Direct Ink Writing of Graphene-Based Solutions for Gas Sensing

In the energy industry, there is a great need for novel low-cost gas-sensing solutions. This is particularly true for shale gas operations where there is a need to monitor both performance and compliance with environmental regulations. Specifically, there is a need to monitor the integrity of well casings as oil and gas producers try to understand and mitigate environmental issues, as well as avoid unfair claims against the industry. To address this need, we report studies on the additive fabrication and characterization of a graphene-based gas sensor through multilayer direct ink writing of graphene-based inks. An evaporation-assisted solvent exchange method allows tunability of graphene concentration while the addition of ethyl cellulose (EC) allows tuning of rheological properties in printable ink formulations. Robotically controlled direct ink writing enables the deposition of films with arbitrary size and shape. Printed films incorporated into sensor packages exhibit voltage dependent sensitivity to chemical effects of CH4 and H2 in an Ar environment. Surface analysis of the printed sensors suggests disordered layering and orientation of the graphene flakes because of distributed nondecomposed residues of EC from film processing. Capitalizing on the EC residues to form 3D scaffolding enables the spatial arrangement of graphene flakes. The disordered arrangement of flakes resulting from their interaction with the EC residue scaffolding contributes to increased surface area availability for gas sensing.