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Abstract

Polymeric materials have gained increasing attention as key components for next-generation energy storage devices due to their lightweight nature, tunable conductivity, and eco-friendly properties. Conducting polymers such as polyaniline, polypyrrole, and PEDOT have demonstrated high specific capacitance values, for instance up to 480 F g⁻¹ for PANI hydrogels and 438.8 F g⁻¹ for PANI/rGO films, with conductivities reaching 1138 S cm⁻¹. Redox-active polymers including PTMA exhibit discharge capacities of 77 Ah kg⁻¹ with retention over 500 cycles at a high current density of 1.0 mA cm⁻², while ferrocene-based polymers maintain coulombic efficiencies greater than 99.8% even after 100 cycles. In supercapacitors, cellulose-based polymer composites have delivered energy densities as high as 45.7 mWh cm⁻² with power densities up to 283.63 kW kg⁻¹, and nitrogen-doped porous carbons derived from hyper-crosslinked polymers achieved almost 100% capacitance retention over 10,000 cycles. For fuel cells, sulfonated poly(ether ether ketone) membranes have shown proton conductivities of 0.03–0.1 S cm⁻¹, while Nafion-layered sulfonated polysulfone membranes enhanced power generation up to four times compared to pristine Nafion. Despite these advances, limitations remain such as capacity fading, mechanical degradation, and relatively low permittivity (k ≈ 3.5 for most polymers except PVDF), restricting large-scale commercialization. Nevertheless, the development of multifunctional polymer composites with carbon nanostructures and metal oxides, together with eco-friendly synthesis strategies, offers significant potential to achieve higher energy densities exceeding 100 mAh g⁻¹, cycling stability beyond 10,000 cycles, and energy conversion efficiencies up to 65%, positioning polymers as indispensable materials for sustainable energy storage technologies.