Amplification of energy density with zero compromise on power density is a major challenge in capacitive science. Since energy density has a quadratic dependence on voltage, broadening the operating voltage window of the supercapacitors (SCs) could be an effective strategy to boost the energy density over improving the electrode’s capacitance if one can avoid excessive leakage current density. On extending the voltage window of the SC beyond the water electrolysis potentials in an aqueous medium, the combined effect of the choice of the electrode material and pH of the electrolyte plays an important role. In the present work, activated carbon (ACTS-800) derived from Tamarind seeds, a widely available cheap bio-mass, pyrolyzed at 800 °C, is explored as a potential electrode material for fabricating a high voltage SC in aqueous 1 M Na2SO4. Interestingly, the beneficial interaction between the surface functional groups and electrolyte resulted in the high overpotentials for both hydrogen and oxygen evolution reactions in the neutral medium. ACTS-800 exhibited superior performance in terms of energy density (28 Wh kg−1), and leakage current density (0.33 mA cm−2) to many reported carbon materials derived from various bio-sources.

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