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.