Reversible change of high-temperature oxidation resistance of graphene‑copper nanocomposites by interplay of catalytic effect of copper and structural disorder of few-layer graphene

High-temperature stability of nanocomposite materials based on metal nanoparticles embedded in the graphene matrix play an important role in modern technology, especially in the field of energy storage and thermal management materials. Few-layer graphene (FLG) nanosheets/Cu nanoparticles (Cu-NPs) composites were prepared by decomposition of ethanol in TIAGO (Torche à Injection Axial sur Guide d'Ondes) microwave plasma torch at atmospheric pressure using erosion of copper nozzle electrode as source of Cu. Delivered microwave power and subsequent heat treatment annealing of the composite material led to the controllable change of its high-temperature oxidation resistance, determined by thermogravimetry in argon and air. As-synthesized and annealed Cu-NPs and FLG structures were analyzed by scanning and transmission electron microscopy and Raman and X-Ray photoelectron spectroscopy and Energy-dispersive X-ray analysis. The amount of copper was determined by X-ray powder diffraction using the internal standard method. Results show that the copper fraction - nanoparticle's size and their quantity, together with amounts of disorder in the FLG structure are the critical factors controlling the observed modification of high-temperature resistance. Partial removal of both Cu-NPs as well as highly disordered graphene fraction using high temperature (800–1050 °C) annealing in Ar or vacuum, led to the controlled variation of nanocomposite's thermal stability under oxidation atmosphere, with continuous change of maximum oxidation rate between 500 and 750 °C. Moreover, the purposeful admixture of disordered fraction of graphene nanosheets enabled recovery of initial state of nanocomposite properties and recovery of its high-temperature original oxidation resistance.