High-energy aqueous Li-ion hybrid capacitor based on metal-organic-framework-mimicking insertion-type copper hexacyanoferrate and capacitive-type graphitic carbon electrodes

A high-performance aqueous Li-ion hybrid capacitor (LHC) using sonochemically prepared copper hexacyanoferrate (Cu-HCF) and sodium alginate-derived graphitic carbon (GC) nanoparticles are capable of serving as positive and negative electrodes, respectively, is described in this report. The electrode materials were prepared in a cost-effective manner and characterized using X-ray diffraction (XRD) and Fourier transform-infrared spectroscopy (FT-IR). High-resolution transmission electron microscopy (HRTEM) and surface area measurements revealed the formation of 30- to 60-nm Cu-HCF and 40- to 60-nm GC particles with specific surface areas of 48 and 802 m(2)g(-1), respectively. Electrochemical studies including cyclic voltammetry (CV), galvanostatic charge-discharge (CD) analysis and electrochemical impedance spectroscopy (EIS) using a three-electrode configuration confirmed the presence of intercalative capacitance in the Cu-HCF electrode and double-layer capacitance in the GC electrode. Furthermore, the constructed Cu-HCF GC aqueous LHC system operates over a wide voltage window (2.2 V) and delivers a high capacitance (63.64 F g(-1)) and high energy density (42.78 Wh kg(-1)) with a good rate capability. These key features make the LHC system an ideal candidate for next-generation electrochemical energy storage devices. (C) 2018 Elsevier B.V. All rights reserved.