Abstract
Transition metal oxides with high theoretic capacities are promising materials as battery-type electrodes for hybrid supercapacitors, but their practical applications are limited by their poor electric conductivity and unsatisfied rate capability. In this work, a hybrid structure of CoO nanowires coated with conformal polypyrrole (Ppy) nanolayer is proposed, designed and fabricated on a flexible carbon substrate through a facile two-step method. In the first step, porous CoO nanowires are fabricated on flexible carbon substrate through a hydrothermal procedure combined with an annealing process. In the second step, a uniform nanolayer of Ppy is further coated on the surfaces of the CoO nanowires, resulting in a hybrid core-shell CoO@Ppy nanoarrays. The CoO@Ppy aligned on carbon support can be directly utilized as electrode material for hybrid supercapacitors. Since the conductive Ppy coating layer provides enhanced electric conductivity, the hybrid electrode demonstrates much higher capacity and superior rate capability than pure CoO nanowires. As a further demonstration, Ppy layer can also be realized on SnO2 nanowires. Such facile conductive-layer coating method can be also applied to other types of conducting polymers (as the shell) and metal oxide materials (as the core) for various energy-related applications.
Highlights
Recent years have witnessed the fast-growing requirements for clean energy and ever-growing costume demands are constantly driving research attentions to sustainable energy storage devices with better performance
Among the candidates for hybrid supercapacitors, carbonaceous materials, including carbon nanotubes, graphene and active carbon, could provide high electric conductivity with good chemical stability and stable cycling ability; they only store charges at their surfaces cannot provide high capacitance with high energy density [6,7,8,9]. As another type of electrode materials, transition metal oxides used as battery-type electrodes have much higher theoretical capacities based on redox reaction mechanism; their poor electric conductivity limit the wide applications of transition metal oxides [10,11,12,13,14,15,16]
Several strategies have been applied for the enhancement of the electrochemical performance of transition metal oxides, among which a promising way is the construction of nanostructured metal oxides with high specific surface areas, because the large surface-to-bulk ratio provides more sufficient sites for the effective electrochemical reaction between the electrode material and the electrolyte ions [17,18,19,20]
Summary
Recent years have witnessed the fast-growing requirements for clean energy and ever-growing costume demands are constantly driving research attentions to sustainable energy storage devices with better performance. Among the candidates for hybrid supercapacitors, carbonaceous materials, including carbon nanotubes, graphene and active carbon, could provide high electric conductivity with good chemical stability and stable cycling ability; they only store charges at their surfaces cannot provide high capacitance with high energy density [6,7,8,9]. As another type of electrode materials, transition metal oxides used as battery-type electrodes have much higher theoretical capacities based on redox reaction mechanism; their poor electric conductivity limit the wide applications of transition metal oxides [10,11,12,13,14,15,16]. Core-shell structured electrodes of MnO2@Ppy, MoS2/Polyaniline and SnO2@PEDOT have been fabricated and demonstrated to effectively integrate the advantages of each single component with enhanced electrochemical performance [22,23,24,25]
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