Ion beam modified molybdenum disulfide-reduced graphene oxide/ polypyrrole nanotubes ternary nanocomposite for hybrid supercapacitor electrode

Abstract

Modifying the surface properties of 2-D reduced graphene oxide (rGO) nanosheets, transition metal dichalcogenides molybdenum disulfide (MoS2) nanosheets and conducting polymer such as polypyrrole nanotubes (PPyNTs) is worth exploring for the application of electrochemical supercapacitors. Herein, hybrid supercapacitor electrodes are prepared from ternary nanocomposites of MoS2-rGO/PPyNTs. The ternary MoS2-rGO/PPyNTs nanocomposites were synthesized by incorporating pre-synthesized PPyNTs in layered MoS2-GO nanocomposites followed by hydrothermal reduction of GO. The layered MoS2-GO nanocomposites were prepared by using layer-by-layer self-assembly of MoS2 (positively charged) and graphene oxide (GO, negatively charged) nanosheets. The synthesized supercapacitor electrodes were modified with 100 MeV O7+ swift heavy ions (SHI) irradiation at four different fluence of 3.3 × 1011, 1012, 3.3 × 1012 and 1013 ions cm−2. The structure and morphology of SHI irradiated samples were analyzed with FESEM, XRD, FTIR, RAMAN and contact angle measurements. Electrochemical performances of both pristine (unirradiated) and irradiated nanocomposite electrodes were evaluated in 10 mM ferri-ferro solution with 0.1 M KCl to study the electrode kinetics and electro-active surface area. Cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) have been carried out to understand the fluence dependent electrochemical behaviour of the hybrid supercapacitor electrode in 1 M KCl electrolyte. Upon SHI irradiation, the desired properties such as specific capacitance, energy density, cycling stability, rate capability and coulombic efficiency are improved up to the fluence 3.3 × 1012 ions cm−2 and degraded at the highest fluence of 1013 ions cm−2 employed in this work. The specific capacitance of 1561 F g−1 for the pristine nanocomposite electrode has been enhanced to 1875 F g−1 after SHI surface modification. The increased capacitive response can be attributed to increased crystallinity, enhanced electro-active surface area and improved electrode kinetics upon SHI irradiation. The irradiated electrodes were found to be more stable with 91% of cycling stability after 10,000 GCD cycles than that of the pristine electrodes (72% cycling stability) as the oxidation states of PPyNTs are stabilized through the increased π−π interaction in the polymer chain after SHI irradiation. MoS2-rGO/PPyNTs/ITO electrodes irradiated at the fluence of 3.3 × 1012 ions cm−2 exhibit highly reproducible capacitive response, rate capability and cycle life.