The researchers deposited their PEDOT films on glassy carbon electrodes by cyclic voltammetry, sweeping between −0.30 and +1.00 volts versus a saturated calomel electrode in a 0.05 M solution of the EDOT monomer in acetonitrile, with lithium perchlorate as the supporting electrolyte. Fifteen deposition cycles at 50 millivolts per second built up a uniform, conductive coating whose current density climbed steadily with each sweep. The first voltammetric cycle showed an irreversible monomer oxidation peak and a characteristic nucleation loop; as the surface became coated, the oxidation peak shifted to lower potentials in subsequent cycles. The result was a fibrillar polymer network that the team then deliberately abused, subjecting it to seven consecutive scans from 0.00 to +1.30 volts in 0.01 M sulfuric acid.

That abuse had a clear electrochemical signature. Although the overall shape of the cyclic voltammogram survived the overoxidation treatment, the currents shrank dramatically, signaling a reduction in the number of electroactive regions within the film. The authors attribute the decline to chemical bonds in the thiophene ring breaking at potentials above about 1 volt, generating non-conductive groups such as carbonyls. Those structural changes eliminate electron-transfer pathways through the polymer network and reduce the population of charge carriers. High potentials also detach part of the film from the electrode, shrinking the active surface area and further suppressing the oxidation and reduction reactions that generate measurable current.

The quantitative comparison across electrode types tells the story in a single table. The bare glassy carbon electrode produced an anodic peak current of just 1.22 microamperes. The PEDOT-coated electrode reached 121.95 microamperes, while the overoxidized version managed only 51.45 microamperes. Both coatings shifted the oxidation potential to more negative values, with the pristine PEDOT film showing the largest shift, from 330 millivolts on the bare electrode to 177.40 millivolts, evidence of its superior ability to promote electron transfer. The overoxidized film shifted the potential to 278.20 millivolts, still an improvement over bare carbon but far short of the intact polymer’s performance.

Scanning electron microscopy revealed the physical damage behind the electrical decline. Before overoxidation, the film displayed a fibrillar framework with a porous, high-surface-area morphology. After the high-potential treatment, porosity dropped sharply, with surface pores nearly disappearing altogether. Crystallite-like structures appeared, and the polymer no longer covered the entire electrode uniformly. Energy-dispersive X-ray spectroscopy confirmed the presence of carbon, oxygen and sulfur peaks expected for PEDOT, along with signals pointing to incorporated ionic species within the polymer structure. The microscopy findings dovetail with earlier work by G. Láng and colleagues, who reported that overoxidation of PEDOT films in sulfuric acid begins above +0.8 volts versus SCE, with minimal degradation up to +1.2 volts but significant electrochemical and morphological changes beyond that threshold, including partial film cracking and the emergence of crystalline regions.

To test whether the degradation matters for real applications, the team evaluated the films as sensors for three biologically important molecules: dopamine, ascorbic acid and uric acid. Dopamine is a catecholamine neurotransmitter whose low levels have been linked to disorders such as schizophrenia and Parkinson’s disease; uric acid is the end product of purine metabolism, with abnormal concentrations associated with gout, hyperuricemia and Lesch–Nyhan syndrome; and ascorbic acid, vitamin C, supports iron uptake, collagen formation, immune function and antioxidant defense. All three compounds were measured in 0.06 M phosphate buffer at pH values of 4, 5 and 7, at a scan rate of 50 millivolts per second.

The pristine PEDOT electrode outperformed its overoxidized counterpart across the board. Dopamine oxidation produced an anodic peak current of 339 microamperes on PEDOT versus 187 microamperes on the overoxidized film, with both electrodes showing quasi-reversible behavior. Uric acid yielded 215 versus 109 microamperes, and ascorbic acid 490 versus 203 microamperes. The voltammograms for uric acid showed low-intensity oxidation peaks around 0.13 and 0.34 volts, indicating relatively slow electron transfer, but the intact polymer clearly offered the larger electroactive area and faster kinetics. Repeatability testing over nine successive measurements produced relative standard deviations of 2.5 percent or less for the PEDOT electrode detecting all three analytes, while the overoxidized electrode showed slightly higher variability, which the authors link to the reduced surface and retarded electron transfer.

Stability over storage told a subtler story. After seven days in air at ambient temperature, the PEDOT electrode retained 97.7 percent of its dopamine response, 96.2 percent for ascorbic acid and 95.1 percent for uric acid. The overoxidized electrode retained 97.3, 95.9 and 94.8 percent respectively. Both films held up well, but the consistent, if modest, gap confirms that overoxidation slightly degrades the durability of the modification as well as its sensitivity.

The theoretical half of the study brought quantum-chemical rigor to the same question. The team optimized oligo(EDOT) structures and their complexes with the three analytes using density functional theory at the B3LYP/6-311++G(d,p) level, then built two-probe molecular junctions in which sulfur linkers connected the molecules to platinum electrodes modeled on their (111) surfaces. Using the non-equilibrium Green’s function formalism within the TRANSIESTA-C package, they computed current–voltage characteristics under bias ranges spanning −0.30 to 1.30 volts at 300 kelvin. The simulated 2EDOT junction carried a maximum current of approximately 6.25 microamperes, while the overoxidized structure managed only 0.46 microamperes, a transition the authors describe as a switch from a low-resistance on state to a high-resistance off state.

The simulations extended gracefully to the analyte complexes and even to the choice of electrode metal. Overoxidized 2EDOT bound to ascorbic acid, dopamine and uric acid carried computed currents of 8.00, 10.54 and 9.32 microamperes, compared with 18.00, 25.08 and 19.94 microamperes for the non-overoxidized complexes, mirroring the experimental peak-current hierarchy. Replacing platinum with gold lowered the computed currents, from 11.33 to 5.20 microamperes for the non-overoxidized junction and from 8.47 to 3.92 microamperes for the overoxidized one, which the authors attribute to gold’s higher electrical resistance. Finally, four-point probe measurements on films grown on graphite substrates gave sheet resistances of 52.14 × 10⁻³ ohms per square for PEDOT and 61.89 × 10⁻³ ohms per square for the overoxidized film, against 65.64 × 10⁻³ ohms per square for bare graphite, providing direct physical evidence that overoxidation raises resistance and impairs charge transport. Taken together, the experimental and computational results converge on a practical conclusion: for electrochemical sensing of dopamine, ascorbic acid and uric acid, keeping PEDOT within its stable potential window, below roughly 1 volt, preserves the electroactive sites, porosity and charge-carrier population that make the polymer such a powerful electrode coating, while pushing it into the overoxidation regime sacrifices sensitivity, reproducibility and conductivity in one stroke.

Subject of Research: Electrochemical overoxidation and degradation of PEDOT conducting polymer films for sensing applications

Article Title: Impact of electrochemical overoxidation on the performance metrics of PEDOT films: experimental and theoretical studies

Article References: Hosseini, M., Nikoofard, H., & Ajloo, D. (2026). Impact of electrochemical overoxidation on the performance metrics of PEDOT films: experimental and theoretical studies. Results in Chemistry, 31, Article 104009. https://doi.org/10.1016/j.rechem.2026.104009

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.104009

Keywords: PEDOT, overoxidation, conducting polymers, cyclic voltammetry, electrochemical sensing, dopamine, ascorbic acid, uric acid, DFT calculations, molecular junctions, sheet resistance, glassy carbon electrode