is stronger than that for carbon atoms because of their native electron characteristics. Thus, the PEDOT component induced the formation of MnO 2 nanostructures on graphene sheets.…”

Functionalized polypyrrole nanotube arrays as electrochemical biosensor for the determination of copper ions

“…The generally used two types of templates are track-etched polymeric membranes and porous anodic aluminum oxide (AAO) membranes [15,16]. The templates especially attracted extensive interest due to their uniform pore diameters and ordered porous distribution [17]. However, upon removal of the templates the CP nanoarrays collapse onto the substrate, losing their orientation.…”