(354d) Thermodynamically Favorable Synthesis of Alkali Sulfide Nanomaterials for Next Generation Battery Technology through Reaction with Hydrogen Sulfide

Li₂S has a specific capacity of 1166 mAh/g, and could be paired with a lithium-free anode, addressing safety concerns and low Coulomb efficiency of lithium metal in Li-S batteries. Likewise, Na₂S is a promising cathode material for Na-S rechargeable batteries, which are considered as an option for stationary energy storage in the future. Existing technologies for M₂S production are complex and energy inefficient.  In this presentation we describe the efficient synthesis of anhydrous, phase pure M₂S nanopowders through reaction of alkali metals with H₂S, a hazardous chemical produced in large quantities through desulfurization of natural gas and petroleum reserves.  The ideal reaction is described by the following equation:

             2M  +  H₂S → H₂  +  M₂S

where M = Li, Na, K.  As the Gibbs energy of this reaction is very negative (ΔG_rxn < -300 kJ/mol), the reaction is expected to be spontaneous and irreversible. A practical challenge of course is developing an efficient route to effectively introduce the alkali metals, which have limited surface areas in solid state.  Here we demonstrate this approach by scrubbing an H₂S-containing gas stream with a solution of alkali metal-naphthalene complexes (Na-NAP, Li-NAP).  It is demonstrated that the reaction between these species and H₂S proceeds spontaneously to completion at ambient temperature and pressure, scavenging H₂S to below detection limit.  X-ray diffraction and electron microscopy confirmed that the solid product is phase pure, nanocrystalline M₂S powders, whose size and shape may be manipulated by reaction conditions. Detailed analysis of both the gas- and liquid phase byproducts using mass spectrometry, FTIR, NMR, and gas chromatography was used to better understand the reaction mechanism. A small amount of H₂ was observed to evolve directly during the reaction, but the majority of hydrogen reacts with naphthalene to form 1,4-dialin, which itself is useful as organic solvent and jet fuel. Studies are underway to assess the electrochemical properties of the resulting nanopowders. The proposed route offers a green chemistry solution that generates valuable products while remediating a hazardous waste.