Exploring a new electrochemical treatment to significantly improve the electrochemical performance of 3D-printed polylactic acid/carbon fibre electrodes

It is quite well-known that the differential pulse voltammetric technique (DPV) and a reversible redox probe of ruthenium hexamine (RuHex, [Ru(NH₃)₆]²⁺/3+) are commonly used in sensitively characterising the electrochemical performances of the newly fabricated 3D-printed electrodes. Herein, 3D-printed electrodes were fabricated via fused deposition modelling (FDM) using a polylactic acid/carbon fibre (PLA/CF) composite filament. A novel electrochemical treatment involving DPV in RuHex solution was introduced to improve the electrodes’ performance. Scanning electron microscopy (SEM) revealed that the DPV-RuHex treatment induces surface cracking and pore formation on the PLA/CF electrodes. This is attributed to the interaction of the reduced form of [Ru(NH₃)₆]²⁺ ions as a superior electron mediator for the ester groups in the PLA structure, resulting in the formation of unstable ester radical anions. This anion can fragment into the PLA ester radicals and alkoxide anions. The breakdown of PLA is further promoted by the resultant oxidation ester radicals, which increases the exposure of conductive carbon fibers and thereby enhances surface conductivity. Electrochemical characterisation using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) confirmed the performance improvement. Specifically, EIS in a ferrocyanide/ferricyanide [Fe(CN)₆]³⁻/⁴⁻ solution showed significantly lower charge transfer resistance (Rct) and a fourfold increase in surface conductivity, alongside a higher heterogeneous electron transfer rate constant (k₀) for the treated electrodes. With an approximate geometrical surface area of 0.88 cm², the 3D-printed PLA/CF electrodes were also evaluated as both reference and counter electrodes using reversible [Ru(NH₃)₆]²⁺/³⁺ and [Fe(CN)₆]³⁻/⁴⁻ redox probes under a simple experimental procedure. Although their mid-point potential (Emid) values differ from those of standard reference electrodes (SCE and Ag/AgCl), the electrodes produced stable, reproducible voltammetric responses. These results support their reliability in electrochemical applications, provided baseline offsets are accounted for. To evaluate the versatility of the treatment, the same DPV-RuHex protocol was applied to PLA/graphene (PLA/G) nanocomposite electrodes, yielding comparable performance enhancements. This consistency supports the proposed degradation mechanisms and demonstrates the broader applicability of the treatment for improving 3D-printed PLA carbon nanocomposite electrode devices.