Characterization of alginate hydrogel electrolytes for use in symmetric supercapacitor based on polypyrrole-modified electrodes

The use of biopolymers for the preparation of gel polymer electrolytes (GPEs) to construct high-performance energy storage devices contributes to the development of new sustainable materials. Herein, an alginate-based gel electrolyte was used in the construction of a supercapacitor, to aim for an environmentally friendly device. Alginate was crosslinked with calcium ions (ALG-Ca2+) resulting in gels with good mechanical properties and ionic conductivity, suitable for their use as electrolyte and separator for a symmetric supercapacitor, assembled in a coin cell architecture and using polypyrrole as the electrode. The device presented a specific cell capacitance of 39.5 F g-1 at 0.2 A g − 1, and durability of 70.9% after 2000 galvanostatic charge-discharge (GCD) cycles. Based on these properties, three devices were connected in series and demonstrated to be able to light up a 3.0 V LED. The influence of temperature on supercapacitor performance was verified by varying the temperature from 10 to 60 °C and evaluating the characteristic cyclic voltammograms and GCD profiles. The devices were able to operate in the temperature range of 10 to 60 °C, with no loss of their capacity properties.