Direct Synthesis and Electrochemical Deintercalation of Mg-Intercalated Graphullerite

Two-dimensional (2D) carbon allotropes have unique properties, synthetic tunability, and potential applications across several fields including catalysis, energy storage, and electronics. One such allotrope is the recently discovered graphullerite, which results from the oxidation and deintercalation of the layered rhombohedral fullerene polymer (Mg4C60)∞. The current synthetic approach to (Mg4C60)∞ is limited by low yield, phase impurity, and small crystal size, all of which preclude a comprehensive investigation of the physical and electronic properties of bulk graphullerite and its 2D derivative, graphullerene. Here, we demonstrate two chemical vapor transport methods that produce rhombohedral (Mg4C60)∞ and tetragonal (Mg2C60)∞ as millimeter-sized single crystals with near-complete conversion. Our methods spatially separate the starting materials to circumvent both the thermal decomposition of (Mg4C60)∞ and the significant disparity in vapor pressure between C60 and Mg. We find that using Mg foil results in a near-complete conversion of C60 into a mixture of (Mg4C60)∞ and (Mg2C60)∞. Replacing the foil with Mg2Si produces phase-pure (Mg4C60)∞ with an isolated crystalline yield of 55 to 62%. This high-yielding, phase-pure synthesis enables us to investigate the electrochemical intercalation and deintercalation of Mg2+ into the lattice.