Oxidant‑Free Hydrothermal Anchoring of Ultrathin PEDOT on Reduced Graphene Oxide for High‑Performance Flexible Supercapacitors

Abstract

We present a simple, oxidant‑free hydrothermal synthesis that deposits ultrathin poly(3,4‑ethylenedioxythiophene) (PEDOT) directly onto reduced graphene oxide (rGO) nanosheets. The hydroxyl and epoxide groups on graphene oxide (GO) act as in‑situ oxidants, triggering EDOT polymerization while concurrently reducing GO to rGO. The resulting rGO/PEDOT composite exhibits a conductivity of 88.5 S cm⁻¹ and a specific capacitance of 202.7 F g⁻¹ in 1 M H₂SO₄. Electrochemical tests show >90 % capacitance retention after 9 000 cycles and 98 % retention after 3 000 bending cycles when deposited on cotton fabric, underscoring its promise for flexible energy‑storage devices.

Research Highlights

• Functional groups on GO drive both reduction and PEDOT polymerization without external oxidants.
• Resulting rGO/PEDOT achieves record conductivity and specific capacitance among hydrothermal composites.
• Electrodes retain high stability under prolonged cycling and mechanical bending.

Introduction

Conducting polymers (CPs) such as PEDOT have emerged as key materials for high‑power energy storage due to their reversible redox behavior and excellent electrical conductivity. However, pure CP electrodes often suffer from poor mechanical robustness and limited conductivity. Hybridizing CPs with carbon nanostructures—particularly graphene derivatives—has proven effective in enhancing both capacitance and durability. Conventional synthesis methods typically require chemical oxidants, complicating purification and potentially introducing residual impurities. Here we demonstrate a green, oxidant‑free hydrothermal route that leverages GO’s intrinsic functional groups to simultaneously reduce it and polymerize PEDOT, yielding a synergistic composite with superior electrochemical performance.

Materials and Methods

Materials

Graphite flakes (Sigma‑Aldrich) were converted to GO via the Hummers method. EDOT monomer (Bayer) and all reagents were analytical grade.

Preparation of rGO/PEDOT

A 50 µL EDOT solution was added to 50 mL DI water, stirred for 2 h. GO (1.5 g) was dispersed in 30 mL water, stirred 1 h, and centrifuged at 2500 rpm. The EDOT solution was then drop‑wise introduced to the GO dispersion and stirred at 60 °C for 6 h, followed by 90 °C for 2 h to complete polymerization and reduction. Variations in GO loading (1.5 g, 3 g, 4 g, 4.5 g) yielded rGO/PEDOT1–4 composites. Pure rGO was prepared under identical conditions without EDOT.

Characterization and Electrochemical Testing

Morphology was examined by SEM (Hitachi S‑2400) and TEM. UV‑Vis (Shimadzu UV‑1700), FT‑IR (ALPHA), Raman (WITec), XPS (Thermo Fisher), and electrical conductivity (Four‑probe SX193) were used. Electrochemical measurements employed a CHI600 workstation with 1 M H₂SO₄ electrolyte, Pt counter, Ag/AgCl reference. CV, GCD, and EIS data were collected at ambient temperature.

Results and Discussion

Spectroscopic Confirmation of In‑Situ Polymerization

UV‑Vis spectra show the characteristic π→π* shift from 225 nm (GO) to 241 nm (rGO) and a broad PEDOT absorption band (450–800 nm). FT‑IR and Raman spectra confirm removal of C–OH and C–O–C groups and appearance of PEDOT C–S, C–O–C, and C=C vibrations. XPS reveals C/S/O ratios indicative of successful polymerization and partial retention of functional groups that facilitate further reactions.

Morphology and Conductivity

SEM images display rGO sheets with uniformly coated PEDOT nanoparticles; TEM corroborates the thin PEDOT layer. Conductivity measurements show a four‑order‑of‑magnitude increase from rGO (≈0.02 S cm⁻¹) to rGO/PEDOT (88.5 S cm⁻¹), with optimal GO loading at 4 g. The high conductivity arises from both the pristine graphene lattice and the highly conductive PEDOT shell.

Electrochemical Performance

CV curves of rGO/PEDOT exhibit enlarged redox peaks and increased area relative to rGO, reflecting combined pseudocapacitance (PEDOT) and double‑layer capacitance (rGO). GCD tests show specific capacitance rising from 120.5 F g⁻¹ (rGO) to 202.7 F g⁻¹ (rGO/PEDOT3) and maintaining >90 % after 9 000 cycles. EIS data reveal reduced series resistance (Rs) and faster charge transfer in the composite. Flexible electrodes fabricated on cotton fabric retain 98 % of initial capacitance after 3 000 free‑bending cycles, demonstrating mechanical robustness.

Mechanistic Insight

During hydrothermal treatment, GO’s epoxide and hydroxyl groups oxidize EDOT, generating EDOT radicals that polymerize into PEDOT while GO is reduced. The resulting interlayer interaction improves electronic pathways and mechanical adhesion, accounting for the observed electrochemical stability.

Conclusions

We have developed an oxidant‑free hydrothermal method that simultaneously reduces GO and anchors ultrathin PEDOT, producing rGO/PEDOT nanocomposites with 88.5 S cm⁻¹ conductivity, 202 F g⁻¹ capacitance, and exceptional cycling and bending stability. These findings provide a scalable route toward high‑performance, flexible supercapacitor electrodes.

Availability of Data and Materials

All datasets are included in the main manuscript or supplementary files.