Ecofriendly-synthesized pro-microporous C-Co3O4 nanoparticles conjugated with controlled electropolymerization of pyrrole for high-efficient symmetric supercapacitors

Abstract

High energy density and high power density supercapacitor electrode materials are prepared by a simple pseudo sol-gel method, followed by electrochemical polymerization for electrochemical energy storage. A thin graphitic carbon-film coated Co3O4 (C-Co3O4) is synthesized as an efficient energy storage material with the help of an aqueous phytochemical extract. The green-synthesized C-Co3O4 is pro-microporous with the maximum pore volume centered at 0.7 nm pore width with a distribution of >85 % pore volume with ≤4.5 nm pore width. A thin layer of conducting polypyrrole (PPy) is electropolymerized on a nickel foam/C-Co3O4 electrode (NF/C-Co3O4/PPy). Specific capacitance of NF/C-Co3O4 and NF/C-Co3O4/PPy electrodes are 320 F g−1 and 1176 F g−1, respectively, at 20 mV/s and 221 F g−1 and 695 F g−1, respectively, at 0.5 A g−1. The enhanced capacitance of NF/C-Co3O4/PPy could be ascribed to the synergistic effect between C-Co3O4 and the conducting PPy nanolayer. The energy density of the symmetric supercapacitor (SC) fabricated with NF/C-Co3O4 is 8.1 Wh kg−1 at 800 W kg−1 with a potential window of 0.8 V. The energy density of the symmetric SC fabricated with NF/C-Co3O4/PPy is enhanced ~5 times with the use of the PPy thin film and is 34.4 Wh kg−1 at 1100 W kg−1 with a potential window of 1.1 V. The capacitance retention of NF/C-Co3O4/PPy was 93.9 % over 8000 cycles while that of NF/C-Co3O4 was 79.6 % only. The symmetric SC exhibited a high power density of 35.2 kW kg−1 with an energy density of 4.2 Wh kg−1. The inexpensive green approach coupled with the promising superior capacitance characteristics made C-Co3O4/PPy nanocomposites excellent candidates for high energy density aqueous supercapacitors.