Electric double layer capacitors (EDLCs) are known for their high-power densities due to the fast mechanism of charge-discharge processes. However, producing eco-friendly and economically viable materials for supercapacitors is one of the most important challenges. Also, a high-rate capability of the supercapacitor is desirable for pulse applications. In the present work, a high cell-potential and high-rate supercapacitor was created using biocarbon derived from a rubberwood-sawdust biomass at three different temperature. Bio-AC carbonized at 900 degrees C shows a high specific surface area of 1932 m(2) g(-1) and a pore volume of 1.44 cm(3) g(-1). A symmetrical supercapacitor of bio-AC(900 degrees C) with 1.0 M LiTESI(aq.) displays a high practical cell potential of 1.8V with an impressive rate up to 100 A g(-1). A specific capacitance of similar to 100 F g(-1) at 0.1 A g(-1) was estimated by a galvanostatic charge-discharge method. Besides, an excellent capacitance retention is retained at higher specific currents, for instance, 71% and 49% were estimated at 60 A g(-1) and 100 A g(-1), respectively. An excellent long-term stability of 84% at 1.8 V was evaluated for the symmetrical supercapacitor in 1.0 M LiTFSI(aq.) after 50,000 cycles at 3.0 A g(-1). Also, gas chromatography coupled with the electrochemical cell was employed for the in situ determination of electrolytically generated gases in real time at the positive and negative applied potentials. H(2 )and CO2 gasses can be generated at too high applied potentials. Understanding the gas evolution in this work may be useful for further development of supercapacitors. Also, high cell-potential and high-rate neutral aqueous supercapacitors using activated biocarbon may be useful for high-power applications. (C) 2019 Elsevier Ltd. All rights reserved.