Title : Bitter Gourd pericarp derived porous activated carbon for high energy density supercapacitor devices
The rapid growth of the human population and the ever-increasing demand for energy resources have resulted in massive consumption of fossil fuels. This has also led to associated harmful impacts on the environment. Current energy demand has triggered a shift towards environmentally friendly and sustainable energy sources. Intermittent energy storage is an alternative to current scenarios, where energy available from fluctuating primary sources can be stored and used as needed. Therefore, scientific efforts are now focused at developing better and new energy storage systems.
Common electrochemical energy storage devices include batteries, supercapacitors, fuel cells and hybrid supercapacitors. Among them, batteries and battery-supercapacitors have gained remarkable attention in recent years owing to their excellent electrochemical performance. Even though batteries exhibit appreciable energy density in the range of 150-300 Wh kg-1, supercapacitors dominate batteries in terms of displaying better cyclability (>100000 cycles), faster charging and discharging rates, higher power density (>10000) W kg-1, longer longevity, least maintenance requirement, better deformability and flexibility, wider operating temperatures, zero memory effect issues and more importantly bridges the gap between rechargeable batteries and conventional dielectric capacitors.
Porous structured activated carbon has attracted a great deal of attention for supercapacitor applications because of their viability, sustainability and environmental friendliness. In particular, decentralized and sustainable production of materials related to energy technologies would be enabled through bio-source derived materials. Numerous biomass precursors have been explored to date to obtain activated carbon.
In this work, we explore a bio-source not used till date to derive KOH activated porous structured activated carbon towards supercapacitor application. The pericarp of bitter gourd, scientifically called Momordica Charantia, available widely is used as the bio-source here. The bio-derived activated carbon shows an excellent surface area of 1125 m2g-1 at an activation temperature of 900°C. It exhibits a specific capacitance of 186 F g-1 at 1 A g-1. Symmetric supercapacitor device fabricated delivers a power density of 750 W kg-1 at an energy density of 8 Wh kg-1 with 98% capacitance retention after 5000 cycles in 1M H2SO4. A further improvement of energy density to a maximum of 23 Wh kg-1 and a maximum power density of 6000 W kg-1 is achieved using dual redox mediators (KI + HQ) in H2SO4 due to the redox activity of the I2/I- and Q/HQ redox species at the positive electrode.