An electrical double-layer capacitor is fabricated with biomass-derived activated carbon (AC) and multi-walled carbon nanotubes (MWCNTs), which are synthesized from Pongamia pinnata fruit shell and its seed oil, respectively. The activated carbon is produced by the chemical activation process at varying carbonization temperatures from 600 to 900 °C for 5 h at a rate of 10 min in an N2 atmosphere. The surface area of activated carbon and MWCNTs is 1170 m2 g− 1 and 216 m2 g− 1, respectively. The total pore volumes of activated carbon and MWCNTs are 1.51 cm3 g− 1 and 0.5907 cm3 g− 1, respectively. The as-prepared AC and MWCNTs are characterized by surface area analysis Brunner–Emmett–Teller method (BET), X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopic analysis, field emission scanning electron microscopy, high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy. The electrochemical performances of AC-AC, MWCNTs-MWCNTs and AC-MWCNTs (25:75) symmetric electrodes are studied by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy. The AC-MWCNTs (25:75) single electrode performance is also studied in two different electrolytes, such as 0.5 M Na2SO4 and 0.5 M H2SO4. The fabricated AC-MWCNTs (25:75) symmetric supercapacitor cell exhibits excellent electrochemical performance in 0.5 M Na2SO4. It shows a specific capacitance of 55.51 Fg− 1, energy density 4.852 Wh Kg− 1 and power density of 199.18 W Kg− 1 at a current density of 1 Ag− 1 in the voltage window of 0–1.8 V. The AC-AC and AC-MWCNTs (25:75) symmetric supercapacitor electrodes show outstanding performance.

    Abstract
    1 Introduction
    2 Experimental section
        2.1 Materials
        2.2 Synthesis of activated carbon
        2.3 Preparation of multi-walled carbon nanotubes
        2.4 Preparation of stainless steel (SS) current collector electrode
        2.5 Preparation of AC-AC and MWCNTs-MWCNTs electrode
        2.6 Preparation of AC-MWCNTs working electrode
        2.7 Characterization of the electroactive materials
        2.8 Electrochemical measurement
    3 Results and discussion
        3.1 XRD, XPS and Raman spectroscopic analysis of activated carbon and MWCNTs
        3.2 Surface morphology
    4 Conclusion
    Acknowledgements 
    References

• Dhanapal Thillaikkarasi(PG and Research Department of Chemistry, Chikkanna Government Arts College)
• Srinivasan Karthikeyan(PG and Research Department of Chemistry, Chikkanna Government Arts College)
• Rajendran Ramesh(Department of Physics, Energy and Functional Materials Laboratory, Periyar University)
• Prabhu Sengodan(Department of Physics, Saveetha School of Engineering, Saveetha Institute of Medical and Technical Sciences, Saveetha University)
• Dhamodaran Kavitha(Department of Chemistry, Dr. M. G. R. Educational and Research Institute)
• Malarvizhi Muthubalasubramanian(Department of Physics, K.S.Ranagasamy College of Technology)