Inkjet Printable Conductive Activated Carbon Ink from Sustainable Sources

Inkjet printing offers an attractive manufacturing method for flexible and large-area electronics, yet formulating sustainable inks not derived from fossil fuels represents a major challenge toward environmentally friendly technologies. Here, we present a conductive ink formulated for inkjet printing, consisting only of renewable and nontoxic components, namely electrically conductive activated carbon nanoparticles, ethyl cellulose as binder and stabilizer, and ethanol-terpineol mixture as the dispersant. The ink is composed of activated carbon nanoparticles with a diameter between 30 and 120 nm and exhibits high colloidal stability, dynamic viscosity and surface tension within an ideal range for inkjet printing. The ink produces electrically conductive patterns, achieving a resistivity of 6.6 Ω cm. Such result enables the manufacturing of printed resistive elements in electronic circuits, where the sheet resistance is tunable by the drop spacing and/or layers number of the printing process. As a proof-of-concept of future printed sustainable sensors, we employed this formulation to produce a resistive humidity sensor capable of detecting the moisture content in the air exhaled during respiration. The conductive ink herein presented is a step toward the quest for sustainable materials for environmentally friendly printed electronics.