Sustainable and cost-effective edge oxidized graphite/PEDOT:PSS nanocomposites with improved electrical conductivity

Abstract

Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) is a soft and conjugated polymer whose conductive properties can be properly tuned through doping with various additives or solvents, preserving its excellent processability. In this work PEDOT:PSS was combined with a cost-effective graphite derivative named Edge Oxidized Graphite (EOG) for developing a nanocomposite with improved electrical conductivity, with respect to the pristine PEDOT:PSS, through an easy and environmentally friendly doping process. Firstly, the EOG powders, produced by a green oxidation process of graphite, were deeply characterized through Fourier transform infrared (FT-IR), Thermogravimetric (TGA), and Wide-angle X-ray scattering (WAXD) analysis, showing that this nanofiller has oxygenated functional groups on the sheet edges. The quality and the stability of the EOG dispersions within PEDOT:PSS were investigated at different carbon-filler concentrations, up to high loading of 25 %wt/V of EOG through rheological analyses, demonstrating pseudo-plastic behavior and excellent long-term stability of the inks due to the absence of inhomogeneities and aggregates over time; in fact, the same inks were tested under the same rheological conditions after 21 days, showing the same viscosity trend for all EOG concentrations (%wt/V). Transmission electron microscopy (TEM) and (Scanning Electron microscopy) SEM investigation of spin-coated samples onto glass substrates were performed to morphologically evaluate the nanocomposites and estimate the average size of the sheets, particularly the mean length of 1.2 μm and an approximated thickness of 26 nm of the EOG sheets dispersed into the polymer matrix (PEDOT:PSS) was determined, while WAXD analysis allowed to identify the average layer number of the EOG sheets, obtaining thus, a direct measurement of the EOG sheets aspect ratio equal to 45. Finally, sheet resistance tests showed that the increasing concentration of EOG leads to a significant improvement in the electrical conductivity of the nanocomposites, from 1.1 S/cm for pristine PEDOT:PSS to 21.9 S/cm for nanocomposites with the highest EOG content (25 %wt/V). This work demonstrates the successful development of nanocomposite based on PEDOT:PSS doped with carbon-based filler synthesized through a green and cost-effective process, promoting their use in the production of bio/electrochemical sensors or optoelectronic devices.