Abstract
Amorphous chalcogels are an emerging class of nanoparticle aggregates, porous, lightweight, and semiconducting materials. However, the formation mechanism and their local structure are not clearly understood. Here, we report the synthesis process, the local structure, and electrochemical energy storage properties of the amorphous molybdenum polysulfides (Mo₃S₁₃) chalcogel materials. The gelation of the Mo₃S₁₃ gel occurs by the covalent interactions through S-S bonding among the discrete molecular precursor of Mo₃S₁₃^2- ions as determined by time-dependent Raman spectroscopy. The morphologies, electronic states, and the local structural motifs of the Mo₃S₁₃chalcogel were investigated by the combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), synchrotron X-ray pair distribution function (PDF), X-ray absorption near-edge spectroscopy (XANES), and extended X-ray photoelectron spectroscopy (EXAFS). We show that the local structure of the Mo₃S₁₃chalcogel is similar to the Mo₃S₁₃^2- molecular precursor but its formation is attributed via the condensation of the monomeric molecular building block of Mo₃S₁₃^2- ion into polymer Mo₃S₁₃through -S-S- bonding interactions. The amorphous Mo₃S₁₃ is a semiconductor showing quantum confinement-driven bandgap energy ranging from 1.4 to 1.75 eV for its xero- to wet gels. The prepared amorphous Mo₃S₁₃chalcogel materials have high porosity and unique nanonetwork structure which are important for high electrochemical performance of lithium-ion batteries. As a result, the prepared amorphous Mo₃S₁₃electrode materials show a high lithium-ion storage capacity of ~1000 mAh/g with stable cycle stability for ~ 135 cycles.

Ruhul Amin

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