Temperature-controlled polypyrrole with tuned conductivity for Zn-ion hybrid supercapacitors

Polypyrrole (PPy) was synthesized at three different temperatures (−5, 10, and 25 °C) to investigate the influence of synthesis temperature on its electrical conductivity and electrochemical behavior. A clear relationship between synthesis temperature, the polaron/bipolaron ratio, and conductivity was established, which further governed the electrochemical performance of the PPy. Among the synthesized samples, PPy prepared at −5 °C (PPy/−5) exhibited the highest conductivity of 32.7 ± 0.05 S/cm. Electrochemical studies were carried out in 1 M H 2 SO 4 aqueous electrolyte, and zinc-ion hybrid supercapacitors (ZIHSC) were fabricated using PPy/25 and PPy/−5 as cathode materials with 1 M ZnSO 4 aqueous electrolyte. The PPy/−5-based ZIHSC delivered the highest gravimetric capacitance, 337 F/g at 0.5 A/g, compared to 258 F/g at 0.5 A/g for PPy/25-based device with operating voltage of 1.5 V . Furthermore, the PPy/−5-based ZIHSC demonstrated superior cycling stability, retaining 64% of its initial capacitance after 15,000 charge–discharge cycles, compared to 59% for the PPy/25-based device. Moreover, PPy/−5 achieved an energy density of 105 Wh/kg, surpassing the 81 Wh/kg of PPy/25. These findings highlight the significant potential of low-temperature-synthesized PPy, particularly PPy/−5, as an efficient cathode material for ZIHSC and other related energy storage devices.