High-Energy-Density Solid-State Symmetric Supercapacitor Based on a Solution-Processable PEDOT:PSS/WSe ₂ Nanocomposite

The ongoing drive to achieve high-energy-density supercapacitors (SCs) requires the continuous exploration of advanced electrode materials and the development of optimized device architectures. Here, we report a solution-processed binary nanocomposite comprising poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and tungsten diselenide (WSe 2 ) nanosheets (NSs) synthesized through a simple chemical route with WSe 2 loadings of 1 and 5 % w/v. Raman and X-ray photoelectron spectroscopy (XPS) analyses reveal distinct spectral shifts relative to pristine PEDOT:PSS, confirming successful composite formation and strong interfacial interactions. The electrochemical measurements reveal that the PEDOT:PSS/WSe 2 nanocomposite with the optimum 1 % w/v of WSe 2 NSs delivers a high areal capacitance of 207.6 mF cm –2 at a current density of 0.5 mA cm –2 in 1 M H 2 SO 4 solution. The charge storage analysis of the nanocomposite reveals the dominance of a capacitive-controlled process. A solid-state symmetric SC device with optimized nanocomposite electrodes exhibits a high areal energy density of 15 μWh cm –2 at an areal power density of 250 μW cm –2 . The fabricated device exhibits excellent cycling stability, retaining 95.35% of its capacitance with a Coulombic efficiency of 94.03% after 10,000 charge–discharge cycles. The suppressed self-discharge and low leakage current further highlight its strong energy retention capability. The excellent solution processability of PEDOT:PSS/WSe 2 nanocomposites, coupled with the rational design of a high-performance symmetric SC, offers a scalable and effective strategy for the development of low-cost, high-performance portable energy storage devices.