Studies of Hydrogen Interaction with Metal Hexaborides Surfaces: Insights from DFT, CPMD and Experimental Results


Alkaline earth hexaborides are thermoelectric materials with unique thermophysical properties that have a broad variety of applications with great potential for new uses in fields such as lightweight armor development, gas storage, n-type thermoelectrics. In this work, we present and described results of hydrogen interacting with metal hexaboride surfaces using density functional theory methods (DFT), Car-Parrinello molecular dynamics (CPMD), and X-Ray photoelectron spectroscopy (XPS). We observe both chemisorption and physisorption phenomena when hydrogen interacts with surfaces of calcium, strontium, and barium hexaborides. Interestingly, the adsorption/absorption phenomena seem to occur preferentially on the first two layers of the materials. The nature of the surface, metal terminated versus boron terminated, also seems to play a major role on the energetic interactions of hydrogen with these surfaces, with hydrogen adsorption preferentially occurring on the metal terminated surfaces. We also characterize the energetics of hydrogen adsorption using DFT by estimating the difference in energies of the materials with and without hydrogen in the surface. These simulation methods and results provide very valuable insights on the physical and chemical mechanisms of hydrogen adsorption in metal hexaboride materials.

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