Large quantities of thermal energy can be stored reversibly in composite materials containing SrCl2 and Expanded Natural Graphite (ENG) upon exo-/endothermal ab-/desorption of ammonia. Therefore, we use the composite materials to build a compact and cost-efficient Thermochemical Heat Storage (TCHS) system optimized for the reutilization of industrial low-grade waste heat of temperatures up to 150 degree Celsius. In this study, we are aiming at investigating the evolution of the pore size distribution in the composite material (SrCl2+ENG) in relation to the degree of NH3 absorption. The experiments will be performed on a cell representing a basis element of the TCHS system reactor. Findings of the study will be correlated with our previous imaging and diffraction studies, as well as future TEM imaging, to evaluate the evolution of nano-/microstructure of the material during NH3 cycling.