Controlling the Structure of Self-Doped Poly(3,4-ethylenedioxythiophene) via In Situ Sulfuric Acid Addition for Enhanced Supercapacitor Performance

Sulfuric acid treatment is a key strategy for enhancing the conductivity and capacitive performance of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) complexes, yet its role in single-component self-doped PEDOT (PEDOT-S) remains unclear. This study systematically compares the effects of introducing sulfuric acid during in situ polymerization and after polymerization as a post-treatment. The results reveal that, unlike in PEDOT:PSS where acid treatment primarily removes insulating components, introducing sulfuric acid during the polymerization of EDOT-S more effectively elevates its oxidation level and promotes molecular ordering. As a result, the in situ acid-modified PEDOT-S exhibits a 98% higher electrical conductivity (185.2 S cm –1 ) than its post-treated counterpart (93.6 S cm –1 ) along with a higher gravimetric capacitance (49.1 vs 41.4 F g –1 at 0.4 A g –1 ) and improved cycling stability (85.4% vs 80.8% capacitance retention after 5000 cycles). These findings demonstrate that for self-doped systems, the critical function of sulfuric acid lies in in situ structural regulation during polymerization, rather than post-treatment restructuring. This insight offers a direction for the rational design of high-performance, polymer-based electrode materials.