On the dynamics of metal filled CNOs fusion: The case of sp³-rich Cu filled carbon foam

In the last decade, important research efforts have been posed towards the fabrication of novel carbon polymorphs with controlled sp³/sp² properties. Nucleation of novel carbon polymorphs has been reported with the use of (1) cold compression experiments and (2) high temperature annealing. In the latter, the formation of a novel foam-like carbon (CFM) material has been reported as the result of an unusual spontaneous process of high temperature fusion of Fe₃C-filled carbon nano-onions (Fe₃C@CNOs). Being interested in investigating further such CNOs-fusion mechanism we have considered the use of Cu crystals as catalyst for the formation of the filled CNOs to be used as precursor for the CFM nucleation. The choice of these CNOs as precursors relies on their characteristic mass transport properties. This kind of effect is of important interest also for electrochemical battery-related processes. Specifically, we find that a complete conversion of the filled CNOs-precursors into CFM can be achieved within very short timescales of 6 h of annealing. This implies the presence of fast diffusion and mass transport dynamics. In addition, through the use of multiple characterization techniques, such as TEM, HRTEM, XRD, Raman Spectroscopy and XPS we investigate the variation of structural and surface characteristics of the Cu@CNOs and we demonstrate the formation of a sp³-rich mm-scale CFM material completely filled with crystalline copper after the annealing stage. Further investigations are then performed at high pressures of 5 GPa. These measurements reveal a substantial change in the CFM network-morphology and a comprehensive increase in the sp³-content.