Improved energy storage performance of sonochemically synthesized Ni-Co-Zn ternary metal phosphate composites by incorporating PANI functionalized CNTs

The multi-walled carbon nanotubes (MWCNTs) were initially functionalized with polyaniline (PANI) through an in-situ polymerization approach. The ternary transition metal phosphate of Ni0.50Co0.25Zn0.25(PO4)2 was then chemically grafted onto different masses of PANI/CNTs (20, 40, 60, 100, and 130 mg) aided with probe sonication. The structural morphology and elemental analysis of the nanocomposites were evaluated by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM), whereas chemical grafting and compositional analysis were evaluated by EDX, XRD, Raman spectroscopy and FTIR analysis. The hierarchical structure of ternary metal phosphates nanocomposites with 100 mg PANI/CNTs provided excellent specific capacity of 1438 Cg-1 (2400 Fg � 1, at 1.5 Ag � 1). An asymmetric supercapacitor device (ASC) of Ni0.50Co0.25Zn0.25 (PO4)2-100 mg PANI/CNT//AC demonstrated excellent electrochemical performance with an energy density of 104 Whkg � 1 (@540 Wkg � 1 and very good cyclic stability and columbic efficiency (100 %)). According to a capacitive-diffusive investigation, the ASC device has 63.5 % diffusive and 33.5 % capacitive behavior at low scan rates. The reason for the excellent electrochemical performance of nanocomposite is the combined contribution of PANI/CNTs and uniform chemical grafting of tri-metallic phosphate structures onto the PANI/CNTs. As a result, the Ni0.50Co0.25Zn0.25 (PO4)2-100mg PANI/CNTs composite exhibited good potential to be used in energy storage devices.