The preparation of polypyrrole/carboxyl functionalized multi-walled carbon nanotube@cobalthexacyanoferrate hybrid composite for high-performance supercapacitor application

Hybrid electrode materials based on nanostructured metal oxide, conductive polymer, and carbon derivative have promising properties for supercapacitors. Herein, a novel hybrid material consisting of cobalt hexacyanoferrate (CoHCF), multi-walled carbon nanotube with carboxyl functionalized (fMWCNT), and polypyrrole (PPy) was prepared as a supercapacitor element on a pencil graphite electrode (PGE) in this study. This hybrid material (PPy-CoHCF-fMWCNT) was characterized by X-Ray Diffraction (XRD), Fourier Transform-Infrared Spectroscopy (FT-IR), and Field Emission-Scanning Electron Microscope (FE-SEM) techniques and exhibited superior supercapacitive performance and long charge-discharge cycle life in an acidic medium. Supercapacitor behaviors of PPy and PPy-CoHCF-fMWCNT coated electrodes were investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic charge-discharge (GCD) methods in a 0.5 mol L−1 H2SO4 aqueous solution. The specific capacitance (Cm) values of PPy and PPy-CoHCF-fMWCNT hybrid composite were calculated as 431.6 F g−1 and 495.0 F g−1 at a current density of 5 A g−1 under optimum coating conditions, respectively. Electrochemical tests demonstrated excellent energy storage properties with an energy density (E) of 38.67 Wh kg−1 and a power density (P) of 1.96 kW kg−1 at 5 A g−1. The stability of the charge-discharge process obtained with 4500 cycles at 10 A g−1 of the ultra-thin hybrid composite increased from 68.9 % to 79.9 % when carboxymethyl cellulose (CMC) was added to the hybrid composite structure. Moreover, we prepared a symmetrical supercapacitor to use the optimized electrodes in the energy storage application, and it managed to light the red, green, and blue light-emitting diodes (LED).