A redox mediator doped gel polymer as an electrolyte and separator for a high performance solid state supercapacitor

Abstract

A stable and effective redox-mediator gel electrolyte has been prepared by doping indigo carmine (IC) into a polyvinyl alcohol sulfuric acid polymer system (PVA–H₂SO₄), and a high performance solid state supercapacitor is fabricated by utilizing activated carbon as electrodes and the prepared gel polymer (PVA–H₂SO₄–IC) as an electrolyte and separator. The PVA–H₂SO₄–IC gel polymer has excellent bending, compressing and stretching mechanical properties. As expected, the ionic conductivity of the gel polymer electrolyte increased by 188% up to 20.27 mS cm⁻¹ while introducing IC as the redox mediator in the PVA–H₂SO₄ gel electrolyte. Simultaneously, specific capacitance is increased by 112.2% (382 F g⁻¹) and energy density (13.26 W h kg⁻¹) is also increased. Furthermore, the fabricated device shows superior charge–discharge stability. After 3000 cycles, its capacitive retention ratio is still as high as 80.3%. This result may be due to the fact that the IC can act as a plasticizer and redox mediator, and the supercapacitor combines the double-layer characteristic of carbon-based supercapacitors and the faradaic reaction characteristic of batteries energy-storage processes.