Compositionally engineered poly(3,4-ethylenedioxythiophene):Poly(styrene sulfonate) electrodes for next–generation metal–free zinc–ion hybrid supercapacitors

Zinc-ion hybrid supercapacitors (ZHSCs) are promising next generation energy storage systems that aim to bridge the gap between batteries and supercapacitors by integrating high energy density with rapid charge–discharge capability. However, conventional ZHSCs rely on using metallic Zn anodes, which suffer from dendrite growth, unstable cycling, and safety concerns. Herein, we report a novel metal–free ZHSC configuration that employs porous activated carbon as the anode and compositionally engineered poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as the pseudocapacitive polymeric cathode in aqueous ZnSO₄ electrolyte. By tailoring the composition of PEDOT:PSS via controlled oxidant and PSS ratios during hydrothermal polymerization, we obtained an optimized polymeric cathode achieving a specific capacitance of 56.1 F g⁻¹ at 1 A g⁻¹ in a three–electrode system. The enhanced performance originates from a higher oxidation level and well–integrated PEDOT:PSS network that can facilitate electrolyte penetration and enhance both the electrochemical activity and structural stability of the electrode. The resulting metal–free ZHSC device achieved a maximum energy density of 58 Wh kg⁻¹ and retained 94.1% of its initial capacitance after 15,000 cycles operating across a wide potential window of 1.9 V. Post–cycling analysis confirmed effective suppression of Zn dendrite formation. The novel metal–free ZHSC architecture established in this work would be further utilized for engineering polymeric cathodes for next–generation energy storage devices.