High cell-potential and high-rate neutral aqueous supercapacitors using activated biocarbon: In situ electrochemical gas chromatography

Highlights: • High surface area and pore volume bio-AC from rubberwood-sawdust is synthesized. • Supercapacitor with high rate upto 100 A g⁻¹ and high cell potential of 1.8 V. • Stability of 92% and 84% at 1.6 V and 1.8 V after 50,000 cycles is measured. • It delivers high specific power of 24.8 kW kg⁻¹. • In situ gas analysis using online electrochemical gas chromatography is performed. -- Abstract: 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 °C shows a high specific surface area of 1932 m² g⁻¹ and a pore volume of 1.44 cm³ g⁻¹. A symmetrical supercapacitor of bio-AC(900 °C) with 1.0 M LiTFSI_(aq.) displays a high practical cell potential of 1.8 V with an impressive rate up to 100 A g⁻¹. A specific capacitance of ∼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. H₂ 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.