Aqueous\nIntercalation of Graphite at a Near-Neutral pH

Abstract

Graphite has been\nextensively studied as a battery electrode, but few investigations\nhave explored its behavior in water at neutral pH. Here, we investigate\ngraphite intercalation in an aqueous ammonium sulfate electrolyte\nwith a pH of 6. We identified potentials at which bisulfate intercalation\nand deintercalation compete with water oxidation. In situ X-ray diffraction\nrevealed that the interlayer space of graphite expands during intercalation,\nreaching a stage-two graphite intercalation compound. Irreversible\nchanges to the graphite occurred during intercalation, as demonstrated\nby the appearance of sp³-type carbon, hydroxyl, and carbonyl\ngroups in Raman and X-ray photoemission spectra. Our findings indicate\nthat intercalation of graphite in aqueous media at a near-neutral\npH and modest potentials is possible, but improved chemical and structural\nstability of the graphite and electrolyte are required to achieve\nlong-term operation.