One pot low-temperature growth of hierarchical δ-MnO2 nanosheets on nickel foam for supercapacitor applications

Hierarchical delta-MnO2 nanosheets as electroactive materials have been directly deposited on nickel foam substrate by one-pot chelation-mediated aqueous method. The morphological evolution process has been investigated by scanning electron microscopy (SEM) at different time intervals in detail. The hierarchical delta-MnO2 electrodes which are synthesized at 30 degrees C, 40 degrees C and 50 degrees C are directly served as binder- and conductive-agent-free electrodes for supercapacitors and have been explored by cyclic voltammetry, galvanostatic charge-discharge test and electrochemical impedance spectroscopy. With the decrease of reaction temperature the specific capacitance of delta-MnO2 electrode increases. The vertically aligned delta-MnO2 nanosheets which have been synthesized at 30 degrees C exhibit a highest capacitance of 325 Fg(-1) at the current density of 1 Ag-1. The capacitance loss is less than 15% after 1000 cycles at the scan rate of 30 mVs(-1). Furthermore, it is found that the equivalent series resistance and charge transfer resistance of the electrode are 0.36 Omega and 1.7 Omega, respectively. Such superior electrochemical performance of the electrode made by directly growing porous delta-MnO2 nanosheets on nickel foam makes it has very promising applications in high-performance supercapacitors. (C) 2015 Elsevier Ltd. All rights reserved.