Over the years, various processing techniques have been explored to synthesize three-dimensional graphene (3DG) composites with tunable properties for advanced applications. In this work, we have demonstrated a new procedure to join a 3D graphene sheet (3DGS) synthesized by chemical vapor deposition (CVD) with a commercially available carbon veil (CV) via cold rolling to create 3DGS-CV composites. Characterization techniques such as scanning electron microscopy (SEM), Raman mapping, X-ray diffraction (XRD), electrical resistance, tensile strength, and Seebeck coefficient measurements were performed to understand various properties of the 3DGS-CV composite. Extrusion of 3DGS into the pores of CV with multiple microinterfaces between 3DGS and the graphitic fibers of CV was observed, which was facilitated by cold rolling. The extruded 3D graphene revealed pristine-like behavior with no change in the shape of the Raman 2D peak and Seebeck coefficient. Thermoelectric (TE) power generation and photothermoelectric responses have been demonstrated with in-plane TE devices of various designs made of p-type 3DGS and n-type CV couples yielding a Seebeck coefficient of 32.5 μV K-1. Unlike various TE materials, 3DGS, CV, and the 3DGS-CV composite were very stable at high relative humidity. The 3DGS-CV composite revealed a thin, flexible profile, good moisture and thermal stability, and scalability for fabrication. These qualities allowed it to be successfully tested for temperature monitoring of a Li-ion battery during charging cycles and for large-area temperature mapping.
Keywords: 3D graphene sheet; carbon veil; cold rolling; flexible thermoelectric; photothermoelectric; thermocouples.