As global population and subsequent energy demand increases, there has been a call for new, robust energy materials, especially those with small carbon footprints. Interest in expanding battery storage capabilities, specifically in the multivalent-battery space for higher energy densities are amongst these new energy material investigations. To this end, developing refined control over stoichiometry of guest metal species in multinary materials and a better understanding of structural changes as a function of guest metal species identity and amount is vital. Through stoichiometric control of guest metal species, we abilitate the tunability of electro/photoelectrochemical properties (e.g. interfacial charge transfer kinetics, adsorption thermodynamics, small-molecule conversion selectivity) and charge storage and transfer properties (e.g. charge transfer resistance, electrochemical capacitance, conductivity) of the host material. To probe these phenomena, we investigate the stoichiometric control of Cu-ion intercalation into Chevrel-phase sulfides (Mo6S8) in aqueous media via electrochemical methods. Chevrel-phase (CP) MxMo6T8 (M=alkali/transition metal; x=0-4; T=S, Se, or Te) materials have shown promise as intercalant hosts for multivalent transition metals, owing to their unique intercalation capacity which in turn affects their structural and electronic properties. In this work, we use powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) to investigate changes in crystal structure, electron localization, structural disorder, and elucidate electron transfer within the CP-sulfide host as a function of stoichiometric Cu content. We report the successful identification of intercalation/deintercaltion potentials for Cu into/out of the CP host, stoichiometric control of electrochemical intercalation CuxMo6S8; x=1-3, and a suite of analytical characterization (e.g. PXRD, EDX, XPS, and XAS). An interesting finding in this work is the identification of a pre-edge feature change in the XANES data as a function of Cu content in the CP-sulfide host. Lastly, we report findings from the electrochemical studies (e.g. Cyclic voltammetry and Linear sweep voltammetry) that further the understanding of Cu intercalation kinetics in the CP host in aqueous media.

Elucidating structural modifications of Chevrel phase sulfides as a function of stoichiometric control of Cu-ion content via electrochemical intercalation in aqueous media

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ACS Fall 2022

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