Soft-assembled, bio-gel electrolytic double layer capacitor system for sustainable energy storage

Carrageenan is an attractive bio-derived polymer electrolyte due to its high ionic conductivity, cyclic stability, and cost-effectiveness in copolymerizing with other biocompatible polymers such as polyvinyl alcohol (PVA). This paper discusses the physical and chemical characterizations of the bio-electrolyte(s): PVA, carrageenan, and PVA-carrageenan copolymer blend. We also describe a fabrication method to create a soft-printed, thin-film, bio-gel electrolytic double-layer capacitor (bio-EDLC) using a PVA-carrageenan polymer blend. The addition of PVA to carrageenan provided structural and mechanical stability to the biopolymer, as confirmed by the hydrogen bonds detected using attenuated Fourier-transform infrared spectroscopy analysis. The assembled bio-EDLCs were analyzed for their electrical properties including their internal charge transfer mechanism, electrical breakdown, specific capacitance, power density, and energy density. It was determined that the bio-EDLC offers specific capacitance of 84 F/g and power density of 4.15E-02 W/kg and has a breakdown voltage of ~1.1 V. Furthermore, preliminary optimization was performed on the bio-EDLC with a drop casting of reduced graphene oxide at the electrode/electrolyte interface to create surface micro-roughness resulting in a bio-EDLC system which demonstrated superior electrical characteristics with an overall specific capacitance of up to 118 F/g, breakdown voltage of ~1.3 V, and improved maximum charging capability to 80%.