Charging Mechanisms in PEDOT:PSS Electrodes for Bioelectronics

The conducting polymer PEDOT:PSS has emerged as a promising candidate in bioelectronics for electrical stimulation applications. However, the safety regarding charge injection remains a subject of debate, and a better understanding of electrochemical processes is required to evaluate possible adverse effects and advance next-generation stimulators. Here, we investigate the charging mechanisms of PEDOT:PSS with a focus on reversible capacitive charging versus irreversible oxygen reduction reactions (ORR). Although the results show that PEDOT:PSS can volumetrically store large amounts of charge, extracted capacitance values vary by as much as 55% depending on the measurement method and operating potential. At cathodic potentials, PEDOT:PSS exhibits high selectivity for the 2-electron reduction of oxygen, facilitating efficient generation of hydrogen peroxide. However, with an onset potential of −0.25 V versus Ag/AgCl, initiating ORR requires a relatively large overpotential, which enables high current densities while avoiding harmful side reactions. While ORR activity is independent of PEDOT:PSS thickness, charge injection capacity scales linearly, ranging from 0.7 to 3.5 mC/cm 2 across thicknesses of 140–870 nm. This study establishes electrochemical properties and thresholds that inform the optimal design and operation of efficient, safe PEDOT:PSS-based bioelectronics.