Coconut-husk derived graphene for supercapacitor applications: comparative analysis of polymer gel and aqueous electrolytes

Abstract

Herein, we propose the synthesis of reduced graphene oxide (rGO) using coconut husk as a green and natural resource for supercapacitor (SC) applications. The electrochemical performance of graphene sheets is studied over two different electrolytes, i.e., sulfuric acid (1 M) and polymer-gel electrolyte. The polyvinyl alcohol, potassium iodide, and sulfuric acid-base polymer gel electrolyte are developed using a simple solvolysis approach. The developed polymer gel electrolyte membrane shows a fine pore structure, providing appropriate channels for ionic transportation and charge transfer within materials, alternatively enhancing the overall performance of the device in comparison to commercial polyvinyl alcohol-based membranes and polyvinyl alcohol and acid-base membranes. This is accredited to lower resistance and higher ionic conductivity of the developed materials, and electrolytes within the supercapacitor device. The electrode with 1 M H2SO4 exhibits outstanding performance with a decent equivalent resistance of 4.75 Ω cm−2 and a specific capacitance (Cs) of 650 F g−1 at 1 mV s−1. Conversely, the polymer gel-containing device shows an equivalent sheet resistance (ESR) of 8 Ω cm−2 and a high specific capacitance of 500 F g−1 at 1 mV s−1. In 1 M H2SO4, the device showed 88% cycling stability after 4400 cycles with a coulombic efficiency of 67.56% and an energy density of 50.00 W h kg−1 with a very high-power density of 1000.00 W kg−1 at 1 A g−1. The polymer-gel electrolyte-containing device shows 99% cycling stability after 4400 cycles with a coulombic efficiency of 70.27% and an energy density of 36.11 W h kg−1 with a power density of 996.92 W kg−1 at 1 A g−1