Poly(3,4-ethylenedioxythiophene) (PEDOT) is a prime example of conducting polymers materials for supercapacitors electrodes that offer ease of processability and sophisticated chemical stability during operation and storage in aqueous environments. Yet, continuous improvement on its electrochemical capacitance and stability upon long cycles remains a major interest in the field, such as the developing PEDOT-based composites. This work evaluates the electrochemical performances of hydroxymethyl PEDOT (PEDOTOH) coupled with hydrogel additives, namely poly(ethylene oxide) (PEO), poly(acrylic acid) (PAA), and polyethyleneimine (PEI), fabricated via a single-step electrochemical polymerization method in an aqueous solution. The PEDOTOH/PEO composite exhibits the highest capacitance (195.2 F g-1) compared to pristine PEDOTOH (153.9 F g-1), PEDOTOH/PAA (129.9 F g-1), and PEDOTOH/PEI (142.3 F g-1) at a scan rate of 10 mV s-1. The PEDOTOH/PEO electrodes were then assembled into a symmetrical supercapacitor in an agarose gel. The type of supporting electrolytes and salt concentrations were further examined to identify the optimal agarose-based gel electrolyte. The supercapacitors comprising 2 M agarose-LiClO4 achieved a specific capacitance of 27.6 F g-1 at a current density of 2 A g-1, a capacitance retention of ~94% after 10,000 charge/discharge cycles at 10.6 A g-1, delivering a maximum energy and power densities of 11.2 Wh kg-1 and 3.45 kW kg-1, respectively. The performance of the proposed supercapacitor outperformed several reported PEDOT-based supercapacitors, including PEDOT/carbon fiber, PEDOT/CNT, and PEDOT/graphene composites. This study provides insights into the effect of incorporated hydrogel in the PEDOTOH network and the optimal conditions of agarose-based gel electrolytes for high-performance PEDOT-based supercapacitor devices.
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