Confined Synthesis of Amorphous Al2 O3 Framework Nanocomposites Based on the Oxygen-Potential Diagram as Sulfur Hosts for Catalytic Conversion

Abstract

Sulfur cathodes in Li-S batteries suffer significant volumetric expansion and lack of catalytic activity for polysulfide conversion. In this study, a confined self-reduction synthetic route is developed for preparing nanocomposites using diverse metal ions (Mn²⁺ , Co²⁺ , Ni²⁺ , and Zn²⁺ )-introduced Al-MIL-96 as precursors. The Ni²⁺ -introduced Al-MIL-96-derived nanocomposite contains a "hardness unit", amorphous aluminum oxide framework, to restrain the volumetric expansion, and a "softness unit", Ni nanocrystals, to improve the catalytic activity. The oxygen-potential diagram theoretically explains why Ni²⁺ is preferentially reduced. Postmortem microstructure characterization confirms the suppressive volume expansion. The in situ ultraviolet-visible measurements are performed to probe the catalytic activity of polysulfide conversion. This study provides a new perspective for designing nanocomposites with "hardness units" and "softness units" as sulfur or other catalyst hosts.

Keywords: Ni nanocrystals; amorphous aluminum oxide; catalysis; confined synthesis; oxygen-potential diagram.