Augmentation of conductive pathways in carbon black/PLA 3D-printed electrodes achieved through varying printing parameters

Abstract

3D-printing of conductive carbon materials in sensing applications and energy storage devices has significant potential, however high resistivity of 3D-printed filaments poses a challenge. Strategies to enhance sensors post printing are time consuming and can reduce structural integrity. In this work, we investigated the effects different printing layer thickness and orientation can have on the electron transfer kinetics and resistivity of conductive materials. The response of these electrodes was investigated by cyclic voltammetry, electrochemical impedance spectroscopy and imaging. Electrodes printed with the lowest layer thickness of 0.1 mm in a vertical orientation had the greatest conductivity. With increasing print layer thickness and printing in a horizontal orientation, the electrode was more resistive. This work is the first to demonstrate the significant impact 3D-printing parameters can have on the electron transfer kinetics of carbon conductive electrodes. The implications of this study are important in defining the manufacturing process of electrodes for all applications.

Introduction

Three-dimensional (3D) fused filament fabrication (FFF) printing has emerged as an important manufacturing approach for the development of conductive carbon materials, mainly in the fields of electronics, sensors and energy storage devices as it offers flexibility in design and potential that supersedes traditional manufacturing systems [[1], [2], [3], [4], [5], [6]]. Studies have shown that commercial conductive carbon 3D-printed filament has poor conductivity [[7], [8], [9], [10]]. To overcome these limitations, varying post-printing modifications have been utilised in order to enhance the electrical properties of the 3D-printed material, such as chemical and electrochemical treatment [[11], [12], [13], [14]]. Although these strategies can effectively enhance the electron transfer kinetics of the printed electrode [15], they add an additional time consuming step, which is often detrimental to the electrode geometry when making small fine prints.

On the other hand, studies that focus on enhancing the conductivity of 3D-printed devices through the improvement of printing parameters are seldom explored [[16], [17], [18]]. There are various parameters that govern the properties of the printed artefact. Studies have shown that anisotropy and orientation of print layers are two factors in the construct of 3D-printed materials which introduce significant variations in electrochemical activity [18]. This study aims to understand the influence of print layer thickness and orientation on the electron transfer kinetics of 3D-printed carbon black (CB)/polylactic acid (PLA) electrodes.

Herein, we utilise cone-shaped CB/PLA electrodes printed with layer thicknesses varying from 0.1 to 0.4 mm in vertical and horizontal orientation. Electrochemical characterisation was conducted using voltammetric measurements of two different redox species, via cyclic voltammetry (CV) and impedance electrochemical spectroscopy (EIS). Structural integrity of the different layer thicknesses was analysed through chemical pre-treatment with tetrahydrofuran (THF) while the CB particles present within the 3D-printing filament were characterized using SEM and particle size analysis. Our findings show that layer thickness and printing orientation has significant influence on the electrochemical activity of the printed material and determines the prevalence of conductive pathways and resistivity within the structure.