Morphological Modulation of Conducting Polymer Nanocomposites with Nickel Cobaltite/Reduced Graphene Oxide and Their Subtle Effects on the Capacitive Behaviors

This work reports on the urchin-like architecture-based nickel cobaltite (NiCo2O4)/reduced graphene oxide (rGO)/conducting polymer [polyaniline (PANI) or polypyrrole (PPy)] nanocomposites prepared through a hydrothermal synthesis procedure, followed by in situ polymerization techniques. Subsequently, these materials are subjected to electrochemical investigation to search for promising electrode materials for energy storage applications. Interestingly, the morphology of NiCo2O4 varies upon the addition of rGO as well as nitrogen-doped rGO (N-rGO). When it is composite with rGO, it forms an urchin-like architecture, and with N-rGO, it forms nanopartide structures having a diameter of 90 +/- 10 nm. Further, these nanostructures are intricately coated by conducting polymers (such as PAM and PPy) as evidenced from the field emission scanning electron microscopy and high-resolution transmission electron microscopy observations, and the overall shape does not alter after the modification. All composites are investigated thoroughly by Fourier transform infrared, Raman, X-ray powder diffi-action, and X-ray photoelectron spectroscopies to confer the formation and presence of polymers. The NiCo2O4/rGO/PPy nanocomposites exhibit an excellent specific capacitance of 1547 +/- 5 F/g at a current density of 0.5 A/g, a better energy density of 34.37 +/- 0.11 W h/kg at 0.5 A/g, a notable power density of 99.98 +/- 0.31 W/kg at 0.5 A/g, and retains its 94 +/- 1% specific capacitance after 5000 charge-discharge cycles. The uniform coating over the urchin-like architecture by conducting polymers constructs a typical morphology, and possibly, it is the key factor behind gaining such superior electrochemical behavior owing to (a) the enhancement of surface area and (b) the combination of double-layer capacitive and pseudocapacitive properties. Furthermore, a symmetric flexible supercapacitor device made of NiCo2O4/rGO/PPy nanocomposites provides superior electrochemical behavior.