Adsorption Behavior of Ammonia on Strontium Bromide Surface: First-Principles Study

Thermochemical heat storage based on a gas–solid interaction is an effective long-term energy storage technology and is considered as one of the important technologies for the recovery of industrial waste heat and renewable energy sources such as solar energy. There are many working pairs used for thermochemical heat storage, among which ammonium halides are widely trusted for their good thermodynamic properties. It has attracted a lot of attention in the past decade, but it is still in the laboratory-scale research stage. In this study, the adsorption behavior of strontium bromide surfaces on the atomic scale is investigated using density functional theory with SrBr2/NH3 as the working pair. The optimal adsorption location of ammonia molecules on the strontium bromide surface is determined. Meanwhile, different metal atoms were doped to explore the microscopic factors affecting the adsorption. The energy barrier of the SrBr2/NH3 reaction was 4.507 kcal/mol, which was reduced to 4.145 kcal/mol after doping Mg. The thermodynamics of the Ca atoms doped with SrBr2 were significantly improved, with a reduction in the energy barrier to 0.727 kcal/mol. Comparing the three energy barrier results, Ca doping has a significant optimization effect on the thermal storage process. The results could provide relevant information for the investigation of thermochemical adsorption heat storage, provide insight into the adsorption mechanism of ammonium molecules on strontium bromide, and also facilitate the design of efficient composite adsorbents.