(178l) Self-Assembling Three-Dimensional PEDOT:BF4 Electrodes with Diverse Electrodeposition Pathways

Poly(3,4-ethylenedioxythiophene), PEDOT, is a highly promising conductive polymer widely employed in diverse electronic applications owing to its electrochemical stability and ability to reduce interfacial impedance. Recently, there has been extensive research into bioelectronics employing PEDOT doped with tetrafluoroborate (PEDOT:BF4), as it not only demonstrates biocompatibility but also enhances the impedances of electrodes for chronic neural stimulating and recording. However, despite PEDOT:BF4 exhibiting different characteristics depending on the electrochemical synthesis method used, there remains a lack of fundamental studies on PEDOT:BF4 across various electrodeposition pathways. This insufficient understanding of the electrochemical synthesis of PEDOT:BF4 leads to uncertainty and confusion among researchers regarding which electrodeposition route to pursue for optimal performance.

In this study, we investigate the electrochemical synthesis of PEDOT:BF4 via diverse electrodeposition pathways and examine the characteristics of each PEDOT:BF4 sample deposited using different electrochemical routes. Additionally, we propose a novel fabrication method involving the self-assembly of three-dimensional (3D) PEDOT:BF4 electrodes within 3D printed channels, presenting the potential for utilization in neural electrode arrays for bioelectronics applications.

Microchannels, with diameters ranging from 30 to 100 µm, were created using two-photon 3D printing and immersed in an electrolyte solution for the electrochemical deposition of 3D PEDOT:BF4 electrodes. Subsequently, we explored three distinct pathways for synthesizing 3D PEDOT:BF4 vertical electrodes within the microchannels: galvanostatic, potentiostatic, and cyclic voltammetry methods. The resulting 3D PEDOT:BF4 electrodes exhibited varying 3D configurations and morphologies depending on the synthesis pathway. Additionally, the electrochemical properties of each PEDOT:BF4 electrode deposited via different pathways were investigated and compared.

Furthermore, we examined the limitations encountered during the reactions involved in configuring PEDOT:BF4 electrodes. Two main limitations were identified: reaction limitation and diffusion limitation arising from the diffusion of the electrolyte from the bulk into the microchannels. Appropriate variables such as current and voltage were determined by considering these diffusion and reaction limitations.

As a result, the findings from the fundamental study offer valuable insights into the direction for PEDOT:BF4 electrodeposition. Furthermore, the self-assembled 3D PEDOT:BF4 electrodes present promising opportunities for utilization in bioelectronics, particularly in neural electrodes.