Electropolymerized Polyaniline Nanocomposites from Multi-Walled Carbon Nanotubes with Tuned Surface Functionalities for Electrochemical Energy Storage

The effects of the surface functional groups on the electrochemical properties and electrochemical energy storage were systematically studied by employing the as-received multi-walled carbon nanotubes (MWNTs) and two other MWNTs modified with ether and carboxylic acid functionalities (-C-O-C and -COOH), and ester functional groups (–COOR). The structure and morphology of the films prepared by electropolymerizing aniline onto MWNTs- coated carbon paper substrate were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The band gaps obtained from ultraviolet–visible spectroscopy suggested slight difference in the structure of the nanocomposite films induced by the functional groups in the MWNTs. Electrochemical measurements revealed that all the nanocomposite films with MWNTs exhibited an enhanced capacitance compared to the film grown onto pure carbon paper. An energy density as high as 30 μWh/cm 2 corresponding to a power density of around 8 mW/cm 2 was obtained even at a high current density of 20 mA/cm 2 for the nanocomposite films. An equivalent circuit consisting of a combined resistance and a capacitor is well fitted with the electrochemical impedence spectroscopy data. Stability study showed that the nanocomposite films retained around 80% of the discharge capacity even after 1000 charge-discharge cycles, rendering these films promising for supercapacitor applications.