High‑Performance Flexible Microsupercapacitors Based on 3‑D rGO/PEDOT Open‑Network Architectures

Introduction

Emerging smart microelectronic systems—wireless sensor networks, biomedical implants, and real‑time tracking chips—drive the demand for lightweight, flexible, and low‑cost micro‑scale energy storage. Commercial thin‑film and 3‑D micro‑batteries often suffer from poor rate performance, abrupt failure, and safety concerns. In contrast, interdigital microsupercapacitors (MSCs) provide superior power density, safety, and longevity, making them the leading candidate for self‑powered micro‑devices. Two‑dimensional (2D) interdigital MSCs, while offering reduced thickness, require thicker electrodes to meet energy demands, which can hinder electrolyte access and increase charge‑transport distances. Enhancing energy and power densities within a constrained footprint remains a challenge. Three‑dimensional (3‑D) open‑network architectures address these limitations by offering high surface area, rapid ion transport, and structural flexibility during cycling. Conventional fabrication methods—colloidal/hard templates, hydrothermal synthesis, or deposition on 3‑D substrates—often involve toxic reagents, harsh conditions, or complex steps that impede large‑scale, eco‑friendly production. Laser‑assisted patterning, which can precisely sculpt conductive networks on polymer substrates, and vapor‑phase polymerization (VPP), which allows polymer growth on arbitrary surfaces without vacuum equipment, provide a scalable alternative. Key to high‑performance MSCs is the use of electrode materials that combine high surface area, hydrophilicity, and efficient ion intercalation. Reduced graphene oxide (rGO) offers low cost, high conductivity, and a surface area of ~2630 m² g⁻¹. However, rGO alone relies on double‑layer capacitance, limiting specific capacitance. Conducting polymers such as PEDOT provide fast, reversible faradaic reactions and can be grown via VPP on rGO to create a synergistic composite. This work combines laser‑reduced rGO with VPP‑grown PEDOT to form a 3‑D open‑network microelectrode, enabling high‑capacitance, flexible, all‑solid‑state MSCs without binders or additional additives.

Experimental Methods

Materials

3,4‑Ethylene‑dioxothiophene (EDOT) monomers were supplied by Bayer AG. Iron(III) p‑toluenesulfonate (Fe(PTS)₃) and polyvinyl alcohol (PVA) powders were obtained from Sigma‑Aldrich. Graphene oxide (GO) nanosheets were purchased from Pioneer Nanomaterials Technology. Polyethylene terephthalate (PET) substrates, sodium dodecyl benzenesulfonate (NaDBS), phosphoric acid (H₃PO₄), acetone, ethanol, and other reagents were sourced from Kelon Chemical Industry Co., Ltd. All chemicals were used as received. Laser patterning was performed with a 788 nm infrared laser (max 5 mW) in a consumer‑grade LightScribe optical drive, enabling rapid, computer‑controlled patterning. All experiments were conducted at ambient conditions.

Synthesis of 3‑D Opened Network rGO/PEDOT Interdigital Electrodes

The fabrication process is illustrated in Figure 1a. A 2 cm × 2 cm PET substrate was cleaned with ethanol, acetone, and deionized water, then a 2 % GO dispersion in water (prepared by ultrasonic dispersion) was drop‑cast onto the substrate and dried for 24 h. The GO‑coated PET was loaded into the LightScribe unit, where a 100 mW, 788 nm laser exposed each voxel for 500 µs. After 30 min of pulsed irradiation, a 3‑D rGO interdigital pattern was formed. The rGO film was then treated in 0.5 mg m⁻¹ NaDBS for 20 min and baked at 80 °C for 5 min to improve wettability. For VPP, a 1:1 molar mixture of Fe(PTS)₃ and isopropanol was prepared and selectively sprayed onto the rGO pattern using a mask. The substrate was then placed in a small chamber containing 100 µL EDOT monomers and heated at 30 °C, 50 °C, 80 °C, or 100 °C for 30 min under vacuum. This produced rGO/PEDOT composites with distinct porous morphologies, labeled rGO/PEDOT‑30, ‑50, ‑80, and ‑100. Pristine rGO electrodes were also fabricated for comparison.

Assembly of Highly Opened Network rGO/PEDOT‑Based Flexible Interdigital MSCs

1 g PVA was dissolved in 10 mL deionized water at 90 °C for 2 h. 2 mL H₃PO₄ was slowly added under stirring until a transparent gel formed. The rGO/PEDOT electrodes were sputter‑coated with a thin metal layer to act as current collectors, then the gel electrolyte was drop‑cast onto the interdigital pattern. The assembly was soaked at room temperature for 10 h to ensure full wetting and solvent removal, yielding an all‑solid‑state MSC.

Characterization and Measurement

SEM, FTIR, Raman, and XPS were used to analyze morphology, structure, and composition. Electrochemical performance (CV, GCD, EIS) was evaluated on a two‑electrode CHI660D workstation at room temperature. Volumetric capacitance (C_v), energy density (W), and power density (P) were calculated from GCD curves using equations (1)–(3) as defined in the text.

Results and Discussion

Morphology and Structure of the GO, rGO, and rGO/PEDOT Electrode Materials

Figure 2 shows SEM images of GO, rGO, and rGO/PEDOT at various VPP temperatures. Laser reduction creates a highly wrinkled rGO scaffold that maximizes exposed sites and facilitates ion transport. The 3‑D porous PEDOT grown at 50 °C (rGO/PEDOT‑50) exhibits the most homogeneous network, which promotes a high surface area and continuous conductive pathways. Higher temperatures (80 °C, 100 °C) lead to denser morphologies due to accelerated polymerization, while 30 °C results in incomplete growth. FTIR spectra confirm the removal of oxygen groups after laser reduction and the presence of PEDOT characteristic peaks (as shown in Figure 3b). Raman analysis (Figure 3c) reveals a reduced D/G intensity ratio and a prominent 2D band, indicating successful restoration of sp² domains and few‑layer graphene formation. XPS spectra (Figure 4) further validate the removal of oxygen functionalities and the incorporation of sulfur‑containing PEDOT, with clear S 2p doublets at 162.6 eV and 163.8 eV.

Electrochemical Behavior of the Flexible MSCs with Opened Network rGO/PEDOT

The rGO/PEDOT‑based MSCs were assembled with PVA/H₃PO₄ gel electrolyte, avoiding binders or conductive additives. CV curves (Figure 5a) at 20 mV s⁻¹ show that rGO/PEDOT‑50 delivers the largest quasi‑rectangular area, indicating ideal capacitive behavior. GCD curves (Figure 5b) exhibit nearly triangular profiles with linear voltage–time relationships, and rGO/PEDOT‑50 achieves the longest discharge time. EIS (Figure 5c) reveals a nearly vertical line at low frequencies and the lowest charge‑transfer resistance among all samples. The specific capacitance versus current density (Figure 5d) demonstrates that rGO/PEDOT‑50 reaches 35.12 F cm⁻³ at 80 mA cm⁻³ and retains 31.04 F cm⁻³ at 400 mA cm⁻³, outperforming the other composites. Further cycling tests (Figure 6f) show 90.2 % capacitance retention after 4000 cycles at 80 mA cm⁻³, with coulombic efficiencies between 97 % and 99 %. Flexibility tests (Figure 6c–d) confirm that CV profiles remain unchanged up to 180° bending, and capacitance retention is 96.8 % after 1000 bending cycles, highlighting excellent mechanical resilience. The Ragone plot (Figure 6e) indicates a peak energy density of 4.876 mWh cm⁻³ at 40 mW cm⁻³ and 4.422 mWh cm⁻³ at 200 mW cm⁻³, comparable or superior to recent reports of MSCs with PVA gel electrolytes. To overcome the limited voltage and capacity of a single MSC, series/parallel arrays were fabricated (Figure 7). The MSC array integrated with solar cells demonstrates that a 2P × 3S configuration increases the operating voltage to 3 V (three times a single cell) and approximately doubles the charge‑discharge time. The array’s energy density is six times that of a single device, confirming the effectiveness of network architecture and the synergy between rGO and PEDOT.

Conclusions

We have demonstrated a scalable, binder‑free method to fabricate flexible microsupercapacitors based on a 3‑D rGO/PEDOT open‑network. The laser‑assisted patterning and VPP growth enable precise control of electrode geometry and porosity. The resulting MSCs deliver a volumetric capacitance of 35.12 F cm⁻³, an energy density of 4.876 mWh cm⁻³, retain 90.2 % capacity after 4000 cycles, and exhibit excellent flexibility and coulombic efficiency. Series/parallel arrays further enhance voltage and energy density, making these devices promising for next‑generation wearable electronics and micro‑energy systems.