INFLUENCE OF ELECTRODEPOSITION POTENTIAL ON COBALT(II) NITRATE-DOPED POLY(3,4-ETHYLENEDIOXYTHIOPHENE) SURFACE PROPERTIES FOR SENSING APPLICATIONS

Abstract

Fabrication of cobalt (II) nitrate-doped poly (3,4-ethylenedioxythiophene) (Co-PEDOT) on SPCE via electrochemical deposition is necessary to enhance the sensitivity of the modified electrode for sensing applications. The 3,4-ethylenedioxythiophene (EDOT) monomer was prepared in aqueous solution with sodium dodecyl sulfate (SDS) and cobalt (II) nitrate to improve its dispersion and solubility in water. Electrochemical deposition of Co-PEDOT was carried out using cyclic voltammetry (CV), where the applied potential induces oxidation of EDOT into radical cations, leading to polymerization and PEDOT formation. In this study, the effect of CV upper potential limits (+1.0 to +2.0 V) on Co-PEDOT surface properties, overoxidation behaviour, and electrochemical performance toward the [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ redox system was investigated. The formation of PEDOT was confirmed by Raman spectroscopy through characteristic bands. The spectra also suggested that the doped Co appeared as cobalt (II) oxide (CoO), although several CoO peaks could not be conclusively identified due to overlapping with PEDOT peaks. Morphologically, all films exhibited a cauliflower-like structure, confirming successful Co-PEDOT growth on SPCE. Increasing the upper potential from +1.0 to +1.2 V promoted PEDOT formation, as evidenced by the highest sulfur content and branch-like structures. At +1.6 V, these structures fragmented into leaf-like features due to overoxidation, and they disappeared at +2.0 V, consistent with reduced sulfur content and surface roughness. This is further supported by the decreased C=C stretching of thiophene rings at +1.6 V, indicating onset of overoxidation, while presence of sulfone (SO₂) bands at +2.0 V confirming further degradation. The film prepared at +1.2 V, prior to overoxidation, exhibited the roughest surface and highest redox activity toward the [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ probe. These findings demonstrate that applied potential plays a critical role in tuning Co-PEDOT properties and optimizing sensor performance.